Shape control of few-layer 1T′-WTe2 flakes via space-restricted chemical vapor deposition

Transition metal dichalcogenides, particularly WTe2, have attracted significant attention due to their unique electronic properties, such as the quantum spin Hall effect, which makes them promising for applications in topological electronics and quantum devices. However, achieving precise shape control during the growth of the low-symmetry 1T′ phase of WTe2 remains a significant challenge. In this work, we investigate the physical mechanism driving shape evolution in WTe2 during chemical vapor deposition growth. By utilizing a double-temperature zone to create a W concentration gradient, we observe a systematic evolution of shapes from irregular flakes to ribbons, triangles, hexagons, and snowflakes. This shape evolution is driven by temperature- and concentration-induced growth dynamics, where local concentration gradients and anisotropic growth behavior play a key role in the formation of distinct morphologies. Our experimental observations and density functional theory calculations show that increasing the Te:W ratio enhances the material's thermodynamic stability, with hexagonal flakes exhibiting greater stability than triangular ones. Our findings provide a deeper understanding of shape evolution in low-symmetry 2D materials with controlled morphology, enabling future applications in quantum devices.