Shape Evolution of Monolayer MoS₂ Crystals Grown by Chemical Vapor Deposition

TLDR

Atmospheric‑pressure chemical vapor deposition is employed to grow monolayer MoS₂ crystals on silicon substrates with a 300 nm oxide layer at elevated temperatures. The study aims to investigate how a sharp gradient of MoO₃ precursor concentration on the growth substrate influences MoS₂ domain growth under a relatively uniform temperature range. A hydrogen‑free CVD process is used, with sulfur and MoO₃ precursors heated in separate furnaces to independently control their profiles and create the desired concentration gradient on the substrate. The resulting MoS₂ domains exhibit shapes that vary from triangular to hexagonal depending on their spatial location, a change driven by local Mo:S precursor ratios (1:>2, 1:2, 1:<2) that alter edge‑growth kinetics, thereby enhancing understanding of shape evolution during growth.

Abstract

Atmospheric-pressure chemical vapor deposition (CVD) is used to grow monolayer MoS2 two-dimensional crystals at elevated temperatures on silicon substrates with a 300 nm oxide layer. Our CVD reaction is hydrogen free, with the sulfur precursor placed in a furnace separate from the MoO3 precursor to individually control their heating profiles and provide greater flexibility in the growth recipe. We intentionally establish a sharp gradient of MoO3 precursor concentration on the growth substrate to explore its sensitivity to the resultant MoS2 domain growth within a relatively uniform temperature range. We find that the shape of MoS2 domains is highly dependent upon the spatial location on the silicon substrate, with variation from triangular to hexagonal geometries. The shape change of domains is attributed to local changes in the Mo:S ratio of precursors (1:>2, 1:2, and 1:<2) and its influence on the kinetic growth dynamics of edges. These results improve our understanding of the factors that influence the growth of MoS2 domains and their shape evolution.