Supported metal films represent a model binary metallic system wherein the surface properties can be finely tuned with the composition/thickness of the film. Thus, it has raised increasing research interests from various aspects. In this work, the adsorption and assembly behavior of melamine on the Cu films grown on the (22 × √3) reconstructed Au(111) substrate were investigated as a function of Cu thickness. The atomically resolved scanning tunneling microscopy (STM) images in combination with density functional theory (DFT) calculations reveal that the ultrathin submonolayer copper film forms a pseudomorphic (1 × 1) lattice by agglomerating at the subsurface, while the true Cu adlayers start to appear on the three-layer thick films and hold the bulk Cu(111) lattice. Correspondingly, the adsorption and assembly of the melamine molecules significantly differ from those on pure metals, experiencing a gradual transformation from physisorption to chemisorption assemblies with the Cu film thickening. These findings shed light on the self-assembly behavior of organics on binary metallic surfaces. In addition, the evaporated metal films also register a diversified substrate for tuning the properties of adsorbed molecular films.

Supported metal films are often found to display extraordinary properties compared to their bulk counterparts. In this work, we investigate the atomic and electronic structures of both the Au/Cu(111) and Cu/ Au(111) thin films with low-temperature scanning tunneling microscopy (STM) and synchrotron radiation photoelectron spectroscopy (SRPES). The high-resolution STM images revealed that the Au films evaporated on Cu(111) at room temperature grow with compressed lattices, which gradually evolve and restore to that of the bulk gold from the fourth layer. Both STM and SRPES evidenced that there are considerable Cu atoms incorporated into each layer of the Au films, whose concentrations decrease stepwise along with the film thickening. As a reversed system, the growth of Cu films on Au(111) starts with agglomerating at the subsurface and adopting a (1 × 1) lattice within a submonolayer coverage. The lattice quickly shrinks to that of bulk Cu(111) from the second layer, yet the electronic property is restored slowly until the third layer. In each Cu film, there were also intermixed Au atoms coming from the substrate, and their concentrations also decrease along with the film thickening. On both the Au/Cu(111) and Cu/Au(111) submonolayer films, CO adsorption was investigated and found to be significantly higher than bare Au(111) but still weaker than the Cu(111) surface. The adsorbed CO molecules were apparently connected to the incorporated Cu atoms in the surface layers, yet the enhanced CO bindings were closely related to the electronic properties of the films. These findings are believed to shed new light on the atomic details of the Cu/Au bimetallic systems, thus deepening the understanding of the specific catalytic activities of the Cu/ Au alloys.

The doping effect of Cu on the self-assembly film of melamine on an Au(111) surface has been investigated with scanning tunneling microscopy (STM). The evaporated Cu adatoms occupy the positions underneath the amino groups and change the hydrogen bonding pattern between the melamine molecules. Accordingly, the self-assembly structure has changed stepwise from a well-defined honeycomb into a track-like and then a triangular structure depending on the amount of Cu adatoms. The interaction between Cu adatom and melamine is moderate thus the Cu adatoms can be released upon mild heating to around 100 °C. These findings are different from previous observations of either the coordination assembly or the physically trapped metal adatoms.