Shape Evolution of Monolayer MoS₂ Crystals Grown by Chemical Vapor Deposition

Abstract

Atmospheric-pressure chemical vapor deposition (CVD) is used to grow monolayer MoS 2 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 MoO 3 precursor to individually control their heating profiles and provide greater flexibility in the growth recipe. We intentionally establish a sharp gradient of MoO 3 precursor concentration on the growth substrate to explore its sensitivity to the resultant MoS 2 domain growth within a relatively uniform temperature range. We find that the shape of MoS 2 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 MoS 2 domains and their shape evolution.

Stacking-controllable interlayer coupling and symmetric configuration of multilayered MoS2

“…By varying the Mo:S ratio, the shapes of the MoS 2 crystals evolve from a triangle to a truncated triangle and finally become hexagonal 29,30 , as shown in Figure 1e. The shape transformation process along the direction perpendicular to the carrier-gas flow stipulates that the Mo:S ratio change is the primary reason for the shape transformation.…”

“…The confined Mo:S atomic ratio controls the final shape of the MoS 2 crystals, as explained by the Wulff construction principle, 29,30 which states that specific crystal shapes are preferred over others depending on their surface energies. In other words, the surface energy and its dependence on the crystallographic orientation can define the equilibrium shape of a crystal.…”

“…Therefore, the lateral layer size decreases with an increasing height, and monolayer-by-monolayer-stacked MoS 2 crystals are finally formed. [29][30][31][32][33][34] Stacking-oriented phonon frequencies in the Raman spectra We critically examined the high-energy phonons in the Raman spectra of multi-stacked MoS 2 crystals and exploited the stacking-induced structural changes and interlayer vdW interactions. As illustrated in Figure 2a, a MoS 2 crystal consists of two well-defined, strong Raman bands attributed to lattice vibrations in two specific directions, which are denoted as in-plane (E 2g 1 ) and out-of-plane (A 1g ) vibrations.…”

Characteristics of layered tin disulfide deposited by atomic layer deposition with H2S annealing

“…Another method to obtain TMDs is chemical vapor deposition (CVD), which uniformly produces large, high-quality TMDs. [12][13][14][15][16] many precursors have been investigated for deposition of TMDs. Although this method can produce mono-or few-layer TMDs with large areas, the process is generally carried out at high temperatures, which is not an appropriate condition for flexible, wearable devices.…”

Controlled synthesis of high-quality crystals of monolayer MoS2 for nanoelectronic device application

“…While mechanical exfoliated monolayer MoS 2 flakes display excellent electronic and optoelectronic properties, the small size and the low production of these monolayer MoS 2 flakes hinder them from further development. Synthesis of large-area MoS 2 films have been reported in the past few years [22][23][24][25][26][27]. However, the preparation of large-size monolayer MoS 2 single crystals remain to be improved in view of its superior electronic and optoelectronic characteristics [28][29][30][31].…”