Atomistic mechanisms of seeding promoter-controlled growth of molybdenum disulphide

Abstract

Seeding promoters facilitate the nucleation and growth of transition metal dichalcogenides in chemical vapor deposition (CVD). However, sophisticated roles of seeding promoter remain unclear. Here, adopting triangular-shaped crystal violet (CV) consisting of nonpolar and polar parts as the seeding promoter, we study the role of seeding promoter for the growth of molybdenum disulfide (MoS2). We systematically control the geometrical configuration of CV on SiO2/Si substrate by changing the solvent polarity and find that it strongly affects the growth of monolayer or multilayer MoS2 domains via CVD. Monolayer MoS2 domains were predominantly grown on randomly lying-down CV configurations on SiO2/Si substrate, whereas multilayer MoS2 domains are synthesized at concentrated polar parts in CV micelle on the substrate. Density functional theory calculations reveal that the initial nucleation step for the MoS2 growth is the adsorption of S on CV and the most favourable S adsorption site is the polar part in CV. Furthermore, it is found that the CV adsorption to SiO2 is mediated by the polar CV part and additionally strengthened in the lying-down CV configuration. Enhancing the thermal stability as well as hindering the re-aggregation of CV at high temperature, the lying down CV configuration allows the predominant growth of monolayer MoS2. This work provides a general framework to understand the growth of MoS2 from aromatic seeding promoters.