Surface and subsurface oxide formation on Ni(100) and Ni(111)

The oxidation of Ni(100) and Ni(111) at elevated temperatures and large oxygen exposures, typical of the methods used in the preparation of NiO(100) films for surface studies, has been investigated by medium energy ion scattering (MEIS) using 100 keV H+ incident ions. Oxide film growth proceeds significantly faster on Ni(111) than on Ni(100), but on both surfaces oxide penetration occurs to depths significantly greater than 100 Å with total exposures of 1200 and 6000 L respectively. The metal/oxide interface is extremely rough, with metallic Ni extending to the surface, even for much thicker oxide films on Ni(111). On Ni(111), NiO growth occurs with the (100) face parallel to the Ni(111) surface and the close-packed (110) directions parallel. On Ni(100) the MEIS blocking curves cannot be reconciled with a single orientation of NiO(100) (with the〈110〉 directions parallel) on the surface, but is consistent with the substantial orientational disorder (including tilt) previously identified by spot-profile analysis LEED.