Thermal Release of Inert Gases from a (100) Tungsten Surface

Abstract

A clean (100) tungsten surface has been bombarded with beams of 40 eV to 5 keV ions of Ne, Ar, Kr, and Xe. Gas desorption rates, measured as the crystal was subsequently heated at 40°K/sec, show a number of fairly clearly defined peaks between 400° and 2200°K. The characteristics of these peaks with varying ion energy, mass, and direction of incidence suggest the following interpretation: (a) All peaks below 1650°K (4 for Ne, 5 for Ar, Kr, and Xe) are the result of desorption via a single activated step from sites within, at most, 10 Å of the crystal surface, and (b) the single peak above 1700°K is the result of isotropic diffusion of more deeply penetrating ions with an activation energy 104 kcal/mole, the same for all four gases.