EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

We report for the first time the trapping of few-atom indium (In) clusters on substitutional silicon (Si) dopant atoms in the graphene lattice. Here, indium was evaporated onto suspended monolayer graphene (that intrinsically includes a small fraction of substitutional Si heteroatoms) using a custom-built preparation chamber (base pressure ~10-9 mbar) directly coupled to an atomic resolution scanning transmission electron microscope (STEM). Our element-sensitive STEM results show that the resulting structure incorporates indium clusters anchored onto the graphene lattice via the substitutional Si atoms. These structures appear stable at room temperature under 60 keV electron irradiation. We find that the exact atomic arrangements of these In clusters depend strongly on the original coordination of Si in the graphene lattice. As an example, 3-fold symmetric In clusters form on 3-fold coordinated Si atoms, whereas 4-fold symmetric clusters are found on 4-fold coordinated Si atoms. In addition, single In atoms and In dimers can also stabilize at Si impurity sites. On the basis of population analysis of semi-local density-functional theory (DFT) calculations, the In clusters anchored on Si are divalent electron donors, where one hole resides on the Si atom and the 2nd hole is being shared (not equally unless required by symmetry) by the In atoms. Such artificial, anchored few-atom molecules may find applications for example as few-atom catalysts in heterogeneous catalysis.