Formation of a new type of chromium oxide by deposition of chromium onto water precovered Cu(1 1 1)

Thin chromiumoxide layers (ΘCr up to 10 ML) on Cu(1 1 1) were produced by evaporating chromium onto multilayers of water (D2O) at 120 K. Their composition and structure were studied by X-ray photoelectron spectroscopy, low-energy electron diffraction and temperature programmed desorption. Annealing the sample to 750 K leads to a new type of chromium oxide CrxOy with a square two-dimensional lattice and a lattice constant of 2.70 Å. It is stable upon heating up to 950 K. Further oxidation of this oxide layer in an oxygen atmosphere of 10−8 mbar leads to the formation of α-Cr2O3 oriented with its hexagonal (0 0 0 1) plane parallel to the surface. Adsorption/desorption experiments show that the square oxide surface is essentially unable to adsorb CO at 90 K which is in contrast to the hexagonal α-Cr2O3 surface.