Migration-Enhanced Synthesis of 2D Copper Telluride Ultrathin Thermoelectrics

Ultrathin thermoelectric materials offer significant potential for high-performance cooling, on-chip thermal management, and wearable energy-harvesting applications. Copper telluride is a particularly attractive ultrathin thermoelectric owing to its combination of high electronic conductivity and intrinsically low thermal conductivity arising from liquid-like phonon behavior. Realizing these advantages, however, requires the synthesis of highly crystalline Cu₂Te films which has remained a challenge due to its complex phase diagram and the tendency to form a 3D morphology under high-temperature growth. Here, we report a migration-enhanced chemical vapor deposition strategy that overcomes these limitations and enables the synthesis of ultrathin Cu₂Te crystals with large grain size and controlled 2D morphology. Introducing a graphene barrier to separate thecopper and tellurium precursors was shown to produce a diffusion-rate-limited growth process that yields ultrathinCu₂Te crystals with large lateral size. The importance of the copper-graphene interaction was shown through ab initio modeling of the copper transport and experimental observation of ultralow growth temperatures and epitaxial ordering. The resulting 2D Cu₂Te exhibits superior thermoelectric performance that was exploited in wearable and self-powered sensors. This work establishes a general approach for tailoring surface-migration kinetics in 2D material growth and enables the development of high-efficiency ultrathin thermoelectric devices.