Atomic-Scale Local Work Function Characterizations Of Br Islands On Cu(111)

The electronic properties of halogens on the surface of metals have attracted substantial attention due to their promotion effects on surface molecular dehydrogenation reactions. Herein, the electronic properties of the submonolayer Br on Cu(111) were studied by combining scanning tunneling microscopy and density functional theory (DFT) calculations. The local work function of Br islands is found to range from 5.1 to 5.8 eV, which is higher than that of the Cu substrate (similar to 4.3 eV). Intriguingly, the Br atoms at the edge of islands possess a lower work function than the internal atoms, which originates from a larger local dipole induced by the stronger interfacial charge transfer between internal Br atoms and Cu, as supported by the DFT calculations. This phenomenon is in sharp contrast to the common intuition that the edge atoms tend to receive more charges from the substrate due to the contact with more neutral substrate atoms. Such a counterintuitive observation can be attributed to the stabilization of charged internal Br by neighboring atoms. These findings provide a deep insight of the interactions between halogen adsorbates and the metal surface, which leads to a comprehensive understanding of the microscopic mechanism of halogen-promoted reactions.