Axial Temperatures and Electron Densities in a Flowing Cascaded arc

Abstract

Since about 1985 a cascaded arc is used as a particle source in the deposition machine described by Kroesen [1a,1b]. This method of deposition showed to be very fast and efficient to grow amorphous carbon films (a–C:H), varying from graphite and diamond to polymers [1,2]. The most important difference of this method, with respect to R.F. techniques, is that the three most important functions of a deposition process, as there are dissociation/ionization, transport and deposition are spatially separated. The dissociation takes place in a cascaded arc burning on argon. The temperatures in the arc are about 10000–12000 K. At the end of this arc hydrocarbons are injected which are then dissociated and ionized effectively. At the end of the arc the plasma expands supersonically into a vacuum vessel. That means that the plasma cools down and the formed hydrocarbon fractions are transported towards the substrate, where an amorphous carbon film can grow. The quality of the films depend mainly on the amount of energy available for each injected carbon atom. The behavior of the refractive index as a function of this energy could be a confirmation that in our deposition method the carbon ions rather than radicals govern the deposition process [1,3,4]. Therefore the cascaded arc is investigated numerically and experimentally in order to improve the ionization efficiency. The conservation laws for mass, momentum and energy for both the electrons and the heavy particles are solved 2 dimensionally by a control volume numerical method with a non, staggered grid. By Fabry Perot interferometry heavy particle temperatures, electron temperatures and electron densities as a function of the axial position in the cascaded arc are measured. The obtained numerical results are compared to the experimental data, obtained by the optical Fabry Perot diagnostics.