SiO 2 and TiO2, with their high refractive index contrast, are interesting candidates for the fabrication of graded-index optical filters. In this work, SiO2/TiO2 mixtures were prepared by plasma-enhanced chemical vapor deposition from SiCl4 and TiCl4. By controlling the gas flow ratio, it is possible to obtain coatings with refractive index values between 1.48, for SiO2, and 2.35, for TiO2, and with an extinction coefficient below 10−4 in the visible and near-infrared regions. The optical properties of the mixtures do not respect the Bruggeman effective medium approximation that supposes two separate phases. Using a combination of x-ray photoelectron spectroscopy, Fourier transform infrared spectrometry, and elastic recoil detection, we demonstrate that SiO2/TiO2 is a single-phase material. Two separate phases can develop at certain compositions by annealing-induced precipitation.
The stress evolution of plasma enhanced chemical vapor deposition a-SiC:H films was studied by increasing the annealing temperature from 300 to 850 °C. A large stress range from −1 GPa compressive to 1 GPa tensile was investigated. Infrared absorption, x-ray photoelectron spectroscopy, and elastic recoil detection analysis techniques were used to follow the Si-C, Si-H, and C-H absorption band evolutions, the Si2p and C1s chemical bondings, and the a-SiC:H film hydrogen content variations with the annealing temperatures, respectively. It is pointed out that the compressive stress relaxation is due to the hydrogenated bond (Si—H and C—H) dissociation, whereas the tensile stress is caused by additional Si—C bond formation. At high annealing temperatures, a total hydrogen content decrease is clearly observed. This total hydrogen loss is interpreted in terms of hydrogen molecule formation and outerdiffusion. The results are discussed and a quantitative model correlating the intrinsic stress variation to the Si—H, C—H, and Si—C bond density variations is proposed.
Amorphous silicon carbide films (a–SixC1−x :H) deposited by the argon- or helium-diluted PECVD technique were studied as a function of their composition. Microstructural investigations were mainly achieved by means of FTIR and XPS techniques. Nuclear techniques were used to obtain precise information on the film hydrogen content. The Si–H IR-absorption band was deconvoluted in different monohydride and dihydride silicon environments. The existence of SiH2 bonds in the Si-rich composition was evidenced. From the analysis of the C–H and Si–H absorption bands it is shown that hydrogen atoms are preferentially bonded to carbon atoms. The deconvolution of the Si2p core level peak suggests that above a composition of x ∊ 0.5, the noncarburized (Si, Si, H) local environment contribution increases to the detriment of the hydrocarburized (Si, C, H) environments. From the evolution of the C1s peak, it can be deduced that there is a change in the carbon atom bonding states when the film composition is varied. These results are correlated and discussed in terms of the local bonding environments and their evolution with film composition.
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