Formation of a new type of chromium oxide by deposition of chromium onto water precovered Cu(111)

Thin chromiumoxide layers (Theta (Cr), up to 10 ML) on Cu(1 1 1) were produ ced 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. An nealing the sample to 750 K leads to a new type of chromium oxide CrxO3 wit h a square two-dimensional lattice and a lattice constant of 2.70 Angstrom. It is stable upon heating up to 950 K. Further oxidation of this oxide lay er in an oxygen atmosphere of 10(-8) mbar leads to the formation of alpha - Cr2O3 oriented with its hexagonal (0 0 0 1) plane parallel to the surface. Adsorption/desorption experiments show that the square oxide surface is ess entially unable to adsorb CO at 90 K which is in contrast to the hexagonal alpha -Cr2O3 surface. (C) 2001 Elsevier Science B.V. All rights reserved.