Simultaneous measurement of anisotropic thermal conductivity and thermal boundary conductance of 2-dimensional materials

Abstract

The rapidly increasing number of 2-dimensional (2D) materials that have been isolated or synthesized provides an enormous opportunity to realize new device functionalities. Whereas their optical and electrical characterization have been more readily reported, quantitative thermal characterization is more challenging due to the difficulties with localizing heat flow. Optical pump-probe techniques that are well-established for the study of bulk materials or thinfilms have limited sensitivity to in-plane heat transport, and the characterization of the thermal anisotropy that is common in 2D materials is therefore challenging. Here we present a new approach to quantify the thermal properties based on the magneto-optical Kerr effect that yields quantitative insight into cross-plane and in-plane heat transport. The use of a very thin magnetic material as heater/thermometer increases in-plane thermal gradients without complicating the data analysis in spite of the layer being optically semi-transparent. The approach has the added benefit that it does not require the sample to be suspended, providing insight of thermal transport in supported, device-like environments. We apply this approach to measure the thermal properties of a range of 2D materials which are of interest for device applications, including single layer graphene, few-layer h-BN, single and few layer MoS2, and bulk MoSe2 crystal. The measured thermal properties will have important implications for thermal management in device applications.

Reduced thermal conductivity of supported and encased monolayer and bilayer MoS2

“…Again, we find the suppression of in-plane atomic motion drives the overall reduction in thermal conductivity. Experimentally, a larger thermal conductivity in supported 2L MoS 2 than 1L MoS 2 has also been observed[57].…”

Substrate-dependence of monolayer MoS2 thermal conductivity and thermal boundary conductance

“…When MoS 2 is on c-AlN or c-Al 2 O 3 , its TC is in the range of ~66 to 68 Wm -1 K -1 , whereas MoS 2 has a TC of only ~42 Wm -1 K -1 when supported by c-SiO 2 (quartz). Of these structures, only MoS 2 on a-SiO 2 has been studied experimentally, with a reported MoS 2 TC of 63 ± 22 Wm -1 K -1 [55], although a sputtered Ni capping layer is known to damage monolayer MoS 2 [45], likely affecting their TC measurement.…”

“…Since h-BN is a stiffer, high-TC material [55,67,68], it has, on average, 1.5 to 2 times fewer phonon modes than MoS 2 over the acoustic mode frequencies of MoS 2 (see Fig. S9), with this difference being as high as 7.7× between 0 THz to 2 THz.…”

Methods for Measuring Thermal Conductivity of Two-Dimensional Materials: A Review

“…Additionally, FDTR, which is an improved TDTR method, is used in measuring the thermal conductivity of 2D materials. Rahman et al [46] implemented frequency domain magnetooptical Kerr effect (FD-MOKE) to measure the thermal conductivity of various 2D materials, such as graphene, monolayer MoS 2 , and four-layer h-BN.…”

“…Yet, due to the ignorance of surface defects, the accuracy of these methods is limited. Experimental methods, such as the suspended micro-bridge method [27][28][29][30][31][32], 3ω method [33][34][35][36], timedomain thermoreflectance method [37][38][39][40][41][42][43][44][45][46], and Raman method [47][48][49][50][51][52][53], have been developed to study the thermal conductivity of 2D materials. Bao et al [54] introduced heat transfer research methods in micro-nano structures from the perspective of theoretical calculation.…”