Revealing the Role of Gold in the Growth of Two-Dimensional Molybdenum Disulfide by Surface Alloy Formation.

The formation of Mo/Au surface alloy during Au-assisted chemical vapor deposition (CVD) of MoS is confirmed by a series of control experiments. A metal-organic chemical vapor deposition (MOCVD) system is adapted to conduct two-dimensional MoS growth in a controlled environment. Sequential injection of Mo and S precursors, which does not yield any MoS on SiO /Si, grows atomically thin MoS on Au, indicating the formation of an alloy phase. Transmission electron microscopy of a cross-section of the specimen confirms the confinement of the alloy phase near the surface only. These results show that the reaction intermediate is the surface alloy, and that the role of Au in the Au-assisted CVD is the formation of an atomically thin reservoir of Mo near the surface. This mechanism is clearly distinguished from that of MOCVD, which does not involve the formation of any alloy phases.