Mo Concentration Controls the Morphological Transitions from Dendritic to Semicompact, and to Compact Growth of Monolayer Crystalline MoS on Various Substrates.

The domain morphology in the growth of transition-metal dichalcogenides (TMDCs) is mostly triangular but rarely dendritic. Here, we report a robust chemical vapor deposition method to fabricate atomic-thin 2H-phase MoS dendrites on several single-crystalline substrates with different lattice structures, such as rutile-TiO(001), SrTiO(001), and sapphire(0001). It is found that by tuning the concentration of Mo adatoms, the morphology of MoS domains on these substrates evolves from tridentate dendrites at a low Mo concentration to semicompact fractal domains at an intermediate Mo concentration, and to a compact triangular shape at a high Mo concentration. First-principles calculations reveal that the edge diffusion barrier of Mo is comparable to the attachment barrier, inhibiting fast Mo atom diffusion along the edge. Kinetics Monte Carlo simulations with varying Mo concentrations well reproduce the experimental results. Our combined experimental and theoretical analyses evidently show that the growth of MoS dendritic domains at a low Mo concentration is a nonequilibrium process, which is dominated by the kinetics of Mo adatoms. Our study presents an effective route to control the morphology of TMDCs by simply tuning the transition-metal adatom concentration.