Volume 88, Issue 1, 01 July 2000
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
88(2000); http://dx.doi.org/10.1063/1.373618View Description Hide Description
The expanding use of low pressure high frequency plasmas in various applications has stimulated research toward increased operating efficiency. In order to optimize a particular plasma process, the operator can vary several “external” (operator-set) parameters, among which the excitation frequency f has received relatively little attention in the literature over the years, probably due to the difficulties encountered in designing meaningful frequency-dependent experiments. These difficulties can be avoided by the use of surface-wave discharges (SWDs), which possess great flexibility: a very broad (continuous) range of excitation frequencies, and wide ranges of operating pressures and plasma densities, under noncritical, almost perfect impedance matching with the power source. In earlier work in these laboratories, we have examined the f dependence of plasma deposition and etching experiments; the present experiments have been designed to investigate the f dependence more “directly” by turning to the plasma through its optical emission. The vacuum ultraviolet to visible emission from SWD plasmas in pure hydrogen or in Ar mixture has been investigated over a broad range of excitation frequency using a spectrophotometer with a known transfer function. The observed f dependence of emission intensity (atomic lines and molecular bands) as f is increased is interpreted in the case of the pure discharge in terms of changes from a nonstationary to a stationary electron energy distribution function(EEDF) while, in the mixture, it is related to changes in the form of the stationary EEDF.
Characterization and study of the thermodynamic equilibrium departure of an argon plasma flame produced by a surface-wave sustained discharge88(2000); http://dx.doi.org/10.1063/1.373619View Description Hide Description
Surface wave induced plasma (SWP) is a particular class of microwave induced plasma. It is used in atomic emission and mass spectrometry as a source of excitation for the elemental analysis of samples in analytical chemistry. This discharge is mainly used at powers less than 300 W. At such low power, an efficient process of desolvation, atomization, excitation and ionization of the analyte can only be reached provided the density of power absorbed in the discharge is large. This requires a plasma whose volume increases very little with increasing absorbed power. At atmospheric pressure in the SWP, such a volume limitation can be achieved by having the plasma extending into ambient air in the form of a flame (open air discharge). This article presents the results of the experimental characterization and study of the degree of thermodynamic equilibrium of an argon plasmaflame produced by a surfatron. The values of the plasma parameters and (departure from equilibrium) parameter for the ArI levels show that the discharge is a two-temperature plasma. By comparing the results with those obtained for a classical surface-wave plasma column, it can be concluded that the plasma in flame is more suited to be used as a source of excitation in analytical chemistry, due to its higher electronic density and temperatures values.
88(2000); http://dx.doi.org/10.1063/1.373620View Description Hide Description
Making use of hydrodynamicstheory, we have studied effects of electron emission from a solid surface on steady-state argon plasma sheaths in which the emitted electron-neutral atom collisions and the ion-neutral atom collisions are taken into account. Numerical results indicate that the effects of electron emission on the distributions of the sheath parameters such as the sheathelectric field and the ion densities are obvious as the neutral gas density increases or the beam current density of the emitted electrons increases.