The observation of oxygen disorder on the V,O,( 001) surface using scanning tunneling microscopy

Constant current scanning tunneling microscope images of the V,O,(OOl) surface were recorded in ultrahigh vacuum (UHV). The conductivity of the V,O, crystal was increased by doping with NaOduring the crystal growth and flat surfaces were created by cleavage in N, or UHV. All images exhibit the 11.5 A X 3.65 A periodicity expected for a bulk terminated surface. However, images from different areas of the surface have different contrast and these variations are explained by assuming incomplete and inhomogeneous occupation of the vanadyl oxygen sites. This assumption is supported by image simulations which demonstrate that loss of the surface vanadyl 0 could account for the observed changes in contrast. Because these surface 0 vacancies are thought to influence the catalytic properties of the surface, their characterization is an important step towards understanding how the atomic-scale structure of a surface influences its properties.