Chemisorption of oxygen on tungsten (100): combined molecular beam and scanning electron beam study

Abstract

A molecular beam technique has been used to deposit accurately controlled patches of oxygen onto the (100) surface of a tungsten single crystal, rigorously cleaned under ultra-high vacuum conditions, and a detailed examination of the spatial behaviour of these patches was made during thermal treatment using a low-resolution scanning electron beam to probe the surface. It is estimated that as little as 0.01 of a monolayer of oxygen can be detected with the electron probe. The work function was studied as a function of thermal treatment for various preadsorbed amounts and a useful correlation made with a model for oxygen adsorption on tungsten developed from flash desorption studies. The scanning electron probe revealed a novel one-dimensional boundary effect during thermal treatment of the crystal after oxygen preadsorption.