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 el
ectron diffraction, and scanning tunneling microscopy (STM) and spectroscop
y. After Art sputtering a clean surface is obtained. Subsequent short annea
ling at 1300 K gives rise to segregation of oxygen from the bulk to the sur
face. The presence of oxygen induces a long-range ordered superstructure as
inferred from the electron diffraction patterns in different azimuths. Thi
s is confirmed by STM images which reveal a regularly arranged network of f
inite chains rotated 5 degrees with respect to the Nb(1 1 1) directions. Th
is orientation, the symmetry of the network, and the in-plane interatomic d
istances 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 (1) over bar] parallel to Nb[0 0 1] and NbO[1 (2
) over bar 1]) parallel to Nb[1 (1) over bar 0]. (C) 2001 Elsevier Science
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