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  • 201.
    Maghanga, C. M.
    et al.
    Kabarak University.
    Mghendi, M. M.
    Moi University.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Influence of Deposition Parameters on the Optical Properties of DC Magnetron Sputtered Tungsten Oxide Films2014In: Proceedings Kabarak Conference, Kenya, July, 2014Conference paper (Refereed)
  • 202.
    Maghanga, C M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mwamburi, M
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Optoelectronic Properties of DC Magnetron Sputtered Thin Films of Niobium Doped Titanium Oxide2009Conference paper (Refereed)
  • 203. Maghanga, C. M.
    et al.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mwamburi, M.
    Optical modeling of spectrally selective reflections based on TiO2:Nb transparent conducting oxide films for silicon solar cell applications2009In: Proceedings of SPIE, Vol. 7407, no 74070F1-6Article in journal (Refereed)
  • 204.
    Maghanga, C M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mwamburi, M
    Optical Modeling of Spectrally Selective Reflectors Based on TiO2:Nb Transparent Conducting Oxide Films for Silicon Solar Cell Applications2009Conference paper (Refereed)
  • 205.
    Maghanga, C M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mwamburi, M
    Transparent and Conducting TiO2:Nb Films made by Sputtering: Influence of H2 in the Plasma2009Conference paper (Refereed)
  • 206.
    Maghanga, Christopher M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Jensen, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Ion Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mwamburi, M.
    Transparent and conducting TiO2:Nb films made by sputter deposition: Application to spectrally selective solar reflectors2010In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 94, no 1, p. 75-79Article in journal (Refereed)
    Abstract [en]

    Transparent and conducting thin films of TiO2:Nb were prepared on glass and aluminum substrates by dual-target reactive DC magnetron sputtering in an Ar+O-2 plasma. The Nb content lay between 0 and 4.9 at% as determined by ion beam analyses. X-ray diffraction showed that vacuum annealing at 450 degrees C led to crystallinity and prevalence of the anatase phase. The influence of Nb doping was studied with regard to structural, optical, and electrical data. Optical constants were determined from spectrophotometric recordings for films on glass, and the onset of free-electron behavior was documented for annealed films. The latter films, deposited onto Al2O3-coated Al, were found to display optically selective reflectance and to be useful for solar energy applications.

  • 207.
    Maghanga, Christopher M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes G
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mwamburi, Mghendi
    Physics Department, Moi University, Eldoret, Kenya.
    Spectrally selective reflector surfaces for heat reduction in concentrator solar cells: modeling and applications of TiO(2):Nb-based thin films2011In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, no 19, p. 3296-3302Article in journal (Refereed)
    Abstract [en]

    The energy conversion efficiency of a conventional pn junction solar cell decreases as the temperature increases, and this may eventually lead to failures in the photovoltaic system, especially if it uses concentrated solar radiation. In this work, we show that spectrally selective reflector (SSR) surfaces can be important for reducing the heat buildup on passively cooled solar cells. We outline a computational scheme for optimizing DC magnetron-sputtered TiO(2):Nb-based SSRs tailored for silicon solar cells and find good agreement of the reflectance with an experimental realization of the optimal SSR. A figure of merit for SSRs has also been derived and applied to the experimental data.

  • 208.
    Maghanga, Christopher M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Optical Properties of Sputter Deposited Transparent and Conducting TiO2:Nb Films2009In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 518, no 4, p. 1254-1258Article in journal (Refereed)
    Abstract [en]

    Transparent and conducting thin films of TiO2:Nb were prepared on glass by reactive dc magnetron sputtering in Ar + O-2. Post-deposition annealing in vacuum at 450 degrees C led to good electrical conductivity and optical transparency. The optical properties in the sub-bandgap region were in good agreement with Drude free electron theory, which accounts for intraband absorption. The band gap of the films was found to be in the range of 3.3 to 3.5 eV and signifies the onset of interband absorption. Electrical conductivities in the 10(-3) Omega cm range were obtained both from dc electrical measurements and from analysis of the optical measurements.

  • 209.
    Mahanga, C. M.
    et al.
    Kabarak University.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Effects of Hydrogen on the Structural, Optical and Electrical Properties of DC Magnetron Sputtered TiO2:Nb TCO Films2011In: Kabarak University First International Conference, Kenya, 12-14 October 2011, 2011, p. 1-14Conference paper (Refereed)
  • 210.
    Malmgren, Sara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Green, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Anomalous diffusion of ions in electrochromic tungsten oxide films2017In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 247, p. 252-257Article in journal (Refereed)
    Abstract [en]

    Amorphous tungsten oxide thinfilms were deposited by sputtering at different O2/Ar ratios onto conducting substrates. Ion intercalation and diffusion in thefilms was studied by electrochemical impedance spectroscopy measurements in the frequency range 10 mHz–100 kHz and for potentials between 1.0 and 3.2 V vs. Li/Li+, using the film as working electrode in a Li+ containing electrolyte. The impedance data were in very good agreement with anomalous diffusion models. Different models were found to be applicable at potentials >1.8 V and <1.8 V. At high potentials ion intercalation was found to be reversible and an anomalous diffusion model describing ion hopping was favored. At low potentials ion intercalation was found to be irreversible and ion trapping takes place. In this latter range an anomalous diffusion model for the case of non-conserved number of charge carriers gave the best fit to experimentaldata. We obtained potential dependent diffusion coefficients in the range from 109 to 1011cm2/s, and anomalous diffusion exponents in the range 0.1 to 0.4, with the films deposited at lower O2/Ar ratios exhibiting the higher values.

  • 211.
    Mlyuka, Nuru
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mg Doping of Thermochromic VO2 Films Enhances the Optical Transmittance and Decreases the Metal-Insulator Transition Temperature2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 95, no 17, p. 171909-Article in journal (Refereed)
    Abstract [en]

    Thermochromic films of MgxV1-xO2 were made by reactive dc magnetron   sputtering onto heated glass. The metal-insulator transition   temperature decreased by similar to 3 K/at. %Mg, while the optical   transmittance increased concomitantly. Specifically, the transmittance   of visible light and of solar radiation was enhanced by similar to 10%   when the Mg content was similar to 7 at. %. Our results point at the   usefulness of these films for energy efficient fenestration.

  • 212.
    Mlyuka, Nuru
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Thermochromic Multilayer Films of VO2 and TiO2 with Enhanced Transmittance2009In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 93, no 9, p. 1685-1687Article in journal (Refereed)
    Abstract [en]

    Thermochromic films Of VO2, as well as multilayer films Of VO2 and   TiO2, were made by reactive DC magnetron sputtering. Spectrophotometrically measured transmittance and reflectance were used   to determine optical constants pertinent to temperatures below and   above a temperature-induced structural change at tau(c)approximate to 60 degrees C. We then used computations to optimize multilayer films   for specific applications and, specifically, demonstrated that   TiO2/VO2/TiO2 films Could display a luminous transmittance   significantly higher than that of bare VO2 films, and that   TiO2/VO2/TiO2/VO2/TiO2 films could yield a large change of solar transmittance for temperatures above and below tau(c). Our data can   serve as starting points for developing novel coatings for windows With Superior energy efficiency.

  • 213.
    Mlyuka, Nuru
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Thermochromic VO2-Based Multilayer Films with Enhanced Transmittance and Solar Modulation2009In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 206, no 9, p. 2155-2160Article in journal (Refereed)
    Abstract [en]

    Vanadium dioxide (VO2) shows an abrupt and reversible change in optical   and electrical properties when the temperature is raised beyond a   critical point of similar to 68 degrees C. Films made from this   material have a potential to be used in energy efficient "smart"   windows with temperature-dependent throughput of solar radiation. Two   of the drawbacks of this material have been its low luminous   transmittance and limited solar modulation of transmittance during   switching. In this work we report calculations and experiments on   multilayers Of VO2 and TiO2, produced by reactive DC magnetron   sputtering, that significantly improve the luminous transmittance and   solar modulation of the films during switching. We also explore the   angular-dependent transmittance of five-layer TiO2/VO2/TiO2/VO2/TiO2   films and demonstrate that the modulation of luminous and solar   transmittance can be enhanced at non-normal angles of incidence.

  • 214. Montero, J
    et al.
    Guillén, C
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Herrero, J
    Niklasson, G A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Beyond transparency and low resistivity in Antimony-doped tin oxide thin films2017In: Abstracts, 2017Conference paper (Refereed)
  • 215.
    Montero, Jose
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ji, Yu-Xia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Li, Shu-Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sputter deposition of thermochromic VO2 films on In2O3: Sn, SnO2, and glass: Structure and composition versus oxygen partial pressure2015In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 33, no 3, p. 1-7, article id 031805Article in journal (Refereed)
    Abstract [en]

    Thermochromic thin films of VO2 were produced by reactive DC magnetron sputtering and were characterized by atomic force microscopy, scanning electron microscopy, x-ray diffraction, spectrophotometry, and resistance measurements. Depositions took place onto substrates of glass with and without layers of electrically conducting ITO (i.e., In2O3: Sn) and nonconducting SnO2. The substrate conditions were of large importance; thus, VO2 could be prepared on ITO within a significantly wider process window of oxygen partial pressure than for the other substrates and could yield highly granular deposits. VO2 films on ITO typically showed some lattice compression. Our results are valuable for the preparation and implementation of thermochromic glazings, which are of importance for energy efficient buildings.

  • 216.
    Montero, José Amenedo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sputter Deposited Thermochromic VO2 Thin Films on Tin-Doped Indium Oxide Coated Glass: Electrical, Structural and Optical Properties2014In: European Materials Research Society (E-MRS) Spring Meeting, Lille, France, 26-30 May: Symposium L: Chromogenic Materials and Devices, 2014Conference paper (Refereed)
  • 217.
    Montero, José Amenedo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Guillen, C
    Department of Energy, CIEMAT, Madrid, Spain.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Herrero, J
    Department of Energy, CIEMAT, Madrid, Spain.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lithium intercalation in sputter deposited antimony-doped tin oxide thin films: Evidence from electrochemical and optical measurements2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 15, p. 153702/1-/8Article in journal (Refereed)
    Abstract [en]

    Transparent conducting oxides are used as transparent electrical contacts in a variety of applications, including in electrochromic smart windows. In the present work, we performed a study of transparent conducting antimony-doped tin oxide (ATO) thin films by chronopotentiometry in a Li+-containing electrolyte. The open circuit potential vs. Li was used to investigate ATO band lineups, such as those of the Fermi level and the ionization potential, as well as the dependence of these lineups on the preparation conditions for ATO. Evidence was found for Li+ intercalation when a current pulse was set in a way so as to drive ions from the electrolyte into the ATO lattice. Galvanostatic intermittent titration was then applied to determine the lithium diffusion coefficient within the ATO lattice. The electrochemical density of states of the conducting oxide was studied by means of the transient voltage recorded during the chronopotentiometry experiments. These measurements were possible because, as Li+ intercalation took place, charge compensating electrons filled the lowest part of the conduction band in ATO. Furthermore, the charge insertion modified the optical properties of ATO according to the Drude model.

  • 218.
    Montero, José Amenedo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Guillen, C.
    CIEMAT.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Herrero, J.
    CIEMAT.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Preparation of Reactively Sputter Deposited Nanocrystalline Antimony-Based Tin Oxide Thin Films: Control of Preferential Orientation2014In: European Materials Research Society (E.MRS) Spring Meeting, Lille, France, 26-30 May: Symposium Y: Advanced Materials and Characterization Techniques for Solar Cella II, 2014Conference paper (Refereed)
  • 219.
    Montero, José Amenedo
    et al.
    Solar Energy Department, IFE, Kjeller, Norway..
    Guillén, C
    Department of Energy, Ciemat, Madrid, Spain.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Herrero, J
    Department of Energy, Ciemat, Madrid, Spain.
    Niklasson, G A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Beyond transparency and low resistivity in Antimony-doped tin oxide thin films2017Conference paper (Refereed)
  • 220.
    Montero, José Amenedo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Institutt for Energiteknik, IFE, Kjeller, Norway.
    Ji, Yu -Xia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Light Scattering in Thermochromic Particulate VO2 Coatings2017Conference paper (Refereed)
    Abstract [en]

    Particulate films consisting of thermochromic (TC) vanadium dioxide (VO2) have been obtained by reactive magnetron sputtering onto In2O3:Sn coated glass substrates. These films consist of VO2 particles of adequate size to cause light scattering -and hence an increase of the diffuse transmittance- in the visible region. When these films are heated up above the temperature at which the thermochromic transition takes place, the particles switch from a semiconducting to a metallic state, affecting the overall scattering properties. In this work, layers consisting of particles of different shapes and sizes have been studied by scanning electron microscopy, atomic force microscopy and optical spectrophotometry. The optical properties of the films, including the spectral absorption and scattering coefficients, have been studied below and above the transition temperature. In addition, the experimental optical properties have been reconciled with a semi-quantitative model based on Lorentz-Mie theory and the Grenfell-Warren approximation. 

  • 221.
    Montero, José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Guillén, C
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Herrero, J
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Preferential Orientation and Surface Oxidation Control in Reactively Sputter Deposited Nanocrystalline SnO2:Sb Films: Electrochemical and Optical Results2014In: ECS Journal of Solid State Science and Technology, ISSN 2162-8769, E-ISSN 2162-8777, Vol. 3, no 11, p. N151-N153Article in journal (Refereed)
  • 222.
    Montero, José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ji, Yu-Xia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Thermochromic light scattering from particulate VO2 layers2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 8, article id 085302Article in journal (Refereed)
    Abstract [en]

    Particulate layers of thermochromic (TC) VO2 were made by reactive DC magnetron sputtering of vanadium onto In2O3: Sn-coated glass. The deposits were characterized by scanning electron microscopy, atomic force microscopy, and X-ray diffraction. Specular and diffuse optical transmittance and reflectance were recorded in the 300-2500-nm wavelength range and displayed pronounced TC effects. These properties could be reconciled with a semi-quantitative model based on Lorentz-Mie theory applied to the distribution of particle sizes and accounting for particle shapes by the Grenfell-Warren approach with equal-volume-to-area spheres.

  • 223.
    Morales-Luna, Michael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Ctr Invest & Estudios Avanzados IPN, Dept Nanociencias & Nanotecnol, AP 14-740, Mexico City 07360, DF, Mexico..
    Arvizu, Miguel A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromic properties of W1-x-yNixTiyO3 thin films made by DC magnetron sputtering2016In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 615, p. 292-299Article in journal (Refereed)
    Abstract [en]

    We investigated the electrochromic properties of tungsten-nickel-titanium oxide (W1-x-yNixTiyO3) thin films. Special emphasis was put on W0.83-xNixTi0.17O3 since this composition gave the highest electrochemical durability. The films were deposited onto indium-tin oxide coated glass by reactive DC magnetron sputtering, and cyclic voltammetry as well as optical transmittance measurements were performed in an electrolyte of 1 M LiClO4 in propylene carbonate. The potential window was chosen so as to cause rapid degradation of the samples. Elemental compositions were obtained by Rutherford backscattering spectroscopy and structural information by X-ray diffraction. We verified that the titanium additive improved the electrochemical durability of tungsten-oxide-based films and also documented that a further addition of nickel was unable to enhance the EC performance to any significant degree.

  • 224.
    Morales-Luna, Michael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Centro de Investigacion y de Estudios Avanzados de I.P.N..
    Arvizu, Miguel A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sputter deposited W1-x-yNixTiyO3 thin films: Electrochromic properties and durability2016In: INERA Conference: Book of Abstracts / [ed] Nesheva, D; Chamati, H; Genova, J; Gesheva, K; Ivanova, T; Szekeres, A, Institute of Physics (IOP), 2016, article id 012021Conference paper (Refereed)
    Abstract [en]

    Previous research demonstrated that a small amount of nickel enhances the coloration efficiency of tungsten-nickel oxide electrochromic (EC) thin films with respect to that of pure tungsten oxide (WO3) films. Furthermore the incorporation of titanium gives an improvement in the durability of tungsten-titanium oxide EC thin films. In this work we investigated the EC performance of tungsten-nickel-titanium oxide (W1-x-yNixTiyO3) EC thin films with emphasis on durability. The films were deposited on indium tin oxide covered glass by reactive dc sputtering from tungsten, tungsten-titanium alloy and nickel targets. Cyclic voltammetry was performed using 1 M LiClO4 in propylene carbonate as electrolyte. The voltage window was chosen to induce fast degradation of the samples within 80 cycles. Elemental compositions were obtained by Rutherford Backscattering Spectroscopy.

  • 225.
    Niklasson, G A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Berggren, L
    Larsson, A.-L
    Electrochromic tungsten oxide: The role of defects.2003In: ISES Solar World Congress, Göteborg, Sweden, June 14-19, 2003. Paper W5.2, 2003Conference paper (Refereed)
  • 226.
    Niklasson, G A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Fasta tillståndets fysik.
    Jonsson, A K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Fasta tillståndets fysik.
    Strömme, M
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Nanoteknologi o funktionella material.
    Impedance response of electrochromic materials and devices2005In: Impedance Spectroscopy 2nd ed, Wiley, New York , 2005, p. 302-326Chapter in book (Other academic)
  • 227.
    Niklasson, G A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Karmhag, R
    Oxidation Kinetics of Metallic Nanoparticles2003In: Surf. Sci., 532-535 324-327 (2003)Article in journal (Refereed)
  • 228.
    Niklasson, G A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wen, Rui-Tao
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Qu, Hui-Ying
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Arvizu, M A
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Durability of electrochromic films: Ageing kinetics and rejuvenation2017In: ECS Transactions, ISSN 1938-5862, E-ISSN 1938-6737, p. 1659-1669Article in journal (Refereed)
  • 229.
    Niklasson, G A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wen, Rui-Tao
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Qu, Hui-Ying
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Arvizu, MA
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Durability of Electrochromic films: Ageing kinetics and rejuvenation2017In: Abstracts, 2017, Vol. 1843, p. 1-, article id MA2017Conference paper (Refereed)
  • 230.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochemical Measurements of the Electronic Density of States2014In: Joint 12th Russia/CIS/Baltic/Japan Symposium on Ferroelectricity and 9th International Conference Functional Materials and Nanotechnologies / [ed] Andris Sternbergs and Liga Grinberga, 2014, p. 254-Conference paper (Refereed)
    Abstract [en]

    The electronic density of states of metal oxides can in many cases be measured by electrochemical techniques [1], such as chronopotentiometry or impedance spectroscopy. When small ions such as protons or Li ions are intercalated into a material, which is used as the working electrode in an electrochemical cell, electrons must be inserted from the back contact to maintain charge neutrality. These electrons will enter into previously unoccupied states and the Fermi level will shift upwards in energy as intercalation proceeds. Provided that the rigid band approximation holds, measuring the inserted charge during this process will give an image of the electronic densityof states over 1 to 2 eV from the band edge.

    We have compared the so called electrochemical density of states obtained by this method to density functional calculations for a number of oxides. The electrochemical technique is able to give results in qualitative agreement with calculations. We have studied a number of metal oxides such as WO3, TiO2, V2O5, Sb:SnO2, In:SnO2, IrO2 as well as some NiO based coatings.

    There are a number of questions that need to be better understood in order to make the technique fully quantitative, though. A limitation is that the number of ions that can be intercalated in a given material is restricted. In addition, the ions do not distribute uniformly in the coating but probably exhibit a gradient in concentration, due to slow kinetics of the process. In addition, the validity of the rigid band approximation is largely an open question. The technique will be useful for screening the density of states of a large amount of coatings in the laboratory. Then interesting materials and specimen can be selected for further studies by advanced techniques, such as photoelectron or X-ray spectroscopies at synchrotron facilities.

    References

    1. M. Strömme, R. Ahuja and G.A. Niklasson, Phys. Rev. Lett. 93 (2004) 206403

  • 231.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochemical measurements of the electronic density of states2015In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, no 9, article id 094005Article in journal (Refereed)
    Abstract [en]

    We present a simple electrochemical method, called intercalation spectroscopy, to study the electronic density-of-states of intercalation materials. It is based on the realization that electrochemical quasi-steady state potential curves of a number of materials exhibit fine structure in good agreement with features in the density of electronic states. Different electrochemical techniques are able to give this information, but chronopotentiometry appears to have advantages from an experimental viewpoint. In this paper we compare the so called 'electrochemical density-of-states' of amorphous and crystalline structures. We also address the limitations of intercalation spectroscopy due to kinetic effects, i.e. very slow relaxations of the charge carriers. Intercalation spectroscopy is in principle very sensitive, although in limited energy ranges, and is able to give information complementary to electron and x-ray spectroscopies for a number of materials.

  • 232.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromic flms for smart windows: Coloration and degradation mechanisms2017Conference paper (Other academic)
  • 233.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromic materials: Electronic, ionic and optical properties.2014In: European Materials Research Society, Spring Meeting, Lille, France, May 26th-30th, 2014: Symposium L Chromogenic Materials and Devices / [ed] Aline Rougier, Claes G. Granqvist, Bernard Dam and Martyn Pemble, 2014, p. 2-3Conference paper (Refereed)
    Abstract [en]

    Electrochromic materials have the ability to change their optical properties, gradually and reversibly, when an electrical potential is applied across them. Thin films of transition metal oxides impart electrochromic functionality to the emerging smart window technology. Together with transparent contacts and a solid or gel-like electrolyte they constitute the building blocks of electrochromic devices. A typical device consists of five layers between two substrates, or alternatively deposited on a single substrate. In the former configuration, each substrate is coated by a transparent conducting layer and subsequently by an electrochromic layer. The two sides of the device are laminated by an ion conductor, preferably a polymer-based one. The electrochromic layers are chosen to be complementary. One of them is cathodic (i.e. it colors under cation/electron insertion) and the other is anodic (coloring under cation/electron extraction).

    Some of the important performance parameters of an electrochromic device are the optical contrast between transparent and dark states, the charge capacity and the switching speed. Each of these has its roots in the fundamental physical and electrochemical properties of the materials. The optical properties depend on the nature of the electronic transitions and whether the electrons are free or localized. It appears that in many electrochromic materials intervalence transitions between localized states is the most important mechanism. Basically, a good description of the optical properties depends on a good understanding of the electronic band structure. The charge capacity of an electrochromic film depends on the magnitude of the electronic density of states in the reversible potential range. It should be noted that the achievable density of states may be less than the theoretically expected one, since intercalated ions may not be able to penetrate all parts of the material. The switching speed depends on the diffusion coefficient of ions in the electrochromic films, as well as in the electrolyte. The sheet resistance of the transparent conductors is also important in this respect.

    A number of electrochemical techniques are suitable for studying ionic transport in intercalation materials, such as for example electrochromic films in contact with an electrolyte. Impedance spectroscopy gives the most detailed characterization of the transport processes but measurements are time consuming, and in certain situations more simple techniques such as chronopotentiometry or choronoamperometry may be preferable. Electronic transport may be studied with conventional electrical measurements with the film samdwiched between two metal electrodes.

    In this contribution we will focus on the determination of the diffusion coefficient and the electronic density of states (DOS) by electrochemical methods, and how to use this knowledge to describe the optical properties. It is shown that the features observed in the “electrochemical density of states” often show good agreement with the theoretically computed DOS. However, the magnitude of the electrochemical DOS is always lower that the theoretical one. It seems that the whole film is not accessible to the ion intercalation process. We also address the question whether the electronic states are extended or localized and how to determine this experimentally. Theories for optical properties are reviewed based on the intervalence transfer concept. In some, but not all, cases the transitions may be identified as polaronic. We also comment on the existence of electrochromism due to free electrons and its possible limitations. Examples are given mainly from our work on WO3, but also results on SnO2, IrO2 and NiO-based films will be discussed.

  • 234.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Modeling the optical properties of nanoparticles2006In: SPIE NewsroomArticle in journal (Refereed)
    Abstract [en]

    Recent advances in modeling the unique optical properties of nanoparticles and nanocomposites pave the way for designing and modeling coatings.

  • 235.
    Niklasson, Gunnar A.
    Chalmers Tekniska Högskola.
    Optical properties and solar selectivity of inhomogeneous metal-insulator coatings1982Doctoral thesis, monograph (Other academic)
  • 236.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Proton diffusion in polyethylene oxide: Relevance to electrochromic device design2008In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 92, no 10, p. 1293-1297Article in journal (Refereed)
    Abstract [en]

    Polyethylene oxide is a frequently used component in polymer electrolytes developed for applications in electrochromic devices. The transmittance variation may occur as a result of either proton or lithium ion intercalation into the electrochromic films. Impedance spectroscopy data in the low-frequency space-charge relaxation regime can be used to obtain estimates of ion concentrations and ion diffusion coefficients in ion-conducting materials. We apply this method to literature data for pure polyethylene oxide where the residual conductivity is believed to be due to protons. The obtained diffusion coefficient is found to be in the order of, or higher than, reported lithium ion diffusion coefficients in low molecular weight polyethylene oxide. Hence it is likely that proton intercalation will be of importance for electrochromic devices, provided there is a significant amount of protons present.

  • 237.
    Niklasson, Gunnar A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Fasta tillståndets fysik.
    Ahuja, R
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Nanoteknologi och Funktionella material.
    Electronic states in intercalation materials studied by electrochemical techniques.2006In: Modern Phys. Lett.B, Vol. 20, p. 863-875Article in journal (Refereed)
  • 238.
    Niklasson, Gunnar A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Fasta tillståndets fysik.
    Berggren, Lars
    Jonsson, A K
    Ahuja, R
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Skorodumova, N V
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Backholm, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Fasta tillståndets fysik.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Nanoteknologi.
    Electrochemical studies of the electron states of disordered electrochromic oxides2006In: Solar Energy Materials & Solar Cells, Vol. 90, p. 385-394Article in journal (Refereed)
  • 239.
    Niklasson, Gunnar A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Boström, Tobias K
    NORUT Northern Research Institute AS, Narvik, Norge.
    Tuncer, Enis
    Dielectrics & Electrophysics Lab, GE Global Research Center, Niskayuna, NY, USA.
    Spectral density analysis of the optical properties of Ni-Al 2O 3 nano-composite films2011In: Advances in Optical Thin Films IV, September 5 2011, Marseille, France / [ed] Michel Lequime, H. Angus Macleod, Detlev Ristau, 2011, Vol. 8168, p. 81680S-1-81680S-11Conference paper (Refereed)
    Abstract [en]

    Thin films consisting of transition metal nanoparticles in an insulating oxide exhibit a high solar absorptance together with a low thermal emittance and are used as coatings on solar collector panels. In order to optimise the nanocomposites for this application a more detailed understanding of their optical properties is needed. Here we use a highly efficient recently developed numerical method to extract the spectral density function of nickel-aluminum oxide (Ni-Al 2O 3) composites from experimental data on the dielectric permittivity in the visible and near-infrared wavelength ranges. Thin layers of Ni-Al 2O 3 were produced by a sol-gel technique. Reflectance and transmittance spectra were measured by spectrophotometry in the wavelength range 300 to 2500 nm for films with thicknesses in the range 50 to 100 nm. Transmission electron microscopy showed crystalline Ni particles with sizes in the 3 to 10 nm range. The spectral density function shows a multi-peak structure with three or four peaks clearly visible. The peak positions are influenced by particle shape, local volume fraction distributions and particle-particle interactions giving rise to structural resonances in the response of the composite to an electromagnetic field.

  • 240.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Delsol, B.
    Green, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lansåker, Pia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Chronopotentiometry on indium-tin oxide films: Evidence for lithium intercalation2010Conference paper (Refereed)
  • 241.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ekman, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Multifractal analysis of nanoparticle aggregates1998Conference paper (Other academic)
    Abstract [en]

    In this paper we assess the suitability of box-counting for determining the multifractal dimensions of nanoparticle aggregates. The algorithm was first tested on deterministic multifractal structures. The method was also applied to electron micrographs of gas evaporated cobalt particle aggregates. The finite fractal range due to a rather small correlation length complicated the analysis. Clear evidence of a multifractal structure was found for a sample consisting of superparamagnetic particles, which generally have diameters below 10 nm. No indications of multifractality was found for aggregates consisting of larger ferromagnetic particles.

  • 242.
    Niklasson, Gunnar A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes G
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromics for Smart Windows: Thin Films of Tungsten Oxide and Nickel Oxide, and Devices Based on These2007In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 17, no 2, p. 127-156Article, review/survey (Refereed)
    Abstract [en]

    Electrochromic (EC) materials are able to change their optical properties, reversibly and persistently, by the application of an electrical voltage. These materials can be integrated in multilayer devices capable of modulating the optical transmittance between widely separated extrema. We first review the recent literature on inorganic EC materials and point out that today's research is focused on tungsten oxide ( colouring under charge insertion) and nickel oxide ( colouring under charge extraction). The properties of thin films of these materials are then discussed in detail with foci on recent results from two comprehensive investigations in the authors' laboratory. A logical exposition is obtained by covering, in sequence, structural features, thin film deposition ( by sputtering), electronic band structure, and ion diffusion. A novel conceptual model is given for structural characteristics of amorphous W oxide films, based on notions of defects in the ideal amorphous state. It is also shown that the conduction band density of states is obtainable from simple electrochemical chronopotentiometry. Ion intercalation causes the charge-compensating electrons to enter localized states, implying that the optical absorption underlying the electrochromism can be described as ensuing from transitions between occupied and empty localized conduction band states. A fully quantitative theory of such transitions is not available, but the optical absorption can be modeled more phenomenologically as due to a superposition of transitions between different charge states of the W ions (6+, 5+, and 4+). The Ni oxide films were found to have a porous structure comprised of small grains. The data are consistent with EC coloration being a surface phenomenon, most likely confined to the outer parts of the grains. Initial electrochemical cycling was found to transform hydrated Ni oxide into hydroxide and oxy-hydroxide phases on the grain surfaces. Electrochromism in thus stabilized films is consistent with reversible changes between Ni hydroxide and oxy-hydroxide, in accordance with the Bode reaction scheme. An extension of this model is put forward to account for changes of NiO to Ni2O3. It was demonstrated that electrochromism is associated solely with proton transfer. Data on chemical diffusion coefficients are interpreted for polycrystalline W oxide and Ni oxide in terms of the lattice gas model with interaction. The later part of this review is of a more technological and applications oriented character and is based on the fact that EC devices with large optical modulation can be accomplished essentially by connecting W-oxide-based and Ni-oxide-based films through a layer serving as a pure ion conductor. Specifically, we treat methods to enhance the bleached-state transmittance by mixing the Ni oxide with other oxides characterized by wide band gaps, and we also discuss pre-assembly charge insertion and extraction by facile gas treatments of the films, as well as practical device manufacturing and device testing. Here the emphasis is on novel flexible polyester-foil-based devices. The final part deals with applications with emphasis on architectural "smart'' windows capable of achieving improved indoor comfort jointly with significant energy savings due to lowered demands for space cooling. Eyewear applications are touched upon as well.

  • 243.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lansåker, Pia C.
    Uppsala University, Disciplinary Domain of Science and Technology, Faculty of Science and Technology.
    Li, Shu-Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Granqvist, Claes G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Plasmonic thin films for application to inproved chromogenic windows2015In: INERA Conference: Book of Abstracts / [ed] Nesheva, D; Chamati, H; Genova, J; Gesheva, K; Ivanova, T; Szekeres, A, 2015, article id 012003Conference paper (Refereed)
    Abstract [en]

    Nanocomposites consisting of noble metal nanoparticles in a transparent matrix exhibit plasmonic absorption in the visible wavelength range. On the other hand conducting oxide nanoparticles display a localized plasma absorption in the near infrared. These effects can be exploited in the design of energy-efficient windows in order to obtain improved performance. Electrochromic coatings that switch in the near infrared make use of the modulation of the plasma absorption of oxide nanoparticles due to charge insertion/extraction induced by an external voltage. Thermochromic nanocomposites are predicted to exhibit a much improved energy efficiency, as compared to thermochromics thin films. Plasmonic thermochromics switching in the near infrared has the potential to be significantly larger than in the case of a thin film. Very thin noble metal films are an interesting alternative to conducting oxides as transparent contacts to electrochromic devices. However, in this latter case plasmonic effects are to be avoided rather than exploited.

     

    In order to model and optimize chromogenic devices, a good theoretical understanding of plasmonic effects is necessary. The optical properties of nanocomposites are commonly described by effective medium theories. They describe the effective dielectric function of the composite using as input the dielectric functions of the constituents and their respective volume fractions. However, theoretical modelling by effective medium theories is not straightforward since the effective dielectric function is also sensitively dependent on the actual microgeometry of the composite. These structural effects can be described by the so-called spectral density function. In this paper we describe recent work on three topics related to energy efficient chromogenic window coatings: (1) The performance limits of plasmonic electrochromic coatings, (2) the performance of thermochromics nanocomposites and (3) a study of the optical properties of ultrathin silver films by the spectral density formalism.

  • 244.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Li, Shu-Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Thermochromic vanadium oxide thin films: Electronic and optical properties2014In: INERA Workshop: Transition Metal Oxides as Functional Layers in Smart windows and Water Splitting Devices / Parallel session of the 18th International School on Condensed Matter Physics / [ed] Kostadinka Gesheva, Institute of Physics Publishing (IOPP), 2014, p. 012001-Conference paper (Refereed)
    Abstract [en]

    Vanadium dioxide, VO2, is a widely studied thermochromic material with potential applications in energy efficient window technology. It undergoes a first-order metal-to-insulator transition, accompanied by a crystal structure transformation from monoclinic to tetragonal rutile, at a critical temperature of 68 oC. Below this temperature, VO2 is semiconducting and infrared transmitting whereas it is metallic and infrared reflecting above the transition temperature. However, in order to achieve significant thermochromic switching, the luminous transmittance of thin films will be less than 0.5 . Here we report on recent research to improve the luminous transmittance as well as the transmittance change at the transition temperature. We systematically evaluate the effect of antireflection coatings, doping with Mg and the performance of coatings comprising thermochromic nanoparticles in a transparent matrix. The last option is shown to give the best performance and holds great promise for practical applications.

  • 245.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Malmgren, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
    Green, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Backholm, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Determination of electronic structure by impedance spectroscopy2010In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 356, no 11-17, p. 705-709Article in journal (Refereed)
    Abstract [en]

    We present a novel method, based on electrochemical intercalation and impedance spectroscopy, to determine the electronic density of states of disordered transition metal oxides. Specifically, we have determined the "electrochemical density of states" of tungsten and iridium oxide thin films over energy ranges as wide as 1-2 eV. Our experimental results show a number of qualitative features exhibited by state-of-the-art band structure computations. Differences in details are probably due to the disordered, porous and sometimes amorphous nature of our films. The results suggest that the impedance spectroscopy method can be used to obtain the density of states only if the conduction band states are localized. The electrochemical density of states is often smaller than the computed one due to kinetic effects, i.e. very slow relaxations of the charge carriers. Nevertheless, our sensitive method opens new vistas for studying the electronic structure of disordered materials.

  • 246.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Malmgren, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Green, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ageing of electrochromic tungsten oxide thin films studied by impedance spectroscopy.2016In: / [ed] M. Labardi and E. Tombari, Pisa, 2016, p. O-89-Conference paper (Refereed)
    Abstract [en]

    Tungsten oxide is the most widely used cathodic electrochromic material for smart window applications and a major challenge is to ensure the durability over a service life of more than 20 years. Hence, the degradation under operating conditions must be better understood and preferably prevented. Recent progress in this field includes studies of the power-law kinetics of the degradation process [1] as well as the possibility to rejuvenate degraded films, thereby restoring them to their initial state [2]. In this paper we use impedance spectroscopy to investigate electrochemical ageing of sputter deposited tungsten oxide thin films. Impedance spectroscopy measurements were carried out in a Li+-containing electrolyte, from the open circuit potential at about 3.2V vs. Li down to (1) 2.2 V, which is in the reversible intercalation range; (2) 1.5 V and (3) 1.0 V; at these latter voltages Li intercalation has been found to be irreversible. Subsequently, measurements were carried out for increasing voltages up to the starting point at 3.2 V vs. Li. The intercalated charge capacity was unaffected when potentials below 2.0 V were avoided, while it decreased drastically on the return path from 1.5 V and 1.0 V vs. Li. We interpret this ageing behaviour as an effect of trapping of Li ions irreversibly in the film. Secondly, after the films had been subjected to the low potentials known to induce degradation, the charge transfer resistance in the usual operating range above 2.0 V vs. Li showed a marked increase. This is interpreted as a signature of the development of a solid-electrolyte interface. In conclusion, our measurements suggest that the development of the solid-electrolyte interface may be responsible for the slow degradation observed under normal operating conditions, while Li ion trapping is mainly responsible for severe degradation at potentials significantly below 2.0 V vs. Li.

     

    [1] R.-T. Wen, C. G. Granqvist, and G. A. Niklasson: Cyclic voltammetry on sputter-deposited films of electrochromic Ni oxide: Power-law decay of the charge density exchange. Appl. Phys. Lett. 105  163502 (2014)

     

    [2] R.-T. Wen, G.A. Niklasson and C.G. Granqvist: Eliminating degradation and uncovering ion-trapping dynamics in electrochromic WO3 thin films. Nature Materials 14  996-1002 (2015)

  • 247.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nettelblad, Bo
    SAAB Electronic Defense Systems, Göteborg.
    Dielectric Properties of Water-Containing Porous Materials: Low Frequency Response of Sandstones2013In: ISEMA 2013: Proceedings of the 10th International Conference on Electromagnetic Wave Interaction with Water and Moist Substances / [ed] Klaus Kupfer and Norman Wagner, Weimar, Germany: MFPA Weimar , 2013, p. 195-202Conference paper (Refereed)
    Abstract [en]

    We present results of dielectric spectroscopy measurements on natural sandstones, where the pores were impregnated with water solutions of different conductivity. The measurements were fitted to an equivalent circuit containing a high-frequency Maxwell-Wagner relaxation and a low frequency response due to ion conduction and relaxation in the electrochemical double layer at the interfaces between the solid grains and the water. We propose a novel expression for the low frequency response based on a transmission line model. We also study in detail the shape of the Maxwell-Wagner relaxation in samples of porous polypropylene impregnated with transformer oil.

  • 248.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Maria H.
    Musikinstitutet Betel, Bromma Folkhögskola.
    Non-Gaussian distributions of melodic intervals in music: The Lévy-stable approximation2015In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 112, no 4, article id 40003Article in journal (Refereed)
    Abstract [en]

    The analysis of structural patterns in music is of interest in order to increase ourfundamental understanding of music, as well as for devising algorithms for computer-generatedmusic, so called algorithmic composition. Musical melodies can be analyzed in terms of a “music walk” between the pitches of successive tones in a notescript, in analogy with the “random walk”model commonly used in physics. We find that the distribution of melodic intervals between tones can be approximated with a L´evy-stable distribution. Since music also exibits self-affine scaling,we propose that the “music walk” should be modelled as a L´evy motion. We find that the L´evy motion model captures basic structural patterns in classical as well as in folk music.

  • 249.
    Niklasson, Gunnar A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Sara
    Lundellska Skolan, Uppsala.
    Determination of scattering and absorption coefficients from experimental data: Application to sunscreen lotions2013In: Optics & Photonics in Sweden 2013, 2013Conference paper (Other academic)
    Abstract [en]

    Materials with pronounced light scattering are of large interest in a variety of scientific and technical disciplines. Their optical properties can to a good approximation be described by two-flux (Kubelka-Munk) theory [1]. This theory considers one light beam propagating in the forward direction and one beam propagating in the backward direction in the material. The optical properties of the material are described by phenomenological scattering (S) and absorption (K) coefficients. Additional parameters are the internal reflection coefficients for diffuse light at the interfaces and the reflection coefficient for incident collimated light at the front interface. The large amount of parameters makes it difficult to invert experimental measurements of transmittance (T) and reflectance (R) in order to obtain the parameters S and K characterizing the material [2,3]. We propose a method to partially overcome this problem in special cases by invoking physically realistic approximations for the reflection coefficients. 

    We consider viscous emulsions or polymeric materials positioned between two transparent substrates separated by a spacer. Many organic and polymeric materials have refractive indices sufficiently close to those of glass and quartz substrates so that reflections between the material and the glass can be neglected. The reflection coefficient of the substrate for collimated light is known from its refractive index. Measurements of R and T in a region of weak scattering and absorption allow us to put quite stringent limits on the internal reflection coefficients for diffuse light. In this way good approximative values for S and K can be obtained.

    We apply this method to spectrophotometric measurements on two commercial sunscreen lotions. A drop of lotion was applied on a quartz substrate and a second quartz plate was put on top. The quartz plates were separated by aluminium foil of thickness 11 mm, except in the area covered by the lotion. Measurements of total R and T were taken by a Perkin-Elmer lambda-900 spectrophotometer equipped with an integrating sphere, in the wavelength range 250-800 nm. The samples were completely diffuse scattering and measurements in a low scattering region indicated a preferential forward scattering. The absorption coefficient was found to be low in the visible region and increased very much in the ultraviolet (UV). The scattering coefficient increased towards shorter wavelengths in the visible but exhibited differing behaviours in the UV. A sunscreen containing TiO2 particles exhibited a very low UV scattering together with higher scattering in the visible range, see fig. 1.

      

    Fig. 1. Scattering (S) and absorption (K) coefficients for a sunscreen containing a mix of chemical pigments and TiO

    [1] P. Kubelka, J. Opt. Soc. Am. 38 (1948) 448.

    [2] R. Levinson, P. Berdahl and H. Akbari, Solar Energy Mater. Solar Cells, 89  (2005) 319.

    [3] D. Barrios, R. Vergaz, J.M. Sanchez-Pena, C.G. Granqvist and G.A. Niklasson, Solar Energy Mater. Solar Cells, 111 (2013) 115.

  • 250.
    Niklasson, Gunnar A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Norling, A K
    Berggren, L
    Charge transport Between Localized states in Lithium-intercalated Amorphous Tungsten Oxide2006Conference paper (Other academic)
2345678 201 - 250 of 378
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