Professor Xiangdong Zhu joined the Physics Department in 1989. He is a fellow of American Physical Society and a fellow of Optical Society of America. His research activities are centered on development and application of laser-based techniques for investigation of atomic and molecular processes on solid surfaces such as mass transport, thin film growth, surface-bound electromagnetic waves, chemical reactions, and biomolecular interactions. His recent work includes (1) novel optical studies of thin film growths and nanostructures under a wide range of conditions; (2) experimental studies of classical and quantum diffusion of adsorbates on solids; (3) optical platforms for high-throughput label-free characterization of biomolecular interactions.
Novel Optical Studies of Thin Film Growth - Fundamentals of growth and functionality of conventional as well as novel materials involve individual and collective behaviors of molecular constituents on surfaces of host materials (crystalline solids or otherwise). The increasing demands in complexity and range of application for better functional materials and often limited financial and time resources makes characterization of these behaviors always a major challenge in material science and experimental solid-state physics. For decades this challenge has continued to fuel creative efforts for development and application of better and more efficient experimental techniques that meet the challenge in one aspect or another. Professor Zhu's group focuses on development and application of optics-based techniques for characterization of molecular constituents on solid surfaces and at the interfaces between two condensed media, by exploring and using the correlation between measurable properties of reflected optical waves and the structure/composition of the molecular constituents.
Classical and Quantum Mass Transport on Metals - Transport of atoms and molecules on a solid surface is one of the elementary kinetic processes in formation and behavior of solid-state materials. Individual and collective properties of such a transport play key roles on determining the morphology and composition of material growth. In addition detailed transport behaviors of individual atoms on a solid offer a unique window of opportunity for looking into fundamental aspects of quantum dissipation in various phases of the solid. Professor Zhu's research on this topic involves measurement of time-varying structural factors of optically patterned adatom density profiles (i.e., 1-D gratings) with linear optical diffraction, - one of the few experimental techniques capable of measuring both classical and quantum diffusion of adatoms over a wide range of temperature. His group has recently developed new methods of adatom density pattern formation that are generally applicable to all types of crystalline solids, particularly those with low melting points and thus prone to optically induced damage.
Ellipsometry-based Optical Platform for High-Throughput Label-free Detection of Biomolecular Interactions on Solid Support - It has been 10 years since the historical declaration of the human genome completion and the promise of individualized healthcare and medicine. We now know the road to that Promised Land is much longer than anticipated. The living organisms are far more complex than what can be deduced from the list of their genes. This is because .the phase space. of parameters that govern intricate behaviors of even the simplest of life is orders of magnitude larger than the genetic blueprint. Beyond the identification of protein-coding genes, individual and collective characteristics of DNA-RNA and RNA-RNA interactions, post-transcriptional modification of proteins, protein interactions with DNA, RNA, proteins, small molecule drugs, carbohydrates (sugar) and lipids are required and yet for the most part uncharacterized. The task of determining and understanding even a subset of these interactions and their interplays is necessary and daunting (if not impossible). The nature is shy in leaving us many clues to navigate through the vast parameter space toward understanding even simple diseases and the remedies for them. There are two schools of approaches to this enormous task: one is to let the evolutionary machinery of living organisms to select the .magic paths. to special molecules or special modifications of proteins and higher order structures that modify the behavior of a biological pathway to our liking; another is to develop and use experimental tools that characterize biomolecular interactions in a highly parallel fashion, as integrated circuits have revolutionized our ways of life. Professor Zhu's approach so far belongs to the second school. Based on measurements of oblique-incidence reflectivity difference (OI-RD) (a special form of ellipsometry signal), his group has developed a scanning microscopy platform that detects over 10,000 biomolecular reactions on a single solid surface without fluorescence labeling. This enables his group to study the interaction of a protein molecule with large chemical libraries from NIH (~ 500,000 to 1,000,000 compounds), NCI (~ 100,000 compounds), and commercial vendors (~ 1,000,000 or more compounds) in matter of days or weeks, instead of months or years. The potential impact of this platform to genomics, proteomics, glycomics, and cytomics research and to drug discovery is most promising and exciting.
- Ph.D., University of California, Berkeley, 1989
- Assistant Professor, University of California, Davis,
- Associate Professor, University of California, Davis,
- Professor, University of California, Davis, 1999-Present
- Fellow, American Physical Society
- Fellow, Optical Society of America