[en] Inspired by the novel mechanism of reducing thermal conductivity by local phonon resonance instead of by inducing structural defects, we investigate the effect of side branching on the thermoelectric properties of nanoribbons, and prove that side branching is a highly efficient mechanism for enhancing the thermoelectricity of different kinds of nanoribbons. For both armchair and zigzag nanoribbons, the side branches result in not only significant blocking of phonon transport but also notable increase of the Seebeck coefficient. Consequently, the thermoelectric figure of merit of the armchair nanoribbon is boosted from 0.72 to as high as 1.93, and the originally non-thermoelectric metallic zigzag nanoribbon is turned into a thermoelectric material due to the appearance of the band gap induced by the side branches. These results mean that the mechanism of branching is not only very efficient, but also takes effect regardless of the original properties of the nanoribbons, and thus will hold great promise for its application in the thermoelectric field. (paper)

[en] New classes of two-dimensional (2D) materials beyond graphene are now attracting intense interest owing to their unique properties and functions. By combining first-principle calculation and the Boltzmann transport equation, we investigated the thermal transport properties of monolayer honeycomb structures of group-IV (C, Si, Ge, Sn) binary compounds. It is found that the thermal conductivity (κ) of these compounds span an enormously large range from 0.04 to 144.29 W m⁻¹ K⁻¹, demonstrating promising applications to nanoscale thermoelectrics and thermal management. The κ of low-buckled structures such as SiGe, SiSn and GeSn is lower than that of planar structures such as SiC, GeC and SnC, which can be ascribed to heavy atomic mass and broken in-plane reflection symmetry. Moreover, the κ of planar or low-buckled compounds with Sn atom is much lower than others, and the detailed origin for this phenomenon and contribution of different phonon modes to the κ are investigated. This work has fully studied the diversity of the thermal phenomenon and provides more options for application on thermal transport. (paper)

[en] Herein, thermoelectric properties of MoS₂/MoSe₂ lateral and van der Waals heterostructure are investigated by using density functional theory calculations and non-equilibrium Green’s function method. Compared with pure MoS₂, the thermoelectric performance of MoS₂/MoSe₂ lateral heterostructure is significantly improved due to the sharply decreased thermal conductance and slightly reduced power factor. Moreover, the thermoelectric performance can be further improved by constructing MoS₂/MoSe₂ van der Waals heterostructure. The room temperature ZT can reach 3.5, which is about 3 and 6 times greater than MoS₂/MoSe₂ lateral heterostructure and pure MoS₂, respectively. This is because the strongly local electron and phonon states result in an ultralow thermal conductance in MoS₂/MoSe₂ van der Waals heterostructure. Furthermore, we also find that the thermoelectric performance of MoS₂/MoSe₂ van der Waals heterostructure is insensitive to contact areas due to the competing influence of PF and total thermal conductance. The current study presents an effective strategy to improve the thermoelectric performance of 2D heterostructures, which can be extended to a variety of materials for different applications. (paper)