First-principles Study Of Thermal Properties Of Monolayer MoS₂

Monolayer MoS₂ as the novelty channel material of field-effect transistor has been attracted tremendous attention and research. Its electronic and optical properties have been widely studied, but the thermal properties of monolayer MoS₂ are not well understood yet. Investigating the vibrational properties and thermal properties of monolayer MoS₂ is beneficial to the stability and efficiency of monolayer MoS₂ device under different temperature. Therefore, the paper “First principle calculation of the lattice vibration and thermal properties of monolayer MoS₂” is of great theoretical and practical significance. The dissertation is devoted to study of lattice vibrational properties and thermal properties of monolayer MoS₂ from CASTEP soft and first principles with density functional theory and density functional perturbation theory.Firstly, the lattice constants and electronic structures of monolayer MoS₂ with strain were calculated in the case of considering the calculation accuracy and computational efficiency. Results show that the present calculated results are close to other theoretical and experimental data, suggesting that the present research method is credible.Secondly, this paper comparatively investigated the lattice vibrational properties of monolayer MoS₂, bulk MoS₂ and monolayer graphene. Analysis shows that the phonon dispersion of monolayer MoS₂ and bulk MoS₂ exhibits the same band gap, but the number of phonon dispersion of monolayer MoS₂ and bulk MoS₂ is different. In addition, contrast to monolayer MoS₂, the grüneisen parameters of monolayer MoS₂ are positive. Moreover, the grüneisen parameters of acoustic phonon modes of monolayer MoS₂ show asymmetric character in the first brillouin zone, whereas the grüneisen parameters of optical phonon modes of monolayer MoS₂ show symmetric character in the first brillouin zone. Besides, the frequencies of optical phonon modes of monolayer MoS₂ linear with biaxial strain. Notably, A1 mode shows the lowest change rate.Finally, this paper investigated the thermal properties of monolayer MoS₂.Results show the Debye temperature, isochoric specific heat capacity and thermal expansion coefficient of monolayer MoS₂ increase with the increasing temperature,and then approach to fix data of 603 K, 17.6 Cal/cell.K and 1.5×10^-5 K^-1, respectively.Moreover, the thermal expansion coefficient of monolayer is positive, contrasting to that of monolayer MoS₂. The results of relaxation time and mean free path show that LA mode is the main thermal carriers of monolayer MoS₂, the effect of optical phononmodes of monolayer MoS₂ can be neglected. At room temperature, the calculated thermal conductivity of monolayer MoS₂ of 29.2 Wm^-1K^-1is higher than other theoretical data that was obtained by molecular dynamics, but it is in good agreement with the experimental value of 34.5 ± 4 Wm^-1K^-1.