Growth, structure and thermal properties of chromium oxide films on Pt(111)

We have prepared chromium oxide films on Pt(111) with thicknesses ranging from less than a monolayer to more than eight monolayers. The films were grown by Cr vapor deposition under an oxygen background pressure of 2 x 10(-6) mbar and a sample temperature of 600 K. The growth, structure and thermal properties of the resulting overlayers have been studied using a combination of ISS, XPS, LEED and STM. During the initial stage of growth, the film nucleates at Pt step edges, and grows in a step-flow mode. For the first two monolayers, a well-ordered p(2 x 2) structure is observed and attributed to the epitaxial growth of metastable Cr3O4. At higher coverage, a (root 3 x root 3)R30 degrees structure appears, due to the formation of the stable Cr2O3 phase. After heating in vacuum to about 700 K, the p(2 x 2) film begins to decompose and agglomerate, and finally becomes a (root 3 x root 3)R30 degrees overlayer. The latter is stable up to the highest temperature used in these studies (1000 K), although at this temperature it also shows dewetting and further clustering. (C) 1997 Elsevier Science B.V.