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Thermoelectric Powerfactor and Interface Thermal Resistance in 2D MoS2

Speaker: 
Kedar Hippalgaonkar (IMRE, A*STAR)
Date: 
Wed, 30/09/2015 - 11:00am to 12:00pm
Location: 
Physics Conference Room (S11-02-07)
Event Type: 
Seminars

Thermoelectric devices require large Seebeck and simultaneously large electrical conductivity, while maintaining a low thermal conductivity. Significant progress in the thermoelectric performance of materials has been made by exploring ultralow thermal conductivity at high temperature, reducing thermal conductivity by nanostructuring, resonant doping and energy-dependent scattering. For a given thermal conductivity and temperature, 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. Emerging 2D transition metal dichalcogenide (TMDC) semiconductors represent a new class of thermoelectric materials not only because of their discretized density of states, but also due to their large effective masses and high carrier mobilities, different from gapless semi-metallic graphene. We have observed 2D crystals of MoS2 with a powerfactor as large as 8.5 mWm−1K−2 at room temperature, which is the highest among all thermoelectric materials. Moreover, measurement of thermoelectric properties of monolayer MoS2 in the metallic regime allows us to determine the confined 2D DOS near the conduction band edge for the first time, which cannot be measured by electrical conductivity alone. Further, we measure the interlayer thermal resistance in MoS2/hBN heterostructures, which can be used to tune the in-plane thermal conductivity allowing for an additional tunable knob for future thermoelectrics. The demonstrated high electronically modulated powerfactor in 2D TMDCs with tunable thermal conductivity holds promise for efficient thermoelectric energy conversion.

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