Thermal desorption of Xe from the W(110) plane

Abstract

The thermal desorption of Xe from the (110) plane of W was investigated. Desorption could be followed layer by layer for three adsorbed layers, each containing equal amounts of Xe. In each case desorption rates were nearly coverage independent (i.e., of zero order) until θ=0.25−0.3 (in the layer under study), at which point a sharp transition to first order desorption occurred. If only one monolayer of Xe was adsorbed small amounts of preadsorbed oxygen led to first order desorption over the entire coverage regime. Possible mechanisms for the zero order regime in terms of desorption from the edges of islands with constant total island perimeter, or via more complicated mechanisms are given. The activation energies of desorption are shown to be less than the enthalpies of desorption for all layers and the meaning of this result is discussed. Results for Xe adsorbed on O/W layers preheated to 90 K and 900 K are also presented.