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  • 1.
    Adamczyk, Krzysztof
    et al.
    Department of Materials Science and Engineering, Trondheim, Norway.
    Søndenå, Rune
    Department for Solar Energy, IFE, Kjeller, Norway.
    Stokkan, Gaute
    Sintef Materials and Chemistry, Trondheim, Norway.
    Looney, Erin
    Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
    Jensen, Mallory
    Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
    Lai, Barry
    Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, USA.
    Rinio, Markus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Di Sabatino, Marisa
    Department of Materials Science and Engineering, NTNU, A. Getz vei 2B, NO-7491 Trondheim, Norway.
    Recombination activity of grain boundaries in high-performance multicrystalline Si during solar cell processing2018In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 123, no 5, p. 1-6, article id 055705Article in journal (Refereed)
    Abstract [en]

    In this work, we applied internal quantum efficiency mapping to study the recombination activity of grain boundaries in High Performance Multicrystalline Silicon under different processing conditions. Wafers were divided into groups and underwent different thermal processing, consisting of phosphorus diffusion gettering and surface passivation with hydrogen rich layers. After these thermal treatments, wafers were processed into heterojunction with intrinsic thin layer solar cells. Light Beam Induced Current and Electron Backscatter Diffraction were applied to analyse the influence of thermal treatment during standard solar cell processing on different types of grain boundaries. The results show that after cell processing, most random-angle grain boundaries in the material are well passivated, but small-angle grain boundaries are not well passivated. Special cases of coincidence site lattice grain boundaries with high recombination activity are also found. Based on micro-X-ray fluorescence measurements, a change in the contamination level is suggested as the reason behind their increased activity.

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  • 2.
    Adamczyk, Krzysztof
    et al.
    Department of Materials Science and Engineering, Trondheim, Norway.
    Søndenå, Rune
    Department for Solar Energy, IFE, Kjeller, Norway.
    You, Chang Chuan
    Department for Solar Energy, IFE, Kjeller, Norway.
    Stokkan, Gaute
    Sintef Materials and Chemistry, Trondheim, Norway.
    Lindroos, Jeanette
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Rinio, Markus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Di Sabatino, Marisa
    Department of Materials Science and Engineering, Trondheim, Norway.
    Recombination Strength of Dislocations in High-Performance Multicrystalline/Quasi-Mono Hybrid Wafers During Solar Cell Processing2018In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 215, no 2, article id 1700493Article in journal (Refereed)
    Abstract [en]

    Wafers from a hybrid silicon ingot seeded in part for High Performance Multicrystalline, in part for a quasi-mono structure, are studied in terms of the effect of gettering and hydrogenation on their final Internal Quantum Efficiency.The wafers are thermally processed in different groups – gettered and hydrogenated. Afterwards, a low temperature heterojunction with intrinsic thin layer cell process is applied to minimize the impact of temperature. Such procedure made it possible to study the effect of different processing steps on dislocation clusters in the material using the Light Beam Induced Current technique with a high spatial resolution. The dislocation densities are measuredusing automatic image recognition on polished and etched samples. The dislocation recombination strengths are obtained by a correlation of the IQE with the dislocation density according to the Donolato model. Different clusters are compared after different process steps. The results show that for the middle of the ingot, the gettering step can increase the recombination strength of dislocations by one order of magnitude. A subsequent passivation with layers containing hydrogen can lead to a decrease in the recombination strength to levels lower than in ungettered samples.

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  • 3.
    Ahlskog, Markus
    et al.
    University Jyvaskyla, FIN.
    Hokkanen, Matti J.
    University Jyvaskyla, FIN.
    Levshov, Dmitry
    Southern Federal University, RUS..
    Svensson, Krister
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Volodin, Alexander
    Katholieke University Leuven, BEL.
    van Haesendonck, Chris
    Katholieke University Leuven, BEL.
    Individual arc-discharge synthesized multiwalled carbon nanotubes probed with multiple measurement techniques2020In: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, ISSN 2166-2746, E-ISSN 2166-2754, Vol. 38, no 4, article id 042804Article in journal (Refereed)
    Abstract [en]

    Arc-discharge synthesized multiwalled carbon nanotubes (AD-MWNT), or related MWNTs, exhibit a good quality compared to the more common type of MWNT synthesized by catalytic chemical vapor deposition methods. Yet experimental measurements on these are rather few and typically have not correlated data from different measurement techniques. Here, the authors report Raman spectroscopy, scanning probe microscopy, conductivity measurements, and force microscopy on single AD-MWNTs. The results demonstrate the high quality of AD-MWNTs and are compatible with the view of them as the best approximation of MWNTs as an assembly of defect-free concentric individual single-walled carbon nanotubes. The authors also demonstrate conductance measurements over a step on the surface of an AD-MWNT, which is due to an abruptly broken outer layer(s), whereby the interlayer resistance is measured.

  • 4.
    Alho, Artur
    et al.
    Univ Lisbon, Ctr Math Anal Geometry & Dynam Syst, Inst Super Tecn, Av Rovisco Pais, P-1049001 Lisbon, Portugal..
    Carloni, Sante
    Univ Lisbon, Ctr Multidisciplinar Astrofis CENTRA, Inst Super Tecn, Av Rovisco Pais, P-1049001 Lisbon, Portugal..
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    On dynamical systems approaches and methods in f (R) cosmology2016In: Journal of Cosmology and Astroparticle Physics, E-ISSN 1475-7516, no 8, article id 064Article in journal (Refereed)
    Abstract [en]

    We discuss dynamical systems approaches and methods applied to flat Robertson Walker models in f(R)-gravity. We argue that a complete description of the solution space of a model requires a global state space analysis that motivates globally covering state space adapted variables. This is shown explicitly by an illustrative example, f(R) = R + alpha R-2, alpha > 0, for which we introduce new regular dynamical systems on global compactly extended state spaces for the Jordan and Einstein frames. This example also allows us to illustrate several local and global dynamical systems techniques involving, e.g., blow ups of nilpotent fixed points, center manifold analysis, averaging, and use of monotone functions. As a result of applying dynamical systems methods to globally state space adapted dynamical systems formulations, we obtain pictures of the entire solution spaces in both the Jordan and the Einstein frames. This shows, e.g., that due to the domain of the conformal transformation between the Jordan and Einstein frames, not all the solutions in the Jordan frame are completely contained in the Einstein frame. We also make comparisons with previous dynamical systems approaches to f (R) cosmology and discuss their advantages and disadvantages.

  • 5.
    Alho, Artur
    et al.
    University of Lisbon, Portugal.
    Hell, Juliette
    Free University Berlin, Germany.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Global dynamics and asymptotics for monomial scalar field potentials and perfect fluids2015In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 32, no 14, article id 145005Article in journal (Refereed)
    Abstract [en]

    We consider a minimally coupled scalar field with a monomial potential and a perfect fluid in flat Friedmann-Lemaitre-Robertson-Walker cosmology. We apply local and global dynamical systems techniques to a new three-dimensional dynamical systems reformulation of the field equations on a compact state space. This leads to a visual global description of the solution space and asymptotic behavior. At late times we employ averaging techniques to prove statements about how the relationship between the equation of state of the fluid and the monomial exponent of the scalar field affects asymptotic source dominance and asymptotic manifest self-similarity breaking. We also situate the ’attractor’ solution in the three-dimensional state space and show that it corresponds to the one-dimensional unstable center manifold of a de Sitter fixed point, located on an unphysical boundary associated with the dynamics at early times. By deriving a center manifold expansion we obtain approximate expressions for the attractor solution. We subsequently improve the accuracy and range of the approximation by means of Pade approximants and compare with the slow-roll approximation. 

  • 6.
    Alho, Artur
    et al.
    Universidade de Lisboa, Portugal.
    Lim, Woei Chet
    University of Waikato, New Zealand.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Cosmological global dynamical systems analysis2022In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 39, no 14, p. 1-14, article id 145010Article in journal (Refereed)
    Abstract [en]

    We consider a dynamical systems formulation for models with an exponential scalar field and matter with a linear equation of state in a spatially flat and isotropic spacetime. In contrast to earlier work, which only considered linear hyperbolic fixed point analysis, we do a center manifold analysis of the non-hyperbolic fixed points associated with bifurcations. More importantly though, we construct monotonic functions and a Dulac function. Together with the complete local fixed point analysis this leads to proofs that describe the entire global dynamics of these models, thereby complementing previous local results in the literature. 

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  • 7.
    Alho, Artur
    et al.
    Technical University of Lisbon, Portugal.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Global dynamics and inflationary center manifold and slow-roll approximants2015In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 56, no 1, article id 012502Article in journal (Refereed)
    Abstract [en]

    We consider the familiar problem of a minimally coupled scalar field with quadratic potential in flat Friedmann-Lemaître-Robertson-Walker cosmology to illustrate a number of techniques and tools, which can be applied to a wide range of scalar field potentials and problems in, e.g., modified gravity. We present a global and regular dynamical systems description that yields a global understanding of the solution space, including asymptotic features. We introduce dynamical systems techniques such as center manifold expansions and use Padé approximants to obtain improved approximations for the “attractor solution” at early times. We also show that future asymptotic behavior is associated with a limit cycle, which shows that manifest self-similarity is asymptotically broken toward the future and gives approximate expressions for this behavior. We then combine these results to obtain global approximations for the attractor solution, which, e.g., might be used in the context of global measures. In addition, we elucidate the connection between slow-roll based approximations and the attractor solution, and compare these approximations with the center manifold based approximants.

  • 8.
    Alho, Artur
    et al.
    Center for Mathematical Analysis, Geometry and Dynamical Systems, Instituto Superior Técnico, Universidade de Lisboa, Portugal.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Inflationary alpha-attractor cosmology: A global dynamical systems perspective2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 95, no 8, article id 083517Article in journal (Refereed)
    Abstract [en]

    We study flat Friedmann-Lemaitre-Robertson-Walker alpha-attractor E- and T-models by introducing a dynamical systems framework that yields regularized unconstrained field equations on two-dimensional compact state spaces. This results in both illustrative figures and a complete description of the entire solution spaces of these models, including asymptotics. In particular, it is shown that observational viability, which requires a sufficient number of e-folds, is associated with a particular solution given by a one-dimensional center manifold of a past asymptotic de Sitter state, where the center manifold structure also explains why nearby solutions are attracted to this "inflationary attractor solution." A center manifold expansion yields a description of the inflationary regime with arbitrary analytic accuracy, where the slow-roll approximation asymptotically describes the tangency condition of the center manifold at the asymptotic de Sitter state.

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  • 9.
    Alho, Artur
    et al.
    Universidade de Lisboa, Portugal.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Quintessential α-attractor inflation: a dynamical systems analysis2023In: Journal of Cosmology and Astroparticle Physics, E-ISSN 1475-7516, no 11, article id 083Article in journal (Refereed)
    Abstract [en]

    The equations for quintessential alpha-attractor inflation with a single scalar field, radiation and matter in a spatially flat FLRW spacetime are recast into a regular dynamical system on a compact state space. This enables a complete description of the solution space of these models. The inflationary attractor solution is shown to correspond to the unstable center manifold of a de Sitter fixed point, and we describe connections between slow-roll and dynamical systems approximations for this solution, including Pade approximants. We also introduce a new method for systematically obtaining initial data for quintessence evolution by using dynamical systems properties; in particular, this method exploits that there exists a radiation dominated line of fixed points with an unstable quintessence attractor submanifold, which plays a role that is reminiscent of that of the inflationary attractor solution for inflation.

  • 10.
    Alho, Artur
    et al.
    Univ Lisbon, Inst Super Tecn, Ctr Math Anal Geometry & Dynam Syst, P-1049001 Lisbon, Portugal..
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Scalar field deformations of Lambda CDM cosmology2015In: Physical Review D, ISSN 1550-7998, Vol. 92, no 10, article id 103502Article in journal (Refereed)
    Abstract [en]

    This paper treats nonrelativistic matter and a scalar field phi with a monotonically decreasing potential minimally coupled to gravity in flat Friedmann-Lemaitre-Robertson-Walker cosmology. The field equations are reformulated as a three-dimensional dynamical system on an extended compact state space, complemented with cosmographic diagrams. A dynamical systems analysis provides global dynamical results describing possible asymptotic behavior. It is shown that one should impose global and asymptotic bounds on lambda = -V-1 dV/d phi to obtain viable cosmological models that continuously deform Lambda CDM cosmology. In particular we introduce a regularized inverse power-law potential as a simple specific example.

  • 11.
    Alho, Artur
    et al.
    University Lisbon, PRT.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Wainwright, John
    University Waterloo, CAN.
    Dynamical systems in perturbative scalar field cosmology2020In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 37, no 22, article id 225011Article in journal (Refereed)
    Abstract [en]

    We derive a newregulardynamical system on a three-dimensionalcompactstate space describing linear scalar perturbations of spatially flat Robertson-Walker geometries for relativistic models with a minimally coupled scalar field with an exponential potential. This enables us to construct the global solution space, illustrated with figures, where known solutions are shown to reside on special invariant sets. We also use our dynamical systems approach to obtain new results about the comoving and uniform density curvature perturbations. Finally we show how to extend our approach to more general scalar field potentials. This leads to state spaces where the state space of the models with an exponential potential appears as invariant boundary sets, thereby illustrating their role as building blocks in a hierarchy of increasingly complex cosmological models.

  • 12.
    Alho, Artur
    et al.
    Univ Lisbon, Portugal..
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Wainwright, John
    Univ Waterloo, Canada..
    Perturbations of the Lambda-CDM model in a dynamical systems perspective2019In: Journal of Cosmology and Astroparticle Physics, E-ISSN 1475-7516, no 9, article id 045Article in journal (Refereed)
    Abstract [en]

    The observational success and simplicity of the ACDM model, and the explicit analytic perturbations thereof, set the standard for any alternative cosmology. It therefore serves as a comparison ground and as a test case for methods which can be extended and applied to other cosmological models. In this paper we introduce dynamical systems and methods to describe linear scalar and tensor perturbations of the ACDM model, which serve as pedagogical examples that show the global illustrative powers of dynamical systems in the context of cosmological perturbations. We also study the asymptotic properties of the shear and Weyl tensors and discuss the validity of the perturbations as approximations to the Einstein field equations. Furthermore, we give a new approximation for the linear growth 5 rate, f (z) = d ln delta/d ln a = Omega(6/11)(m) - 1/70(1-Omega(m))(5/2), where z is the cosmological redshift, Omega(m) = Omega(m)(z), while a is the background scale factor, and show that it is much more accurate than the previous ones in the literature.

  • 13.
    Alho, Artur
    et al.
    Universidade de Lisboa, PRT.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Wainwright, John
    University of Waterloo, CAN.
    Quintessence from a state space perspective2023In: Physics of the Dark Universe, E-ISSN 2212-6864, Vol. 39, article id 101146Article in journal (Refereed)
    Abstract [en]

    We use dynamical systems methods to study quintessence models in a spatially flat and isotropic spacetime with matter and a scalar field with potentials for which lambda(v) = -V,v/V is bounded, thereby going beyond the exponential potential for which lambda(v) is constant. The scalar field equation of state parameter wv plays a central role when comparing quintessence models with observations, but with the dynamical systems used to date wv is an indeterminate, discontinuous, function on the state space in the asymptotically matter dominated regime. Our first main result is the introduction of new variables that lead to a regular dynamical system on a bounded three-dimensional state space on which wv is a regular function. The solution trajectories in the state space then provide a visualization of different types of quintessence evolution, and how initial conditions affect the transition between the matter and scalar field dominated epochs; this is complemented by graphs wv(N), where N is the e-fold time, which enables characterizing different types of quintessence evolution.

  • 14.
    Alho, Artur
    et al.
    Universidade de Lisboa, Portugal.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Wainwright, John
    University of Waterloo, Canada.
    Tracking Quintessence2024In: Physics of the Dark Universe, E-ISSN 2212-6864, Vol. 44, article id 101433Article in journal (Refereed)
    Abstract [en]

    Tracking quintessence, in a spatially flat and isotropic space–time with a minimally coupled canonical scalar field and an asymptotically inverse power-law potential V(φ)∝φ−p, p>0, as φ→0, is investigated. This is done by introducing a new three-dimensional regular dynamical system, which enables a rigorous explanation of the tracking feature: (1) The dynamical system has a tracker fixed point T with a two-dimensional stable manifold that pushes an open set of nearby solutions toward a single tracker solution originating from T. (2) All solutions, including the tracker solution and the solutions that track/shadow it, end at a common future attractor fixed point that depends on the potential. Thus, the open set of solutions that shadow the tracker solution share its properties during the tracking quintessence epoch. We also discuss similarities and differences of underlying mechanisms for tracking, thawing and scaling freezing quintessence, and, moreover, we illustrate with state space pictures that all of these types of quintessence exist simultaneously for certain potentials. 

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  • 15.
    Al-Jaff, Mohammed
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    The ZX-Calculus: A graphical calculus for multipartite qubit systems2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this thesis we will give a presentation of a graphical/diagrammatic calculus for quantum systems involving interacting quantum observables such as multi-partite systems of qubits, the ZX-Calculus. Unlike the Hilbert space formulation of quantum mechanics, the ZX-Calculus is based on category theory, more specically on the notion of a compact dagger symmetric monoidal category and as a consequence the graphical language associated with such a category is inherited by the calculus. This enables us to think about and deal with many calculations in quantum computation and information in a purely graphical and intuitive fashion. Although being formulated in a more general mathematical framework, huge parts of the Hilbert space formulation of quantum mechanics can be extracted from the ZX-calculus. In this thesis we will begin by giving a motivation for the need of such a calculus and then key concepts of category theory will be introduced in an intuitive manner in order to understand the ZX-calculus that will be presented afterwards. We then apply the calculus to'model' and describe certain quantum circuits and quantum teleportation.

  • 16.
    Allan, Dan
    et al.
    Stockholm University.
    Hörnedal, Niklas
    Stockholm University.
    Andersson, Ole
    Stockholm University.
    Time-optimal quantum transformations with bounded bandwidth2021In: Quantum, E-ISSN 2521-327X, Vol. 5, p. 1-19, article id 462Article in journal (Refereed)
    Abstract [en]

    In this paper, we derive sharp lower bounds, also known as quantum speed limits, for the time it takes to transform a quantum system into a state such that an observable assumes its lowest average value. We assume that the system is initially in an incoherent state relative to the observable and that the state evolves according to a von Neumann equation with a Hamiltonian whose bandwidth is uniformly bounded. The transformation time depends intricately on the observable's and the initial state's eigenvalue spectrum and the relative constellation of the associated eigenspaces. The problem of finding quantum speed limits consequently divides into different cases requiring different strategies. We derive quantum speed limits in a large number of cases, and we simultaneously develop a method to break down complex cases into manageable ones. The derivations involve both combinatorial and differential geometric techniques. We also study multipartite systems and show that allowing correlations between the parts can speed up the transformation time. In a final section, we use the quantum speed limits to obtain upper bounds on the power with which energy can be extracted from quantum batteries.

  • 17. Almotasem, Ahmed
    et al.
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Gåård, Anders
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Holleboom, Thijs Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    A molecular dynamic study on the influence of carbide particles in ferrite on material transfer during nanoscratching of ferritic iron2016In: Proceedings of the 10th International Tool Conference: TOOL, 10th International TOOL Conference : 04th to 07th October 2016, Bratislava, Slovakia / [ed] Simancik, Frantisek, 2016Conference paper (Refereed)
  • 18.
    Almén, Anton
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Photophysics of the polymer acceptor PF5-Y5 in organic photovoltaics: A first principles theory based study2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Non-fullerene Acceptors (NFAs) have gathered a great deal of interest for use inorganic photovoltaics (OPVs) due to recent breakthroughs in their power conversion efficiency and other advantages they offer over their Fullerene-based counterparts.

    In this work, a new promising non-fullerene polymer acceptor, PF5-Y5, have been studied using density functional theory and time-dependent density functional theory; and the effects that oligomer length, geometry relaxation and exchange-correlation interaction has on the exciton binding energies (the difference between optical and fundamental energy gaps) have been investigated.

    Both the fundamental and optical gaps are significantly affected by the choice of functional (i.e., the description of the exchange-correlation interaction). However, it does not appear to significantly impact obtained exciton binding energies as the effects of the fundamental and optical gaps cancel each other out.

    Both the fundamental and optical energy gap are shown to slightly reduce as a function of the oligomer length (~0.1 - 0.3 𝑒𝑉 reduction for each repeated monomer). As both gaps are reduced by a similar amount per repeated monomer, they counteract each other and the total effect that oligomer length has on the exciton binding energy is very low.

    Geometry relaxation and thermal effects showed the largest impact on the fundamental gap and exciton binding energy, with their combined effect resulting in a ~0.5 𝑒𝑉 reduction in binding energy. 

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  • 19.
    Andersson, Jonatan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    A lattice model for topological phases2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Matter exists in many different phases, for example in solid state or in liquid phase. There are also phases in which the ordering of atoms is the same, but which differ in some other respect, for example ferromagnetic and paramagnetic states. According to Landau's symmetry breaking theory every phase transition is connected to a symmetry breaking process. A solid material has discrete translational symmetry, while liquid phase has continuous translational symmetry. But it has turned out that there also exist phase transitions that can occur without a symmetry breaking. This phenomenon is called topological order. In this thesis we consider one example of a theoretical model constructed on a two dimensional lattice in which one obtains topological order.

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  • 20.
    Andersson, Jonatan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    AFM study of Micro Fibrllated Cellulose, (MFC) in controlled atmosphere2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis, Atomic Force Microscopy (AFM) is used to characterize Micro Fibrillated Cellulose (MFC) produced by two different methods according to their size and shape. For one of these MFC-types, their interaction with the humidity in the atmosphere is investigated and their swelling is calculated. MFC is a relatively new material based on cellulose fibres extracted from wood. This study is performed in co-operation with Stora Enso research centre. Stora Enso is a renewable material company which uses mostly wood based raw materials in their production. The measured swelling is ~ 5 % and depends on the number of elementary fibrils included in the fibre.

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  • 21. Andersson, Lars
    et al.
    van Elst, Henk
    Lim, Woei Chet
    Uggla, Claes
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Asymptotic silence of generic cosmological singularities2005In: Phys.Rev.Lett. 94 (2005) 051101Article in journal (Refereed)
    Abstract [en]

    In this letter we investigate the nature of generic cosmological singularities using the framework developed by Uggla et al. We do so by studying the past asymptotic dynamics of general vacuum G2 cosmologies, models that are expected to capture the singular behavior of generic cosmologies with no symmetries at all. In particular, our results indicate that asymptotic silence holds, i.e., that particle horizons along all timelines shrink to zero for generic solutions. Moreover, we provide evidence that spatial derivatives become dynamically insignificant along generic timelines, and that the evolution into the past along such timelines is governed by an asymptotic dynamical system which is associated with an invariant set -- the silent boundary. We also identify an attracting subset on the silent boundary that organizes the oscillatory dynamics of generic timelines in the singular regime. In addition, we discuss the dynamics associated with recurring spike formation

  • 22. Andersson, Lars
    et al.
    van Elst, Henk
    Uggla, Claes
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Gowdy phenomenology in scale-invariant variables2004In: Class.Quant.Grav. 21 (2004) S29-S57Article in journal (Refereed)
    Abstract [en]

    The dynamics of Gowdy vacuum spacetimes is considered in terms of Hubble-normalized scale-invariant variables, using the timelike area temporal gauge. The resulting state space formulation provides for a simple mechanism for the formation of ``false'' and ``true spikes'' in the approach to the singularity, and a geometrical formulation for the local attractor

  • 23.
    Andersson, Mattias
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Scalar fields on star graphs2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

     A star graph consists of a vertex to which a set of edges are connected. Such an object can be used to, among other things, model the electromagnetic properties of quantum wires. A scalar field theory is constructed on the star graph and its properties are investigated. It turns out that there exist Kirchoff's rules for the conserved charges in the system leading to restrictions of the possible type of boundary conditions at the vertex. Scale invariant boundary conditions are investigated in detail.

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  • 24.
    Andersson, Mattias
    Karlstad University, Faculty of Technology and Science.
    Yang-Baxter equations for systems with boundaries and defects2009Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    The Yang-Baxter equation appear in various situations in physics and mathematics. For example it arises as a consistency condition in integrable models. The reflection equation (boundary Yang-Baxter equation) is a generalization of the Yang-Baxter equation to systems with a boundary. A further generalization to systems with defects which admits both reflection and transmission can be made, which results in reflection-transmission Yang-Baxter equations.In this thesis the Yang-Baxter equation and the reflection equation are presented. Representations of the Temperley-Lieb algebra and the blob algebra are used to construct matrices which solve the respective equations. For the reflection-transmission Yang-Baxter equations, steps toward a solution are taken by using a similar approach as for the first two cases, namely by finding an algebra whose representations can be used to construct matrices which solve the equations.

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  • 25.
    ANDERSSON, MONICA
    Karlstad University, Faculty of Arts and Social Sciences (starting 2013), Department of Educational Studies (from 2013).
    ”Barnens intresse styr över hur vi arbetar med naturvetenskap och teknik i förskolan”: En studie av förskollärarens sätt att beskriva hur de kan tillvarata och utveckla de yngsta barnens, 1–3 år, intresse för ämnena fysik och teknik2019Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of this study is to gain an in-depth understanding of how a preschool can work with the subjects of science and technology in a well-thought-out way. The purpose of the study is also to provide more knowledge about which different ways pedagogues can use and develop the children's interest in technology and physics. The study is qualitative and has been carried out by studying documentation from social media published by the preschool. The documentation has since been a basis for the semi-structured interviews that were conducted. To reach the result, the phenomenographic analysis model has been used.

    The result shows that the three teachers interviewed at this preschool see no obstacles to working with the subjects of science and technology with the youngest children, 1-3 years, even though they lack a formal in-depth education in the subjects. The preschool teachers only see opportunities. To create the best conditions for teaching science and technology the preschool has worked out a community of practice inspired by Reggio Emilia.

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  • 26.
    Andersson, Ole
    Stockholms universitet, Fysikum.
    Holonomy in Quantum Information Geometry2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis we provide a uniform treatment of the two most popular non-adiabatic geometric phases for dynamical systems of mixed quantum states, namely those of Uhlmann and of Sjöqvist et al. We develop a holonomy theory for the latter which we also relate to the already existing theory for the former. This makes it clear what the similarities and differences between the two geometric phases are. We discuss and motivate constraints on the two phases. Furthermore, we discuss some topological properties of the holonomy of `real' quantum systems, and we introduce higher-order geometric phases for not necessarily cyclic dynamical systems of mixed states. In a final chapter we apply the theory developed for the geometric phase of Sjöqvist et al. to geometric uncertainty relations, including some new "quantum speed limits''.

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  • 27.
    Andersson, Ole
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013). Stockholm University.
    Badziag, Piotr
    Stockholm University.
    Bengtsson, Ingemar
    Stockholm University.
    Dumitru, Irina
    Stockholm University.
    Cabello, Adan
    Universidad de Sevilla, Spain.
    Self-testing properties of Gisin's elegant Bell inequality2017In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 96, no 3, article id 032119Article in journal (Refereed)
    Abstract [en]

    An experiment in which the Clauser-Horne-Shimony-Holt inequality is maximally violated is self-testing (i.e., it certifies in a device-independent way both the state and the measurements). We prove that an experiment maximally violating Gisin's elegant Bell inequality is not similarly self-testing. The reason can be traced back to the problem of distinguishing an operator from its complex conjugate. We provide a complete and explicit characterization of all scenarios in which the elegant Bell inequality is maximally violated. This enables us to see exactly how the problem plays out.

  • 28.
    Andersson, Ole
    et al.
    Stockholm University.
    Badziąg, Piotr
    Stockholm University.
    Dumitru, Irina
    Stockholm University.
    Cabello, Adán
    Universidad de Sevilla, Spain.
    Device-independent certification of two bits of randomness from one entangled bit and Gisin's elegant Bell inequality2018In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 97, no 1, article id 012314Article in journal (Refereed)
    Abstract [en]

    We prove that as conjectured by Acín et al. [Phys. Rev. A 93, 040102(R) (2016)], two bits of randomness can be certified in a device-independent way from one bit of entanglement using the maximal quantum violation of Gisin's elegant Bell inequality. This suggests a surprising connection between maximal entanglement, complete sets of mutually unbiased bases, and elements of symmetric informationally complete positive operator-valued measures, on one side, and the optimal way of certifying maximal randomness, on the other.

  • 29.
    Andersson, Ole
    et al.
    Stockholm University.
    Bengtsson, Ingemar
    Stockholm University.
    Clifford tori and unbiased vectors2017In: Reports on mathematical physics, ISSN 0034-4877, E-ISSN 1879-0674, Vol. 79, no 1, p. 33-51Article in journal (Refereed)
    Abstract [en]

    The existence problem for mutually unbiased bases is an unsolved problem in quantum information theory. A related question is whether every pair of bases admits vectors that are unbiased to both. Mathematically this translates to the question whether two Lagrangian Clifford tori intersect, and a body of results exists concerning it. These results are however rather weak from the point of view of the first problem. We make a detailed study of how the intersections behave in the simplest nontrivial case, that of complex projective 2-space (the qutrit), for which the set of pairs of Clifford tori can be usefully parametrized by the unistochastic subset of Birkhoff's polytope. Pairs that do not intersect transversally are located. Some calculations in higher dimensions are included to see which results are special to the qutrit.

  • 30.
    Andersson, Ole
    et al.
    Dept. of Physics, Stockholm University, Sweden.
    Bengtsson, Ingemar
    Dept. of Physics, Stockholm University, Sweden.
    Ericsson, Marie
    Uppsala universitet, Kvantkemi.
    Sjöqvist, Erik
    Uppsala universitet, Institutionen för fysik och astronomi.
    Geometric phases for mixed states of the Kitaev chain2016In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 374, no 2069, article id 20150231Article in journal (Refereed)
    Abstract [en]

    The Berry phase has found applications in building topological order parameters for certain condensed matter systems. The question whether some geometric phase for mixed states can serve the same purpose has been raised, and proposals are on the table. We analyze the intricate behaviour of Uhlmann’s geometric phase in the Kitaev chain at finite temperature, and then argue that it captures quite different physics from that intended. We also analyze the behaviour of a geometric phase introduced in the context of interferometry. For the Kitaev chain, this phase closely mirrors that of the Berry phase, and we argue that it merits further investigation. 

  • 31.
    Andersson, Ole
    et al.
    Stockholm University.
    Dumitru, Irina
    Stockholm University.
    Aligned SICs and embedded tight frames in even dimensions2019In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, E-ISSN 1751-8121, Vol. 52, no 42, article id 425302Article in journal (Refereed)
    Abstract [en]

    Alignment is a geometric relation between pairs of Weyl-Heisenberg SICs, one in dimension d and another in dimension d(d - 2), manifesting a well-founded conjecture about a number-theoretical connection between the SICs. In this paper, we prove that if d is even, the SIC in dimension d(d - 2) of an aligned pair can be partitioned into (d - 2)(2) tight d(2)-frames of rank d(d - 1)/2 and, alternatively, into d(2) tight (d - 2)(2) -frames of rank (d - 1) (d - 2)/2. The corresponding result for odd d is already known, but the proof for odd d relies on results which are not available for even d. We develop methods that allow us to overcome this issue. In addition, we provide a relatively detailed study of parity operators in the Clifford group, emphasizing differences in the theory of parity operators in even and odd dimensions and discussing consequences due to such differences. In a final section, we study implications of alignment for the symmetry of the SIC.

  • 32.
    Andersson, Ole
    et al.
    Stockholm University.
    Heydari, Hoshang
    Stockholm University.
    A symmetry approach to geometric phase for quantum ensembles2015In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, E-ISSN 1751-8121, Vol. 48, no 48, article id 485302Article in journal (Refereed)
    Abstract [en]

    We use tools from the theory of dynamical systems with symmetries to stratify Uhlmann's standard purification bundle and derive a new connection for mixed quantum states. For unitarily evolving systems, this connection gives rise to the 'interferometric' geometric phase of Sjqvist et al (2000 Phys. Rev. Lett. 85 2845-9), and for more generally evolving open systems it gives rise to the generalization of the interferometric geometric phase due to Tong et al (2004 Phys. Rev. Lett. 93 080405).

  • 33.
    Andersson, Ole
    et al.
    Stockholms universitet, Fysikum.
    Heydari, Hoshang
    Stockholms universitet, Fysikum.
    Dynamic Distance Measure on Spaces of Isospectral Mixed Quantum States2013In: Entropy, E-ISSN 1099-4300, Vol. 15, no 9, p. 3688-3697Article in journal (Refereed)
    Abstract [en]

    Distance measures are used to quantify the extent to which information is preserved or altered by quantum processes, and thus are indispensable tools in quantum information and quantum computing. In this paper we propose a new distance measure for mixed quantum states, which we call the dynamic distance measure, and we show that it is a proper distance measure. The dynamic distance measure is defined in terms of a measurable quantity, which makes it suitable for applications. In a final section we compare the dynamic distance measure with the well-known Bures distance measure.

  • 34.
    Andersson, Ole
    et al.
    Stockholms universitet, Fysikum.
    Heydari, Hoshang
    Stockholms universitet, Fysikum.
    Geometric uncertainty relation for mixed quantum states2014In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 55, no 4, article id 042110Article in journal (Refereed)
    Abstract [en]

    In this paper we use symplectic reduction in an Uhlmann bundle to construct a principal fiber bundle over a general space of unitarily equivalent mixed quantum states. The bundle, which generalizes the Hopf bundle for pure states, gives in a canonical way rise to a Riemannian metric and a symplectic structure on the base space. With these we derive a geometric uncertainty relation for observables acting on quantum systems in mixed states. We also give a geometric proof of the classical Robertson-Schrodinger uncertainty relation, and we compare the two. They turn out not to be equivalent, because of the multiple dimensions of the gauge group for general mixed states. We give examples of observables for which the geometric relation provides a stronger estimate than that of Robertson and Schrodinger, and vice versa.

  • 35.
    Andersson, Ole
    et al.
    Stockholms universitet, Fysikum.
    Heydari, Hoshang
    Stockholms universitet, Fysikum.
    Geometry of quantum evolution for mixed quantum states2014In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T160, article id 014004Article in journal (Refereed)
    Abstract [en]

    The geometric formulation of quantum mechanics is a very interesting field of research which has many applications in the emerging field of quantum computation and quantum information, such as schemes for optimal quantum computers. In this work we discuss a geometric formulation of mixed quantum states represented by density operators. Our formulation is based on principal fiber bundles and purifications of quantum states. In our construction, the Riemannian metric and symplectic form on the total space are induced from the real and imaginary parts of the Hilbert-Schmidt Hermitian inner product, and we define a mechanical connection in terms of a locked inertia tensor and moment map. We also discuss some applications of our geometric framework.

  • 36.
    Andersson, Ole
    et al.
    Stockholms universitet, Fysikum.
    Heydari, Hoshang
    Stockholms universitet, Fysikum.
    Quantum speed limits and optimal Hamiltonians for driven systems in mixed states2014In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, E-ISSN 1751-8121, Vol. 47, no 21, article id 215301Article in journal (Refereed)
    Abstract [en]

    Inequalities of Mandelstam-Tamm (MT) and Margolus-Levitin (ML) type provide lower bounds on the time that it takes for a quantum system to evolve from one state into another. Knowledge of such bounds, called quantum speed limits, is of utmost importance in virtually all areas of physics, where determination of the minimum time required for a quantum process is of interest. Most MT and ML inequalities found in the literature have been derived from growth estimates for the Bures length, which is a statistical distance measure. In this paper we derive such inequalities by differential geometric methods, and we compare the quantum speed limits obtained with those involving the Bures length. We also characterize the Hamiltonians which optimize the evolution time for generic finite-level quantum systems.

  • 37.
    Andersson, Ole
    et al.
    Stockholms universitet, Fysikum.
    Heydari, Hoshang
    Stockholms universitet, Fysikum.
    Spectral weighted geometric phase for mixed quantum states2014In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T163, article id 014027Article in journal (Refereed)
    Abstract [en]

    Geometric phase has found a broad spectrum of applications in both classical and quantum physics. In this work we discuss a geometric phase for mixed quantum states based on traces of spectral weighted holonomies. Our approach applies to general unitary evolutions of both nondegenerate and degenerate mixed states, and it generalizes the standard definition of geometric phase for mixed states, which is based on quantum interferometry. We provide an explicit formula for the geometric phase that can be easily implemented for computations in quantum physics, and we discuss higher order analogs of the geometric phase that might be defined at points where the ordinary geometric phase is undefined.

  • 38.
    Andersson, Roger
    Karlstad University, Faculty of Technology and Science.
    Teaching and learning geometrical optics with computer assisted instruction: changing conceptions about vision, image and ray2007Report (Other academic)
    Abstract [en]

    The information and communication technology, ICT, is opening new possibilities for the educational arena. Previous research shows that achieving positive educational outcomes requires more than simply providing access to computer hardware and software. How does this new technology affect the teaching and learning of physics? This thesis focuses on the field of geometrical optics. It reports two studies, both in Swedish upper secondary school. Important for the use of the ICT in physics education is the teaching strategy for using the new technology. The first study investigates with a questionnaire, how 37 teachers in a region of Sweden use computers in physics education and what intentions they follow while doing so. The results of this study show that teachers’ intentions for using ICT in their physics teaching were to increase students' interest for physics, to increase their motivation, to achieve variation in teaching, and to improve visualization and explanation of the phenomena of physics. The second study investigates students’ conceptual change in geometrical optics during a teaching sequence with computer-assisted instruction. For this purpose we choose the computer software "Constructing Physics Understanding (CPU)", which was developed with a base in research on students conceptions in optics. The thesis presents the teaching sequence developed together with the teacher. The study is based on a constructivist view of learning. The concepts analysed in this study were vision, image, ray and image formation. A first result of this study is a category system for conceptions around these concepts, found among the students. With these categories we found that students even at this level, of upper secondary school, have constructed well-known alternative conceptions before teaching, e.g. about a holistic conception of image. The results show also some learning progress: some alternative conceptions vanish, in some cases the physics conceptions are more often constructed after teaching. The students and the teacher also report that the CPU program gave new and useful opportunities to model multiple rays and to model vision.

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  • 39. Andersson, S.
    et al.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Dissociation of Physisorbed H_ $$2$$ through Low-Energy Electron Scattering Resonances2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, p. 216101-216105Article in journal (Refereed)
    Abstract [en]

    Electron induced dissociation of physisorbed H2, HD, and D2 proceeds, as we observe in electron energy-loss measurements of the resulting atomic species, with a high quantum efficiency via the 2Σg+ core excited electron scattering resonances. We find that the predominant decay of the temporary H2- state to the neutral excited 3Σu+ parent state, which is intramolecularly antibonding, provides a sufficiently long-lived channel for dissociation to occur with high probability, even in the proximity of a metal surface.

  • 40.
    Andersson, S.
    et al.
    Department of Physics, Göteborg University.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Electron-Induced Desorption of Physisorbed H_ $$2$$ via Resonance Vibrational Excitation2009In: Physical review letters, ISSN 0031-9007, Vol. 102, no Issue 15, p. 156104-Article in journal (Refereed)
    Abstract [en]

    We show by electron energy-loss measurements that desorption of physisorbed H2 and D2 induced by low-energy electrons takes place with large cross sections, predominantly via resonance excitation of the molecule-surface vibrational mode. The observed H2, D2 cross-section ratio supports a picture where rotation-translation conversion of the resonance excited j=0→2 rotational transition contributes to the desorption of H2, while this channel is energetically closed for D2

  • 41.
    Andersson, Stig
    et al.
    Göteborgs Universitet.
    Svensson, Krister
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Excitation and desorption of physisorbed H2 via the 2Σu electron scattering resonance.2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, p. 114703-1-114703-11, article id 114703Article in journal (Refereed)
    Abstract [en]

    Our high-resolution electron energy-loss measurements concern physisorbed H2 and comprise dif- ferential cross sections for the excitation of the internal H2 modes and the H2-surface bonding mode and their combinations and extend over the electron impact energy range of the classical low-energy H2 2Σu resonance. Comparison with corresponding data for the excitation of the internal modes of gas phase H2 reveals that strong elastic electron reflectivity from the Cu(100) substrate profoundly distorts the inelastic scattering pattern for physisorbed H2. We find that this influence can be corrected for and that the resulting peak cross sections agree with the H2 gas phase data, in accordance with theoretical predictions for the excitation of the internal H2 vibration. We have used corrected cross sections for the rotational mode spectra of physisorbed H2, HD, and D2 in a model concerning elec- tron induced desorption via rotation-translation energy conversion. These spectra include transitions from the ground state as well as excited levels of the physisorption potential well. H2 and HD can desorb from all levels while D2, for energetic reason, can only desorb from the excited levels. This model gives a satisfactory account of the observed desorption cross sections and predicts character- istic velocity distributions of the desorbing molecules. The cross section data for H2 and HD reveals that direct bound-free transitions also contribute to the electron induced desorption. 

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  • 42.
    Andronic, L.
    et al.
    Transilvania University of Braso, Romania.
    Moldarev, D.
    Institute for Energy Technology, Norway.
    Deribew, Dargie
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Karazhanov, S. Z.
    Institute for Energy Technology, Norway.
    Photocatalytic self-cleaning properties of thin films of photochromic yttrium oxyhydride2022In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 316, article id 123599Article in journal (Refereed)
    Abstract [en]

    Oxyhydride of yttrium (YHO) belongs to an emerging class of materials, with oxide and hydride anions sharingthe same sites in the lattice. Under sunlight irradiation, the material is transparent to visible light with trans-parency exceeding 85% and can absorb about 10% of sunlight. Furthermore, increasing light transmittance in thevisible light enhanced the self-cleaning properties of the coated materials, making these materials promisingcandidates for smart windows applications. However, the light-absorbing properties of the materials wereincreased with exposure time, and in the photodarkening state, they can absorb about 40% of sunlight. Kelvinprobe measurements show work function values between 2.9 and 4.2 eV for YHO, depending on the H2/Arpressure in the deposition chamber. Using the Kelvin probe, we demonstrate that the work function decreaseswith decreasing deposition pressure and hydrogen flow. Measurements under solar light reveal a decrease of workfunction by 0.2 eV followed by a slow relaxation with the light off. Moreover, the self-cleaning test shows that theoxyhydroxide thin films have excellent photocatalytic activity and total self-cleaning in 40 h.

  • 43.
    André, Johansson
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    A photodegradation study of conjugated polymers for organic solar cells by absorption spectroscopy and atomic force microscopy2021Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The effect of light exposure in ambient air on thin films made from an electron acceptor polymer poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (N2200), an electron donor polymer Poly[[2,3-bis(3-octyloxyphenyl)-5,8-quinoxalinediyl]-2,5-thiophenediyl] (TQ1) and their blends, has been studied using UV-vis spectroscopy and Atomic Force Microscopy (AFM). For solutions of TQ1, N2200 and blends, the linearity of the Beer-Lambert law for absorption spectroscopy has been verified. The measured UV-vis spectra show that TQ1 thin films are more sensitive to degradation by simulated sunlight than N2200 films. They also show that among the polymer blends, the N2200-rich blend with volume ratio 1:2 (TQ1:N2200) was less sensitive to degradation by simulated sunlight than blends of ratio 1:1 and 2:1. The AFM images showed a change in roughness between the undegraded and degraded films, where the TQ1, 1:1 and 1:2 films obtained lower roughness after 45 hours of degradation, and the N2200 and the 2:1 films obtained higher roughness.

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    A photodegradation study of conjugated polymers for organic solar cells by absorption spectroscopy and atomic force microscopy
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  • 44.
    Anselmo, Ana Sofia
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Materials aspects in spin-coated films for polymer photovoltaics2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Polymer-based photovoltaics have the potential to contribute to boosting photovoltaic energy conversion overall. Besides allowing large-area inexpensive processing, polymeric materials have the added benefit of opening new market applications for photovoltaics due to their low-weight and interesting mechanical properties. The energy conversion efficiency values of polymer photovoltaics have reached new record values over the past years. It is however crucial that stability issues are addressed together with efficiency optimization. Understanding fundamental materials aspects is key in both areas.

    In the work presented in this thesis, the morphology of polymer:fullerene films and its influence on device performance was studied, as well as the effect of light exposure on the surface of fullerene films. Several polyfluorene copolymers were used for the morphology studies, where the effects of changing spin-coating solvent and of side chain engineering were investigated with dynamic secondary ion mass spectrometry (dSIMS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Polymer-enriched surfaces were found in all blend films, even in the cases with homogeneous distributions in the bulk. Side chain engineering of the polymer led to gradual changes in the compositional variations perpendicular to the surface, and to slight variations in the photocurrent. The electronic structure of the fullerene derivative PCBM was studied in detail and the spectroscopic fingerprint of the materials was analysed by comparison with theoretically simulated spectra. Photo-stability studies done in air showed that the surface of fullerene films underwent severe damages at the molecular level, which is evident from changes in the valence band and X-ray absorption spectra. These changes were explained by transitions from sp2-type to sp3 hybridization of the carbon atoms in the cage that resulted in the destruction of the fullerene cage.

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    Anselmo_2013_03
  • 45.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Rysz, Jakub
    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.
    Budkowski, Andrzej
    M. Smoluchowski Insitute of Physics, Jagiellonian University, Reymonta 4, Krakow 30–059, Poland.
    Andersson, Mats R.
    Department of Chemical and Biological Engineering, Chalmers University of Technology.
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Characterisation of vertical phase separation in polymer: fullerene blend films for photovoltaics by dSIMS and NEXAFS2011In: E-MRS 2011 Spring Meeting: Bilateral Energy Conference, Malden, MA: John Wiley & Sons, 2011, p. 62-63Conference paper (Refereed)
    Abstract [en]

    Morphological control and characterization of blend films is key in the development of viable polymer solar cells. Spontaneous formation of vertical compositional gradients during solution processing has been shown for polyfluorene:PCBM blends and rationalized with thermodynamic and kinetic models of nucleation and spinodal decomposition.[1, 2] The extent of vertical stratification is affected by polymer side-chain modification aimed at controlling polymer:fullerene miscibility.[3] Here we present high-resolution film morphology results for several polymer:fullerene systems as obtained from near-edge X-ray fine structure spectroscopy (NEXAFS) in partial and in total electron yield modes. Blend films were found to be polymer- enriched at the surface. Dynamic secondary ion mass spectrometry (dSIMS) and NEXAFS give compositional information at different depths, resulting in a more complete picture of the film morphology.

     

  • 46.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Rysz, Jakub
    M. Smoluchowski Insitute of Physics, Jagiellonian University, Reymonta 4, Krakow 30–059, Poland.
    Budkowski, Andrzej
    M. Smoluchowski Insitute of Physics, Jagiellonian University, Reymonta 4, Krakow 30–059, Poland.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Polymer solar cells: Visualizing vertical phase separation in solution-processed films of polymer fullerene blends2012In: Proceedings of the 5th International Symposium Technologies for Polymer Electronics - TPE 12 / [ed] Hans-Klaus Roth, Klaus Heinemann, Ilmenau, Germany: Universitätsverlag Ilmenau , 2012, p. 125-128Conference paper (Refereed)
  • 47.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Molecular Orientation and Composition at the Surface of Spin-Coated Polyfluorene:Fullerene Blend Films2013In: Journal of Polymer Science Part B: Polymer Physics, ISSN 0887-6266, E-ISSN 1099-0488, Vol. 51, no 3, p. 176-182Article in journal (Refereed)
    Abstract [en]

    The surface composition in spin-coated films of polyfluorene:fullerene blends was determined quantitatively by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. By comparing partial and total electron yield spectra, we found vertical compositional differences in the surface region. Furthermore, the orientation of the polymer chains was investigated by variable-angle NEXAFS. Blend films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole] with [6,6]-phenyl-C61-butyric acid methyl ester in two different blend ratios were studied. Results showed polymer enrichment of the surfaces for films with a polymer:fullerene weight ratio of 20:80 and of 50:50, spin-coated from both chlorobenzene and chloroform solutions. The angular dependence of the NEXAFS spectra of the pure polymer films showed a preferential plane-on orientation, which was slightly stronger in the subsurface region than at the surface. In blend films, this orientational preference was less pronounced and the difference between surface and subsurface vanished

  • 48.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Photodegradation of the electronic structure of PCBM and C60 films in air2016In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 652, p. 220-224Article in journal (Refereed)
    Abstract [en]

    Fullerenes are common electron acceptors in organic solar cells. Here the photostability in air of the electronic structures of spin-coated PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) and evaporated C60 films are studied using ultraviolet photoelectron spectroscopy (UPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. After exposing these materials in air to simulated sunlight, the filled and empty molecular orbitals are strongly altered, indicating that the conjugated π-system of the C60-cage has degraded. Even a few minutes in normal lab light induces changes. These results stress the importance of protecting fullerene-based films from light and air during processing, operation, and storage.

  • 49.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Wang, Ergang
    Department of Chemical and Biological Engineering, Chalmers University of Technology.
    Andersson, Mats R.
    Department of Chemical and Biological Engineering, Chalmers University of Technology.
    Hörmann, Ulrich
    Institute of Physics, Augsburg University.
    Opitz, Andreas
    Institute of Physics, Augsburg University.
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Surface Organization in Thin-Films of Conjugated Polymers for Organic Photovoltaics2011Conference paper (Other academic)
  • 50.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Wang, Ergang
    Chalmers University of Technology.
    Andersson, Mats R.
    Chalmers University of Technology.
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Molecular orientation and composition at the surface of APFO3:PCBM blend films2012In: Hybrid and Organics Photovoltaics Conference: Uppsala, Sweden, 2012 / [ed] Anders Hagfeldt, SEFIN, Castelló (Spain), 2012, p. 278-Conference paper (Refereed)
1234567 1 - 50 of 962
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