Electron-stimulated desorption of cesium atoms from cesium layers adsorbed on tungsten coated by a gold film

Abstract

The yield and energy distributions of cesium atoms escaping in electron-stimulated desorption (ESD) from cesium layers adsorbed on tungsten coated by a gold film have been studied as a function of the incident electron energy, gold film thickness, adsorbed cesium concentration, and surface temperature. The measurements are carried out by the time-of-flight method with a surface ionization-based detector. The Cs ESD is observed only after deposition of more than one monolayer of gold and more than one cesium monolayer on the tungsten surface at T = 300 K, which is accompanied by the formation of a film of the semiconductor compound CsxAuy with a submonolayer of Cs atoms. The dependence of the ESD yield on the incident electron energy follows a resonance pattern and consists of two peaks with appearance thresholds of 57 eV at T = 300 K and 24 eV at T = 160 K, which can be assigned to excitation of the Au 5p3/2 level in the substrate and the Cs 5s level in the cesium adlayer. Upon excitation of the Au 5p3/3 level, the Cs energy distribution at T = 300 K exhibits one broad peak with a maximum at E ∼ 0.45 eV. This peak is split at T = 160 K into two peaks with maxima at E ∼ 0.36 and ∼0.45 eV, which are associated with different Cs ESD channels. Upon excitation of the Cs 5s level in the adlayer at T = 160 K, the Cs energy distribution exhibits a peak with a maximum at E ∼ 0.51 eV, which is seen only at T = 240 K and low cesium concentrations. Mechanisms are proposed for all channels of electron-stimulated desorption of Cs atoms, which are compared with the Na ESD channels observed in the Na-Au-W system.