Termination-dependent electronic structure and atomic-scale screening behavior of the Cu2O(111) surface

By combining differential conductance (dI/dV) spectroscopy with a scanning tunneling microscope and hybrid density functional theory simulations we explore the electronic characteristics of the (1 x 1) and (root 3 x root 3)R30 degrees terminations of the Cu2O(111) surface close to thermodynamic equilibrium. Although frequently observed experimentally, the composition and atomic structure of these two terminations remain controversial. Our results show that their measured electronic signatures, such as the conduction band onset deduced from dI/dV measurements, the bias-dependent appearance of surface topographic features, as well as the work function retrieved from field emission resonances unambiguously confirm their recent assignment to a (1 x 1) Cu-deficient (CuD) and a (root 3 x root 3)R30 degrees nano-pyramidal reconstruction. Moreover, we demonstrate that due to a different localization of the screening charges at these Cu-deficient terminations, their electronic characteristics qualitatively differ from those of the stoichiometric (1 x 1) and O-deficient (root 3 x root 3) terminations often assumed in the literature. As a consequence, aside from the topographic differences recently pointed out, also their electronic characteristics may contribute to a radical change in the common perception of the Cu2O(111) surface reactivity.