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.