Xiaoqing Pan

Xiaoqing Pan, PhD

Biography

Xiaoqing Pan is a professor and Henry Samueli Endowed Chair in Engineering, at UC Irvine in The Henry Samueli School of Engineering’s Department of Chemical Engineering & Materials Science and the School of Physical Sciences Department of Physics & Astronomy. He is also the inaugural director of the Irvine Materials Research Institute (IMRI).

Previously, Pan was the endowed Chair Professor (Richard F. and Eleanor A. Towner Professor of Engineering) at the University of Michigan’s Department of Materials Science and Engineering.  He was also Director of Electron Microbeam Analysis Laboratory at the University of Michigan, Ann Arbor. He received his bachelor’s and master’s degrees in physics from Nanjing University, and his doctorate in physics (1991) from the University of Saarland, Germany. After postdoctoral research at the Max-Planck Institut für Metallforschung in Stuttgart, he joined the faculty of MS&E at Michigan as an associate professor without tenure in 1996 and was promoted to professor with tenure in 2004. Pan has received many awards, including the National Science Foundation’s CAREER Award and the Chinese NSF’s Outstanding Young Investigator Award. He was awarded a named Cheung-Kong Distinguished Visiting Professorship (Nanjing University 2008 – 2010) and was also awarded the National Distinguished Professorship (China 1000 Talent Program) as Visiting Professor at Nanjing University in 2009.  He was an overseas member of the Scientific Review Board, Chinese Academy of Science, 2005-2010.  He has been serving as a member of the Advisory Committee of the Overseas Chinese Affairs Office of the State Council, China, since 2011. He is also a member of the Physical Sciences Panel of the Hong Kong Research Grants Council (RGC) since 2013. Pan was elected to be a Fellow of the American Ceramic Society in 2011, a Fellow of the American Physical Society in 2013, and a Fellow of the Microscopy Society of America.

Pan has published over 200 peer-reviewed scientific papers in scholarly high impact factor journals, including e.g. Nature, Science, Nature Materials, Nature Communications, Physical Review Letters, Nano Letters, and Advanced Materials. His work has been cited over 7000 times with his highest single paper citation of 639 and his publication h-factor is 47.

He has given more than 150 invited talks or keynote presentations at conferences, and more than 120 invited seminars. He was the leading organizer of a number of national/international conferences and meetings. Pan is also committed to education in materials science, electron microscopy, and has mentored a number of graduate students and postdoctoral researchers.

Research Interests

Pan’s research interests center on understanding 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 materials physics and electron microscopy that have led to the discovery of new properties and novel functionalities in technologically important materials. His pioneering contributions include the development of methods to quantitatively map the electrical polarization in ferroelectrics at atomic resolution and methods to uncover the effects of boundary conditions on ferroelectricity, including polarization mapping, the first observation of ferroelectric vortices, and dynamic behaviors of ferroelectric domains during electrical switching under applied electric field in TEM. Polarization vortex arrays with electric flux closure, similar to the magnetization patterns ubiquitous to ferromagnetic materials, were directly observed for the first time in a ferroelectric heterostructure, which was made possible by sub-Ångström resolution TEM in combination with a unique image processing technique developed in Pan’s group to map the polarization [Nelson et al., Nano Letters 11, 828–834 (2011)]. The existence of the spontaneous polarization vortices at the ferroelectric interfaces can fundamentally change the switching mechanism of domains in ferroelectric memories and spintronic devices based on multiferroic materials due to the unique polarization configurations near the vortices. This work represents the forefront of spatially resolved polarization “imaging,” enabling the effect of interfaces and defects on the polarization in ferroelectric heterostructures relevant to ferroelectric device structures to be seen.

Pan and his students also demonstrated, for the first time, the ability to directly observe nanoscale ferroelectric switching in real-time [Nelson et al., Science 334, 968 (2011); Gao et al., Nat. Commun. 2, 591 (2011); Gao et al., Adv. Mater. 24, 1106–1110 (2012)]. They observed the formation and dynamic evolution of nanometer-scale ferroelectric domains by an applied electric field in TEM.  They directly observed the nucleation events at the electrode interface, ferroelectric domain wall pinning on point defects and the formation of metastable ferroelectric states with the electric “dipole glass” structure during ferroelectric domain-mediated polarization switching. These studies show how defects and interfaces impede the full ferroelectric switching of a thin film. They also found that even thermo-dynamically favored domain orientations are still subject to retention loss, if the newly formed domain is smaller than a critical size. These findings were made possible by a novel in situ scanning probe built into a TEM holder that enables one to apply an electric field across a cross-sectional specimen while domain structures are imaged in TEM. The ferroelectric domains observed in situ TEM can serve as memory “bits” similar to current magnetic memories, but potentially with much higher densities. The in situ TEM techniques were also used to study conducting filament growth in nanoscale resistive memories [Yang et al., Nat. Commun., 3:732(2012)]. Resistive switching effects in dielectric-based devices are normally assumed to be caused by conducting filament formation across the electrodes, but the nature of the filaments and their growth dynamics remain controversial. Pan’s group performed direct TEM imaging and structural and compositional analysis of the nanoscale conducting filaments. Through systematic ex-situ and in-situ TEM studies on devices under different programming conditions, they found that the filament growth can be dominated by cation transport in the dielectric film.  Unexpectedly, two different growth modes were observed for the first time in materials with different microstructures. Regardless of the growth direction, the narrowest region of the filament was found to be near the dielectric/inert-electrode interface in these devices, suggesting that this region deserves particular attention for continued device optimization. These findings have made a significant step towards making ferroelectric and resistive memories a reality.

Pan has also used novel methods of in situ electron microscopy to explore mechanisms of “self-regeneration” in automotive catalysts. Pan’s research group has investigated the atomic-scale processes underlying the self-regenerating catalyst concept in, e.g., Pd-, Pt- and Rh-doped perovskite structures, and surprisingly observed differences between the behavior of Pd-doped material, and the Pt- and Rh-doped materials, in redox reaction treatments [Katz et al., J. Am. Chem. Soc. 133, 18090–18093 (2011); J. of Catalysis 293, 145–148 (2012)]. These studies provide direct evidence of self-regeneration in novel perovskite-based automotive catalysts. A new understanding, based on recognition of the novel mechanism of self-stabilization observed, may help further development and eventual implementation of a more sustainable automotive catalyst technology.

Education

B.S., Nanjing University (China), Physics
M.S., Nanjing University (China), Physics
Ph.D., Saarland University (Germany), Solid State Physics, 1991