Spontaneous Formation of Gold Cluster Anions on ZnO/Cu(111) Bilayer Films

Recently, bilayer ZnO films grown on Cu, Ag, and Au supports have been reported as new materials with potentially interesting properties. In this work we have investigated the structure and stability of small Au n clusters (n = 2, 3, 4) and of a larger gold aggregate, Au 20 , deposited on ZnO/Cu(111) ultrathin films using a spin-polarized DFT+U/D2′ approach which includes dispersion corrections. The properties of Au clusters on ZnO/Cu(111) are completely different from those of the corresponding gas-phase units, but also from the same Au clusters deposited on an unsupported ZnO bilayer. On ZnO/Cu(111) small Au n clusters (n = 3, 4) are linear and Au 20 is two-dimensional (2D), at variance with the free counterparts. The stability of Au clusters on ZnO/Cu(111) is governed by a spontaneous charge transfer from the underlying Cu(111) substrate via electron tunneling through the thin ZnO film, resulting in negatively charged Au clusters. A Bader charge analysis shows that the excess electrons are localized on the edges of the Au clusters to minimize Coulomb interactions