On the interaction of oxygen with Nb(110) and Nb(750)

Abstract

The interaction of Nb(110) and Nb(750) with oxygen has been studied using LEED, AES, SIMS and ELS. The Nb single-crystal samples contained an amount of ≈ 0.1 at.% oxygen dissolved in the bulk as determined by microhardness measurements. Segregation of oxygen from the bulk to the surface results in a very complex LEED pattern on Nb(110) which corresponds to about two thirds of a monolayer of chemisorbed oxygen. Oxygen segregation causes the Nb(750) surface to break up into (110) terraces and (310) steps with a minimum length of ≈ 50 Å. At temperatures below ≈ 200°C, a very thin oxide layer builds up when admitting oxygen from the gas phase to the surfaces. For PO2 ≤ 5 × 10-8 Torr, the film teaches its final thickness of 5-6 Å after exposures to several hundred Langmuirs. AES, SIMS and ELS measurements suggest that the topmost layer of the oxide consists of a highly irregular two-dimensional network of NbO6 octahedra linked together in a way to yield the stoichiometry of Nb2O5. At temperatures > 250°C the oxide film decomposes rapidly, probably by oxygen diffusion into the bulk, and the complex chemisorbed oxygen overlayer is restored. © 1980.