AES, XPS, and TDS study of the adsorption and desorption of NH on ultra-thin chromium oxide films formed on chromium 3 single crystal surfaces

Ultra-thin films of Cr2O3 have been produced by oxidation of Cr 110.surfaces in O2 pO2s3=10y8 mbar. at 1908C. The adsorption and desorption of NH3on the thin Cr2O3 films have been studied by LEED, AES, XPS, and TDS. The kinetics of ammonia adsorption was investigated by AES and adsorbed NH3 states on chromium oxide surfaces were identified by XPS. After exposure to NH3, N 1s signals were observed at 398.6 and 400.7 eV. These results were interpreted by the existence of two types of adsorbed species resulting from the interaction of NH3 with acid sites of the chromium oxide surface. Accordingly, two desorption peaks corresponding to NH2and NH3were observed by TDS at 1508C.. q1999 Elsevier Science B.V. All rights reserved