Photoemission and low-energy-electron-diffraction study of clean and oxygen-dosed Cu2O (111) and (100) surfaces.

Abstract

The geometric and electronic structure of clean and oxygen-dosed ${\mathrm{Cu}}_{2}$O single-crystal surfaces was studied with x-ray and ultraviolet photoelectron (UPS) spectroscopies and low-energy electron diffraction. The nonpolar (111) surface can be prepared in a nearly stoichiometric (1\ifmmode\times\else\texttimes\fi{}1) form by ion bombardment and annealing in vacuum. Oxygen adsorbs molecularly on the stoichiometric (111) surface at 300 K, but adsorbs dissociatively on a defective (111) surface prepared by ion bombardment. For the polar ${\mathrm{Cu}}_{2}$O(100) face it was possible to prepare a reconstructed, Cu-terminated surface with a (3\ensuremath{\surd}2 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}2 )R45\ifmmode^\circ\else\textdegree\fi{} periodicity by ion bombardment and annealing in vacuum. Preparation of an unreconstructed, (1\ifmmode\times\else\texttimes\fi{}1), O-terminated (100) surface was possible by large (${10}^{9}$-L) oxygen exposures. UPS investigations of the O-terminated (100) surface suggest a mixture of incorporated (i.e., lattice) oxygen and adsorbed atomic oxygen (i.e., adatoms) in the terminating layer. The annealing behavior of the ${\mathrm{Cu}}_{2}$O(100) surface was history dependent. Early in the sample history, bulk lattice oxygen diffused to the surface at temperatures above 800 K giving domains of (\ensuremath{\surd}2 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}2 )R45\ifmmode^\circ\else\textdegree\fi{} periodicity associated with half a terminating layer of oxygen atoms. After repeated ion bombardment and annealing cycles, heating above 800 K gave only a Cu-terminated surface, apparently because of a depletion of bulk lattice oxygen.