Daniel C. Schram

Dissociative recombination in cascaded arc generated Ar–N2 and N2 expanding plasma

The expanding plasma obtained from a cascaded arc thermal source is analyzed with double probe, mass spectrometric, and Faraday cup measurements. In the argon–nitrogen mixtures a decrease in ion fluence is observed, contrary to pure argon plasmas in which recombination is insignificant. The recombination in argon–nitrogen plasmas is caused by charge exchange between atomic ions and N2 molecules followed by dissociative recombination. Hence, these processes account for the enhanced axial decay of the plasma density and also for the change in the ion mass spectra of the ion beam extracted from the expanding plasma. The total ion beam current density is also governed by charge exchange followed by dissociative recombination and is thus dependent on the recirculating neutral molecules.

The energy balance of a plasma in partial local thermodynamic equilibrium

The energy balance for electrons and heavy particles constituting a plasma in partial local thermodynamic equilibrium is derived. The formulation of the energy balance used allows for evaluation of the source terms without knowledge of the particle and radiation transport situation, since most of the contributions that arise from that situation (diffusion, local capture of radiation, etc.) are taken into account in the nonequilibrium term. The small correction for the contribution of the loss of excited states, which is slightly overestimated in this approach, can usually be neglected. The overpopulation factor, which can often be evaluated from measurements of the pressure, electron density, and temperature, becomes one of the most important plasma parameters; in the energy balance it accounts for most of the phenomena which may be difficult to evaluate otherwise. As an illustration, some rate coefficients are given for an argon plasma, and the evolution of the several terms of the electron energy equation in a flowing cascaded arc is discussed. >

Plasma ion sources CVD plasma aspects, limits and possibilities

The process of plasma deposition and surface modification depends on the nature and intensity of the particle and energy fluxes incident on the substrate. By way of examples of plasma beam deposition possible mechanisms will be shown, which influence the growth of good quality layers with high growth rates. The possible contributions of ion, radical and energy fluxes will be summarised. The possibility of replacing the ion (and radical) fluxes by ion (and radical) beams will be discussed. At hand is a short summary of available ion beams and a discussion of restraints and necessary conditions to the source plasma for ion beam formation possibilities to achieve high brightness sources with a large efficiency will be indicated.