Fig. 2

Atomic and electronic structure of the (111) surface of \({\hbox {Cu}}_2 {\hbox {O}}\). (a) Hardsphere model (copper: blue balls, oxygen: red balls) of the proposed surface structure of a bulk-like oxygen-terminated (1 \(\times\) 1) surface and (b) of a surface containing ordered oxygen vacancies in a \((\sqrt{3}\times \sqrt{3}) {\hbox {R30}}^{\circ }\) reconstruction. The unit cells of the surface (pink lines) and of the subsurface layers (orange dashed lines) are indicated. Insets: LEED images taken at 28 eV from these surfaces. (c) The electronic structure close to the valence band maximum measured with He I\(\alpha\) radiation of 21.2 eV, and (d) the band bending in the near-surface region as measured on the \({\hbox {Cu 2p}}_{3/2}\) core level using Mg K\(\alpha\) radiation (1253.6 eV) for both surfaces: The (1 \(\times\) 1) data are plotted as solid green triangles and the \(\sqrt{3}\) data as open blue circles. The error bars in (d) were determined from the global fit.