Surface Atomic Structure of Ca1.9Sr0.1RuO4 at Low Temperature

The surface atomic structure of Ca1.9Sr0.1RuO4 at low temperature has been investigated by using Low Energy Electron Diffraction (LEED) I-V. The observed LEED pattern indicates that the sample of Ca1.9Sr0.1RuO4 surface is flat and single crystal. LEED I-V data, six in-equivalent beams of the layered perovskite Ca1.9Sr0.1RuO4 were recorded at the temperature of 90 K. LEED I-V calculations was performed to fit experimental data to obtain the surface atomic structure. Our results show that the RuO6 in the Ca1.9Sr0.1RuO4 surface at low temperature are rotated in-plane alternatingly. The in-plane rotation of the RuO6 octahedra at the surface is reduced by 10.8 % from the bulk value. The RuO6 octahedra in the surface are tilted but it is reduced by 52.5 % for O (1) and 33.0 % for O (2) from the bulk value. The bond-length of Ru O (1) at the surface is about the same as in the bulk. However, the bond length of Ru O (2) at the surface is shoter by 9.1 % than its bulk value. The volume of RuO6 octahedron at the surface is smaller by 8.8 % than its bulk value. Obviously, the atomic structure at the Ca1.9Sr0.1RuO4 is different than that in the bulk. By comparing to the previous study, it is found that the surface structure of Ca1.9Sr0.1RuO4 at low temperature is different than that at room temperature. This finding would explain why the metal insulator transition temperature in the surface of Ca1.9Sr0.1RuO4 is different than that in the bulk. It shows that the lattice distortions at Ca1.9Sr0.1RuO4 strongly influence its electronic properties.