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.
Alloying is widely applied to tailor properties of 2D materials. Herein, a space‐confined chemical vapor deposition (CVD) strategy to homogeneously grow 100 μm‐sized monolayer 1T’‐MoTe2 in batches is developed. Aberration‐corrected annular dark‐field scanning transmission electron microscopy combined with density functional theory calculations is applied to investigate the atomic structural alteration of 1T’‐MoTe2 alloyed with sulfur. 1T’‐to‐2H phase transition is observed, triggered by both thermodynamic (stability improvement) and kinetic (phase transition barrier reduction) reasons. The alloying degrees of MoS2xTe2(1−x) grown at different temperatures display homophilic and random configurations, respectively, providing a feasible approach to tailor the atomic mixture of the alloying elements. The intralayer reconstruction and the interlayer displacement take place as defect concentration increases at elevated alloying temperatures. In contrast, 1T’‐MoTe2 displays high susceptibility in the presence of oxygen. An encapsulation method is developed using CVD‐grown monolayer MoS2, extending the lifetime of monolayer tellurides from several minutes to at least 24 h. These results gain fundamental insights into the structural change in both the beneficial (sulfurization) and detrimental (oxidation) alloying processes of atomically thin 1T’‐MoTe2 and provide a new degree of freedom for the controllable growth of 2D alloys (i.e., tailoring the alloying degree).
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