Interface energetics and atomic structure of epitaxial La1−xSrxCoO3 on Nb:SrTiO3

The energetics at oxide semiconductor/La1−xSrxCoO3 heterojunctions, including the respective alignment of the valence and conduction bands, govern charge transfer and have to be determined for the design of future La1−xSrxCoO3-based devices. In this letter, the electronic and atomic structures of epitaxial La1−xSrxCoO3 on Nb-doped strontium titanate are revealed by scanning transmission electron microscopy, electron energy loss spectroscopy, and in situ x-ray and ultra violet photoelectron spectroscopies. For LaCoO3, a valence band (VB) offset of 2.8 ± 0.1 eV is deduced. The large offset is attributed to the orbital contributions of the Co 3d states to the VB maximum of the LaCoO3 thin films, with no evidence of interface dipole contributions. The sensitivity of the valence band orbital character to spin state ordering and oxygen vacancies is assessed using density functional theory.