Surface structure of niobium-dioxide overlayer on niobium(100) identified by scanning tunneling microscopy

The surface structures of an oxide overlayer on Nb(100) single crystal form ed by numerous cycles of Ar-ion sputtering and flash annealing at 1973 K in an ultra-high-vacuum chamber have been investigated by scanning tunneling microscopy. Flat terraces with a monatomic step height of Nb(100) are obser ved; where two orthogonal domains are alternately evident. A ladder-like (3 x10) structure of Nb(100) with no long-range order is identified at atomic resolution in the domain on the terrace. The ladder-like (3x10) structure i s interpreted to be a modulated NbO2(010) overlayer on the Nb(100) surface and an atomic structural model of the ladder-like (3x10) structure is propo sed. (C) 2001 American Institute of Physics.