Thermal expansion coefficient of few-layer MoS studied by temperature-dependent Raman spectroscopy.

The thermal expansion coefficient is an important thermal parameter that influences the performance of nanodevices based on two-dimensional materials. To obtain the thermal expansion coefficient of few-layer MoS, suspended MoS and supported MoS were systematically investigated using Raman spectroscopy in the temperature range from 77 to 557 K. The temperature-dependent evolution of the Raman frequency shift for suspended MoS exhibited prominent differences from that for supported MoS, obviously demonstrating the effect due to the thermal expansion coefficient mismatch between MoS and the substrate. The intrinsic thermal expansion coefficients of MoS with different numbers of layers were calculated. Interestingly, negative thermal expansion coefficients were obtained below 175 K, which was attributed to the bending vibrations in the MoS layer during cooling. Our results demonstrate that Raman spectroscopy is a feasible tool for investigating the thermal properties of few-layer MoS and will provide useful information for its further application in photoelectronic devices.