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Advanced science: new progress in phonon heat transfer: the first temperature measurement of optical and acoustic phonons

wallpapers News 2020-12-20
With the development of miniaturization high power of electronic devices

the problem of heat transfer enhancement in micro nano scale is becoming more more important. However due to the decrease of scale the measurement of thermophysical properties in nano scale is particularly complex. For example the phonon heat transfer process of materials heated by laser includes complex physical processes such as photons electrons phonon coupling. In some applications optical phonon acoustic phonon will have non-equilibrium effect then there is a certain temperature difference. The research of these complex physical problems has been limited by measurement methods difficult to break through which has become the focus difficulty of micro nano scale heat transfer research.

recently Professor Xinwei Wang of Iowa State University Associate Professor Wang Ridong of Tianjin University Professor Zhang Xing of Tsinghua University Professor Yue Yanan of Wuhan University jointly developed energy transport state resolved Raman (energy transport state resolved Raman) technology on the basis of traditional time domain Raman spectroscopy (TD Raman) The temperature measurement of optical phonon acoustic phonon in the material is realized for the first time the energy coupling factor between the two phonons is further measured. The article is entitled "distinctive optical acoustic phonon temperatures their energy coupling factor under photon exception in nm 2D materials" published in advanced science( DOI:10.1002/advs.202000097 )In the magazine. The first author of the thesis is Professor Wang a doctoral student of the research group: Wang Ridong who returned to work after graduation. Now he is an associate professor of Tianjin University. The collaborators of the thesis include assistant professor Xie Yangsu of Shenzhen University others.

[key points analysis]

have a wide range of applications in micro nano devices due to the unique thermal conductivity of new two-dimensional materials. Molybdenum disulfide (MoS2) molybdenum selenide (MoSe2) graphene were selected for verification. When the laser is heated at a certain wavelength the energy of the laser photons is absorbed by the electrons in the material the electrons transition from the low energy level to the high energy level. In the process of electron returning to low energy level energy is transferred to optical phonon. After the energy is transferred from optical phonon to acoustic phonon it diffuses to the outside of the heating region in the way of heat conduction. The temperature changes measured by photothermal Raman spectroscopy include two parts: one is the temperature difference between optical phonons acoustic phonons (inversely proportional to the square of the heating zone size) the other is the temperature of acoustic phonons which is closely related to the thermal conductivity of materials. Based on the same wavelength of nano pulse laser continuous laser the project team designed the experimental device to carry out transient steady-state heating on the material. With the expansion of the heating region the temperature difference between the optical phonon the acoustic phonon decreases gradually the thermal conductivity measured by ET Raman method will approach the real value. The energy coupling characteristics of optical phonon acoustic phonon are studied by differential analysis. The energy coupling coefficients (0.549 × 1016 w · M-3 · k-1) of optical phonons acoustic phonons for P- S-waves in graphene are in good agreement with the theoretical prediction (0.41 × 1016 w · M-3 · k-1). At the same time the energy coupling coefficients of optical phonon acoustic phonon in MoS2 MoSe2 heated by continuous laser nanosecond pulse laser are obtained the correlation between these coefficients heating state is also obtained.

the temperature evolution of optical phonon acoustic phonon in the material is distinguished obtained for the first time by ET Raman method the energy coupling factors of the two kinds of phonons are obtained. At the same time the intrinsic thermal conductivity of the material without the influence of optical phonon acoustic phonon temperature difference is measured accurately. This research is the further development promotion of Raman thermal measurement technology. It lays a foundation for further study of the energy transfer mechanism in two-dimensional nanomaterials the realization of high-precision physical understing control of the thermal conductivity of two-dimensional nanomaterials. The research was supported by the National Science Foundation of the United States the key project of strategic international scientific technological innovation cooperation of the Ministry of science technology of China the National Natural Science Foundation of China the scientific research start-up project of Shenzhen high-level talents. The corresponding authors are professor Xinwei Wang of Iowa State University Professor Zhang Xing of Tsinghua University Professor Yue Yanan of Wuhan University. In the process of research Professor Ruan Xiulin of Purdue University provided valuable suggestions for the research.

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