Metal Seed Layer Thickness-Induced Transition From Vertical to Horizontal Growth of MoS₂ and WS₂

Abstract

Two-dimensional (2D), layered transition metal dichalcogenides (TMDCs) can grow in two different growth directions, that is, horizontal and vertical. In the horizontal growth, 2D TMDC layers grow in planar direction with their basal planes parallel to growth substrates. In the vertical growth, 2D TMDC layers grow standing upright on growth substrates exposing their edge sites rather than their basal planes. The two distinct morphologies present unique materials properties suitable for specific applications, such as horizontal TMDCs for optoelectronics and vertical TMDCs for electrochemical reactions. Precise control of the growth orientation is essential for realizing the true potential of these 2D materials for large-scale, practical applications. In this Letter, we investigate the transition of vertical-to-horizontal growth directions in 2D molybdenum (or tungsten) disulfide and study the underlying growth mechanisms and parameters that dictate such transition. We reveal that the thickness of metal seed layers plays a critical role in determining their growth directions. With thick (>∼ 3 nm) seed layers, the vertical growth is dominant, while the horizontal growth occurs with thinner seed layers. This finding enables the synthesis of novel 2D TMDC heterostructures with anisotropic layer orientations and transport properties. The present study paves a way for developing a new class of 2D TMDCs with unconventional materials properties.

Electron-Beam Induced Transformations of Layered Tin Dichalcogenides

“…For example, it has been shown that the conversion of metallic Mo (and W) films to MoS 2 (WS 2 ) can lead to horizontal or vertical stacking of the resulting layered materials, depending on the metal film thickness. 35 Table S4), we find low m* for SnS, suggesting high electron mobility in the phonon-scattering limited regime. Quantum transport calculations show a pronounced anisotropy in the in-plane conductance of Sn 2 S 3 , whereas basal-plane oriented SnS has anisotropic conductance within a narrower energy range and the conductance in SnS 2 is nearly perfectly isotropic, similar to TMDs such as MoS 2 ( Fig.…”

E’’ Raman Mode in Thermal Strain-Fractured CVD-MoS2

“…It is well known that the amount of catalytic active sites along the edges of MoS2 is one of the key factors for the hydrogen evolution reaction (HER). It is enhanced heavily by growing MoS2 thin films with vertically aligned layers in previous reports [17,18]. Recently, Our group reported the underlying formation mechanism of SF-MoS2 [19], where the number of edges increased heavily [14,20].…”

“…For normal (OF-) MoS 2 , the two characteristic modes E' and A' 1 are located at 382.5 (383.7) and 402.9 (402.9) cm −1 , respectively, indicating both samples are in high quality. Although it is reported that the intensity ratio between E' and A' 1 mode decreases with the amount of exposed 2D edge sites when the MoS 2 plane is vertical to the substrate due to the polarization dependence [17,18], we do not observe noticeable ratio difference for the three specimen (0.65, 0.66 and 0.60 for normal, OFand SF-MoS 2 , respectively), which can be attributed to the MoS 2 plane parallel to the substrate. Table 1 summarizes the positions of Raman modes for 1H-(normal), OF-, SF-and 1T/1T'-MoS 2 .…”

Large-area MoS 2 grown using H 2 S as the sulphur source

“…Depending on the growth conditions, two types of crystal orientations were obtained, with the basal plane of the crystallites being predominantly oriented either in parallel or perpendicular directions relative to the substrate surface. Recently, a rapid sulfurization/ selenization process to convert Mo and W thin films into polycrystalline molybdenum dichalcogenide films was also demonstrated, where sulfur/selenium powders as the precursors and Ar as a carrier gas were used [29][30][31]. Due to chemically reactive edge sites, such structures are useful as an active material for catalytic reactions [32,33].…”