The surface oxide: A LEED, DFT and STM study

Using low energy electron diffraction (LEED), density functional theory (DFT) and scanning tunneling microscopy (STM), we have re-analyzed the Pd ( 1 0 0 ) - ( 5 × 5 ) R 27 ° – O surface oxide structure consisting, in the most recent model, of a strained PdO(101) layer on top of the Pd(100) surface [M. Todorova et al., Surf. Sci. 541 (2003) 101]. Both, DFT simulations using the Vienna Ab initio Simulation Package (VASP) and tensor LEED I(V) analysis of newly acquired LEED experimental data, show that the PdO(101) model is essentially correct. However, compared to the previous study, there is a horizontal shift of the PdO(101) layer with respect to the Pd(100) substrate. The atomic coordinates derived by DFT and LEED (R P =0.162) are in excellent agreement with each other. We also present STM images with atomic resolution showing domain boundaries on the surface oxide and discuss the bonding geometry between the surface oxide and the substrate.