Review on Techniques for Thermal Characterization of Graphene and Related 2D Materials

Abstract

The discovery of graphene and its analog, such as MoS_2, has boosted research. The thermal transport in 2D materials gains much of the interest, especially when graphene has high thermal conductivity. However, the thermal properties of 2D materials obtained from experiments have large discrepancies. For example, the thermal conductivity of single layer suspended graphene obtained by experiments spans over a large range: 1100-5000 W/m·K. Apart from the different graphene quality in experiments, the thermal characterization methods play an important role in the observed large deviation of experimental data. Here we provide a critical review of the widely used thermal characterization techniques: the optothermal Raman technique and the micro-bridge method. The critical issues in the two methods are carefully revised and discussed in great depth. Furthermore, improvements in Raman-based techniques to investigate the energy transport in 2D materials are discussed.

Keywords: 2D materials; optothermal Raman technique; thermal transport.

Figure 1

Schematic of the optothermal Raman technique. Reprinted with permission from ref. [3]. Copyright 2008 American Chemical Society.

Figure 2

(a) Hot carrier diffusion in MoS₂/c-Si under laser illumination (not to scale): E_v and E_c are the valence band and conduction band, respectively, E_g is the bandgap of MoS₂, E is the photon energy of the incident laser; (b) schematic of the experiment setup (not to scale): ρc_p is the volumetric heat capacity of the sample; (c,d) continuous wave (CW) laser is used to heat the sample under 20× and 100× objective lens to achieve different hot aera size: R and D are the interface thermal resistance and hot carrier diffusion coefficient, respectively; (e) picosecond pulsed laser is used under 50× objective lens to achieve zero thermal transport state. Reprinted with permission from ref. [27]. Copyright 2017 American Chemical Society.

Figure 3

(A,B) SEM images of micro-bridge method setup; (C) circuit of the thermal resistance. Reprinted with permission from ref. [6]. Copyright 2010 American Association for the Advancement of Science.

Figure 4

Experiment setup of the TET technique. Reprinted from ref. [12].