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  • 301.
    Strömme, Maria Mattsson
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Isothermal transient ionic current as a characterization technique for ion transport in Ta2O51999In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 85, no 12, p. 8199-8204Article in journal (Refereed)
    Abstract [en]

    The Isothermal Transient Ionic Current (ITIC) technique was applied to β-Ta2O5 samples made by chemical vapor deposition. The mobility, conductivity, and number of protons in the material could be extracted from the measurements. Li ions were intercalated electrochemically into the β-Ta2O5 and it was found that the ITIC method could separate the contribution from proton and Li ion conduction in such a way that the mobilities of both species could be extracted. Furthermore, the lattice-gas model [A. J. Berlinsky, W. G. Unruh, W. R. McKinnon, and R. R. Haering, Solid State Commun. 31, 135 (1979)] was employed to describe the Li interaction process. This model showed that the Li ions tended to distribute uniformly, rather then to attract each other and form clusters in the material.

  • 302.
    Strömme, Maria Mattsson
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Forsgren, K
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Hårsta, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    A frequency response and transient current study of beta-Ta2O5: Methods of estimating the dielectric constant, direct current conductivity, and ion mobility1999In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 85, article id 2185Article in journal (Refereed)
    Abstract [en]

    Dielectric ac measurements in the frequency range of ∼1 mHz–1 MHz were performed on β-Ta2O5 samples made by chemical vapor deposition. A method of estimating the dielectric constant and the dc conductivity from the dielectric response was developed. The high-frequency dielectric constant was found to be 25.84 with no detectable temperature dependence and the dc conductivity due to protons had an activation energy of about 0.4 eV in the studied temperature range (from 24 to 90 °C). Evidence for the conduction mechanism being protonic rather then electronic was found from isothermal transient ionic current (ITIC) measurements. The ITIC recordings could also determine conduction parameters, such as protonmobility, number of charge carriers, and dc conductivity.

  • 303.
    Strömme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Mihranyan, Albert
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Ek, Ragnar
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Fractal dimension of cellulose powders analyzed by multilayer BET adsorption of water and nitrogen2003In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 107, no 51, p. 14378-14382Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to show that multilayer fractal Brunauer-Emmett-Teller (mfBET) theory can be used as a tool to obtain information about the distribution of water in cellulose powder particles of varying crystallinity. Microcrystalline cellulose, agglomerated micronized cellulose, low-crystallinity cellulose, and cellulose powders from green and brown algae were characterized by scanning electron microscopy and mfBET analysis on water and nitrogen adsorption isotherms. The distribution of water in the cellulose materials was found to be characterized by a fractal dimension smaller than 1.5 for all powders. The results showed that for highly crystalline cellulose materials, such as Cladophora cellulose, the cellulose-water interactions take place mainly on cellulose fibril surfaces adjacent to open pores without causing any significant swelling of the material. For less ordered celluloses the water interaction was found to take place inside the bulk material and the water uptake process caused the pore volume to swell between 1 and 2 orders in magnitude. For the Cladophora cellulose, the thickness of the adsorbed water layer at the outer cut off of the fractal region was found to coincide very well with the average pore size obtained from nitrogen adsorption measurements. The multilayer fractal BET analysis on nitrogen adsorption isotherms showed that the particles could be characterized by fractal dimensions between 2.13 and 2.50. We conclude that water adsorption has the ability to alter the structure of the studied material and reveal a sorption-induced, "apparent" fractal structure over a relatively narrow length scale interval, while nitrogen adsorption probes the substrate morphology over a wide range of length scales and reveals the "true" fractal structure.

  • 304.
    Strömme, Maria
    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.
    Ek, Ragnar
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Densification-induced conductivity percolation in high-porosity pharmaceutical microcrystalline cellulose compacts2003In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 82, no 4, p. 648-650Article in journal (Refereed)
    Abstract [en]

    The percolation theory is established as a useful tool in the field of pharmaceutical materials science.It is shown that percolation theory, developed for analyzing insulator–conductor transitions, can beapplied to describe imperfect dc conduction in pharmaceutical microcrystalline cellulose duringdensification. The system, in fact, exactly reproduces the values of the percolation threshold andexponent estimated for a three-dimensional random continuum. Our data clearly show a crossoverfrom a power-law percolation theory region to a linear effective medium theory region at a celluloseporosity of ;0.7.

  • 305.
    Strömme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Determination of fractal dimension by cyclic I-V studies: The Laplace-transform method1995In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 52, no 19, article id 14192Article in journal (Refereed)
    Abstract [en]

    A method is introduced for the determination of fractal dimension df from cyclic voltammograms taken on films in contact with an electrolyte. It is based on a Laplace transform of the Nernst equations using Riemann-Liouville transform expressions for the surface concentrations. Diffusion-limited conditions are required. The method is applicable even when resistance drops are present in the electrolyte or across the film. Our Laplace transform method gave correct results for gold electrodes with known df and it also provided a fractal dimension of a partially active In oxide surface in good agreement with that obtained from an independent technique.

  • 306.
    Strömme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Diffusion of Li, Na and K in fluorinated Ti dioxide films: Applicability of the Anderson-Stuart Model1997In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 81, p. 2167-2172Article in journal (Refereed)
    Abstract [en]

    Fluorinated Ti dioxide films were made by reactive sputtering. The mobility of Li, Na, and K in this host was studied by electrochemical techniques. Chronopotentiometry suggested that the cations occupy one type of site for cation/Ti ratios below 0.5, and that other sites are populated at higher ratios. Li and Na intercalation appeared to progress without major structural changes, whereas the intercalation of the larger K ions caused structural rearrangement. Impedance spectra were interpreted within a Randles circuit with a finite length Warburg element from which chemical diffusion coefficients were obtained at different intercalation levels and temperatures. The ion diffusion could be understood in detail from the classical Anderson–Stuart model [O. L. Anderson and D. A. Stuart, J. Am. Ceram. Soc. 37, 573 (1954)] as long as the structure remained unchanged, i.e., for the Li and Na intercalation, whereas K intercalation, expectedly, could not be reconciled with this model.

  • 307.
    Strömme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Fractal dimension of Li insertion electrodes studied by diffusion-controlled voltammetry and impedance spectroscopy1996In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 54, no 5, p. 2968-2971Article in journal (Refereed)
    Abstract [en]

    We show that a unique fractal dimension can be obtained for Li insertion electrodes by applying two different electrochemical methods to samples of porous Sn oxide and Ti oxide. The first method relies on the assumption that the current recorded in voltammetric experiments, conducted in a Li containing electrolyte, is limited by Li diffusion from the fractal working electrode surface into the oxide matrix. The second method is based on the capacitance dispersion observed in impedance spectroscopy. Simple scaling arguments show that this capacitance dispersion is related to the fractal structure of surface roughness

  • 308.
    Strömme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Fractal surface dimension from cyclic I-V studies and Atomic Force Microscopy; Role of non-contiguous reaction sites1996In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 54, no 24, p. 17884-17887Article in journal (Refereed)
    Abstract [en]

    Films of In oxide and Sn oxyfluoride were made by magnetron sputtering and spray pyrolysis, respectively. Cyclic voltammetry on films in contact with an electrolyte, and atomic-force microscopy (AFM) on as-deposited films, showed that the fractal dimension obtained from the voltammetric peak-current technique is in excellent agreement with the fractal hillock distribution received via the mass-radius method applied to thresholded AFM images.

  • 309.
    Strömme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Li diffusion in Ti oxyfluoride films: Thermal activation energy and jump length derived from impedance spectroscopy1996In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 80, no 4, p. 2169-2174Article in journal (Refereed)
    Abstract [en]

    Li ions were electrochemically intercalated into sputtered Ti oxyfluoride films. The process was found to be thermally activated with an activation energy depending on the amount of intercalated Li and decreasing with increasing Li content. The chemical diffusion coefficient was thermally activated as well with an activation energy of ∼0.5 eV independent of the amount of intercalated Li. The origin of the activation energy was discussed in terms of the Anderson–Stuart model. It was found likely that strain energy is needed to open up ‘‘doorways’’ in the Ti oxyfluoride structure to allow Li ion transport. The jump length for the Li ions inside the Ti oxyfluoride was estimated to lie in the 4–8 Å interval.

  • 310.
    Strömme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    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 Materials Science. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Voltammetry on fractals1995In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 96, no 3, p. 151-154Article in journal (Refereed)
    Abstract [en]

    New methods are introduced for determining the fractal dimension df of a surface from cyclic voltammograms. The separation between current peaks is strongly dependent on df, provided that the current is diffusion limited. We also derive a new Randles-Sevcik equation-relating the diffusion coefficient to the peak current of a voltammogram—that holds for electrodes with fractal surfaces. This equation gives a simple additional method of determining df from voltammetry using recordings of the peak current at different scan rates.

  • 311.
    Strömme, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Ritala, M
    Leskela, M
    Kukli, K
    (Ta1-xNbx)(2)O-5 films produced by atomic layer deposition: Temperature dependent dielectric spectroscopy and room-temperature I-V characteristics2001In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 90, no 9, p. 4532-4542Article in journal (Refereed)
    Abstract [en]

    Temperature dependent ac dielectric spectroscopy and room-temperature I–V characterization were performed on atomic layer deposited(Ta1−xNbx)2O5films. The high frequency permittivity, as well as the dc conductivity of the films, were found to increase with increasing Nb content. The conduction mechanism in the mixed Ta–Nb oxide films was of the Poole–Frenkel type, while the high field conduction in pure Ta2O5 was space-charge limited. The activation energy for dc conduction was higher in mixed Ta–Nb oxides compared to pure Ta2O5 and Nb2O5films. Irreversible changes in the conduction mechanism took place upon heat treatment above a certain irreversibility temperature. This temperature was higher for the mixed oxides than for the binary ones.

  • 312.
    Topalian, Zareh
    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.
    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.
    Kish, Laszlo B.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Resistance noise at the metal-insulator transition in thermochromic VO2 films2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 2, p. 1-7, article id 025303Article in journal (Refereed)
    Abstract [en]

    Thermochromic VO2 films were prepared by reactive DC magnetron sputtering onto heated sapphire substrates and were used to make 100-nm-thick samples that were 10 lm wide and 100 lm long. The resistance of these samples changed by a factor similar to 2000 in the 50<T-s<70 degrees C range of temperature T-s around the "critical" temperature T-c between a low-temperature semiconducting phase and a high-temperature metallic-like phase of VO2. Power density spectra S(f) were extracted for resistance noise around T-c and demonstrated unambiguous 1/f behavior. Data on S(10 Hz)/R-s(2) scaled as R-s(x), where R-s is sample resistance; the noise exponent x was -2.6 for T-s< T-c and +2.6 for T-s>T-c. These exponents can be reconciled with the Pennetta-Trefan-Reggiani theory [Pennetta et al., Phys. Rev. Lett. 85, 5238 (2000)] for lattice percolation with switching disorder ensuing from random defect generation and healing in steady state. Our work hence highlights the dynamic features of the percolating semiconducting and metallic-like regions around T-c in thermochromic VO2 films. (C) 2015 AIP Publishing LLC.

  • 313.
    Topalian, Zareh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Li, S-Y
    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, CG
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kish, Laszlo B
    Percolation noise at the metal-insulator transition of nanostructured VO2 films2015In: Extended Abstracts, 2015Conference paper (Refereed)
  • 314.
    Topalian, Zareh
    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-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Spectroscopic study of the photofixation of SO2 on anatase TiO2 thin films and their oleophobic properties2012In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 4, no 2, p. 672-679Article in journal (Refereed)
    Abstract [en]

    Photoinduced SO2 fixation on anatase TiO2 films was studied by in situ Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The TiO2 films were prepared by reactive DC magnetron sputtering and were subsequently exposed to 50 ppm SO2 gas mixed in synthetic air and irradiated with UV light at substrate temperatures between 298 and 673 K. Simultaneous UV irradiation and SO2 exposure between 373 and 523 K resulted in significant sulfur (S) deposits on crystalline TiO2 films as determined by XPS, whereas amorphous films contained negligible amounts of S. At substrate temperatures above 523 K, the S deposits readily desorbed from TiO2. The oxidation state of sulfur successively changed from S4+ for SO2 adsorbed on crystalline TiO2 films at room temperature without irradiation to S6+ for films exposed to SO2 at elevated temperatures with simultaneous irradiation. In situ FTIR was used to monitor the temporal evolution of the photoinduced surface reaction products formed on the TiO2 surfaces. It is shown that band gap excitation of TiO2 results in photoinduced oxidation of SO2, which at elevated temperatures become coordinated to the TiO2 lattice through interactions with O vacancies and form sulfite and sulfate surface species. These species makes the surface acidic, which is manifested in nondetectable adherence of stearic acid to the modified surface. The modified films show good chemical stability as evidenced by sonication and repeated recycling of the films. The results suggest a new method to functionalize wide band gap oxide surfaces by means of photoinduced reactions in reactive gases at elevated substrate temperatures. In the case of anatase TiO2 in reactive SO2 gas, we here show that such functionalization yields surfaces with excellent oleophobic properties, as probed by adhesion of stearic acid.

  • 315.
    Topalian, Zareh
    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.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Photo-Fixation of SO2 in Nanocrystalline TiO2 Films Prepared by Reactive DC Magnetron Sputtering2009In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 518, no 4, p. 1341-1344Article in journal (Refereed)
    Abstract [en]

    We report on photo-fixation of SO2 onto nanostructured TiO2 thin films prepared by reactive DC magnetron sputtering. The films were exposed to 50 PPM SO2 gas mixed in synthetic air and illuminated with UV light at 298 and 473 K. The evolution of the adsorbed SOx species was monitored by in situ Fourier transform infrared specular reflection spectroscopy. Significant photo-fixation occurred only in the presence of UV illumination. The SO2 uptake was dramatically enhanced at elevated temperatures and then produced strongly bonded surface-coordinated SO, complexes. The total SO, uptake is consistent with Langmuir adsorption kinetics. The sulfur doping at saturation was estimated from X-ray photoelectron spectroscopy to be similar to 2.2 at.% at 473 K These films were pale yellowish and had an optical absorption coefficient being similar to 3 times higher than in undoped film. The S-doped films exhibit interesting oleophobic properties, exemplified by the poor adherence of stearic acid. Our results suggest a new method for sulfur doping of TiO2 to achieve combined anti-grease and photocatalytic properties.

  • 316.
    Topalian, Zareh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Smulko, J M
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Granqvist, Claes G
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Resistance Noise in TiO2-Based Thin Film Gas Sensors under Ultraviolet Irradiation2007Conference paper (Refereed)
  • 317.
    Triana, C. A.
    et al.
    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.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromic Properties of Amorphous Tungsten Oxide α-WO3-x (0 ≤ x ≤ 1)2014In: Abstracts European Materials Research Society (E-MRS) Spring Meeting: Abstract L VII-5, 2014, Vol. L VII-5Conference paper (Refereed)
  • 318.
    Triana, C. A.
    et al.
    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.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromic Properties of Li+-Intercalated Amorphous Tungsten (aWO3-x) and Titanium (aTiO2-x) Oxide Thin Films2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 559, no 1, article id 012004Article in journal (Refereed)
    Abstract [en]

    ABSTRACT: We report on electrochromic properties of stoichiometric and oxygen-deficient amorphous films, denoted aWO3-x and aTiO2-x, under Li+-ion-electron inter/deintercalation. Optical characterization of the films in their as-deposited, fully intercalated (dark), and bleached states were performed by in-situ optical transmittance measurements. We explore electrochromism and optical absorption phenomena in the context of oxygen deficiency and nanostructure. Studies by cyclic voltammetry suggest good optical modulation and charge capacity upon Li+-ion-electron inter/deintercalation for almost stoichiometric films.

    Full-text · Article · Nov 2014 · Journal of Physics Conference Series

  • 319.
    Triana, C. A.
    et al.
    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.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Optical Absorption and Small-Polaron Hopping in Oxygen Deficient and Lithium Intercalated Amorphous Tungsten Oxide Films2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 024901, p. 024901/1-024901/9Article in journal (Refereed)
  • 320.
    Triana, C. A.
    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.
    Electrochromism in Li+-intercalated amorphous titanium oxide thin films.2014In: 5th International Symposium on Transparent Conductive Materials, 12-17 October 2014, Chania, Crete, Greece, 2014Conference paper (Other academic)
  • 321.
    Triana, Carlos A.
    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
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromic Properties of Li+-Intercalated Amorphous Tungsten (aWO(3-x)) and Titanium (aTiO(2-x)) Oxide Thin Films2014In: INERA WORKSHOP: Transition Metal Oxide Thin Films-Functional Layers In Smart Windows And Water Splitting Devices. Parallel Session Of The 18th International School On Condensed Matter Physics / [ed] Ivanova, T; Gesheva, K; Chamatti, H; Popkirov, G, 2014, p. UNSP 012004-Conference paper (Refereed)
    Abstract [en]

    We report on electrochromic properties of stoichiometric and oxygen-deficient amorphous films, denoted aWO(3-x) and aTiO(2-x), under Li+-ion-electron inter/deintercalation. Optical characterization of the films in their as-deposited, fully intercalated (dark), and bleached states were performed by in-situ optical transmittance measurements. We explore electrochromism and optical absorption phenomena in the context of oxygen deficiency and nanostructure. Studies by cyclic voltammetry suggest good optical modulation and charge capacity upon Li+-ion-electron inter/deintercalation for almost stoichiometric films.

  • 322.
    Triana, Carlos A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Araujo, C. Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Modeling of Electronic Properties of Amorphous Oxides2017In: Encyclopedia of Interfacial Chemistry: Surfaces and Electrochemistry / [ed] K. Wandelt, Elsevier, 2017Chapter in book (Refereed)
    Abstract [en]

    Amorphous transition metal oxides [aTMOs] are used as multifunctional materials in many technological applications. Adetailed understanding of the electronic density of states is a necessary prerequisite for modeling their functional properties. The electronic properties, however, are structure-dependent making the description of the electronic structure of disordered and amorphous materials challenging. Here we present a scheme based on obtaining atomic model-structures from simulations of experimental X-ray-Absorption spectra, together with first principles electronic structure calculations. This approach provides a self-consistent framework to assess fundamental electronic processes in aTMOs and can be applied to the study of disordered and amorphous materials in general.

  • 323.
    Triana, Carlos A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Disentangling the intricate atomic short-range order and electronic properties in amorphous transition metal oxides2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 2044Article in journal (Refereed)
    Abstract [en]

    Solid state materials with crystalline order have been well-known and characterized for almost a century while the description of disordered materials still bears significant challenges. Among these are the atomic short-range order and electronic properties of amorphous transition metal oxides [aTMOs], that have emerged as novel multifunctional materials due to their optical switching properties and high-capacity to intercalate alkali metal ions at low voltages. For decades, research on aTMOs has dealt with technological optimization. However, it remains challenging to unveil their intricate atomic short-range order. Currently, no systematic and broadly applicable methods exist to assess atomic-size structure, and since electronic localization is structure-dependent, still there are not well-established optical and electronic mechanisms for modelling the properties of aTMOs. We present state-of-the-art systematic procedures involving theory and experiment in a self-consistent computational framework to unveil the atomic short-range order and its role for the electronic properties. The scheme is applied to amorphous tungsten trioxide aWO(3), which is the most studied electrochromic aTMO in spite of its unidentified atomic-size structure. Our approach provides a one-to-one matching of experimental data and corresponding model structure from which electronic properties can be directly calculated in agreement with the electronic transitions observed in the XANES spectra.

  • 324.
    Triana, Carlos A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Modeling of Electronic Properties of Amorphous Oxides2018In: Encyclopedia of Interfacial Chemistry:: Surface Science and Electrochemistry / [ed] Wandelt, K., Elsevier, 2018, p. 319-331Chapter in book (Refereed)
    Abstract [en]

    Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry summarizes current, fundamental knowledge of interfacial chemistry, bringing readers the latest developments in the field. As the chemical and physical properties and processes at solid and liquid interfaces are the scientific basis of so many technologies which enhance our lives and create new opportunities, its important to highlight how these technologies enable the design and optimization of functional materials for heterogeneous and electro-catalysts in food production, pollution control, energy conversion and storage, medical applications requiring biocompatibility, drug delivery, and more. This book provides an interdisciplinary view that lies at the intersection of these fields.

  • 325.
    Triana, Carlos A.
    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.
    Electrochromism and small-polaron hopping in oxygen deficient and lithium intercalated amorphous tungsten oxide films2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 2, p. 1-9, article id 024901Article in journal (Refereed)
    Abstract [en]

    Thin films of LixWO3-z with 0 <= x <= 0.27 and 0 <= z <= 0.27 were prepared by sputter deposition followed by electrochemical lithiation. Kramers-Kronig-consistent complex dielectric functions were obtained for these films by numerical inversion of experimental spectra of optical transmittance and reflectance by using a superposition of Tauc-Lorentz and Lorentz oscillator models. Low-energy optical absorption bands were induced by oxygen vacancies and/or by electrochemical intercalation of Li+ species together with charge compensating electrons. The experimental optical conductivity was fitted to a small-polaron model for disordered systems with strong electron-phonon interaction, taking into account transitions near the Fermi level. The optical absorption is due to small-polaron hopping and associated with the formation of W5+ states due to transfer of electrons from oxygen vacancies and/or insertion of Li+ species. The results also show increases in the Fermi level, caused by oxygen deficiency or Li+ insertion, which occur along with a band gap shift towards higher energies for the Li+ intercalated films.

  • 326.
    Triana, Carlos A.
    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.
    Elektrochromic Properties of Amorphous Tungsten Oxide a-WO3-x(0≤x≥1)2014In: European Materials Research Society (E-MRS) Spring Meeting, Lille, France, 26-30 May: Symposium L: Chromogenic Materials and Devices, 2014Conference paper (Refereed)
  • 327.
    Triana, Carlos A.
    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.
    Optical absorption and small-polaron hopping in oxygen deficient and lithium-ion-intercalated amorphous titanium oxide films2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 1, article id 015701Article in journal (Refereed)
    Abstract [en]

    Optical absorption in oxygen-deficient and Li+-ion inserted titanium oxide films was studied in the framework of small-polaron hopping. Non-stoichiometric TiOy films with 1.68 <= y <= 2.00 were deposited by reactive DC magnetron sputtering and were subjected to electrochemical intercalation of Li+-ions and charge-balancing electrons to obtain LixTiOy films with 0.12 <= x <= 0.34. Dispersion analysis was applied to calculate the complex dielectric function epsilon((h) over bar omega) =epsilon(1) ((h) over bar omega) + i epsilon(2)((h) over bar omega) from numerical inversion of optical transmittance and reflectance spectra; a superposition of Tauc-Lorentz and Lorentz oscillator models was used for this purpose. Data on epsilon(2)((h) over bar omega) were employed to calculate the optical conductivity and fit this property to a small-polaron model for disordered systems with strong electron-phonon interaction and involving transitions near the Fermi level. The introduction of oxygen vacancies and/or Li+ insertion yielded band gap widening by similar to 0.20-0.35 eV, and both processes induced similar low-energy optical absorption. The small-polaron-based analysis indicated increases in the Fermi level by similar to 0.15-0.3 eV for sub-stoichiometric and/or Li+-inserted films. This suggests the existence of polaronic Ti3+ states in the lower part of the conduction band arising from transfer of electrons from oxygen vacancies and/or inserted Li+ species. The present article is a sequel to an earlier paper on oxygen-deficient and/or Li+-inserted amorphous WOy thin films and forms part of a comprehensive investigation of optical absorption in amorphous transition metal oxides with different valence states of the metallic ions.

  • 328.
    Triana, Carlos
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electronic transitions induced by short-range structural order in amorphous TiO22016In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 94, no 16, article id 165129Article in journal (Refereed)
    Abstract [en]

    Several promising applications of amorphous titanium dioxide, aTiO2, have appeared recently, but thecorrelation between electronic properties and atomic short-range structural order is poorly understood. Herein weshow that structural disorder yields local undercoordinated TiOx units which influence electronic hybridization ofTi-[4p] andTi-[3d] orbitals with a lowcrystal-field splitting [E(eg)-E(t2g) = 2.4 ± 0.3 eV]. The short-range orderand electronic properties of aTiO2 thin-film oxides are described through an integrated approach based on x-rayabsorptionexperiments and ab initio computational simulations where the energy splitting of the electronic levelsin the Ti-[4p-3d]manifold are analyzed. Structural disorder provides enough p-d orbitalmixing for the hybridizedelectronic transitions from the Ti-[1s] core level into the [Ti-t2g] and [Ti-eg] bands [1s → 4p-3d excitations],to be allowed. This yields an intense pre-edge structure in the Ti K-edge x-ray-absorption near-edge structurespectrum of aTiO2, which is consistent with the projected density of states on the photoabsorbing Ti atoms.

  • 329. Tuncer, Enis
    et al.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Optical properties of non-dilute metal-insulator composites2008In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 281, no 17, p. 4374-4379Article in journal (Refereed)
    Abstract [en]

    The description of the optical properties of metal-insulator composites in the non-dilute region is a long standing problem. In this letter we extract the spectral density function of cobalt-amorphous aluminum oxide composites from optical and near-infrared data. The spectral functions are accurately computed numerically with the help of a recently developed technique. It is observed that the spectral features of the prepared composites change with increasing cobalt content. For low concentrations of cobalt, only one depolarization peak is found that corresponds to the Maxwell Garnett approximation. For concentrations higher than 11% cobalt, three effective depolarization factors are resolved that move towards low spectral parameter values with increasing cobalt content. Such a multi-peak structure arises naturally in fractal equivalent Circuit models for the optical properties. A comparison with a deterministic fractal model is presented to illustrate the strength of the spectral density representation and to better comprehend our results. We conclude that the observed behavior gives important information on the relation of the optical characteristics to the composite micro-structure.

  • 330.
    Tuncer, Enis
    et al.
    Texas Instruments Inc..
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Properties of Bruggeman Dielectric Mixture Expression2014In: Proceedings IEEE Conference on Electrical Insulation and Dielectric Phenomena, IEEE conference proceedings, 2014, p. 875-878Conference paper (Refereed)
    Abstract [en]

    Bruggeman dielectric mixture expression is one of the widely used methods to characterize properties of heterogeneous materials. In this contribution, dielectric response ofmixture systems generated with the Bruggeman effective mixture expression is studied to investigate the broadening of dielectric relaxation at various filler contents. The mixture is composed of two dielectric media. The studies are conducted below and above the percolation threshold for three-dimensional systems, where the percolation threshold qc is at 1/3. The percolating and non percolatingparts of the mixture are estimated with the spectral density representation using a non-parametric numerical analysis technique based on the Monte Carlo integration hypothesis. A conventional dielectric relaxation model is also applied to represent data.

  • 331. Valizadeh, Sima
    et al.
    Coleman, Victoria
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Strömberg, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Welch, Ken
    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, Nanotechnology and Functional Materials.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Focused ion beam fabricated nanowire based electrodes for transport studies of biomolecules and nanoparticles2007In: IVC-17/ICSS-13 and ICN+T 2007, 2007Conference paper (Refereed)
  • 332. Valyukh, I.
    et al.
    Green, S.
    Granqvist, C.-G.
    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.
    Valyukh, S.
    Wäckelgård, Ewa
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Arwin, H.
    Optical Properties of Thin Films of Mixed W-Ni Oxides Made by DC Magnetron Sputtering2010Conference paper (Refereed)
  • 333.
    Valyukh, I
    et al.
    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.
    Arwin, H
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wäckelgård, Ewa
    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 Amorphous Tungsten Oxide Films Deposited by Reactive DC Magnetron Sputtering2009Conference paper (Refereed)
  • 334.
    Valyukh, I
    et al.
    Laboratory of Applied Optics, Dept of Physics, Chemistry and Biology, Linköping University, Linköping.
    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.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Valyukh, S
    Laboratory of Applied Optics, Dept of Physics, Chemistry and Biology, Linköping University, Linköping.
    Arwin, H
    Laboratory of Applied Optics, Dept of Physics, Chemistry and Biology, Linköping University, Linköping.
    Optical properties of thin films of mixed Ni-W oxide made by reactive DC magnetron sputtering2011In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 9, p. 2914-2918Article in journal (Refereed)
    Abstract [en]

    Thin films of NixW1-x oxides with x = 0.05, 0.19, 0.43 and 0.90 were studied. Films with thicknesses in the range 125-250 nm were deposited on silicon wafers at room temperature by reactive DC magnetron co-sputtering from targets of Ni and W. The films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectroscopic ellipsometry (SE). XRD spectra and SEM micrographs showed that all films were amorphous and possessed a columnar structure. The ellipsometric angles psi and Delta of as-deposited films were measured by a rotating analyzer ellipsometer in the UV-visible-near infrared range (0.63-6.18 eV) and by an infrared Fourier transform rotating compensator ellipsometer in the 500-5200 cm(-1) wavenumber range. SE measurements were performed at angles of incidence of from 50 degrees to 70 degrees. Parametric models were used to extract thicknesses of the thin films and overlayers of NixW1-x oxide at different compositions, band gaps and optical constants. Features in the optical spectra of the NixW1-x oxides were compared with previous data on tungsten oxide, nickel oxide and nickel tungstate.

  • 335. Valyukh, I.
    et al.
    Johansson, M. B.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Valyukh, S.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Arwin, H.
    Influence of Gas Pressure on Optical Properties of Polycrystalline WO3 Films Deposited by Reactive DC Magnetron Sputtering2011Conference paper (Refereed)
  • 336.
    Valyukh, Iryna
    et al.
    Department of Material Science, Dalarna University.
    Green, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Arwin, Hans
    Laboratory of Applied Optics, Department of Physics, Chemistry and Biology, Linköping University.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wäckelgård, Ewa
    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.
    Spectroscopic ellipsometry characterization of electrochromic tungsten oxide and nickel oxide thin films made by sputter deposition2010In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 94, no 5, p. 724-732Article in journal (Refereed)
    Abstract [en]

    Electrochromic films of tungsten oxide and nickel oxide were made by reactive dc magnetron sputtering and were characterized by X-ray diffraction, Rutherford backscattering spectrometry, scanning electron microscopy, and atomic force microscopy. The optical properties were investigated in detail by spectroscopic ellipsometry and spectrophotometry, using a multiple-sample approach. The W oxide film was modeled as a homogeneous isotropic layer, whereas the Ni oxide film was modeled as an anisotropic layer with the optical axis perpendicular to the surface. Parametric models of the two layers were then used to derive complex refractive index in the 300-1700-nm-range, film thickness, and surface roughness. A band gap of 3.15 eV was found for the W oxide film, using a Tauc-Lorentz parameterization. For the Ni oxide film, taken to have direct optical transitions, band gaps along the optical axis, perpendicular to it, and in an isotropic intermediate layer at the bottom of the film were found to be 3.95, 3.97, and 3.63 eV, respectively. Parameterization for the Ni oxide was made by use of the Lorentz model.

  • 337.
    Valyukh, Iryna
    et al.
    Laboratory of Applied Optics, Dept of Physics, Chemistry and Biology, Linköping University.
    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.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Arwin, Hans
    Laboratory of Applied Optics, Dept of Physics, Chemistry and Biology, Linköping University.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ellipsometrically determined optical properties of nickel-containing tungsten oxide thin films: Nanostructure inferred from effective medium theory2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, no 4, p. 044308-Article in journal (Refereed)
    Abstract [en]

    Films of NixW1−x oxide with 0.05 ≤ x ≤ 0.53 were produced by reactive dc magnetron co-sputtering onto Si. Such films have documented electrochromism. Spectroscopic ellipsometry was used to extract accurate data on the dielectric function in the photon range 0.062 to 5.62 eV. The results for 0.62 to 5.62 eV were compared with computations from the Bruggeman effective medium theory applied to two nanostructural models: one representing a random mixture of structural entities characterized by the dielectric functions of WO3 and NiWO4 and the other describing a random mixture of WO3 and NiO. Unambiguous evidence was found in favor of the former model, and hence the films are composed of nanosized tungsten oxide and nickel tungstate. This agrees excellently with an earlier investigation of ours on NixW1−x oxide films, where nanostructure was inferred from Raman spectroscopy, x-ray photoelectron spectroscopy, and x-ray diffraction.

  • 338.
    Valyukh, Iryna
    et al.
    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.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Valyukh, Sergiy
    Arwin, Hans
    Optical properties of thin films of mixed Ni–W oxide made by reactive DCmagnetron sputtering2011In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 9, p. 2914-2918Article in journal (Refereed)
    Abstract [en]

    Thin films of NixW1−x oxides with x=0.05, 0.19, 0.43 and 0.90 were studied. Films with thicknesses in the range 125–250 nm were deposited on silicon wafers at room temperature by reactive DC magnetron co-sputtering from targets of Ni and W. The films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectroscopic ellipsometry (SE). XRD spectra and SEMmicrographs showed that all films were amorphous and possessed a columnar structure. The ellipsometric angles Ψ and Δ of as-deposited films were measured by a rotating analyzer ellipsometer in the UV–visible-near infrared range (0.63–6.18 eV) and by an infrared Fourier transform rotating compensator ellipsometer in the 500–5200 cm−1 wavenumber range. SE measurementswere performed at angles of incidence of from50 ° to 70 °. Parametricmodelswere used to extract thicknesses of the thin films and overlayers of NixW1−x oxide at different compositions, band gaps and optical constants. Features in the optical spectra of the NixW1−x oxideswere compared with previous data on tungsten oxide, nickel oxide and nickel tungstate.

  • 339. Vargas, W E
    et al.
    Amador, A
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Diffuse Reflectance of TiO2 Pigmented Paints: Spectral Dependence of the Average Pathlength Parameter and the Forward Scattering Ratio2006In: Optics Commun., no 261, p. 71-78Article in journal (Refereed)
  • 340.
    Vargas, W. E.
    et al.
    Acad Nacl Ciencias Costa Rica, San Jose, Costa Rica;Univ Costa Rica, Ctr Invest Ciencia & Ingn Mat & Escuela Fis, San Jose 11501, Costa Rica.
    Clark, N.
    Univ Costa Rica, Ctr Invest Ciencia & Ingn Mat & Escuela Fis, San Jose 11501, Costa Rica.
    Munoz-Rojas, F.
    Univ Costa Rica, Ctr Invest Ciencia & Ingn Mat & Escuela Fis, San Jose 11501, Costa Rica.
    Azofeifa, D. E.
    Univ Costa Rica, Ctr Invest Ciencia & Ingn Mat & Escuela Fis, San Jose 11501, Costa Rica.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Optical, charge transport and magnetic properties of palladium retrieved from photometric measurements: approaching the quantum mechanics background2019In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 94, no 5, article id 055101Article in journal (Refereed)
    Abstract [en]

    A parametric Drude-Lorentz (DL) model is used to describe the spectral variation of the dielectric functions of bulk palladium samples at low and room temperature. In addition to the contribution of conduction electrons, the contribution of holes is also explicitly accounted for in the model. A simulated annealing method is applied to obtain the optimized values of the parameters involved in the model: volume plasma frequency of conduction electrons, high frequency dielectric constant, collision frequency of holes and corresponding relaxation time, and two additional parameters from which the effective mass of holes and collision frequency of conduction electrons are evaluated. Oscillatior strengths, resonance frequencies, and widths entering in the Lorentz contribution to the dielectric function are also optimized. Renormalization of the oscillator strengths requires the introduction of a new parameter in the context of the DL model: the ratio between number density of conduction electrons and number density of metal atoms, whose optimized value fits very well with its evaluation from band structure calculations and from independent measurements. Inclusion of this parameter in the framework allows us to evaluate additional quantities related to the charge-carrier transport: average effective masses, Fermi energies and electronic densities of states at the corresponding Fermi energies, intrinsic electrical resistivity, intrinsic mean free paths, heat capacities, mobilities, as well as paramagnetic and diamagnetic susceptibilities, for both electrons and holes. The optimized resonance frequencies are compared with energy differences between plausible interband transitions, in accordance with reported band structure diagrams and with our own band structure obtained from density functional theory calculations.

  • 341.
    Waita, S. M.
    et al.
    Department of Physics, University of Nairobi.
    Aduda, B. O.
    Department of Physics, University of Nairobi.
    Mwabora, J. M.
    Department of Physics, University of Nairobi.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lindquist, Sten-Eric
    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.
    Hagfeldt, Anders
    KTH, Fysikalisk kemi, Physical Chemistry.
    Boschloo, Gerrit K.
    KTH, Fysikalisk kemi, Physical Chemistry.
    Electron Transport and Recombination in Dye Sensitized Solar Cells Fabricated from Obliquely Sputter Deposited and Thermally Annealed TiO2 Films2007In: Journal of Electroanalytical Chemistry, ISSN 0022-0728, E-ISSN 1873-2569, Vol. 605, no 2, p. 151-156Article in journal (Refereed)
    Abstract [en]

    Dye sensitized solar cells based on annealed titanium dioxide films prepared by oblique reactive DC magnetron sputtering have been investigated in detail. Electron transport and recombination were studied using intensity-modulated photocurrent and photovoltage spectroscopy. Electron transport time as well as lifetime were found to increase upon lowering of the light intensity and to increase upon increasing the thickness of the TiO2 film. The properties are very similar to those observed for solar cells based on colloidal TiO2 films despite the morphologies being very different. In all cases, films are composed of a porous assembly of TiO2 nanocrystals. Grain boundaries with associated trap and/or energy barriers may explain the observed transport properties.

  • 342.
    Waita, Sebastian M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Aduda, B O
    Mwabora, J M
    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.
    Boschloo, Gerrit
    Electrochemical Characterization of TiO2 Blocking Layers Prepared by Reactive DC Magnetron Sputtering2009In: Journal of Electroanalytical Chemistry, ISSN 0022-0728, E-ISSN 1873-2569, Vol. 637, no 1-2, p. 79-83Article in journal (Refereed)
    Abstract [en]

    Thin TiO2 (anatase) films were prepared by reactive DC magnetron sputtering and characterized in detail. Specifically, they were tested as compact blocking underlayers in dye-sensitized solar cells. Elastic recoil detection analysis and optical measurement showed some porosity in the sputtered films, but electrochemical measurements demonstrated good blocking characteristics. This suggests the presence of small voids rather than pinholes in the deposited films. In the case of an iodide/iodine redox couple, thin underlayers (similar to 20 nm) improved the fill factor without affecting other properties of the cell. in case of a ferrocene/ferrocenium-based electrolyte, the presence of underlayers was necessary to obtain functional dye-sensitized solar cells.

  • 343.
    Wang, JunXin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nilsson, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Fernandes, Daniel L. A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Angle dependent light scattering by gold nanospheres2015In: INERA Conference: Book of Abstracts, 2015, p. 71-, article id 012018Conference paper (Refereed)
    Abstract [en]

    Gold nanocrystals exhibit unique optical properties in enhanced light absorption and scattering owing to their extremely large scattering/absorption cross. sections and large electric field enhancements generated by localized surface plasmon resonance. In this work, the optical properties of gold nanospheres with diameters of 60 nm and 200 nm with remarkable uniformity in size were studied both numerically and experimentally. The total transmittance and reflectance as well as the angle. resolved light scattering intensities of the gold nanospheres were measured. The absorption and scattering coefficients were obtained by fitting the experimental data to the two. flux theory and were in qualitative agreement with single. scattering calculations using the Mie theory.

  • 344.
    Wang, JunXin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nilsson, Annica M.
    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 by 2D- and 3D- Angle-Resolved Spectroscopy2016In: INERA Conference: Vapor Phase Technologies for Metal Oxide and Carbon Nanostructures, 2016Conference paper (Refereed)
  • 345.
    Wang, JunXin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Xu, Changgang
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Xian Univ Sci & Technol, Sch Mat Sci & Engn, Xian 710054, Shaanxi, Peoples R China.
    Nilsson, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Fernandes, Daniel L. A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    A novel phase function describing light scattering of layers containing colloidal nanospheres2019In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 11, no 15, p. 7404-7413Article in journal (Refereed)
    Abstract [en]

    Light scattering from small particles exhibit unique angular scattering distributions, which are strongly dependent on the radius to wavelength ratio as well as the refractive index contrast between the particles and the surrounding medium. As the concentration of the particles increases, multiple scattering becomes important. This complicates the description of the angular scattering patterns, and in many cases one has to resort to empirical phase functions. We have measured the angle dependence of light scattering from a polymer layer containing sub-micron metallic and dielectric particles. The samples exhibited strongly forward and backward peaked scattering patterns, which were fitted to a number of empirical approximative phase functions. We found that a novel two-term Reynolds-McCormick (TTRM) phase function gave the best fit to the experimental data in all cases. The feasibility of the TTRM approach was further validated by good agreement with numerical simulations of Mie single scattering phase functions at various wavelengths and sizes, ranging from the Rayleigh scattering regime to the geometrical optics regime. Hence, the widely adaptable TTRM approach is able to describe angular scattering distributions of different kinds of nanospheres and nanocomposites, both in the single scattering and multiple scattering regimes.

  • 346.
    Wang, JunXin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Xu, Changgang
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Xi'an University of Science and Technology.
    Nilsson, Annica M
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Fernandes, Daniel L. A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Strömberg, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wang, Jianfang
    Chinese University of Hong Kong.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    General Method for Determining Light Scattering and Absorption of Nanoparticle Composites2018In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 6, no 4, article id 1801315Article in journal (Refereed)
    Abstract [en]

    Scattering and absorption from nanoparticles are of major importance in optical research as well as in a range of applications. The Kubelka–Munk two-flux radiative transfer model gives a simple description of light scattering in nanoparticle composite materials, but inversion of experimental transmittance and reflectance data to obtain backscattering and absorption coefficients remains challenging. Here, a general method for evaluating these parameters from transmittance and reflectance spectra, combined with spectral angle resolved light scattering measurements is developed. The angular dependence is approximatedby an extension of the empirical Reynolds–McCormick phase function, which is fitted to the experimental angle resolved light scattering data. This approach is verified by measurements on three typical nanoparticle/polymer composites containing plasmonic Au, ferromagnetic Fe3O4, and dielectric TiO2 particles. An approximation to the angular scattering pattern is further demonstrated, which can be applied to obtain the optical parameters using only reflectance and transmittance data, in cases where angle-resolved measurements are not available. These results can be extended to a wide range of isotropic, anisotropic, and multiple scattering systems, and will be highly useful in the fields of light scattering coatings/metamaterials, UV-shielding films, displays, absorption/scattering layers in solar cells and biological scatterers.

  • 347.
    Wen, R.-T.
    et al.
    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.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Cyclic Voltammetry on Sputter-Deposited Films of Electrochromic Ni Oxide: Power-Law Decay of the Charge Density Exchange2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 163502, p. 163502/1-163502/4Article in journal (Refereed)
    Abstract [en]

    ABSTRACT: Ni-oxide-based thin films were produced by reactive direct-current magnetron sputtering and were characterized by X-ray diffraction and Rutherford backscattering spectroscopy. Intercalation of Li+ ions was accomplished by cyclic voltammetry (CV) in an electrolyte of LiClO4 in propylene carbonate, and electrochromism was documented by spectrophotometry. The charge density exchange, and hence the optical modulation span, decayed gradually upon repeated cycling. This phenomenon was accurately described by an empirical power law, which was valid for at least 10(4) cycles when the applied voltage was limited to 4.1V vs Li/Li+. Our results allow lifetime assessments for one of the essential components in an electrochromic device such as a "smart window" for energy-efficient buildings. (C) 2014 AIP Publishing LLC.

    Full-text · Article · Oct 2014 · Applied Physics Letters

  • 348.
    Wen, R.-T.
    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, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Anodic Electrochromic Nickel Oxide: The Role of Film Composition and Working Potential2014In: Abstracts European Materials Research Society (E-MRS) Spring Meeting: Abstract L VII-2, 2014, Vol. L VII-2Conference paper (Refereed)
  • 349. Wen, R.-T.
    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.
    Electrochromic Iridium Oxide: Compatibility with Propionic Acid, Potassium Hydroxide, and Lithium Perchlorate in Propylene Carbonate2014In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 120, p. 151-156Article in journal (Refereed)
  • 350.
    Wen, R.-T.
    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, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromic Nickel Oxide Films and Their Compatibility with Potassium Hydroxide and Lithium Perchlorate in Propylene Carbonate: Optical, Electrochemical and Stress-Related Properties2014In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 565, p. 128-135Article in journal (Refereed)
45678 301 - 350 of 378
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