Recently, Nature (IF 42.7) published a paper online entitled with “Single-defect phonons imaged by electron microscopy”. The detection and analysis of a single plane defect has been realized by the combination of experiment and theoretical calculation. The detailed phonon states of defect near the brillouin zone are achieved by moving the location of momentum space. The thermal conductivity of materials significantly affects the heat dissipation and actual lift of devices. For nonmetallic materials, phonon is considered to be the main carrier of heat conduction. Generally, it is believed that the introduction of defective structures hinders the propagation of phonons and causes a decrease in thermal conductivity of materials. However, the interaction mechanism between phonons and internal defects of materials is still unclear. Specifically, how the defect affects the local phonon dispersion relationship E(q) and phonon scattering has not been resolved. Limited by the spatial resolution of measuring tools and the development of theoretical methods, there are few reports on the measurement and analysis of thermal conductivity and phonon spectrum of a single defect, both experimentally and theoretically.

The corresponding authors are Prof. Xiaoqing Pan and Prof. Ruqian Wu in university of California, Irvine. Theoretical calculations are completed by Chengyan Liu in School of Materials Science and Engineering, Henan University. Henan University is the collaboration department.

Dr. Chengyan Liu is engaged in the study of theoretical calculation in materials science. He studied for a bachelor degree at the department of physics in Zhengzhou university from 2007 to 2011 and a master degree at department of physics of Zhengzhou university from 2011 to 2014. He studied for a Ph. D degree at the department of physics in Fudan university from 2014 to 2017. From 2017 to 2019, he studied as a postdoctoral fellow at the department of astronomy and physics, university of california, irvine. He was introduced in school of materials science and engineering, Henan university on january 1st, 2020. The representative papers are published on Nature, AEM, Nano Lett., PRB et. al.

Fig. selected parameters, real-space image and momentum space diffraction pattern obtained in experiment.

This work adopts spatially resolved, momentum-resolved, and energy-resolved electron energy loss spectra combining with theoretical calculations to study the phonon spectrum of a single plane defect in SiC material. The authors find that the widespread stacking fault in SiC forms defective phonon states, which leads to lowering 3.8 meV of a transverse acoustic phonon (TA) energy. Simultaneously, the corresponding density of states have a great enhancement compared with these of bulk system. This result can explain the mechanism of reducing thermal conductivity of SiC by introducing stacking faults. The present work plays a guiding role in understanding the interaction relationship between phonons and internal defects in materials. Using this model, a series of basic theoretical studies on the influence of different defect structures can be launched. In this work, the authors select the stacking fault widely existing in 3C phase of SiC as a sample. By rotating the sample, the stacking fault is observed by electron microscope from the side of SiC, thereby spatially distinguishing the stacking fault and the surrounding defect-free regions. Theoretically, the density functional perturbation theory, combining with the calculation methods of Green’s function and electron energy loss spectrum, is used to analyze the influence of stacking fault on the phonon of bulk phase. They successfully explain the redshift (millielectron voltage magnitude) of transverse acoustic wave branch under the influence of a single stacking fault.

Article link：https://www.nature.com/articles/s41586-020-03049-y