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Direct Characterization of Thermal Nonequilibrium between Optical and Acoustic Phonons in Graphene Paper under Photon Excitation
Advanced Science ( IF 14.3 ) Pub Date : 2021-05-01 , DOI: 10.1002/advs.202004712 Hamidreza Zobeiri 1 , Nicholas Hunter 1 , Ridong Wang 2 , Tianyu Wang 3 , Xinwei Wang 1
Advanced Science ( IF 14.3 ) Pub Date : 2021-05-01 , DOI: 10.1002/advs.202004712 Hamidreza Zobeiri 1 , Nicholas Hunter 1 , Ridong Wang 2 , Tianyu Wang 3 , Xinwei Wang 1
Affiliation
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Raman spectroscopy has been widely used to measure thermophysical properties of 2D materials. The local intense photon heating induces strong thermal nonequilibrium between optical and acoustic phonons. Both first principle calculations and recent indirect Raman measurements prove this phenomenon. To date, no direct measurement of the thermal nonequilibrium between optical and acoustic phonons has been reported. Here, this physical phenomenon is directly characterized for the first time through a novel approach combining both electrothermal and optothermal techniques. While the optical phonon temperature is determined from Raman wavenumber, the acoustic phonon temperature is precisely determined using high-precision thermal conductivity and laser power absorption that are measured with negligible nonequilibrium among energy carriers. For graphene paper, the energy coupling factor between in-plane optical and overall acoustic phonons is found at (1.59–3.10) × 1015 W m−3 K−1, agreeing well with the quantum mechanical modeling result of 4.1 × 1015 W m−3 K−1. Under ≈1 µm diameter laser heating, the optical phonon temperature rise is over 80% higher than that of the acoustic phonons. This observation points out the importance of subtracting optical–acoustic phonon thermal nonequilibrium in Raman-based thermal characterization.
中文翻译：
光子激发下石墨烯纸中光学和声学声子之间热非平衡的直接表征
拉曼光谱已广泛用于测量二维材料的热物理性质。局部强烈的光子加热导致光学和声学声子之间强烈的热不平衡。第一原理计算和最近的间接拉曼测量都证明了这一现象。迄今为止，还没有直接测量光学和声学声子之间的热不平衡的报道。在这里，首次通过结合电热和光热技术的新颖方法直接表征这种物理现象。光学声子温度是根据拉曼波数确定的，而声学声子温度是利用高精度热导率和激光功率吸收来精确确定的，这些热导率和激光功率吸收是在能量载体之间可忽略不平衡的情况下测量的。对于石墨烯纸，面内光学声子和整体声学声子之间的能量耦合因子为 (1.59–3.10) × 10 15 W m −3 K −1 ，与量子力学建模结果 4.1 × 10 15 W 非常吻合m -3 K -1 。在直径约1 µm的激光加热下，光学声子温升比声声子温升高80%以上。这一观察结果指出了在基于拉曼的热表征中减去光声声子热非平衡的重要性。
更新日期：2021-06-24
中文翻译：
光子激发下石墨烯纸中光学和声学声子之间热非平衡的直接表征
拉曼光谱已广泛用于测量二维材料的热物理性质。局部强烈的光子加热导致光学和声学声子之间强烈的热不平衡。第一原理计算和最近的间接拉曼测量都证明了这一现象。迄今为止，还没有直接测量光学和声学声子之间的热不平衡的报道。在这里，首次通过结合电热和光热技术的新颖方法直接表征这种物理现象。光学声子温度是根据拉曼波数确定的，而声学声子温度是利用高精度热导率和激光功率吸收来精确确定的，这些热导率和激光功率吸收是在能量载体之间可忽略不平衡的情况下测量的。对于石墨烯纸，面内光学声子和整体声学声子之间的能量耦合因子为 (1.59–3.10) × 10 15 W m −3 K −1 ，与量子力学建模结果 4.1 × 10 15 W 非常吻合m -3 K -1 。在直径约1 µm的激光加热下，光学声子温升比声声子温升高80%以上。这一观察结果指出了在基于拉曼的热表征中减去光声声子热非平衡的重要性。
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