Condutividade térmica de filmes finos de MoS2

Abstract

This master's thesis presents a study on the thermal properties of monolayers and thin films of MoS2. Theoretical concepts of phonon-phonon interaction are introduced in a more objective way than usually found in the literature. The temperature dependence of Raman spectroscopy and photoluminescence spectroscopy are measured, and measurements of the dependence on the excitation laser power are also made. It is possible to observe the variation in the energy of the excitons and the frequency of the phonons with the temperature and these phenomena are analyzed with empirical equations, which provide calibration parameters to describe the local temperature of the sample by varying the power of the excitation laser. The experimental results of the variation of the frequencies of the modes〖 A〗_1g and E_2g^1 with the temperature are also studied in the concept of interaction of three and four phonons, demonstrating a large intensity in the decay of an optical phonon into two acoustic phonons than the decay of an optical phonon in three acoustic ones. The diffusion of heat in the sample in the region illuminated by the laser beam is analyzed; an equation is proposed that relates the thermal conductivity and the interfacial conductance to the experimental measurements of local crystal temperature. Through measurements with two objectives of different energy densities, the termal interfacial conductance between MoS2 and silicon dioxide is calculated; we find the value of 1,21 MW⁄(m^2 K). The value of the thermal conductivity found was dependent on the thickness of the sample, and we associate this dependence with the suppression of the ZA acoustic mode.