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

Abstract

Using X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) we studied the properties of thin Cr films in the nominal coverage 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 small amounts of Cr (<0.5 ML) onto thick benzene layers (>4 ML) at 100 K leads to the formation of non-metallic bis(benzene)chromium (Cr(C 6H 6) 2) rather 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 annealing 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 species is seen in XPS and the Cr 2p 3/2 peak shape does then not change upon annealing. The development of the C 1s spectra upon annealing reveals that there is a significant amount of benzene buried under the Cr layer, which is partially dissociated, depending on the annealing temperature and the Cr coverage.