The effect of driving frequency (13.56–50 MHz) on the electrical characteristics and the optical properties of hydrogen discharges has been studied, under constant power conditions. The determination of the discharge power and impedance was based on current and voltage wave form measurements, while at the same time spatially resolved $H_{\alpha }$ emission profiles were recorded. As frequency is increased, the rf voltage required for maintaining a constant power level is reduced, while the discharge current increases and the impedance decreases. Concurrently the overall $H_{\alpha }$ emission intensity decreases and its spatial distribution becomes more uniform. Further analysis of these measurements through a theoretical model reveals that frequency influences the motion of charged species as well as the electron energy and the electric field, resulting in a modification of their spatial distribution. Moreover, the loss rate of charged species is reduced, leading to an increase of the plasma density and to a decrease of the electric field. Under these conditions, the total power spend for electron acceleration increases with frequency, but combined to the higher electron density, leads to a drop of the average energy gained per electron, a drop of the mean electron energy, and an enhancement of the low-energy electron-molecule collision processes against high energy ones.

A gas phase and surface simulator of highly diluted silane in hydrogen rf discharges used for the deposition of microcrystalline silicon has been developed. The model uses the spatial density distribution of SiH ${\mathrm{(X }}^2\mathrm{\Pi )}$ radicals measured using laser induced fluorescence and the total silane consumption for estimating the primary electron induced silane dissociation, thus avoiding fluid or statistical approaches commonly used for the prediction of electron impact rate coefficients. A critical analysis is made for the relative importance of all the parameters involved either in the gas phase chemistry or in the surface processes. The model results are compared to experimental data concerning disilane production and film growth rate over a wide range of rf power densities in 2% and 6% ${\mathrm{SiH}}_{\mathrm{4}}$ in ${\mathrm{H}}_{\mathrm{2}}$ discharges. The good agreement between experimental and model results allows for the extension of the discussion to the composition of the radical flux reaching the substrate, the relative contribution of each of the radicals to the film growth, and the most probable mechanism of microcrystalls formation under typical conditions of low and high microcrystalline silicon deposition rate.

An investigation of the effect of the total gas pressure on the deposition of microcrystalline thin films form highly diluted silane in hydrogen discharges was carried out at two different frequencies. The study was performed in conditions of constant power dissipation and constant silane partial pressure in the discharge while using a series of plasma diagnostics as electrical, optical, mass spectrometric, and in situ deposition rate measurements together with a simulator of the gas phase and the surface chemistry of $\mathrm{Si}{\mathrm{H}}_4∕{\mathrm{H}}_2$ discharges. The results show that both the electron density and energy are affected by the change of the total pressure and the frequency. This in turn influences the rate of high energy electron–$\mathrm{Si}{\mathrm{H}}_4$ dissociative processes and the total $\mathrm{Si}{\mathrm{H}}_4$ consumption, which are favored by the frequency increase for most of the pressures. Furthermore, frequency was found to have the weakest effect on the deposition rate that was enhanced at $27.12\mathrm{MHz}$ only for the lowest pressure of $1\text{Torr}$ . On the other hand, the increase of pressure from $1\text{to}10\text{Torr}$ has led to an optimum of the deposition rate recorded at $2.5\text{Torr}$ for both frequencies. This maximum is achieved when the rate of $\mathrm{Si}{\mathrm{H}}_4$ dissociation to free radical is rather high; the flux of species is not significantly hindered by the increase of pressure and the secondary gas phase reactions of $\mathrm{Si}{\mathrm{H}}_4$ act mainly as an additional source of film precursors.

Crystalline TiO₂ films were prepared on unheated glass substrates by radio frequency (RF) reactive magnetron sputtering at normal angle of incidence (a = 0°) and at glancing angle (a = 87°). The effect of the glancing angle on the structure, microstructure, and wetting properties of the films was investigated. The inclination of the substrate led to phase transformation of the deposited films from rutile to either rutile/anatase or anatase, depending on the working pressure. Extreme shadowing at 87° results in a remarkable increase of the films’ porosity and surface roughness. The mechanism of the glancing-angle-induced crystalline phase formation is thoroughly discussed based on the thermodynamic, kinetic, and geometrical aspects of the nucleation and is related with the microstructural changes. Both crystalline phase and microstructure significantly affect the wetting properties of the TiO₂ films. Glancing-angle-deposited anatase TiO₂ exhibits a high degree of porosity and roughness, a high rate of UV-induced wettability conversion, and a long-term highly hydrophilic nature in dark. Therefore, anatase TiO₂ is potentially a good candidate for applications as dye-sensitized solar cells (DSSC)/perovskite solar cells, microfluidic devices, and self-cleaning surfaces prepared on thermosensitive substrates.