Kinetics of Cs+ Desorption from Tungsten

Abstract

The mean adsorption lifetime τ₃ of Cs⁺ on tungsten has been measured in the 1000°—1200°K temperature range, using a pulsed beam technique. Under conditions of low surface coverage and with either Cs or CsI as beam materials $${\tau }_3{\text{=(1.0±0.5)×10}}^{\text{−12}}\exp \text{[(23\hspace{0.17em}600±500)/T]}\sec$$ was obtained. The heat of desorption can be calculated as the energy required to remove an isolated Cs⁺ ion from the surface of an electrical conductor. The presence of an adsorbed contaminating layer, arising from residual vacuum gases, decreased the Cs⁺—W binding energy by 0.5 eV and increased the pre‐exponential factor by about two orders of magnitude. Anomalous results were obtained when CsCl was used for a beam material, suggesting a reaction between the surface tungsten atoms and atomic chlorine.