D. Schalch

Tungsten and fluorine co-doping of VO2 films

Abstract Fluorine- and tungsten-doped vanadium dioxide (VO2) is a promising coating material for applications as energy-conserving windows. We prepared VO2 films simultaneously co-doped with fluorine and tungsten and report on the results of optical measurements and photoelectron spectrometry. A comparison is given to single-element doping. Clear evidence for an interaction of fluorine and tungsten in VO2 is found in the switching behaviour at the semiconductor-to-metal phase transition. An explanation is given based on two different effects of fluorine incorporation observed in the ultraviolet photoelectron spectrometry results. Concerning other film properties, the two elements act independently of each other.

W- and F-doped VO2 films studied by photoelectron spectrometry

Thermochromic tungsten- and fluorine-doped vanadium dioxide films, which are in discussion as intelligent window coatings, were deposited by reactive sputtering. Results of optical measurements and photoelectron spectrometry (XPS, UPS) at low doping levels (≤2.6%) are presented, and together with structural properties they can be well correlated. By applying antireflective coatings the transmittance of films in the visible spectral range may be enhanced to more than 60% with fairly good switching characteristics at room temperature in the case of tungsten doping.

Thermochromic VO2 thin films studied by photoelectron spectroscopy

Abstract Thermochromic vanadium dioxide films which are discused as “intelligent” window coatings were deposited by reactive rf-sputtering. The films are grown on quartz polycrystalline and unidirectional. Photoelectron spectroscopy (XPS, UPS) was applied to study the density of states distribution in the valence band regime below and above the phase transition temperature. It is shown that the band structure of the polycrystalline films bears resemblance to single-crystalline vanadium dioxide to a large extent, e.g. bandgap, valence band energy position, and valence band structure and width in the semiconducting phase. In contrast to single crystals, e.g. the metal-semiconductor transition in the films occurs in a broad temperature range of about 20 to 30 K, dependent mainly on deposition temperature. Correlations between optical, electronical, and structural properties of the film are evident.

The role of hydrogen in silicon nitride and silicon oxynitride films

Abstract Amorphous silicon nitride and silicon oxynitride films were deposited by reactive r.f. sputtering. Hydrogen-containing films were prepared by adding hydrogen to the sputter gas and by implanting 10 keV hydrogen ions into the films. The effects of adding hydrogen and/or oxygen on the properties of silicon (oxy)-nitride films were studied by means of optical and IR transmission spectroscopy and investigations of the refractive index. The results for hydrogen-free and hydrogen-containing films prepared by reactive sputtering were compared with those reported for chemically vapour-deposited films.

IR transmittance studies of hydrogen-free and hydrogenated silicon nitride and silicon oxynitride films deposited by reactive sputtering

Abstract Amorphous silicon nitride and silicon oxynitride films were deposited by reactive r.f. sputtering in various reactive ambients of nitrogen, oxygen and hydrogen of different compositions. The IR transmittance of the films was studied as a function of their hydrogen content and the oxygen:nitrogen ratio. The results were discussed in terms of compensation of gap states by hydrogenation. The microscopic structure of the silicon oxynitride films is believed to depend on the oxygen:nitrogen atomic ratio.

Plasmon excitation in vanadium dioxide films

Abstract Thermochromic vanadium dioxide (VO 2 ) films, which are considered as intelligent window coatings, have been deposited in mixed argon/oxygen atmospheres. The properties of the films have been studied by electron energy loss spectroscopy (EELS) and ultraviolet-excited photoelectron spectrometry (UPS) at different temperatures in order to get a better understanding of the physics of the metal-semiconductor transition in thin polycrystalline VO 2 films. The present article mainly discusses plasmon excitation, which is found at an electron energy loss of 1.2 eV, both in the semiconducting and the metallic phase. This is in contrast to results from a single crystalline material.

Characterization of reactively sputtered BeO films

Abstract Amorphous BeO films were deposited by reactive r.f. sputtering from metallic beryllium. The electrical, optical and structural properties of these films were investigated using Auger electron spectroscopy, particle-induced X-ray emission and optical and IR transmission spectroscopy and by measurements of the refractive index and the electrical conductivity, including the electron-irradiation-induced conductivity. The sputtered films are of high quality, with regard to purity, homogeneity, adherence and stability towards thermal treatment. The refractive index of stoichiometric films was determined to about 1.71, and the electrical resistivity to about 10 16 ωcm in the electric field range 10 7 −10 8 V m −1 . The mobility-lifetime product of the charge carriers was estimated to be of the order of 10 −13 cm 2 V −1 .