Gas Adsorption by Refractory Metal Single Crystals

Abstract

The results are considered of a mass spectrometric investigation of the low-pressure oxygen interaction with surfaces of tungsten and molybdenum single crystals of different crystallographic orientation. It has been established that oxygen thermodesorption occurs only in the form of unbound oxygen atoms (atomic phase) and a set of metal oxides (oxide phase); and that the oxygen quantities in the atomic and the oxide phases are comparable. A correlation is discussed between quantitative data on the surface concentration, the sticking probability and the adsorption heat of oxygen on tungsten, and the atomic structure of different faces of a single crystal. The problem is considered of a correspondence between the composition of thermodesorption products and that of the adsorbed film. Some data are also considered on the inhibition of the adsorption ability of the surface of the single crystal of tungsten in respect to carbon monoxide or nitrogen when that surface is partially covered with electronegative or electropositive adatoms. The analysis of the results shows that the inhibition effect of the adsorption ability largely depends on the charge state of the adatoms and the electron structure of the adsorbed molecules.