Adsorption and Absorption of Nitrogen on a W(001) Surface Studied by Thermal Desorption Spectroscopy

Abstract

The adsorption states of nitrogen on a W(001) surface, particularly the β1 state appearing at high coverage, have been studied by two new approaches based on thermal desorption spectroscopy (TDS). First, the isotope 15N was used to discriminate the β1 state from the β2 state saturated with 14N at low coverage. It is proposed for the β1 state formation that 15N exposed later stamps 14N into the octahedral site of the subsurface mainly through single steps around which the atomic distance is extended by nitrogen-induced contracted islands. Secondly, a vicinal surface was investigated to elucidate the role of the steps. Only a small β1 peak was found, which is interpreted to be a result of suppressed formation of contracted islands due to a large number of surface defects. Other features observed on the vicinal surface are well explained with the proposed model.