The analysis of the Doppler profile of the Balmer Halpha line in the cathode sheath and negative glow of a hydrogen glow discharge shows an important concentration of anisotropic energetic atoms. This translational energy is regarded as mainly resulting from reactions including ions accelerated by the cathode sheath electric field. The mechanisms involved are gas-phase charge-exchange collisions producing fast atoms moving toward the cathode and simultaneous neutralisation and backscattering of the ions at the cathode surface leading to energetic atoms moving in the other direction. Quantitative analysis shows that most of the emission of the fast atoms results from excitation directly produced by these ion impact reactions.

It is now generally accepted that the frequency ω/2π at which a high frequency (hf) discharge is sustained has considerable influence on the properties of the plasma. For example, the electron density obtained for a given hf power density deposited into the plasma is usually higher at microwave than at radio frequencies (rfs). This paper reviews a series of experiments at the Université de Montréal designed to investigate the influence of ω on the power balance between the hf field and the plasma, and the plasma processing of materials. For the two particular etching and deposition processes which are described here, the ‘‘optimum’’ frequency (at which the process is most efficient) appears to be in the range between 50 and 100 MHz. This suggests that converting a plasma process from 13.56 to 2450 MHz does not necessarily lead to the greatest possible process enhancement, and that optimization may require the plasma reactor to be constructed in such a way as to allow the excitation frequency to be changed. To provide insight into these results, the most recent models dealing with the influence of ω on the electron energy distribution are reviewed and extended to calculate parameters that can be compared with our experimental data.

Spatially resolved electric field measurements in the cathode region of a dc glow discharge in hydrogen are performed using polarization-dependent Stark broadening of plasma-induced emission of the Balmer lines. The large concentrations of excited atoms in the sheath provide an accurate, sensitive measure of discharge electric fields.