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Notes: 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 surface topography 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. © 1996 American Institute of Physics.

Notes: Tin oxide films doped with oxygen vacancies, F, Sb, or Mo were made by reactive rf magnetron sputtering of Sn, Sn-Sb, or Sn-Mo in Ar+O2(+CF4) onto glass heated to a temperature up to 530 °C. Electrical dc resistivity, mobility, free-electron density, spectral optical properties, and microstructure were investigated as a function of sputtering parameters. Optimized deposition parameters gave SnOx:(Sb,F) films with high luminous transmittance, low luminous absorptance, high infrared reflectance, and dc resistivity down to 9.1×10−4 Ω cm. Refractive index n and extinction coefficient k were evaluated from spectrophotometric transmittance. In the luminous range, the films had 1.90〈n〈2.0 and k of the order of 10−2. Hall-effect measurements showed n-type conduction with electron densities in the 1020–1021 cm−3 range. Band-gap broadening from 4.06 to 4.45 eV was observed with increasing electron density. X-ray diffractometry and transmission electron microscopy showed that the structure factor of the films depended on the oxygen content as well as on the specific doping species. A preferred direction of film growth was probably also present. Transmission electron microscopy indicated different grain sizes, between 6 and 30 nm, depending on oxygen content, substrate temperature, and doping species. Optical and electrical properties were compared with results from a quantitative model for wide band-gap semiconductors. The theory is based on heavy n doping by oxygen vacancies or by Sb or/and F and encompasses ionized impurity scattering of the free electrons. It was found that ionized impurity scattering, as well as an additional scattering mechanism tentatively ascribed to grain boundaries, prevailed in the films.

Notes: 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. © 1997 American Institute of Physics.

Notes: Total and diffuse reflectance spectra were measured on Al surfaces covered with electrochromic W oxide films in colored and bleached states. Vector perturbation theory was used for analyzing the spectra. The diffuse reflectance appeared to originate from correlated (uncorrelated) interface roughness when the W oxide film was fully colored (bleached). Assuming partially correlated interfaces led to agreement between experimental and calculated spectra. The use of an electrochromic film appears a promising method to control the relative contributions of the interfaces to the resulting scattering. © 1997 American Institute of Physics.

Notes: Films of Ti oxide and Ti oxyfluoride were produced by reactive magnetron sputtering of Ti in Ar+O2(+CF4). Compositional and structural analyses 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 WO3 films. 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. © 1996 American Institute of Physics.

Notes: Thin Cr-based films were made by sputtering with oblique incidence of the deposition flux onto a substrate. The films had an inclined columnar microstructure, as verified by atomic force microscopy and scanning electron microscopy. The optical transmittance showed pronounced angular selectivity as well as spectral selectivity. Scaling relations were found for the thickness-dependent transmittance. The optical data could be reconciled with a model based on the Bruggeman effective medium theory. © 1995 American Institute of Physics.

Notes: Thermochromic VO2−xFx thin films were prepared by reactive rf magnetron sputtering followed by annealing post-treatment. Electrical and optical properties were measured as a function of temperature. The transmittance and reflectance were essentially wavelength independent at 65 °C, i.e., at the metal-insulator transition.

Notes: We review work on In2O3:Sn films prepared by reactive e-beam evaporation of In2O3 with up to 9 mol % SnO2 onto heated glass. These films have excellent spectrally selective properties when the deposition rate is ∼0.2 nm/s, the substrate temperature is (approximately-greater-than)150 °C, and the oxygen pressure is ∼5×10−4 Torr. Optimized coatings have crystallite dimensions (approximately-greater-than)50 nm and a C-type rare-earth oxide structure. We cover electromagnetic properties as recorded by spectrophotometry in the 0.2–50-μm range, by X-band microwave reflectance, and by dc electrical measurements. Hall-effect data are included. An increase of the Sn content is shown to have several important effects: the semiconductor band gap is shifted towards the ultraviolet, the luminous transmittance remains high, the infrared reflectance increases to a high value beyond a certain wavelength which shifts towards the visible, phonon-induced infrared absorption bands vanish, the microwave reflectance goes up, and the dc resisitivity drops to ∼2×10−4 Ω cm. The corresponding mobility is ∼30 cm2/V s. The complex dielectric function ε is reported.These data were obtained from carefully selected combinations of spectrophotometric transmittance and reflectance data. It is found that ε can be reconciled with the Drude theory only by assuming a strongly frequency-dependent relaxation energy between the plasma energy and the band gap. We review a recently formulated quantitative theoretical model for the optical properties which explicitly includes the additive contributions to ε from valence electrons, free electrons, and phonons. The theory embodies an effective-mass model for n-doped semiconductors well above the Mott critical density. Because of the high doping, the Sn impurities are singly ionized and the associated electrons occupy the bottom of the conduction band in the form of an electron gas. The Sn ions behave approximately as point scatterers, which is consistent with pseudopotential arguments. Screening of the ions is described by the random phase approximation. This latter theory works well as a consequence of the small effective electron radii. Exchange and correlation in the electron gas are represented by the Hubbard and Singwi–Sjölander schemes. Phonon effects are included by three empirically determined damped Lorentz oscillators. Free-electron properties are found to govern the optical performance in the main spectral range. An analysis of the complex dynamic resistivity (directly related to ε) shows unambiguously that Sn ions are the most important scatterers, although grain-boundary scattering can play some role in the midvisible range.As a result of this analysis one concludes that the optical properties of the best films approach the theoretical limit. Band-gap shifts can be understood as the net result of two competing mechanisms: a widening due to the Burstein–Moss effect, and a narrowing due to electron-electron and electron-ion scattering. The transition width—including an Urbach tail—seems to be consistent with these notions. Window applications are treated theoretically from detailed computations of integrated luminous, solar, and thermal properties. It is found that In2O3:Sn films on glass can yield∼78% normal solar transmittance and ∼20% hemispherical thermal emittance. Substrate emission is found to be insignificant. Antireflection with evaporated MgF2 or high-rate sputtered aluminum oxyfluoride can give ∼95% normal luminous transmittance, ∼5% normal luminous reflectance, little perceived color and little increase in emittance. A color purity 〈1% in normal transmission and 〈10% in normal reflection is achievable for a daylight illuminant within extended ranges of film thickness.

Notes: Advanced gas deposition was used to produce nanocrystalline gold films under conditions giving four different deposition rates. Grain growth and structural modification of the grain boundaries were probed during annealing by use of in situ electrical transport measurements. Time dependent resistivity data were fitted to a relaxation model whose activation energy went up upon increased isothermal annealing temperature. The grain boundary transmission coefficient for the samples scaled, up to a certain limit, with the deposition rate; this is believed to be due to a higher concentration of pores, or a wider grain boundary region containing a disordered structure, in samples prepared at low deposition rates. Such samples also displayed enhanced thermal stability with negligible grain growth up to 773 K upon annealing in vacuum for 2 h. Samples prepared above this limit, at the highest deposition rate, exhibited a decreased grain boundary transmission coefficient. © 2002 American Institute of Physics.

Notes: Thin Al films were deposited onto glass by magnetron sputtering. Spectral transmittance and reflectance were wavelength independent at a thickness tc consistent with the percolation threshold and minimum metallic conductivity. We found tc ≈1 nm, which is much less than for evaporated Al films.