Spherical aberration correction marks a great milestone in the recent advancement of transmission electron microscopy (TEM). The availability of direct electron detector and monochromator unlocked a door for a new era of discovery by electron microscopy. Today, the advanced TEM enables the determination of 3D structure, composition, chemical bonding, and local electronic properties of materials with atomic resolution. It has been recently shown that local electric field mapping can be measured using scanning diffraction in scanning transmission electron microscopy (STEM). In this talk, I will present our recent development of a 4D STEM technique to map the local electric field and charge density with the sub-Å spatial resolution. Using this technique, we are able to directly image the interfacial charge distribution and gain deep insight into the origin of ferroelectric polarization and the electronic charge transfer at oxide interfaces. Furthermore, using our new Nion’s UltraSTEM 200, we achieved a record high energy resolution (~4.2 meV at 30 kV) for electron energy-loss spectroscopy (EELS), which enables us to see single atoms, measure molecular vibration, and probe phonon modes with a nanometer resolution. With SiC as a model system, we demonstrate that the EELS measurement of phonon energy as function of temperature offers a new avenue to measure local temperature in nanostructures and nanodevices.
Xiaoqing Pan is the Henry Samueli Endowed Chair in Engineering, and Professor of Chemical Engineering & Materials Science, Professor of Physics & Astronomy at the University of California-Irvine (UCI). He is also the inaugural Director of the Irvine Materials Research Institute (IMRI) at UCI. Before joining UCI, he was the Richard F. and Eleanor A. Towner Endowed Chair Professor of Engineering, Professor of Materials Science and Engineering, and Director of Electron Microbeam Analysis Laboratory at the University of Michigan, Ann Arbor. He earned his bachelor’s and master’s degrees in Physics at Nanjing University, China, and his Ph.D. degree in Physics at the University of Saarland, Germany. He was elected to be a Fellow of the American Ceramic Society in 2011, a Fellow of the American Physical Society in 2013, a Fellow of the Microscopy Society of America in 2014, and a Fellow of Materials Research Society in 2018. Pan's research interests center on the development of atomic resolution transmission electron microscopy (TEM) and in situ techniques, leading understanding of the atomic-scale structure-property relationships of advanced functional materials, including oxide electronics, nanostructured ferroelectrics and multiferroics, and catalysts. He is recognized internationally for his work in TEM. He has published over 400 peer-reviewed scientific papers in scholarly high impact factor journals, including e.g. Nature, Science, Nature Materials, Nature Chemistry, Nature Nanotechnologies, Nature Communications, Advanced Materials, PNAS, Journal of the American Chemical Society, Physical Review Letters, Nano Letters, and ACS Nano. His work has been cited over 20,000 times and his h-factor is 76 (Google Scholar). He has given more than 250 plenary, keynote or invited presentations at national and international conferences, and more than 200 invited seminars in national and international institutions.