ON THE ORIGIN OF TEMPERATURE EFFECTS IN THE PHOTOEMISSION SPECTRA OF NIO

The photoemission measurements of vacuum cleaved NiO single crystals and thin layers of NiO deposited on gold substrate performed with a monochromatized Al Kalpha radiation indicate that the changes in the photoelectron spectra at elevated temperatures are not a result of higher concentration of Ni3+ in the surface layer as proposed in our previous report (G. Tyuliev and M. Sokolova, Appl. Surf. Sci., 52 (1991) 343). A detailed analysis of the Ni2P3/2 (main line) for UHV cleaved NiO(100) and NiO/Au (polycrystalline) samples recorded at different temperatures and for nickel oxides with different stoichiometry (i < O/Ni < 2) is presented. These data allow one to separate the temperature effects from those originating from the additional oxidative treatment of nickel oxide. For the explanation of observed temparature effects, a simple model is proposed according to which the vibronic mixing of different final states increases with temperature.