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  • 1.
    Abelow, Alexis
    et al.
    University of Utah, Salt Lake City, USA.
    Persson, Kristin
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Jager, Edwin
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, The Institute of Technology.
    Berggren, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zharov, Ilya
    University of Utah, Salt Lake City, USA.
    Electroresponsive Nanoporous Membranes by Coating Anodized Alumina with Poly(3,4-ethylenedioxythiophone) and Polypyrrole2014In: Macromolecular materials and engineering (Print), ISSN 1438-7492, E-ISSN 1439-2054, Vol. 299, no 2, p. 190-197Article in journal (Refereed)
    Abstract [en]

    Electrically-active nanoporous membranes are prepared by coating the surface of anodized alumina with electroactive polymers using vapor phase polymerization with four combinations of conjugated polymers and doping ions: poly(3,4-ethylenedioxythiophone) and polypyrrole, FeCl3 and FeTs3. The permeability of the polymer-coated membranes is measured as a function of the applied electric potential. A reversible three-fold increase is found in molecular flux of a neutral dye for membranes in oxidized state compared to that in the reduced state. After analyzing various factors that may affect the molecular transport through these membranes, it is concluded that the observed behavior results mostly from swelling/deswelling of the polymers and from the confinement of the polymers inside the nanopores.

  • 2.
    Abrikosov, Igor A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Steneteg, Peter
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Hultberg, Lasse
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Yu Mosyagin, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Department of Theoretical Physics and Quantum Technologies, National Research, Technological University MISiS, Moscow, Russia.
    Lugovskoy, Andrey V.
    Department of Theoretical Physics and Quantum Technologies, National Research, Technological University MISiS, Russia.
    Barannikova, Svetlana A.
    Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Science, Tomsk, Russia; Department of Physics and Engineering, Tomsk State University, Tomsk, Russia.
    Finite Temperature, Magnetic, and Many-Body Effects in Ab Initio Simulations of Alloy Thermodynamics2013In: TMS2013 Supplemental Proceedings, John Wiley & Sons, 2013, p. 617-626Chapter in book (Refereed)
    Abstract [en]

    Ab initio electronic structure theory is known as a useful tool for prediction of materials properties. However, majority of simulations still deal with calculations in the framework of density functional theory with local or semi-local functionals carried out at zero temperature. We present new methodological solution.s, which go beyond this approach and explicitly take finite temperature, magnetic, and many-body effects into account. Considering Ti-based alloys, we discuss !imitations of the quasiharmonic approximation for the treatment of lattice vibrations, and present an accurate and easily extendable method to calculate free ,energies of strongly anharmonic solids. We underline the necessity to going beyond the state-of-the-art techniques for the determination of effective cluster interactions in systems exhibiting mctal-to-insulator transition, and describe a unified cluster expansion approach developed for this class of materials. Finally, we outline a first-principles method, disordered local moments molecular dynamics, for calculations of thermodynamic properties of magnetic alloys, like Cr1-x,.AlxN, in their high-temperature paramagnetic state. Our results unambiguously demonstrate importance of finite temperature effects in theoretical calculations ofthermodynamic properties ofmaterials.

  • 3.
    Abrikosov, Igor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Knutsson, Axel
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Tasnádi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Lind, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Phase Stability and Elasticity of TiAlN2011In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 4, no 9, p. 1599-1618Article in journal (Refereed)
    Abstract [en]

    We review results of recent combined theoretical and experimental studies of Ti1−xAlxN, an archetypical alloy system material for hard-coating applications. Theoretical simulations of lattice parameters, mixing enthalpies, and elastic properties are presented. Calculated phase diagrams at ambient pressure, as well as at pressure of 10 GPa, show a wide miscibility gap and broad region of compositions and temperatures where the spinodal decomposition takes place. The strong dependence of the elastic properties and sound wave anisotropy on the Al-content offers detailed understanding of the spinodal decomposition and age hardening in Ti1−xAlxN alloy films and multilayers. TiAlN/TiN multilayers can further improve the hardness and thermal stability compared to TiAlN since they offer means to influence the kinetics of the favorable spinodal decomposition and suppress the detrimental transformation to w-AlN. Here, we show that a 100 degree improvement in terms of w-AlN suppression can be achieved, which is of importance when the coating is used as a protective coating on metal cutting inserts.

  • 4.
    Afshari, Davood
    et al.
    School of Mechanical Engineering, Iran University of Science and Technology, Iran .
    Mohammd, Sedighi
    School of Mechanical Engineering, Iran University of Science and Technology, Iran .
    Zuhier, Barsoum
    Department of Aeronautical and Vehicle Engineering, KTH – Royal Institute of Technology, Sweden .
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    An Approach in Prediction of Failure in Resistance Spot Welded Aluminum 6061-T6 under Quasi-static Tensile Test2012In: Proceedings of the Institution of mechanical engineers. Part B, journal of engineering manufacture, ISSN 0954-4054, E-ISSN 2041-2975, Vol. 226, no 6, p. 1026-1032Article in journal (Refereed)
    Abstract [en]

    The aim of this article is to predict the failure load in resistance spot welded aluminum 661-T6 sheets with 2 mm thickness under quasi-static tensile test. Various welding parameters, e.g. welding current, welding time and electrode force are selected to produce welded joints with different quality. The results show that for all the samples in this study only interfacial failure mode was observed in tensile-shear test and no pull-out mode was observed. According to the failure mode, an empirical equation was used for the prediction of failure load based on nugget size and hardness of failure line. Microstructure study has been carried out to investigate microstructural changes in the welded joints. For determination of the minimum hardness, microhardness tests have been carried out to find hardness profiles. The minimum hardness value was observed for a thin layer around the nugget with large and coarse grains. The results show that by using the presented empirical equation, the failure can be predicted with a good agreement only by measuring nugget size.                   .

  • 5. Agmell, Mathias
    et al.
    Ahadi, A
    Zhou, J M
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Bushlya, Volodymyr
    Stahl, J-E
    Modeling Subsurface Deformation Induced by Machining of Inconel 7182017In: Machining science and technology, ISSN 1091-0344, E-ISSN 1532-2483, Vol. 21, no 1, p. 103-120Article in journal (Refereed)
    Abstract [en]

    Traditionally, the development and optimization of the machining process with regards to the subsurface deformation are done through experimental method which is often expensive and time consuming. This article presents the development of a finite element model based on an updated Lagrangian formulation. The numerical model is able to predict the depth of subsurface deformation induced in the high- speed machining of Inconel 718 by use of a whisker-reinforced ceramic tool. The effect that the different cutting parameters and tool microgeometries has on subsurface deformation will be investigated both numerically and experimentally. This research article also addresses the temperature distribution in the workpiece and the connection it could have on the wear of the cutting tool. The correlation of the numerical and experimental investigations for the subsurface deformation has been measured by the use of the coefficient of determination, R2. This confirms that the finite element model developed here is able to simulate this type of machining process with sufficient accuracy.

  • 6.
    Ahmad, Maqsood
    et al.
    Base Engine & Materials Technology, Volvo Group, Gothenburg.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    König, Mathias
    Materials Technology for Basic Engine, Scania CV, Södertälje.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Bending Fatigue Behavior of Blast Cleaned Grey Cast Iron2017In: Residual Stresses 2016: ICRS-10, Materials Research Proceedings 2 (2016), 2017, Vol. 2, p. 193-198Conference paper (Refereed)
    Abstract [en]

    This paper presents a detailed study on the effect of an industrial blast cleaning process on the fatigue behavior of a grey cast iron with regard to the residual stresses and microstructural changes induced by the process. A comparison was also made to the effect of a machining operation which removed the casting skin layer. The blast cleaning process was found to greatly improve the fatigue resistance in both the low and high cycle regimes with a 75% increase in the fatigue limit. Xray diffraction measurements and scanning electron microscopic analyses showed that the improvement was mainly attributed to compressive residual stresses in a surface layer up to 800 μm in thickness in the blast cleaned specimens. The machining also gave better fatigue performance with a 30% increase in the fatigue limit, which was ascribed to the removal of the weaker casting skin layer.

  • 7.
    Aid, Graham
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Environmental Technology and Management. Ragn-sells, Sweden.
    Kihl, Anders
    Ragn Sells AB.
    Driving forces and inhibitors of secondary stock extraction2014Conference paper (Other academic)
    Abstract [en]

    Even though it’s well known to mankind that our common resources are limited and that recycling is a key for a sustainable future; in reality we see few examples of true recycling where virgin raw material is substituted by waste. There are endless number of examples where waste is utilized to some extent without solving the core issue: reducing the need of extracting virgin raw materials. This article analyses some of the driving forces and inhibitors that explains why it’s so difficult establish secondary stock extraction although technology is available. The authors discuss and suggest possible ways for reducing the some of the main barriers.

  • 8.
    Albertini, Gianni
    et al.
    Dipartimento di Scienze dei Materiali e della Terra, Universita, Ancona, Italy.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Manescu, Adrian
    Instituto di Scienze Fisiche, Universita, Ancona, Italy.
    Ponzetti, Araldo
    NUOVA M.A.I.P SpA, Viale Cavalotti n 30, Jesi, Italy.
    Neutron Diffraction Measurement of Residual Stress in a centrifugal Bowl of Duplex Steel2001In: Journal of Neutron Research, ISSN 1023-8166, E-ISSN 1477-2655, Vol. 9, p. 305-312Article in journal (Refereed)
  • 9. Alkaisee, Rasha
    et al.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Influence of Layer Removal Methods in Residual Stress Profiling of a Shot Peened Steel using X-ray Diffraction2014In: Residual Stresses IX, 2014, Vol. 996, p. 175-180Conference paper (Refereed)
  • 10.
    Altgärde, Noomi
    Linköping University, Department of Physics, Chemistry and Biology.
    Local release of lithium from sol-gel coated orthopaedic screws: an in vitro and in vivo study2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

     

    In orthopaedic practice, fractures are usually stabilised with metal screws or rods. This is done in order to keep the fracture parts in place during the rather slow healing process. The healing time can potentially be reduced by local- or systemic treatment with different bone promoting drugs. In later years, lithium, otherwise used to treat bipolar disease, has shown promise to be such a drug.

     

    The aim of this master thesis was to find a way to coat metal bone screws with lithium and to characterise the coating. The coating was to be designed in such a way that it could release lithium to the surrounding bone tissue.

     

    Lithium chloride was incorporated into a titanate sol-gel and attached to silicon wafers and stainless steel screws by dip coating. Wafers were used for initial in vitro studies of how lithium changed coating characteristics. This was studied using ellipsometry, AFM and SEM. Lithium is most probably physisorbed and not incorporated into the network building up the sol-gel. Coating structure is changed as more lithium is incorporated. For large amounts of lithium, the nanoparticles normally formed when curing the sol-gel are inhibited. One effect of this is reduced bioactivity, seen as a reduced ability for calcium phosphate crystals to nucleate on the coating when immersed in simulated body fluid.

    Lithium release was investigated using AAS. Lithium is released from the coating, showing a burst effect. By changing the number of coating layers used, the release profile can be partly altered. The coating was also applied to screws, showing good attachment, and the lithium release profile was similar to the one seen from wafers.

    Finally, a screw model was used in rats to assess the effect of local lithium treatment from screws and systemic lithium treatment on fracture healing. In the model, a screw was inserted in tibia, mimicking a fracture. When the bone around the screw was healed, a pullout test was performed, giving information about the strength of the bone surrounding the screw. No significant difference could be found for either local- or systemic lithium treatment compared to control. However, when evaluating the strength of intact bone in a similar way, a positive effect of systemic lithium treatment could be seen. Therefore, it is still likely that lithium has a positive effect on bone and further studies are needed to fully evaluate its role in fracture healing.

     

  • 11.
    Anderberg, Elin
    Linköping University, Department of Physics, Chemistry and Biology.
    LED Array Frequency Dependent Photocurrent Imaging of Organic Solar Cell Modules2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To mitigate the risk for devastating climate changes, there is an urgent need to change the energy production from the current fossil based to renewable sources. Solar cells will contribute to an increasing share of the future energy systems. Today silicon solar cells dominate the market but printed organic solar cells are promising alternatives in terms of cost, flexibility, possibilities for building integrations and energy payback times. Printing enables roll-to-roll processing that is quick and renders huge volumes. Thus, also characterization and quality control must be fast. Recent tests have been performed showing that a LED array with amplitude modulated LEDs can be used to provide photocurrent images of modules with series connected sub cells in-line during manufacturing. The purpose of this thesis work is to further evaluate and develop this LED array characterization technique focusing on contact methods and signal interpretation. Two modes were examined; a contact mode and a capacitive contact-less mode. Both modes gave comparable results and indicated strong variations in performance of sub cells in the measured modules. Other methods to address individual cells also showed similar behavior. However, by manually adding extra contact points, current-voltage curves could be measured on the individual sub cells in the modules. Extraction of photocurrents were similar, but the parallel resistances varied strongly between the cells in the module. Increasing the frequency of the LEDs resulted in less variations. Calculations indicated that this frequency dependence could be used to separate the photocurrent generation and parallel resistance in the sub cells.

  • 12.
    Andersen Söderbergh, Kim
    Linköping University, Department of Management and Engineering, Carl Malmsten - furniture studies. Linköping University, The Institute of Technology.
    Blästring av trä: Ett materialbibliotek av blästrade och ytbehandladeträytor2012Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    In my thesis I have sand blasted different type of woods - ring-porous and diffuseporous deciduous tree species and conifers - to show different results depending on the species, the direction of the grain and the effects of surface treatment of a blasted surface.

    The results of my tests were sometimes unexpected, such as that the sand from blasting almost completely disappeared, that all wood surfaces after blasting exhibited a much lighter or paler surface than before and that the diffuse-porous tree species showed differences in hardness between the beginning and end of annual rings.

    By creating a library of different kinds of wood and sandblasted surface treatment, I have created a reference bank that I will be able to use me in the manufacturing of interiors, furniture and other objects.

  • 13.
    Andersson, Mike
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, The Institute of Technology.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, The Institute of Technology.
    Technology and application opportunities for SiC-FET gas sensors2012In: Solid State Gas Sensors - Industrial Application / [ed] Maximilian Fleischer and Mirko Lehmann, Springer Berlin/Heidelberg, 2012, p. 189-214Chapter in book (Refereed)
    Abstract [en]

    The development of SiC-FET gas sensors has proceeded for about fifteen years. The maturity of the SiC material and a deeper understanding of the transduction mechanisms and sensor surface processes behind the sensitivity to a number of target substances have recently allowed the development of market-ready sensors for certain applications. Some examples presented below are a sensor system for domestic boiler control, an ammonia sensor for control of the SCR (selective catalytic reduction) and SNCR (Selective Non-Catalytic Reduction) NOx abatement processes as well as other more or less market-ready applications. In parallel, the basic research continues in order to reach more demanding markets/new applications and also to possibly lower the production costs of the sensors. Therefore, current research and future challenges are also treated, such as the development of new types of conducting ceramics for ohmic contacts to SiC in order to increase the operation temperature beyond the present state of the art.

  • 14.
    Andersson, Niklas
    Linköping University, Department of Management and Engineering.
    Gesällprovets tillverkningsprocess2008Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Examensarbetet är en beskrivande rapport om tillverkningsprocessen av ett gesällprov. Rapportens syfte är att beakta olika konstruktioner och hur de förvärvade kunskaperna används för att utföra en slutprodukt, i det här fallet ett gesällprov. Rapporten försöker svara på vilka faktorer som varit mest avgörande för ett lyckat resultat.

    Tyngdpunkten i arbetet ligger i att beskriva tillverkningsprocessen. Rapporten beskriver resonemanget kring valet av en möbel. Den presenterar olika träslag och hur de kan påverka möbelns uttryck. Vidare berättar rapporten om olika alternativ på skivmaterial att använda som blindträ. Uttag och hantering av faner och massivträ förklaras. Rapporten visar även olika konstruktioner och sammansättningar.

    I den avslutande delen presenteras resultatet av tillverkningen och granskarnas betygssättning. Ett resonemang förs angående vilka faktorer, så som erfarenheter, förvärvade kunskaper, noggrannhet etc. som påverkat resultatet. Slutligen beskrivs olika svårigheter och vad som skulle kunna göras annorlunda.

  • 15.
    Andric, Jelena
    et al.
    Chalmers University of Technology.
    Fredriksson, Sam T.
    Chalmers University of Technology.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sasic, Srdjan
    Chalmers University of Technology.
    Nilsson, Håkan
    Chalmers University of Technology.
    A study of a flexible fiber model and its behavior in DNS of turbulent channel flow2013In: Acta Mechanica, ISSN 0001-5970, E-ISSN 1619-6937, Vol. 224, no 10, p. 2359-2374Article in journal (Refereed)
    Abstract [en]

    The dynamics of individual flexible fibers in a turbulent flow field have been analyzed, varying their initial position, density and length. A particle-level fiber model has been integrated into a general-purpose, open source computational fluid dynamics code. The fibers are modeled as chains of cylindrical segments connected by ball and socket joints. The equations of motion of the fibers contain the inertia of the segments, the contributions from hydrodynamic forces and torques, and the connectivity forces at the joints. Direct numerical simulation of the incompressible Navier-Stokes equations is used to describe the fluid flow in a plane channel, and a one-way coupling is considered between the fibers and the fluid phase. We investigate the translational motion of fibers by considering the mean square displacement of their trajectories. We find that the fiber motion is primarily governed by velocity correlations of the flow fluctuations. In addition, we show that there is a clear tendency of the thread-like fibers to evolve into complex geometrical configurations in a turbulent flow field, in fashion similar to random conformations of polymer strands subjected to thermal fluctuations in a suspension. Finally, we show that fiber inertia has a significant impact on reorientation timescales of fibers suspended in a turbulent flow field.

  • 16.
    Andric, Jelena
    et al.
    Chalmers University of Technology, Göteborg, Sweden.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sasic, Srdjan
    Chalmers University of Technology, Göteborg, Sweden.
    Nilsson, Håkan
    Chalmers University of Technology, Göteborg, Sweden.
    Rheological properties of dilute suspensions of rigid and flexible fibers2014In: Journal of Non-Newtonian Fluid Mechanics, ISSN 0377-0257, E-ISSN 1873-2631, Vol. 212, p. 36-46Article in journal (Refereed)
    Abstract [en]

    Particle-level simulations are used to study the rheology of monodispersed suspensions of rigid and flexible fibers in a creeping, simple shear flow of a Newtonian fluid. We also investigate the influence of different equilibrium shapes (straight and curved) of the fibers on the behavior of the suspension. A parametric study of the impacts of fiber flexural rigidity and morphology on rheology quantifies the effects of these realistic fiber features on the experimentally accessible rheological properties. A fiber is modeled as a chain of rigid cylindrical segments, interacting through a two-way coupling with the fluid described by the incompressible three-dimensional Navier–Stokes equations. The initial fiber configuration is in the flow–gradient plane. We show that, when the shear rate is increased, straight flexible fibers undergo a buckling transition, leading to the development of finite first and second normal stress differences and a reduction of the viscosity. These effects, triggered by shape fluctuations, are dissimilar to the effects induced by the curvature of stiff, curved fibers, for which the viscosity increases with the curvature of the fiber. An analysis of the orbital drift of fibers initially oriented at an angle to the flow–gradient plane provides an estimate for the time-scale within which the prediction of the rheological behavior is valid. The information obtained in this work can be used in the experimental characterization of fiber morphology and mechanics through rheology.

  • 17.
    Arbring Sjöström, Theresia
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Jonsson, Amanda
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Stanford University, CA 94305 USA.
    Gabrielsson, Erik
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Kergoat, Loig
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Aix Marseille University, France.
    Tybrandt, Klas
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Berggren, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Simon, Daniel
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Cross-Linked Polyelectrolyte for Improved Selectivity and Processability of lontronic Systems2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 36, p. 30247-30252Article in journal (Refereed)
    Abstract [en]

    On-demand local release of biomolecules enables fine-tuned stimulation for the next generation of neuromodulation therapies. Such chemical stimulation is achievable using iontronic devices based on microfabricated, highly selective ion exchange membranes (IEMs). Current limitations in processability and performance of thin film LEMs hamper future developments of this technology. Here we address this limitation by developing a cationic IEM with excellent processability and ionic selectivity: poly(4-styrenesulfonic acidco-maleic acid) (PSS-co-MA) cross-linked with polyethylene glycol (PEG). This enables new design opportunities and provides enhanced compatibility with in vitro cell studies. PSSA-co-MA/PEG is shown to out-perform the cation selectivity of the previously used iontronic material.

  • 18.
    Armakavicius, Nerijus
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Study of novel electronic materials by mid-infrared and terahertz optical Hall effect2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Development of silicon based electronics have revolutionized our every day life during the last three decades. Nowadays Si based devices operate close to their theoretical limits that is becoming a bottleneck for further progress. In particular, for the growing field of high frequency and high power electronics, Si cannot offer the required properties. Development of materials capable of providing high current densities, carrier mobilities and high breakdown fields is crucial for a progress in state of the art electronics.

    Epitaxial graphene grown on semi-insulating silicon carbide substrates has a high potential to be integrated in the current planar device technologies. High electron mobilities and sheet carrier densities make graphene extremely attractive for high frequency analog applications. One of the remaining challenges is the interaction of epitaxial graphene with the substrate. Typically, much lower free charge carrier mobilities, compared to free standing graphene, and doping, due to charge transfer from the substrate, is reported. Thus, a good understanding of the intrinsic free charge carriers properties and the factors affecting them is very important for further development of epitaxial graphene.

    III-group nitrides have been extensively studied and already have proven their high efficiency as light sources for short wavelengths. High carrier mobilities and breakdown electric fields were demonstrated for III-group nitrides, making them attractive for high frequency and high power applications. Currently, In-rich InGaN alloys and AlGaN/GaN high electron mobility structures are of high interest for the research community due to open fundamental questions.

    Electrical characterization techniques, commonly used for the determination of free charge carrier properties, require good ohmic and Schottky contacts, which in certain cases can be difficult to achieve. Access to electrical properties of buried conductive channels in multilayered structures requires modification of samples and good knowledge of the electrical properties of all electrical contact within the structure. Moreover, the use of electrical contacts to electrically characterize two-dimensional electronic materials, such as graphene, can alter their intrinsic properties. Furthermore, the determination of effective mass parameters commonly employs cyclotron resonance and Shubnikov-de Haas oscillations measurements, which require long scattering times of free charge carriers, high magnetic fields and low temperatures.

    The optical Hall effect is an external magnetic field induced optical anisotropy in  conductive layers due to the motion of the free charge carriers under the influence of the Lorentz force, and is equivalent to the electrical Hall effect at optical frequencies. The optical Hall effect can be measured by generalized ellipsometry and provides a powerful method for the determination of free charge carrier properties in a non-destructive and contactless manner. In principle, a single optical Hall effect measurement can provide quantitative information about free charge carrier types, concentrations, mobilities and effective mass parameters at temperatures ranging from few kelvins to room temperature and above. Further, it was demonstrated that for transparent samples, a backside cavity can be employed to enhance the optical Hall effect.

    Measurement of the optical Hall effect by generalized ellipsometry is an indirect technique requiring subsequent data analysis. Parameterized optical models are fitted to match experimentally measured ellipsometric data by varying physically significant parameters. Analysis of the optical response of samples, containing free charge carriers, employing optical models based on the classical Drude model, which is augmented with an external magnetic field contribution, provide access to the free charge carrier properties.

    The main research results of the graduate studies presented in this licentiate thesis are summarized in the five scientific papers.

    Paper I. Description of the custom-built terahertz frequency-domain spectroscopic ellipsometer at Linköping University. The terahertz ellipsometer capabilities are demonstrated by an accurate determination of the isotropic and anisotropic refractive indices of silicon and m-plane sapphire, respectively. Further, terahertz optical Hall effect measurements of an AlGaN/GaN high electron mobility structures were employed to extract the two-dimensional electron gas sheet density, mobility and effective mass parameters. Last, in-situ optical Hall effect measurement on epitaxial graphene in a gas cell with controllable environment, were used to study the effects of environmental doping on the mobility and carrier concentration.

    Paper II. Presents terahertz cavity-enhanced optical Hall measurements of the monolayer and multilayer epitaxial graphene on semi-insulating 4H-SiC (0001) substrates. The data analysis revealed p-type doping for monolayer graphene with a carrier density in the low 1012 cm−2 range and a carrier mobility of 1550 cm2/V·s. For the multilayer epitaxial graphene, n-type doping with a carrier density in the low 1013 cm−2 range, a mobility of 470 cm2/V·s and an effective mass of (0.14 ± 0.03) m0 were extracted. The measurements demonstrate that cavity-enhanced optical Hall effect measurements can be applied to study electronic properties of two-dimensional materials.

    Paper III. Terahertz cavity-enhanced optical Hall effect measurements are employed to study anisotropic transport in as-grown monolayer, quasi free-standing monolayer and quasi free-standing bilayer epitaxial graphene on semi-insulating 4H-SiC (0001) substrates. The data analysis revealed a strong anisotropy in the carrier mobilities of the quasi freestanding bilayer graphene. The anisotropy is demonstrated to be induced by carriers scattering at the step edges of the SiC, by showing that the mobility is higher along the step than across them. The scattering mechanism is discussed based on the results of the optical Hall effect, low-energy electron microscopy, low-energy electron diffraction and Raman measurements.

    Paper IV. Mid-infrared spectroscopic ellipsometry and mid-infrared optical Hall effect measurements are employed to determine the electron effective mass in an In0.33Ga0.67N epitaxial layer. The data analysis reveals slightly anisotropic effective mass and carrier mobility parameters together with the optical phonon frequencies and broadenings.

    Paper V. Terahertz cavity-enhanced optical Hall measurements are employed to study the free charge carrier properties in a set of AlGaN/GaN high electron mobility structures with modified interfaces. The results show that the interface structure has a significant effect on the free charge carrier mobility and that the sample with a sharp interface between an AlGaN barrier and a GaN buffer layers exhibits a record mobility of 2332±73 cm2/V·s. The determined effective mass parameters showed an increase compared to the GaN value, that is attributed the the penetration of the electron wavefunction into the AlGaN barrier layer.

    List of papers
    1. Cavity-enhanced optical Hall effect in epitaxial graphene detected at terahertz frequencies
    Open this publication in new window or tab >>Cavity-enhanced optical Hall effect in epitaxial graphene detected at terahertz frequencies
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    2017 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 421, p. 357-360Article in journal (Refereed) Published
    Abstract [en]

    Cavity-enhanced optical Hall effect at terahertz (THz) frequencies is employed to determine the free charge carrier properties in epitaxial graphene (EG) with different number of layers grown by high-temperature sublimation on 4H-SiC(0001). We find that one monolayer (ML) EG possesses p-type conductivity with a free hole concentration in the low 1012 cmᅵᅵᅵ2 range and a free hole mobility parameter as high as 1550 cm2/Vs. We also find that 6 ML EG shows n-type doping behavior with a much lower free electron mobility parameter of 470 cm2/Vs and an order of magnitude higher free electron density in the low 1013 cmᅵᅵᅵ2 range. The observed differences are discussed. The cavity-enhanced THz optical Hall effect is demonstrated to be an excellent tool for contactless access to the type of free charge carriers and their properties in two-dimensional materials such as EG.

    Place, publisher, year, edition, pages
    Elsevier, 2017
    Keywords
    THz optical Hall effect, Epitaxial graphene, Free charge carrier properties
    National Category
    Physical Sciences Condensed Matter Physics Atom and Molecular Physics and Optics Ceramics
    Identifiers
    urn:nbn:se:liu:diva-132407 (URN)10.1016/j.apsusc.2016.10.023 (DOI)000408756700015 ()
    Note

    Funding agencies: Swedish Research Council (VR) [2013-5580]; Swedish Governmental Agency for Innovation Systems (VINNOVA) under the VINNMER international qualification program [2011-03486, 2014-04712]; Swedish foundation for strategic research (SSF) [FFL12-0181, RIF14-055]

    Available from: 2016-11-09 Created: 2016-11-09 Last updated: 2018-01-12Bibliographically approved
    2. Properties of two-dimensional electron gas in AlGaN/GaN HEMT structures determined by cavity-enhanced THz optical Hall effect
    Open this publication in new window or tab >>Properties of two-dimensional electron gas in AlGaN/GaN HEMT structures determined by cavity-enhanced THz optical Hall effect
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    2016 (English)In: Physica Status Solidi C-Current Topics in Solid State Physics, Vol 13 No 5-6, Wiley-VCH Verlagsgesellschaft, 2016, Vol. 13, no 5-6, p. 369-373Conference paper, Published paper (Refereed)
    Abstract [en]

    In this work we employ terahertz (THz) ellipsometry to determine two-dimensional electron gas (2DEG) density, mobility and effective mass in AlGaN/GaN high electron mobility transistor structures grown on 4H-SiC substrates. The effect of the GaN interface exposure to low-flow-rate trimethylaluminum (TMA) on the 2DEG properties is studied. The 2DEG effective mass and sheet density are determined tobe in the range of 0.30-0.32m0 and 4.3-5.5×1012 cm–2, respectively. The 2DEG effective mass parameters are found to be higher than the bulk effective mass of GaN, which is discussed in view of 2DEG confinement. It is shown that exposure to TMA flow improves the 2DEG mobility from 2000 cm2/Vs to values above 2200 cm2/Vs. A record mobility of 2332±61 cm2/Vs is determined for the sample with GaN interface exposed to TMA for 30 s. This improvement in mobility is suggested to be due to AlGaN/GaN interface sharpening causing the reduction of interface roughness scattering of electrons in the 2DEG.

    Place, publisher, year, edition, pages
    Wiley-VCH Verlagsgesellschaft, 2016
    Series
    Physica Status Solidi C-Current Topics in Solid State Physics, ISSN 1862-6351
    Keywords
    AlGaN/GaN HEMTs, THz ellipsometry, 2DEG properties, THz optical Hall effect
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-133135 (URN)10.1002/pssc.201510214 (DOI)000387957200045 ()
    Conference
    11th International Conference on Nitride Semiconductors (ICNS), Beijing, China, August 30-September 4. 2015
    Available from: 2016-12-12 Created: 2016-12-09 Last updated: 2017-10-23Bibliographically approved
  • 19.
    Armakavicius, Nerijus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Bouhafs, Chamseddine
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Stanishev, Vallery
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kühne, Philipp
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Knight, Sean
    Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, USA.
    Hofmann, Tino
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, USA / Department of Physics and Optical Science, University of North Carolina at Charlotte, USA.
    Schubert, Mathias
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, USA.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Cavity-enhanced optical Hall effect in epitaxial graphene detected at terahertz frequencies2017In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 421, p. 357-360Article in journal (Refereed)
    Abstract [en]

    Cavity-enhanced optical Hall effect at terahertz (THz) frequencies is employed to determine the free charge carrier properties in epitaxial graphene (EG) with different number of layers grown by high-temperature sublimation on 4H-SiC(0001). We find that one monolayer (ML) EG possesses p-type conductivity with a free hole concentration in the low 1012 cmᅵᅵᅵ2 range and a free hole mobility parameter as high as 1550 cm2/Vs. We also find that 6 ML EG shows n-type doping behavior with a much lower free electron mobility parameter of 470 cm2/Vs and an order of magnitude higher free electron density in the low 1013 cmᅵᅵᅵ2 range. The observed differences are discussed. The cavity-enhanced THz optical Hall effect is demonstrated to be an excellent tool for contactless access to the type of free charge carriers and their properties in two-dimensional materials such as EG.

  • 20.
    Arvidsson, Emma
    et al.
    Linköping University, Department of Mechanical Engineering.
    Ekblad, Emma
    Linköping University, Department of Mechanical Engineering.
    Framtagning av krypmodell för termomekanisk FE-analys av grenrör2006Independent thesis Advanced level (degree of Magister), 20 points / 30 hpStudent thesis
    Abstract [sv]

    Grenrören i en motor utsätts för stora termiska och mekaniska belastningar, vilka gör att grenrören ofta spricker. Idag kan inte sprickbildningen fullständigt uttydas ur beräkningarna, syftet med arbetet är därför att se om dessa kan förbättras genom att använda en mer avancerad krypmodell än den som används idag.

    Ett förslag till krypmodell har tagits genom att studera ett antal i litteraturen funna modeller. De som valts ut är modeller enligt Norton, Bailey-Norton, Marin-Pao, Picket och Findley. Parametrarna i de olika modellerna har bestämts genom kurvanpassning av enaxliga prov på de aktuella grenrörsmaterialen. Resultaten visar att modellerna enligt Marin-Pao, Picket och Findley alla kan beskriva mätkurvorna nästan exakt. Problem uppstår dock med att man får parametrar som beror av både spänning och temperatur. Av dessa tre modeller anses Marin-Pao vara den bästa, då det är den av de tre som har minst antal parametrar. Utvärderingen ger vidare att Norton är den modell som är enklast, och beaktat över alla prover, den vars resultat bäst ansluter sig till mätdata. Valet görs att gå vidare med både Marin-Paos och Nortons modell.

    De två aktuella modellerna har lagts in som subrutiner till FE-programmet ABAQUS. Tester av modellerna görs först på ett litet kubiskt element och sedan på hela grenröret. Jämförelser görs mellan Norton, Marin-Pao och den modell som används idag – ”Two-layer viscoplasticity model”. Såväl Marin-Paos modell som Nortons beskriver verkligheten bättre än den idag använda modellen och av de båda är Nortons modell den som mest tillfredställande speglar verkligheten. Det är dessutom den modell som är mest stabil och beräkningsmässigt effektivast. Som en rekommendation inför fortsatt arbete föreslås därför användning av Nortons modell, samt ett utökat antal krypprover.

  • 21.
    Ashraf, Hina
    Linköping University, The Department of Physics, Chemistry and Biology.
    Investigation of the Symmetries of the Phonons in 4H and 6H-SiC by Infrared Absorption and Raman Spectroscopy2005Independent thesis Basic level (professional degree), 20 points / 30 hpStudent thesis
    Abstract [en]

    The goal of the project work has been to study the symmetry of the phonons in 4H and 6H-SiC for different measuring geometries by using two experimental techniques, Raman and infrared absorption (IR) spectroscopy, and a theoretical model. The Raman spectra were measured in different scattering configurations in order to obtain experimental data for detailed investigation of the phonon symmetries.

    The gross features of the spectra obtained in different geometries can be explained using general group-theoretical arguments. Using a lattice-dynamics model, we have also calculated the angular dependence of the phonon energies near the centre of the Brillouin zone, as well as the phonon displacements in some high-symmetry directions. The theoretical results are used to interpret the Raman lines in different configurations, and it was possible to estimate that if ionicity of the bonding of 12% is taken in the theoretical model for 4H-SiC, the splitting of the polar TO mode and the shift of the polar LO mode observed in our spectra are well reproduced theoretically. It was also observed that these polar modes have to be classified as longitudinal and transversal with respect to the direction of phonon wave vector, while the rest of the modes remain longitudinal or transversal with respect to the c-axis of the crystal. The Raman lines in the case of 4H SiC have been tentatively labelled with the irreducible representations of the point group of the crystal (C6v).

  • 22.
    Ashutosh, Tiwari
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics.
    Bioengineered stimuli-responsive nanosystems for biomedical devices2013Conference paper (Refereed)
  • 23.
    Aspenberg, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Jergeus, Johan
    Volvo Cars Safety Centre, Göteborg.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Robust optimisation of front members in a full frontal car impactManuscript (preprint) (Other academic)
    Abstract [en]

    In the search of a lightweight design of automobiles, it is necessary to assure that a robust crashworthiness performance is achieved. Structures that are optimised to handle a finite number of load cases may perform poorly when subjected to various dispersions. Thus, uncertainties must be accounted for in the optimisation process. This paper presents an approach to optimisation where all design evaluations include an evaluation of the robustness. Metamodel approximations are applied both to the design space and the robustness evaluations, using Artifical Neural Networks and polynomials, respectively. The features of the robust optimisation approach are displayed in an analytical example, and further demonstrated in a large scale design example of front side members of a car. Different optimisation formulations are applied and it is shown that the proposed approach works well. It is also concluded that a robust optimisation puts higher demands on the FE model performance than normally.

  • 24.
    Atakan, Aylin
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Mesoporous material systems for catalysis and drug delivery2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Hybrid material systems possess multi-functional properties which make them intriguing for the materials science community since very early dates. However, it is not straightforward to produce such material systems. A smart and efficient approach is necessary to extract the desired properties of each component under the desired conditions. This study evolved to its last form primarily around this notion, where the development of a hybrid material is the core of the work. This hybrid material is then further explored for two different applications in the catalysis and drug delivery fields.

    A nanoassembly was established around a mesoporous silica support. SBA-15 was picked as this support among the other mesoporous silica due to its well-defined pore structure and accessible pore volume. The silica framework was doped with Zr atoms and the pores were partly infiltrated with Cu nanoparticles resulting in a hybrid material with tunable properties. SBA-15 was synthesized by a sol-gel method where a micellar solution was employed as a template for the silica framework. To achieve the doped version, a Zr precursor was added to the synthesis solution. The effects of different synthesis conditions, such as the synthesis catalyst (F-or a Cl-salt) and the Si source (tetraethyl orthosilicate (TEOS) or sodium metasilicate (SMS)) on the characteristics of the final material were investigated. It was observed that these changes in the synthesis conditions yielded different particle morphology, pore size (11-15 nm), and specific surface area (400-700 m2/g). Cu nanoparticles (NPs) were grown in the (Zr-)SBA-15 support using infiltration (Inf) or evaporation induced wetness impregnation (EIWI) methods. The infiltration method is based on functionalizing the (Zr-)SBA-15 support surfaces before the Cu ion attachment whereas EIWI is based on slow evaporation of the liquid from the (Zr-)SBA-15 - Cu aqueous suspension. Both methods are designed to yield preferential growth of Cu NPs in the pores with a diameter smaller than 10 nm and in oxidized form. However, depending on the loading method used, different chemical states of the final material were achieved, i.e. Zr content and porous network properties are different. 

    Cu-Zr-SBA-15 nanoassemblies produced under various synthesis conditions were used for the catalytic conversion of CO2into valuable fuels such as methanol and dimethyl ether (DME). The effect of different chemical states of the catalyst arising from variations in the synthesis parameters was investigated. It was found that the Si precursor (TEOS or SMS) had a considerable impact on the overall performance of the catalyst whereas the Cu loading method (Inf or EIWI) changed the catalytic selectivity between DME and methanol. The activity of the catalyst was further investigated in a time-evolution study where the accumulation of each product in the gas phase and the molecular groups attached to the catalyst surface were recorded over time. Accordingly, thermodynamic equilibrium was achieved on the 14th day of the reaction under 250°C and 33 bar. The resulting total CO2conversion was 24%, which is the thermodynamically highest possible conversion, according to theoretical calculations. It was also concluded from the experimental results that, DME is formed by a combination of two methoxy surface groups. Additionally, the formation of DME boosts the total CO2conversion to fuels, which otherwise is limited to 9.5%.

    The design of Cu-Zr-SBA-15 was also investigated for drug delivery applications, due to its potential as a biomaterial, e.g., a filler in dental composites, and the antibacterial properties of Cu. Also, the bioactivity of SiO2and ZrO2was considered to be an advantage. With this aim, Cu infiltrated Zr doped SBA-15 material was prepared by using TEOS as the silica precursor and the Inf-method to grow Cu NPs. The performance of the final material as a drug delivery vehicle was tested by an in-vitro delivery study with chlorhexidine digluconate.The nanoassemblies show a drug loading capacity of 25-40% [mg drug / mg (drug+carrier)]. The drug release was determined to be composed of two steps. First, a burst release of the drug molecules that are loosely held in the voids of the mesoporous carrier followed by the diffusion of the drug molecules that are attached to the carrier surface. The presence of Zr and Cu limits the burst release and beneficially slows down the drug release process. 

    The effect of pore properties of SBA-15 was explored in a study where the antibiotic doxycycline hyclate was loaded in SBA-15 materials with different pore sizes. It was observed that the pore size is directly proportional to the drug loading capacity [mg drug / mg (drug+carrier)] and the released drug percentage (the released drug amount/total amount of loaded drug). The drug release was fast due to its weak interactions with the SBA-15 materials. 

    In summary, this work demonstrates the multifunctional character of a smart-tailored nanoassembly which gives valuable insights for two distinct applications in catalysis and drug delivery.

    List of papers
    1. Synthesis of a Cu-infiltrated Zr-doped SBA-15 catalyst for CO2 hydrogenation into methanol and dimethyl ethert
    Open this publication in new window or tab >>Synthesis of a Cu-infiltrated Zr-doped SBA-15 catalyst for CO2 hydrogenation into methanol and dimethyl ethert
    Show others...
    2017 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 29, p. 19139-19149Article in journal (Refereed) Published
    Abstract [en]

    A catalytically active nanoassembly comprising Cu-nanoparticles grown on integrated and active supports (large pore Zr-doped mesoporous SBA-15 silica) has been synthesized and used to promote CO2 hydrogenation. The doped mesoporous material was synthesized using a sal-gel method, in which the pore size was tuned between 11 and 15 nm while maintaining a specific surface area of about 700 m(2) g (1). The subsequent Cu nanoparticle growth was achieved by an infiltration process involving attachment of different functional groups on the external and internal surfaces of the mesoporous structure such that 7-10 nm sized Cu nanoparticles grew preferentially inside the pores. Chemisorption showed improved absorption of both CO2 and H-2 for the assembly compared to pure SBA-15 and 15% of the total CO2 was converted to methanol and dimethyl ether at 250 degrees C and 33 bar.

    Place, publisher, year, edition, pages
    ROYAL SOC CHEMISTRY, 2017
    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:liu:diva-139804 (URN)10.1039/c7cp03037a (DOI)000406334300033 ()28702581 (PubMedID)
    Note

    Funding Agencies|EUs Erasmus-Mundus program; Swedish Research Council; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 11 2009-00971]; Knut och Alice Wallenbergs Foundation [KAW 2012.0083]

    Available from: 2017-08-17 Created: 2017-08-17 Last updated: 2018-04-16
    2. Time evolution of the CO2 hydrogenation to fuels over Cu-Zr-SBA-15 catalysts
    Open this publication in new window or tab >>Time evolution of the CO2 hydrogenation to fuels over Cu-Zr-SBA-15 catalysts
    Show others...
    2018 (English)In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 362, p. 55-64Article in journal (Refereed) Published
    Abstract [en]

    Time evolution of catalytic CO2 hydrogenation to methanol and dimethyl ether (DME) has been investigated in a high-temperature high-pressure reaction chamber where products accumulate over time. The employed catalysts are based on a nano-assembly composed of Cu nanoparticles infiltrated into a Zr doped SiOx mesoporous framework (SBA-15): Cu-Zr-SBA-15. The CO2 conversion was recorded as a function of time by gas chromatography-mass spectrometry (GC-MS) and the molecular activity on the catalyst’s surface was examined by diffuse reflectance in-situ Fourier transform infrared spectroscopy (DRIFTS). The experimental results showed that after 14 days a CO2 conversion of 25% to methanol and DME was reached when a DME selective catalyst was used which was also illustrated by thermodynamic equilibrium calculations. With higher Zr content in the catalyst, greater selectivity for methanol and a total 9.5% conversion to methanol and DME was observed, yielding also CO as an additional product. The time evolution profiles indicated that DME is formed directly from methoxy groups in this reaction system. Both DME and methanol selective systems show the thermodynamically highest possible conversion.

    Keywords
    Cu-Zr-SBA-15, CO2 hydrogenation, Catalysis, Time evolution, Thermodynamics, Methanol, Dimethyl ether
    National Category
    Nano Technology Physical Chemistry
    Identifiers
    urn:nbn:se:liu:diva-147297 (URN)10.1016/j.jcat.2018.03.023 (DOI)000432770900007 ()
    Note

    Funding agencies: EUs Erasmus-Mundus program (The European School of Materials Doctoral Programme - DocMASE); Knut och Alice Wallenbergs Foundation [KAW 2012.0083]; Swedish Government Strategic Research Area (SFO Mat LiU) [2009 00971]; Swedish Energy Agency [42022-1]

    Available from: 2018-04-16 Created: 2018-04-16 Last updated: 2018-06-14Bibliographically approved
  • 25.
    Azam, Sher
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Wide Bandgap Semiconductor (SiC & GaN) Power Amplifiers in Different Classes2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    SiC MESFETs and GaN HEMTs have an enormous potential in high-power amplifiers at microwave frequencies due to their wide bandgap features of high electric breakdown field strength, high electron saturation velocity and high operating temperature. The high power density combined with the comparably high impedance attainable by these devices also offers new possibilities for wideband power microwave systems. In this thesis, Class C switching response of SiC MESFET in TCAD and two different generations of broadband power amplifiers have been designed, fabricated and characterized. Input and output matching networks and shunt feedback topology based on microstrip and lumped components have been designed, to increase the bandwidth and to improve the stability. The first amplifier is a single stage 26-watt using a SiC MESFET covering the frequency from 200-500 MHz is designed and fabricated. Typical results at 50 V drain bias for the whole band are, 22 dB power gain, 43 dBm output power, minimum power added efficiency at P 1dB is 47 % at 200 MHz and maximum 60 % at 500 MHz and the IMD3 level at 10 dB back-off from P 1dB is below ‑45 dBc. The results at 60 V drain bias at 500 MHz are, 24.9 dB power gain, 44.15 dBm output power (26 W) and 66 % PAE.

    In the second phase, two power amplifiers at 0.7-1.8 GHz without feed back for SiC MESFET and with feedback for GaN HEMT are designed and fabricated (both these transistors were of 10 W). The measured maximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W), with a PAE of 32 % and a power gain above 10 dB. At a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4 %. The measured results for GaN amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34 % and a power gain above 10 dB. The SiC amplifier gives better results than for GaN amplifier for the same 10 W transistor.

    A comparison between the physical simulations and measured device characteristics has also been carried out. A novel and efficient way to extend the physical simulations to large signal high frequency domain was developed in our group, is further extended to study the class-C switching response of the devices. By the extended technique the switching losses, power density and PAE in the dynamics of the SiC MESFET transistor at four different frequencies of 500 MHz, 1, 2 and 3 GHz during large signal operation and the source of switching losses in the device structure was investigated. The results obtained at 500 MHz are, PAE of 78.3%, a power density of 2.5 W/mm with a switching loss of 0.69 W/mm. Typical results at 3 GHz are, PAE of 53.4 %, a power density of 1.7 W/mm with a switching loss of 1.52 W/mm.

    List of papers
    1. Single-stage, High Efficiency, 26-Watt power Amplifier using SiC LE-MESFET
    Open this publication in new window or tab >>Single-stage, High Efficiency, 26-Watt power Amplifier using SiC LE-MESFET
    2006 (English)In: Microwave Conference, 2006. APMC 2006. Asia-Pacific December 12-15, 2006, p. 441-444Conference paper, Published paper (Refereed)
    Abstract [en]

    This paper describes a single-stage 26 W negative feedback power amplifier, covering the frequency range 200-500 MHz using a 6 mm gate width SiC lateral epitaxy MESFET. Typical results at 50 V drain bias for the whole band are, around 22 dB power gain, around 43 dBm output power, minimum power added efficiency at P1 dB is 47% at 200 MHz and maximum 60% at 500 MHz and the IMD3 level at 10 dB back-off from P1 dB is below -45 dBc. The results at 60 V drain bias at 500 MHz are, 24.9 dB power gain, 44.15 dBm output power (26 W) and 66% PAE.

    Keywords
    Schottky gate field effect transistors, feedback, microwave power amplifiers, silicon compounds, SiC, frequency 200 MHz to 500 MHz, lateral epitaxy MESFET, negative feedback, power 26 W, power amplifier, size 6 mm, voltage 50 V
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13283 (URN)10.1109/APMC.2006.4429458 (DOI)
    Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2009-09-24Bibliographically approved
    2. Designing, Fabrication and Characterization of Power Amplifiers Based on 10-Watt SiC MESFET & GaN HEMT at Microwave Frequencies
    Open this publication in new window or tab >>Designing, Fabrication and Characterization of Power Amplifiers Based on 10-Watt SiC MESFET & GaN HEMT at Microwave Frequencies
    2008 (English)In: IEEE European Microwave Week, October 10-15, Amsterdam, The Netherlands, 2008, p. 444-447Conference paper, Published paper (Refereed)
    Abstract [en]

    This paper describes the design, fabrication and measurement of two single-stage class-AB power amplifiers covering the frequency band from 0.7-1.8 GHz using a SiC MESFET and a GaN HEMT. The measured maximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W), with a PAE of 32% and a power gain above 10 dB. At a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4%. The measured results for GaN amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34% and a power gain above 10 dB. The results for SiC amplifier are better than for GaN amplifier for the same 10-W transistor.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13284 (URN)10.1109/EUMC.2008.4751484 (DOI)
    Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2009-09-24Bibliographically approved
    3. Pulse Input Class-C Power Amplifier Response of SiC MESFET using Physical Transistor Structure in TCAD
    Open this publication in new window or tab >>Pulse Input Class-C Power Amplifier Response of SiC MESFET using Physical Transistor Structure in TCAD
    2008 (English)In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 52, no 5, p. 740-744Article in journal (Refereed) Published
    Abstract [en]

    The switching behavior of a previously fabricated and tested SiC transistor is studied in Class-C amplifier in TCAD simulation. The transistor is simulated for pulse input signals in Class-C power amplifier. The simulated gain (dB), power density (W/mm) and power added efficiency (PAE%) at 500 MHz, 1, 2 and 3 GHz was studied using computational TCAD load pull simulation technique. A Maximum PAE of 77.8% at 500 MHz with 45.4 dB power gain and power density of 2.43 W/mm is achieved. This technique allows the prediction of switching response of the device for switching amplifier Classes (Class-C–F) before undertaking an expensive and time consuming device fabrication. The beauty of this technique is that, we need no matching and other lumped element networks for studying the large signal behavior of RF and microwave transistors.

    Keywords
    Pulse, Class-C, Power amplifier, New technique, Silicon carbide, MESFET
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13285 (URN)10.1016/j.sse.2007.09.022 (DOI)
    Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2017-12-13Bibliographically approved
  • 26.
    Bakoglidis, Konstantinos
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Manchester, England.
    Palisaitis, Justinas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    dos Santos, Renato B.
    Univ Fed Bahia, Brazil.
    Rivelino, Roberto
    Univ Fed Bahia, Brazil.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Gueorguiev, Gueorgui Kostov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Self-Healing in Carbon Nitride Evidenced As Material Inflation and Superlubric Behavior2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 19, p. 16238-16243Article in journal (Refereed)
    Abstract [en]

    All known materials wear under extended mechanical contacting. Superlubricity may present solutions, but is an expressed mystery in C-based materials. We report negative wear of carbon nitride films; a wear-less condition with mechanically induced material inflation at the nanoscale and friction coefficient approaching ultralow values (0.06). Superlubricity in carbon nitride is expressed as C-N bond breaking for reduced coupling between graphitic-like sheets and eventual N-2 desorption. The transforming surface layer acts as a solid lubricant, whereas the film bulk retains its high elasticity. The present findings offer new means for materials design at the atomic level, and for property optimization in wear-critical applications like magnetic reading devices or nanomachines.

  • 27.
    Bakoglidis, Konstantinos
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Schmidt, Susann
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Greczynski, Grzegorz
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Improved adhesion of carbon nitride coatings on steel substrates using metal HiPIMS pretreatments2016In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 302, p. 454-462Article in journal (Refereed)
    Abstract [en]

    We investigate the effect of low-temperature metal pretreatments in order to improve the adhesion of CNx coatings on steel substrates, which is crucial for tribological applications. The substrate pretreatments were conducted using five different metal targets: Ti, Zr, Al, Cr, and W, operated in high power impulse magnetron sputtering mode, known to produce significant ionization of the sputtered material flux. The CNx adhesion, as assessed by Rockwell C tests, did not improve upon Ti and Zr pretreatments. This is primarily ascribed to the fact that no interlayer was formed owing to severe re-sputtering due to high fluxes of doubly-ionized metal species in the plasma. A slight improvement in adhesion was observed in the case an Al pretreatment was carried out, while the best results were obtained using Cr and W. Here, 30-s-long pretreatments were sufficient to clean the steel surface and form a metallic interlayer between substrate and coating. Transmission electron microscopy in combination with energy dispersive X-ray spectroscopy revealed that Al, Cr, and W created intermixing zones at the interlayer/substrate and the interlayer/CNx interfaces. The steel surfaces, pretreated using Cr or W, showed the highest work of adhesion with W-adh(Cr) = 1.77 J/m(2) and W-adh(W) = 1.66 J/m(2), respectively. (C) 2016 Elsevier B.V. All rights reserved.

  • 28.
    Barazande, Saina
    Linköping University, Department of Management and Engineering, Carl Malmsten - furniture studies. Linköping University, The Institute of Technology.
    Om att berätta något: en undersökning av skapandeprocessen med berättelsen och jaget som utgångspunkt2014Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    This work is a search for a creative process that suits me. I gaze outwards to find new ways to do and provide more opportunities for me in my making and ultimately get closer to my own way of creating. Through interviews with active creative performers in various media, such as designers, a cartoonist, a musician and a poet I search for possible new methods and processes. Like the people I interview, I want to share stories, through my making, from my self and origin. I want to share stories to evoke thoughts, memories and reflection.

    My starting point is the methodology that Carl Malmsten Furniture Studies advocates. Through the interviews my process and methodology has evolved and I have explored new paths for my creativity. This has also resulted in two physical objects, a book of poetry and a storage. These two unitedly speaks my thoughts on the innermost room, which we all have within us.

  • 29.
    Beni, Valerio
    et al.
    Tyndall National Institute, University College Cork, Ireland.
    Valsesia, Andrea
    Joint Research Centre, Ispra, Italy.
    Colpo, Pascal
    Joint Research Centre, Ispra, Italy.
    Bretagnol, Frederic
    Joint Research Centre, Ispra, Italy.
    Rossi, Francois
    Joint Research Centre, Ispra, Italy.
    Arrigan, Damien
    Tyndall National Institute, University College Cork, Ireland.
    Electrochemical properties of polymeric nanopatterned electrodes2007In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 9, no 7, p. 1833-1839Article in journal (Refereed)
    Abstract [en]

    An investigation of the electrochemical behaviour of gold electrodes coated with poly(ethylene glycol) (PEG), poly(acrylic acid)(PAA) and nanopatterned PAA/PEG layers is presented. Plasma-enhanced chemical vapour deposition and colloidal lithography wereused to produce nanodomes of PAA in a matrix of PEG. The electrochemical response at these nanostructured electrodes was studied asa function of the probe ion charge. Results show that the film structures allow the electrodes to retain their electrochemical activity whileminimising surface fouling and will thus be useful in the development of electrochemical nanobiosensors for various applications.

  • 30.
    Bentzer, Justinius Erik
    Linköping University, Department of Management and Engineering, Carl Malmsten - furniture studies. Linköping University, The Institute of Technology.
    Textil, faner och jag: en möbelkollektion sprungen ur en undersökning av materialkombinationer faner och textil2014Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [sv]

    Jag har ett intresse för att utforska och undersöka olika material och hur vi upplever dessa material. I detta examensarbete skapar jag två möbler genom en gestaltningsprocess som grundar sig i ett undersökande av materialkombinationen faner och textil. Arbetet är uppdelat i två delar, en undersökande del där jag testar att kombinera olika faner, textilier och limmer, för att se hur jag upplever dessa och för att få en grund till min gestaltningsprocess. I den andra delen formger jag två möbler som har till syfte att väcka intresse för materialet hos betraktaren. Det blir ett klädskåp och en sittmöbel, som visar på olika sido !och mervärden med materialkombinationerna. Förhoppningsvis kan detta  arbete väcka intresset för nya materialkombinationer även hos er läsare.

  • 31.
    Bergström, Alexander
    Linköping University, Department of Management and Engineering, Carl Malmsten - furniture studies. Linköping University, The Institute of Technology.
    Träkärnor i alpina skidor: ett examensarbete kring olika träslag och dess egenskaper som träkärna i alpina skidor.2014Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    The purpose of this work is to produce the most optimal wood core with the desired requirements in an all-mountain ski using Scandinavian wood. The study is descriptive and quantitative as it aims to measure the rate of change under the influence of wood species. In order to collect data for my research questions, tests have been carried out which generate data collection. A preliminary investigation was done with interviews to obtain a more detailed basis for constructing the method I would use in the final work. The results of the study showed that the wood type beech had the best results in terms of flexural strength. Ash had the best results when it came to tests on torsional rigidity. The down side of these woods is that they are too heavy. The lightest wood species of those involved in the tests was poplar. Therefore, I have chosen to combine species in the final wood core. Two different suggestions have been developed. One with a combination of beech and poplar, the other one with ash and poplar. The first provides a relatively light ski with good flexural strength. The second produced a light ski with good torsional rigidity. These two wood cores will be used in the construction of my skis and tested on the mountain.

  • 32.
    Bernard, Antoine
    Linköping University, Department of Management and Engineering.
    Offshore Oil and Gas Platform: Construction methods applied to Jackets erection2007Independent thesis Advanced level (degree of Magister), 20 points / 30 hpStudent thesis
    Abstract [en]

    My Master thesis was carried out from mid June 2006 until March 2007 within a major oil & gas subcontractor. My firm had been awarded a contract for the development of a new promising offshore oil field. Our role was limited to the fabrication of six Jackets designed to support the newly developed Topsides, each weighing more than fifteen thousands tonnes. Throughout the project, jacket after jacket, it has been felt that some room for improvement existed in the construction methods used for their erection. Safety always being the first motto of any oil & gas project, it is always of high interest to improve the erection methods used to carry out the most potentially dangerous operations. This is to be reached through a more detailed and careful approach of the heavy lifting operations design. More specifically, as part of the methods engineering department, my master thesis aimed at supporting the designing and setting up of all heavy lifting operations used for the erection and assembly of the external frames of the last Jacket to be fabricated. As an outcome of the work carried out by our department and all company’s teams, the Jacket was assembled and erected in due time with no remarkable incident.

  • 33.
    Bernard, Christophe
    et al.
    Aix Marseille Université, INS, Marseille, France; Inserm, UMR_S 1106, Marseille, France.
    Simon, Daniel
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Malliaras, George G
    Department of Bioelectronics, Ecole Nationale Supérieure des Mines, CMP-EMSE, MOC, Gardanne, France.
    Organic Bioelectronics for Interfacing with the Brain2016In: The WSPC Reference on Organic Electronics: Organic Semiconductors: Volume 2: Fundamental Aspects of Materials and Applications / [ed] Seth R Marder, Jean-Luc Bredas, World Scientific, 2016, p. 345-368Chapter in book (Other academic)
    Abstract [en]

    Understanding how the brain works represents probably the most important fundamental endeavor of humankind and holds the key for the development of new technologies that can help improve the lives of people suffering from neurological conditions such as epilepsy and Parkinson's disease. Over the past decade, the use of organic electronic devices to interface with the biological world has received a great deal of attention and bloomed into a field now called “organic bioelectronics”. One of the key differences of organic from traditional electronic materials is their capacity to exchange ions with electrolytes. We discuss how this property can be leveraged to design new types of devices that interface with the brain.Read 

  • 34.
    Bi, Yanyan
    et al.
    Sandvik Int Trading, Peoples R China.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Sandvik Mat Technology, Sweden.
    Forsberg, Urban
    Sandvik Mat Technology, Sweden.
    Darkey, Glenn
    Sandvik Int Trading, Peoples R China.
    Investigation of cold-forming properties of Sanicro 25-a potential candidate for superheater and reheaters in high efficiency A-USC fossil power plants2017In: PROCEEDINGS OF THE ASME POWER CONFERENCE JOINT WITH ICOPE-17, 2017, VOL 1, AMER SOC MECHANICAL ENGINEERS , 2017, article id UNSP V001T01A008Conference paper (Refereed)
    Abstract [en]

    Sanicro 25 material is approved for use in pressure vessels and boilers according AMSE code case 2752, 2753 and VdTuN blatt 555. It shows good resistance to steam oxidation and flue gas corrosion, and has higher creep rupture strength than any other austenitic stainless steels available today. It is a candidate material for superheater and reheaters, enabling higher steam parameters of up to about 650 degrees C steam (ie about max 700 degrees C metal) without the need for expensive nickel based alloys. The effect of cold-forming on time and temperature-dependent deformation and strength behavior has been examined in a comprehensive study. The objective was to determine the maximum allowable degree of cold-forming to be used without additional heat treatment. The findings of these investigations indicate that the maximum allowed cold deformation could be possible to increase from todays maximum 20 % (VdTuV 555), 15 % (540-675 degrees C) and 10 % (higher than 675 degrees C) respectively (ASME 2011a Sect I PG19). A solution annealing after the cold bending will recover creep ductility but will also at the same time increase manufacturing costs. Higher allowed degree of cold-forming without the need for post bend heat treatments, would allow for more narrow bending radii and thereby a more compact construction that would result in a significant decrease in production costs. This paper presents the findings in the mentioned study and is to be a background for possible coming discussions with involved entities on a revision of the max allowed deformation of this material without the need for solution annealing.

  • 35.
    Björnsson, Andreas
    Linköping University, Department of Management and Engineering, Manufacturing Engineering. Linköping University, Faculty of Science & Engineering.
    Automated layup and forming of prepreg laminates2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Composite materials like carbon fiber-reinforced polymers (CFRPs) present highly appealing material properties, as they can combine high strength with low weight. In aerospace applications, these properties help to realize lightweight designs that can reduce fuel consumption. Within the aerospace industry, the use of these types of materials has increased drastically with the introduction of a new generation of commercial aircraft. This increased use of CFRP drives a need to develop more rational manufacturing methods.

    For aerospace applications, CFRP products are commonly manufactured from a material called prepreg, which consists of carbon fibers impregnated with uncured polymer resin. There are two dominant manufacturing technologies for automated manufacturing using prepreg, automated tape layup and automated fiber placement. These two technologies are not suitable for all types of products, either due to technical limitations or a combination of high investment costs and low productivity. Automation alternatives to the two dominant technologies have been attempted, but have so far had limited impact. Due to the lack of automation alternatives, manual manufacturing methods are commonly employed for the manufacturing of complex-shaped products in low to medium manufacturing volumes.

    The research presented in this thesis aims to explore how automated manufacturing systems for the manufacturing of complex CFRP products made from prepreg can be designed so that they meet the needs and requirements of the aerospace industry, and are suitable for low to medium production volumes. In order to explore the area, a demonstrator-centered research approach has been employed. A number of demonstrators, in the form of automated manufacturing cells, have been designed and tested with industrial and research partners. The demonstrators have been used to identify key methods and technologies that enable this type of manufacturing, and to analyze some of these methods and technologies in detail. The demonstrators have also been used to map challenges that affect the development of enabling methods and technologies.

    Automated manufacturing of products with complex shapes can be simplified by dividing the process into two steps. Thin layers of prepreg are laid up on top of each other to form flat laminates that are formed to the desired shape in subsequent forming operations. The key methods and technologies required to automate such a system are methods and technologies for automated prepreg layup, the automated removal of backing paper and the forming of complex shapes. The main challenges are the low structural rigidity and tacky nature of prepreg materials, the extensive quality requirements in the aerospace industry and the need for the systems to handle a wide array of prepreg shapes.

    The demonstrators show that it is possible to automate the manufacturing of complexshaped products using automated layup and forming of prepreg laminates. Tests using the demonstrators indicate that it is possible to meet the quality requirements that apply to manual manufacturing of similar products.

    List of papers
    1. Composite Manufacturing: How Improvement Work Might Lead to Renewed Product Validation
    Open this publication in new window or tab >>Composite Manufacturing: How Improvement Work Might Lead to Renewed Product Validation
    2012 (English)In: Proceedings of the 5th International Swedish Production Symposium / [ed] Mats Björkman, 2012, p. 505-513Conference paper, Published paper (Refereed)
    Abstract [en]

    High-performance polymer composites are mainly used in applications where the benefits of high strength and low weight justify the high material and manufacturing costs. Many of these applications are found today in the aerospace, space and defense industries. Most of today’s commonly used manufacturing methods within this area are highly labor intensive. Furthermore, the quality requirements from the customers require a high level of process control. The purpose of this paper is to explore how changes that are introduced in order to improve productivity in a manufacturing system are managed, particularly with regard to who takes the decision to implement a change and how a change is validated. The study is based on qualitative interviews performed at several companies that manufacture composite components for the aerospace, space and defense sectors. The findings show that the responsibility for deciding to implement a change and the need for validating it are based on many diverse and interconnected factors. Therefore, it is difficult to construct guidelines for early assessment of the scope and cost of a proposed change. Hence each individual change request must be evaluated on its own. The study also shows that the validation process can be adapted to a level that is based on the type of change. In addition, it highlights that control over process parameters in manufacturing is essential.

    Keywords
    composite manufacturing, validation, change request management
    National Category
    Production Engineering, Human Work Science and Ergonomics
    Identifiers
    urn:nbn:se:liu:diva-85268 (URN)978-91-7519-752-4 (ISBN)
    Conference
    5th International Swedish Production Symposium (SPS 2012), 6-8 November 2012, Linköping, Sweden
    Available from: 2012-11-14 Created: 2012-11-14 Last updated: 2017-05-17
    2. Automated Removal of Prepreg Backing Paper - A Sticky Problem
    Open this publication in new window or tab >>Automated Removal of Prepreg Backing Paper - A Sticky Problem
    2013 (English)In: Proceedings of the SAE 2013, Aerotech Congress and Exhibition, 24th-26th September 2013, Montreal,Canada, 2013Conference paper, Published paper (Refereed)
    Abstract [en]

    Automated solutions for manufacturing composite products based on prepreg often imply Automatic Fiber Placement or Automatic Tape Laying. These systems are generally associated with huge investments. For certain manufacturing applications it is interesting to investigate alternatives to find simpler and less costly automation. One example of an automated system could be the use of a standard industrial robot to pick single prepreg plies from an automated cutting machine and stack them to form a plane laminate. This paper is based on a case illustrating a product from the aircraft manufacturing industry. The case will demonstrate a pick and place concept on a general level and illustrate challenges that must be solved. The challenge selected to be the main focus for this paper is an automated process for backing paper removal. A literature review of different gripping technologies reveals several interesting technologies, and the most promising are tested for backing paper removal. The tests show that an automated removal process can be designed by using standard vacuum grippers in combination with mechanical clamping grippers. In order to lift the backing paper with a vacuum gripper an initial separation between the backing paper and prepreg is needed. This separation is most easily mechanically induced by bending the material. The proposed solution for automatic backing paper removal can be integrated in a manufacturing cell for manufacturing of the studied product.

    Keywords
    composite manufacturing, automation, prepreg, gripping technology
    National Category
    Production Engineering, Human Work Science and Ergonomics
    Identifiers
    urn:nbn:se:liu:diva-99344 (URN)10.4271/2013-01-2289 (DOI)
    Conference
    SAE 2013 Aerotech Congress and Exhibition, September 24-26, 2013, Montréal, Quebec, Canada
    Note

    SAE Technical Paper 2013-01-2289

    Available from: 2013-10-16 Created: 2013-10-16 Last updated: 2017-05-17Bibliographically approved
    3. Automation of Composite Manufacturing Using Off-the-shelf Solutions, Three Cases from the Aerospace Industry
    Open this publication in new window or tab >>Automation of Composite Manufacturing Using Off-the-shelf Solutions, Three Cases from the Aerospace Industry
    2015 (English)In: Proceedings of the 20th International Conference on Composite Materials, 2015Conference paper, Published paper (Other academic)
    Abstract [en]

    With an increased use of composite materials follows a need for rational, cost-efficient manufacturing processes. This paper explores how off-the-shelf solutions, developed for other purposes than composite manufacturing, can be used to build systems for automated composite manufacturing. Three demonstrators, each of them dealing with a specific type of material and all of them representing different manufacturing technologies for automated composite manufacturing, are presented and analyzed to find aspects that affect the ability to use off-the-shelf solutions. The three demonstrators target low to medium manufacturing volumes of complex products and they have been developed in collaboration with industrial partners within the aerospace industry. The conclusions drawn from the development of the demonstrators are that it is technically feasible to use off-the-shelf solutions in the three cases while adhering to the high quality standards of the industry. Furthermore three groups of aspects, quality aspects, product aspects and system aspects, which affect the ability to use off-the-shelf solutions for automated composite manufacturing, are identified.

    Keywords
    composite manufacturing, automation, off-the-shelf, aerospace
    National Category
    Production Engineering, Human Work Science and Ergonomics
    Identifiers
    urn:nbn:se:liu:diva-120300 (URN)
    Conference
    ICCM20 - The 20th International Conference on Composite Materials, 19-24th July 2015, Copenhagen Denmark
    Available from: 2015-07-27 Created: 2015-07-27 Last updated: 2017-05-17
    4. Low-cost Automation for Prepreg Handling - Two Cases from the Aerospace Industry
    Open this publication in new window or tab >>Low-cost Automation for Prepreg Handling - Two Cases from the Aerospace Industry
    2016 (English)In: SAE International Journal of Materials & Manufacturing, ISSN 1946-3979, E-ISSN 1946-3987, Vol. 9, no 1, p. 68-74Article in journal (Refereed) Published
    Abstract [en]

    With an increased use of composite materials within the aerospace industry follows a need for rational and cost-effective methods forcomposite manufacturing. Manual operations are still common for low to medium manufacturing volumes and complex products.Manual operations can for example be found in material handling, when picking prepreg plies from a cutter table and stacking them toform a plane laminate in preparation for a subsequent forming operation. Stacking operations of this kind often involves a greatnumber of different ply geometries and removal of backing paper and other protecting materials like plastic. In this paper two differentdemonstrator cells for automated picking of prepreg plies and stacking of plane laminates are presented. One demonstrator is utilizinga standard industrial robot and an advanced end-effector to handle the ply variants. The other demonstrator is using a dual arm robotwhich allow for simpler end-effector design. In combination with a previously developed system for automated removal of backingpapers both systems have shown to be capable of automatically picking prepreg plies from a plane surface and stack them to generate aflat multistack laminate. The dual arm approach has shown advantageous since it result in simpler end-effector design and a successivelay down sequence that result in good adhesion between the plies in the laminate.

    Place, publisher, year, edition, pages
    Warrendale, USA: SAE International, 2016
    Keywords
    Composite, Manufacturing, Automation, Low-cost, Prepreg
    National Category
    Production Engineering, Human Work Science and Ergonomics
    Identifiers
    urn:nbn:se:liu:diva-121602 (URN)10.4271/2015-01-2606 (DOI)000386445700008 ()
    Available from: 2015-09-28 Created: 2015-09-28 Last updated: 2018-02-02Bibliographically approved
    5. Robot-Forming of Prepreg Stacks ‐ Development of Equipment and Methods
    Open this publication in new window or tab >>Robot-Forming of Prepreg Stacks ‐ Development of Equipment and Methods
    Show others...
    2016 (English)In: Proceedings of the 17th European Conference on Composite Materials (ECCM17), 2016Conference paper, Published paper (Other academic)
    Abstract [en]

    Within the aerospace industry the manufacturing of composite components with complex shapes, such as spars, ribs and beams are often manufactured using manual layup and forming of prepreg material. Automated processes for prepreg layup and efficient forming techniques like vacuum forming are sometimes difficult to employ to these type of products due to technical limitations. This paper describes the development of tools and the forming sequence needed to automate sequential forming of a complex shape using an industrial robot. Plane prepreg stacks are formed to the final shape using a dual-arm industrial robot equipped with rolling tools. Tests show that the developed tools and the employed sequence can be used to form stacks to the desired shape with acceptable quality.

    National Category
    Production Engineering, Human Work Science and Ergonomics
    Identifiers
    urn:nbn:se:liu:diva-129925 (URN)
    Conference
    ECCM17 - 17th European Conference on Composite Materials 26-30th June 2016, Munich, Germany
    Available from: 2016-07-01 Created: 2016-07-01 Last updated: 2017-05-17Bibliographically approved
  • 36.
    Björnsson, Andreas
    Linköping University, Department of Management and Engineering, Manufacturing Engineering. Linköping University, The Institute of Technology.
    Enabling Automation of Composite Manufacturing through the Use of Off-The-Shelf Solutions2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Composite materials offer an appealing combination of low weight and high strength that is especially sought after in high-performance applications. The use of composite materials has and is continuing to increase, and the use of the material has been shown to provide substantial weight savings in for example aircraft design. With an increased use of composite materials follows an increased demand for cost-efficient manufacturing methods.

    Composite products are in many cases manufactured either by manual operations or by the use of complex automated solutions associated with high investment costs. The objective for this research is to explore an approach to develop automated composite manufacturing based on commercially available off-the-shelf solutions as an alternative to the existing automated solutions for composite manufacturing.

    The research, which was carried out in collaboration with industrial partners within the aerospace sector, is based on a demonstrator-centered research approach. Three conceptual demonstrators, focusing on three different manufacturing methods and a number of physical demonstrators, are used to show that off-the-shelf solutions can be used for automated manufacturing of composite products.

    Two aspects that affect if it is possible to use off-the-shelf solutions for automated composite manufacturing are the rigorous quality standards used by the aerospace industry and the great variety in product properties and material properties that is associated with composite manufacturing.

    The advantages in using off-the-shelf solutions has shown to be that the solutions generally are associated with low investments and that published information about the solutions, and the solutions themselves, is generally available for evaluation and testing. When working with the demonstrators it has been shown to be useful to break down a manufacturing system into basic tasks and consider off-the-shelf solutions for each particular task. This approach facilitates the search for a suitable off-the-shelf solution to solve a particular task. However, each of the separate tasks can affect other areas of the manufacturing system, and an overall systems perspective is required to find solutions that are compatible with the entire manufacturing system.

    List of papers
    1. Automated Removal of Prepreg Backing Paper - A Sticky Problem
    Open this publication in new window or tab >>Automated Removal of Prepreg Backing Paper - A Sticky Problem
    2013 (English)In: Proceedings of the SAE 2013, Aerotech Congress and Exhibition, 24th-26th September 2013, Montreal,Canada, 2013Conference paper, Published paper (Refereed)
    Abstract [en]

    Automated solutions for manufacturing composite products based on prepreg often imply Automatic Fiber Placement or Automatic Tape Laying. These systems are generally associated with huge investments. For certain manufacturing applications it is interesting to investigate alternatives to find simpler and less costly automation. One example of an automated system could be the use of a standard industrial robot to pick single prepreg plies from an automated cutting machine and stack them to form a plane laminate. This paper is based on a case illustrating a product from the aircraft manufacturing industry. The case will demonstrate a pick and place concept on a general level and illustrate challenges that must be solved. The challenge selected to be the main focus for this paper is an automated process for backing paper removal. A literature review of different gripping technologies reveals several interesting technologies, and the most promising are tested for backing paper removal. The tests show that an automated removal process can be designed by using standard vacuum grippers in combination with mechanical clamping grippers. In order to lift the backing paper with a vacuum gripper an initial separation between the backing paper and prepreg is needed. This separation is most easily mechanically induced by bending the material. The proposed solution for automatic backing paper removal can be integrated in a manufacturing cell for manufacturing of the studied product.

    Keywords
    composite manufacturing, automation, prepreg, gripping technology
    National Category
    Production Engineering, Human Work Science and Ergonomics
    Identifiers
    urn:nbn:se:liu:diva-99344 (URN)10.4271/2013-01-2289 (DOI)
    Conference
    SAE 2013 Aerotech Congress and Exhibition, September 24-26, 2013, Montréal, Quebec, Canada
    Note

    SAE Technical Paper 2013-01-2289

    Available from: 2013-10-16 Created: 2013-10-16 Last updated: 2017-05-17Bibliographically approved
    2. Three-Dimensional Ultrasonic Cutting of RTM-Preforms – A Part of a High Volume Production System
    Open this publication in new window or tab >>Three-Dimensional Ultrasonic Cutting of RTM-Preforms – A Part of a High Volume Production System
    2013 (English)In: Proceedings of the 19th International Conference on Composite Materials, 28th July - 2nd August 2013, Montreal, Canada: Composite Materials:The Great Advance / [ed] Suong Van Hoa & Pascal Hubert, Electronic Publishing BytePress.com , 2013, p. 8960-8969Conference paper, Published paper (Refereed)
    Abstract [en]

    The process parameters for an automated, three-dimensional ultrasonic cutting process of RTM-preforms are examined in order to find how they affect the cutting quality.

    Place, publisher, year, edition, pages
    Electronic Publishing BytePress.com, 2013
    Keywords
    composite manufacturing, ultrasonic cutting, preform, RTM, automation
    National Category
    Production Engineering, Human Work Science and Ergonomics
    Identifiers
    urn:nbn:se:liu:diva-95875 (URN)978-0-9696797-1-4 (ISBN)
    Conference
    19th International Conference on Composite Materials (ICCM19), July 28 - August 2, 2013, Montréal, Canada
    Available from: 2013-08-05 Created: 2013-08-05 Last updated: 2016-09-26
    3. Automated Composite Manufacturing Using Off-the-shelf Automation Equipment – A Case from the Space Industry
    Open this publication in new window or tab >>Automated Composite Manufacturing Using Off-the-shelf Automation Equipment – A Case from the Space Industry
    2014 (English)In: Proceedings of the 16th European Conference on Composite Materials, 22nd-26th June 2014, Seville, Spain, 2014Conference paper, Published paper (Refereed)
    Abstract [en]

    A novel approach to the manufacturing of composite products using off-the-shelf automation equipment is explored in this article. A manufacturing concept for a specific product is developed and analyzed, from a technical perspective, in order to find areas where off-the-shelf automation equipment can be used. The article also highlights areas where case-specific solutions need to be developed. In this particular case, off-the-shelf automation equipment can be used for most of the tasks that the manufacturing system needs to perform. The most challenging process is identified as the application of adhesive. The manufacturing concept described in the article shows that it is possible to build a system for the manufacturing of composite components using a high degree of off-the-shelf automation equipment.

    Keywords
    composite, automation, off-the-shelf, adhesive joining
    National Category
    Production Engineering, Human Work Science and Ergonomics
    Identifiers
    urn:nbn:se:liu:diva-109107 (URN)978-84-616-9798-4 (ISBN)
    Conference
    16th European Conference on Composite Materials (ECCM16), June 22-26, 2014, Seville, Spain
    Available from: 2014-08-08 Created: 2014-08-08 Last updated: 2016-09-26
    4. Composite Manufacturing: How Improvement Work Might Lead to Renewed Product Validation
    Open this publication in new window or tab >>Composite Manufacturing: How Improvement Work Might Lead to Renewed Product Validation
    2012 (English)In: Proceedings of the 5th International Swedish Production Symposium / [ed] Mats Björkman, 2012, p. 505-513Conference paper, Published paper (Refereed)
    Abstract [en]

    High-performance polymer composites are mainly used in applications where the benefits of high strength and low weight justify the high material and manufacturing costs. Many of these applications are found today in the aerospace, space and defense industries. Most of today’s commonly used manufacturing methods within this area are highly labor intensive. Furthermore, the quality requirements from the customers require a high level of process control. The purpose of this paper is to explore how changes that are introduced in order to improve productivity in a manufacturing system are managed, particularly with regard to who takes the decision to implement a change and how a change is validated. The study is based on qualitative interviews performed at several companies that manufacture composite components for the aerospace, space and defense sectors. The findings show that the responsibility for deciding to implement a change and the need for validating it are based on many diverse and interconnected factors. Therefore, it is difficult to construct guidelines for early assessment of the scope and cost of a proposed change. Hence each individual change request must be evaluated on its own. The study also shows that the validation process can be adapted to a level that is based on the type of change. In addition, it highlights that control over process parameters in manufacturing is essential.

    Keywords
    composite manufacturing, validation, change request management
    National Category
    Production Engineering, Human Work Science and Ergonomics
    Identifiers
    urn:nbn:se:liu:diva-85268 (URN)978-91-7519-752-4 (ISBN)
    Conference
    5th International Swedish Production Symposium (SPS 2012), 6-8 November 2012, Linköping, Sweden
    Available from: 2012-11-14 Created: 2012-11-14 Last updated: 2017-05-17
  • 37.
    Blomstedt, Mats
    et al.
    Siemens Industrial Turbomachinery AB, Finspång.
    Lindgren, Håkan
    Siemens Industrial Turbomachinery AB, Finspång.
    Olausson, Hans-Lennart
    Siemens Industrial Turbomachinery AB, Finspång.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Innovative starting procedure of Siemens SGT-600 in cold climate conditions2011In: ASME 2011 Turbo Expo:Turbine Technical Conference and Exposition: Volume 4: Cycle Innovations; Fans and Blowers; Industrial and Cogeneration; Manufacturing Materials and Metallurgy; Marine; Oil and Gas Applications, The American Society of Mechanical Engineers (ASME) , 2011, Vol. 4, p. 1021-1026Conference paper (Refereed)
    Abstract [en]

    A start-up of a gas turbine means that stress and forces are put on the machine. A start-up in cold climate conditions means that the forces are more critical since the material in the machine becomes more brittle. At a certain temperature the material is utilized to its limits (with appropriate margins applied) and for the SGT-600 ambient temperatures below -30°C (-22°F) become critical. In earlier installations in an arctic climate, an electric pre- heater has been utilized to prevent the critical components from becoming too brittle. This additional hardware costs money, is consuming auxiliary power and may contribute to unavailability. Another way to solve this issue may be to install material that is less brittle, but this will also increase the cost of the installation. Siemens is now applying an improved control logic during start-up, solving this issue in the software, without any additional hardware and avoiding unnecessary material changes. This new innovative start-up procedure is performing an automatic check of the stress levels before loading the machine, resulting in a safe and reliable start at temperatures below -30°C (-22°F). 

  • 38.
    Boota, Muhammad
    et al.
    Linköping University, The Department of Physics, Chemistry and Biology.
    Rahmatalla, Reem
    Linköping University, The Department of Physics, Chemistry and Biology.
    Growth of GaN on lattice matched AlInN substrates2008Independent thesis Basic level (professional degree), 20 points / 30 hpStudent thesis
    Abstract [en]

    This project was planed in order to study the effect of growth and crystalline quality of GaN on lattice matched Al1-xInxN seed layer. The GaN lattice matched Al0.81Ino.19N seed layer was grown by co-sputtering of Al and In target using only N2 as a sputtering gas in a direct current (DC) reactive magnetron sputter deposition chamber under UHV conditions at low temperature (230 oC) on different substrates. The Indium composition was calculated using vegards law from lattice parameters determined by XRD. The Indium composition was determined by Rutherford Backscattering Spectroscopy (RBS) as well. X-rays diffraction (XRD) showed high crystalline quality wurtzite hexagonal Al1-xInxN seed layers grown at this temperature. The GaN was grown on top of Al0.81Ino.19N seed layer by halide vapour phase epitaxy (HVPE) using a mixture of N2 and H2 and only N2 as a carrier gas in order to study the effect of carrier gas on crystalline quality of GaN. The GaN films were characterised by high resolution X-rays diffraction (HRXRD), scanning electron microscopy (SEM), cathode luminescence (CL) and high resolution transmission electron microscopy (HRTEM) in order to study stress, strain, crystalline quality, surface morphology and optoelectronic properties in relation with the defect density and the microstructure of grown GaN films.

  • 39.
    Bouhafs, Chamseddine
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Structural and Electronic Properties of Graphene on 4H- and 3C-SiC2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Graphene is a one-atom-tick carbon layer arranged in a honeycomb lattice. Graphene was first experimentally demonstrated by Andre Geim and Konstantin Novoselov in 2004 using mechanical exfoliation of highly oriented pyrolytic graphite (exfoliated graphene flakes), for which they received the Nobel Prize in Physics in 2010. Exfoliated graphene flakes show outstanding electronic properties, e.g., very high free charge carrier mobility parameters and ballistic transport at room temperature. This makes graphene a suitable material for next generation radio-frequency and terahertz electronic devices. Such applications require fabrication methods of large-area graphene compatible with electronic industry. Graphene grown by sublimation on silicon carbide (SiC) offers a viable route towards production of large-area, electronic-grade material on semi-insulating substrate without the need of transfer. Despite the intense investigations in the field, uniform wafer-scale graphene with very high-quality that matches the properties of exfoliated graphene has not been achieved yet. The key point is to identify and control how the substrate affects graphene uniformity, thickness, layer stacking, structural and electronic properties. Of particular interest is to understand the effects of SiC surface polarity and polytype on graphene properties in order to achieve large-area material with tailored properties for electronic applications. The main objectives of this thesis are to address these issues by investigating the structural and electronic properties of epitaxial graphene grown on 4HSiC and 3C-SiC substrates with different surface polarities. The first part of the thesis includes a general description of the properties of graphene, bilayer graphene and graphite. Then, the properties of epitaxial graphene on SiC by sublimation are detailed. The experimental techniques used to characterize graphene are described. A summary of all papers and contribution to the field is presented at the end of Part I. Part II consists of seven papers.

    List of papers
    1. Structural properties and dielectric function of graphene grown by high-temperature sublimation on 4H-SiC(000-1)
    Open this publication in new window or tab >>Structural properties and dielectric function of graphene grown by high-temperature sublimation on 4H-SiC(000-1)
    Show others...
    2015 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 8, p. 085701-Article in journal (Refereed) Published
    Abstract [en]

    Understanding and controlling growth of graphene on the carbon face (C-face) of SiC presents a significant challenge. In this work, we study the structural, vibrational, and dielectric function properties of graphene grown on the C-face of 4H-SiC by high-temperature sublimation in an argon atmosphere. The effect of growth temperature on the graphene number of layers and crystallite size is investigated and discussed in relation to graphene coverage and thickness homogeneity. An amorphous carbon layer at the interface between SiC and the graphene is identified, and its evolution with growth temperature is established. Atomic force microscopy, micro-Raman scattering spectroscopy, spectroscopic ellipsometry, and high-resolution cross-sectional transmission electron microscopy are combined to determine and correlate thickness, stacking order, dielectric function, and interface properties of graphene. The role of surface defects and growth temperature on the graphene growth mechanism and stacking is discussed, and a conclusion about the critical factors to achieve decoupled graphene layers is drawn. (C) 2015 AIP Publishing LLC.

    Place, publisher, year, edition, pages
    American Institute of Physics (AIP), 2015
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-117253 (URN)10.1063/1.4908216 (DOI)000351132500070 ()
    Note

    Funding Agencies|Marie Curie actions [264613-NetFISiC]; Swedish Research Council (VR) [2011-4447, 2013-5580]; Swedish Governmental Agency for Innovation Systems (VINNOVA) under the VINNMER international qualification program [2011-03486]; Swedish foundation for strategic research (SSF) [FFL12-0181]; FP7 EU project Nano-Rf [FP7-ICT-2011-8]; French ANR under the Grafonics Project [ANR-10-NANO-0004]; European Union Seventh Framework Programme under Graphene Flagship [604391]; Knut and Alice Wallenbergs foundation

    Available from: 2015-04-22 Created: 2015-04-21 Last updated: 2017-12-04
    2. Cavity-enhanced optical Hall effect in epitaxial graphene detected at terahertz frequencies
    Open this publication in new window or tab >>Cavity-enhanced optical Hall effect in epitaxial graphene detected at terahertz frequencies
    Show others...
    2017 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 421, p. 357-360Article in journal (Refereed) Published
    Abstract [en]

    Cavity-enhanced optical Hall effect at terahertz (THz) frequencies is employed to determine the free charge carrier properties in epitaxial graphene (EG) with different number of layers grown by high-temperature sublimation on 4H-SiC(0001). We find that one monolayer (ML) EG possesses p-type conductivity with a free hole concentration in the low 1012 cmᅵᅵᅵ2 range and a free hole mobility parameter as high as 1550 cm2/Vs. We also find that 6 ML EG shows n-type doping behavior with a much lower free electron mobility parameter of 470 cm2/Vs and an order of magnitude higher free electron density in the low 1013 cmᅵᅵᅵ2 range. The observed differences are discussed. The cavity-enhanced THz optical Hall effect is demonstrated to be an excellent tool for contactless access to the type of free charge carriers and their properties in two-dimensional materials such as EG.

    Place, publisher, year, edition, pages
    Elsevier, 2017
    Keywords
    THz optical Hall effect, Epitaxial graphene, Free charge carrier properties
    National Category
    Physical Sciences Condensed Matter Physics Atom and Molecular Physics and Optics Ceramics
    Identifiers
    urn:nbn:se:liu:diva-132407 (URN)10.1016/j.apsusc.2016.10.023 (DOI)000408756700015 ()
    Note

    Funding agencies: Swedish Research Council (VR) [2013-5580]; Swedish Governmental Agency for Innovation Systems (VINNOVA) under the VINNMER international qualification program [2011-03486, 2014-04712]; Swedish foundation for strategic research (SSF) [FFL12-0181, RIF14-055]

    Available from: 2016-11-09 Created: 2016-11-09 Last updated: 2018-01-12Bibliographically approved
  • 40.
    Brandtberg, Sebastian
    Linköping University, Department of Management and Engineering, Engineering Materials.
    Microstructural inhomogeneity and anisotropicproperties in IN-718 structures fabricated byElectron Beam Melting: Mikrostrukturell inhomogenitet och anisotropa egenskaper i strukturerav IN-718 tillverkade genom Electron Beam Melting2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Additive Manufacturing, or 3D printing, provides an opportunity to manufacture advanced 3D geometrieswith little material waste and reduced need for tooling compared to conventional methods. There are,however, challenges remaining regarding anisotropy in the mechanical properties of built components.

    The aim of this project is to investigate the anisotropy of additive manufactured material and the effect ofdifferent build directions. The material used is Inconel 718, which was manufactured by Electron BeamMelting as vertical and horizontal rods. The tests performed are microstructural investigations about thegrains, precipitates and porosities, but also include hardness testing and tensile testing. The material istested in its as-built state.

    The results show that the material consist of an anisotropic microstructure with elongated grains in thebuild direction. The build height has a bigger influence on the properties of the material than the builddirection for the specimens. The top pieces are consistently different from the others and are the leasthomogeneous. The microstructure consists of large quantities of delta-phase, and solidification pores arefound throughout the material. The hardness of the material differs from 324 HV to 408 HV depending onthe part of the build. The tensile testing shows that the vertically built specimens have a higher yieldstrength and ultimate tensile strength while the horizontally built specimens have a greater ductility.

  • 41.
    Brodin, Håkan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Andersson, Olov
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Mechanical Behaviour and Microstructure Correlation in a Selective Laser Melted Superalloy2013In: ASME Turbo Expo 2013: Turbine Technical Conference and Exposition, American Society of Mechanical Engineers (ASME) , 2013, Vol. 5A, p. 1-7Conference paper (Refereed)
    Abstract [en]

    Selective laser melting (SLM), or, as the industry standard denotes the process, laser sintering, is an additive manufacturing process where metal powder is melted by a laser source layer-wise, forming a solid, dense metallic component. With the SLM process, near net shape components can be manufactured directly from a CAD model. The model is sliced into thin (max 100μm thick) layers. Powder is spread onto a metallic build platform and the powder is fused by a laser as dictated by the CAD model. The laser energy is intense enough to permit full melting (welding) of the particles to form solid metal. The process is repeated layer by layer until the part is complete.

    A number of materials are available, including steel, aluminium, titanium and, in recent time, also superalloys. The material investigated in the current project is an alloy in agreement with the composition of Haynes International Hastelloy X, a solution strengthened superalloy typically used in large welded components exposed to high temperatures in oxidizing as well as reducing environments.

    Microstructurally, the material is different from both a hot-rolled, as well as a cast material due to the manufacturing process. Since the SLM process involves laser melting of powder particles in the size range of <50μm, the structure resembles of a weld structure, however on a smaller scale. Due to the layer-by-layer build strategy, the material will exhibit anisotropy. Different heat treatment approaches can be adopted in order to homogenize the material and to minimize the effect of anisotropy. A stress relieve heat treatment was adopted and compared to the findings of the as manufactured SLM material.

    The current project focuses on evaluating mechanical properties for a material manufactured by the SLM process and comparing to data for established manufacturing processes. For evaluation of the mechanical properties, low cycle fatigue testing and tensile testing has been performed. The microstructure and material deformation / cracking are evaluated by light optical microscopy and SEM, where electron backscatter diffraction is used. Due to the weld-like structure, the material will be transversely isotropic in the as-manufactured condition with one symmetry plane perpendicular to the build direction. Any direction perpendicular to the build direction tends to give increased strength compared to a direction parallel to the build direction if monotonic data are concerned. If fatigue properties are concerned, the anisotropy is also obvious. It is shown that the differences in behaviour can be coupled to microstructure.

  • 42.
    Brodin, Håkan
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Eriksson, Robert
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång.
    Östergren, Lars
    Volvo Aero Corporation, Trollhättan.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Finite Element Modelling and Damage Evaluation of Air Plasma Sprayed Thermal Barrier Coatings2012Conference paper (Refereed)
  • 43.
    Brodin, Håkan
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Saarimäki, Jonas
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Mechanical Properties of Lattice Truss Structures Made of a Selective Laser Melted Superalloy2013Conference paper (Refereed)
  • 44.
    Broitman, Esteban
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Advances in science and technology of polymers and composite materials2018In: E-Polymers, ISSN 1618-7229, E-ISSN 1618-7229, Vol. 18, no 1Article in journal (Other academic)
    Abstract [en]

    n/a

  • 45.
    Broitman, Esteban
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Indentation Hardness Measurements at Macro-, Micro-, and Nanoscale: A Critical Overview2017In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 65, no 1Article, review/survey (Refereed)
    Abstract [en]

    The Brinell, Vickers, Meyer, Rockwell, Shore, IHRD, Knoop, Buchholz, and nanoindentation methods used to measure the indentation hardness of materials at different scales are compared, and main issues and misconceptions in the understanding of these methods are comprehensively reviewed and discussed. Basic equations and parameters employed to calculate hardness are clearly explained, and the different international standards for each method are summarized. The limits for each scale are explored, and the different forms to calculate hardness in each method are compared and established. The influence of elasticity and plasticity of the material in each measurement method is reviewed, and the impact of the surface deformation around the indenter on hardness values is examined. The difficulties for practical conversions of hardness values measured by different methods are explained. Finally, main issues in the hardness interpretation at different scales are carefully discussed, like the influence of grain size in polycrystalline materials, indentation size effects at micro-and nanoscale, and the effect of the substrate when calculating thin films hardness. The paper improves the understanding of what hardness means and what hardness measurements imply at different scales.

  • 46.
    Broitman, Esteban
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Advanced Carbon-Based Coatings2014In: Comprehensive Materials Processing, Elsevier, 2014, 4, p. 389-412Chapter in book (Refereed)
    Abstract [en]

    This chapter focuses on the development of alloyed diamondlike coatings, in particular a new class of fullerene-like (FL) materials. We describe unique resilient FL compounds by self-organization of nano-curved sp2-hybridized carbon features, with tuned mechanical and surface energy properties. These unique resilient materials consist of bent and intersecting hexagonal basal planes, fabricated by the incorporation of odd-member rings. Cross-linking enables the material to extend the strength of the covalently 2D hexagonal graphene network into 3D. The microstructural properties of three types of coatings, which have the possibility to be applied on a large scale, are described: carbon nitride, phosphorous carbide, and carbon fluoride.

  • 47.
    Broitman, Esteban
    et al.
    University of Buenos Aires, Argentina.
    Latorre, Daniel
    University of Buenos Aires, Argentina.
    Sendra, Claudia
    University of Buenos Aires.
    Zimmerman, Rosa
    University of Buenos Aires.
    Thin Film Humidity Sensors (Sensores de Humedad de Película Delgada)1991In: Anales AFA, ISSN 1850-1158, Vol. 2, no 1, p. 277-279Article in journal (Refereed)
    Abstract [en]

    In this paper the construction and characterization of a humidity sensor with an alumina thin film responsive element is described. The capacitive sensor, made by thin film technology, consists of a dielectric layer of Al2O3 film deposited between metal electrodes.

  • 48.
    Broitman, Esteban
    et al.
    University of Buenos Aires, Argentina.
    Latorre, Daniel
    University of Buenos Aires, Argentina.
    Zimmerman, Rosa
    University of Buenos Aires, Argentina.
    Thin Film Temperature Sensors (Sensores de Temperatura de Película Delgada)1990In: Anales AFA, ISSN 1850-1158, Vol. 1, no 1, p. 336-338Article in journal (Refereed)
    Abstract [en]

    Ni thin films of 1800 Å thick were deposited by ion-plating and designed by photolithography to be used as temperature sensors. The resistive paths were finished with contact Cu welding terminals. After being coated with a protective layer of SiOx, they were subjected to heat stabilization treatments. Small, stable and accurate sensors were obtained.

  • 49.
    Broitman, Esteban
    et al.
    Carnegie Mellon University, Pittsburgh, PA, USA .
    Neihardt, Jörg
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Fullerene-like Carbon Nitride: A New Carbon-based Tribological Coating2008In: Tribology of Diamond-Like Carbon Films: Fundamentals and Applications, Springer, 2008, 1, p. 620-653Chapter in book (Refereed)
    Abstract [en]

    In 1994, researchers at Linköping University discovered the fullerene-like allotrope of carbon nitride (FL-CNx) by using reactive magnetron sputtering in a nitrogen-containing atmosphere at rather low ion energy assistance. FL-CNx is a predominantly sp2-hybridized material with nitrogen structurally incorporated either substitutionally in a graphite sheet or in a pyridine-like manner, which initiates bending by formation of pentagons and cross-linking, respectively. The assumed nitrogen-induced cross-linkage between the sheets contributes considerably to the strength of FL-CNx by preventing interplanar slip. This results in an extremely fracture tough, elastic, and compliant material, which deforms by reversible bond rotation and bond angle deflection rather than slip and bond breaking.

  • 50.
    Brooke, Robert
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. University of S Australia, Australia.
    Fabretto, Manrico
    University of S Australia, Australia.
    Krasowska, Marta
    University of S Australia, Australia.
    Talemi, Pejman
    University of S Australia, Australia; University of Adelaide, Australia.
    Pering, Samuel
    University of Bath, England.
    Murphy, Peter J.
    University of S Australia, Australia.
    Evans, Drew
    University of S Australia, Australia.
    Organic energy devices from ionic liquids and conducting polymers2016In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 4, no 7, p. 1550-1556Article in journal (Refereed)
    Abstract [en]

    The use of smart technologies in our daily lives, from smartphones to auto-dimming windows to touch sensors, has become pervasive. With growing desire for these devices to be conformable and flexible, traditional materials are being replaced to create a class of products known as active organic electronic devices (OEDs). These new devices owe their ability to switch electrical and/or optical function to the intimate interaction between an inherently conducting polymer and electrolyte, typically an ionic liquid. Herein, we provide the first observations that specific ionic liquids can reduce or oxidise conducting polymers upon intimate contact in the absence of any electrical stimuli. The ability to reduce or oxidise the inherently conducting polymer depends on the cation and anion pair within the ionic liquid. Extending the utility of this phenomenon is made by fabricating OEDs such as prototype fuel cells, supercapacitors and smart windows.

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