Thermal Interface Resistance of 2D Materials (Liu Yi et. al. in press, Scientific Reports)

The interface thermal conductance (G) at the MoS2/h-BN interface is measured by Raman spectroscopy, and the room-temperature value is (17.0±0.4) MW.m-2K-1. For comparison, G between graphene and h-BN is also measured, with a value of (52.2±2.1) MW.m-2K-1. Non-equilibrium Green’s function (NEGF) calculations, from which the phonon transmission spectrum can be obtained, show that the lower G at the MoS2/h-BN interface is due to the weaker cross-plane transmission of phonon modes compared to graphene/h-BN. This study demonstrates that the MoS2/h-BN interface limits cross-plane heat dissipation, and thereby could impact the design and applications of 2D devices while considering critical thermal management.

2D_interface_expt

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High Thermoelectric Powerfactor in 2D Crystals of Molybdenum Disulfide (K. Hippalgaonkar et. al. in

The quest for high-efficiency heat-to-electricity conversion has been one of the major driving forces towards renewable energy production for the future. Efficient thermoelectric devices require high voltage generation from a temperature gradient and a large electrical conductivity, while maintaining a low thermal conductivity. For a given thermal conductivity and temperature, the thermoelectric powerfactor is determined by the electronic structure of the material. Low dimensionality (1D and 2D) opens new routes to high powerfactor due to the unique density of states (DOS) of confined electrons and holes. 2D transition metal dichalcogenide (TMDC) semiconductors represent a new class of thermoelectric materials not only due to such confinement effects, but especially due to their large effective masses and valley degeneracies. Here we report a powerfactor of MoS2 as large as 8.5 mWm−1K−2 at room temperature, which is amongst the highest measured in traditional, gapped thermoelectric materials. To obtain these high powerfactors, we perform thermoelectric measurements on few-layer MoS2 in the metallic regime, which allows us to access the 2D DOS near the conduction band edge and exploit the effect of 2D confinement on electron scattering rates, which result in a large Seebeck coefficient. The demonstrated high, electronically modulated powerfactor in 2D TMDCs holds promise for efficient thermoelectric energy conversion.