Thermal expansion coefficient of few-layer MoS₂ 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 MoS₂, suspended MoS₂ and supported MoS₂ 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 MoS₂ exhibited prominent differences from that for supported MoS₂, obviously demonstrating the effect due to the thermal expansion coefficient mismatch between MoS₂ and the substrate. The intrinsic thermal expansion coefficients of MoS₂ 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 MoS₂ layer during cooling. Our results demonstrate that Raman spectroscopy is a feasible tool for investigating the thermal properties of few-layer MoS₂ and will provide useful information for its further application in photoelectronic devices.