Generation of vapor and concomitant plasma production in an electron-beam evaporator

Abstract

Electron beam heating is a technique to generate vapor of refractory and high melting point metals. Vapor production finds application in thin film deposition and laser-based purification of materials. A strip electron-gun whose filament is heated by AC current is generally used because of larger molten pool formation and quiet evaporation. Electron-gun thus generates vapor. The incident beam of electrons is backscattered with large angular distribution. Both the electron groups, namely the primary and the backscattered electrons participate in production of plasma by electron-impact ionization. The plasma is weakly ionized (∼ 0.1% degree of ionization) with ion density ∼ 108 cm−3 and has low electron temperature (∼ 0.3 eV). The vapor and the simultaneously produced plasma expand in the space above the target. Plasma expands by ambipolar diffusion in a transverse magnetic field while the vapor expands as a collision-less atomic beam. In this paper we study vapor and plasma formation of copper and zirconium. Details shall be discussed.