The growth of ultrathin Cr films on benzene-covered Ni(111)

Using X-ray photoelectron spectroscopy (XPS) and temperature programmed des orption (TPD) we studied the properties of thin Cr films in the nominal cov erage range between 0.13 and 4 monolayers (ML), which were evaporated onto a Ni(111) surface pre-covered with up to 14 ML benzene. Evaporation of smal l amounts of Cr (< 0.5 ML) onto thick benzene layers (> 4 ML) at 100 K lead s to the formation of non-metallic bis(benzene)chromium (Cr(C6H6)(2)) rathe r than condensation of small clusters in the benzene matrix, as can be seen from the positions and shapes of the Cr 2p(3/2) peaks in XPS. Upon anneali ng to 400 K these films transform into metallic Cr as is indicated by a Cr 2p(3/2) peak shift of -0.8 eV, and significant changes in the peak shapes. For 0.5-2 ML a metallic Cr species, in addition to the non-metallic species , is already seen at 100 K. For higher coverages > 2 ML only the metallic s pecies is seen in XPS and the Cr 2p(3/2) peak shape does then not change up on annealing. The development of the C 1s spectra upon annealing reveals th at there is a significant amount of benzene buried under the Cr layer, whic h is partially dissociated, depending on the annealing temperature and the Cr coverage. (C) 1999 Elsevier Science B.V. All rights reserved.