Shape-Controlled Synthesis of Nanostructures:

Simple Chemistry Meets Complex Physics

Younan Xia

Department of Chemistry, University of Washington, Seattle, WA 98195

Control of nanostructure shape may initially seem like a scientific curiosity, but its goal goes far beyond aesthetic appeal.  For metal nanostructures, shape not only determines their intrinsic chemical, plasmonic, and catalytic properties but also their relevance for electronic, optical, and sensing applications.  Part of my research in the last five years has focused on shape-controlled synthesis of silver and gold nanostructures.  While the synthetic methodology mainly involves solution-phase redox chemistry, we have been working diligently to understand the complex physics behind the simple chemistry ? that is, the nucleation and growth mechanisms leading to the formation of nanostructures with a specific shape.  Polyol synthesis of silver nanostructures provides a good example to illustrate this concept.  We discovered that the shape of silver nanostructures were dictated by both the crystallinity and shape of nanocrystallite seeds, which were, in turn, controlled by factors such as reduction rate, oxidative etching, and surface capping.  We also exploited the galvanic replacement reaction between silver and chloroauric acid to transform silver nanocubes into gold nanocages with controlled void size, wall thickness, and wall porosity.  We were able to engineer the optical properties of resulting gold nanocages with optical resonance peaks ranging from the blue (400 nm) to the near infrared (1200 nm) simply by controlling the molar ratio of silver to chloroauric acid.  Thanks to their exceptionally large scattering and absorption coefficients in the transparent window for soft tissues, this novel class of gold nanostructures has great potential emerging as both a contrast agent for optical imaging in early-stage tumor detection, and a therapeutic agent for photothermal cancer treatment. 

Younan Xia is a Professor of Chemistry at the University of Washington (UW) in Seattle.  His research interests include development of new methodologies for shape-controlled synthesis of nanomaterials and fabrication of functional nanostructures and devices.  He received a B.S. degree in chemical physics from the University of Science and Technology of China (USTC) in 1987 and worked as a graduate student on inorganic nonlinear optical crystals at the Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences.  He came to the United States in 1991, received a M.S. degree in inorganic chemistry from the University of Pennsylvania (with Professor Alan G. MacDiarmid) in 1993, and a Ph.D. degree in physical chemistry from Harvard University (with Professor George M. Whitesides) in 1996.  He continued his work at Harvard as a postdoctoral fellow with both Professors George M. Whitesides and Mara Prentiss.  Dr. Xia joined the UW faculty as an Assistant Professor of Chemistry in 1997, and was promoted to the rank of Full Professor in 2004.  He has received a number of awards, including the NIH Director’s Pioneer Award (2006); the Leo Hendrik Baekeland Award from the North Jersey Section of ACS (2005); the Camille Dreyfus Teacher Scholar (2002); the David and Lucile Packard Fellow in Science and Engineering (2000); the National Science Foundation CAREER Award (2000); the Alfred P. Sloan Research Fellow (2000); the ACS Victor K. LaMer Award (1999); and the Camille and Henry Dreyfus New Faculty Award (1997).  He has co-authored more than 250 publications in peer-reviewed journals and has edited a number of special issues and books on nanostructured materials and microfabrication techniques.  He currently serves as an Associate Editor of the ACS journal Nano Letters, and sits on the advisory boards of Langmuir, Chemistry of Materials, Advanced Functional Materials, Nano Today, International Journal of Nanotechnology, and International Journal of Nanoscience.