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  • 301. Heister, Karin
    et al.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Grunze, Michael
    Zharnikov, Michael
    A detailed Analysis of the C 1s Photoemission of n-Alkanethiolate Films on Noble Metal Substrates2003In: Surface Science, 529, 36 (2003)Article in journal (Refereed)
    Abstract [en]

    High-resolution C 1s X-ray photoemission spectra for the series of n-alkanethiolate (AT) self-assembled monolayers (SAMs) with different lengths of the alkyl chain have been acquired and analyzed in terms of initial and final state effects and fine structure of the C 1s emission. Independent of the alkyl chain length, the binding energy position of this emission was found to be higher by ?0.35 eV for AT SAMs on Ag substrate as compared to Au, which was attributed to the differences in the final state screening mediated by the intermolecular charge transfer. It was assumed that the extent of this effect is a function of the detailed molecular arrangement in the alkyl matrix and demonstrated that the difference in the C 1s peak position disappears as soon as this arrangement is distorted by the incorporation of sulfone moiety in the alkyl chain. In addition, a change of the C 1s peak shape from a symmetric to asymmetric line with increasing alkyl chain length has been observed. This development could be described assuming the existence of a fine structure in the C 1s emission, with two low-intensity components at the higher and lower BE sides of the main emission peak. An assignment of these components has been considered

  • 302.
    Hellman, Anders
    et al.
    Chalmers Tekniska Högskola.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Andersson, Stig
    Göteborgs Universitet.
    Hydrogen-Induced Reconstruction of Cu(100): Two-Dimensional and One-Dimensional Structures of Surface Hydride2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, article id 15773Article in journal (Refereed)
    Abstract [en]

    Adsorption of atomic hydrogen has a remarkable influence on the structure and morphology of the Cu(100) surface. We have examined two specific situations; the well-known reconstructed p(2 × 2)-H surface and a one-dimensional (6 × 1)-H surface resembling the stripe reconstruction observed in an electrochemical environment. High resolution electron energy loss spectroscopy and density functional calculations show that the H atoms occupy only surface sites and that H bonding in induced 3-fold Cu surface hollow sites is a structural key element. The calculations support a transient scenario in which H absorption in subsurface sites is a critical intermediate step in the reconstruction of the Cu surface. We find clear evidence in terms of characteristic properties, like the H–Cu bond lengths and the dipole excited vibrational mode spectra, that these structures consist of two-dimensional and one-dimensional structures of surface hydride.

  • 303.
    Hertz, Hans
    et al.
    KTH.
    von Hofsten, Olov
    KTH.
    Bertilson, Mikael
    KTH.
    Vogt, Ulrich
    KTH.
    Holmberg, Anders
    KTH.
    Reinspach, Julia Antonia
    KTH.
    Martz, Dale
    KTH.
    Selin, Mårten
    KTH.
    Christakou, Athanasia
    KTH.
    Jerlström-Hultqvist, J
    Uppsala University.
    Svärd, S
    Uppsala University.
    Laboratory cryo soft X-ray microscopy2012In: Journal of Structural Biology, ISSN 1047-8477, E-ISSN 1095-8657, Vol. 177, no 2, p. 267-272Article in journal (Refereed)
    Abstract [en]

    Lens-based water-window X-ray microscopy allows two- and three-dimensional (2D and 3D) imaging of intact unstained cells in their near-native state with unprecedented contrast and resolution. Cryofixation is essential to avoid radiation damage to the sample. Present cryo X-ray microscopes rely on synchrotron radiation sources, thereby limiting the accessibility for a wider community of biologists. In the present paper we demonstrate water-window cryo X-ray microscopy with a laboratory-source-based arrangement. The microscope relies on a lambda = 2.48-nm liquid-jet high-brightness laser-plasma source, normal-incidence multilayer condenser optics, 30-nm zone-plate optics, and a cryo sample chamber. We demonstrate 2D imaging of test patterns, and intact unstained yeast, protozoan parasites and mammalian cells. Overview 3D information is obtained by stereo imaging while complete 3D microscopy is provided by full tomographic reconstruction. The laboratory microscope image quality approaches that of the synchrotron microscopes, but with longer exposure times. The experimental image quality is analyzed from a numerical wave-propagation model of the imaging system and a path to reach synchrotron-like exposure times in laboratory microscopy is outlined.

  • 304.
    Hervik, Sigbjørn
    et al.
    Faculty of Science and Technology, University of Stavanger, Norway.
    Lim, Woei Chet
    Albert-Einstein-Institut, Am-Mûhlenberg, Germany.
    Sandin, Patrik
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Uggla, Claes
    Karlstad University, Faculty of Technology and Science.
    Future Asymptotics of Tilted Bianchi Type II Cosmologies2010In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 27, p. 185006-Article in journal (Refereed)
  • 305.
    Hirvonen Grytzelius, Joakim
    Karlstad University, Division for Engineering Sciences, Physics and Mathematics.
    Atomic Force and Scanning Tunneling Microscopy Studies of Single Walled Carbon Nanotubes2006Independent thesis Advanced level (degree of Magister), 20 points / 30 hpStudent thesis
    Abstract [en]

    In this diploma work I present the first experimental investigations

    of carbon nanotubes at Karlstads University. Raw nanotube powder

    of single walled carbon nanotubes have been dispersed primarily in

    1,2-dichloroethane. The solutions have been spincoated on Au(111)

    substrates. In order to determine the solubility of carbon nanotubes

    in the solution the samples have been investigated in an atomic force

    microscope.

    Single walled carbon nanotubes deposited on a Au(111) substrate

    have been investigated in a scanning tunneling microscope. Atomically

    resolved STM images of single walled carbon nanotubes were obtained.

    Scanning tunneling spectroscopy spectra was taken on a tube revealing

    its chirality. The measured data from the nanotubes was compared to

    calculations and confirmed their properties.

    Dry direct contact transfers of individual single walled carbon nanotubes

    have been done as a first step when trying to deposit carbon

    nanotubes on reactive surfaces in ultra-high vacuum. Individual nanotubes

    were found, confirming the success of dry direct contact transfer.

  • 306.
    Hirvonen Grytzelius, Joakim
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Thin Mn silicide and germanide layers studied by photoemission and STM2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The research presented in this thesis concerns experimental studies of thin manganese silicide and germanide layers, grown by solid phase epitaxy on the Si(111)7×7 and the Ge(111)c(2×8) surfaces, respectively. The atomic and electronic structures, as well as growth modes of the epitaxial Mn-Si and Mn-Ge layers, were investigated by low-energy electron diffraction (LEED), angle-resolved photoelectron spectroscopy (ARPES), core-level spectroscopy (CLS), and scanning tunneling microscopy and spectroscopy (STM and STS). The magnetic properties of the Mn-Ge films were investigated by X-ray magnetic circular dichroism (XMCD).

    The Mn-Si layers, annealed at 400 °C, showed a √3×√3 LEED pattern, consistent with the formation of the stoichiometric monosilicide MnSi. Up to 4 monolayers (ML) of Mn coverage, island formation was observed. For higher Mn coverages, uniform film growth was found. Our results concerning morphology and the atomic and electronic structure of the Mn/Si(111)-√3×√3 surface, are in good agreement with a recent theoretical model for a layered MnSi structure and the √3×√3 surface structure.

    Similar to the Mn-Si case, the grown Mn-Ge films, annealed at 330 °C and 450 °C, showed a √3×√3 LEED pattern. This indicated the formation of the ordered Mn5Ge3 germanide. A strong tendency to island formation was observed for the Mn5Ge3 films, and a Mn coverage of about 32 ML was needed to obtain a continuous film. Our STM and CLS results are in good agreement with the established model for the bulk Mn5Ge3 germanide, with a surface termination of Mn atoms arranged in a honeycomb pattern. Mn-Ge films grown at a lower annealing temperature, 260 °C, showed a continuous film at lower coverages, with a film structure that is different compared to the structure of the Mn5Ge3 film. XMCD studies showed that the low-temperature films are ferromagnetic for 16 ML Mn coverage and above, with a Curie temperature of ~250 K.

  • 307.
    Hirvonen Grytzelius, Joakim
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Zhang, Hanmin
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Core-level spectroscopy studies of Mn/Si(111)-sqrt3xsqrt32008Conference paper (Refereed)
  • 308.
    Hirvonen Grytzelius, Joakim
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Zhang, Hanmin
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Coverage dependence and surface atomic structure of Mn/Si(111)-√3×√3 studied by scanning tunneling microscopy and spectroscopy2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, p. 235324-1-235324-6Article in journal (Refereed)
    Abstract [en]

    Thin manganese silicide films of different thicknesses on Si(111) have been studied in detail by low-energy electron diffraction (LEED), scanning tunneling microscopy, and scanning tunneling spectroscopy (STM/STS). Up to a Mn coverage of 3–4 monolayers (ML), island formation is favored. For higher Mn coverages up to 12 ML uniform film growth is found. The silicide film morphology at low coverages supports a layered Mn-Si film structure. The silicide surfaces displayed a √3×√3 LEED pattern. STM images recorded from the √3×√3 surfaces mostly show a hexagonal pattern but a honeycomb pattern has also been observed. A surface atomic structure based on chained Mn triangles is proposed. Our STM results are in good agreement with a recent theoretical model. The high-quality STS spectra recorded from the different surfaces show a clear metallic character at 1.5 ML and higher coverages. The filled-state features in the STS spectra at surfaces with 3–4 ML Mn coverages are similar to earlier published angle-resolved photoelectron spectroscopy data.

  • 309.
    Hirvonen Grytzelius, Joakim
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Zhang, Hanmin
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Electronic structure of Mn/Si(111)-sqrt3xsqrt32007Conference paper (Refereed)
  • 310.
    Hirvonen Grytzelius, Joakim
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Zhang, Hanmin
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Mn5Ge3 film formation on Ge(111)c(2×8)2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 12, p. 125313-1-125313-7Article in journal (Refereed)
    Abstract [en]

    Thin manganese germanide films with different thicknesses on Ge(111) have been studied in detail by low-energy electron diffraction (LEED), scanning tunneling microscopy, and core-level spectroscopy (CLS). Annealing of the deposited Mn on Ge(111)c(2×8) between 330-450 C resulted in well-ordered Mn5Ge3 surfaces as seen by intense 3×3 LEED spots. Up to a coverage of 24 monolayers (ML), island formation is favored. At a coverage of 32 ML a well ordered Mn5Ge3 film was found to fully cover the surface. High-resolution Ge 3d CLS spectra were recorded with photon energies between 50 and 110 eV at normal and 60 emission angles. In contrast to earlier results, three components have been used in the line-shape analysis to achieve a consistent fit over the energy and angular range. In addition, three components have been identified for the Mn 2p CLS spectra. The two major components fit well with a layered Mn germanide structure suggested in the literature.

  • 311.
    Hirvonen Grytzelius, Joakim
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Zhang, Hanmin
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Surface atomic and electronic structure of Mn5Ge3 on Ge(111)2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, ISSN 1098-0121, Vol. 84, no 19, p. 195306-1-195306-6Article in journal (Refereed)
    Abstract [en]

    The atomic and electronic structure of the Mn5Ge3(001) surface grown on Ge(111) c(2×8) has been studied in detail by angle-resolved photoelectron spectroscopy (ARPES), scanning tunneling microscopy (STM), and scanning tunneling spectroscopy. ARPES spectra recorded from the Γ̅ -K̅ -M̅ and Γ̅ -M̅ -Γ̅ directions of the surface Brillouin zone show six surface-related features. The STM images recorded at biases higher/lower than ±0.4 V always show a honeycomb pattern with two bright protrusions in each unit cell. At lower biases, a hexagonal, intermediate transition, and a honeycomb pattern are observed. These can be explained as arising from Mn and Ge atoms in the sublayer arranged in triangular structures and Mn atoms in the top layer arranged in a honeycomb structure, respectively. The photoemission and STM data from the germanide surface are discussed and compared to earlier published theoretical, photoelectron spectroscopy, and scanning tunneling microscopy studies.

  • 312.
    Hirvonen Grytzelius, Joakim
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Zhang, Hanmin
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Johansson, Lars
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Surface electronic structure of Mn/Si(111)-√3×√32008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 15, p. 155406-1-155406-6Article in journal (Refereed)
    Abstract [en]

    The Mn/Si(111)-√3×√3 surface has been studied in detail by low energy electron diffraction (LEED), angle-resolved photoelectron spectroscopy (ARPES), and core-level photoelectron spectroscopy (CLS). Annealing of the deposited manganese resulted in a well-ordered surface as seen by intense √3×√3 LEED spots. ARPES spectra recorded in the Γ̅ -K̅ -M̅ direction of the √3×√3 surface Brillouin zone show five surface related features in the band gap while in the Γ̅ -M̅ -Γ̅ direction four surface features are observed. The high-resolution Si 2p CLS data were recorded at photon energies between 108–140 eV both at normal and 60° emission angle. The bulk component was identified from the bulk sensitive spectrum recorded at a photon energy of 108 eV. To achieve a consistent core-level fitting over the whole energy and angular range, five components were introduced in the line-shape analysis. The photoemission data from the √3×√3 surface have been discussed and compared with a recent theoretical model. The findings here support a layered Mn silicide film structure.

  • 313.
    Holmes, Natalie P.
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). University of Newcastle, Australia.
    Marks, Melissa
    University of Newcastle, Australia.
    Cave, James M.
    University of Bath, United Kingdom.
    Feron, Krishna
    University of Newcastle, Australia.
    Barr, Matthew G.
    University of Newcastle, Australia.
    Fahy, Adam
    University of Newcastle, Australia.
    Sharma, Anirudh
    Flinders University, Australia; University of Bordeaux, France.
    Pan, Xun
    Flinders University, Australia.
    Kilcoyne, David A. L.
    Lawrence Berkeley National Laboratory, United States.
    Zhou, Xiaojing
    University of Newcastle, Australia.
    Lewis, David A.
    Flinders University, Australia.
    Andersson, Mats R.
    Flinders University, Australia.
    van Stam, Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Walker, Alison B.
    University of Bath, United Kingdom.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Belcher, Warwick J.
    University of Newcastle, Australia.
    Dastoor, Paul C.
    University of Newcastle, Australia.
    Engineering Two-Phase and Three-Phase Microstructures from Water-Based Dispersions of Nanoparticles for Eco-Friendly Polymer Solar Cell Applications2018In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 30, no 18, p. 6521-6531Article in journal (Refereed)
    Abstract [en]

    Nanoparticle organic photovoltaics, a subfield of organic photovoltaics (OPV), has attracted increasing interest in recent years due to the eco-friendly fabrication of solar modules afforded by colloidal ink technology. Importantly, using this approach it is now possible to engineer the microstructure of the light absorbing/charge generating layer of organic photovoltaics; decoupling film morphology from film deposition. In this study, single-component nanoparticles of poly(3-hexylthiophene) (P3HT) and phenyl-C61 butyric acid methyl ester (PC61BM) were synthesized and used to generate a two-phase microstructure with control over domain size prior to film deposition. Scanning transmission X-ray microscopy (STXM) and electron microscopy were used to characterize the thin film morphology. Uniquely, the measured microstructure was a direct input for a nanoscopic kinetic Monte Carlo (KMC) model allowing us to assess exciton transport properties that are experimentally inaccessible in these single-component particles. Photoluminescence, UV-vis spectroscopy measurements, and KMC results of the nanoparticle thin films enabled the calculation of an experimental exciton dissociation efficiency (ηED) of 37% for the two-phase microstructure. The glass transition temperature (Tg) of the materials was characterized with dynamic mechanical thermal analysis (DMTA) and thermal annealing led to an increase in ηED to 64% due to an increase in donor-acceptor interfaces in the thin film from both sintering of neighboring opposite-type particles in addition to the generation of a third mixed phase from diffusion of PC61BM into amorphous P3HT domains. As such, this study demonstrates the higher level of control over donor-acceptor film morphology enabled by customizing nanoparticulate colloidal inks, where the optimal three-phase film morphology for an OPV photoactive layer can be designed and engineered.

  • 314.
    Holmes, Natalie P.
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). University of Newcastle, Australia.
    Munday, Holly
    University of Newcastle, Australia.
    Barr, Matthew G.
    University of Newcastle, Australia.
    Thomsen, Lars
    Australian Synchrotron, Australia.
    Marcus, Matthew A.
    Lawrence Berkeley National Laboratory, USA.
    Kilcoyne, A. L. David
    Lawrence Berkeley National Laboratory, USA.
    Fahy, Adam
    University of Newcastle, Australia.
    van Stam, Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Dastoor, Paul C.
    University of Newcastle, Australia.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Unravelling donor–acceptor film morphologyformation for environmentally-friendly OPV inkformulations2019In: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270Article in journal (Refereed)
    Abstract [en]

    The challenge of coating organic photovoltaics (OPV) from green solvents is to achieve the requirednanostructured interpenetrating network of donor and acceptor domains based on a rational choice ofsolvent approach as opposed to the usual trial-and-error methods. We demonstrate here that we canachieve a bicontinuous interpenetrating network with nanoscale phase separation for the chosen donor–acceptor material system poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl]:phenyl-C61 butyric acid methyl ester (TQ1:PC61BM) when processing from green solvent ink formulations.This structure is achieved by first calculating the Hansen solubility parameters (HSP) of the donor andacceptor materials, followed by careful choice of solvents with selective relative solubilities for the twomaterials based on the desired order of precipitation necessary for forming a nanostructured interdigitatednetwork morphology. We found that the relative distances in Hansen space (Ra) between TQ1 andthe primary solvent, on the one hand, and PC61BM and the primary solvent, on the other hand, could becorrelated to the donor–acceptor morphology for the formulations based on the solvents d-limonene,anisole, and 2-methyl anisole, as well as the halogenated reference solvent o-dichlorobenzene. Thisnanostructured blend film morphology was characterised with scanning transmission X-ray microscopy(STXM) and transmission electron microscopy (TEM), and the film surface composition was analysed bynear edge X-ray absorption fine structure (NEXAFS) spectroscopy. Hansen solubility theory, based onsolution thermodynamics, has been used and we propose an HSP-based method that is a general platformfor the rational design of ink formulations for solution-based organic electronics, in particular facilitatingthe green solvent transition of organic photovoltaics. Our results show that the bulk heterojunctionmorphology for a donor–acceptor system processed from customised solvent mixtures can be predictedby the HSP-based method with good reliability.

  • 315. Horzel, Jörg
    et al.
    Seidl, A.
    Buss, W.
    Westram, I.
    Mosel, F.
    Guenther, S.
    Novak, J.
    Sticksel, J.
    Blendin, G.
    Jahn, M.
    Rinio, Markus
    von Campe, H.
    Schmidt, W.
    Inherent material quality advantages for thin EFG si solar cells compared to thick EFG si solar cells2007Conference paper (Other academic)
  • 316.
    Hultgren, Kristoffer
    Karlstad University, Faculty of Technology and Science.
    Cosmological Density Perturbations2007Independent thesis Basic level (degree of Bachelor), 10 points / 15 hpStudent thesis
    Abstract [en]

    This thesis presents a brief review of gravitation and cosmology, and then gives an overview of the theory of cosmological perturbations; subsequently some applications are discussed, such as large-scale structure formation. Cosmological perturbations are here presented both in the Newtonian paradigm and in two di¤erent relativistic approaches. The relativistic approaches are (i) the metric approach, where small variations of the metric tensor are considered, and (ii) the covariant approach, which focusses on small variations of the curvature. Dealing with these two approaches also involves addressing the gauge problem –how to map an idealized world model into a more accurate world model.

  • 317.
    Hwang, Stephen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Semi-infinite cohomology of affine Lie algebras1998In: Commun. Math.Phys. 194, 591-611 (1998)Article in journal (Refereed)
  • 318.
    Hwang, Stephen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Unitarity of Strings and Non-compact Hermitian Symmetric spaces1998In: Physics Letters B435, 331-336 (1998)Article in journal (Refereed)
  • 319.
    Hwang, Stephen
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Fjelstad, Jens
    Equivalence of Chern-Simons gauge theory and the WZNWmodel using a BRST symmetry1999In: Physics Letters B 466 (1999) 227-233Article in journal (Refereed)
  • 320.
    Hwang, Stephen
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Liu, Yang
    Zhang, Genkai
    Hilbert spaces of tensor-valued holomorphic functions on the unit ball of C^n2004In: Pacific J. of Math 214 (2004)Article in journal (Refereed)
  • 321.
    Hwang, Stephen
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Marnelius, Robert
    Saltsidis, Panagiotis
    A general BRST approach to string theories with zeta function regularizations1999In: Journal of Mathematical Physics 40 (1999) 4639-57Article in journal (Refereed)
    Abstract [en]

    Within the operator version of BRST quantization one may proceed as follows: First define a hermitian and formally nilpotent BRST charge. Then look for possible state spaces which yield nontrivial cohomologies. Two of us have previously used this procedure for finite degrees of freedom. In the case of infinite degrees of freedom the procedure requires a precise regularization.

    We propose here a general precise regularization of the basic commutators which makes the divergent sums we encounter to be expressed in terms of Hurwitz zeta function.

    A new feature is that the formally nilpotent BRST operator need not be nilpotent on the found state space. A modification might be necessary.

    The method is applied to three string models: The ordinary bosonic string, the tensionless string and the conformal tensionless string. In the first two models we recover old results, but we believe our treatment further deepens the understanding of the BRST formulation. For the conformal tensionless string model our result is new. Here we show that there is no critical dimension

  • 322.
    Högblad, Jon
    Karlstad University, Division for Engineering Sciences, Physics and Mathematics.
    Auger Electron Spectroscopy of Controlled Delaminating Materials on Aluminium Surfaces2008Independent thesis Basic level (professional degree), 20 points / 30 hpStudent thesis
    Abstract [en]

    This master thesis in physics mainly treats Auger spectroscopy of interfaces that has been adhesively bond together with so called controlled delaminating materials (CDM). CDM is a new technology which involves adhesives with the distinctive property that they by the appliance of electricity can be released from a substrate. The reason for using Auger spectroscopy was that it gives a surface sensitive view of the chemical composition of the samples examined and this was believed to give hints of the mechanisms behind loss of adhesion. The samples were so called laminates which is an aluminium foil, CDM adhesive, aluminium foil structure. As expected Auger spectroscopy produced some promising results, especially regarding the breakdown of a certain anion contained into the examined CDM adhesive. This awoke new questions regarding how this anion was decomposed and the idea that it could be due to hydrolysis took form. The by far most important result within this work is that the anion breaks down. This could lead to the formation of hydrofluoric acid if this breakdown in fact is due to hydrolysis and the hydrofluoric acid could then react with the aluminium causing loss of adhesion. This could be the good starting point of a continuing work on CDM.

  • 323.
    Hörmann, Ulrich
    et al.
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Lorch, Christopher
    Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany.
    Hinderhofer, Alexander
    Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany.
    Gerlach, Alexander
    Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany.
    Gruber, Mark
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Kraus, Julia
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Sykora, Benedikt
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Grob, Stefan
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Linderl, Theresa
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Wilke, Andreas
    Department of Physics, Humboldt University of Berlin, Brook-Taylor-Straße 15, 12489 Berlin, Germany.
    Opitz, Andreas
    Department of Physics, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Anselmo, Ana Sofia
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Ozawa, Yusuke
    Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
    Nakayama, Yasuo
    Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
    Ishii, Hisao
    Center for Frontier Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan and Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
    Koch, Norbert
    Department of Physics, Humboldt University of Berlin, Brook-Taylor-Straße 15, 12489 Berlin, Germany and Helmholtz-Zentrum Berlin für Materialien und Energie GmbH - BESSY II, Albert-Einstein-Straße 15, 12489 Berlin, Germany.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Schreiber, Frank
    Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany.
    Brütting, Wolfgang
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Voc from a Morphology Point of View: the Influence of Molecular Orientation on the Open Circuit Voltage of Organic Planar Heterojunction Solar Cells2014In: Journal of physical chemistry C, ISSN 1932-7455, Vol. 118, no 46, p. 26462-26470Article in journal (Refereed)
    Abstract [en]

    The film morphology and device performance of planar heterojunction

    solar cells based on the molecular donor material α-sexithiophene (6T) are investigated.

    Planar heterojunctions of 6T with two different acceptor molecules, the C60 fullerene and

    diindenoperylene (DIP), have been prepared. The growth temperature of the 6T bottom

    layer has been varied between room temperature and 100 °C for each acceptor. By means

    of X-ray diffraction and X-ray absorption, we show that the crystallinity and the molecular

    orientation of 6T is influenced by the preparation conditions and that the 6T film

    templates the growth of the subsequent acceptor layer. These structural changes are

    accompanied by changes in the characteristic parameters of the corresponding

    photovoltaic cells. This is most prominently observed as a shift of the open circuit

    voltage (Voc): In the case of 6T/C60 heterojunctions, Voc decreases from 0.4 to 0.3 V,

    approximately, if the growth temperature of 6T is increased from room temperature to 100

    °C. By contrast, Voc increases from about 1.2 V to almost 1.4 V in the case of 6T/DIP solar

    cells under the same conditions. We attribute these changes upon substrate heating to

    increased recombination in the C60 case while an orientation dependent intermolecular coupling seems to change the origin of the photovoltaic gap in the DIP case.

  • 324.
    Inglese, Alessandro
    et al.
    Department of Micro- and Nanosciences, Aalto University, Tietotie 3, 02150 Espoo, Finland.
    Focareta, Alessia
    Department of Micro- and Nanosciences, Aalto University, Tietotie 3, 02150 Espoo, Finland.
    Schindler, Florian
    Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstraße 2, 79110 Freiburg im Breisgau, Germany.
    Schön, Jonas
    Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstraße 2, 79110 Freiburg im Breisgau, Germany.
    Lindroos, Jeanette
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Schubert, Martin C.
    Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstraße 2, 79110 Freiburg im Breisgau, Germany.
    Savin, Hele
    Department of Micro- and Nanosciences, Aalto University, Tietotie 3, 02150 Espoo, Finland.
    Light-induced degradation in multicrystalline silicon: the role of copper2016In: PROCEEDINGS OF THE 6TH INTERNATIONAL CONFERENCE ON CRYSTALLINE SILICON PHOTOVOLTAICS (SILICONPV 2016) / [ed] Ribeyron, PJ; Cuevas, A; Weeber, A; Ballif, C; Glunz, S; Poortmans, J; Brendel, R; Aberle, A; Sinton, R; Verlinden, P; Hahn, G, Elsevier, 2016, Vol. 92, p. 808-814Conference paper (Refereed)
    Abstract [en]

    In this contribution, we provide an insight into the light-induced degradation of multicrystalline (mc-) silicon caused by copper contamination. Particularly we analyze the degradation kinetics of intentionally contaminated B- and Ga-doped mc-Si through spatially resolved photoluminescence (PL) imaging. Our results show that even small copper concentrations are capable of causing a strong LID effect in both B- and Ga-doped samples. Furthermore, the light intensity, the dopant and the grain quality were found to strongly impact the degradation kinetics, since faster LID was observed with stronger illumination intensity, B-doping and in the grains featuring low initial lifetime. Interestingly after degradation we also observe the formation of bright denuded zones near the edges of the B-doped grains, which might indicate the possible accumulation of copper impurities at the grain boundaries.

  • 325.
    Inglese, Alessandro
    et al.
    Aalto University.
    Lindroos, Jeanette
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics. Aalto University.
    Savin, Hele
    Aalto University.
    Accelerated light-induced degradation for detecting copper contamination in p-type silicon2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 5, article id 052101Article in journal (Refereed)
  • 326.
    Inglese, Alessandro
    et al.
    Department of Micro- and Nanosciences, Aalto University, Tietotie 3, 02150 Espoo, Finland.
    Lindroos, Jeanette
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Vahlman, Henri
    Department of Micro- and Nanosciences, Aalto University, Tietotie 3, 02150 Espoo, Finland.
    Savin, Hele
    Department of Micro- and Nanosciences, Aalto University, Tietotie 3, 02150 Espoo, Finland.
    Recombination activity of light-activated copper defects in p-type siliconstudied by injection- and temperature-dependent lifetime spectroscopy2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 120, no 12, article id 125703Article in journal (Refereed)
  • 327.
    Irshad, Yasir
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Some estimation concepts applied to networked control systemsManuscript (preprint) (Other academic)
  • 328.
    Irshad, Yasir
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Some problems of modeling and parameter estimation in continous-time for control and communication2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Stochastic system identification is of great interest in the areas of control and communication. In stochastic system identification, a model of a dynamic system is determined based on given inputs and received outputs from the system, where stochastic uncertainties are also involved. The scope of the report is to consider continuous-time models used within control and communication and to estimate the model parameters from sampled data with high accuracy in a computational efficient way. Continuous-time models of systems controlled in a networked environment, stochastic closed-loop systems, and wireless channels are considered. The parameters of a transfer function based model for the process in a networked control system are first estimated by a covariance function based approach, relying upon the second order statistical properties of the output signal. Some other approaches for estimating the parameters of continuous-time models for processes in networked environments are also considered. Further, the parameters of continuous-time autoregressive exogenous models are estimated from closed-loop filtered data, where the controllers in the closed-loop are of proportional and proportional integral type, and where the closed-loop also contains a time-delay. Moreover, a stochastic differential equation is derived for Jakes's wireless channel model, describing the dynamics of a scattered electric field with the moving receiver incorporating a Doppler shift.

  • 329.
    Irshad, Yasir
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Mossberg, Magnus
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Wireless channel modeling based on stochastic differential equations2011Other (Other academic)
  • 330.
    Isaksson, Mikael
    Karlstad University, Faculty of Technology and Science.
    Aspects of spatially homogeneous and isotropic cosmology2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this thesis, after a general introduction, we first review some differential geometry to provide the mathematical background needed to derive the key equations in cosmology. Then we consider the Robertson-Walker geometry and its relationship to cosmography, i.e., how one makes measurements in cosmology. We finally connect the Robertson-Walker geometry to Einstein's field equation to obtain so-called cosmological Friedmann-Lemaître models. These models are subsequently studied by means of potential diagrams.

  • 331.
    Jackman, Henrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Mechanical behaviour of carbon nanostructures2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Abstract

    Carbon nanotubes (CNTs) have extraordinary mechanical and electrical properties. Together with their small dimensions and low density, they are attractive candidates for building blocks in future nanoelectromechanical systems and for many other applications. The extraordinary properties are however only attained by perfectly crystalline CNTs and quickly deteriorate when defects are introduced to the structure. The growth technique affects the crystallinity where in general CNTs grown by arc-discharge are close to perfectly crystalline, while CVD-grown CNTs have large defect densities. Mechanical deformation also affects these properties, even without introducing defects. When CNTs are bent they behave similarly to drinking straws, i.e. they buckle or ripple and their bending stiffness drops abruptly.

    In this thesis, the mechanical behaviour of individual CNTs and vertically aligned carbon nanofibers (VACNFs) has been studied by performing force measurements inside electron microscopes. Cantilevered CNTs, and VACNFs, were bent using a force sensor, yielding force-deflection curves while their structure was imaged simultaneously.

    We have found that CNTs grown by arc-discharge have a high enough crystallinity to possess a Young’s modulus close to the ideal value of 1 TPa. CVD-grown CNTs possess a Young’s modulus that is about one order of magnitude smaller, due to their large defect density. The VACNFs are yet another order of magnitude softer as a result of their cup-stacked internal structure.  We also found that a high defect density will increase the critical strain for the rippling onset and the relative post-rippling stiffness. Multi-walled CNTs with a small inner diameter are less prone to ripple and have a larger relative post-rippling stiffness. Our findings show large variations in the onset of rippling and the bending stiffness before and after rippling. These variations open up possibilities of tailoring the mechanical properties for specific applications.

  • 332.
    Jackman, Henrik
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Mechanical properties of carbon nanotubes and nanofibers2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Carbon nanotubes (CNTs) have extraordinary electrical and mechanical properties, and many potential applications have been proposed, ranging from nanoscale devices to reinforcement of macroscopic structures. However, due to their small sizes, characterization of their mechanical properties and deformation behaviours are major challenges. Theoretical modelling of deformation behaviours has shown that multi-walled carbon nanotubes (MWCNTs) can develop ripples in the walls on the contracted side when bent above a critical curvature. The rippling is reversible and accompanied by a reduction in the bending stiffness of the tubes. This behaviour will have implications for future nanoelectromechanical systems (NEMS). Although rippling has been thoroughly modelled there has been a lack of experimental data thus far. In this study, force measurements have been performed on individual MWCNTs and vertically aligned carbon nanofibers (VACNFs). This was accomplished by using a custom-made atomic force microscope (AFM) inside a scanning electron microscope (SEM). The measurements were done by bending free-standing MWCNTs/VACNFs with the AFM sensor in a cantilever-to-cantilever fashion, providing force-displacement curves. From such curves and the MWCNT/VACNF dimensions, measured from SEM-images, the critical strain for the very onset of rippling and the Young’s modulus, E, could be obtained. To enable accurate estimations of the nanotube diameter, we have developed a model of the SEM-image formation, such that intrinsic diameters can be retrieved. We have found an increase in the critical strain for smaller diameter tubes, a behaviour that compares well with previous theoretical modelling. VACNFs behaved very differently, as they did not display any rippling and had low bending stiffnesses due to inter-wall shear. We believe that our findings will have implications for the design of future NEMS devices that employ MWCNTs and VACNFs.

  • 333.
    Jackman, Henrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Bending modulus of freestanding carbon nanotubes2010Conference paper (Other academic)
  • 334.
    Jackman, Henrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Direct Measurements Of Bending Stiffness And Rippling Phenomena In Free-Standing Carbon Nanotubes2011Conference paper (Refereed)
  • 335.
    Jackman, Henrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    High resolution SEM imaging of carbon nanotubes: deconvolution and retrieval of intrinsic nanotube dimensions2012Conference paper (Refereed)
    Abstract [en]

    Characterizing physical properties of individual nanotubes is crucial for their implementation in nano electromechanical systems (NEMS). This requires measurements on suspended or free-standing structures together with accurate determination of the nanotubes dimensions. In situ methods are often used where physical measurements are performed inside electron microscopes [1-3]. Transmission electron microscopy (TEM) has the advantage of high resolution, providing accurate determination of both dimensions and the internal structure. The space inside a TEM is however rather restricted, leaving limited room for additional probes [4]. Scanning electron microscopy (SEM) on the other hand, has a large specimen chamber which facilitates the addition of probes, but the image resolution is lower, making the evaluation of material properties less accurate or even impossible for very thin nanotubes [1]. One way to solve this is to first measure the physical properties inside an SEM, and then determine the diameter using a TEM afterwards [1]. This approach requires transfer of the nanotube from the SEM to a suitable TEM sample holder, and analysis of the same sample-location in both instruments. It would thereby be advantageous to obtain accurate structural information directly inside the SEM [2]. We have studied the mechanisms involved in SEM image formation of small multiwalled nanotubes, 2-5 nm in diameter. The electron-probe shape in an SEM broadens the sample details, and the image can be seen as a convolution of the secondary electron yield at each sample position and the probe shape. By comparing SEM and TEM images, we found that the probe intensity profile was best described by a linear combination of Gaussian and Lorentzian distributions. Using the obtained probe shape, the SEM images could then be deconvoluted to reveal more details, including the inner diameter in some cases. We also show how the outer diameter can be obtained by differentiating image profiles, a method that does not require any detailed knowledge regarding the probe shape and is reliable down to dimensions comparable to the electron-probe size. This significantly improves the capabilities of in-situ SEM experiments by enabling accurate characterizations of nanofibres inside SEM instruments, without the need for subsequent TEM imaging

  • 336.
    Jackman, Henrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Image formation mechanisms in scanning electron microscopy of carbon nanotubes,and retrieval of their intrinsic dimensions.2013In: Ultramicroscopy, ISSN 0304-3991, Vol. 124, p. 35-39Article in journal (Refereed)
    Abstract [en]

    We present a detailed analysis of the image formation mechanisms that are involved in the imaging of carbon nanotubes with scanning electron microscopy (SEM). We show how SEM images can be modelled by accounting for surface enhancement effects together with the absorption coefficient for secondary electrons, and the electron-probe shape. Images can then be deconvoluted, enabling retrieval of the intrinsic nanotube dimensions. Accurate estimates of their dimensions can thereby be obtained even for structures that are comparable to the electron-probe size (on the order of 2 nm). We also present a simple and robust model for obtaining the outer diameter of nanotubes without any detailed knowledge about the electron-probe shape.

  • 337.
    Jackman, Henrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Large variations in the onset of rippling in concentric nanotubes.2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, article id 021910Article in journal (Refereed)
    Abstract [en]

    We present a detailed experimental study of the onset of rippling in highly crystalline carbon nanotubes. Modeling has shown that there should be a material constant, called the critical length, describing the dependence of the critical strain on the nanotube outer radius. Surprisingly, we have found very large variations, by a factor of three, in the critical length. We attribute this to a supporting effect from the inner walls in multiwalled concentric nanotubes. We provide an analytical expression for the maximum deflection prior to rippling, which is an important design consideration in nanoelectromechanical systems utilizing nanotubes.

  • 338.
    Jackman, Henrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Measurements of the critical strain for rippling in carbon nanotubes2011In: Applied Physics Letters, ISSN 0003-6951, Vol. 98, no 18, p. 3 pages-Article in journal (Refereed)
    Abstract [en]

    We report measurements of the bending stiffness in free standing carbon nanotubes, using atomic force microscopy inside a scanning electron microscope. Two regimes with different bending stiffness were observed, indicative of a rippling deformation at high curvatures. The observed critical strains for rippling were in the order of a few percent and comparable to previous modeling predictions. We have also found indications that the presence of defects can give a higher critical strain value and a concomitant reduction in Youngs modulus.

  • 339.
    Jackman, Henrik
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Svensson, Krister
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Mechanical behavior of carbon nanotubes in the rippled and buckled phase2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 8, p. 084318-Article in journal (Refereed)
    Abstract [en]

    We have studied the mechanical behavior of multi-walled carbon nanotubes for bending strains beyond the onset for rippling and buckling. We found a characteristic drop in the bending stiffness at the rippling and buckling onset and the relative retained stiffness was dependent on the nanotube dimensions and crystallinity. Thin tubes are more prone to buckle, where some lose all of their bending stiffness, while thicker tubes are more prone to ripple and on average retain about 20\% of their bending stiffness. In defect rich tubes the bending stiffness is very low prior to rippling but these tubes retain up to 70\% of their initial bending stiffness.

  • 340.
    Jackman, Henrik
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Svensson, Krister
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Mechanical beviour of carbon nanotubes in the rippled phaseManuscript (preprint) (Other academic)
  • 341.
    Jaczewska, Justyna
    et al.
    Institute of Physics, Jagiellonian University, Krakow, Poland.
    Budkowski, Andrzej
    M. Smoluchowski Insitute of Physics, Jagiellonian University, Reymonta 4, Krakow 30–059, Poland.
    Bernasik, Andrzej
    Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Al. Mickiewicza 30, Krakow 30–059, Poland.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Rysz, Jakub
    M. Smoluchowski Insitute of Physics, Jagiellonian University, Reymonta 4, Krakow 30–059, Poland.
    Polymer vs Solvent Diagram of Film Structures Formed in Spin-Cast Poly(3-alkylthiophene) Blends2008In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 41, p. 4802-4810Article in journal (Refereed)
    Abstract [en]

    A polymer vs solvent diagram of film structures, formed in polystyrene (PS) blends (1:1 w:w PS/PT) with poly(3-alkylthiophenes) PT [regioregular R-P3DDT, R-P3HT and regiorandom P3BT, P3DDT] spincoated onto oxidized silicon surfaces from various common solvents [p-xylene, toluene, chloroform, chlorobenzene, cyclohexanone] is presented. The structures were determined with microscopic techniques (atomic, AFM and lateral, LFM, force microscopy, fluorescent microscopy FM) and dynamic secondary ion mass spectrometry (dSIMS). The diagram, arranged according to the solubility parameter of the PTs and the solvents, exhibits three main structural classes: dewetting, lamellar, and lateral (quasi-2-dim) morphology. Decrease in PT solubility parameter δPT inhibits dewetting of polymer films. It induces also a transition from lamellar to lateral film structure. Increase in solvent solubility parameter δS has similar effects. Such behavior is related to the stability of transient homogeneous films and multilayers in the course of spin-casting. The role of δPT and δS is elucidated based on the stability analysis performed in terms of spreading coefficient (dependent on δPT) and effective interfacial tension of solvent-rich polymer phase (dependent on δS).

  • 342.
    Jaczewska, Justyna
    et al.
    Institute of Physics, Jagiellonian University, Krakow, Poland.
    Budkowski, Andrzej
    M. Smoluchowski Insitute of Physics, Jagiellonian University, Reymonta 4, Krakow 30–059, Poland.
    Bernasik, Andrzej
    Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Al. Mickiewicza 30, Krakow 30–059, Poland.
    Raptis, Ioannis
    Institute of Microelectronics, NCSR ‘‘Demokritos’’, Aghia Paraskevi, Athens 15310, Greece.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Goustouridis, Dimitrios
    Institute of Microelectronics, NCSR ‘‘Demokritos’’, Aghia Paraskevi, Athens 15310, Greece.
    Haberko, Jakub
    Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Al. Mickiewicza 30, Krakow 30–059, Poland.
    Rysz, Jakub
    M. Smoluchowski Insitute of Physics, Jagiellonian University, Reymonta 4, Krakow 30–059, Poland.
    Ordering domains of spin cast blends of conjugated and dielectric polymers on surfaces patterned by soft- and photo-lithography2009In: Soft Matter, ISSN 1744-683X, Vol. 5, no 1, p. 234-241Article in journal (Refereed)
    Abstract [en]

    Spin casting polymer blends of conjugated and dielectric macromolecules onto chemically patterned metal and oxidized silicon surfaces might provide a simple method to fabricate polymer-based circuitries that can be integrated with conventional electronics. Such solution-processing of the blend components offers simultaneous deposition and pattern-directed alignment of the phase separated polymer domains. The alignment is driven by self-organization guided by preferential surface segregation. Here we demonstrate that the laterally arranged domain structures in spin cast films of the

    conjugated poly(3-alkylthiophenes) (P3ATs): P3BT, P3DDT and regioregular R-P3HT, blended with dielectric polystyrene (PS), can be ordered by three different surface templates. The templates are formed by a patterned self-assembled monolayer (SAM), micro-contact printed on the surface of interest, i.e. hexadecanethiols on gold (for alignment of P3DDT/PS blend) and octadecyltrichlorosilanes on oxidized silicon (for R-P3HT/PS). Additionally gold lines are micropatterned on SiO2 with photo-lithography (for P3BT/PS mixture). The forces driving pattern-directed self-organization of the polymers are discussed based on complementary studies of preferential surface segregation, observed for blend films spin cast on homogeneous surfaces that correspond to the different regions of the surface templates

  • 343.
    Jakobsson, Andreas
    et al.
    Karlstad University, Faculty of Arts and Education.
    Butt, Naveed
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Somasundaram, S. D.
    Rowe, M. D.
    Smith, J. A. S.
    Althoefer, K.
    Robust Detection of Stochastic Nuclear Quadrupole Resonance Signals: to appear2009In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 56, no 9, p. 4221-4229Article in journal (Refereed)
  • 344.
    Jakobsson, Liza
    Karlstad University, Faculty of Arts and Social Sciences (starting 2013), Department of Educational Studies (from 2013).
    ”För att de måste sitta ihop, för att kunna åka in överallt”: En studie om att undersöka förskolebarns uppfattningar om elektricitet2018Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The purpose of the study is to determine how pre-school children between the ages of four and six perceive electricity. The study used observation as a method and a field study equipped with a video camera. A semi-structured interview was also conducted to capture the pre-school teacher’s experiences and perceptions of the study. The observation took place on three different occasions: a gathering, a lesson and a reading session. The material used was a fact-based children’s book with associated experimental material and tutorials. The result of the study showed that the children related their knowledge of what electricity is to their daily lives. They could distinguish whether things required electricity,and there was some knowledge that electricity has a source and of electricity's dangers. During the study, pre-school teachers raised both opportunities and challenges to design activities with electricity. The children showed great dedication and general knowledge of electricity and thought that the subject was interesting. There is a need for further education within physics and natural sciences for pre-school teachers. The goal for the pre-school teachers is to create a balance so that each and every child is offered meaningful education.

  • 345.
    Jansson, Anna
    et al.
    Chalmers University of Technology.
    Nafari, Alexandra
    Chalmers University of Technology.
    Hedfalk, Kristina
    Göteborgs Universiet.
    Olsson, Eva
    Chalmers University of Technology.
    Svensson, Krister
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Sanz-Velasco, Anke
    Chalmers Tekniska Högskola.
    Monitoring the osmotic response of single yeast cells through force measurements in the environmental scanning electron microscope2014In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 25, article id 025901Article in journal (Refereed)
    Abstract [en]

    We present a measurement system that combines an environmental scanning electron microscope (ESEM) and an atomic force microscope (AFM). This combination enables studies of static and dynamic mechanical properties of hydrated specimens, such as individual living cells. The integrated AFM sensor provides direct and continuous force measurement based on piezoresistive force transduction, allowing the recording of events in the millisecond range. The in situ ESEM-AFM setup was used to study Pichia pastoris wild-type yeast cells. For the first time, a quantified measure of the osmotic response of an individual yeast cell inside an ESEM is presented. With this technique, cell size changes due to humidity variations can be monitored with nanometre accuracy. In addition, mechanical properties were extracted from load–displacement curves. A Young's modulus of 13–15 MPa was obtained for the Ppastoris yeast cells. The developed method is highly interesting as a complementary tool for the screening of drugs directed towards cellular water transport activity and provides new possibilities of studying mechanosensitive regulation of aquaporins.

  • 346.
    Jansson, Anna
    et al.
    Fysik, Chalmers Tekniska Högskola.
    Nafari, Alexandra
    Sanz-Velasco, Anke
    MC2, Chalmers Tekniska Högskola.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Gustafsson, Stefan
    Fysik, Chalmers Tekniska Högskola.
    Hermansson, Ann-Marie
    Kemi, Chalmers Tekniska Högskola.
    Olsson, Eva
    Fysik, Chalmers Tekniska Högskola.
    Novel Method for Controlled Wetting of Materials in the Environmental Scanning Electron Microscope2013In: Microscopy and Microanalysis, ISSN 1431-9276, E-ISSN 1435-8115, Vol. 19, no 1, p. 30-7Article in journal (Refereed)
    Abstract [en]

    Environmental scanning electron microscopy has been extensively used for studying the wetting properties of different materials. For some types of investigation, however, the traditional ways of conducting in situ dynamic wetting experiments do not offer sufficient control over the wetting process. Here, we present a novel method for controlled wetting of materials in the environmental scanning electron microscope (ESEM). It offers improved control of the point of interaction between the water and the specimen and renders it more accessible for imaging. It also enables the study of water transport through a material by direct imaging. The method is based on the use of a piezo-driven nanomanipulator to bring a specimen in contact with a water reservoir in the ESEM chamber. The water reservoir is established by local condensation on a Peltier-cooled surface. A fixture was designed to make the experimental setup compatible with the standard Peltier cooling stage of the microscope. The developed technique was successfully applied to individual cellulose fibers, and the absorption and transport of water by individual cellulose fibers were imaged.

  • 347.
    Jansson, Anton
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Characterization of epitaxial graphene grown on silicon carbide2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis work several manufacturing methods for graphene is discussed followed by an indepth study of graphene grown by a high temperature sublimation method (sublimation of siliconcarbide). The graphene surfaces studied have been grown by Graphensic AB, both graphenegrown on the Si-face and the C-face of the silicon carbide were studied. Six graphene samplesgrown 4H-SiC substrates were examined for homogeneity and surface morphology as well assome surface roughness parameters using Atomic Force Microscopy (AFM). The graphene wasstudied to get a better understanding of the surfaces and the growth mechanisms to improvemanufacturing parameters while also being informative for graphene sample customers. Anadditional graphene sample grown on 6H-SiC epitaxial layer was also studied to get a betterunderstanding of the sublimation mechanism. If graphene could be manufactured in a cheaprepeatable way the applications are endless and a new era of technology could emerge muchlike the silicon era that began several decades ago. In this thesis work the results are presentedas topography images as well as tables and histograms in the results section. The growth onthe Si-face is found to be well ordered when compared to the C-face which shows signs of alargely complex growth. The graphene on the Si-face lies on top of silicon carbide steps like acarpet with a buer layer interface against the silicon carbide. On the C-face this buer layeris not present but the graphene is deformed by buckling which is suspected to originate fromdierences in thermal properties between the graphene and the C-face. The in uence of AFMsettings for characterization of graphene while using intermittent mode have been evaluated andrecommendations are given. Finally a method for evaluating the homogeneity of the graphenelm is proposed but is in need of further verication.

  • 348. Janßen, Lars
    et al.
    Rinio, Markus
    Borchert, Dietmar
    Windgassen, Horst
    Bätzner, D. L.
    Kurz, H.
    Passivating thin bifacial silicon solar cells for industrial production2007In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 15, no 6, p. 469-475Article in journal (Refereed)
    Abstract [en]

    A scheme for passivating thin multi-crystalline silicon solar cells compatible to massproduction is presented. Wafers with a thickness of 180 mm were processed into solarcells. The otherwise severe bowing has been avoided by reduced aluminium coverageon the rear surface. The process scheme includes a silicon nitride firing through stepfor conventional screen printed contacts, where a silicon nitride layer on the rearsurface acts as surface passivation layer and enables a gain in efficiency of 0.6%[abs.].

  • 349. Janßen, Lars
    et al.
    Rinio, Markus
    Borchert, Dietmar
    Windgassen, Horst
    Bätzner, D. L.
    Kurz, H.
    Thin bifacial multicrystalline silicon solar cells for industrial production2006Conference paper (Other academic)
  • 350. Janßen, Lars
    et al.
    Rinio, Markus
    Windgassen, Horst
    Nositschka, W. A.
    Borchert, Dietmar
    Kurz, H.
    Double sided silicon nitride passivated thin screen printed multicrystalline silicon solar cells2005Conference paper (Other academic)
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