GROWTH, STRUCTURE AND THERMAL-PROPERTIES OF CHROMIUM-OXIDE FILMS ON PT(111)

We have prepared chromium oxide films on Pt(111) with thicknesses rang ing from less than a monolayer to more than eight monolayers. The film s were grown by Cr vapor deposition under an oxygen background pressur e of 2 x 10(-6) mbar and a sample temperature of 600 K. The growth, st ructure and thermal properties of the resulting overlayers have been s tudied using a combination of ISS, XPS, LEED and STM. During the initi al 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 meta stable Cr3O4. At higher coverage, a (root 3 x root 3)R30 degrees struc ture appears, due to the formation of the stable Cr2O3 phase. After he ating 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 ov erlayer. The latter is stable up to the highest temperature used in th ese studies (1000 K), although at this temperature it also shows dewet ting and further clustering. (C) 1997 Elsevier Science B.V.