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Publication
Applications of Surface Science
Paper
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.