Ligancy-Driven Controlling of Covalency and Metallicity in a Ruthenium Two-Dimensional System

The homopolar network and conjugation in d-block single elements can materialize a highly anisotropic and robust structure of a noble-metal system. Here, we have prepared ruthenium (Ru) atomic monolayers of a nonmetallic hexagonal lattice, and determined their layering scheme and metallization. The two-dimensional (2D) network is retained at the first stacking of the monolayer, while maintaining the nonmetallic features. We find out that the atop (AA) related stacking structure of bilayered Ru nanosheets occurs due to the ligancy-driven covalency, and the inception of the metallic electronic states is from trilayered stacking. These results indicate that the metallic states can be separated from covalent-bonding linkage and unpaired electrons in spd hybrid orbital systems. Our approach enables the molecular structure of noble-metal atoms to be induced via controlling the ligancy of d-block atomic bonds.