Mechanism of Inert Gas Cleanup in a Gaseous Discharge

Abstract

An investigation has been made of the cleanup of inert gases by a gas discharge. The cleanup of rare gases in a tube in which metal is being sputtered is governed largely by two factors. First, the rate at which the metal is sputtered, and second, the potential of the surface on which the metal lands. At small negative or positive potentials on the surface collecting sputtered metal there is a slow cleanup rate caused by uncharged species being buried by sputtered metal. At more negative potentials burial of ions becomes important, and cleanup is much more rapid. Recovery has been effected by heating to the evaporation temperatures of the metal. As the metal evaporates the buried gas is liberated. Hundreds of equivalent monolayers of argon have been cleaned up with only a total recovery of about one equivalent monolayer by heating at 1500°C. This shows that even with a forced ``solubility'' of the order of one per cent we find no evidence for significant diffusion of argon in metals. An electrode collecting ions at a uniform current density over the surface will have a net cleanup rate of zero on that surface after the initial cleanup of a small amount of gas. After the initial disappearance of some gas, resputtering will occur liberating the cleaned up gas as fast as it is being cleaned up.