Dual-wavelength flash Raman mapping method for measuring thermal diffusivity of the suspended nanowire

In this paper, we present a dual-wavelength flash Raman (DFR) mapping method for measuring the thermal diffusivity of a suspended nanowire. A heating pulse is used to heat the nanowire sample, and a probing pulse of different wavelength is used to measure the increase in temperature. The laser absorption coefficient can be eliminated by normalization, and the thermal diffusivity of the sample can be extracted from the normalized temperature increase. An infinite heat conduction model is used in this method to avoid the influence of boundary thermal resistance. By changing the position of the probing laser center, the measurement sensitivity of thermal diffusivity can be further improved. The position of maximum sensitivity is influenced by the thermal diffusivity of the nanowire, width of the heating pulse, radius of the heating laser spot, and characteristic length of the sample. To comprehensively analyze the influences of the various parameters, obtain the best measurement conditions, and attain maximum sensitivity, we propose a dimensionless physical model to analyze the heat conduction of the suspended nanowire. Based on the analysis of the best dimensionless parameters, the corresponding appropriate measurement conditions can be determined. Sensitivity analysis shows that when the radius of the heating laser spot is 1% of the length of the nanowire, the sensitivity of the DFR mapping method can be more than four times that of the concentric DFR method for measuring the thermal diffusivity of the nanowire.