van der Waals Epitaxial Growth of Atomically Thin 2D Metals on Dangling‐Bond‐Free WSe₂ and WS₂

Abstract

Abstract2D metals have attracted considerable recent attention for their special physical properties, such as charge density waves, magnetism, and superconductivity. However, despite some recent efforts, the synthesis of ultrathin 2D metals nanosheets down to monolayer thickness remains a significant challenge. Herein, by using atomically flat 2D WSe2 or WS2 as the growth substrate, the synthesis of atomically thin 2D metallic MTe2 (M = V, Nb, Ta) single crystals with the thickness down to the monolayer regime and the creation of atomically thin MTe2/WSe2 (WS2) vertical heterojunctions is reported. Comparison with the growth on the SiO2/Si substrate under the same conditions reveals that the utilization of the dangling‐bond‐free WSe2 or WS2 as the van der Waals epitaxy substrates is crucial for the successful realization of atomically thin MTe2 (M = V, Nb, Ta) nanosheets. It is further shown that the epitaxial grown 2D metals can function as van der Waals contacts for 2D semiconductors with little interface damage and improved electronic performance. This study defines a robust van der Waals epitaxy pathway to ultrathin 2D metals, which is essential for fundamental studies and potential technological applications of this new class of materials at the 2D limit.

Morphology Control of Two-Dimensional Tin Disulfide on Transition Metal Dichalcogenides Using Chemical Vapor Deposition for Nanoelectronic Applications

“…This impedes the free migration of adsorbed species and the morphology of SnS2 grown on SiO2 often exhibits clusters or non-hexagon crystal shape. 35 The similar growth dependence on the substrate has also been observed in the case of other 2D materials such as NbS2 and ReS2, [48][49][50][51] which demonstrate the importance of substrate selection on the growth of 2D crystals with high quality. It is noted that some of the SnS2 crystals could also grow in the out-of-plane direction on the WS2 surface, which is indicated by the red dashed circle in Figure 3(e).…”

Structure, Preparation, and Applications of 2D Material‐Based Metal–Semiconductor Heterostructures

“…[131][132] Because of their similarity to graphene, semiconducting TMDCs can also be used as templates for the growth of metallic TMDCs on their surface by vdW epitaxy. In such a growth method, a wide range of vertical TMDC MSHSs has been fabricated, including NbS2/MoS2, [133] WTe2/WSe2, [134] NbTe2/WSe2, [135] VTe2/WSe2, [135] TaTe2/WSe2 [135] and VSe2/WSe2. [136] Precisely defining the location of the nucleation site on the TMDC 2D flake is critical for the CVD growth of the heterostructure.…”

Wafer‐scale vertical van der Waals heterostructures

“…120,121 The extremely clean and dangling-bond-free surface of 2D TMDs semiconductors contribute to the reduction of nucleation density. 8,122,123 Given that the large-size, low-defect underlying 2D materials can be synthesized through suppressing nucleation, [124][125][126] increasing precursor supply, 127,128 seamless stitching, 129,130 substrate engineering, 39,41 and phase engineering, 131 when defects are introduced artificially, the damaged areas with high energy and chemical disorder became the preferred nucleation sites, and then the nucleation and growth process of upper 2D materials will be controlled, leading to well-designed vdWHs with large scale. The controlled nucleation and growth of VSe 2 on large-area WSe 2 is illustrated in Figure 5A.…”

“…The chemically inert and atomically flat surfaces of 2D materials facilitate the suppression of nucleation density. 8,123 By introducing defects or seed crystals regularly, the nuclear formation energy in these areas will be lowered, becoming the initial sites for crystal growth. 118,119 There are two key points to obtain wafer-scale vdWHs through seeded-growth: (a) adopting an appropriate strategy to synthesize the large-area underlying 2D materials with as few defects as possible, which is the hinge to expel excess nucleation sites.…”

“…In short, controlling the nucleation and growth process of the top material by generating artificial defects on the surface of the underlying material is an effective strategy to produce high quality heterostructure arrays. The chemically inert and atomically flat surfaces of 2D materials facilitate the suppression of nucleation density 8,123 . By introducing defects or seed crystals regularly, the nuclear formation energy in these areas will be lowered, becoming the initial sites for crystal growth 118,119 .…”