Suspended 2D anisotropic materials thermal diffusivity measurements using dual-wavelength flash Raman mapping method

Abstract This paper presents a dual-wavelength flash Raman (DFR) mapping method for characterizing the thermal diffusivity of suspended 2D anisotropic materials. Using one heating laser beam and another probing laser beam with different wavelength, the crystal orientation can be determined by steady-state temperature map. Then modulating the two continuous wave laser beams into periodic pulsed laser beams, the transient heating and cooling curves at various positions along principle axes can be measured by varying the delay time between two pulsed laser beams and changing the position of the probing laser spot. The temporal resolution can reach 100 ps while the spatial resolution can reach 50 nm which are significantly better measurement accuracies. Phase processing method and optimal measurement positions of various thermal diffusivities were presented to further reduce the uncertainty. The effect of the laser absorption coefficient can be eliminated and no other physical parameters are required unlike in existing methods. Feasibility analysis verified that this method is applicable to ultrathin 2D anisotropic materials and even for monolayer materials. When the probing spots are selected around the optimal positions, the measurement uncertainty can be within ±5%.