Influence of the defects of a thin NiO(100) film on the adsorption of NO

Abstract

Defects often play an important role for the adsorption and reaction behavior of a surface. This, however, is not the case with the adsorption of NO on NiO(100), as our experiments with a thin NiO(100) film grown on a Ni(100) substrate demonstrate. This film possesses a three-dimensional band structure, which is comparable to that of a NiO(100) single crystal. A spot profile analysis low-energy electron diffraction investigation shows that the film consists of crystallites, which are tilted with respect to the Ni substrate. The film must exhibit a high defect density where the crystallites border on each other. Moreover, x-ray photoelectron spectroscopic (XPS) measurements indicate the presence of O− or OH species on the surface. We have studied the adsorption of NO on a NiO(100) film via high-resolution electron energy-loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS), and XPS. With HREELS and TDS we could only detect one kind of NO species on the surface. Comparing the TD and XP spectra of NO adsorbed on the film and on a bulk NiO(100) surface, which exhibits a much lower defect density, we can show that this species is NO adsorbed on regular, nondefect NiO sites.