Structure and electronic state of the TiO₂ and SrO terminated SrTiO₃(100) surfaces

Structure and electronic state of two kinds of SrTiO₃(100) surfaces, selectively formed TiO₂ terminated and SrO terminated surfaces, are studied by means of reflection high energy electron diffraction (RHEED), XPS and UPS. It is revealed that for both terminated surfaces, the distances between the 1st and 2nd layer are expanded, where that for the TiO₂ and SrO surfaces are 1.95 + 0.07 A ̊ and 1.95 + 0.10 A ̊, respectively. Furthermore, the oxygen atoms on the outermost surface are pulled out for 0.10 Å and 0.16 Å, respectively. The electronic state near the Fermi level mainly consists of the Ti3d and O2p orbitals and is found to be sensitive to the coordination around the Ti atom; i.e., for the SrO terminated surface, where Ti is coordinated octahedrally by oxygen, a narrow band is observed, while for the TiO₂ terminated surface changes in the symmetry from O_h to C_4v result in the broadening of the band structure.