hide
Free keywords:
-
Abstract:
A Ni(100) surface exposing terraces of approximately 100 Å width which are separated from each other by monatomic steps descending along the [010] direction has been oxidized above room temperature. Via intermediate formation of the well-known p(2×2) and c(2×2) chemisorbed phases, which are identified by LEED (low energy electron diffraction) and STM (scanning tunneling microscopy) in the present study, a thin film of 4–5 layers of NiO(100) builds up on the surface. The NiO layer consists of crystallites with a typical lateral extension of 50 Å as revealed by the STM data. SPA-LEED (LEED spot profile analysis) measurements allowed us to determine that the crystallite surfaces are tilted preferentially along the [011] and [01̅1] directions of the Ni(100) plane by an average angle of 8° with a half width of the angular distribution of 6°. We show that the development of the oxide islands most probably starts at the terrace edges of the metal surface. While the islands grow in size the strain between oxide and metal increases due to the large differences in the lattice constants of Ni and NiO. Part of the strain is compensated by a tilt of the islands induced via migration of Ni atoms from the step edges underneath the oxide islands. The generated NiO surface is characterized by two types of regions, namely the regions on the islands which are basically flat and contain regular NiO sites, covering 75–80% of the crystal surface, and the regions between the islands with many defect sites (20–25% of the surface area). The consequences of the structural properties of the NiO film on the adsorption of molecules, i.e., NO, are discussed in line with results of a previous study.
