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

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 ReS2, both the morphology control technique and comprehension are lacking. Here, the lateral shape and vertical thickness engineering of 2D ReS2 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 ReS2 monolayers via a diffusion-limited mechanism, leading to highly oriented square, triangular, and strip-like domains synthesized on the fourfold symmetry SrTiO3 (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.

Automated summary

The lateral shape and vertical thickness engineering of 2D ReS2 was achieved by tailoring the growth temperature and substrate symmetry. The increase in temperature induced an isotropic-to-anisotropic transition of domain shapes and a decrease in domain thickness, enhancing the electrocatalytic performance. The substrate rotational symmetry determined the shape anisotropy of polycrystalline ReS2, leading to highly oriented domains synthesized on different symmetry substrates. Various stacking configurations in bilayers were observed, some of which showed potential in photovoltaics as type-II band alignment.