Raman spectroscopic study of the layer-dependent Davydov splitting and thermal conductivity of chemically vapor deposited two-dimensional MoSe₂

Atomically thin MoSe₂ is of interest from the perspective of estimating the layer-dependent material properties necessary for the translation of two-dimensional materials into devices. This work presents Raman spectroscopic protocols to determine a multitude of material parameters of two-dimensional MoSe₂ films, including the layer thickness as well as the layer-dependent thermal conductivity, interlayer interactions, and anharmonicity. The Davydov splitting (factor-group splitting) observed in an out-of-plane A_1g Raman mode, being layer-dependent in both the number and the peak positions, provides a method for estimating the number of layers. Furthermore, this work demonstrates the determination of the thermal conductivity (K) from the temperature-dependent Davydov split Raman modes of the multi-layers. The measurement of K by conventional methods is otherwise challenging for the micrometer sizes of the two-dimensional materials. The value of K thus determined increases significantly from 9 W m⁻¹ K⁻¹ for a four-layer thick MoSe₂ film to 52 W m⁻¹ K⁻¹ for a monolayer. The diminishing effect of anharmonicity observed in the monolayer as compared to multi-layer MoSe₂ supports the layer-dependent trend in the thermal conductivity. Overall, the findings are relevant for the applications of 2D MoSe₂ in low power electronic, optoelectronic, and thermoelectric devices.