CO与蜜勒胺自组装膜协同作用制备Au单原子及多原子物种

金属单原子物种的可控制备对于包括多相催化在内的各种表面化学过程非常重要。在本工作中，我们在Au(111)表面制备了由蜜勒胺分子形成的具有周期性孔道结构的自组装薄膜。这种有机分子薄膜所携载的官能团能与金属原子进行有效作用。通过在室温下暴露CO气体，在表面上成功制备出Au单原子。由于蜜勒胺分子中的杂环氮原子与Au原子作用较强，因此所形成的Au原子具有突出的稳定性，并且具有多种形式的空间分布构型，有望为一些结构敏感性的表面反应提供合适的催化位点。

CO Induced Single and Multiple Au Adatoms Trapped by Melem Self-Assembly

The controllability of metal adatoms has been attracting ever-growing attention because the metal species in particular single-atom metals can play an important role in various surface processes, including heterogeneous catalytic reactions. On the other hand, organic self-assembly films have been regarded as an efficient and versatile bottom-up method to fabricate surface nanostructures, whose functionality and periodicity can be highly designable. In this work, we have developed a novel strategy to steer the generation and distribution of metal adatoms by combining the surface self-assemblies with exposure to small inorganic gaseous molecules. More specifically, we have prepared a honeycomb structure of melem (triamino-s-heptazine) on the Au(111) surface based on a well-structured hydrogen bonding network. The achieved melem self-assembly contains periodic hexagonal pores having diameters as large as around 1 nm. More importantly, the peripheries of the nanopores are decorated with heterocyclic N atoms that can probably form strong interactions with the metal species. Upon exposing the melem self-assembly to a CO atmosphere at room temperature, a fair number of Au adatoms were produced and trapped inside the nanopores encircled by the melem molecules. Single or clustered Au vacancies were concomitantly formed that were also trapped by the melem pores and stabilized by the surrounding molecules, as confirmed by high-resolution scanning tunneling microscopy (STM) images. Both types of added species showed positive correlations with the CO exposure and saturated at around 0.01 monolayer. In addition, owing to the large pore size, as well as the presence of multiple docking sites inside the nanopores, more than one Au adatom can reside in a melem nanopore; they can be distributed in a variety of configurations for bi-Au (two Au adatoms) and tri-Au (three Au adatoms) species, whose population can be manipulated with the CO exposure. Moreover, control experiments demonstrated that these CO-induced Au species, including the adatoms and vacancies, can survive annealing treatments up to the temperature at which the melem molecules start to desorb, indicating a substantial thermal stability. The formed Au species may hold great potential for serving as active sites for surface reactions. More interestingly, the bi-Au and tri-Au species have moderate Au-Au intervals, and can be potentially active for certain structurally sensitive bimolecular reactions. Considering all these aspects, we believe that this work presents a fresh approach to utilizing organic self-assembly films and has demonstrated a rather novel strategy for preparing various single-atom metal species on substrate surfaces.