(Invited, Digital Presentation) Ultra-Low Thermal Conductance across Hetero-Structured Four-Layered Van Der Waals Materials

Abstract

Tuning the thermal properties of materials and exploring their heat transport mechanisms are of critical significance for optimizing the performance of current electronic and thermoelectric devices. Regarding flexible thermoelectric, recently, gigantic power factor is achieved in carbon nanotube fibers with tuned Fermi energy level [1]. Thus, control of heat transport across van der Waals (vdW) interfaces, which are the origins of flexibility, is very important for improvement of thermoelectric conversion efficiency. Considering that thermal transport is mainly affected by phonon-boundary scattering, development a route to tune such scattering at vdW interfaces is important. Ultrathin two-dimensional (2D) materials have been widely studied in electronic and photonic fields due to the distinctly unique geometrical and electronic structures of such materials. Regarding thermal transport properties, they have a lot of degrees of freedom in their integration, and the layered vdW integrated structure of these materials, in which building blocks are physically assembled together through weak vdW interactions, provides a strategy to reduce thermal conductance. The rich interfacial lattice mismatch in layered vdW structures is promising for enhancing phonon-boundary scattering at interfaces. For instance, Vaziri et al. studied the thermal boundary resistance of various heterointerfaces via the stacking of exfoliated several-micron-sized graphene, MoS2, and WSe2 monolayers using Raman thermometry, suggesting great potential for controlling heat flow by using the interfaces of vdW heterostructures [2]. However, there has been no systematic study on how homo- and hetero-interfaces with or without lattice matches influence heat flow. Therefore, a systematic study on the thermal conductance (G) of vdW structures with various comparable interfaces is urgently required to understand how homo- and heterointerfaces and the coupling effect influence thermal transport. Here we demonstrate the thermal conductance across four layered (4L) homo- and hetero-structured MoS2 and MoSe2 using time-domain thermo-reflectance method. Compared with the thermal conductance of homo-structured sample, the thermal conductance across hetero-structured 4L sample was significantly reduced, indicating that hetero-interface is an efficient way to reduce thermal conductance [3]. In addition, we have combined electrochemical gating method and TDTR measurements, and employed our technique on the 4L sample and investigated how the intercalation can influence the thermal conductance on the 4L sample. In this presentation, I would like to discuss our recent results.