Abstract
Two-dimensional (2D) materials and their corresponding van der Waals heterostructures have drawn tremendous interest due to their extraordinary electrical and optoelectronic properties. Insulating 2D hexagonal boron nitride (h-BN) with an atomically smooth surface has been widely used as a passivation layer to improve carrier transport for other 2D materials, especially for Transition Metal Dichalcogenides (TMDCs). However, heat flow at the interface between TMDCs and h-BN, which will play an important role in thermal management of various electronic and optoelectronic devices, is not yet understood. In this paper, for the first time, 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.
Highlights
Two-dimensional (2D) materials with atomic-scale thickness have drawn tremendous interest since the successful exfoliation of graphene[1]
Compared to the numerous studies[13,14,22,23,24,25,26,27] on the electronic and optoelectronic properties of 2D materials and the van der Waals heterostructures mentioned above, there is a paucity of research on their thermal properties in spite of their relevance to heat management, which is critical for maintaining optimal functionality of these devices[14,28,29,30]
Transition Metal Dichalcogenides (TMDCs) flakes situated on another 2D material such as hexagonal boron nitride (h-BN) being the substrate, i.e., two 2D-material interface/heterostructure, is far less investigated, which is in great demand in the emerging heterostructures and optoelectronic devices involving stacked 2D materials
Summary
Two-dimensional (2D) materials with atomic-scale thickness have drawn tremendous interest since the successful exfoliation of graphene[1]. By Joule/optical heating graphene and measuring temperatures via Raman spectroscopy, Yue et al measured G between epitaxial graphene and 4H-SiC to be 0.0189 MW/m2K, which is five orders of magnitude lower than that expected from their molecular dynamics (MD) simulations[50] They attributed the much lower measured G to the significantly enhanced phonon scattering effect from the structural change at the interface caused by 1) the high stress induced by covalent bonds between graphene/SiC and 2) the thermal expansion mismatch caused by separation at the interface. For MoS2, Taube et al measured the total G across MoS2/Si including a thin SiO2 layer to be 1.94 MW/m2K41, and Zhang et al measured G to be 0.44 MW/m2K for MoS2/Au40 These results were obtained by solving the heat diffusion equation based on the temperatures obtained from Raman spectroscopy, and the thermal conductivity was obtained simultaneously. This method requires the precise determination of absorbed laser power, to which interface thermal conductance and the thermal conductivity are sensitive
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