Role of hydrogen on the ZnO(0001¯)-(1×1) surface

Abstract

A structural study has been performed on the polar ZnO(000$\overline{1}$)-(1$\ifmmode\times\else\texttimes\fi{}$1) surface using ab initio calculations and low-energy electron diffraction (LEED). The experiment was performed with a delay line detector LEED system to minimize electron damage of the surface. The top O-Zn interlayer spacing was found to be $0.51\ifmmode\pm\else\textpm\fi{}0.04$ \AA{}, a 16% $\ifmmode\pm\else\textpm\fi{}$ 6% contraction from the bulk spacing. The second and third interlayer spacings were found to be more bulklike at $2.01\ifmmode\pm\else\textpm\fi{}0.02$ \AA{} ($0\ifmmode\pm\else\textpm\fi{}1%$) and $0.61\ifmmode\pm\else\textpm\fi{}0.02$ \AA{} ($0\ifmmode\pm\else\textpm\fi{}3%$), respectively. When compared with calculations of several hydrogen coverages, the experimental surface relaxations suggest a monolayer (ML) coverage of hydrogen. The density of states of the ML H-terminated surface indicates that the O-2$p$ level is raised above the Fermi energy with respect to its bulk energy. However, the O-2$p$ level is shifted to lower energy when compared with the clean, H-free surface.