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  • 301.
    Smulko, J
    et al.
    Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Polen.
    Kotarski, M
    Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Polen.
    Topalian, Zareh
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Kish, L B
    Dept of Electrical Engineering, Texas A&M University, College Station, USA.
    Fluctuation-enhanced gas sensing in practice2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The technique of fluctuation-enhanced sensing (FES) in resistive gas sensors was proposed a few years ago. The method improves the selectivity and sensitivity of gas detection. This was confirmed in numerous laboratory experiments. Some of the latest results obtained for practical applications of the FES method are presented (toxic gases detection; problems of detection repeatability; detection of essential oils intensity during aromatherapy, biological agent detection). Additionally, a new prototype nanoparticle gas sensor was introduced with an additional potential of gas detection using noise induced by UV irradiations.

  • 302. Sorar, I.
    et al.
    Pehlivan, E.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, C.-G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromism of DC Magnetron-Sputtered TiO2: Role of Film Thickness2014Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 318, s. 24-27Artikkel i tidsskrift (Fagfellevurdert)
  • 303.
    Sorar, Idris
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Hatay Mustafa Kemal University, Antakya, Turkey..
    Bayrak Pehlivan, Ilknur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Rojas Gonzalez, Edgar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Potentiostatic Rejuvenation of Electrochromic W,Ti Oxide Thin films.2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Electrochromic W–Ti oxide thin films were prepared by reactive DC magnetron sputtering and cycled voltammetrically in an electrolyte comprised of lithium perchlorate in propylene carbonate. The films were degraded  for up to 500 voltammetric cycles in thefor voltage ranges of 1.5–4.0, 1.6–4.0, 1.7–4.0 and 2.0–4.0 V vs. Li/Li+. The films were subjected to a potentiostatic rejuvenation at a constant voltage of 6 V for 20 h to accomplish ion de-trapping. Optical changes were recorded during the electrochemical degradation and rejuvenation. The degradation kinetics was parametrized by a power-law model based on dispersive chemical kinetics. The results showed that optical transmittance contrast between bleached and colored states was regained after the ion de-trapping. It was also found that Ti containing films were more stable than pure W oxide ones.

  • 304.
    Sorar, Idris
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Pehlivan, Esat
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. ChromoGenics AB.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromic properties of TiO2 thin films deposited by DC magnetron sputtering: The effect of total gas pressure and oxygen gas flow rate.2012Inngår i: IME-10. Tenth International meeting on Electrochromism, Holland, MI USA, August 12-16, 2012., 2012, s. 40-Konferansepaper (Fagfellevurdert)
  • 305.
    Sorar, Idris
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Pehlivan, Esat
    ChromoGenics AB, Uppsala.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromism of DC magnetron sputtered TiO2: Role of film thickness2014Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 318, s. 24-27Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Titanium dioxide films were prepared by reactive DC magnetron sputtering and the role of the film thick-ness d on the electrochromism was analyzed for 100 < d < 400 nm. The best properties were obtainedfor the thickest films, which yielded a mid-luminous transmittance modulation of 58% and a corre-sponding coloration efficiency of 26.3 cm2/C. The films were amorphous according to X-ray diffractionmeasurements and showed traces of adsorbed water as revealed by infrared spectroscopy.

  • 306.
    Sorar, Idris
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Pehlivan, Esat
    ChromoGenics AB.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromism of DC magnetron sputtered TiO2 thin films: Role of deposition parameters2013Inngår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 115, s. 172-180Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We performed a comprehensive study on the electrochromism in TiO2 thin films made by reactive DC magnetron sputtering and elucidated the roles of sputter gas pressure p, O-2/Ar gas ratio gamma and substrate temperature tau(s). Good mid-luminous optical modulation taken to be similar to 50% in similar to 200-nm-thick films was obtained under charge exchange in a Li+ electrolyte for p > 15 mTorr and tau(s) < 100 degrees C, whereas gamma was less important. The deposition rate dropped for increasing p, and hence p approximate to 15 mTorr was optimal. These films were X-ray amorphous and contained some water. The coloration efficiency eta was 25 cm(2)/C, which exceeds data on eta in most prior studies on sputter deposited TiO2 and verifies that such films can display the same values of eta as those of TiO2 films made by several chemical techniques.

  • 307.
    Sotelo, Juan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. University of Technology, Sydney, Australia.
    Ederth, Jesper
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Optical properties of polycrystalline metallic films2003Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, s. 195106-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We extend the Mayadas and Shatkes’s approach @Phys. Rev. B 1, 1382 ~1970!# to study the optical propertiesof polycrystalline metal thick films in the visible and far infrared range of the spectrum. We show that in thisrange grain boundary scattering can account for the experimentally observed lowering of the film reflectivity asthe mean size of its constituent grains decreases.

  • 308.
    Stefanov, Bozhidar
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Gunnar, Niklasson
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Österlund, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Quantitative relation between photocatalytic activity and degree of〈001〉orientation for anatase TiO2 thin films2015Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, nr 33, s. 17369-17375Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate a quantitative relation between exposed crystal surfaces and photocatalytic activity of nanocrystalline anatase TiO2. Thin films with controlled amount of 〈001〉 preferential orientation were prepared by reactive DC magnetron sputtering in Ar/O2 atmosphere with the partial O2 pressure as control parameter. The samples were characterized with X-ray diffraction, transmission electron microscopy and atomic force microscopy, from which the degree of preferential 〈001〉 orientation and exposed facets were determined by an extension of the March–Dollase model. Photocatalytic degradation of methylene blue dye shows that the photocatalytic reaction rate increases approximately with the square of the fraction of 〈001〉 oriented surfaces, with about eight times higher rate on the {001} surfaces, than on {101}, thus quantifying the effect of crystal facet abundancy on the photocatalytic activity of anatase TiO2.

  • 309.
    Stefanov, Bozhidar
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Österlund, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Gas-phase photocatalytic activity of sputter-deposited anatase TiO2 films: Effect of <001> preferential orientation, surface temperature and humidity2016Inngår i: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 335, s. 187-196Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a systematic in situ study of the environmental reaction conditions on the photocatalytic activity of sputter deposited anatase TiO2 films with controlled amounts of preferential <001> orientation. In particular, the effects of relative humidity (RH) and substrate temperature ( ) are investigated. It is found that {001} facets, which are present in higher abundance on highly oriented samples, exhibit an order of magnitude higher reactivity for gas-phase photocatalytic oxidation of the indoor air pollutant acetaldehyde (CH3CHO) than {101} facets do, and a functional dependence of the reaction rate on facet orientation is determined. It is proposed that water adsorbed on the film contributes with two counteracting effects on the photocatalytic activity: (i) It provides hole acceptors to complete the photo-induced redox cycle and subsequent OH– radical formation for pollutant degradation, and (ii) it creates a diffusion barrier between the catalyst interface and pollutant molecules adsorbed in the water layer. As a consequence, increasing  at high RH has the beneficial effect of removing excess water and reducing the diffusion barrier, thereby improving the photocatalytic activity. A comparison is also made with a commercial anatase TiO2 film, with less developed surface crystallinity and random facet distribution, where the improvement is even more pronounced. Films with a higher degree of orientation exhibit much more stable performance over a range of operating conditions, which suggests that it is possible to tune the effects of water and exposed facet orientation to achieve optimum activity and making TiO2 films amenable to a larger (RH, ) parameter space for practical applications.

  • 310.
    Strömme, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Azens, A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Purans, A.
    Li intercalation in transparent Ti-Ce oxide films: Energetics and ion dynamics1997Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 81, nr 9, s. 6432-6437Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Films of Ti dioxide, mixed Ti–Ce oxide, and Ce dioxide were produced by reactive dc magnetron sputtering.Electrochemical lithiation was probed by chronopotentiometry, cyclic voltammetry together with optical transmittance recording, and impedance spectroscopy. Evidence was found for inserted electrons being accommodated in Ce4f states; this contention was supported by preliminary results from x-rayabsorption fine-structure spectroscopy. These electrons do not produce luminous electrochromism. The variation of the chemical diffusion coefficient of Li, with film composition and Li content, was also studied.

  • 311.
    Strömme, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Gutarra, A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Impedance spectroscopy on lithiated Ti oxide and Ti oxyfluoride thin films1996Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 79, s. 3749-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Films of Ti oxide and Ti oxyfluoride were produced by reactive magnetron sputtering of Ti in Ar+O2(+CF4). Compositional and structuralanalyses were accomplished by Rutherford backscattering spectrometry, x‐ray diffraction(XRD), infrared absorption spectrometry, and atomic force microscopy(AFM).Electrochemical characterization of films immersed in a Li conducting electrolyte was performed with cyclic voltammetry and coulometric titration. Detailed impedance spectra were recorded for the 2×105–1×10−3 Hz range. The impedance responses of pure and fluorinated Ti oxide films in the lithium containing electrolyte differed significantly even if their structures, according to AFM and XRD, were very similar. One main difference was the size of the charge transfer resistance, presumably connected to the Li ion injection from the electrolyte into the film. A modest fluorination lowered this resistance by about two orders of magnitude. The voltammetric and the impedance responses, as well as the magnitude of the chemical diffusion coefficient, of the fluorinated Ti oxide film were strikingly similar to the response of WO3films. This similarity does not occur for the pure Ti oxide films, where a process, believed to be the Li ion injection, could be identified with the main features of the frequency‐dependent impedance. Underlying this charge transfer mechanism, however, a process represented by a constant phase element seems to be operating. This latter process may have its origin in Li diffusion into the film.

  • 312.
    Strömme, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Isidorsson, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Impedance studies on Li insertion electrodes of Sn oxide and oxyfluoride1996Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 80, nr 1, s. 233-241Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Films of Sn oxide and oxyfluoride were made by reactive rf magnetron sputtering onto ITO‐coated glass. We analyzed the composition by Rutherford backscattering spectrometry, the structure by x‐ray diffraction, and the surfacetopography by atomic force microscopy. Li intercalation from a liquid electrolyte was more facile in the oxide than in the oxyfluoride, as found from cyclic voltammetry. Impedance spectra were taken for a wide range of frequencies and polarizing voltages. Nyqvist diagrams were interpreted from a circuit model with elements representing Li insertion at the electrolyte/film interface and electron insertion at the film/ITO interface. The data were consistent with a fractal surface of the Sn oxide film, with a dimension in excellent agreement with measures obtained through several independent techniques. The chemical diffusion coefficient was ∼10−13 cm2/s and slightly decreasing with increasing potential for all films.

  • 313.
    Strömme, Maria Mattsson
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Isothermal transient ionic current as a characterization technique for ion transport in Ta2O51999Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 85, nr 12, s. 8199-8204Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 314.
    Strömme, Maria Mattsson
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Niklasson, Gunnar A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Forsgren, K
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Oorganisk kemi.
    Hårsta, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Oorganisk kemi.
    A frequency response and transient current study of beta-Ta2O5: Methods of estimating the dielectric constant, direct current conductivity, and ion mobility1999Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 85, artikkel-id 2185Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 315.
    Strömme, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    Mihranyan, Albert
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci.
    Ek, Ragnar
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    Fractal dimension of cellulose powders analyzed by multilayer BET adsorption of water and nitrogen2003Inngår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 107, nr 51, s. 14378-14382Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 316.
    Strömme, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Ek, Ragnar
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci.
    Densification-induced conductivity percolation in high-porosity pharmaceutical microcrystalline cellulose compacts2003Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 82, nr 4, s. 648-650Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 317.
    Strömme, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Niklasson, Gunnar A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Determination of fractal dimension by cyclic I-V studies: The Laplace-transform method1995Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 52, nr 19, artikkel-id 14192Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 318.
    Strömme, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Diffusion of Li, Na and K in fluorinated Ti dioxide films: Applicability of the Anderson-Stuart Model1997Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 81, s. 2167-2172Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 319.
    Strömme, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Fractal dimension of Li insertion electrodes studied by diffusion-controlled voltammetry and impedance spectroscopy1996Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 54, nr 5, s. 2968-2971Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 320.
    Strömme, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Fractal surface dimension from cyclic I-V studies and Atomic Force Microscopy; Role of non-contiguous reaction sites1996Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 54, nr 24, s. 17884-17887Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 321.
    Strömme, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Li diffusion in Ti oxyfluoride films: Thermal activation energy and jump length derived from impedance spectroscopy1996Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 80, nr 4, s. 2169-2174Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 322.
    Strömme, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Voltammetry on fractals1995Inngår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 96, nr 3, s. 151-154Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 323.
    Strömme, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap.
    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 characteristics2001Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 90, nr 9, s. 4532-4542Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 324.
    Topalian, Zareh
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Li, Shu-Yi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Kish, Laszlo B.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Resistance noise at the metal-insulator transition in thermochromic VO2 films2015Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, nr 2, s. 1-7, artikkel-id 025303Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 325.
    Topalian, Zareh
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Li, S-Y
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, CG
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Kish, Laszlo B
    Percolation noise at the metal-insulator transition of nanostructured VO2 films2015Inngår i: Extended Abstracts, 2015Konferansepaper (Fagfellevurdert)
  • 326.
    Topalian, Zareh
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Österlund, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Spectroscopic study of the photofixation of SO2 on anatase TiO2 thin films and their oleophobic properties2012Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 4, nr 2, s. 672-679Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 327.
    Topalian, Zareh
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Österlund, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Photo-Fixation of SO2 in Nanocrystalline TiO2 Films Prepared by Reactive DC Magnetron Sputtering2009Inngår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 518, nr 4, s. 1341-1344Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 328.
    Topalian, Zareh
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Fasta tillståndets fysik.
    Smulko, J M
    Niklasson, Gunnar A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Fasta tillståndets fysik.
    Granqvist, Claes G
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Fasta tillståndets fysik.
    Resistance Noise in TiO2-Based Thin Film Gas Sensors under Ultraviolet Irradiation2007Konferansepaper (Fagfellevurdert)
  • 329.
    Triana, C. A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, C.-G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromic Properties of Amorphous Tungsten Oxide α-WO3-x (0 ≤ x ≤ 1)2014Inngår i: Abstracts European Materials Research Society (E-MRS) Spring Meeting: Abstract L VII-5, 2014, Vol. L VII-5Konferansepaper (Fagfellevurdert)
  • 330.
    Triana, C. A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, C.-G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromic Properties of Li+-Intercalated Amorphous Tungsten (aWO3-x) and Titanium (aTiO2-x) Oxide Thin Films2014Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 559, nr 1, artikkel-id 012004Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 331.
    Triana, C. A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, C.-G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Optical Absorption and Small-Polaron Hopping in Oxygen Deficient and Lithium Intercalated Amorphous Tungsten Oxide Films2015Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, nr 024901, s. 024901/1-024901/9Artikkel i tidsskrift (Fagfellevurdert)
  • 332.
    Triana, C. A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromism in Li+-intercalated amorphous titanium oxide thin films.2014Inngår i: 5th International Symposium on Transparent Conductive Materials, 12-17 October 2014, Chania, Crete, Greece, 2014Konferansepaper (Annet vitenskapelig)
  • 333.
    Triana, Carlos A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromic Properties of Li+-Intercalated Amorphous Tungsten (aWO(3-x)) and Titanium (aTiO(2-x)) Oxide Thin Films2014Inngår i: 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, s. UNSP 012004-Konferansepaper (Fagfellevurdert)
    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.

  • 334.
    Triana, Carlos A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Araujo, C. Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Modeling of Electronic Properties of Amorphous Oxides2017Inngår i: Encyclopedia of Interfacial Chemistry: Surfaces and Electrochemistry / [ed] K. Wandelt, Elsevier, 2017Kapittel i bok, del av antologi (Fagfellevurdert)
    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.

  • 335.
    Triana, Carlos A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Araujo, Carlos Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Disentangling the intricate atomic short-range order and electronic properties in amorphous transition metal oxides2017Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, artikkel-id 2044Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 336.
    Triana, Carlos A
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Araujo, Carlos Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Modeling of Electronic Properties of Amorphous Oxides2018Inngår i: Encyclopedia of Interfacial Chemistry:: Surface Science and Electrochemistry / [ed] Wandelt, K., Elsevier, 2018, s. 319-331Kapittel i bok, del av antologi (Fagfellevurdert)
    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.

  • 337.
    Triana, Carlos A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electrochromism and small-polaron hopping in oxygen deficient and lithium intercalated amorphous tungsten oxide films2015Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, nr 2, s. 1-9, artikkel-id 024901Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 338.
    Triana, Carlos A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Elektrochromic Properties of Amorphous Tungsten Oxide a-WO3-x(0≤x≥1)2014Inngår i: European Materials Research Society (E-MRS) Spring Meeting, Lille, France, 26-30 May: Symposium L: Chromogenic Materials and Devices, 2014Konferansepaper (Fagfellevurdert)
  • 339.
    Triana, Carlos A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Optical absorption and small-polaron hopping in oxygen deficient and lithium-ion-intercalated amorphous titanium oxide films2016Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, nr 1, artikkel-id 015701Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 340.
    Triana, Carlos
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Araujo, Carlos Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Electronic transitions induced by short-range structural order in amorphous TiO22016Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 94, nr 16, artikkel-id 165129Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 341. Tuncer, Enis
    et al.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Optical properties of non-dilute metal-insulator composites2008Inngår i: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 281, nr 17, s. 4374-4379Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 342.
    Tuncer, Enis
    et al.
    Texas Instruments Inc..
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Properties of Bruggeman Dielectric Mixture Expression2014Inngår i: Proceedings IEEE Conference on Electrical Insulation and Dielectric Phenomena, IEEE conference proceedings, 2014, s. 875-878Konferansepaper (Fagfellevurdert)
    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.

  • 343. Valizadeh, Sima
    et al.
    Coleman, Victoria
    Topalian, Zareh
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Strömberg, Mattias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Welch, Ken
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Strömme, Maria
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Focused ion beam fabricated nanowire based electrodes for transport studies of biomolecules and nanoparticles2007Inngår i: IVC-17/ICSS-13 and ICN+T 2007, 2007Konferansepaper (Fagfellevurdert)
  • 344. Valyukh, I.
    et al.
    Green, S.
    Granqvist, C.-G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Valyukh, S.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Arwin, H.
    Optical Properties of Thin Films of Mixed W-Ni Oxides Made by DC Magnetron Sputtering2010Konferansepaper (Fagfellevurdert)
  • 345.
    Valyukh, I
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Green, Sara
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Arwin, H
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Optical Properties of Amorphous Tungsten Oxide Films Deposited by Reactive DC Magnetron Sputtering2009Konferansepaper (Fagfellevurdert)
  • 346.
    Valyukh, I
    et al.
    Laboratory of Applied Optics, Dept of Physics, Chemistry and Biology, Linköping University, Linköping.
    Green, Sara
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    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 sputtering2011Inngår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, nr 9, s. 2914-2918Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 347. Valyukh, I.
    et al.
    Johansson, M. B.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Valyukh, S.
    Granqvist, C.-G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Arwin, H.
    Influence of Gas Pressure on Optical Properties of Polycrystalline WO3 Films Deposited by Reactive DC Magnetron Sputtering2011Konferansepaper (Fagfellevurdert)
  • 348.
    Valyukh, Iryna
    et al.
    Department of Material Science, Dalarna University.
    Green, Sara
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Arwin, Hans
    Laboratory of Applied Optics, Department of Physics, Chemistry and Biology, Linköping University.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Spectroscopic ellipsometry characterization of electrochromic tungsten oxide and nickel oxide thin films made by sputter deposition2010Inngår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 94, nr 5, s. 724-732Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 349.
    Valyukh, Iryna
    et al.
    Laboratory of Applied Optics, Dept of Physics, Chemistry and Biology, Linköping University.
    Green, Sara
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Gunnarsson, Klas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Arwin, Hans
    Laboratory of Applied Optics, Dept of Physics, Chemistry and Biology, Linköping University.
    Niklasson, Gunnar A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Ellipsometrically determined optical properties of nickel-containing tungsten oxide thin films: Nanostructure inferred from effective medium theory2012Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, nr 4, s. 044308-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 350.
    Valyukh, Iryna
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Green, Sara
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Valyukh, Sergiy
    Arwin, Hans
    Optical properties of thin films of mixed Ni–W oxide made by reactive DCmagnetron sputtering2011Inngår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, nr 9, s. 2914-2918Artikkel i tidsskrift (Fagfellevurdert)
    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.

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