Photoemission study of the Li/Ge(111)-3 x 1 and Na/Ge(111)-3 x 1 reconstructions

Full text: The Li/Ge(111)-3 x 1 and Na/Ge(111)-3 x 1 reconstructions have been studied by means of angle-resolved photoemission spectroscopy (ARUPS) and core-level spectroscopy using synchrotron radiation. These surfaces are believed to share the same geometry as those of the alkali and Ag induced Si(111)-3 x 1 reconstructions, commonly referred to as the Honeycomb chain-channel (HCC) model. Angle-resolved measurements were performed along the Γ-bar-K-bar and Γ-bar-M-bar directions of the 1 x 1 Brillouin zone. The experimental results have been compared to density functional theory (DFT) calculations using the General Gradient Approximation for that of the HCC model. The reconstruction was modelled using a periodic slab geometry consisting of 12 Ge layers mirrored halfway along the z-direction with the reconstructed surface on both sides of the slab. Each slab was separated by a 20 Angstroms vacuum gap, which corresponds to approximately 8 atomic layers. Experimental core-level shifts were fit using voigt line-shapes. It was found that a consistent fit could be achieved using one bulk component and two surface components for both the Li/Ge(111)-3 x 1 and Na/Ge(111)-3 x 1 reconstructions. These peak positions were compared to both initial and final state DFT calculations. Final state effects were modelled using so-called Slater-Janak transition states