Unravelling Orientation Distribution and Merging Behavior of Monolayer MoS₂ Domains on Sapphire

Abstract

Monolayer MoS2 prepared by chemical vapor deposition (CVD) has a highly polycrystalline nature largely because of the coalescence of misoriented domains, which severely hinders its future applications. Identifying and even controlling the orientations of individual domains and understanding their merging behavior therefore hold fundamental significance. In this work, by using single-crystalline sapphire (0001) substrates, we designed the CVD growth of monolayer MoS2 triangles and their polycrystalline aggregates for such purposes. The obtained triangular MoS2 domains on sapphire were found to distributively align in two directions, which, as supported by density functional theory calculations, should be attributed to the relatively small fluctuations of the interface binding energy around the two primary orientations. Using dark-field transmission electron microscopy, we further imaged the grain boundaries of the aggregating domains and determined their prevalent armchair crystallographic orientations with respect to the adjacent MoS2 lattice. The coalescence of individual triangular flakes governed by unique kinetic processes is proposed for the polycrystal formation. These findings are expected to shed light on the controlled MoS2 growth toward predefined domain orientation and large domain size, thus enabling its versatile applications in next-generation nanoelectronics and optoelectronics.

A universal etching-free transfer of MoS2 films for applications in photodetectors

“…In a typical growth, argon gas at a rate of 50 sccm was used as the carrier gas, and the growth time was 1 h. More detailed growth parameters are described in Refs. [37,38,43,44].…”

“…Compared to the methods of mechanical exfoliation [13,26], liquid exfoliation [27][28][29], and solvothermal synthesis [30], chemical vapor deposition (CVD) [31][32][33][34][35][36][37][38][39][40][41][42][43][44] has been proved to be the most effective route to synthesize millimeter-scale uniform monolayer MoS 2 on various substrates such as SiO 2 on Si (SiO 2 /Si) [32,[40][41][42], mica [38], strontium titanate (STO) [37], Nano Res. and sapphire [35,39,43,44].…”

“…and sapphire [35,39,43,44]. However, a major challenge is transferring CVD-grown MoS 2 onto target substrates for characterization and further device fabrication while maintaining high fidelity, keeping both the morphological and physicochemical properties intact.…”

Vapor Deposition Techniques for Synthesis of Two-Dimensional Transition Metal Dichalcogenides

“…2D and E. Recent studies on the CVD with MO 3 and X powder have been focused on the synthesis of MoS 2 and WS 2 on single crystal substrate for enhancing grain size. In particular, orientation aligned growth of CVD MoS 2 on c-plane sapphire has been reported by Ji et al (2014) and Dumcenco et al (2015). They have shown that the same hexagonal lattice symmetry induces van der Waals epitaxy of MoS 2 on c-plane sapphire, which suggests possibility of wafer-scale growth of single-crystal MoS 2 similar with graphene on hydrogenterminated germanium (Lee et al, 2014b).…”

“…Thus, significant efforts have been devoted to synthesize high quality and large area 2D TMDCs. Recently several studies have shown synthesis of 2D TMDCs using various methods based on the vapor deposition techniques: sulfurization of metal and metal oxide thin films Zhan et al, 2012;Elías et al, 2013;Liu et al, 2014b), chemical vapor deposition (CVD) Najmaei et al, 2013;van der Zande et al, 2013;Cong et al, 2014;Ji et al, 2014;Ling et al, 2014;Shaw et al, 2014;Dumcenco et al, 2015;Kang et al, 2015) and atomic layer deposition (ALD) (Song et al, 2013;Jin et al, 2014;Tan et al, 2014;Song et al, 2015). In this review, synthetic methods for 2D TMDCs, mainly focused on the MoS 2 and WS 2 which are the most studied 2D TMDCs, will be presented.…”