Two-dimensional materials exhibit great potential for high-performance electronics applications and the knowledge of their thermal properties is extremely necessary, since they are closely related to efficient heat dissipation and electron-phonon interactions. In this study we report the temperature-dependence of the out-of-plane A1g Raman mode of suspended and supported CVD-grown single-crystalline tungsten diselenide (WSe2) monolayer. The A1g phonon wavenumber is linearly red-shifted for temperature ranging from 98 to 513 K, with first-order temperature coefficients β of -0.0044 and -0.0064 cm−1/K for suspended and supported monolayer WSe2, respectively. The higher β module value for supported sample is attributed to the increase of the phonon anharmonicity due to the phonon scattering with the surface roughness of the substrate. Our analysis of the temperature-dependent phonon dynamics reveal the influence of the substrate on thermal properties of monolayer WSe2 and provide fundamental information for developing of atomically-thin 2D materials devices.

Phonons play a fundamental role in the electronic and thermal transport of 2D materials which is crucial for device applications. In this work, we investigate the temperature-dependence of A and A Raman modes of suspended and supported mechanically exfoliated few-layer gallium sulfide (GaS), accessing their relevant thermodynamic Grüneisen parameters and anharmonicity. The Raman frequencies of these two phonons soften with increasing temperature with different temperature coefficients. The first-order temperature coefficients θ of A mode is ∼ −0.016 cm−1/K, independent of the number of layers and the support. In contrast, the θ of A mode is smaller for two-layer GaS and constant for thicker samples (∼ −0.006 2 cm−1 K−1). Furthermore, for two-layer GaS, the θ value is ∼ −0.004 4 cm−1 K−1 for the supported sample, while it is even smaller for the suspended one (∼ −0.002 9 cm−1 K−1). The higher θ value for supported and thicker samples was attributed to the increase in phonon anharmonicity induced by the substrate surface roughness and Umklapp phonon scattering. Our results shed new light on the influence of the substrate and number of layers on the thermal properties of few-layer GaS, which are fundamental for developing atomically-thin GaS electronic devices.

Understanding the thermodynamic properties of materials is a fundamental issue in physics, and its knowledge is crucial for targeting a specific material for possible applications. In this work, we report a temperature‐ and pressure‐dependent Raman study of bulk GaSe0.5Te0.5 alloy, besides their relevant thermodynamic parameters. Our results show a nonlinear redshift for the A1g and E2g vibrational modes as the temperature increases in the temperature range from 10 to 748 K. Such behavior is well described by considering both thermal expansion and phonon–phonon coupling contributions. By combining density functional theory (DFT) calculations and Raman spectroscopy experiments, the anharmonic constants relative to the three‐ and four‐phonon decay processes, mode‐Grüneisen parameters, Debye temperature, thermal expansion coefficient, and bulk modulus were estimated for GaSe0.5Te0.5 alloy. Furthermore, the high‐pressure measurements and DFT calculations, performed in the pressure range from 0 to 26.4 GPa, show a quadratic trend for the ωA1g and ωE2g modes as a function of pressure, with the A1g modes being more compressible than E2g one, that is, ∂ωA1g∂P>∂ωE2g∂P. No structural phase transition is observed until the maximum pressure reached in the experiment. This study took a step forward in the understanding of mechanical and thermal properties related to GaSe0.5Te0.5 alloy, whose determined parameters are important for designing new applications.