Expert Profile:

Dr.Peng Gao is a Boya Distinguished Professor at the Center for Quantum Materials Science, and the Director of the Electron Microscopy Laboratory at Peking University. He earned his Ph.D. in Condensed Matter Physics from the Institute of Physics, Chinese Academy of Sciences, and Bachelor of Physics from University of Science and Technology of China. He has conducted research at the University of Michigan, Brookhaven National Laboratory, and the University of Tokyo. After that, he has held positions as Assistant Professor, Tenured Associate Professor, and Full Professor at Peking University.

His research focuses on atomic‑scale interface science, with over 300 published papers. He has been recognized as a Highly Cited Researcher by Clarivate and Elsevier on multiple occasions. Some of his work has been selected for national highlights, including Candidate of TOP Breakthrough of the Year of China, TOP Breakthrough of the Year in Semiconductor of China, TOP Breakthrough of the Year in Optics of China, TOP Breakthrough of the Year in ELECTRONIC SCIENCE and TECHNOLOGY of China. He has received awards such as the XPLORER PRIZE, the China Youth Science and Technology Award, and the Beijing Outstanding Undergraduate Thesis Supervisor, and has been recognized as an Outstanding Doctoral Thesis Advisor at Peking University. He has led major research programs including the National Science Fund for Distinguished Young Scholars and National Key Research and Development Programs.

Probing Phonons and Visualizing Heat Transport at the Sub-Nanometer Scale

Abstract:

Phonons, the quasiparticles describing collective atomic vibrations, govern the thermal, optical, electrical, and mechanical properties of materials. In 1912, Born and von Kármán first introduced the energy–momentum dispersion relation to describe phonons under periodic boundary conditions, a theoretical framework that has since formed the foundation of phonon research. In the 1950s, Nobel laureate Brockhouse successfully validated this dispersion theory using inelastic neutron scattering in large single crystals.Nevertheless, for over a century, the precise measurement of phonon dispersion at the nanoscale has remained a formidable challenge, constrained by the fundamental trade-off between spatial and momentum resolution imposed by the Heisenberg uncertainty principle.

To more closely approach this intrinsic limit, we have developed four dimensional electron energy loss spectroscopy (4D EELS), which simultaneously achieves spatial, momentum, and energy resolution. Based on inelastic scattering of monochromated high energy electrons, this technique enables direct measurement of phonon dispersion at the nanoscale and phonon density of states at the atomic scale. It has allowed experimental determination of phonon dispersion and density of states across individual hetero interfaces, single nanowires, and nanotubes, and established direct links to their corresponding physical properties. In this talk, I will highlight some advances achieved with this approach in phonon measurement and thermal property studies of semiconductor interfaces, crystal defects, and individual nanostructures.