The Surface Structure of Cu2O(100): Nature of Defects

The Cu2O(100) surface is most favorably terminated by a (3,0;1,1) reconstruction under ultrahigh-vacuum conditions. As most oxide surfaces, it exhibit defects, and it is these sites that are focus of attention in this study. The surface defects are identified, their properties are investigated, and procedures to accurately control their coverage are demonstrated by a combination of scanning tunneling microscopy (STM) and simulations within the framework of density functional theory (DFT). The most prevalent surface defect was identified as an oxygen vacancy. By comparison of experimental results, formation energies, and simulated STM images, the location of the oxygen vacancies was identified as an oxygen vacancy in position B, located in the valley between the two rows of oxygen atoms terminating the unperturbed surface. The coverage of defects is influenced by the surface preparation parameters and the history of the sample. Furthermore, using low-energy electron beam bombardment, we show that the oxygen vacancy coverage can be accurately controlled and reach a complete surface coverage (1 per unit cell or 1.8 defects per nm2) without modification to the periodicity of the surface, highlighting the importance of using local probes when investigating oxide surfaces.