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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.
    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.

  • 3.
    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.

  • 4.
    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.

  • 5.
    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.

  • 6.
    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.

  • 7.
    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.

  • 8.
    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.

  • 9.
    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.

  • 10.
    Fjälling, Arne
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Assessment and reduction of the conflicts between commercial fisheries and grey seals (Halichoerus grypus) in Swedish waters2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Along with the recovery of the Baltic Sea grey seal population from very low figures in the late 1970 's, there were clear signs of a rapidly increasing conflict between grey seals and fisheries. The set trap fisheries for salmonids seemed to be suffering the worst, but such data as were available were bard to evaluate. This lack of usable data fuelled a heated debate between commercial fishermen and seal biologists; it also made it difficult to take administrative decisions on compensatory programs to fishermen and inhibited research into mitigation methods. Available methods for the calculation of lost catches were imperfect. It was evident that the usual procedure, of simply counting the number of damaged fish found, would not reveal the total losses. It seemed likely that as well as the damaged and stolen fish, there could be other factors which would be negative for the outcome of the fishing operation. Finally, mitigation methods described were few and were said to be largely ineffective.

    A database was therefore built with detailed information on catches and seal disturbance from contracted commercial fishermen. A model was developed for the calculation of seal-induced Josses in salmon set traps. The mode] compared catches on consecutive days, i.e. in day-pairs. It was found that the total catch losses in set traps were high, at above 50% of the potential catch. A significant part of these losses was 'hidden', for example in the form of fish wholly removed from the gear. The mode! was also used for an analysis of the damage process. It was found that there were negative after-effects of seal visits and that increasing seal damage coincided with rising catches. It was suggested that the traditional estimation of damage by counting fish remains should be calibrated when used and that the new mode! with day-pairs should be tried in analyses of seal interference in other fishing operations. Data from the new model, together with logbook data, was then used in an estimation of seal damages to the Swedish fisheries as a whole. The overall losses, of catch plus gear damages, were estimated at over 40 million SEK in 2003.

    An attempt was then made to design a seal-safe salmon trap on the basis of previous observations of seal behaviour. In this experiment a set trap for salmonids was built using a larger mesh than the standard design and then compared with a standard trap. The basic idea was to use meshes small enough to guide an undisturbed fish further into the gear, towards the fish chamber, but large enough to allow a panicking fish being chased by a seal into the net panel to pass through, leaving the seal behind. Seal activity in and around the test trap was found to be only 6% of what it was around the standard trap; the activity level decreased further the following year when only large-meshed traps were used in the area. An estimate indicated that 65% of the potential catch was lost in the standard trap owing to seal predation, while the escape rate through the large meshes in the test trap was 52%. The standard trap had a total of 269 holes owing to seal damage, while only six holes were found in the test trap. A strategy that deprives seals of a reward makes the gear uninteresting to seals and may have long-term mitigation effects.

  • 11.
    Greczynski, Grzegorz
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Photoelectron spectroscopy of conjugated polymer surfaces and interfaces for light emitting devices2000Licentiate thesis, comprehensive summary (Other academic)
  • 12.
    Hjort, Mattias
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Theoretical studies on one-, two- and three-dimensional carbon structures2000Licentiate thesis, monograph (Other academic)
    Abstract [en]

    This thesis deals with electronic structure calculations in large carbon based materials, Especially graphite like structures have been studied. For this the tight binding method together with more sophisticated quantum chemical methods has been utilised. The first part of this thesis provides a background to the theoretical models used in the papers.

    In paper one, single bonded fulleride polymers of all dimensions have been studied as a function of charge state.

    In paper two, the effect of vacancies in graphite is modelled within the tight binding formulation.

    In paper three, electron localization in quasi-one dimensional systems in the presence of disorder are investigated.

  • 13.
    Jaksch, Peter
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Spin and charge in low-dimensional semiconductors2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis we investigate the trapping of spin-polarized electrons in edge states around a pair of antidots (Paper I). This study supports a proposal for using the trapped electrons to realize quantum gates - the building blocks of a quantum computer. The main advantage of our proposal is that the edge states have a very long lifetime, which will reduce problems with decoherence.

    We also address the issue of dimensionality by studying the local density of states in a quantum point contact (QPC). This is important since many results, regarding electron transport through the QPC, rely on an assumption of one­ dimensionality. We show that in order for this assumption to be valid, certain conditions regarding the shape of the potential have to be fulfilled (Paper II).

    Furthermore, we study electron transport in quantum wires, with emphasis on electron-electron interaction effects. In Papers III and IV we provide an explanation, based on these effects, of the experimentally observed 0.7 analogues, using Density Functional Theory (DFT).

  • 14.
    Joelsson, Torbjörn
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Growth, structure and properties of ternary transition metal nitride thin films prepared by reactive magnetron sputtering2003Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Early transition metal nitrides have found an extensive use in a range of applications. Even though the use is wide there are still large fields to explore. The work in this thesis has been directed towards increasing the fundamental understanding of the synthesis, characterization, and properties for some technologically relevant nitrides. Both binary and ternary phases of transition metal nitrides have been studied. In order to do so pure film materials were achieved by Ultra-High Vacuum Reactive Magnetron Sputtering. Findings from the TiN/TaN system show a correlation between phase composition in TaN and the stress evolution measured in-situ during deposition. It is also shown how the individual layers in a multilayer (thickness ~30 Å) effects the stress with a sub-nm resolution. The contribution from thermal stress is seen and the increase in temperature due to bombardment of energetic particles is calculated from that stress. In the NbxZr1-xN system experiments and calculations on the phase are used to derive a valence electron concentration, corresponding to x = 0.5, for which the films exhibit an enhanced number of stacking faults. This result in an effective hardness increase by 20 % compared to ZrN and NbN. MAX-structured Ti2A1N is synthesized for the first time in the thin film form and a pure single phase epitaxial film is grown on MgO(111) at 830°C. The Ti2A1N is characterized with respect to structure and mechanical properties. The room-temperature resistivity found is 39 µΩcm and the Young's modulus and hardness 210 and 16.1 GPa, respectively.

  • 15.
    Jönsson, Ulf
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Immobilization and Interaction of Biomolecules at the Solid-Liquid Interface: Applications to Solid-Phase Analytical Techniques1986Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The development of solid-phase-analytical techniques based on surface-concentration-measuring devices requires a stable and reproducible immobilization of biomolecules on well-characterized solid surfaces. This study reports on the immobilization of Immunoglobulin G, Protein A and Fibronectin on chemically modified silica surfaces. Reactive groups were introduced to the silica surfaces by chemical-vapour deposition of silane. The silanized surfaces were characterized by ellipsometry, contact angle measurements and scanning electron microscopy, which revealed smooth, stable and reproducible silane films of monolayer character. Immobilization by adsorption as well as covalent immobilization by the use of thiol-disulphide exchange reactions, thereby controlling the maximum number of covalent bonds to the surface, were studied. The immobilization was quantitated in a study applying both ellipsometry and radiotracer techniques. The amounts of immobilized proteins obtained from the radiolabeling experiments agreed well with those calculated from ellipsometric data. The results outline the possibilities of obtaining a controlled covalent binding of biomolecules to solid surfaces with an optimal stability and biological activity of the immobilized molecules.

  • 16.
    Karlsson, Susanne
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Phenols, anisoles and fatty acids causing odour problems in drinking water2003Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Taste and odour problems are the major causes of consumer complaints regarding drinking water in the industrialised world. Nevertheless, as yet there are no mandatory requirements to identify the compounds that are responsible for the observed off-flavour. This thesis shows that gas chromatographic analysis with mass spectrometric and sensory detection provides an efficient tool for such investigations. The enrichment that precedes the gas chromatographic analysis can normally be based on stripping volatile or semi-volatile organic compounds. Due to the low blank level obtained with the open stripping system used in the present study, well-known odorous compounds, such as geosmin, 2- methylisoborneol (MIB) and 2,4,6-trichloroanisole (2,4,6-TCA), could be detected at levels below their threshold odour concentrations. However, this thesis also shows that compounds that are too hydrophilic to be enriched by stripping can play an important role, either as precursors of odorous compounds or as the direct cause of off-flavours. In particular, we found that natural formation of 2,4,6-trichlorophenol (2,4,6-TCP) may lead to the formation of 2,4,6-TCA in the distribution system. Furthermore, a study of a municipal treatment plant showed that short-chain carboxylic acids can be formed in slow sand filters, giving the finished water a rancid or nauseating flavour. Collectively, the results of the present study clearly show the importance of regarding the entire process from raw water supply to the consumer's tap as an integrated system. Off-flavours may originate from processes in the raw water supply, during treatment and in the distribution system.

  • 17.
    Kindlihagen, Anders
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Theoretical modeling of bipolar double-barrier resonant-tunneling light emitting diodes1996Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is about firms determined to gain competitive advantages from environmental demands, about the efforts of engineers employed with the challenge of fulfilling environmental performance targets and about the management and organisation of product development. It is about incremental change, built on established technological knowledge, as well as about radical technological change. In the title, the nation of "environmental compliance" has a dual meaning. It implies that industrial organisations have to comply with ecological constraints, but also that they have to comply more generally with contextual factors such as competition, technology, customer preferences and market characteristics. However to avoid confusion, "environment" will henceforth be used to describe the ecological aspects, which is the traditional meaning of this term in environmental management and eco-design literature.

  • 18.
    Kreij, Karl
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Bioprocess monitoring of mammalian cell cultures using modern sensors2003Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The need for better monitoring and control of mammalian cell cultures and the quality and safety control of products obtained from these processes is still high. In an attempt to enable better monitoring of the process and the glycosylation pattern of typical mammalian cell cultures two modem sensor methods were used on a chinese hamster ovary (CHO) cell culture producing the glycoprotein macrophage colony stimulating factor (M-CSF). An electronic nose was connected to the reactor and measurements were made online. Surface plasmon resonance (SPR) measurement were performed on cell culture supernatant samples.

    The electronic nose was used to study microbial and fungal infections in a cell culture. Principal component analysis and cluster analysis were used to evaluate the multivariate data obtained from the electronic nose. The results indicate that it is possible to use the electronic nose to detect contaminations in cell cultures.

    A novel method that combines the strong affinity of an antibody with the weak affinity of lectins was used in SPR measurements of the crude cell culture supernatant. It is suggested that this method could be used to monitor the glycosylation pattern of recombinant glycoproteins on-line.

  • 19.
    Kroon, Lars
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Delocalization in nonperiodic systems2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The localization properties of non-interacting linear excitations in one-dimensional aperiodically ordered structures are investigated from a theoretical point of view. The models used have various relevance for real systems, like quasicrystals, photonic crystals, and deterministic aperiodic superlattices. The main objective is to gain a conceptual understanding of the localization phenomenon in different lattice models, especially with respect to their correlation measures.

    The localization properties of electronic wavefunctions in various nearest neighbor tight -binding models are studied in the framework of the dynamical systems induced by the trace maps of their corresponding transfer matrices. With a unit hopping and an on-site potential modulated by the Rudin-Shapiro sequence, which in analogy with a random potential has an absolutely continuous correlation measure, the electronic spectrum is proved to be purely singular continuous and of zero Lebesgue measure. The absence of localization is also confirmed by numerical simulations of the dynamics of electronic wavepackets showing weakly anomalous diffusion and an algebraic decay of the temporal autocorrelation function. These results are also found to be invariant under the introduction of correlated hopping integrals.

    The nature of localization of elastic vibrations in harmonic lattices is also studied. The generalized eigenvalue problem arising from classical interactions in diatomic chains can be mapped to mixed tight-binding models, which enables the use of the spectral theory of discrete Schrödinger operators. Like for the Rudin-Shapiro model, it is found that the vibrational spectra of harmonic chains with masses distributed according to the Thue-Morse sequence and the period-doubling sequence are purely singular continuous. These results are obtained by transforming the lattices to on-site models by the use of certain renormalization procedures.

    Remembering that the correlation measure of the T hue-Morse sequence is purely singular continuous, while that of the period-doubling sequence is pure point, these results strongly suggest that the criticality of localization in deterministic aperiodic lattices is generic and quite independent of the character of the correlation measure associated to the modeling sequence.

  • 20.
    Lennholm, Erik
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Effects of aperiodic order for Josephson junction arrays and discrete breathers2000Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Effects of the combination of nonlinearities and aperiodic order is studied in this thesis. The nonlinear systems considered are Josephson junction arrays (JJA) and Fermi-Pasta-Ulam (FPU) lattices. Both systems are discrete and one-dimensional. The traveling waves in a JJA are solitons, i.e., coherent structures which retain their shape and speed as they propagate. The properties of both these system is influenced by the ordering of their respective constituents. In the thesis some aperiodicaly orderd structures are described, including some typical effects on systems which are aper iodically orderd. Next, a description of Josephson junctions are given and also some physical features for system sconsisting of these junctions. A number of practical applications are given, Finally discrete breathers are described, including existence conditions and some possible applications.

    Paper 1: Fluxon propagation in discrete Josepson junction arrays is examined. Sometimes a fluxon can be pinned in the array and we derive an effective potential which can explain why this happens, and predict at which positions a fluxon can get pinned.

    Paper2; Discrete breathers are shown to exist in aperiodically ordered, diatomic FPU lattices. Localized modes survives for longer times in Fibonacci and Thue-Morse lattices compared to a periodic lattice. The conjecture is that the gaps in the linear phonon spectrum of the aperiodically orderd structures hinder resonances with the linear spectrum.leading to the longer life times.

    Paper 3: Moving breathers in FPU lattices are examined. These have frequencies in the linear bands. Interaction with noise and imourity atoms are further considered.

    Paper 4: Current-voltage (I-V) curves are calculated for Josephson junction arrays, which consist of two different types of junctions. A monoarray is compared to a periodic array and a Fibonacci array. There are marked differences in the I-V curves for these systems. New states with kink a structure superimposed on the rotating McCumber background are found in periodic array and in the Fibonacci array.

  • 21.
    Marcus, Carina
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Faceted conformal antenna arrays analyzed with the uniform theory of diffraction2004Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Faceted conformal antenna arrays are analyzed with the uniform theory of diffraction (UTD). Parameters such as mutual coupling, scattering parameters, isolated and embedded element patterns are calculated.

    A ray tracing algorithm for handling rays on a faceted surface, which is needed for the UTD calculations, is also described.

  • 22.
    Persson, Per
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Electron microscopy of ion implanted silicon carbide2000Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis investigates structural defects into Silicon Carbide (SiC) in processed Al and B ion implantated samples. Ion implantation is currently the preferred way to introduce impurity atoms into the SiC crystal lattice. The structural defects found was concluded to be extrinsic dislocation loops composed of excess Si interstitials. A model for these loops was developed and the mechanisms for loop evolution during processing were identified. The results of this thesis contributes to an improved processing technology of SiC as a semiconducting material, which will be used in electrical components for high power, high temperature and high frequency applications.

  • 23.
    Seppänen, Timo
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Magnetron sputter epitaxy of 2h-Al1-xInxN thin films2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes the growth and structural characterization of epitaxial 2h­ A11-xInxN ranging from pure A1N to InN [0<x<1]. Thin A11-xInxN films were synthesized by dual DC reactive Magnetron Sputter Epitaxy (MSE) in an ultra-high vacuum (UHV) system. Growth parameters such as deposition temperature and magnetron power settings were adjusted in order to control the film stoichiometry. The role of in-situ deposited TiN(111) and ZrN(111) seed layers on the A11-xInxN growth was also investigated. It was found that ZrN(111) seed layers provide a wider stoichiometric composition region at elevated temperatures due to its low lattice mismatch as compared to TiN(111). Microstructural characterization of A11-xInxN deposited at temperatures from 300 to 900 °C was carried out by X-ray diffraction (XRD) techniques and transmission electron microscopy (TEM). TEM micrographs revealed a dense and columnar microstructure with column widths ranging from 10 to 200 nm depending on growth temperature and seed layer. In addition, a novel generic growth mode giving rise to extremely curved, though stress- free, crystal lattices was observed and investigated. It was found that these, so called, nano-grass structures arise due to specific kinetic and geometrical limitations during growth. Compositional differences are formed over the columns due to self-shadowing effects, which are partly preserved due to the low surface ad-atom mobility. Thus resulting in extremely curved crystalline columns. XRD investigations showed that single-phase wurtzite epitaxial A11-xInxN was obtainable throughout the whole composition range for deposition temperatures of up to 600 °C onto ZrN(111) seed layers. At higher temperatures almost pure hexagonal A1N was formed. XRD and selected area electron diffraction also showed that the A11-xInxN films were grown hetero-epitaxially onto TiN and ZrN with the epitaxial relationship: A11-xInxN(0001)//TiN(ZrN)(111) and A11-xInxN[10-10]//TiN(ZrN)[110]. In the case of A11-xInxN depositions onto TiN(111) seed layers, a phase separation of A11-xInxN was observed when mid-x compositions was targeted at deposition temperatures of 600 °C. This observation was confirmed by TEM results, which revealed a layered structure with epitaxial 2h-A11-xInxN followed by a nano-crystalline structure. Based on the results, pseudo-binary phase diagrams for MSE deposition of 2h-A11-xInxN, at temperatures up to 1000°C, onto TiN(111) and ZrN(111) coated MgO(111) could be established.

  • 24.
    Shi, Jing
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Design and synthesis of glycose-derivatives and related molecules for cell membrane mimetics2004Licentiate thesis, monograph (Other academic)
    Abstract [en]

    A series of glucopyranose (α-D-glucose, β-D-glucose, D-gluconic acid and 6-amino-6-deoxy-D-glocuse) terminated alkanethiol acetals have been successfully synthesized. α and β-D-glucose were configured in controlled ways coupling with alkanethiol, in which bromosugar and trichloroacetirnidates were selected as activated glycosyl donors using different promoters tetraalkylammonium bromide (Et4NBr) and trimethylsilanetriflate (TMSOTf) respectively.

    The glycosylation of glucuronic acid and 6-amino-6-deoxy-β-D-glucose to ω-mercaptohexadecanol depends on powerful donors and stronger promoters. The corresponding trichloroacetimidates of the methyl D-glucuronic ester and 6-azido-6-deoxy-β-D-glucose were used as active donors, and strong Lewis acid, trimethylsilyl triflate (TMSOTf) was also involved in this study.

    These structures were mixed in different proportions with HO(CH2)16SH, and the corresponding SAMs on gold were characterized by ellipsometry, contact angle goniometry, and infrared reflection-absorption spectroscopy. Infrared reflection­absorption spectroscopy (IRAS) indicated well-ordered SAMs with a high degree of crystallinity on the hydrocarbon layer. Different orientation between α and β-D-glucose self-assembled monolayers, and the functionality of carboxyl acid and amine were explored on surface for further immobilization of lipid bilayers.

    New model systems were developed, in which amphiphilic hexadecly OEG derivative or glucose derivatives were designed to present self-assembled monolayers on gold. HS(CH2)15CONH-EG6-CH2CONH(CH2)15CH3 displayed particularly sharp features in IRAS spectra at room temperature. Carbohydrate unit instead of OEG moiety could be more natural and it possesses three-dimensional water-filled space.

  • 25.
    Svensson, Johan
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Optical properties of some complex defects in silicon1990Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    lnfrared absorption spectroscopy has been used study transitions between electronic states related to some complex defects in silicon. Three different defects have been studied: a complex defect involving carbon as one of its constituents, a divacancy, and a defect found in silicon containing tin. All defects studied were created by means of irradiating the silicon crystal at room temperature with 2.0 MeV electrons. The experimental method used in the study was Fourier Transform lnfrared (FTIR) spectroscopy.

    The study is focused on the electronic structure of defects and the coupling between the electronic states and vibrational states. Furthermore, the formation of the divacancy in silicon is found to very likely be formed by the pairing of single vacancies for irradiation of silicon with 2.0 MeV electrons at room temperature.

    A previously unknown absorption spectrum of a defect in silicon is presented. The absorption spectrum is interpreted as being due to the transitions between a non-degenerate ground state of the defect to hydrogen-like single-particle electron states. The final states of the transition are found to be s­ states. Transitions to p-states are not observed. The final electronic states are referred to as pseudodonor states. The term "pseudo" is used to emphasize that only the final states of the transitions can be referred to as donor states. The ionization energy of the excited and final pseudo-donor s-states with large amplitudes at the defect site (A1-symmetry), is found to be much larger than that for s-states with a node or a small amplitude at the defect site. The s-states with a node at the defect site are found to have ionization energies that are close to the energies estimated with the effective mass approximation. A comparison is made of this new spectrum with spectra related to other defects in silicon, and principal similarities are found that indicate that excited electron states of pseudo-donor character are common for defects in silicon. The defect is also found to be metastable. A change in configuration of the defect is observed via the increase in absorption of the spectrum of the defect versus time of optical excitation at temperatures of the crystal below 65K. The spectrum is found to disappear when the sample is heated in darkness at temperatures exceeding 70K. This is interpreted as being a thermally-induced change from the metastable to the stable configuration of the defect. The activitation energy for the disappearence of the absorption spectrum is found to be 0.21 eV. An Auger recombination of excitons at the defect is found to be the most likely process for initiating the change in configuration of the defect.

    Furthermore, carbon is found to be one of the constituents of this complex defect. Uniaxial stress measurements have been performed and the effect of the stress on the spectrum is found to be in agreement with the interpretation of the excited states of the defects as being due to a pseudodonor.

  • 26.
    Tulldahl, Michael
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Airborne laser depth sounding: model development concerning the detection of small objects on the sea bottom2000Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Airborne laser depth sounding is a promising technique for rapid and high -density sounding of shallow waters. Depth accuracy analysis for laser depth sounding has almost exclusively dealt with horizontal flat bottoms. The objective of this work is to simulate and compare the influence of different shapes of small objects placed on the sea bottom. For this purpose an analytical mode] approach is used to characterize the signals received from objects of size 1 m3 on bottom depths between 5 m and 12 m. Two object types are compared: a cylinder and a cube. The difference in the signal received is small between these objects. Simulated data are compared with experimental data and show good agreement. The probability of small shoal detection critically depends on the horizontal position of the shoal in the laser beam and the shoal height above the bottom. From comparisons between a large number of simulations and measurements the performance is discussed in terms of covered area for one laser shot enabling detection of the shoal.

  • 27.
    Tungasmita, Sukkaneste
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Epitaxial aluminum nitride thin films on 6H-silicon carbide, grown by magnetron sputter deposition2000Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The research presented in this thesis is focused on epitaxial wurtzite-structure Aluminum Nitride (AlN) thin film synthesis, by ultra-high-vacuum (UHV) de magnetron sputter deposition, on Silicon Carbide (6H-SiC) substrates. The emphasis of the work has been put on controlling the growth and quality of the films to be able to use this material in electronic device applications.

    The quality of epitaxial AlN films is significantly improved by using low­ energy ion assistance (Ei = 17-27 eV), during growth. The ion-assisted growth results in an increased surface mobility, which promotes domain boundary annihilation and epitaxial growth. This results in lateral expansion of column width (100 nm-wide at film thickness above 100 nm). The film characterization results show a very good crystal quality as well as high purity material. The measured concentrations of O, C, and Si in the film are at 3.5x1018, l. 3x1018 and 3.5xl 018 cm-3, respectively, which are among the purest AlN material as has been reported. The appearance of near band­ edge CL emission (6.02 eV at 4K) is also an evidence ofa high quality material.

  • 28.
    Unge, Mikael
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Electronic properties of organic molecular materials2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the context of molecular based electronics, different molecular systems have been studied. In molecular crystals of pentacene, the conduction process has been reported to occur in a single layer in field-effect transistor applications. The electron localization length and its sensitivity to disorder of such two-dimensional disordered systems have been calculated. The electron localization in DNA has also been investigated. Our results show that DNA containing an approximately equal amount of the four basis is insulating. For instance, the human chromosome 22 is an insulator even though it has long-range correlation, which elsewhere has been suggested to give delocalized states.

    The on-site Coulomb interaction has been calculated for rubidium-doped tetracyanoethylene (TCNE). If the electronic state is localized to a small region, e.g., a single molecule, the on-site Coulomb interaction becomes important. The interaction is a measure of the work needed to add an extra electron to the system. When the electronic state is localized to a single molecule/site it becomes large. The result has been used to interpret the outcome of ultraviolet photoelectron spectroscopy (UPS) measurements.

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