Monolayer MoS2 prepared by chemical vapor deposition(CVD)has a highly polycrystalline nature largely because of the coalescence of misoriented domains,which severely hinders its future applications.[1] Identifying and even controlling the orientations of individual domains and understanding their merging behavior therefore hold fundamental significance.In this work,by using single-crystalline sapphire(0001)substrates,we designed the CVD growth of monolayer MoS2 triangles and their polycrystalline aggregates for such purposes.