An Extended Strong Metal-Support Interaction Effect: An Ultrathin Gold Wetting Layer on Molybdenum Nitride

The classical strong metal-support interaction (SMSI) effect is predominantly observed in metal/oxide systems, but the fundamental nature of metal/nonoxide interfacial interactions remains somewhat obscure, thus requiring more detailed understanding. Here, we developed an extended SMSI regime of Au/MoN_x synthesized via a controllable vapor-liquid-solid method, where the atomic structure, aggregation state, and electron transfer at the metal-support interface were systematically investigated under varied conditions. It reveals that Au species integrate into a highly dispersed wetting-layer-like structure under a reductive condition, i.e., high-temperature nitridation, which strongly reacts with the MoN_x support, exhibiting a strong interfacial charge transfer. A subsequent oxidation treatment contributed to the severe aggregation of the Au species into nanoparticles and significantly weakened the interfacial electronic interactions. Reversibly, the two interface states enable transforming into each other by alternative nitridation and oxidation reactions. By demonstrating an extended SMSI effect in metal/nitride systems, this study expands the scientific epitaxy over the traditional metal/oxide SMSI concept.