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

A structural study has been performed on the polar ZnO(0001)-(1×1) 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 ± 0.04 A, a 16% ± 6% contraction from the bulk spacing. The second and third interlayer spacings were found to be more bulklike at 2.01 ± 0.02 A (0 ± 1%) and 0.61 ± 0.02 A (0 ± 3%), respectively. When compared with calculations of several hydrogen coverages, the experimental surface relaxations suggest a 1/3 monolayer (ML) coverage of hydrogen. The density of states of the 1/3 ML H-terminated surface indicates that the O-2p level is raised above the Fermi energy with respect to its bulk energy. However, the O-2p level is shifted to lower energy when compared with the clean, H-free surface.