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  • 1.
    Alami, Jones
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Plasma characterisation in high power pulsed magnetron sputtering2003Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, plasma parameters including plasma and floating potentials, electron energy distribution function (EEDF) plasma density and electron temperature are studied in a high power pulsed magnetron (HPPM) discharge at different Argon (Ar) gas pressures and different magnetron powers. It is reported that the EEDF during and shortly after the pulse can be represented by a bi-Maxwellian distribution indicating two energy groups of electrons.

    Furthermore, we report on the variation of the plasma parameters and electron energy distribution function with gas pressure in the pressure range 0.5-20 mtorr. At a high pressure (> 10 mTorr) two density peaks are present, the second of which occurs hundreds of microseconds after the pulse is switched off. It shows that the second peaks occurrence depends on the target material used as well as the chamber pressure and the magnetron power. It is found that the electron density is very high (up to 1019 m-3, during the whole of the measured 2000 µs, indicating the importance of the second density peak in maintaining the high plasma density.

    Measurements on the electron temperature show that this does not exceed 3 eV while the pulse is on, and that it is no more than 0.5 after the pulse is off. A movie is constructed using Langmuir probe measurements data, showing the temporal evolution of the plasma at 20 mTorr argon pressure and 11 J pulse energy. Analysis shows the existence of a magnetic trap underneath the center of the target. Furthermore, the electron flux in the substrate vicinity 10 - 12 cm from the target is found to be homogeneous. Ti thin films are grown along the sidewalls of a hole, 1 cm2 in area and 2 cm in depth, using both de magnetron and HPPM sputtering. Secondary electron microscopy shows that the film grown by de magnetron sputtering shows clear columnar growth, while a dense and flat film was produced using the HPPM sputtering technique.

  • 2.
    Alvandpour, Atila
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Power Estimation and Low Power CMOS Circuit Techniques1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increasing power consumption due to the high integration rate of VLSI digital CMOS circuits has become a major concern. Many important design issues and parameters are strongly dependent on the power dissipation and the accuracy of its estimated value during the design exploration. Among these issues we identify particularly the operation time per battery pack, the computational capacity and performance of the mobile electronic products, as well as more general aspects such as circuit reliability, cost for packaging and power supplies. In this thesis, some issues on power estimation and development of low-power circuit techniques, aimed for medium and high speed operations, are addressed.

    The complex impact of Miller capacitance on power and performance of digital CMOS circuits is investigated. Significant enhancements in characterization and modeling of the Miller effects compared to the existing conclusions, which are based on simplified rules, are achieved.

    A novel estimation technique for the relatively involved average short-circuit power consumption has been developed. Compared to the existing, time-consuming technique, the proposed technique provides a fast estimation with a reasonable accuracy, and has a potential to be used for real measurement.

    A significant portion of the total power consumption in VLSI circuits is due to the capacitance of the interconnections, however, estimating the interconnect length and its RC property at early stages in a large-scale top-down design flow is a hard task. Existing, simplified interconnection length estimation techniques are unacceptably inaccurate and unable to give a useful feedback during the design verification and simulation.

    A new design-sensitive interconnection length estimation technique and a corresponding algorithm has been developed. The technique has the unique quality to estimate the length of each interconnection separately, and therefore detects and localizes most of the potentially long interconnects. The result of the estimation can directly be used to add the important RC properties of the interconnects to the power estimators or circuit simulators, consequently yielding a significant increase in estimation accuracy.

    An investigation on generic low-power circuit techniques aimed for main-stream design styles has been made and various suggestions are proposed. The result has later been used to adapt the design of cell libraries to low power requirements.

    High fan-in dynamic gates can result in lower power consumption, fewer logic levels and very compact layout. Two major disadvantages, which reduce the practical use of such wide gates, are the relatively long propagation delay and the large leakage currents, which are due to the increasing subthreshold current in today's and future submicron devices. For speeding up the wide gates, new and simple sensing elements are proposed, which results in faster gates and lower power consumption compared to the alternative solutions. The issues related to large subthreshold leakage currents is also addressed and a leakage-tolerant multi-phase keeper circuit is presented. The new keeper holds the dynamic output of the wide domino gates statically, with a greater driving strength than that in the conventional solution. Furthermore, an increase in robustness is achieved without any significant delay penalty.

    Large capacitive loads resulting from long on-chip interconnects and the corresponding driver-receiver circuits can consume a significant portion of the total power consumption of a CMOS chip. A low-power, high-speed and robust driver-receiver circuit is proposed. The new bus architecture utilizes a precharge-to-low interconnect and a fast and simple level converter as receiver, which together reduce the power consumption up to 70% below that of a conventional precharged bus architecture without any delay penalty.

    List of papers
    1. Impact of Miller Capacitance on Power Consumption
    Open this publication in new window or tab >>Impact of Miller Capacitance on Power Consumption
    1998 (English)In: In proceedings of: International Workshop on Power and Timing Modeling, Optimization and Simulation, PATMOS, 1998, p. 83-92Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-54107 (URN)
    Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2022-05-04
    2. Separation and Extraction of Short-Circuit Power Consumption in Digital CMOS VLSI Circuits
    Open this publication in new window or tab >>Separation and Extraction of Short-Circuit Power Consumption in Digital CMOS VLSI Circuits
    1998 (English)In: ISLPED '98 Proceedings of the 1998 international symposium on Low power electronics and design, 1998, p. 245-249Conference paper, Published paper (Refereed)
    Abstract [en]

    In this paper, we present a new technique which indirectly separates and extracts the total short-circuit power consumption of digital CMOS circuits. We avoid a direct encounter with the complex behavior of the short-circuit currents. Instead, we separate the dynamic power consumption from the total power and extract the total short-circuit power. The technique is based on two facts: first, the short-circuit power consumption disappears at a Vdd close to VT and, secondly, the total capacitance depends on supply voltage in a sufficiently weak way in standard CMOS circuits. Hence, the total effective capacitance can be estimated at a low Vdd. To avoid reducing Vdd below the specified forbidden level, a polynomial is used to estimate the power versus supply voltage down to VT based on a small voltage sweep over the allowed supply voltage levels. The result shows good accuracy for the short-circuit current ranges of interest.

    Keywords
    Short-circuit current, Power consumption, Power estimation.
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-54104 (URN)10.1145/280756.280919 (DOI)
    Conference
    International Symposium on Low-Power Electronics and Design, 10-12 August 1998, Monterey, California, USA
    Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2022-05-04
    3. A Wire Capacitance Estimation Technique for Power Consuming Interconnections at High Levels of Abstraction
    Open this publication in new window or tab >>A Wire Capacitance Estimation Technique for Power Consuming Interconnections at High Levels of Abstraction
    1997 (English)In: In proceedings of: International Workshop on Power and Timing Modeling, Optimization and Simulation, PATMOS, 1997, p. 305-314Conference paper, Published paper (Refereed)
    Abstract [en]

    A new wire estimation technique is presented. It utilizes the topology of the netlist and is sensitive to the actual design. It has the unique quality to estimate the length of every power consuming interconnection individually. Compared to other wire length estimation techniques which use average or total wire length, the result of the new technique shows a strong correlation with the result of "real" automatic placement and route tools. Hence it can estimate a reasonable wire capacitance for each interconnection. The individual wire lengths, combined with individual node activities, are essential for an accurate power estimation.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-54108 (URN)
    Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2022-05-04
    4. Improving Cell Libraries for Low Power Design
    Open this publication in new window or tab >>Improving Cell Libraries for Low Power Design
    1996 (English)In: In proceedings of: International Workshop on Power and Timing Modeling, Optimization and Simulation, PATMOS, 1996, p. 317-325Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-54109 (URN)
    Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2022-05-04
    5. A Leakage-Tolerant Multi-Phase Keeper for Wide Domino Circuits
    Open this publication in new window or tab >>A Leakage-Tolerant Multi-Phase Keeper for Wide Domino Circuits
    1999 (English)In: In proceedings of: IEEE International Conference on Electronics, Circuits, And System, 1999, p. 209-212Conference paper, Published paper (Refereed)
    Abstract [en]

     

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-54105 (URN)
    Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2022-05-04
  • 3.
    Andersson, Dick
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Conformational Studies of Protein Structure and Dynamics1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The protein folding problem is one of the most important issues to be solved in the field of molecular biology. The subject of this thesis mainly deals with various aspects of the folding process.

    In Paper I, near-UV CD kinetic measurements on mutants, in which one tryptophan (Trp) residue had been replaced, were performed to probe the development of asymmetric environments around specific Trp residues during the refolding of human carbonic anhydrase II (HCA II). The development of the individual (Trp) CD spectra during refolding was obtained by subtracting the CD spectrum of the mutant lacking one Trp from that of HCA II at different time points. The same method was used for the particular Trp residues to obtain the kinetic CD traces monitored at a specific wavelength (270 nm). Three Trp residues were analyzed, each probing different structural regions of the native structure. The investigated Trp residues develop their native CD bands at different rates, showing that formation of native-like tertiary structure is occurring with varying rates indifferent regions of the protein.

    The same approach was applied to the extracellular domain of human tissue factor (sTF), which contains four Trp residues (Paper II). The individual Trp CD spectra showed that all four residues contributed to the CD spectrum in almost the entire wavelength region investigated, including the far-UV region. This leads to uncertain predictions of the amounts of various types of secondary structure. Accordingly, the best prediction of secondary sTF structure content was achieved using a hypothetical Trp-free CD spectrum. The kinetic refolding results suggest that the compact asymmetric environments of the individual Trp residues in sTF are formed simultaneously, leading to the conclusion that the native tertiary structure of the whole protein is formed in a cooperative manner.

    In Paper III, the role of the metal ion cofactor for the refolding of bovine carbonic anhydrase II (BCA II) was studied from the molten globule to the native state. Refolding was possible to achieve by mere addition of the metal ion to the apomolten-globule, because the apoenzyme was less stable than the holoenzyme. The cofactor-effected refolding can be summarized as follows: 1) initially, the metal ion binds to the molten globule; 2) compaction of the metal-binding site region is then induced by the metal ion binding; 3) a functioning active center is formed; 4) finally, the native tertiary structure is generated in the outer parts of the protein.

    In paper IV the aim was to determine the nature of the tetramer contact of human extracellular superoxide dismutase (hEC-SOD). We chose a strategy in which we mapped the subunit interaction interface by studying effects of twelve different mutations in the N-terminal domain fused to HCA II. The results show that the hydrophobic side of a predicted amphiphatic a-helix (formed by residues 14-32) in the N-terminal domain is essential for the subunit interaction.

    List of papers
    1. Contribution of tryptophan residues to the CD spectrum of the extracellular domain of human tissue factor: Application in folding studies and prediction of secondary structure
    Open this publication in new window or tab >>Contribution of tryptophan residues to the CD spectrum of the extracellular domain of human tissue factor: Application in folding studies and prediction of secondary structure
    2001 (English)In: European Journal of Biochemistry, ISSN 0014-2956, E-ISSN 1432-1033, Vol. 268, no 4, p. 1118-1128Article in journal (Refereed) Published
    Abstract [en]

    The contribution to the circular dichroism (CD) spectrum made by each of the four Trp residues in the extracellular domain of human tissue factor, sTF (s designates soluble), was determined from difference CD spectra. The individual Trp CD spectra showed that all four residues contributed to the CD spectrum in almost the entire wavelength region investigated (180-305 nm). The sum of the individual spectra of each Trp residue in the near-UV region was qualitatively identical to the wild-type spectrum, clearly demonstrating that the Trp residues are the major contributors to the spectrum in this wavelength region. Trp CD bands interfere with the peptide bands in the far-UV region, leading to uncertainty in the predictions of the amounts of various types of secondary structure. Accordingly, the best prediction of secondary sTF structure content was achieved using a hypothetical Trp-free CD spectrum obtained after subtraction of all individual Trp spectra from the wild-type spectrum. The mutated Trp residues were also exploited as intrinsic probes to monitor the formation of local native-like tertiary structure by kinetic near-UV CD measurements. The global folding reaction was followed in parallel with a novel functional assay that registered the recovery of cofactor activity, i.e. stimulation of the amidolytic activity of Factor VIIa. From these measurements, it was found that sTF appears to regain FVIIa cofactor activity before the final side-chain packing of the Trp residues. The combined kinetic refolding results suggest that the compact asymmetric environments of the individual Trp residues in sTF are formed simultaneously, leading to the conclusion that the native tertiary structure of the whole protein is formed in a cooperative manner.

    Keywords
    Aromatic residues, Circular dichroism, Folding, Prediction, Secondary structure, Tissue factor
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47393 (URN)10.1046/j.1432-1327.2001.01981.x (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-12-22
  • 4.
    Andersson, Jon M.
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Low-temperature growth of alumina2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Physical phenomena related to the growth of alumina, A12O3, are investigated by experiments and ab initio calculations. Alumina is a well studied material with applications in a variety of areas, due to its many beneficial properties. For example, the α and κ phases are widely used as wear-resistant coatings due to their hardness and thermal stability, while, e.g., the γ and θ phases find applications as catalysts or catalyst supports, since they have large surface areas.

    Alumina growth at low temperatures usually results in one of the metastable phases. These are involved in transition sequences, which all irreversibly end in the transformation to the thermodynamically stable α phase at about 1050°C. Thus, the metastable aluminas can be grown at low temperatures but cannot be used in high temperature applications, while formation of the stable α phase typically require high temperatures, prohibiting the use of temperature sensitive substrates.

    In the experimental part of this work, single-phase α-alumina thin films were grown at temperatures down to 280°C. This was achieved by pre-depositing a chromia template layer, which is shown to promote formation of α-alumina. The results demonstrate that low-temperature α-alumina growth is possible once initial nucleation has occurred.

    In the second part of this work, the effect of additives on the phase stability of α- and θ-alumina is investigated by density functional theory calculations. The studied alumina dopants are 5 at.% of Cr, Mo, Co, or As, which substitute for Al in the lattices, and 5 at.% of N or S, substituting for O. We predict that most tested dopants tend to reverse the stability between α- and θ-alumina, so that, e.g., Mo-doping makes the θ phase energetically favored. The exception is Co, which instead gives a slight increase in the relative stability of the α phase. The stability of some of these compounds is also studied by calculating their energies of formation from their constituents, i.e., related dopant oxides, pure metals, and molecules. The results show that the Cr-, Mo-, and Co-doped aluminas are higher in energy than phase separations into pure alumina and other phases, containing the dopants. Thus, the doped aluminas seem to be metastable and will most likely phase separate at high temperatures.

  • 5.
    Andersson, Kjell
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Development of a Method for Comparing Amphetamine Samples2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The studies presented in this thesis were part of a pan-European project, and they describe the research performed to develop a method for comparing amphetamine samples. The work included the following: optimisation of a method for profiling of amphetamine by gaschromatography (GC); optimisation of a technique for preparing samples for GC analysis; testing and evaluation of the abilities of a number of distance metrics to discern links between amphetamine samples originating from the same batch of synthesis analysed using the method developed in the current studies.

    Street amphetamine contains hundreds of different by-products (target compounds), many of which have been identified and found to come from the different conditions used in the manufacturing process. Therefore, the main objective of developing the GC method was to optimise separation and quantification of the target compounds. The best separation was achieved using a DB-35MS capillary column. For quantification, mass spectrometry (MS) in the scan mode employing one target ion seemed to perform best, because this technique provided superior selectivity, and also made it possible to use mass spectra to identify target compounds. In addition, MS detection proved to offer excellent between-laboratory reproducibility.

    The conditions used to prepare amphetamine samples for liquid-liquid extraction (LLE) andsolid-phase extraction (SPE) were also optimised. The sample preparation methods gave similar results but it was easier to use LLE, hence it was chosen for further sample preparation.

    The ability of various numerical methods to find links between amphetamine samples was tested on GC-MS data of 26 target compounds that had been transformed by various pretreatment techniques. The best results were obtained when using Pearson correlation applied to data transformed by normalisation followed by applying fourth root.

    It was also demonstrated that the amphetamine profiling method developed in the current studies was superior to a procedure already in use in a number of forensic laboratories in Europe.

    List of papers
    1. Development of a harmonised method for the profiling of amphetamines: II. Stability of impurities in organic solvents
    Open this publication in new window or tab >>Development of a harmonised method for the profiling of amphetamines: II. Stability of impurities in organic solvents
    Show others...
    2005 (English)In: Forensic Science International, ISSN 0379-0738, E-ISSN 1872-6283, Vol. 149, no 03-Feb, p. 231-241Article in journal (Refereed) Published
    Abstract [en]

    The present study focused on the stability of 22 amphetamine impurities dissolved in six organic solvents: isooctane, toluene, ethanol, dichloromethane, ethyl acetate, and diethyl ether. The aim was to find the most inert, and thereby most suitable, solvent for amphetamine profiling. Mixtures of the impurities were prepared in the different solvents, and changes in the concentrations of the individual compounds over-time were monitored by gas chromatographic analysis after 0, 4, 12, 24, 48, and 96 h. Isooctane and toluene provided the most inert conditions, although, a few of the impurities were insufficiently stable in these two solvents. The present experiments were performed as a part of the development of a harmonised method for profiling of amphetamine. The results can be used to support the choice of organic solvents for sample preparation. They also provide information about the stability of the impurities that are found in profiles of illicit amphetamine. This is essential due to the fact, that unstable compounds can have a negative influence on the comparison of profiles.

    Place, publisher, year, edition, pages
    Elsevier, 2005
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-72285 (URN)10.1016/j.forsciint.2004.06.019 (DOI)000227862300016 ()
    Available from: 2011-11-24 Created: 2011-11-24 Last updated: 2023-06-21
    2. Development of a harmonised method for the profiling of amphetamines: III. Development of the gas chromatographic method
    Open this publication in new window or tab >>Development of a harmonised method for the profiling of amphetamines: III. Development of the gas chromatographic method
    Show others...
    2007 (English)In: Forensic Science International, ISSN 0379-0738, E-ISSN 1872-6283, Vol. 169, no 1, p. 50-63Article in journal (Refereed) Published
    Abstract [en]

    This study focused on gas chromatographic analysis of target compounds found in illicit amphetamine synthesised by the Leuckart reaction, reductive amination of benzyl methyl ketone, and the nitrostyrene route. The analytical method was investigated and optimised with respect to introduction of amphetamine samples into the gas chromatograph and separation and detection of the target substances. Sample introduction using split and splitless injection was tested at different injector temperatures, and their ability to transfer the target compounds to the GC column was evaluated using cold on column injection as a reference. Taking the results from both techniques into consideration a temperature of 250 °C was considered to be the best compromise. The most efficient separation was achieved with a DB-35MS capillary column (35% diphenyl 65% dimethyl silicone; 30 m × 0.25 mm, df 0.25 μm) and an oven temperature program that started at 90 °C (1 min) and was increased by 8 °C/min to 300 °C (10 min). Reproducibility, repeatability, linearity, and limits of determination for the flame ionisation detector (FID), nitrogen phosphorous detector (NPD), and mass spectrometry (MS) in scan mode and selected ion monitoring (SIM) mode were evaluated. In addition, selectivity was studied applying FID and MS in both scan and SIM mode. It was found that reproducibility, repeatability, and limits of determination were similar for FID, NPD, and MS in scan mode. Moreover, the linearity was better when applying FID or NPD whereas the selectivity was better when utilising the MS. Finally, the introduction of target compounds to the GC column when applying injection volumes of 0.2 μl, 1 μl, 2 μl, and 4 μl with splitless injection respectively 1 μl with split injection (split ratio, 1:40) were compared. It was demonstrated that splitless injections of 1 μl, 2 μl, and 4 μl could be employed in the developed method, while split injection and splitless injections of 0.2 μl should be avoided.

    Place, publisher, year, edition, pages
    Elsevier, 2007
    Keywords
    Amphetamine; Impurities; Profiling; Optimisation; Separation; Gas chromatography–mass spectrometry
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-72288 (URN)10.1016/j.forsciint.2006.10.018 (DOI)000247113600007 ()
    Available from: 2011-11-24 Created: 2011-11-24 Last updated: 2023-06-21Bibliographically approved
    3. Development of a harmonised method for the profiling of amphetamines: IV. Optimisation of sample preparation
    Open this publication in new window or tab >>Development of a harmonised method for the profiling of amphetamines: IV. Optimisation of sample preparation
    Show others...
    2007 (English)In: Forensic Science International, ISSN 0379-0738, E-ISSN 1872-6283, Vol. 169, no 1, p. 64-76Article in journal (Refereed) Published
    Abstract [en]

    The suitability of liquid–liquid extraction (LLE) and solid-phase extraction (SPE) for the preparation of impurity extracts intended for gas chromatographic profiling analyses of amphetamine were evaluated. Both techniques were optimised with respect to the extraction of selected target compounds by use of full factorial designs in which the variables affecting the performance were evaluated. Test samples consisted of amphetamine synthesised by the Leuckart reaction, by reductive amination of benzyl methyl ketone and by the nitrostyrene route. The performance of LLE and SPE were comparable in terms of repeatability and recovery of the target compounds. LLE was considered the better choice for the present harmonised amphetamine profiling method due to the lack of information on the long-term stability of SPE columns.

    Place, publisher, year, edition, pages
    Elsevier, 2007
    Keywords
    Amphetamine; Impurities; Profiling; Optimisation; SPE; LLE; GC-FID; GC–MS
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-72289 (URN)10.1016/j.forsciint.2006.10.017 (DOI)000247113600008 ()
    Available from: 2011-11-24 Created: 2011-11-24 Last updated: 2023-06-21
    4. Development of a harmonised method for the profiling of amphetamines V: Determination of the variability of the optimised method
    Open this publication in new window or tab >>Development of a harmonised method for the profiling of amphetamines V: Determination of the variability of the optimised method
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    2007 (English)In: Forensic Science International, ISSN 0379-0738, E-ISSN 1872-6283, Vol. 169, no 1, p. 77-85Article in journal (Refereed) Published
    Abstract [en]

    This paper is the fifth in a series of six in relation to the development of a harmonised method for the profiling of amphetamine [L. Aalberg, K. Andersson, C. Bertler, H. Borén, M.D. Cole, J. Dahlén, Y. Finnon, H. Huizer, K. Jalava, E. Kaa, E. Lock, A. Lopes, A. Poortman-van der Meer, E. Sippola, Development of a harmonised method for the profiling of amphetamines I. Synthesis of standards and compilation of analytical data, Forensic Sci. Int. 149 (2005) 219–229; L. Aalberg, K. Andersson, C. Bertler, M.D. Cole, Y. Finnon, H. Huizer, K. Jalava, E. Kaa, E. Lock, A. Lopes, A. Poortman-van der Meer, E. Sippola, J. Dahlén, Development of a harmonised method for the profiling of amphetamines II. Stability of impurities in organic solvents, Forensic Sci. Int. 149 (2005) 231–241]. The third paper [K. Andersson, K. Jalava, E. Lock, L. Aalberg, Y. Finnon, H. Huizer, E. Kaa, A. Lopes, A. Poortman-van der Meer, M.D. Cole, J. Dahlén, E. Sippola, Development of a harmonised method for the profiling of amphetamines III. Development of the gas chromatographic method, Forensic Sci. Int., in press] dealt with the optimisation of the gas chromatographic and detection methods whereas the fourth paper [K. Andersson, K. Jalava, E. Lock, Y. Finnon, S. Stevenson, L. Aalberg, H. Huizer, E. Kaa, A. Lopes, A. Poortman-van der Meer, M.D. Cole, J. Dahlén, E. Sippola, Development of a harmonised method for the profiling of amphetamines IV. Optimisation of sample preparation, Forensic Sci. Int., in press] concerned the optimisation of the extraction method prior to GC analysis.

    This paper is a study of the optimised method in order to determine its stability. Investigations of within and between day variations were carried out in four laboratories. Moreover, variations between laboratories were also determined. Both flame ionisation detector (FID) and MS detection were used. One laboratory studied nitrogen-phosphorous detector (NPD) detection as well. For this task, 12 batches of amphetamine were prepared. Six of them were synthesised via the Leuckart route, three via the nitrostyrene route and three via the reductive amination route [A.M.A. Verweij, Impurities in illicit drug preparations: amphetamine and methamphetamine, Forensic Sci. Rev. 1 (1989) 2–11].

    Taking into account all studied target compounds and the average results from four laboratories, the within day variation was around 6% for FID and 5% for MS, the between days variation was around 10% for FID and 8% for MS. For NPD detection, within day variation was 5% and between days variation 9% (only one laboratory). Finally, the inter-laboratory variation was about 12% for FID (four laboratories) and 10% for MS (three laboratories).

    Place, publisher, year, edition, pages
    Elsevier, 2007
    Keywords
    Amphetamine; Profiling; GC-FID; GC–MS; GC-NPD; Inter-laboratory variation
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-72290 (URN)10.1016/j.forsciint.2006.10.019 (DOI)000247113600009 ()17178203 (PubMedID)
    Available from: 2011-11-24 Created: 2011-11-24 Last updated: 2023-06-21
    5. Development of a harmonised method for the profiling of amphetamines VI: Evaluation of methods for comparison of amphetamine
    Open this publication in new window or tab >>Development of a harmonised method for the profiling of amphetamines VI: Evaluation of methods for comparison of amphetamine
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    2007 (English)In: Forensic Science International, ISSN 0379-0738, E-ISSN 1872-6283, Vol. 169, no 1, p. 86-99Article in journal (Refereed) Published
    Abstract [en]

    Amphetamine samples were analysed by gas chromatography–mass spectrometry (GC–MS), and the peak areas of 33 target compounds were transformed by applying various pretreatment techniques. The objective was to optimise the ability of a number of distance metrics to establish links between samples of amphetamine originating from the same batch (henceforth refered to as linked distances). Furthermore, partial least squares discriminant analysis (PLS-DA) was used to evaluate the effects of various pretreatment methods on separation of amphetamine batches synthesised by the Leuckart reaction, reductive amination of benzyl methyl ketone, and the nitrostyrene route. The most efficient way to pretreat GC–MS data varied for the different distance metrics, although best results were obtained when data were normalised to the sum of peak areas, and either the fourth root or a logarithm was applied to the normalised data. When pretreating normalised data by fourth root transformation, Pearson correlation was the distance metric that was most successful at finding linked samples. Normalisation and the use of fourth root also represented the best method of pretreating data when employing PLS-DA to separate samples synthesised by different routes. To achieve a faster and more user-friendly procedure for evaluating chromatograms, experiments were performed in which the number of target compounds used to compare samples was reduced. The effect of each compound that was removed was studied by applying PLS-DA and by using Pearson correlation to calculate linked distances as well as unlinked distances (between samples from different batches of amphetamine). Considering both links between samples from the same batch and separation of samples synthesised by different routes, the best results were obtained with the data set comprising 26 compounds. Finally, it was found that the profiling method developed in this work was superior to an existing technique with respect to separating linked and unlinked distances.

    Place, publisher, year, edition, pages
    Elsevier, 2007
    Keywords
    Amphetamine profiling; Numerical methods; Pretreatment; PLS-DA; Pearson correlation; GC–MS; Fourth root
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-72291 (URN)10.1016/j.forsciint.2006.10.020 (DOI)000247113600010 ()
    Available from: 2011-11-24 Created: 2011-11-24 Last updated: 2023-06-21
  • 6.
    Andersson, Theresa
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Molecular recognition of proteins by functionalized folded polypeptide receptors2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes the design, synthesis and characterization of synthetic receptor molecules for the recognition and binding of proteins with applications in bioseparation and biosensing. A 42-residue polypeptide, designed to fold into a helix-loop-helix motif and dimerize in solution to form a four-helix bundle, was used as the scaffold. In the first part of the thesis it was functionalized by the incorporation of three substituents at the side chains of lysine residues. A library of 343 receptors was created and screened for affinity towards the human IgG fab fragment using SPR technology. The scaffold was reacted in a stepwise and combinatorial procedure with seven active esters in a pH controlled site-selective acylation reaction to form amides at the side chains of three lysine residues. Four receptor candidates were found to have 0.1 mM affinities and were selected for further investigation.

    Both the unfunctionalized scaffold and the four selected receptors were found to bind well also to HCA II and the molecular interactions with this target protein were studied in detail. NMR studies of their interactions with 15N-labeled HCA II revealed that the peptides bound to a hydrophobic patch near the active site cleft, and SPR studies of modified receptor polypeptides led to the conclusion that mainly hydrophobic interactions were involved in binding.

    In the second part of the thesis two scaffolds were functionalized with a benzenesulfonamide ligand linked to the scaffold by a series of aliphatic spacers of varying length. Benzenesulfonamide is a known inhibitor of HCA II with a dissociation constant of 1.5 µM and it was found that the overall affinity of the functionalized peptide was enhanced by increasing the length of the ligand spacer due to cooperativity between the scaffold and the ligand in the binding to HCA II. The receptor with a seven methylene group spacer bound HCA II with a dissociation constant of 4 n M. It was also shown that the sequence of the scaffold polypeptide strongly affected the overall affinity of the peptide conjugate for the target protein.

  • 7.
    Artursson, Tom
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Development of Preprocessing Methods for Multivariate Sensor Data2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this work various aspects of data preprocessing are discussed. Preprocessing of data from multivariate sensor data systems is often necessary to extract relevant information or remove disturbances. Depending on the sensor type different preprocessing techniques have to be used. A number of important problems face the user e.g. drifting sensor data which results in very short-lived calibration models, and complex models with a very high number of variables. A systematic approach to handle and analyse data is necessary. In this work different preprocessing techniques are elaborated to reduce these problems.

    Drift is a gradual change in any quantitative characteristic that is supposed to remain constant. Thus, a drifting chemical sensor does not give exactly the same response even if it is exposed to exactly the same environment for a long time. Drift is a common problem for all chemical sensors, and thus needs to be considered as soon as measurements are made for a long period of time. Drift reduction methods try to compensate for the changes in sensor performance using mathematical models and thus maintaining the identification capability of the chemical sensor. The problem with drifting sensor data and thereby short-lived calibration models is overcome using reference samples and smart algorithms utilizing the relation between the reference measurements and the measurements from the samples. This has been studied in two of the papers in this thesis. Two new approaches have been developed and tested using data from real measurements from the electronic nose and tongue.

    In industry and science more and more variables are used to describe the process under study which lead to complex models and calculations. In order to increase the interpretability of the measurements, decrease the calculation demand on the computer, and/or to reduce noise an alternative, more compact, representation of the measurement can be made which describes the important features of the measurement well but with a much smaller vector. This data reduction is the topic of three of the papers in this thesis. Two different methods have been used: A double exponential model has been developed to approximate electronic tongue data. The parameters from this model describe the signal and are used as inputs to multivariate models. Secondly, the more general approach wavelet compression with different strategies for selection of wavelet coefficients has also been studied for variable reduction of both electronic tongue data and X-ray powder diffraction data.

    List of papers
    1. Drift correction for gas sensors using multivariate methods
    Open this publication in new window or tab >>Drift correction for gas sensors using multivariate methods
    Show others...
    2000 (English)In: Journal of Chemometrics, ISSN 0886-9383, E-ISSN 1099-128X, Vol. 14, no 5-6, p. 711-723Article in journal (Refereed) Published
    Abstract [en]

    Drift is one of the most serious impairments afflicting gas sensors. It can be seen as a gradual change in the sensor response over a long period of time when the external conditions an constant. This paper presents a new simple drift counteraction method based on PCA and PLS. The basic idea is to remove the drift direction component from the measurements. The direction of the drift, p, is calculated from measurements for a reference gas. Projecting the sample gas measurements on this vector gives the score vector t. The drift component tp(T) can then he removed from the sample gas data, which we call component correction (CC). The method is tested on a data set based on a reduced factorial design with four gases and a concentration gradient of hydrogen. It is found that the method works efficiently for both cases. Copyright (C) 2000 John Wiley & Sons, Ltd.

    Keywords
    gas sensors, multivariate drift correction, component correction
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-49560 (URN)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-09-30
    2. Variable reduction on electronic tongue data
    Open this publication in new window or tab >>Variable reduction on electronic tongue data
    2002 (English)In: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 452, no 2, p. 255-264Article in journal (Refereed) Published
    Abstract [en]

    Reduction of the number of variables in data from a so-called electronic tongue contributes to simpler model calculations and less storage requirements. In this study, we have developed a model for this purpose. This model describes the response from the electrodes in the electronic tongue with two exponential functions plus a constant term, i(t) = k + kf e-ta + kc e-tß, where t is the time. From the model, five parameters which describe the signal are extracted. These parameters can be used as inputs instead of the original signal to any multivariate algorithm. The results show that the variables obtained are at least as good as the original data to separate between different classes, even though the number of parameters has been reduced between 80 and 199 times. © 2002 Elsevier Science B.V. All rights reserved.

    Keywords
    Curve-fitting, Electronic tongue, PCA, Pre-processing, Variable reduction
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47106 (URN)10.1016/S0003-2670(01)01448-9 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-10-08
    3. Wavelet transform of electronic tongue data
    Open this publication in new window or tab >>Wavelet transform of electronic tongue data
    2002 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 87, no 2, p. 379-391Article in journal (Refereed) Published
    Abstract [en]

    A measurement in a multi-sensor system is characterized by a large array of numbers (a vector or a matrix), sometimes several thousands. In order to increase the interpretability of the measurements, decrease the calculation demand on the computer, and/or to reduce noise, an alternative, more compact, representation of the measurement can be made which describes the important features of the measurement well but with a much smaller vector. The purpose of this paper is to show that for a particular wet-chemical sensor system (pulsed voltammetry, also called an electronic tongue) the data compression can be made using a wavelet transform together with different wavelet selection algorithms for different purposes. The resulting compressed data can also be used for easy interpretation of the measurements and to give hints for improvements or simplifications of the measurement procedure. Two different criteria for selection of wavelet coefficients have been used, variance and discriminance, in two different cases. The variance criterion was used when variations of any kind in the raw data was studied during monitoring of water in drinking water production plant. In this case, the number of variables was reduced with a factor of 18, without loosing relevant information. In the other case, the focus was to separate different microorganisms, therefore, the discriminance selection criterion was successfully used. The number of variables was reduced by a factor of 144, this smaller data set captured the important information for separating the microorganisms, which led to better classification of the test set. © 2002 Published by Elsevier Science B.V.

    Keywords
    Electronic tongue, PCA, Variable reduction, Wavelet transform
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46787 (URN)10.1016/S0925-4005(02)00270-8 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-09-30
  • 8.
    Bachinger, Thomas
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Multisensor arrays: for bioprocess monitoring1999Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Bioprocess engineering, the technology that is focused on the exploitation of the metabolic potential of biological agents, has attracted growing interest throughout the past 50 years from both scientific and industrial communities. The products that have been brought to market range from pharmaceuticals and enzymes to food products and vitamins. The quality of human life has been improved through these efforts in many ways.

    Despite a strong research effort and the fact that microbial transformations often reach yields close to the theoretical maximum. many bioprocesses still operate at relatively low yields. One of the obstacles in effective operation is the extraction of useful information from the bioprocess. Sensors that acquire real-time information about the cells' state and their interaction with the environment in the bioreactor are seldom available. Hence, the implementation of sophisticated process control is prevented.

    In this thesis a new approach of non-invasive on-line bioprocess monitoring is evaluated. Chemical multisensor arrays (i.e. electronic noses) are used to extract information from the composition of volatiles emitted from the cell culture. The focus is on two specific areas: (i) monitoring of key variables in the bioreactor environment and (ii) monitoring of cell states and physiological events. The overall concern is, besides the increase of yield and reproducibility, the safety operation of bioprocesses.

    To cover a comprehensive area of modern bioprocessing, several organisms are investigated under different modes of operation in laboratory- and production scale processes. In repeated batch cultivations of recombinant Escherichia coli it is shown that an electronic nose can monitor biomass and specific growth rate with high accuracy. Glucose and ethanol concentration are monitored in batch cultivations of Saccharomyces cerevisiae. Bioproduct monitoring is presented in production-scale mammalian cell cultivation. The concentration of a therapeutic protein is monitored on-line in this long-term bioprocess thereby also outlining the stability of the sensor technique.

    In production-scale mammalian cell culture it is possible to follow cell transition states and monitor the reproducibility of the process. The physiological state of the cell population is revealed in laboratory-scale cultivations. It is shown that microbial contamination can be identified earlier than with conventional methods. Finally, the metabolic burden imposed on bacterial cells through strong overexpression of recombinant protein is monitored in fed-batch cultivation.

  • 9.
    Benesch, Johan
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Null Ellipsometry and Protein Adsorption to Model Biomaterials2001Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    When implants are inserted into the human body cascades of events become started that will determine the outcome of wound healing and ultimately the success of the implantation. The events start with the adsorption of small molecules, and proteins that may be activated (enzymes) or are able to activate cells of the immune defense and the healing process. In the biomaterials research that is conducted in our group we often ask two questions: "How much?" and "What?" proteins adsorb to a specific surface after incubation in serum or plasma. In the first two papers in this thesis I studied how well we are able to determine the answer to the first question. In the latter two works I tried to answer both questions for two model biomaterial surfaces: oligo(ethylene glycol) terminated self assembled monolayers on gold and chitosan coated silicon.

    In many null ellipsometric studies the protein film refractive, Nfilm, is assumed to be close to 1.5. In the first paper we analyzed if the assumption of Nfilm = 1.465 is satisfactory for the determination of the surface mass density of a submonolayer thin protein film. Human serum albumin (HSA) was labeled with 125I and mixed with non-labeled HSA, and hydrophobic and hydrophilic silicon pieces were incubated in the solutions. The surface mass densities on all pieces determined by both ellipsometry and gamma counter measurements, and was pair-wise compared. The above assumption regarding the value of Nfilm for the agreement between the methods was satisfactory, although precautions have to be made not to overestimate the surface mass density when studying radiolabelled proteins, especially at rough surfaces.

    Are the assumptions made in Paper I also true for up to 100 nm thick protein films or do we have to use a different protein film refractive index and do the ellipsometric model still hold? Human serum albumin (HSA) and polyclonal anti-HSA were labeled with 125I and mixed with unlabelled proteins. Hydrophobic silicon pieces were alternatingely incubated in the two protein solutions. Again the surface mass density was quantified with null ellipsometry and a gamma counter and the methods compared. The thickest protein layers were also gently scratched and the thickness measured by AFM. It appeared that a protein film refractive index Nfilm = 1.5 was a good choice for the determination of the protein film thickness. However, in order to obtain a good methods agreement for the adsorbed mass density a linear correction term was needed in the Cuypers surface mass density formula for ellipsometry. The physical interpretation of the correction term is presently unclear.

    Self assembled monolayers (SAMs) containing oligo (ethyleneglycol) end groups (OEG) have been successfully used to minimize protein adsorption from single protein solutions. We investigated the protein resistance in a fibrinogen solution, serum and plasma of OEG-SAMs with an increasing number of OEG units and with different end groups. It turned out that the adsorbed amounts after 10 minutes of plasma incubation and 15 minutes of fibrinogen incubation decreased with an increasing number of EG units. In serum, the total deposition and subsequent deposition of antibodies towards complement proteins (C3c, C3d and properdin) did not depend on the number of EG units. In summary, the investigated OEG-SAMs were not protein resistant in complex solutions, although the adsorbed amounts varied with the number of EG units and the terminal chemical group. Complement deposition was observed at OEG surfaces.

    For the last 50 odd years different polysaccharides, such as heparin and cellulose have been used for clinical applications and in recent years also chitin and its deacetylated form chitosan have gained increasing attention as potential biomaterials. Previous studies on complement activation by chitosan derivatives have focused on the soluble complement factors and not the surface bound ones that may be important for the binding of cells to surfaces. In our study about 10 nm thick chitosan films were incubated in plasma or serum and subsequently in polyclonal antibodysolutions. The films did not activate complement and the intrinsic pathway of coagulational though fibrinogen was detectable after plasma incubations. When the chitosan film was acetylated it became a strong alternative complement pathway activator in serum and fibrinogen was then no longer antibody detectable after plasma incubations.

    List of papers
    1. Quantification of adsorbed human serum albumin at solid interfaces: A comparison between radioimmunoassay (RIA) and simple null ellipsometry
    Open this publication in new window or tab >>Quantification of adsorbed human serum albumin at solid interfaces: A comparison between radioimmunoassay (RIA) and simple null ellipsometry
    2000 (English)In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 18, no 2, p. 71-81Article in journal (Refereed) Published
    Abstract [en]

    Radioimmunoassay (RIA) and null ellipsometry are two common methods to quantify adsorbed proteins. However, the accuracy of null ellipsometry with a constant protein refractive index (n=1.465, k=0) at ?=632.8 nm has this far not been explored. The present study compared the methods, and the degree of agreement between the simplified single wavelength null ellipsometry and RIA to quantify adsorbed proteins was explored on different surfaces. The quantification methods agreed well when Angstrom smooth hydrophilic or hydrophobic silicon surfaces, and freshly radio-labelled proteins were used. Some discrepancies were noted when either rough surface or stored and aged labelled proteins were used. The differences decreased when the aged protein solution was equilibrated with freshly dissolved proteins at room temperature (RT) for a few hours prior to the surface incubations. Significant differences were also noted between the methods when albumin was adsorbed at it's iso-electric point (pH 4.8). Copyright (C) 2000 Elsevier Science B.V.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47606 (URN)10.1016/S0927-7765(99)00136-8 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-10-08
    2. The determination of thickness and surface mass density of mesothick immunoprecipitate layers by null ellipsometry and protein 125Iodine labeling
    Open this publication in new window or tab >>The determination of thickness and surface mass density of mesothick immunoprecipitate layers by null ellipsometry and protein 125Iodine labeling
    2002 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 249, no 1, p. 84-90Article in journal (Refereed) Published
    Abstract [en]

    The aim of the present study was to ellipsometrically determine the thickness and surface mass density in air for up to 110-nm-thick organic layers made of alternatingly deposited layers of HSA and polyclonal anti-HSA on hydrophobic silicon. The ellipsometrically determined thickness was compared to that obtained by AFM and the deposited surface mass density calibrated with 125I-labeled proteins. The results indicate a good agreement in protein layer thickness between AFM and ellipsometry when the protein film refractive index Nfilm = 1.5 -0i, although then the calculated surface mass density from the ellipsometry data became grossly overestimated by the Cuypers one-component formula. A good agreement in the surface mass density was obtained when the M/A ratio in this formula was lowered from 4.14 to 2.35. This approach indicates a convenient means of determining the refractive indices and surface mass densities of mesothick organic layers proteins on solid supports. © 2002 Elsevier Science (USA).

    Keywords
    Ellipsometry, Mass, Protein adsorption, Radio labeling, Thickness
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46903 (URN)10.1006/jcis.2002.8247 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-10-08
    3. Protein adsorption to oligo(ethylene glycol) self-assembled monolayers: Experiments with fibrinogen, heparinized plasma, and serum
    Open this publication in new window or tab >>Protein adsorption to oligo(ethylene glycol) self-assembled monolayers: Experiments with fibrinogen, heparinized plasma, and serum
    Show others...
    2001 (English)In: Journal of Biomaterials Science. Polymer Edition, ISSN 0920-5063, E-ISSN 1568-5624, Vol. 12, no 6, p. 581-597Article in journal (Refereed) Published
    Abstract [en]

    Low protein adsorption is believed advantageous for blood-contacting materials and ethylene glycols (EG)-based polymeric compounds are often attached to surfaces for this purpose. In the present study, the adsorption of fibrinogen, serum, and plasma were studied by ellipsometry on a series of well-defined oligo(EG) terminated alkane-thiols self-assembled on gold. The layers were prepared with compounds of the general structure HS-(CH2)15-CONH-EGn, where n = 2, 4, and 6. Methoxy-terminated tri(EG) undecanethiol and hydroxyl-terminated hexadecanethiol self-assembled monolayers (SAMs) were used as references. The results clearly demonstrate that the adsorption depends on the experimental conditions with small amounts of fibrinogen adsorbing from a single protein solution, but larger amounts of proteins from serum and plasma. The adsorption of fibrinogen and blood plasma decreased with an increasing number of EG repeats and was temperature-dependent. Significantly less serum adsorbed to methoxy tri(EG) than to hexa(EG) and more proteins remained on the latter surface after incubation in a sodium dodecyl sulfate (SDS) solution, indicating a looser protein binding to the methoxy-terminated surface. All surfaces adsorbed complement factor 3(C3) from serum and plasma, although no surface-mediated complement activation was observed. The present study points to the importance of a careful choice of the protein model system before general statements regarding the protein repellant properties of potential surfaces can be made.

    Place, publisher, year, edition, pages
    Taylor & Francis, 2001
    Keywords
    Complement, Fibrinogen, Heparinized plasma, Oligo(ethylene glycol), Protein adsorption, Self-assembled monolayers, Serum
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47265 (URN)10.1163/156856201316883421 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-10-08Bibliographically approved
    4. Blood protein adsorption onto chitosan
    Open this publication in new window or tab >>Blood protein adsorption onto chitosan
    2002 (English)In: Biomaterials, ISSN 0142-9612, E-ISSN 1878-5905, Vol. 23, no 12, p. 2561-2568Article in journal (Refereed) Published
    Abstract [en]

    Chitosan was recently indicated to enhance osteogenesis, improve wound healing but to activate the coagulation and the complement systems. In the present study approximately 10nm thick chitosan film were prepared on aminopropyltriethoxysilane (APTES) coated silicon. The surfaces were incubated in serum or plasma and subsequently in antibodies towards key complement and contact activation of coagulation proteins. The deposited amounts were compared with those on hydrophilic and hydrophobic silicon, APTES and IgG coated reference samples. Although large amounts of serum deposited to chitosan only a weak transient activation of the complement system and no activation of the intrinsic pathway was observed. Upon acetylation the chitosan layer became a strong activator of the alternative pathway of the complement. After incubation in human plasma anti-fibrinogen deposited onto chitosan but not onto the acetylated chitosan, a finding that may explain previous observations of procoagulant activity by chitosan. Copyright © 2002 Elsevier Science Ltd.

    Keywords
    Chitosan, Complement activation, Contact activation, Ellipsometry, Serum, Surface immobilization
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47038 (URN)10.1016/S0142-9612(01)00391-X (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-10-08
  • 10.
    Bergman, Karl-Olof
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Ecology and conservation of the butterfly Lopinga achine2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The ecology of the red-listed butterfly Lopinga achine was studied in partly open woodlands in the province of Östergotland, Sweden. Detailed autoecological research is essential for successful conservation of a species, and the present investigation focused on the initial aspects of such work, namely, choice of host plant, habitat selection, and dispersal ability. The effects of patch area, isolation, and successional stages of studied sites were also examined.

    The results indicate that L. achine depends on a single host plant, Carex montana. The females preferred to oviposit near this sedge, and most of the larvae (> 80%) were found on C. montana in the field. Egg-laying females and larvae were restricted to C. montana growing in a narrow zone along the edges of glades. This restriction to forest edges is probably the cause for the dependence of L. achine on a restricted stage of canopy cover. More specifically, no L. achine occurred at sites with less than 60% canopy cover, and population densities decreased sharply with more than 90% cover. Eighty-six percent of the studied sites that were occupied are unmanaged, thus the most important aspect of long-term conservation of L. achine is probably the deterministic changes of its woodland habitat. If the sites remain unmanaged, the system of populations will most likely collapse within 20-40 years. Populations of both L. achine and C. montana increased in size at experimentally managed sites where new glades were created. However, an important prerequisite of successful restoration appears to be the presence of C. montana along the edges of new glades from the start, because the rate of C. montana colonisation was slow.

    Most of the populations (50 of 79) were small (< 500 adults; none larger than 4,500) and seemed to show synchronous interannual fluctuation. The probability that a patch would be occupied increased with increasing patch area and decreasing distance to the nearest occupied patch. This was presumably due to different probabilities of extinctions, colonisations, and survival of the inhabiting populations. All but two of the sites with ≥ 3 individuals were within 740 m of the nearest neighbour. Patch size is also a key factor for occurrence: compared to larger patches, small patches are more dependent on neighbour populations.

    The majority of the movements were small and within sites, although in many cases the distance to other sites was less than 100 m. Only 56 individuals (4.0% of those recaptured) moved between sites. It seems that habitat patches of L. achine should be less than 700 m from each other to ensure inter-population contact. Fifteen to 20 wellconnected populations have been stated as a lower limit for a viable metapopulation.Based on these criteria, there are two groups of viable populations in the studied area,and these two groups will be given priority in future conservation work.

    List of papers
    1. Oviposition, host plant choice and survival of a grass feeding butterfly, the Woodland Brown (Lopinga achine)
    Open this publication in new window or tab >>Oviposition, host plant choice and survival of a grass feeding butterfly, the Woodland Brown (Lopinga achine)
    2000 (English)In: Journal of research on the Lepidoptera, ISSN 0022-4324, Vol. 35Article in journal (Refereed) Published
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-42457 (URN)64702 (Local ID)64702 (Archive number)64702 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2022-06-17
    2. Habitat utilization by Lopinga achine (Nymphalidae: Satyrinae) larvage and ovipositing females
    Open this publication in new window or tab >>Habitat utilization by Lopinga achine (Nymphalidae: Satyrinae) larvage and ovipositing females
    1999 (English)In: Biological Conservation, ISSN 0006-3207, E-ISSN 1873-2917, Vol. 88, p. 69-74Article in journal (Refereed) Published
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-42455 (URN)64699 (Local ID)64699 (Archive number)64699 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2022-06-17
    3. Population structure and movements of a threatened butterfly (Lopinga achine) in a fragmented landscape in Sweden
    Open this publication in new window or tab >>Population structure and movements of a threatened butterfly (Lopinga achine) in a fragmented landscape in Sweden
    2002 (English)In: Biological Conservation, ISSN 0006-3207, E-ISSN 1873-2917, Vol. 108, no 3, p. 361-369Article in journal (Refereed) Published
    Abstract [en]

    The red-listed butterfly Lopinga achine was studied by mark-recapture methods in southern Sweden for three seasons. We examined movement within and between populations and egg production in relation to age. The majority of the movements were small with mean movements between recaptures of 45-54 m for males and 94-116 m for females. There were few movements between sites, 20 of 996 recaptured males moved and 36 of 391 recaptured females, even though the distance to other sites was in many cases < 100 m. The distance moved and the number of females moving between sites increased with increasing age. On average, a female that moves does so after laying two-thirds of its eggs in its natal site. It is therefore important to take account of the proportion of reproductive effort involved in dispersal when estimating colonisation ability. The males did not move more with increasing age. Female behaviour can be seen as a "spread-the-risk" strategy, an adaptation to the successional habitat of L. achine, whose natal site sooner or later will deteriorate. Butterflies like L. achine living in successional habitats may exhibit mobility that is intermediate between butterflies living in ephemeral habitats (very mobile) and in long-lived habitats (sedentary). ⌐ 2002 Elsevier Science Ltd. All rights reserved.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-42460 (URN)10.1016/S0006-3207(02)00104-0 (DOI)64706 (Local ID)64706 (Archive number)64706 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2022-06-17
    4. Distribution of occupied and vacant sites and migration of Lopinga achine (Nymphalidae: Satyrinae) in a fragmented landscape
    Open this publication in new window or tab >>Distribution of occupied and vacant sites and migration of Lopinga achine (Nymphalidae: Satyrinae) in a fragmented landscape
    2001 (English)In: Biological Conservation, ISSN 0006-3207, E-ISSN 1873-2917, Vol. 102, no 2, p. 183-190Article in journal (Refereed) Published
    Abstract [en]

    The distribution of occupied and vacant sites and migration of the threatened butterfly Lopinga achine were studied in the province of ╓sterg÷tland, Sweden. The probability of occupation increased with increasing patch area and decreasing distance to the nearest occupied patch, presumably due to different probabilities of colonisation and survival of the populations inhabiting the patches. Probability of female emigration from and immigration to a patch increased with decreasing area. Middle-sized patches produced the largest number of female migrants, although the highest fraction was noted for the smallest patches, and the greatest number of females was marked in the largest patch. The fraction of resident females, but not males, increased with increasing area. The observed occupancy and migration pattern have important conservation implications: all but two populations comprising three or more individuals were within 740 m of the nearest neighbour, indicating the need for networks of suitable, closely situated patches. ⌐ 2001 Elsevier Science Ltd. All rights reserved.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-42459 (URN)10.1016/S0006-3207(01)00081-7 (DOI)64705 (Local ID)64705 (Archive number)64705 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2022-06-17
    5. Population dynamics and the importance of habitat management for conservation of the butterfly Lopinga achine
    Open this publication in new window or tab >>Population dynamics and the importance of habitat management for conservation of the butterfly Lopinga achine
    2001 (English)Article in journal (Refereed) Published
    Abstract [en]

    1. Like many butterflies, the woodland brown Lopinga achine has disappeared from many locations in western Europe due to habitat loss. The population dynamics and the effects of tree and bush cover on population size were studied experimentally south of Link÷ping, Sweden. 2. Most populations in the study area were small (< 500 individuals) and fluctuated synchronously between years. Long-term population dynamics and occurrence were closely correlated with tree and bush cover. Populations occurred only at sites with = 60% canopy cover, but population density decreased sharply where cover exceeded 90%. Survival from egg to adult was highest at the edges of glades (2.3 adults per female) and lowest in the deepest shade (0.7 adults) or open sun (0.6 adults). The annual rate of canopy closure at unmanaged sites decreased linearly with tree and bush cover, approximately 1% closure at 60% cover and 0.3% at 85% cover, making it possible to predict the impact of habitat changes for L. achine. 3. In 1992-95, vegetation was cleared experimentally to create new glade edges at six unmanaged sites where the risk of extinction was high because few glades remained. On average, population size at five of the managed sites increased by > 90%. The population at the sixth site, managed in 1995, decreased by 30%. 4. Cover of the host-plant Carex montana increased significantly at edges of new glades and decreased in closed unaffected woods. Successful restoration probably requires the presence of C. montana along edges of new glades from the onset of management because this plant was slow to colonize plots where it was initially absent. 5. Currently, 86% of the sites in southern Sweden occupied by L. achine are unmanaged. If this situation continues, the metapopulation in this study will probably collapse within 20-40 years. Recovery programmes for L. achine should emphasize metapopulation dynamics, host-plant cover and vegetation dynamics over time. As with many butterflies, successful conservation requires a blend of detailed autoecology and active site management to produce the required successional conditions.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-42458 (URN)10.1046/j.0021-8901.2001.00672.x (DOI)64703 (Local ID)64703 (Archive number)64703 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2022-06-17
  • 11.
    Bergstedt, Johan
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Boreal vegetation responses to forestry as reflected in field trial and survey data2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis had two objectives: the first objective was to evaluate the response of forest ground vegetation to selected forestry operations, i.e. cutting of different intensities and scarification; the second objective was to compare the use of survey data in vegetation research with that of more traditional research using field trials - i.e. can survey data be used and produce results that comply with those emerging from field trials? Here, the results from an analysis of survey data has been compared with results emerging from a field trial.

    Survey data was analysed from the National Forest Inventory (NFI), using 789 sample plots in central and northern Sweden visited twice at an interval of 10-11 years, 294 of which had been subjected to logging between inventories. This was compared with a field trial in central Sweden: a complete block design with four replicates - three treatments and conventional harvesting as the control.

    The cutting intensity was found to have an impact on the ground-layer flora, the change being mostly differences in abundance rather than change in species richness. Those increasing were early successional species, i.e. crustose lichens, Deschampsia flexuosa. In contrast, Vaccinium myrtillus was decreasing substantially in response to increased cutting intensity. A number of species appeared to be indifferent to cutting, i.e. Vaccinium vitisidaea, Trientalis europaea.

    Scarification had a different impact on the flora than cutting: only Polytrichum spp. increased substantially, while many decreased.

    For those effects that were possible to compare in both studies, the results from survey data comply with those from the field trial, indicating that survey data is possible to use in forest vegetation research.

  • 12.
    Bertilsson, Lars
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Molecular Adsorption on Self Assembled Monolayers studied by Surface Acoustic Waves and Infrared Spectroscopy1997Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Chemical sensors based on the selective absorption of gas/vapors in polymer layers rely on molecular interactions. Details of the mechanisms involved can be obtained by studying the adsorption on well defined model organic surfaces. In this thesis, the adsorption of dimethylmethylphosphonate (DMMP), a model molecule for the nerve gas, sarin, and the influence of humidity on the interaction, have been studied. Well defined organic interfaces were obtained by solution self assembly of long chain co-substituted thiol molecules, SH-(CH2)m-X, on gold surfaces. The interfacial properties are given by the tail group X and the following three different functional groups, -CH3, -OH, -COOH, have been analyzed.

    In the first paper, the properties of the self assembled monolayers (SAMs) were examined. The monolayers form ordered semi-crystalline layers with the tail groups defining the chemical properties of the interfaces. In mixed monolayers the surface concentration of the OH and CH3 terminated thiols corresponds to that of the preparation solution and no signs of macroscopic phase separation could be observed.

    The equilibrium adsorption of DMMP was analyzed under sensor conditions by a surface acoustic wave sensor (SAW), sensitive to changes in surface mass, and infrared reflection absorption spectroscopy (IRAS). It was found that DMMP interacts with hydrogen bond donating groups and that the lone pair electrons of the P=O oxygen is the main interacting part of the molecule. Both the temperature programmed desorption of DMMP adsorbed at 100 K and the SAW results from room temperature measurements indicate that the strongest interaction is on the -COOH surface followedby -OH and -CH3. For the -OH surface there is also a surface coverage dependent in the strength of interaction.

    The influence of humidity on the interaction was studied as DMMP was allowed to adsorb at different levels of relative humidity. For the -OH surface, an increase in the DMMP coverage proportional to the relative humidity was observed both with the SAW and with IRAS. A closer examination, however, revealed that a loss of water occurred during adsorption of DMMP. The conclusion from this experiment is that SAW results and other mass sensitive devices must be corrected if competing adsorption takes place. For the -COOH surface, low humidities tend to increase the DMMP coverage but at higher humidities a clear loss was registered by IRAS and the SAW sensor even after compensation for changes in water coverage. As water is present, the increased interaction can be explained by hydrogen bonding to free OH of the water. On the -COOH surface, the adsorption sites become blocked by water, which is more tightly bound on this surface. In the mixed (OH / CH3) monolayers water vapor starts to influence the DMMP adsorption above a critical concentration of OH groups of 0.6. This is also the OH concentration above which total wetting with DMMP occurs.

    The well defined organic monolayers formed by solution self-assembly was found to be suitable for interaction studies of the hydrogen bond accepting DMMP molecule and the influence of humidity on the interaction. The complementary information resulting from the chosen analytical techniques can be used for both qualitative and quantitative evaluation of the adsorption. For example, an optimal composition for the mixed (OH/CH3) SAM has been identified, where the number of adsorption sites and the interaction is sufficiently high, and the influence from humidity still low.

    List of papers
    1. Interaction of dimethyl methylphosphonate with alkanethiolate monolayers studied by temperature-programmed desorption and infrared spectroscopy
    Open this publication in new window or tab >>Interaction of dimethyl methylphosphonate with alkanethiolate monolayers studied by temperature-programmed desorption and infrared spectroscopy
    1997 (English)In: JOURNAL OF PHYSICAL CHEMISTRY B, ISSN 1089-5647, Vol. 101, no 31, p. 6021-6027Article in journal (Refereed) Published
    Abstract [en]

    The adsorption of dimethyl methylphosphonate (DMMP) on well-defined organic surfaces consisting of self-assembled monolayers (SAMs) of omega-substituted alkanethiolates on gold has been studied. Three different surfaces were examined: one terminated with -OH groups (Au/S-(CH2)(16)-OH), one with -CH3 (Au/S-(CH2)(15)-CH3), and one mixed surface with approximately equal amounts of -OH and -CH3 terminated thiols. Detailed information about the nature and strength of the interaction was gathered by infrared reflection-absorption spectroscopy and temperature-programmed desorption under ultrahigh-vacuum conditions. It is found that the outermost functional groups of the thiol monolayer have a pronounced impact on the interaction with DMMP at low coverage. The -OH surface, allowing for hydrogen bonds with the P=O part of the DMMP molecule, increases the strength of interaction by approximately 3.8 kJ/mol as compared to the -CH3 surface. A preadsorbed layer of D2O leads to stronger interaction on all surfaces. This is explained by additional hydrogen bond formation between free O-D at the ice-vacuum interface and DMMP.

    Place, publisher, year, edition, pages
    AMER CHEMICAL SOC, 1997
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-76335 (URN)10.1021/jp9707605 (DOI)A1997XP10700015 ()
    Available from: 2012-04-04 Created: 2012-04-03 Last updated: 2022-02-09
    2. Adsorption of dimethyl methylphosphonate on self-assembled alkanethiolate monolayers
    Open this publication in new window or tab >>Adsorption of dimethyl methylphosphonate on self-assembled alkanethiolate monolayers
    Show others...
    1998 (English)In: JOURNAL OF PHYSICAL CHEMISTRY B, ISSN 1089-5647, Vol. 102, no 7, p. 1260-1269Article in journal (Refereed) Published
    Abstract [en]

    The adsorption of dimethyl methylphosphonate (DMMP), a model molecule for sarin, on three different organic interfaces, prepared by solution self-assembly of alkanethiols on gold, was followed by a surface acoustic wave mass sensor and infrared reflection-absorption spectroscopy at room temperature. The surfaces, characterized by the following tail groups (-OH, -CH3, -COOH), show both quantitative and qualitative differences concerning the interaction with DMMP, the acid surface giving rise to the strongest adsorption. Results obtained in UHV, at low temperatures using infrared spectroscopy and temperature-programmed desorption, support this observation and give complementary information about the nature of the interaction. The hydrogen-bond-accepting properties of the P=O part of DMMP and its impact on the design of sensing interfaces based on hydrogen bonding, as well as the use of self-assembled monolayers to study molecular interactions, are discussed.

    Place, publisher, year, edition, pages
    AMER CHEMICAL SOC, 1998
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-76333 (URN)10.1021/jp973215c (DOI)000072131500027 ()
    Available from: 2012-04-04 Created: 2012-04-03 Last updated: 2022-02-09
  • 13.
    Boström, Mathias
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Van der Waals and Casimir interactions near metal films2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with van der Waals and Casimir forces near metal films. Thick, thin and strictly two-dimensional metal films will be investigated. For many applications one can model a double quantum-well structure with two strictly two-dimensional metallic sheets. The correlation energy of such structures changes when the carriers in the two sheets drift relative each other. This change in the van der Waals energy gives rise to a current drag. We found that the dragged current varies with separation as d-3.5, this is the same as the separation dependence found for the van der Waals force between thin metal films. We have used both optical data and model dielectric functions to investigate the retarded van der Waals interaction between thin and thick metal films. Usually the correct separation dependence of the van der Waals interaction can be found from simple summation of pair-interactions. Thin metallic sheets are an exception to this general rule. To find the correct separation dependence the longitudinal collective excitations must be accounted for. Using optical data and numerical methods we examined the validity of asymptotic results.

    The extension of the van der Waals interaction between macroscopic objects to finite temperatures is the Helmholz free energy of attraction. We have investigated the temperature dependence of the Casimir attraction between a pair of quantum wells. For many small objects found in nature, thermal effects will be a dominating source of attraction. This is also true for quantum well structures. Thermal corrections will be important already at temperatures less than 1 K. At zero temperature the retarded van der Waals energy has three separation regions. At separations of the order of the Thomas-Fermi screening length and smaller both single-particle and collective excitations contribute; in the intermediate range the collective longitudinal excitations dominate and give rise to the van der Waals forces; at large separations the collective transverse modes dominate and the result is identical to the Casimir attraction. The zero frequency part of the Helmholz free energy gives contributions at all finite temperatures. This part of the interaction will dominate at smaller and smaller separations with increasing temperatures. The interaction between thin metal films has one more conceptually interesting property. We have found that there is a possibility that the retarded van der Waals energy between two thin metal films may be larger than the corresponding non-retarded van der Waals energy. The interaction between two 20 Å gold sheets may constitute a candidate to observe this phenomenon. This is related to an unusually large relative contribution from transverse electric modes. When retardation is neglected these modes do not give any contributions at all. This anomalous effect vanishes with increasing dissipation and with increasing film thickness.

    In a comment on a recent calculation of the zero temperature Casimir force between imperfect conductors we corrected a few errors in the treatment of optical data. We have further investigated the temperature dependence of the Casimir force between real metal surfaces. This thesis presents result from calculations performed on both the real and imaginary frequency axis. The result is the same regardless of integration path. Using both optical data and the Drude dielectric function with dissipation included, we found a long-range high temperature asymptote in agreement with the corresponding asymptote for the interaction between quantum wells. This asymptote is in agreement with the result obtained by E. M. Lifshitz for general dielectric surfaces. It is on the other hand half as large as the result obtained by J. Schwinger and coworkers for perfect conductors. This later result has been used in comparison with experiments. It has very recently been argued that one should ignore the physical behaviour of the dielectric function in such a way as to get agreement between the high temperature asymptotes of real and ideal metals. This can be obtained if a plasma model with no dissipation is used for the dielectric response of the metals. We regard it to be a weak proof to simply claim that the correct thermal corrections to the Casimir force of a real material and an idealisation have to be identical. There is however at least one good reason why one can not simply disregard this argument. The experimental data of a recent experiment seems to agree better with this idealisation. As discussed in this thesis one should have in mind that the experimental data are found after a very large electrostatic contribution is subtracted. We have in particular found that the thermal corrections in the limit of low temperatures and small separations are substantially larger than previously assumed. We consider the disagreement between our theoretical results and the experimental ones by Lamoreaux to be intriguing and we hope that it will act as an inspiration for new experimental and theoretical efforts.

    In article 6 the retarded van der Waals energy of an atom between thin silver sheets was investigated. Film thickness, temperature, and retardation influence this interaction. Nienhaus et al. recently used ultra thin (∼50 Å) Ag films on a Si surface to detect hydrogen gas. Dimensionality effects are important for metallic films of this size. Our result is not relevant for that work, but could be important in other cases where atoms interact with ultra thin metal films.

    We have finally calculated the wetting angle as function of doping concentration for water on ln203:Sn (ITO) and determined the critical concentration for spreading. One has tried to overcome the problem of ice on car windscreens by coating the outer surface of the windshield with ITO. ITO is a both transparent and conducting material. Unfortunately, it turns out that one runs into another problem. The material wets too much. Our calculation relies on the dielectric properties of water and the doped semiconductor. We have modelled these properties.

    List of papers
    1. Temperature effects on the Casimir attraction between a pair of quantum wells
    Open this publication in new window or tab >>Temperature effects on the Casimir attraction between a pair of quantum wells
    2000 (English)In: Microelectronic Engineering, ISSN 0167-9317, E-ISSN 1873-5568, Vol. 51, p. 287-297Article in journal (Refereed) Published
    Abstract [en]

    We present calculations of the free energy of attraction between two quantum wells in which the wells are treated as strictly two-dimensional metallic sheets. The van der Waals force exhibits fractional separation dependence in this system. This is in contrast to the usual integer separation dependence. We have performed numerical calculations at different temperatures and with different carrier densities. Except at very low temperatures thermal effects will be a dominating source of attraction. We have determined temperature criteria that must be fulfilled for the fractional separation dependence to be observable. Thermal corrections will be important already at temperatures less than 1 K. We further make some comments on a recent measurement of the Casimir force.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47653 (URN)10.1016/S0167-9317(99)00486-4 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2022-03-16
    2. Fractional van der Waals interaction between thin metallic films
    Open this publication in new window or tab >>Fractional van der Waals interaction between thin metallic films
    2000 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, no 3, p. 2204-2210Article in journal (Refereed) Published
    Abstract [en]

    The van der Waals (vdW) interaction between thin metallic films varies with separation as the separation to a fractional power. This is in contrast to the usual integer-power separation dependence between objects such as atoms, dielectric films, or thick metallic films. We have calculated the free energy of attraction between sheets of gold, silver, copper, beryllium, and tungsten numerically using experimentally found dielectric functions. The results are compared with the corresponding analytical results obtained using simple model dielectric functions. We have investigated how thin the metallic films must be in order for the fractional vdW interaction to be present. To our knowledge, fractional vdW interaction has not yet been confirmed experimentally.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-49827 (URN)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2022-03-16
    3. Comment on "Calculation of the Casimir force between imperfectly conducting plates"
    Open this publication in new window or tab >>Comment on "Calculation of the Casimir force between imperfectly conducting plates"
    2000 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 61, no 4Article in journal, Editorial material (Other academic) Published
    Abstract [en]

    In a recent paper [Phys. Rev. A 59, R3149 (1999)] Lamoreaux reported calculations of the Casimir force. The experimentally found permittivity was used in the calculations. Large deviations were found between numerically evaluated forces and forces derived from a series expanded plasma model. We would like to comment on a few results presented in this work. First, we claim that important features of the imaginary component of the permittivity of copper, presented in Fig. 1(a) are due to the interpolation procedure and are not caused by physical phenomena. These features influence the calculated permittivity for imaginary frequencies, which is the quantity used to calculate the Casimir attraction. Second, we discuss the extrapolation procedure used for low frequencies. The results depend substantially on how this extrapolation is performed.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-49786 (URN)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2022-03-16
    4. van der Waals energy of an atom in the proximity of thin metal films
    Open this publication in new window or tab >>van der Waals energy of an atom in the proximity of thin metal films
    2000 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 61, no 5, p. art. no.-052703Article in journal (Refereed) Published
    Abstract [en]

    The van der Waals energy of a ground-state atom (or molecule) placed between two metal films is calculated at finite temperature. The attraction between thin metal films and a polarizable object can have half-integer separation dependence. This is in contrast to the usual integer separation dependence, shown for instance in the attraction between an atom and a solid surface. We examine how film thickness, retardation, and temperature influence the interaction. To illustrate the effect of finite thickness of the metal film we calculated the van der Waals energy of ground-state hydrogen and helium atoms, and hydrogen molecules, between thin silver films. We finally, briefly, discuss the possibility to measure this effect.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-49751 (URN)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2022-03-16
    5. Thermal effects on the Casimir force in the 0.1-5 mu m range
    Open this publication in new window or tab >>Thermal effects on the Casimir force in the 0.1-5 mu m range
    2000 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 84, no 20, p. 4757-4760Article in journal (Refereed) Published
    Abstract [en]

    The vacuum stresses between a metal half-space and a metal sphere were recently measured at room temperature, in the 0.6-6 mu m range, with an estimated accuracy of 5%. In the interpretation it was assumed that the accuracy was not good enough for observing any thermal effects. We claim that thermal effects are important in this separation range and back up this claim with numerical calculations of the Casimir force at zero temperature and at 300 K, based on tabulated optical data of gold, copper, and aluminum. The effects of dissipation and temperature are investigated and we demonstrate the importance of considering these two corrections together.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-49749 (URN)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2022-03-16
    6. Retardation-enhanced van der Waals force between thin metal films
    Open this publication in new window or tab >>Retardation-enhanced van der Waals force between thin metal films
    2000 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 62, no 11, p. 7523-7526Article in journal (Refereed) Published
    Abstract [en]

    We recently investigated the van der Waals force between thin metal films. Under certain conditions this force decrease with separation to a fractional power. In the present work we use optical data of metals and the zero-temperature Lifshitz formalism to demonstrate a retardation effect. The retarded attraction between thin metal films may be larger than the nonretarded attraction. This property is related to a comparatively weak retardation dependence of the energy that originates from the transverse magnetic modes. At separations where the transverse electric modes give a significant contribution, the net effect can actually be an increased attraction. This effect vanishes with increasing film thickness and with increasing dissipation.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47585 (URN)10.1103/PhysRevB.62.7523 (DOI)
    Note
    Original Publication: Mathias Boström and Bo Sernelius, Retardation-enhanced van der Waals force between thin metal films, 2000, Physical Review B Condensed Matter, (62), 11, 7523-7526. http://dx.doi.org/10.1103/PhysRevB.62.7523 Copyright: American Physical Society http://www.aps.org/Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2022-03-16
  • 14.
    Bröms, Per
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Polymer Light Emitting Devices: A study on how the electrode-polymer interface affects the performance of polymer light emitting devices1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The research reported in this thesis is concerned with a new type of semiconductor device that can be realised by using thin films of semiconducting polymers, or conjugated polymers. In this thesis only one family of these conjugated polymers is studied, namely poly-(para-phenylene vinylene) and derivatives thereof.

    This thesis focuses on how a change in the interface conditions between electrodes and polymer affects the performance of the devices. Especially on how low workfunction metals, e.g. calcium, magnesium interact with poly-(para-phenylene vinylene), and derivatives thereof. Those low workfunction metals are often used as the negative electrode for polymer light emitting devices. This type of light emitting device is described in this thesis and the issues off charge injection and transport is discussed in detail. Also the difference between the ideal theoretical models and real life system is in focus.

    Studies of different types of degradation mechanisms in the polymer light emitting devices are also included. The degradation of the polymer material due to low energy electrons from the thermal electron beam evaporator during fabrication has been studied in detail. Also included is an investigation and comparison of used and unused polymer light emitting devices that has been done with the help of sputtered depth profile analysis with surface sensitive Auger spectrometry.

  • 15.
    Böhlmark, Johan
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    The effect of extreme power densities applied to a planar magnetron2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In plasma assisted thin film growth control over the energy and direction of the incoming species is desired. If the growth species are ionized this can be achieved by the use of a substrate bias. ions may be accelerated by an applied potential, whereas neutral particles may not. Thin films grown by ionized physical vapor deposition (I­PVD) have lately shown promising results regarding film structure and adhesion. high power pulsed magnetron sputtering (HPPMS) is a newly developed technique, which relies on the creation of a dense plasma in front of the sputtering target to produce a large fraction of ions of the sputtered material.

    High power pulses of length ~100 µs are applied to a conventional planar magnetron. The highly energetic nature of the discharge, which involves power densities of several kW per cm2 creates a very dense plasma in front of the target. Previous measurements on the plasma properties indicate peak plasma densities in the order of 1019-1020 electrons per m3 and average electron energies of a few eV in a close vicinity to the target. This allows a large fraction of the sputtered material to be ionized.

    This work is focused onto two areas: 1. the ionization fraction of the sputtered material and the ionization process itself and 2. how the highly energetic discharge and the plasma dynamics affects the magnetic environment of the magnetron. Knowledge and control of the process is of interest in thin film growth when relating film properties to process parameters.

    Optical emission spectroscopy (OES) measurements of the plasma indicate that the degree of ionization of sputtered Ti is very high, over 90 % in the peak of the pulse. Even at relatively low applied target power (~200 Wcm-2 peak power) the recorded spectrum is totally dominated by radiation from ions. The distribution of electronically excited states roughly follows a Boltzmann distribution, with a characteristic temperature of 0.6 eV in the case of Ta. This indicates that the distribution of excited states differs significantly from the distribution of ionized states within Ta. We expect a high degree of ionization of the sputtered material, this requires a significant amount of electrons with energies over the ionization potential, which is between 6 and 7 eV for many metals. Sputtered material is ionized close to the target to be transported into a cooler plasma region. The recorded HPPMS spectra were compared to a spectrum taken from a d.c. magnetron discharge, showing a completely different appearance. The dependence on the choice of target material is also discussed, and is assumed to strongly affect the fraction of ions.

    Magnetic measurements performed with a coil type probe show significant deformation in the magnetic field of the magnetrons during the pulse. Spatially resolved measurements show evidence of a dense azimuthally Ex B drifting current. Circulating currents mainly flow within 2 away cm from the target surface in an early part of the pulse, to later diffuse axially into the chamber and decrease in intensity. We record peak current densities of the ExB drift to be in the order of 105 A/m2. Comparisons between Langmuir probe measurements and the magnetic field deformation also indicates that the expanding highly energetic plasma creates diamagnetic and paramagnetic changes of the magnetic field.

  • 16.
    Christianou, Maria
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Interaction strength and keystone species in model food webs2003Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ecological communities are often exposed to different kind of disturbances of varied magnitude. The response to disturbances can be affected by, among other factors, the strength of interactions between species within the community. The main purpose of this thesis is the study of the relation between interaction strength (distribution and positioning of strong and weak links) and the response of model communities to disturbances. Additionally, we wish to identify keystone species and keystone links and to recognize species vulnerable to secondary extinctions with respect to the interaction strength concept.

    The first part of this study (paper I) deals with species removal from model ecological communities. The number of secondary extinctions following the loss of one species measures the response to this disturbance. The loss of the following species categories triggered, on average, the largest number of secondary extinctions: a) rare resources strongly interacting with many consumers b) abundant intermediate consumer species strongly interacting with many resources and c) abundant weakly interacting resources. Species vulnerable to secondary extinctions were mainly weakly interacting consumers and strongly interacting resources (excluding primary producers). This vulnerability to secondary extinctions was not only dependent on characteristics of the species themselves but also on which species was initially removed. Some species were facing a high probability of extinction after the deletion of a wide range of species categories, while others were vulnerable only to the deletion of few species categories.

    The second part (paper II) deals with less severe disturbances; small changes in the intrinsic growth rate of species and small changes in the interaction strength of links. In this way the importance of both species and links was revealed. The response of the community was measured as the effect of these changes on the resilience of the system. Overall, the resilience of the model communities was more sensitive to changes in weakly interacting species or weak links.

    The main message of this work is that keystone species and keystone links could be context dependent, both with respect to characteristics of the community and the stability criterion used. Studying the effects of severe disturbances, such as species loss, and using the number of secondary extinctions to measure the community's response, the disturbance of strongly interacting species affected the community most. On the contrary, by applying small perturbations to community parameters and measuring the response as the effect on resilience, the perturbation of weakly interacting species and weak links affected the community most. Thus, both strong and weak agents of the community can be important for stability properties under different regimes of disturbance.

  • 17.
    Cimander, Christian
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Multivariate monitoring, modelling and control for stabilization of bioprocesses2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The obstacles to overcome low reproducibility and stability of bioprocesses are numerous. Underlying biochemical processes are inherently non-linear, complex and subject to shifting initial conditions. Problems with high variability are also associated to production strains and scale-up of a bioprocess to largescale bioreactors. Reliable on-line monitoring of key process variables is still a challenging task and hinders the closed-loop control of these key process variables. In this thesis, methods for stabilization of bioprocesses by means of multivariate on-line monitoring, modelling and control are studied.

    The foundation was laid with the development of integrated multivariate bioprocess monitoring, modelling and control within a real-time knowledge-based expert system. Thereby, a large number of signals from different advanced on-line analyzers ranging from mass spectroscopy via on-line HPLC to nearinfrared spectroscopy and electronic noses, could be used in combination with a variety of multivariate modelling and control tools for a flexible development of methods for stabilization of bioreactor processes. Subsequently, it could be shown how problems related to the initial conditions of a bioprocess can be solved by a multivariate assessment of the preculture quality. Furthermore, it was demonstrated how qualitative and quantitative key process variables can be made available and applied for process supervision; here, multivariate statistical process modelling and neural network sensor fusion from on-line monitoring of bioprocesses with advanced on-line analyzers were used. Finally, a closed-loop control method was presented, showing how feedback control of a multivariate key process variable trajectory can improve adherence to the specifications of the bioprocess. As model systems, aerobic fed-batch cultivations using recombinant Escherichia coli and anaerobic yoghurt batch fermentations have been used. The results provide general methods for multivariate stabilization of bioprocesses in precultivation steps, laboratory-scale and production-scale. They show that multivariate monitoring, modelling and control can provide a functional and versatile framework for reduced batch-tobatch variation and stabilization of bioprocesses with possible implications on product quality and process economics.

    List of papers
    1. Integration of distributed multi-analyzer monitoring and control in bioprocessing based on a real-time expert system
    Open this publication in new window or tab >>Integration of distributed multi-analyzer monitoring and control in bioprocessing based on a real-time expert system
    2003 (English)In: Journal of Biotechnology, ISSN 0168-1656, E-ISSN 1873-4863, Vol. 103, no 3, p. 237-248Article in journal (Refereed) Published
    Abstract [en]

    A computer system solution for integration of a distributed bioreactor monitoring and control instrumentation on the laboratory scale is described. Bioreactors equipped with on-line analyzers for mass spectrometry, near-infrared spectroscopy, electrochemical probes and multi-array gas sensors and their respective software were networked through a real-time expert systems platform. The system allowed data transmission of more than 1800 different signals from the instrumentation, including signals from gas sensors, electrodes, spectrometer detectors, balances, flowmeters, etc., and were used for processing and carrying out a number of computational tasks such as partial least-square regression, principal component analysis, artificial neural network modelling, heuristic decision-making and adaptive control. The system was demonstrated on different cultivations/fermentations which illustrated sensor fusion control, multivariate statistical process monitoring, adaptive glucose control and adaptive multivariate control. The performance of these examples showed high operational stability and reliable function and meet typical requirements for production safety and quality. © 2003 Elsevier B.V. All rights reserved.

    Keywords
    Bioreactor monitoring, Fermentation control, Knowledge-based expert system, Multi-analyzers
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46519 (URN)10.1016/S0168-1656(03)00121-4 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-09-24
    2. Assessment of the performance of a fed-batch cultivation from the preculture quality using an electronic nose
    Open this publication in new window or tab >>Assessment of the performance of a fed-batch cultivation from the preculture quality using an electronic nose
    2002 (English)In: Biotechnology progress (Print), ISSN 8756-7938, E-ISSN 1520-6033, Vol. 18, no 2, p. 380-386Article in journal (Refereed) Published
    Abstract [en]

    An electronic nose, a gas-phase multisensor system, was used to monitor precultivations of a recombinant tryptophan-producing Escherichia coli strain. The electronic nose signals showed a high correlation toward the main stages of the precultivations, namely, exponential growth, oxygen-limited growth, and glucose depletion. Principal component analysis (PCA) of the electronic nose signals was performed and shown to be useful for monitoring preculture progression. More importantly, PCA also allowed a qualitative assessment of the preculture performance during subsequent fed-batch cultivations. The electronic nose signals from the precultures showed, furthermore, a high correlation to the time of phosphate limitation and the tryptophan yield coefficient of the subsequent fed-batch cultivations, which allowed an accurate prediction of these process variables using partial least squares (PLS). The results demonstrate on data from 12 cultivations how the electronic nose can be a useful tool for the assessment of inoculum quality, thereby providing means of reducing batch-to-batch variation and increasing the productivity of bioprocesses.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-44243 (URN)10.1021/bp010166j (DOI)76106 (Local ID)76106 (Archive number)76106 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2021-09-24
    3. Sensor fusion for on-line monitoring of yoghurt fermentation
    Open this publication in new window or tab >>Sensor fusion for on-line monitoring of yoghurt fermentation
    2002 (English)In: Journal of Biotechnology, ISSN 0168-1656, E-ISSN 1873-4863, Vol. 99, no 3, p. 237-248Article in journal (Refereed) Published
    Abstract [en]

    Measurement data from an electronic nose (EN), a near-infrared spectrometer (NIRS) and standard bioreactor probes were used to follow the course of lab-scale yoghurt fermentation. The sensor signals were fused using a cascade neural network: a primary network predicted quantitative process variables, including lactose, galactose and lactate, a secondary network predicted a qualitative process state variable describing critical process phases, such as the onset of coagulation or the harvest time. Although the accuracy of the neural network prediction was acceptable and comparable with the off-line reference assay, its stability and performance were significantly improved by correction of faulty data. The results demonstrate that on-line sensor fusion with the chosen analyzers improves monitoring and quality control of yoghurt fermentation with implications to other fermentation processes. ⌐ 2002 Elsevier Science B.V. All rights reserved.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-44254 (URN)10.1016/S0168-1656(02)00213-4 (DOI)76123 (Local ID)76123 (Archive number)76123 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2021-09-24
    4. Online monitoring of a bioprocess based on a multi-analyser system and multivariate statistical process modelling
    Open this publication in new window or tab >>Online monitoring of a bioprocess based on a multi-analyser system and multivariate statistical process modelling
    2002 (English)In: Journal of chemical technology and biotechnology (1986), ISSN 0268-2575, E-ISSN 1097-4660, Vol. 77, no 10, p. 1157-1168Article in journal (Refereed) Published
    Abstract [en]

    Multivariate statistical process control (MSPC) was for the first time applied to analyse data from a bioprocess on-line multi-analyser system consisting of an electronic nose (EN), a near-infrared spectroscope (NIRS), a mass spectrometer (MS) and standard bioreactor probes. One hundred and fifty sensor signals from the electronic nose, 1050 wavelength signals from the NIRS, carbon dioxide evolution rate calculated from mass spectrometer signals and standard bioreactor data (eg amount of substrate fed) were interrogated for their ability to model a bioprocess using MSPC. The models obtained were validated on a recombinant Escherichia coli fed-batch process for tryptophan production. Limiting trajectories were defined in the MSPC models for warning, action, and process experience with respect to biomass and tryptophan concentrations. The results showed the capacity and robustness of MSPC models for monitoring with multi-analysers and allowed a comparison of the different analysers' suitability for this kind of data processing. Furthermore, the results demonstrate that MSPC models provide a functional and versatile framework for coping with large information flows and are also suited to a variety of other bioprocessing monitoring and control tasks. ⌐ 2002 Society of Chemical Industry.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-44253 (URN)10.1002/jctb.691 (DOI)76120 (Local ID)76120 (Archive number)76120 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2021-09-24
    5. Bioprocess control from a multivariate process trajectory.
    Open this publication in new window or tab >>Bioprocess control from a multivariate process trajectory.
    2004 (English)In: Bioprocess and biosystems engineering (Print), ISSN 1615-7591, E-ISSN 1615-7605, Vol. 26, no 6, p. 401-411Article in journal (Refereed) Published
    Abstract [en]

    A multivariate bioprocess control approach, capable of tracking a pre-set process trajectory correlated to the biomass or product concentration in the bioprocess is described. The trajectory was either a latent variable derived from multivariate statistical process monitoring (MSPC) based on partial least squares (PLS) modeling, or the absolute value of the process variable. In the control algorithm the substrate feed pump rate was calculated from on-line analyzer data. The only parameters needed were the substrate feed concentration and the substrate yield of the growth-limiting substrate. On-line near-infrared spectroscopy data were used to demonstrate the performance of the control algorithm on an Escherichia coli fed-batch cultivation for tryptophan production. The controller showed good ability to track a defined biomass trajectory during varying process dynamics. The robustness of the control was high, despite significant external disturbances on the cultivation and control parameters.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-40927 (URN)10.1007/s00449-003-0327-z (DOI)54656 (Local ID)54656 (Archive number)54656 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2023-11-02
  • 18.
    Dahlgren, Anders
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Design, Synthesis, and Structure-Activity Relationships Analysis of Potential Inhibitors of the Serine Protease Thrombin and the Malarial Aspartic Proteases Plasmepsin I and II2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The design, synthesis, and structure-activity relationships analysis of some potential protease inhibitors are outlined in this thesis. In particular, the serine protease thrombin and the malarial aspartic proteases plasmepsin I and II (Plm I and II) are described in regard to the roles they play in living organisms, and that is followed by discussions concerning the design, synthesis, and biological test results of inhibitors of these enzymes.

    A topic considered is why it is sometimes necessary to pharmacologically regulate the blood-coagulating capacity of thrombin. Moreover, various aspects of malaria arediscussed, including the geographical distribution of the disease, the biological features of the malaria parasites, and the consequences of malaria infection.

    The problems associated with designing enzyme inhibitors in general are briefly explained. Furthermore, the design of inhibitors of thrombin and Pim I and II is considered in greater detail, and the task of designing the novel potential inhibitors reported in the papers underlying this thesis is addressed.

    The synthesis of thrombin inhibitors based on tartaric acid and malic acid, and the synthesis of newly designed plasmepsin inhibitors based on a novel reversed-statine core are described in detail. The utilization of solid support chemistry in the work on plasmepsin inhibitors is explained thoroughly. Additionally, there are discussions extensively covering the challenges encountered regarding the syntesis of all types of inhibitors in this thesis, and alternative synthetic strategies are addressed. Biological test results of the synthesized target compounds are analyzed, and structure-activity relationships (SAR) discussions are conducted as thoroughly as possible.

    List of papers
    1. Synthesis of potential thrombin inhibitors. Incorporation of tartaric acid templates as P2 proline mimetics
    Open this publication in new window or tab >>Synthesis of potential thrombin inhibitors. Incorporation of tartaric acid templates as P2 proline mimetics
    Show others...
    2002 (English)In: Bioorganic & Medicinal Chemistry, ISSN 0968-0896, E-ISSN 1464-3391, Vol. 10, no 5, p. 1567-1580Article in journal (Refereed) Published
    Abstract [en]

    With the objective to prepare novel non-peptidic thrombin inhibitors, bioisosteres of the inhibitory tripeptide D-Phe-Pro-Arg chain have been examined. Thus, the P1 Arg was replaced with p-amidinobenzylamine, an elongated homologue of the same and with 2,5-dichloro benzylamine. The P2-P3, D-Phe-Pro, was replaced with a novel tartaric acid template coupled to a series of readily available, mainly lipophilic, amines. Some of these compounds exhibit promising thrombin inhibition activity in vitro, IC50~5.9 µM. © 2002 Elsevier Science Ltd. All rights reserved.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47060 (URN)10.1016/S0968-0896(01)00426-6 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-09-30
    2. Novel morpholinone-based D-Phe-Pro-Arg mimics as potential thrombin inhibitors: design, synthesis, and X-ray crystal structure of an enzyme inhibitor complex
    Open this publication in new window or tab >>Novel morpholinone-based D-Phe-Pro-Arg mimics as potential thrombin inhibitors: design, synthesis, and X-ray crystal structure of an enzyme inhibitor complex
    Show others...
    2002 (English)In: Bioorganic & Medicinal Chemistry, ISSN 0968-0896, E-ISSN 1464-3391, Vol. 10, no 6, p. 1829-1839Article in journal (Refereed) Published
    Abstract [en]

    A morpholinone structural motif derived from d(+)- and l(−)-malic acid has been used as a mimic of d-Phe-Pro in the thrombin inhibiting tripeptide d-Phe-Pro-Arg. In place of Arg the more rigid P1 truncated p-amidinobenzylamine (Pab) or 2-amino-5-aminomethyl-3-methyl-pyridine have been utilized. The synthetic strategy developed readily delivers these novel thrombin inhibitors used to probe the α-thrombin inhibitor binding site. The best candidate in this series of thrombin inhibitors exhibits an in vitro IC50 of 720 nM. The X-ray crystal structure of this candidate co-crystallized with α-thrombin is discussed.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47039 (URN)10.1016/S0968-0896(02)00023-8 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-09-30
    3. Solid-phase library synthesis of reversed-statine type inhibitors of the malarial aspartyl proteases plasmepsin I and II
    Open this publication in new window or tab >>Solid-phase library synthesis of reversed-statine type inhibitors of the malarial aspartyl proteases plasmepsin I and II
    Show others...
    2003 (English)In: Bioorganic & Medicinal Chemistry, ISSN 0968-0896, E-ISSN 1464-3391, Vol. 11, no 6, p. 827-841Article in journal (Refereed) Published
    Abstract [en]

    With the aim to develop inhibitors of the plasmepsin I and II aspartic proteases of the malaria parasite Plasmodium falciparum, we have synthesized sets of libraries from novel reversed-statine isosteres, using a combination of solution phase and solid phase chemistry. The synthetic strategy furnishes the library compounds in good to high overall yields and with excellent stereochemical control throughout the developed route. The products were evaluated for their plasmepsin I and II inhibiting properties and were found to exhibit modest but promising activity. The best inhibitor exhibits an in vitro activity of 28% inhibition of plasmepsin II at an inhibitor concentration of 0.5 µM (Ki for Plm II=5.4 µM). © 2003 Elsevier Science Ltd. All rights reserved.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46636 (URN)10.1016/S0968-0896(02)00568-0 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-09-30
  • 19.
    Dalfors, Joakim
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Photoluminescence studies of the electronic structure in some III-V quantum structures1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Semiconductor compound materials from groups III and V in the periodic table have attracted much interest during recent years, due to promising properties for optoelectronic devices such as lasers and light emitting diodes. Most of these devices are fabricated from quantum well (QW) structures. This thesis is based on optical studies on quantum wells and modulation doped heterostructures in some important III-V material systems: InGaAs/lnP, InGaN/GaN and GaN/AlGaN. The experimental investigations involve photoluminescence (PL), PL excitation (PLE) and time-resolved PL spectroscopy. Simple theoretical models have been used in some cases to compare with and identify experimental data.

    In the InGaAs/lnP material system, the dependence of the electronic structure on both In content (and thereby built-in strain) and well width has been studied by means of Fourier transform (FT) PL and FTPLE for a set of QW samples. The reduced effective masses for the same set of samples have been determined by applying external magnetic fields and fitting the experimental data to Landau levels. Similar experiments have also been performed on a set of modulation doped heterostructures, where a self-consistent calculation enabled peak identification as well as a suggestion for a probable potential profile.

    Electronic structure and optical transitions have been studied in a modulation doped GaN/AlGaN QW and compared to calculations based on a simple model. Also, the recombination processes involved in the PL from InGaN/GaN multi QW samples have been investigated. The In content and the growth condition for the barriers were varied. In a set of Si doped samples with different doping concentrations, the screening of the strain induced piezoelectric field was studied.

  • 20.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Strain-related structural and vibrational properties of group-III nitride layers and superlattices2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This PhD thesis is focused on strain-related phenomena in group-III nitride layers and heterostructures. Key issues in material properties as phonon mode behavior, structure and lattice parameters of AlN, InN and GaN, as well as of AlN/GaN superlattices are addressed in order to give answers to some open questions. The research is motivated by the enormous technological application potential of the group-III nitride materials for optoelectronic devices and high temperature, and high power devices. Due to the lack of native substrates, the group-III nitrides are typically grown on foreign substrates resulting inbuilt-in strain in the films, as well as, in misorientation and defect formation. Substantial efforts have been concentrated on the research of strain-related fundamental properties of group-III nitrides. However, some of the strain-related structural and vibrational properties of these materials remain unclear and this gap has to be filled in order to fully explore the possibilities for applications.The thesis contributes to the knowledge of the strain-related phenomena ingroup-III nitrides by concentrating on the following: i) lattice parameters and strain relaxation in GaN, AlN, InN films with different thicknesses, as well as free-standing GaN quasi-substrates; ii) phonon mode behavior and deformation potentials of AlN and InN; iii) structural evolution in AlN and GaN; iv)phonon mode behavior and strain evolution in AlN/GaN superlattices. The layers studied were grown by a variety of growth techniques and nucleation schemes aiming at establishing of a comprehensive understanding of the material properties.

    The thesis is organized as follows: In the first part a general description of the basic properties of group-III nitrides is given with a special emphasis on the structural and vibrational properties. The vibrational properties of lowdimensional group-III nitrides are also reviewed. After that, basic concepts of strain phenomenon in group-III nitrides, as well as the strain effects on phonons and on structural properties are discussed. Finally, the experimental techniques used are introduced.

    The second part of the thesis consists of six papers providing informationon specific strain-related structural and vibrational properties of III-nitride layers and superlattices.

    The lattice parameters of GaN films grown by two different techniques on a-plane sapphire are the subject of Paper I. We have determined two different values of the in-plane lattice parameter of the GaN layers in contrast to only one in the case of films grown on c-plane sapphire. We suggest that the observed distortion of the hexagonal symmetry can be attributed to the presence of anisotropic in-plane strain in the films. A new approach to determination of lattice parameters has been proposed.

    Paper II deals with the lattice parameters of GaN quasi-substrates grown by hydride vapor phase epitaxy using two nucleation schemes. The lattice parameters of both, Ga- and N-polar faces of the quasi-substrates were determined and compared. The strain relaxation phenomena in such free-standing layers and the concept of strain-free lattice parameters are discussed.

    Papers III and IV are devoted to the deformation potentials of the E 1 (TO)mode in AlN, and the E1 (TO) and E2 modes in InN, where a combination of infraredellipsometry, infrared reflection, Raman scattering and x-ray diffractionstudies was used. The reported results in Paper III present the first experimentalvalues for the E1 (TO) deformation potentials of AlN and the results for the InN deformation potentials in Paper IV are the first ever reported.

    The strain evolution and its effect on the structural and vibrational properties of thin epitaxial AlN layers with different thicknesses have been studied in Paper V. A model of the strain evolution with film thickness and related defect structure is suggested and it is successfully used in the infrared ellipsometry data analysis.

    Paper VI is focused on the strain evolution in AlN/GaN superlattices withdifferent periods and its effect on their phonon properties. The presence of phonons originating from the superlattice constituents was revealed and their nature is discussed.

    List of papers
    1. Lattice parameters of GaN layers grown on a-plane sapphire: Effect of in-plane strain anisotropy
    Open this publication in new window or tab >>Lattice parameters of GaN layers grown on a-plane sapphire: Effect of in-plane strain anisotropy
    Show others...
    2003 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 82, no 5, p. 703-705Article in journal (Refereed) Published
    Abstract [en]

    The lattice parameters of GaN layers grown on a-plane sapphire were investigated. The hydride vapor phase epitaxy and metalorganic vapor phase epitaxy were used for the determination of parameters. The strain anisotropy was found to have different values in the films and obtained values of parameters were grouped around two values.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46727 (URN)10.1063/1.1542931 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2023-12-28
    2. Deformation potentials of the E-1(TO) mode in AlN
    Open this publication in new window or tab >>Deformation potentials of the E-1(TO) mode in AlN
    Show others...
    2002 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 80, no 13, p. 2302-2304Article in journal (Refereed) Published
    Abstract [en]

    The deformation potentials of the E-1(TO) mode in AlN are experimentally determined by combining infrared reflection spectroscopy and x-ray diffraction measurements and using a reported value of the Raman-stress factor for hydrostatically stressed bulk AlN. The deformation potentials are found to strongly depend on published stiffness constants of AlN. A comparison with earlier theoretically calculated values of the deformation potentials is made. (C) 2002 American Institute of Physics.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47892 (URN)10.1063/1.1465105 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2023-12-28
  • 21.
    Du, Chun-Xia
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Studies of Light Emitting Devices Based on Er-doped Si and SiGe Layered Structures2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Doping with rare earth element erbium (Er) in Si has recently attracted a lot of research interest due to potential applications in Si-based opto-electronics. By using molecular beam epitaxy (MBE), precipitate-free Er-doping in Si has been made together with other co-dopants, e.g., oxygen (0) and fluorine (F), up to a level ∼1020 cm-3. Together with other capabilities of high quality growth of layered structures with desired doping profiles and heterojunctions offered by MBE, several types of dedicated Er-doped Si and Si/SiGe light emitting devices have been designed, processed, and characterized, aiming at finding a possible solution for efficient Sibased light emitters.

    During the thesis work, mainly three types of Er-doped Si light emitting devices: Schottky-type light emitting diode (LED), p-i-n LED, and heterojunction bipolar transistor (HBT), have been studied for light emission from either the surface or an edge. Three kinds of Er-containing sources, namely Er2O3 , ErF3 , and elementa lEr together with SiO were used for doping. In order to get comparative results from electroluminescence (EL) and photoluminescence (PL) measurements using the same sample, Schottky-type LEDs using Er/O structures were fabricated and characterized, where Er3+ ions can be excited using an impact process of hot electrons generated in the depletion region at reverse bias. A number of grown Si:Er:O and Si:Er:F p-i-n structures were processed into LEDs, and EL from these devices was studied both at forward bias and reverse bias conditions. The light emission from forward biased p-i-n diodes was concluded to be due to the carrier-recombination-mediated energy transfer process, however, luminescence could not persist to room temperature (RT) due to the strong quenching process induced by the energy back transfer process and other nonradiative processes. For reverse biased p-i-n diodes, especially for the structure designed favoring the electron tunneling, intense EL was observed via direct carrier impact excitation process, which persisted up to RT or even higher. In order to have independent control over the injection current and the applied bias, and de-couple their influence on the EL intensity, Si/SiGe/Si:Er:O-HBTs with Er3+ ions incorporated in the collector have been fabricated with layered structures prepared by differential MBE growth. Careful EL studies have been carried out by operating an HBT in a linear regime prior to the avalanche breakdown. The effective Er impact cross-section has shown a 100-fold increase compared with conventional Si:Er-LEDs. The temperature dependent EL measurements on different types of devices have indicated that an Er-induced defect level located at 150 meV below the conduction band is mainly responsible for thermal quenching of the luminescence intensity, which is the same value as obtained in PL measurements. Time-resolved EL measurements have exhibited that Auger-carrier de-excitation plays an important role in reducing EL intensity. Moreover, it has revealed that not only ionized equilibrium carriers but also injected excess carriers act as Auger de-excitation centers. Finally, the results of the thesis work suggest that if the HBT structure can be combined with a high optical activation of Er3+ ions, an efficient Si-based light emitter is possible.

    List of papers
    1. Electroluminescence studies of Er and SiO co-doped Si layers prepared by molecular beam epitaxy
    Open this publication in new window or tab >>Electroluminescence studies of Er and SiO co-doped Si layers prepared by molecular beam epitaxy
    Show others...
    2000 (English)In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 14, no 3, p. 259-265Article in journal (Refereed) Published
    Abstract [en]

    Er/O co-doped Si light emitting diodes (LEDs) have been fabricated using layer structures prepared by molecular beam epitaxy (MBE). The Er/O doping was realized by sublimation of elemental Er and silicon monoxide simultaneously with Si during MBE growth. Intense Er-related electroluminescence (EL) at 1.54 mu m was observed at room temperature from p(+)-SiGe/i-SiGe-Si/Si:Er/n(+)-Si LEDs by electron impact excitation under reverse bias. It has been found that the EL intensity was increased with increasing growth temperature of the Si:Er/O layer in the range of 430-575 degrees C. The electrical pumping power dependence of EL intensity has been studied. An excitation cross section value of similar to 1 x 10(-16) cm(2) was estimated based on the experimental data and model fitting. The EL decay behavior under various injection and bias conditions has been studied by time-resolved EL measurements. The overall luminescence decay time is found to strongly depend on the injection parameters. Two types of de-excitation mechanisms due to Auger energy transfer to free carriers introduced by either dopant ionization or carrier injection have been discussed. Both Auger processes play an important role in reduction of the EL intensity when there is a high density of carriers with excited Er ions. (C) 2000 Elsevier Science B.V. All rights reserved.

    Keywords
    electroluminescence, light emitting diode, hot electron, Auger effect, Er, Si
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-49731 (URN)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2022-06-08
    2. Si/SiGe/Si : Er : O light-emitting transistors prepared by differential molecular-beam epitaxy
    Open this publication in new window or tab >>Si/SiGe/Si : Er : O light-emitting transistors prepared by differential molecular-beam epitaxy
    2001 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 78, no 12, p. 1697-1699Article in journal (Refereed) Published
    Abstract [en]

    Si/SiGe/Si:Er:O heterojunction bipolar transistor (HBT) type light-emitting devices with Er3+ ions incorporated in the collector region have been fabricated using a layered structure grown by differential molecular-beam epitaxy. Electroluminescence measurements on processed light-emitting HBTs can be performed in either constant driving current mode or constant applied bias mode, which is an important advantage over conventional Si:Er light-emitting diodes. Intense room-temperature light emission at the Er3+ characteristic wavelength of 1.54 mum has been observed at low driving current density, e.g., 0.1 A cm(-2), and low applied bias, e.g., 3 V, across the collector and emitter. (C) 2001 American Institute of Physics.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-53565 (URN)10.1063/1.1356732 (DOI)
    Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2022-06-08
  • 22.
    Duppils, Mattias
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    CMOS mixed analog/digital building blocks for signal processing1999Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    A mixed analog/digital multiply-accumulate unit is presented. The unit is composed of the multiplying D/A converter and a polarity switching network. It is featured by an analog continuous-time input port, a discrete­time output port, and a digital input port for the quantized multiplying coefficient. This unit constitute a core for mixed analog-digital computations, and its versatility can be compared to the all-digital multiply-accumulate unit. Mixed-signal computations is useful in environments where the input signals are analog in nature, but where signal processing in the digital domain is desired. A traditional system adapted for such an environment consist of an A/D converter, followed by digital signal processing elements, or a digital signal processor. It is shown that the system power drain can be reduced considerable if using the mixed analog/digital MAC unit followed by an A/D converter instead of the former configuration. This is true when the signal processing task reduces the required A/D conversion rate or accuracy, and when a low number of MAC units are required, since the complexity (chip area) of such units are considerable.

    Some proposed suitable signal processing tasks are pattern matching (not shown in the thesis) and narrow­band PIR filtering followed by decimation, which possibly are suitable for radio receiver applications. A design methodology for the realization of PIR filters suitable for implementation with a low number of MAC units is given. Mixed analog/digital MAC units have been designed with 1-bit and 8-bit coefficient resolution respectively and implemented in a double-poly 0.6µm CMOS process. Chip measurements have verified high performance of the 1-bit mixed analog/digital MAC unit, but the 8-bit counterpart still suffers from imperfections of unknown origin. The consequence of the imperfections show up as a coefficient dead zone.

    The bottom-plate sample-and-hold circuit is analyzed with simulations. It is shown that the track-mode linearity depends on the analog input frequency. If the track-mode linearity, the hold-mode introduced thermal noise, and the desired bandwidth as a fraction of the Nyquist frequency is considered - maximum spurious­free dynamic range, is achieved with a low bias voltage, and with a low input voltage swing.

  • 23.
    Edman, Anders
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    High Data Throughput CMOS Circuits1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes some high-performance digital CMOS circuits and the design of these circuits.

    The goal is to have a higher utilization of standard CMOS processes in order to increase performance of digital circuits. This is done without the use of aggressive processes. The designs are targeted towards very high clock rate and low power consumption.

    At the high level, the design are adjusted to fit into a low level architecture optimized for high performance. The architecture is also optimized for the high level design. The logic style and the flip-flops are selected for high performance.

    The digital processing chips presented in this thesis are based on a principle of heavily pipelined uni-directional processing in a data path. The logic is pipelined to a logic depth of one or two gates per pipeline stage. This design method and architecture is used for applications with high throughput processing of data.

    Two chips are designed for processing of 10 Gb/s SDH (Synchronous Digital Hierarchy) data, for use in fiber optic transmission systems. They include processing for the framer and deframer functions of a SDH regenerator. The 10 Gb/s is internally processed with 16 bits in parallel at a clock rate of 622 MHz. The chips are implemented in standard 0.6-0.8 μm CMOS.

    A quadrature 350 MHz Direct Digital Frequency Synthesizer is implemented in 0.8 μm CMOS. This DDFS is a high-speed compact implementation with on-chip DIA converters for the four-phase output. It calculates the sine and cosine values with a precision of 8 bits and with a frequency resolution below 1 Hz by using a sparse ROM-table and interpolation.

    A correlator chip for satellite-based high-performance auto-correlator spectrometers is designed. This chip performs more than 0.5 Tera-Multiply and Accumulate operations per second at a speed of 320 MHz in 1664 multipliers and accumulators. This 58 mm2 chip contains 1.6 million transistors and is implemented in a 0.6 μm process. The power consumption per operation is reduced with more than 5 times compared with other implementations, without any reduction in supply voltage. The internal noise level is reduced by dividing the processing and clock signal distribution into blocks with a clock buffer in between.

    Finally, two different high-speed multiplexers are presented. A 2.4-Gb/s 4:1 multiplexer and a 4-Gb/s 2:1 multiplexer are implemented in 0.8 μm CMOS. Both multiplexers are designed to be clocked by an external high swing clock.

    All chips results have been verified by measurements.

    List of papers
    1. A 0.8 μm CMOS 350 MHz quadrature direct digital frequency synthesizer with integrated D/A converters
    Open this publication in new window or tab >>A 0.8 μm CMOS 350 MHz quadrature direct digital frequency synthesizer with integrated D/A converters
    1998 (English)In: 1998 Symposium on VLSI Circuits, 1998. Digest of Technical Papers, 1998, p. 54-55Conference paper, Published paper (Refereed)
    Abstract [en]

    This quadrature DDFS calculates sine and cosine values with a tuning resolution below 1 Hz, by only using an 8 word ROM and interpolation. Two internal 8-bit differential D/A converters generate the four-phase analog output signal. A spurious free dynamic range of 50 dB for low frequencies and 30 dB near Nyquist is achieved.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-88624 (URN)10.1109/VLSIC.1998.688001 (DOI)0-7803-4766-8 (ISBN)
    Conference
    1998 Symposium on VLSI circuits, Honolulu, Hawaii, June 11-13 1998
    Available from: 2013-02-13 Created: 2013-02-13 Last updated: 2021-12-22
  • 24.
    Edvardsson, Niclas
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Thin Films and Multilayers of Yba2Cu3O7-δ and Srtio3; Growth, Characterization, And secondary Phase Formation1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Sputter-deposited thin films and multilayers of YBa2Cu3O7-δ (YBCO) and SrTi03 (STO) have been grown and studied. Microstructure in general, and formation of secondary phases, in particular, have been studied in relation to growth conditions. The main characterization techniques used have been x-ray diffraction (XRD) to identify phases and to obtain orientational relationships, scanning electron microscopy (SEM) to study surface morphology, transmission electron microscopy (TEM) for micro-structural characterization, and energy-dispersive x-ray spectroscopy (EDS) for chemical characterization.

    The influence of the composition of the sputtering target as well as process gas composition on the phase formation and superconducting transport properties for growth of YBCO single-layer films was investigated. A technique to avoid the formation of CuOx surface particles by using lyttrium-rich targets and N2O in the sputtering gas without any deterioration of superconducting transport properties has been developed. The avoidance of these commonly observed surface particles is a necessity for all investigations and applications of layered structures having layers deposited on top of a YBCO layer.

    Formation of a cubic ( or pseudo-cubic) phase with a lattice parameter of 0.414 nm was found in YBCO/STO multilayers. Chemical analysis showed the presence of Ba, Ti, 0 and Y in these precipitates, which was suggested to be Y-substituted BaTiO3 (Y:BTO). Also, formation of Y2O3 precipitates was found in the multilayers. Phase evolution studies during a ramped thermal anneal revealed that grain growth of Y:BTO and Y2O3 was triggered by the decomposition of YBCO. The STO layers were observed to be occasionally discontinuous in the as-deposited multilayers, indicating a three-dimensional growth mode. Strain in both the YBCO and STO layers were found, which is of importance for the superconducting properties of YBCO as well as the dielectric properties of STO.

    Finally, strain relaxation of STO single-layer films in the 9.3-144.0 nm thickness range deposited on LaAlO3 (LAO) substrates was investigated. It was found to follow the general trend of a predicted strain - thickness relation based on energy density balance considerations regarding misfit dislocations and lattice strain. The STO films on LAO substrates were also utilized in an investigation of different x-ray optics, which showed that a hybrid mirror monochromator in combination with a triple bounce analyzer crystal provides very good conditions for characterization of thin distorted films grown epitaxially onto substrates with high structural order.

  • 25.
    Egilsson, Tryggvi
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Bound excitons in silicon carbide1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The investigation of silicon carbide (SiC) is strongly motivated by the potential of this material for various demanding electronic applications. The main virtue of SiC is its toughness compared to other more common semiconductors. SiC is hard, can withstand high temperatures, high electric fields, chemically hostile environments, high levels of radiation and is able to accommodate high frequencies. An important aspect of any semiconductor crystal is the defects it contains. In fact, semiconductors owe their usefulness to the controlled incorporation of defects, but at the same time their usefulness is often limited by the presence of unwanted defects. This thesis is concerned with the study of defects in SiC by means of photoluminescence (PL) spectroscopy. Many defects can bind excitons at low temperatures. It is the radiative recombination of such bound excitons (BE) that has been investigated in this thesis. The main contribution of the work is to clarify the behaviour and electronic structure of BE's associated with a number of common defects in SiC. The work is presented in six papers.

    In paper I, the properties of a PL spectrum appearing after room temperature electron irradiation of 4H-SiC are reported. The spectrum is very complicated, consisting of a myriad of sharp no-phonon PL lines as well as broader phonon assisted transitions. We show in the paper how the use of PL excitation (PLE) spectroscopy, a technique that has hitherto been largely neglected in the study of SiC, greatly facilitates the investigation of this spectrum. From our results we suggest that the PL spectrum is due to BE recombination at several different isoelectronic defects.

    In papers II and III we report a comprehensive study of the so-called D1-BE in SiC. Paper II contains several novel experimental results pertaining to the D1 -BE in the 4H-polytype of SiC. Paper III extends the investigation to two other polytypes, namely 3C- and 6H-SiC, and offers an explanation to all the experimental findings in the form of a detailed theoretical model. The D1-BE isshown to be bound at an isoelectronic defect. The exciton consists of a tightly bound hole and a weakly bound electron. A series of effective-mass-like excited states associated with the electron are observed with PLE spectroscopy.

    Papers IV and V deal with well known hydrogen related defects in 6HSiC. Paper IV reports the excitation spectra of the BE's residing at these defects. Several excited states of the BE's are detected. Paper V is concerned with the quenching of the hydrogen related PL under prolonged laser excitation. By studying the temporal changes of the PL intensity as a function of excitation energy, it is shown that the quenching is recombination enhanced. Also, we supply evidence for the existence of another configuration of the defect, that cannot be detected directly in the PL spectrum.

    In paper VI, the excitation spectra of BE's associated with nitrogen donors in 4H-, and 6H-SiC are reported. Several high energy excited states are observed. The electronic structure of the BE's is discussed in terms of a shell model.

    List of papers
    1. Excitation properties of hydrogen-related photoluminescence in 6H-SiC
    Open this publication in new window or tab >>Excitation properties of hydrogen-related photoluminescence in 6H-SiC
    Show others...
    2000 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 62, no 11, p. 7162-7168Article in journal (Refereed) Published
    Abstract [en]

    We have studied the excitation properties of a well-known hydrogen-related bound exciton (H-BE) photoluminescence (PL) in 6H-SiC. In the case of the so-called primary H-BE's, photoluminescence excitation (PLE) spectroscopy reveals several excited states that have not been reported previously. In order to explain these states we propose a pseudodonor model. The primary H-BE's are thus regarded as donors where strongly localized holes serve as the positive cores. From a comparison between the PLE spectra of the three different primary H-BE's corresponding to the three inequivalent substitutional lattice sites in 6H-SiC, we attempt to distinguish between the hexagonal and cubic lattice sites. We have also investigated the dependence of the optically induced quenching of the H-BE PL on the energy of the exciting light. We observe that the quenching of the H-BE PL is only efficient when the exciting light has energy above the threshold for phonon-assisted free-exciton (FE) formation or when its energy coincides with the energy needed for resonant absorption into the H-BE states. When creating FE's, we observe different types of behavior depending on the initial conditions. We argue that our results are best explained by the existence of two configurations of the same charge state of the H defect, namely a stable one: A (giving rise to the H-BE PL), and a metastable one: B (not revealed in the PL spectrum). The recombination of excitons bound at these two configurations can give rise to the transformations A?B and B?A. The existence of the B configuration is revealed through the effect of the B?A process on the temporal changes of the H-BE PL.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47581 (URN)10.1103/PhysRevB.62.7162 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2022-05-18
    2. Excitation spectra of nitrogen bound excitons in 4H- and 6H-SiC
    Open this publication in new window or tab >>Excitation spectra of nitrogen bound excitons in 4H- and 6H-SiC
    2002 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 3, p. 2028-2032Article in journal (Refereed) Published
    Abstract [en]

    We report photoluminescence excitation spectra of the nitrogen (N) donor bound excitons (BE) in 4H- and 6H-SiC. The spectra reveal several excited states of the N-BEs. An attempt is made in the article to classify the N-BE states according to a simple shell model. © 2002 American Institute of Physics.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47114 (URN)10.1063/1.1431437 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2022-05-18
  • 26.
    Ekeroth, Johan
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Phosphorylated Monomolecular Layers: Design, Synthesis, Characterization and Application2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes the design, synthesis and characterization of organo-phosphatemonomolecular layers, so called self-assembled monolayers, using the strategy of linking organosulfur substances to a gold surface. Moreover there is also a paper included, which describes the development of synthetic pathways to various phospholipids, for which I have developed an interest in later projects.

    For the first study of the properties of phosphates, and also for concomitant application of developed systems, analogues of the amino acids serine, threonine and tyrosine, phosphorylated and non-phosphorylated, were synthesized. 16-Mercaptohexadecanamide based analogues were characterized as monolayers and large polar and charge effects were observed, introduced by the phosphate. Problems were, however, encountered as a post modification of phosphates was applied and a disordering of the monolayers observed. Moreover there were no expected effects observable upon interaction with Ca2+ and Mg2+.

    Based on the conclusions from the first study 3-mercaptopropionamide based analogues were used instead. Characterization of the analogues including counter ion exchange (H+,Na+, Ca2+ and Mg2+) revealed large electronic and possible structural differences depending on the counter ion.

    Again the charge and polar effects induced by the phosphate were investigated, and the study was also extended to interaction of the phosphate with Ca2+ and Mg2+. Strong effects were observed, which were also dependent on the ion concentration within a significant range. The polarity and charge properties of the phosphate layer were thus found to be variable.

    In the fourth study an additional Ca2+ and Mg2+ sensitive system was applied in combination with the phosphate surface. Phosphate surface/phospholipid vesicle interactions were studied under different conditions of Mg2+ (Ca2+) treatment. For comparison, the corresponding hydroxyl and sulphate surfaces were included and also the most well characterized surface concerning phospholipid vesicle interaction, SiO2. Most importantly, supported phospholipid bilayer (SPB) formation was found to be inducible on both the phosphate and sulphate surfaces, however at defined conditions of Mg2+ (Ca2+) treatment and concentration. The conclusion is that the processes of phospholipid vesicle adsorption and SPB formation are largely dependent on vesicle/surface interaction and vesicle stability.

    The last paper included in this thesis is a synthetic method development aimed at easy preparations of various phospholipid derivatives. In the future these methods could be used for synthesis of functionalized lipids and aid in the development of models mimicking biological systems such as artificial cell membranes.

    List of papers
    1. Electrochemical Evaluation of the Interfacial Capacitance upon Phosphorylation of Amino Acid Analogue Molecular Films
    Open this publication in new window or tab >>Electrochemical Evaluation of the Interfacial Capacitance upon Phosphorylation of Amino Acid Analogue Molecular Films
    Show others...
    2001 (English)In: Analytical Chemistry, ISSN 0003-2700, Vol. 73, no 18, p. 4463-4468Article in journal (Refereed) Published
    Abstract [en]

    An approach based on electrochemistry to differentiate between phosphorylated and nonphosphorylated amino acid analogues adsorbed on gold is presented. Analogues of serine, threonine, and tyrosine, containing thiohexadecyl headgroups, were synthesized and assembled on gold, and the surface capacitance was evaluated using electrochemical impedance spectroscopy. A procedure for deprotection of tert-butyl phosphate protecting groups, on the monolayer, is also described. Characterizations of the assembled analogues by cyclic voltammetry, infrared spectroscopy, and ellipsometry are used to confirm the insulating properties of the monolayers and the outcome of surface modifications. The results from cyclic voltammetry show good insulating properties for the monolayers even after phosphate deprotection. The infrared measurements reveal well-ordered monolayers, and the thickness from ellipsometry is in good agreement with expectations from molecular modeling. The impedance experiments show a capacitance increase up to 0.6 μF/cm2 as phosphate groups are introduced. The results in this study indicate the possibility of using a surface chemical and impedance spectroscopy approach to detect the kinase/phosphatase activity and kinetics involved in phosphorylation reactions.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-14335 (URN)10.1021/ac010487+ (DOI)
    Available from: 2007-03-16 Created: 2007-03-16 Last updated: 2021-09-24
    2. Synthesis and Monolayer Characterization of Phosphorylated Amino Acid Analogs
    Open this publication in new window or tab >>Synthesis and Monolayer Characterization of Phosphorylated Amino Acid Analogs
    2002 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 254, no 2, p. 322-330Article in journal (Refereed) Published
    Abstract [en]

    The synthesis of a series of thiols containing phosphorylated and non-phosphorylated serine, threonine, and tyrosine amino acid residues is described. The synthesized molecules, based on 3-mercaptopropionic acid, were assembled onto gold and subsequently characterized using infrared reflection-absorption spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, and contact angle goniometry. The ellipsometric analysis indicates that they form densely packed and well-oriented monolayers on gold, with thicknesses that are in good agreement with estimated values from space-filling models. The bulky and space-demanding phosphorylated threonine analog was, however, found to be an exception. The increase in layer thickness when adding a phosphate group to the threonine is only 35% of that observed for the two other analogs. A detailed infrared examination of the influence of cation coordination to the phosphorylated serine analog using calcium and magnesium reveals structural similarities to those of the inorganic phosphate compound calcium hydroxy apatite. We furthermore discuss the application of these monolayers as soft templates for biomineralization.

    Place, publisher, year, edition, pages
    Maryland Heights, MO, United States: Academic Press, 2002
    Keywords
    SAM; phosphorylated amino acid; phosphate layer; alkanethiols; gold; counterion influence
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-14336 (URN)10.1006/jcis.2002.8576 (DOI)000178935400016 ()
    Available from: 2007-03-16 Created: 2007-03-16 Last updated: 2021-09-24Bibliographically approved
    3. Monitoring the interfacial capacitance at self-assembled phosphate monolayers on gold electrodes upon interaction with calcium and magnesium
    Open this publication in new window or tab >>Monitoring the interfacial capacitance at self-assembled phosphate monolayers on gold electrodes upon interaction with calcium and magnesium
    Show others...
    2002 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 74, no 9, p. 1979-1985Article in journal (Refereed) Published
    Abstract [en]

    Electrochemical impedance spectroscopy has been used to evaluate the change in interracial capacitance upon calcium and magnesium coordination to a phosphate-modified electrode. The phosphate electrode was prepared via immobilization of phosphorylated, thiol-containing, serine analogues onto gold. Upon subjection to calcium and magnesium, a substantial drop in capacitance was observed. Magnesium displayed the largest influence on the capacitance: a 27% capacitance drop was observed upon introduction of a 1 mM solution of magnesium ions. The lowered capacitance is a result of a change in the potential and charge distribution at the film/electrolyte interface as the cations coordinate to the phosphate groups. Moreover, the relationship between electrode potential and capacitance has been investigated and reveals a significant difference between monovalent and divalent cations. As complementary information, infrared reflection absorption spectra of the phosphorylated monolayer having different counterions are presented. The results reported in this paper indicate that the phosphorylated amino acid analogue monolayers could be used in investigations of the biochemically important coordination of calcium and magnesium to phosphates and phosphorylated amino acids.

    Place, publisher, year, edition, pages
    Washington,DC, USA: American Chemical Society (ACS), 2002
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47026 (URN)10.1021/ac015635a (DOI)000175358800032 ()
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-09-24Bibliographically approved
    4. Bivalent-ion-mediated vesicle adsorption and controlled supported phospholipid bilayer formation on molecular phosphate and sulfate layers on gold
    Open this publication in new window or tab >>Bivalent-ion-mediated vesicle adsorption and controlled supported phospholipid bilayer formation on molecular phosphate and sulfate layers on gold
    2002 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, no 21, p. 7923-7929Article in journal (Refereed) Published
    Abstract [en]

    Strategies to form supported lipid assemblies on organophosphate- and organosulfate-monolayer-modified gold surfaces are described. By varying surface treatment and the Mg2+ (Ca2+) content in a solution containing phosphatidylcholine vesicles, we demonstrate (i) efficient formation of supported phosphatidylcholine bilayers (SPBs), (ii) formation of supported nonruptured phosphatidylcholine vesicles, and (iii) reduced phosphatidylcholine vesicle adsorption. Thus, by simply varying the solution conditions, the system can be tuned to controlled formation of either a SPB, supported nonruptured vesicles, or a surface with fairly low coverage of nonruptured vesicles. The profound effects induced on the system by Mg2+ and Ca2+ are assigned to a combination of ion-coordination to the surface, ion-association to the lipid headgroups, and osmotic pressure.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46894 (URN)10.1021/la026131q (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-09-24
    5. Efficient synthesis of phospholipids from glycidyl phosphates
    Open this publication in new window or tab >>Efficient synthesis of phospholipids from glycidyl phosphates
    2002 (English)In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 67, no 1, p. 194-199Article in journal (Refereed) Published
    Abstract [en]

    New efficient routes to enantiopure phospholipids, starting from (S)-glycidol, are described. Lysophosphatidic acids and phosphatidic acids were obtained in good overall yields from (S)-glycidol, in only three and four steps, respectively. Moreover, the strategy can also be used to produce phosphatidylcholines in three steps. Using dialkylphosphoramidites, (S)-glycidol was phosphorylated to give (R)-1-O-glycidyl dialkyl phosphates. Regiospecific epoxide opening, using hexadecanol or cesium palmitate, followed by phosphate deprotection, provided lysophosphatidic acids. 2-O-Esterification prior to phosphate deprotection provided 1,2-O-diacyl and 1-O-alkyl-2-O-acyl phosphatidic acids. Phosphorylation of (S)-glycidol using phosphorus oxychloride followed by in situ treatment with choline tosylate produced (R)-glycidyl phosphocholine. Subsequent nucleophilic opening of the epoxide using cesium palmitate produced 1-O palmitoyl-sn-glycero-3-phosphocholine, which has been used in syntheses of phosphatidylcholines.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47127 (URN)10.1021/jo010734+ (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-10-01
  • 27.
    Eklund, Jan-Erik
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    A/D Conversion for Sensor Systems1997Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Today, an important field for circuit design research is advanced mixed mode CMOS circuits for the most varying purposes. By designing these for implementation in basic and cheap digital technologies, building blocks for advanced systems are achieved. Two examples are described in this thesis; a smart CMOS camera and AID conversion for carrier frequency signals.

    The CMOS camera is developed using the Near-Sensor Image Processing concept, NSIP. The concept has previously been presented. It is based on a focal plane processor with one processor in each pixel. The two main properties, that make the concept successful are that the light intensity is converted to a time value, which means that we can process single bit information with maintained grey scale information, and an asynchronous propagation net, which can mark connected areas in the image. The contribution of this thesis is the implementation of an NSIP camera. A low power circuit technique with self clocked instructions is developed for this SIMD machine. The processor architecture based on NAND operations is developed for minimizing the area. The light sensor read-out circuitry is developed for low power and small area. A patent is pending for this part. The result is a 32 x 32 pixels test circuit with possibilities to extend to 128 x 128 pixels in existing technologies. The operation speed can be up to 100 MHz. The power consumption is 400 mW@ 10 MHz (in 128 x 128 pixels). The asynchronous mark operation can process 4 · 106 frames/s.

    The carrier frequency ADC is based on a patent describing a novel technique for finding Inphase and Quadrature signals from an intermediate frequency, fIF, signal. It has earlier been tested in a multi chip system. This thesis shows an implementation of this method in a single CMOS chip, by using Multiple Sampling Single Conversion, MSSC. A test circuit that operates on fIF= 30 MHz and gives 10 bits 2 MHz output was fabricated. The experiences from this circuit initiated studies about metastability and about high speed architectures for SA-ADCs. A model, which compares metastability with quantization noise, is presented. Design rules for achieving a desired SNR can be specified from this model. One high speed architecture was developed. The SA-ADC uses binary search among reference levels for finding the correct representation. The new architecture is based on a Reference Pre-Select, RPS, scheme, which minimizes the time between two comparisons. The result is 200 MHz 10 bits simulated performance. Partly working circuits have been fabricated.

  • 28.
    Eklöf, Anna
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Cascading extinctions in food webs: local and regional processes2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ecological communities all over the world are loosing biodiversity due to different kinds of human activities and there is an urgent need of understanding how those losses affect the function of the ecosystems on which we all depend. The community's response to species losses is likely to depend on both the structure of the local community as well as its interactions with surrounding communities. Also the characteristics of the species going extinct do affect how the community structure changes. The main purpose of this thesis is to study how local population dynamics and regional processes in food webs affect ecological communities' response to species loss, especially the risk of cascading extinctions.

    In Paper I we use a set of model food webs with different shapes and connectance to look at how the structure of the community affects its resistance to species loss. We also investigate how the resistance is affected by which species, according to trophic level and connectivity, that is lost initially. What we find is that food webs with lower connectance seem to be more vulnerable than more connected communities. The loss of a species at low trophic level and / or with high connectivity triggers the on average highest number of secondary extinctions. We also discuss about the structure of the post­ extinction community and compare our analysis with topological studies.

    In paper Il we use as set of metacommunities with different connectances and different number of patches and we vary the dispersal distances and migration rates. The aim of this paper is to investigate how web connectance of local communities, number of habitat patches and dispersal patterns affects a metacommunity's response to the global loss of a species. We find that asynchrony among patch dynamics may arise from relatively low rates of migration, and that the inclusion of space significantly reduces the risk of global cascading extinctions. It is shown that communities with sparsely connected food webs are the most sensitive to species loss, but also that they are particularly well stabilised by the introduction of space. In agreement with theoretical studies of non-spatial habitats, species at the highest trophic level are the most vulnerable to secondary extinction.

    Paper III is a book chapter that emerged from a working group during a food web symposium in Giessen, Germany 2003. It is dealing with ideas of how to look at spatial aspects of food webs.

  • 29.
    Eklöv, Tomas
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Methods to Improve the Selectivity of Gas Sensor Systems1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In several situations it is essential to be able to measure the composition of a gas mixture, discriminate between or quantify different gases mixtures (odors), or in some cases to give a 'fingerprint', which represents the gas mixture. A gas sensor system is designed to measure certain attributes of a gas mixture. A property of crucial importance of such a system is the ability to identify/quantify attributes of the examined analytes. This property can be referred to as the selectivity of the system. In this work, the objective has been to examine and develop methods, which improve the selectivity of gas sensor systems.

    In a distributed gas sensor system a gas mixture is catalytically changed in a controlled way and monitored at different stages of catalytic conversion with a gas sensor array. The acquired sensor response profile thus depends on the sensor properties, the catalyst activity, and the applied gas mixture. Such a system has been extensively examined regarding the operating conditions, e.g. flow rate, different sensors and catalysts, and various analytes in different concentrations. Major differences in response profile between different molecule types were observed. It has been shown that by using an array of identical Pd gate metal-oxidesemiconductor field-effect transistor (MOSFET) sensors and a Pd catalyst, the components in a binary mixture could be quantified. Extending the design to two different catalysts and two types of sensors, the components in quaternary mixtures could be accurately estimated. Thus, the catalyst provides information not available from only the sensor, and the selectivity of the system is consequently improved as compared to a system without catalyst.

    From a multi-parameter sensor, more than one signal is acquired, each giving different information. Several approaches can be made to extract multiple parameters from one sensor. A simple method is to analyze the transient response curve from a gas sensor when exposed to a rectangular pulse of test gas. Simple parameters, e.g. responses, derivatives, and integrals, from a single MOSFET sensor, have been shown to provide different information in several applications. These parameters could, furthermore, be used to estimate properties of the analyzed samples with high accuracy. Thus, it was shown that the MOSFET sensor could be used as a multi-parameter sensor as the information content was increased compared to extracting only the steady state response value. A method to optimize these parameters (response, derivative, and integrals), utilizing the leverage from a principal component analysis was developed, further improving the information content.

    If an array of multi-parameter sensors is used in a specific application, a large number of variables are acquired. A feature selection process is thus in many cases necessary. A method, based on a forward selection procedure, applying the error from a multiple linear regression as the selection criteria, was developed. Other methods were also examined, but the forward selection procedure outperformed all other tested algorithms. A practical application of gas sensor systems, estimation of wood hydrolyzate properties, was finally studied. Using a multi-sensor array, extracting several parameters from each sensor, and performing a forward selection procedure, suitable variables were found. The variables were then used to estimate interesting properties of the samples with high accuracy using pattern recognition routines.

  • 30.
    Ellison, Alexandre
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Silicon Carbide Growth by High Temperature CVD techniques1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Silicon Carbide (SiC) is a wide band gap semiconductor, which already W. Shockley in 1959 expected to replace silicon owing to its outstanding figures of merit for high-power, high-frequency and high-temperature electronics.

    Since 1978, there has been a continuous progress in SiC crystal growth, nowadays essentially based on the seeded sublimation technique enabling the realisation of substrates with increasing diameter and quality. This has triggered a strong scientific and technological interest in SiC. On-going research and development in the international community are progressing fast towards an increasing commercial importance of SiC electronics. This in turn increases the demands on growth techniques, because most of the remaining identified limitations for industrial applications originate from the material quality and cost.

    The main contribution of the present work relates to the development and investigation of two growth techniques, which can simply be described as chemical vapour deposition at high temperatures. The first one, carried out between 1650 and 1850 °C in a vertical hotwall, or chimney reactor, is shown to enable one order of magnitude higher growth rates than conventional chemical vapour deposition (CVD) systems, while maintaining acomparable material quality. The second one, carried out at 2000-2300 °C in an inverted vertical reactor, allows growth rates ranging between 0.3 and 0.8 mm/h, which are of interest for crystal growth applications.

    The thesis is divided into seven papers.

    In paper I, we introduce a fast SiC epitaxy process which is carried out in a chimney CVD reactor adapted to growth temperatures ranging from 1650 to 1850 °C. The epitaxial growth of 4H-SiC, with rates of 10 to 50 μm/h, is analysed in terms of gas flow dynamics, rate determining factors as precursor supply and growth temperature. The deposition uniformity is shown to be essentially mass transport limited, whereas the exponential growth rate dependence with temperature is related to gas phase reactions limiting steps. The relation between the growth conditions and the material quality, such as morphology, purity, and carrier lifetime is investigated in paper II. Epitaxial layers grown at 25 μm/h are shown to enable fabrication of high voltage Schottky rectifiers with breakdown voltages as high as 3.8 kV. The incorporation of the nitrogen n-type dopant is studied in paper III, bothin the high doping range (n ∼1018 cm-3) and in the high purity range (n∼1014 to 1015 cm-3), as a function of growth parameters. Accurate control of the doping is shown to be possible both by standard means as C/Si control, but also by the growth pressure and temperature.

    In paper IV we investigate the influence of surface morphology and structural defects on the reverse performance of kV-class Schottky rectifiers. Only diodes processed on areas with low density of screw dislocations are reported to block voltages of 2 kV and more. In paper V, the structural defects present in low doped (1015 cm-3 range), thick (30-40 μm) CVD grown epilayers are investigated using synchrotron X-ray diffraction topography; the observed defects are shown to be either replicated from the substrate or introduced during the epitaxial growth process. Substrate replicated threading edge dislocations aligned within small angle boundaries are shown to relate to local decreases of the carrier lifetime measured on as-grown epilayers. Network of dislocations lines are also found and may becaused by a doping induced misfit between the epilayer and the conductive substrate.

    In paper VI and VII we describe the development of a high growth rate process which may be an attractive alternative to Physical Vapour Transport (PVT) growth techniques for controlled growth of high purity, high quality, SiC crystals.

    In paper VI, we investigate the growth process, described as High Temperature Chemical Vapour Deposition (HTCVD). The conditions leading to growth of both 6H and 4H-SiC crystals with rates ranging from 0.3 to 0.8 mm/h are described. The growth rate limiting steps as process temperature, temperature gradient, precursor supply are analysed, together with gas phase nucleation phenomena. The growth of 6H and 4H-SiC crystals with thickness ranging up to 7 mm and diameter up to 40 mm is reported.

    4H-SiC crystal growth by HTCVD is investigated in paper VII. The conditions leading to a stable growth of the 4H polytype are addressed together with structural properties such a micropipe defect density. Owing to the high purity of the HTCVD technique, growth of high-resistivity 4H-SiC (p > 109 Ω.cm at room temperature) is shown to be achieved without the need of intentional compensation.

    List of papers
    1. Epitaxial growth of SiC in a chimney CVD reactor
    Open this publication in new window or tab >>Epitaxial growth of SiC in a chimney CVD reactor
    2002 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 236, no 1-3, p. 225-238Article in journal (Refereed) Published
    Abstract [en]

    A high growth rate (>10 µm/h) Chemical Vapour Deposition (CVD) process is investigated in a vertical hot-wall, or "chimney", reactor. By the use of increased temperatures (1650-1850°C) and concentrations of reactants, this process is shown to enable growth rates up to 50µm/h and demonstrates a material quality comparable to established CVD techniques until growth rates of 25 µm/h. The gas flow dynamics, the growth rate and the thickness uniformity determining steps are investigated, and the role of homogenous nucleation is analysed. The growth rate is shown to be influenced by two competing processes: the supply of growth species and the etching of the hydrogen carrier gas. The exponential increase of the growth rate with temperature is related to a Si-vapour release from clusters homogeneously nucleated in the inlet of the susceptor and acting as a growth species reservoir. © 2002 Elsevier Science B.V. All rights reserved.

    Keywords
    A1. Growth models, A3. Chemical vapor deposition processes, A3. Hot wall epitaxy, B2. Semiconducting silicon carbide
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47076 (URN)10.1016/S0022-0248(01)02129-7 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2022-06-01
    2. Nitrogen incorporation during 4H-SiC epitaxy in a chimney CVD reactor
    Open this publication in new window or tab >>Nitrogen incorporation during 4H-SiC epitaxy in a chimney CVD reactor
    Show others...
    2001 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 226, no 2-3, p. 267-276Article in journal (Refereed) Published
    Abstract [en]

    Nitrogen incorporation is studied during epitaxial chemical vapour deposition (CVD) of 4H-SiC in a vertical, hot-wall CVD reactor. The nitrogen doping dependencies on input C/Si ratio, growth temperature and process pressure are investigated under the process conditions leading to growth rates in the range of 15-30µm/h. The nitrogen incorporation is observed to be a thermally activated process with a higher apparent activation energy for the Si-face than for the C-face. The site-competition principle is well followed at C/Si ratios higher than 0.3, whereas the nitrogen doping becomes less sensitive to the C/Si ratio on both the Si- and the C-faces at C/Si ratios below 0.3. The pressure has a strong effect on the nitrogen incorporation efficiency, allowing lower doping at the lower pressure. The influence of the growth parameters on the nitrogen incorporation is closely related both to the epitaxial growth mechanisms and to the surface kinetics on the different polarity SiC faces. The doping mechanisms are analysed taking into account the gas-phase chemistry and the surface kinetics. © 2001 Elsevier Science B.V.

    Keywords
    A1. Doping, A3. Chemical vapor deposition processes, B2. Semiconducting silicon compounds
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47359 (URN)10.1016/S0022-0248(01)01369-0 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2022-06-01
  • 31.
    Emmerlich, Jens
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Thin film growth and characterization of Ti-Si-C MAX-phases2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes the growth of Ti-Si-C MAX-phases on A12O3(0001) and MgO(111) substrates with the emphasis on epitaxial Ti3SiC2 thin films by means of DC magnetron sputtering. Ti3SiC2, Ti4SiC3 as well as the two intergrown structures Ti5Si2C3 and Ti7Si2C5 were grown using sputtering from three individual elemental targets of Ti, Si, and C, respectively. X-ray diffraction analysis of the films revealed single-phase and epitaxial growth of Tin+1SiCn(0001) (n = 2, 3) MAX-phases at substrate temperatures above 700 °C. MgO(100) substrates as growth templates provided growth of Ti3SiC2 in a preferred orientation of (1015). TEM and XRD investigations showed that at 700 °C and below Si is accommodated at twin boundaries between TiC(111) planes. Depositions at substrate temperatures of 350 °C and RT resulted in nanocrystalline TiC growth with substitutionally-incorporated Si due to kinetic constraints.

    Mechanical properties were investigated using nanoindentation with cube corner and Berkovich indenters. With small indentation depth, hardness values of up to 24 GPa were measured for Ti3SiC2 films. Increasing maximum loads yielded lower hardnesses approaching bulk values. Young's moduli of 320 and 343 GPa were observed applying cube comer and Berkovich indenter, respectively. Cross-sectional TEM through indentations made with a Berkovich indenter were used to study the deformation behavior of the MAX-phases. Deformation energy is dissipated in kink formation, with edge dislocation pile-ups at the kink boundary, and delamination along basal planes.

    Four-point probe measurements on Ti3SiC2 MAX-phase thin films deposited at 900 °C showed a low room temperature resistivity of ~ 25 µΩcm, which increased with lower deposition temperatures. Ti4SiC3 films demonstrated an increased resistivity up to ~ 50 µΩcm.

  • 32.
    Engström, Carolina
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Sputter Deposition, Mechanical Properties, and Thermal Stability of Nitride Based Superlattices1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Investigations concerning deposition, mechanical properties and thermal stability of nitride-based superlattice films have been performed. X-ray diffraction and transmission electron microscopy techniques were adopted for microstructural characterization, while nanoindentation hardness and abrasive wear resistance measurements were utilized for evaluation of mechanical properties.

    A dual-target sputter deposition system with a solenoid coil serving to increase plasma density in near substrate position was designed. A high ion bombardment intensity at the substrate was achieved for each depositing magnetron, and the coil current strength and direction may be altered in synchrony with each depositing magnetron and its deposition time. The plasma density could exhibit a 25-fold increase of the ion flux to the substrate, with a typical ion-to-neutral arrival rate ratio of ~ 20. The system described offers prospects of realizing layered structures consisting of materials with a large difference in melting temperatures and/or large difference in atomic mass, where the materials need different ion-assisted growth conditions for controlled texture and film density at low deposition temperatures.

    Microstructure, residual stress, nanoindentation hardness, and abrasive wear resistance were investigated for polycrystalline nanolayered TiN/NbN thin films deposited by dual target reactive magnetron sputtering. The hardness showed only a small variation with layer period A, with an overall high value in between the corresponding homogenous nitride films (25-40 GPa). The residual stress in the nanolayer structures (<1.6 GPa), however, was significantly lower than the homogeneous or alloyed films (≥3.2 GPa). Homogeneous hexagonal β-Nb2N films exhibited the largest wear resistance, and alloyed TiNbN films were more wear resistant than the nanolayered TiN/NbN films. The absence of superlattice hardening in the polycrystalline TiN/NbN multilayers was related to rnicrocracking at grain boundaries under the indenter tip.

    A new class of non-iso structural metal/nitride superlattices were investigated, where a bee-metal (Mo, W) was combined with a NaCl-structure nitride (NbN). A substantial hardness enhancement was observed, as compared to the rule-of-mixture, with maximum hardnesses of ~30 GPa at a superlattice period Λ of ~2-3 nm. For Λ above 3 nm, the hardness decreased with a Hall-Petch-type dependence, but with a power law of ~O.3. These superlattices provide features that may be of value for hardcoating applications; the combination of a brittle ceramic with a more-ductile metal which may provide hard coatings with a varying degrees of ductility.

    The interdiffusion behavior of TiN/NbN and Mo/NbN systems was determined. The interdiffusion was investigated by electron microscopy and by studying the evolution of superlattice satellite peaks in x-ray diffraction. In situ x-ray diffraction spectra were recorded, using synchrotron light and a linear detector, during isothermal anneals. The results pointed to a non-linear diffusion behavior in TiN-NbN couples, where the structure maintained abrupt interfaces throughout annealing, while the position of the interfaces was continuously shifted into the TiN layers. A model is proposed, where Ti diffuses into the NbN-layer to form a NbTiN alloy, while the diffusion of Nb in the opposite direction is restricted due to high activation energies of Nb in TiN. Within the temperature range from 750 to 875° C, activation energies for metal interdiffusion were limited to 1.2 eV for the lower temperature end, and 2.5 eV for the higher temperature end.

    For the epitaxial non-iso structural Mo/NbN system, superlattice films with Λ=1.4 and 6.5 nm were investigated. The as-deposited films showed increased nanoindentation hardness values compared to the rule-of mixtures value. Upon annealing in vacuum at 1000°C for up to 3 h, the superlattice layering gradually diminished, while there was no loss in hardness. Remnants of the layering structure were still observed after 3 h at 1000°C. However, annealing of these superlattices promotes the formation of a composite structure with a tetragonal-MoNbN phase, which is as resistant to elasto-plastic deformation as the as-deposited Mo/NbN superlattice.

    List of papers
    1. Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil
    Open this publication in new window or tab >>Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil
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    2000 (English)In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 56, no 2, p. 107-113Article in journal (Refereed) Published
    Abstract [en]

    An original design and solution to the problem of magnetic field interactions in a vacuum chamber between two unbalanced magnetron sputtering sources and a solenoid coil serving to increase plasma density in near substrate position, is presented. By changing the solenoid coil current strength and direction, plasma growth conditions in an argon discharge and Ti-magnetron cathodes were found to vary in a broad region. Langmuir probe analysis shows that an increase in the coil current from 0 to 6 A caused plasma and substrate floating potentials to change from -7 to -30 V and from +1 to -10 V, respectively, as well as increasing the ion densities to a biased substrate from 0.2 to 5.2 mA cm-2 for each of the magnetrons. By using a ferro-powder magnetic field model, as well as finite element method analysis, we demonstrate the interference of the three magnetic fields - those of the two magnetrons and the solenoid coil. X-ray diffraction and transmission electron microscopy were used to study the microstructure and morphology of Ti-films grown under different ion bombardment conditions. At low Ar-ion-to-Ti-atom arrival rate ratios, Jion/Jn to approximately 1.5, at the substrate, variations of the ion energy, Eion, from 8 to 70 eV has only a minor effect on the microstructure and film preferred crystallographic orientation, resulting in an open/porous structure with defect-rich grains. At a higher Jion/Jn value of approximately 20, films with a well-defined dense structure were deposited at ion energies of 80 eV. The increase in ion flux also resulted in changes of the Ti film preferred orientation, from an (0 0 0 2) preferred orientation to a mixture of (0 0 0 2) and (1 0 1¯ 1) orientations.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47702 (URN)10.1016/S0042-207X(99)00177-3 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2022-04-27
  • 33.
    Eriksson, Anders
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Modeling and Characterization of nonlinear Materials for Protection of Optical Sensors2001Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns nonlinear materials and experimental techniques for optical power limiting applications. Theoretical models to analyze and simulate related measurements were studied. Two different numerical modeling tools for propagation of optical radiation through optically nonlinear media were developed. The first, relying on a Gaussian decomposition technique, was developed for multi-mode Gaussian beams and extended to allow for optically thick samples. The method relies on a multi-layer approach, where all layers are treated as independent, and may have different linear and nonlinear optical properties. Hereby the model allows simulation of concentration gradients and several samples in succession, each having arbitrary material properties. The second approach takes into account time-dependent nonlinear systems. A computer program based on the Cranck-Nicholson scheme was written in Matlab code and used to simulate the propagation of irradiance distribution for various temporal pulse-shapes. The differential equations associated with 3- and 5-level systems were solved numerically in each point over the active time-space grid. Instantaneous two-photon absorption and dynamic multi-level systems were used, one at a time, or in combination, to model material responses to optical pulses.

    In addition, several materials were characterized using the Z-scan technique and related techniques. Chloro-aluminium phthalocyanine, CAP, was examined using several different pulse-lengths in the nanosecond regime for both thin and thick samples. A test-bed for investigating the capability of various materials to protect an optical sensor from hazardous laser radiation was constructed. This set-up used a transversal top-hat laser beam focused on 2 mm thick samples in an f/5 optical system, and was used to characterize materials for optical power limiting.

  • 34.
    Eriksson, Fredrik
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Soft X-ray Multilayer Mirrors2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is focused on the design, growth and characterization of soft x-ray multilayer mirrors with the emphasis on the wavelength region called the water window (λ=2.4-4.4 nm). The main application in mind is condenser mirrors for a high resolution compact soft x-ray microscope using a droplet-target laser-produced plasma (LPP) source operating at λ=3.374 nm. However, other applications, utilizing other wavelengths, have also been considered.

    The design of the multilayers which involves understanding of the details of the optical properties of the elements and the interaction between multilayer and electromagnetic radiation is reviewed. To design the multilayers, e.g., to determine the material system, the individual layer thicknesses, and the total number of layers, the simulation software package IMD was used. From the simulations it was also found that in order to realize high-reflectivity multilayer mirrors, interface imperfections, like roughness and intermixing need to be minimized.

    In particular the material systems W/B4C, Cr/Sc, and Ni/V grown by ion-assisted dualtarget magnetron sputter deposition, have been studied. The effect of various process parameters, especially the energy and flux of low-energy ion bombardment have been investigated in order to increase the understanding of the ion-surface interactions and the materials science of the multilayers.

    To characterize the multilayers mainly different x-rays techniques have been used; hard x-ray reflectivity, LPP soft x-ray reflectivity and also soft x-ray synchrotron reflectivity measurements at BESSY in Berlin and at the Advanced Light Source (ALS) in Berkeley. Both specular reflectivity and diffuse scattered intensity has been measured to assess the lateral and vertical structure of the multilayers.

    With an increased knowledge and understanding of the effects of the ion-surface interaction on the structure of the multilayers, advances were made in the development, with a following improvement in performance. The first multilayer material system investigated was W /B,C. However, because of a naturally high absorption of x-rays in W, the theoretically achievable reflectivity is very low, only about 12%.

    Cr/Sc, on the other hand, has potentially a much higher reflectivity of about 60%. Here different energies, but also fluxes, of ion assistance was investigated. It was found that, for a low ion flux, the ion energy, providing the optimum compromise between reduced roughness and induced intermixing, was rather high. By increasing the ion flux,the energy could be lowered, which in turn decreased the intermixing with a subsistent surface smoothening. This resulted in an improved reflectivity, where maximum nearnormal incidence reflectivities of R=5.5% and R=14.5% were achieved at λ=3.374 nm and at the Sc absorption edge (λ=3.115 nm), respectively.

    However, although fairly high reflectivities were obtained, the trade-off between roughness reduction and interface mixing persisted. Analytical calculations, based on a binary collision approximation, revealed that an interface mixing of ±1 atomic distance is unavoidable when a continuous flux of assisting ions is used. To overcome this limitation, a sophisticated interface engineering technique was employed, where the first part of each layer was grown using a high-flux of low energy ions, and the remaining part with a slightly higher ion energy. This method was demonstrated to largely eliminate the intermixing while maintaining the smoothening effect of ion-assistance.

    Using this novel modulated low-energy and high-flux ion-assistance technique extremely flat and abrupt interfaces were obtained. Soft x-ray Cr/Sc and Ni/V multilayer mirrors with near-normal incidence reflectivities of 20.7% and 2.7% at the Sc and V(λ=2.43 nm) absorption edges, respectively, were realized. Multilayer optimized for the Brewster angle showed a reflectance of R=26.7% and a polarizing power of Rs/Rp=5450 for Cr/Sc and R=l0% and Rs/Rp=4190 for Ni/V, when realized with engineered interfaces.

    Finally, also the long-term goal of producing a large-area, spherically-shaped, normalincidence soft x-ray multilayer condenser mirror for a compact soft x-ray microscope was accomplished.

    List of papers
    1. Compact soft x-ray reflectometer based on a line-emitting laser-plasma source
    Open this publication in new window or tab >>Compact soft x-ray reflectometer based on a line-emitting laser-plasma source
    Show others...
    2001 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 72, no 1 I, p. 58-62Article in journal (Refereed) Published
    Abstract [en]

    We describe a compact soft x-ray reflectometer for in-house characterization of water-window multilayer optics. The instrument is based on a line-emitting, liquid-jet, laser-plasma source in combination with angular scanning of the studied multilayer optics. With a proper choice of target liquid and thin-film filters, one or a few lines of well-defined wavelength dominate the spectrum and multilayer periods are measured with an accuracy of 0.003 nm using a multi-line calibration procedure. Absolute reflectivity may also be estimated with the instrument. The typical measurement time is currently 10 min. Although the principles of the reflectometer may be used in the entire soft x-ray and extreme ultraviolet range, the current instrument is primarily directed towards normal-incidence multilayer optics for water-window x-ray microscopy, and is thus demonstrated on W/B4C multilayers for this wavelength range. © 2001 American Institute of Physics.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47494 (URN)10.1063/1.1327307 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-12-29
    2. Enhanced soft x-ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition
    Open this publication in new window or tab >>Enhanced soft x-ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition
    2002 (English)In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 41, no 11, p. 2903-2909Article in journal (Refereed) Published
    Abstract [en]

    Cr/Sc multilayers have been grown on Si substrates using dc magnetron sputtering. The multilayers are intended as condenser mirrors in a soft x-ray microscope operating at the wavelength 3.374 nm. They were designed for normal reflection of the first and second orders, with multilayer periods of 1.692 and 3.381 nm, and layer thickness ratios of 0.471 and 0.237, respectively. At-wavelength soft-x-ray reflectivity measurements were carried out using a reflectometer with a compact soft-x-ray laser-plasma source. The multilayers were irradiated during growth with Ar ions, varying both in energy (9 to 113 eV) and flux, in order to stimulate the adatom mobility and improve the interface flatness. It was found that to obtain a maximum soft x-ray reflectivity with a low flux (Cr=0.76, Sc=2.5) of Ar ions a rather high energy of 53 eV was required. Such energy also caused intermixing of the layers. By the use of a solenoid surrounding the substrate, the arriving ion-to-metal flux ratio could be increased 10 times and the required ion energy could be decreased. A high flux (Cr=7.1, Sc=23.1) of low-energy (9 eV) Ar ions yielded the most favorable growth condition, limiting the intermixing with a subsistent good surface flatness. © 2002 Society of Photo-Optical Instrumentation Engineers.

    Keywords
    Cr/Sc, Ion energy, Ion flux, Ion-assisted sputter deposition, Multilayer, Reflectivity, Soft-x-ray microscopy, Water window
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46863 (URN)10.1117/1.1510750 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-12-29
    3. Recent advances in ion-assisted growth of Cr/Sc multilayer X-ray mirrors for the water window
    Open this publication in new window or tab >>Recent advances in ion-assisted growth of Cr/Sc multilayer X-ray mirrors for the water window
    2002 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    Cr/Sc multilayer X-ray mirrors intended for normal incidence reflection in the water window wavelength range, ?=[2.4-4.4nm], have been grown by ion-assisted sputter deposition and characterized using soft and hard X-ray reflectivity. By extracting low-energy ions, with energies, Eion, ranging from 9 to 113eV and with ion-to-metal flux ratios, F, between 0.76 and 23.1, from the sputtering plasma to the growing film, the nano-structure of the multilayer interfaces could be modified. A significantly increased soft X-ray reflectivity, using ?=3.374nm, for Cr/Sc multilayers with layer thicknesses in the range 0.4-2.8nm, was obtained when high ion-to-metal flux ratios, FCr=7.1 and FSc=23.1, and low energy ions, Eion=9eV, were used. An experimental reflectivity of 5.5% was obtained at 76° for a multilayer with 400 bi-layers. Simulations of the reflectivity data showed that the interface widths are <0.425nm. It could be concluded that roughness of low spatial frequency is reduced at lower ion energies than the high spatial frequency which was eliminated at the expense of intermixing at the interfaces at higher ion energies. The predicted performance of normal incidence multilayer mirrors grown at optimum conditions and designed for ?=3.374 and 3.115nm indicates possible reflectivities of 6.5% and 14%, respectively. © 2002 Elsevier Science Ltd. All rights reserved.

    Keywords
    Chromium, Ion-assisted growth, Multilayer, Scandium, Sputtering, Water window, X-ray mirror
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46853 (URN)10.1016/S0042-207X(02)00457-8 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-12-29
    4. 14.5% near-normal incidence reflectance of Cr/Sc x-ray multilayer mirrors for the water window
    Open this publication in new window or tab >>14.5% near-normal incidence reflectance of Cr/Sc x-ray multilayer mirrors for the water window
    Show others...
    2003 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 28, no 24, p. 2494-2496Article in journal (Refereed) Published
    Abstract [en]

    Cr/Sc multilayer mirrors, synthesized by ion-assisted magnetron sputter deposition, are proved to have a high near-normal reflectivity of R = 14.5% at a grazing angle of 87.5degrees measured at the wavelength A = 3.11 nm, which is an improvement of more than 31% compared with previously published results. Elastic recoil detection analyses show that the mirrors contained as much as 15 at. % of N and traces of C and O. Soft x-ray reflectivity simulations reveal interface widths of sigma = 0.34 nm and an exceptionally small layer thickness drift of similar to1.6 X 10(-5) nm/multilayer period throughout the stack. Simulations show that a reflectivity of R = 25.6% is attainable if impurities and layer thickness drift can be eliminated. The abrupt interfaces are achieved with ion assistance with a low ion energy of 24 eV and high ion-to-metal flux ratios of 7.1 and 23.1 during Cr and Se sputter deposition, respectively. In addition, a near-normal incidence reflectivity of 5.5% for the C VI emission line (lambda = 3.374 nm) from a laser plasma source was verified. (C) 2003 Optical Society of America.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-48449 (URN)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-12-29