Interface energetics and atomic structure of epitaxial La_1−xSr_xCoO₃ on Nb:SrTiO₃

The energetics at oxide semiconductor/La_1−xSr_xCoO₃ heterojunctions, including the respective alignment of the valence and conduction bands, govern charge transfer and have to be determined for the design of future La_1−xSr_xCoO₃-based devices. In this letter, the electronic and atomic structures of epitaxial La_1−xSr_xCoO₃ 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