讲座内容 讲座名称：Colloidal Metal Nanocrystals: From Academic Studies to Industrial Applications
讲座内容：Although the first documented synthesis of colloidal metal nanocrystals can be traced back to the beautiful work on gold colloids by Michael Faraday in 1856, only within the last decade have methods become available for generating samples with the quality, quantity, and reproducibility needed for a systematic study of their properties as a function of size, shape, and structure, and for exploration of their applications. Of particular importance is to control the shape of colloidal metal nanocrystals, which may initially seem like a scientific curiosity but with implications going far beyond aesthetic appeal. For nanocrystals made of noble metals, the shape determines not only their chemical, plasmonic, and catalytic properties but also their relevance for electronic, photonic and catalytic applications. For more than 15 years, we have been working diligently to achieve a quantitative understanding and control of the nucleation and growth mechanisms responsible for the formation of nanocrystals with specific shapes and structures. We have discovered that the shapes of metal nanocrystals are dictated by surface capping and the crystallinity and structure of seeds, which are, in turn, determined by factors such as reduction kinetics and oxidative etching. In this talk, I will discuss some of the recent developments in this field, with a focus on shape-controlled synthesis of noble-metal nanocrystals via seed-mediated growth in the presence/absence of a capping agent and under a thermodynamic or kinetic control. The success of these syntheses has enabled us to tailor the properties of metal nanocrystals for a broad range of applications in photonics, sensing, imaging, biomedicine, catalysis, and fuel cell technology.
讲座名称：Enriching Silver Nanocrystals with a Second Noble Metal
讲座内容：Silver is perhaps the best choice of material for plasmonics and related applications owing to its relatively low cost and favorable dielectric functions. Over the past two decades, significant progress has been made in the synthesis of Ag nanocrystals with controlled shapes and sizes to tailor their properties and thus optimize their performance in a range of applications. In particular, Ag nanocrystals have been prepared with sharp features (e.g., edges and corners) on the surface to drastically augment their surface-enhanced Raman scattering (SERS) activity. However, the sharp features tend to vanish due to the high susceptibility of Ag toward oxidative etching. As another pitfall, Ag is limited in terms of catalytic application as it only shows activity toward oxidation reactions such as epoxidation, not reduction reactions. One can address the aforementioned limitations of Ag nanocrystals by introducing a second noble metal (M) such as Au, Pd, or Pt to generate Ag-M bimetallic nanocrystals. In this talk, I will introduce two approaches to using Ag nanocrystals as seeds for the selective deposition of M. When the M atoms are selectively deposited on the edges of a Ag nanocrystal, a Ag@M core-frame nanocrystal is formed. In this structure, the excellent plasmonic and SERS properties of the Ag core are well retained while the deposited M can bring in new catalytic capabilities. Alternatively, when the M atoms are conformally deposited on the entire surface, a Ag@M core-shell nanocrystal is created. In this case, the M shell can greatly improve the chemical stability of the particle, in addition to the new catalytic properties associated with M. If the shell is kept below 1–2 nm thick, the excellent plasmonic and SERS properties of the Ag core can still be leveraged. Significantly, both SERS and catalytic properties can be integrated in the core-frame and core-shell nanocrystals to offer a unique probe for in situ detection and analysis of catalytic reactions by SERS.
讲座人介绍 Younan Xia is the Brock Family Chair and Georgia Research Alliance (GRA) Eminent Scholar in Nanomedicine at the Georgia Institute of Technology. He received a B.S. degree in chemical physics from the University of Science and Technology of China in 1987, a M.S. degree in inorganic chemistry from 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. His group has invented a myriad of nanomaterials with well-controlled properties. These nanomaterials have found widespread use in applications related to plasmonics, catalysis, fuel cell technology, electronics, photonics, photovoltaics, display, nanomedicine, and regenerative medicine. As a notable example, his technology on silver nanowires has been commercialized for the manufacturing of flexible, transparent, and conductive coatings sought in applications such as touch screen, flexible electronics, and photovoltaics. Xia has co-authored more than 690 publications in peer-reviewed journals, together with a total citation of more than 120,000 and an h-index of 170. He has been named a Top 10 Chemist and Materials Scientist based on the number of citation per publication. He has received a number of prestigious awards, including American Chemical Society (ACS) National Award in the Chemistry of Materials (2013), NIH Director's Pioneer Award (2006), David and Lucile Packard Fellow in Science and Engineering (2000), NSF CAREER (2000), and Alfred P. Sloan Research Fellow (2000). More information can be found at http://www.nanocages.com.