Molybdenum oxide thin films find diverse applications as catalysts, gas sensors, and electrochromic devices. Such films are produced mainly by reactive sputtering and thermal evaporation but other techniques such as chemical vapor deposition and electrochemical deposition have been used. In the present work, the feasibility of an alternative method for the production of molybdenum oxide films using a molybdenum filament heated in a rarefied oxygen atmosphere is demonstrated. The filament heating current, I F , and the oxygen flow rate, F O 2 , are the key deposition parameters and their effect on the deposition rate, R, was investigated. For I F ) 12.5 A, an increase in the R-value from 7.5 to 31 nm/min was observed as F O 2 was increased from 6.0 to 21 sccm. To characterize the chemical bonds, infrared spectroscopy, using both unpolarized and p-polarized infrared beams, and X-ray photoelectron spectroscopy (XPS) were employed. Line shape analysis of the Mo(3d) XPS peak revealed that the Mo atoms were in mixed valence states, Mo 6+ and Mo 5+ , with a high predominance of the former over the latter, thus indicating an oxygen-deficient MoO 3 film. From Rutherford backscattering spectroscopic analysis of the films, an average O/Mo atomic ratio of 2.9 was calculated, consistent with the XPS results. A combination of the XPS and RBS results and the data of other investigators on the oxidation of molybdenum suggests that the film is formed from MoO 2 and MoO 3 species desorbed from the Mo filament. The optical gap, E g , was determined from transmission UV-visible spectra of the films. An average E g value of 3.03 eV was found. The electrochromic properties of the films were investigated for Li + intercalation using an electrochemical cell. A coloration efficiency of 19.5 cm 2 /C at a wavelength of 700 nm was observed.

Infrared (IR) specular reflectance spectra of a semi-infinite sample of vitreous silica (v-SiO2) were obtained with the use of both s- and p-polarized light and oblique incidence angles. The optical constants of the material and hence its longitudinal optic/transverse optic (LO-TO) functions were determined through the Kramers–Krönig analysis (KKA) of its s-polarized 20° off-normal reflectance spectrum. p-Polarized spectra had their reflection maxima blue-shifting as the incidence angle increased, while they remained unchanged for the s-polarized spectra. Since an LO mode generally lies at wavenumbers higher than its respective TO mode, such a blue shift may be due to the detection of the LO mode in addition to the TO mode as incidence angle increased. The only exception to this observation was the high-frequency shoulder, which underwent a sharp intensification as the incidence increased. The present work shows that it is indeed brought about by the weakly IR active asymmetrical mode (AS2) but only because it takes place immediately after the intense AS1 mode, which causes the refraction index spectrum to have a broad dip below unity. Such a dip is proven to be responsible for the sharp increase in the high-frequency shoulder of the reflectance spectra.

Infrared reflection-absorption spectra of TiO 2 thin films deposited by plasma-enhanced chemical vapor deposition onto aluminum and by a sol-gel process onto platinum were obtained using s-and p-polarized light and oblique incidence angles. Prominent bands with variable reflection minima position and line shapes, which were shown to be phase dependent, were observed for all samples in the 800Ϫ900 cm Ϫ1 wave number range when p-polarized light and oblique incidence were used. Such bands were attributed to an LO mode of TiO 2 and their enhancement with the incidence angle is a good example of Berreman effect. Such spectra were analyzed by means of spectral simulation based on the Fresnel equation for a three-layered system. The films' optical constants used in the simulations were obtained through the Kramers-Krönig analysis ͑KKA͒ of the reflectance spectra of pellets of powdered amorphous TiO 2 , anatase and rutile. Optical constants for hypothetical polycrystalline TiO 2 systems were also calculated from the dielectric functions of single crystals by means of effective medium theories ͑EMTs͒, such as those of Bruggeman, Maxwell-Garnett, and Hunderi. These optical constants were used both for spectral simulation and for understanding the bands observed. However, the optical constants for the powdered standards determined through KKA reproduced experimental results more accurately than those determined through the EMTs. In both experimental and simulated spectra, Berreman effect was very clear-cut and a reliable phase characterization could be carried out.

Infrared reflection-absorption spectra of plasma-enhanced chemical vapor deposition (PECVD) amorphous TiO2 thin films on aluminum were obtained with s- and p-polarized light and oblique incidence angles. Such spectra were analyzed by means of spectral simulations based on a Fresnel equation for a three-layered system. The optical constants used in the simulations were obtained through the Kramers–Krönig analysis of the reflectance spectra of a pellet of powdered amorphous TiO2. LO-TO energy-loss functions were also calculated from these optical constants, and a splitting was observed. A good qualitative agreement between experimental and simulated spectra was achieved, and the Berreman effect was observed in both cases when p-polarized light was used. It was shown, therefore, that the Berreman effect makes infrared reflection-absorption spectroscopy a successful technique for the characterization of an amorphous TiO2 thin layer on aluminum.

The effect of the incorporation of oxygen and nitrogen on the structure of films obtained by PECVD of hexamethyldisiloxane (HMDSO)−He−N2 and HMDSO−He−O2 mixtures is investigated using infrared and Raman spectroscopies. From transmittance spectra of films deposited onto single-crystal KBr disks, the transverse optical (TO) and longitudinal optical (LO) functions in the mid-infrared region were calculated. To correlate structural aspects with the observed LO−TO splittings, an identification analysis of functional group based on the infrared and Raman literature was made. It was concluded that the structure of the films deposited from HMDSO−He−O2 discharges was strongly dependent on the proportion of oxygen in the gas feed. In the absence of oxygen, i.e., for a discharge of a HMDSO−He mixture, the resulting film consisted of a network of interconnected siloxane and carbosilane units. Addition of O2 precluded the formation of methylene bridges and induced the formation of a material enriched with Si−O−Si groups. Films formed from the HMDSO−He−N2 plasmas, on the other hand, consisted mainly of interconnected siloxane and carbosilane units in addition to a small quantity of silazane units. On the basis of these results, we propose an interpretation for the variation of the LO−TO splitting amplitude for the asymmetrical stretching mode (AS1) of Si−O in Si−O−Si groups as a function of the oxygen or nitrogen incorporation into the films.