The Adatom Concentration Profile: A Paradigm for Understanding Two-Dimensional MoS Morphological Evolution in Chemical Vapor Deposition Growth.

The two-dimensional (2D) transition metal dichalcogenide (TMD) MoS possesses many intriguing electronic and optical properties. Potential technological applications have focused much attention on tuning MoS properties through control of its morphologies during growth. In this paper, we present a unified spatial-temporal model for the growth of MoS crystals with a full spectrum of shapes from triangles, concave triangles, three-point stars, to dendrites through the concept of the adatom concentration profile (ACP). We perform a series of chemical vapor deposition (CVD) experiments controlling adatom concentration on the substrate and growth temperature and present a method for experimentally measuring the ACP in the vicinity of growing islands. We apply a phase-field model of growth that explicitly considers similar variables (adatom concentration, adatom diffusion, and noise effects) and cross-validate the simulations and experiments through the ACP and island morphologies as a function of physically controllable variables. Our calculations reproduce the experimental observations with high fidelity. The ACP is an alternative paradigm to conceptualize the growth of crystals through time, which is expected to be instrumental in guiding the rational shape engineering of MoS crystals.