Limiting Domain Size of MoS₂: Effects of Stoichiometry and Oxygen

Abstract

Reactive molecular dynamics simulations of MoS2 crystallization from amorphous precursor materials showed that crystal domain size decreased because of excess S or O, relative to the stoichiometric case. Simulation results were corroborated by comparison of calculated limiting domain sizes to experimental measurements of MoS2 crystals grown from thermal decomposition of molybdenum dithiocarbamate. Then, the simulations were used to evaluate two previously proposed domain growth mechanismsthermodynamic and kinetic; both were shown to contribute to MoS2 domain growth and, importantly, to stopping growth at a limiting size. It was shown that S-rich or O-containing precursor materials can inhibit grain growth (i) thermodynamically, by increasing the amount of S at domain edges which decreases boundary energy, making them more stable and lowering the driving force for growth, and (ii) kinetically, by decreasing the probability of Mo–S interactions at domain edges that would otherwise contribute to domain growth. The simulations explain how each of these mechanisms determines the effect of precursor composition on MoS2 domain size and, further, suggest avenues for tunable MoS2 synthesis to achieve application-specific domain size.

New Reactive Force Field for Simulations of MoS2 Crystallization

“… Convex hull diagram of the Mo x S y system, computed via DFT, AIREBO, 16 and ReaxFF parameterizations: Chen, 20 Ostadhossein, 26 Hong, 28 and our new force field parameters. …”

“… Energies of amorphous MoS 2 models computed via DFT and various ReaxFF parameter sets: Ostadhossein, 26 Hong, 28 Chen, 20 and the new force field. …”

“… Final structures of the melt-quench simulations for 216-atom models of MoS 2 with different ReaxFF parameterizations: Ostadhossein 26 (a), Hong 28 (b), Chen, 20 (c) and our new ReaxFF (d) parameter sets. The view is generally along the y -axis; a slight rotation in panels (a) and (d) is added for a better representation of the crystalline phase.…”

“… Final structures of the melt-quench simulations of 1536-atom models of MoS 2 within different ReaxFF parameterizations: Ostadhossein 26 (a), Hong 28 (b), Chen, 20 (c) and the new parameter set (d). …”

“…Several computational studies of MoS 2 crystallization have been published in recent years, utilizing AIREBO 16 − 18 and ReaxFF empirical potentials. 19 , 20 …”