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| 1 | Dual-Wavelength Laser Flash Raman Spectroscopy Method for In-Situ Measurements of the Thermal Diffusivity: Principle and Experimental Verification显示文摘This paper presents an in-situ, non-contact, non-destructive 'dual-wavelength laser flash Raman spectroscopy method' for measuring the thermal diffusivity. In this method, a heating pulse is used to heat the sample and another pulsed laser with a different wavelength and negligible heating effect is used as a probe to measure the sample temperature changes during the heating and cooling periods from the Raman peak shifts. The sample temperature rise and fall curves are measured by changing the delay between the heating pulse and the probing pulse with the thermal diffusivity then characterized by fitting the temperature curves. The time delay between the heating and probing pulses can be precisely controlled with a minimum step of 100 ps. Hence, the temperature variation can be scanned with an ultra-high temporal resolution of up to 100 ps, which significantly improves the measurement accuracy of transient thermal parameters. The measurement accuracy of this method has been verified using a bulk material model and experiments. The measured thermal diffusivity of a silicon sample has been obtained to be 8.8×10^(-5 )m^2/s with a 3% difference between the measured value and the average result for bulk silicon in the literature which verifies the reliability and accuracy of this method. | FAN Aoran HU Yudong MA Weigang WANG Haidong ZHANG Xing | 2019 | Journal of Thermal Science2019，28，2： | 4 |
| 2 | Dual-wavelength flash Raman mapping method for measuring thermal diffusivity of the suspended nanowire显示文摘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. | HU YuDong FAN AoRan WANG HaiDong MA WeiGang ZHANG Xing | 2020 | Science China(Technological Sciences)2020，63，5： | 2 |
| 3 | Reduction in thermal conductivity of monolayer WS_(2) caused by substrate effect显示文摘Understanding the substrate and temperature effect on thermal transport properties of transition metal dichalcogenides(TMDs)monolayers are crucial for their future applications.Herein,a dual-wavelength flash Raman(DF-Raman)method is used to measure the thermal conductivity of monolayer WS_(2) at a temperature range of 200–400 K.High measurement accuracy can be guaranteed in this method since the influence of both the laser absorption coefficient and temperature-Raman coefficient can be eliminated through normalization.The room-temperature thermal conductivity of suspended and supported WS_(2) are 28.5±2.1(30.3±2.0)and 15.4±1.9(16.9±2.1)W/(m·K),respectively,with a~50%reduction due to substrate effect.Molecular dynamics(MD)simulations reveal that the suppression of acoustic phonons is mainly responsible for the striking reduction.The behaviors of optical phonons are also unambiguously investigated using Raman spectroscopy,and the in-plane optical mode,E(Γ),is surprisingly found to be slightly enhanced while out-of-plane mode,A1g(Γ),is suppressed due to substrate interaction,mutually verified with MD results.Our study provides a solid understanding of the phonon transport behavior of WS_(2) with substrate interaction,which provides guidance for TMDs-based nanodevices. | Yufeng Zhang Qian Lv Aoran Fan Lingxiao Yu Haidong Wang Weigang Ma Ruitao Lv Xing Zhang | 2022 | Nano Research2022，15，10： | 1 |
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