Lateral and Vertical Morphology Engineering of Low‐Symmetry, Weakly‐Coupled 2D ReS₂

Abstract

Morphology significantly affects material's electronic, catalytic, and magnetic properties, especially for 2D crystals. Abundant achievements have been made in the morphology engineering of high-symmetry 2D materials, but for the emerging low-symmetry ones, such as ReS 2 , both the morphology control technique and comprehension are lacking. Here, the lateral shape and vertical thickness engineering of 2D ReS 2 by tailoring the growth temperature and the substrate symmetry using chemical vapor deposition, is reported. The temperature increase induces an isotropic-to-anisotropic transition of domain shapes, as well as a monotonic decrease of the domain thickness, which promotes the electrocatalytic performance. The substrate rotational symmetry determines the shape anisotropy of polycrystalline ReS 2 monolayers via a diffusion-limited mechanism, leading to highly oriented square, triangular, and strip-like domains synthesized on the fourfold symmetry SrTiO 3 (001), threefold symmetry c-sapphire, and twofold symmetry a-sapphire substrates, respectively. Various stacking configurations in bilayers are unclosed at the atomic scale. Some are predicted to adopt a type-II band alignment with great potential in photovoltaics. The results give insights into the morphological engineering of a unique class of 2D material with low in-plane lattice symmetry and weak interlayer coupling, which are crucial for their high-quality synthesis and industrial applications.

Large-area single-crystal TMD growth modulated by sapphire substrates

“…While at a higher growth temperature, TMDs can diffuse and rotate on the substrate to achieve a good orientation alignment, which is dependent on the substrate lattice. 22,60 However, too high growth temperature will erase the difference in energy in each direction and lead to disordered directions. Therefore, for better orientation alignment of lattice-guided vdW epitaxial TMDs, first, it is necessary to form smaller TMD crystalline species, because smaller crystalline species are easier to rotate and translate with a lower energy, which can be achieved by adjusting the precursor concentration ratio.…”

“…The diffusion pathways are represented in insets. 60 Copyright 2023, Wiley-VCH. (f) Angle dependence of adsorption energy of the WTe 2 seed on the a-plane sapphire surface.…”

“…(d) SEM images showing the shape difference of monolayer ReS 2 grown on the c-sapphire (top) and a-sapphire (bottom). 60 Copyright 2023, Wiley-VCH.…”

“…Since the supply of Re atoms determines the growth of ReS 2 due to the excess of S during synthesis, the growth rate of ReS 2 is faster along the [101̄0] direction. 60 Zhou et al synthesized WTe 2 nanoribbons with a large aspect ratio along the [11̄00] crystallographic direction on the a -plane sapphire substrates by a water-assisted atmospheric pressure CVD method. 80 They calculated the adsorption energy of WTe 2 at different angles on the a -plane sapphire and showed that the 0° orientation is the most stable conformation, which is consistent with the growth results (Fig.…”

“…(e) DFT-calculated diffusion energy barriers along different paths of the a-sapphire substrate. The diffusion pathways are represented in insets 60. Copyright 2023, Wiley-VCH.…”