Ultralow in-plane thermal conductivity of Cu2-xSe nanobelts prepared by magnetron sputtering

As a thermoelectric material, Cu2-xSe has attracted much attention due to its low thermal conductivity and high figure of merit. The improvement of thermoelectric performance of Cu2-xSe is dominated by reducing thermal conductivity, such as doping and preparation of nanopores. However, there is little research on the thermal conductivity of Cu2-xSe nanostructures. This paper uses magnetron sputtering to prepare Cu2-xSe films on photoresist substrates, and characterizes the material properties by TEM, GIXRD, and XPS. Simultaneously, we successfully prepared Cu2-xSe nanobelts attached on MEMS suspended devices, combined with FIB and tungsten probe for cutting and transfer. The steady-state method was used for the first time to measure the thermal conductivity of Cu2-xSe nanobelts from low temperature to phase transition. Due to the strong interface and boundary scattering of the nanobelts, Cu2-xSe exhibits a thermal conductivity as low as 0.32 W/(m·K), which provides a possibility for improving thermoelectric performance near phase transition. Furthermore, at the phase transition, the temperature difference between the two suspended islands leads to mixed phase of Cu2-xSe nanobelts, which shows broad prospects for thermal regulation.