Chemical, Electronic and Nanostructure Dynamics on Sr(Ti[subscript 1 - x]FE[subscript x])O[subscript 3] Thin-Film Surfaces at High Temperatures

Abstract

The surface structure, chemical composition and electronic structure of Sr(Ti1-xFex)O3 under different temperatures and oxygen pressures were studied by Scanning Tunneling Microscopy / Spectroscopy (STM/S) and X-ray Photoelectron Spectroscopy (XPS). The surface structure remained stable to 430 oC at 10-3 mbar oxygen pressure. When annealing at low oxygen pressure, the A to B site ratio, Sr/(Fe+Ti) decreased, Fe content at the B site increased, and particles that are likely to be Fe enriched, precipitated to the grain boundaries. Moreover, Fe changed its valance state, in part, from Fe3+ to Fe2+, consistent with oxygen vacancy formation. The surface of STF was electrically insulating at room temperature, and exhibited by STS a well defined gap in the electronic density of states at 380 oC. With further increase to 430 oC, the energy gap disappeared. The variation in surface defects during thermal treatment is discussed as a likely reason for electronic structure changes at elevated temperatures.