Surface-to-bulk core level shift in CoFe2O4 thin films

Abstract

In spite of the absence of significant segregation of either cobalt oxide or iron oxide, core level photoemission binding energy shifts tend to indicate that the surface is significantly different from the bulk for CoFe2O4(111) thin films grown on Al2O3(0001). CoFe2O4(111) thin films show a surface-to-bulk core level shift in both the Co 2p and Fe 2p core level photoemission spectra. Surface weighted components in the core level photoemission spectra of both Co 2p3/2 and Fe 2p3/2 can be distinguished from the bulk components, by angle-resolved x-ray photoemission spectroscopy, for CoFe2O4(111) thin films. The surface termination of CoFe2O4(111) contains both Co and Fe with no evidence of strong preferential surface termination of either an iron or cobalt oxide, except for CoFe2O4(111) in the thin film limit. With extensive annealing above room temperature, the cobalt oxide component of very thin CoFe2O4(111) films, grown on Al2O3 (0001), will lose oxygen.