Physical chemistry of the Mn/ZnO (0001̄) interface probed by hard X-ray photoelectron spectroscopy

The oxidation of a thin Mn film grown on a ZnO (0001̄) surface and the subsequent diffusion of Mn into the oxide single crystal are investigated in situ by using high-energy X-ray photoelectron spectroscopy (HAXPES). Using hard X-rays allows one not only to investigate the chemistry at the heterojunction but also to describe in detail the thermal diffusion process and the electron energy band alignment at the Mn/ZnO interface. Charge transfer occurs between the metallic Mn film and the ZnO surface which causes the ZnO valence band to bend downward in the interfacial region. Annealing at 630 K leads to the formation of a thin two-dimensional MnO film which induces an upward bending of ZnO bands. Upon annealing at 800 K, Mn diffuses into the substrate crystal. A Mn concentration profile is derived, and a diffusion coefficient of 1.4 × 10^-19 m²/s is experimentally determined.