Thermally Activated Processes at the Co/ZnO Interface Elucidated Using High Energy X-rays

A detailed picture of the thermally activated proces occurring at the Co/ZnO interface is obtained by a combination of high energy X-ray based techniques: X-ray photoelectron and absorption spectroscopies and the kinematical X-ray standing wave method. At room temperature, the growth of a few monolayers of cobalt proceeds by the nucleation of nanometer-sized clusters on the polar oxygen-terminated (000 (1) over bar surface of a ZnO single crystal. Progressive annealing from 600 to 970 K allows separating the Various interfacial reactions. At the lowest annealing temperature, Co clusters Coalesce while keeping their metallic character. Above 700 K Co-0 is gradually oxidized to Co2+ and a tain Co rich (Zn, Co)O layer is annealing temperature (970 K), Co diffuses deeper into ZnO and Zn vacancies are created at subsurance sites that were previously Occupies by Co.