Oxygen-induced surface structure of Nb(1 1 0)

The Nb(1 1 0) surface is investigated prior to and after thermal treatment in vacuum by in situ Auger electron spectroscopy, reflection high-energy electron diffraction, and scanning tunneling microscopy (STM) and spectroscopy. After Ar+ sputtering a clean surface is obtained. Subsequent short annealing at 1300 K gives rise to segregation of oxygen from the bulk to the surface. The presence of oxygen induces a long-range ordered superstructure as inferred from the electron diffraction patterns in different azimuths. This is confirmed by STM images which reveal a regularly arranged network of finite chains rotated 5° with respect to the Nb〈1 1 1〉 directions. This orientation, the symmetry of the network, and the in-plane interatomic distances measured by STM suggest that the superstructure is a precursor for the formation of an epitaxial f.c.c.-NbO(1 1 1) layer on Nb(1 1 0) with in-plane orientation NbO[1 0 1̄] ∥ Nb[0 0 1] and NbO[1 2̄ 1] ∥ Nb[1 1̄ 0].