Interfacial Influence on Surface Plasmon Resonances in Quantum-Sized Nanoparticles
Speaker: Dr. Yugang Sun
Center for Nanoscale Materials, Argonne National Laboratory, USA.
Place: A306, 1 West Building, Qujiang Campus
Time: 15:00, Dec. 12th, 2014
Brief introduction:
孙玉刚，博士，材料学家。2008年度美国青年科学家总统奖（PECASE）获得者。
2006年开始在美国阿贡国家实验室纳米材料研究中心从事独立研究工作，目前是终身研究员，助理教授，纳米材料合成实验室负责人。
多年从事新型纳米金属材料的构筑以及应用研究，近年来在贵金属纳米颗粒的规格化制备、空心壳纳米金属的结构形成与演化、柔性可伸展纳米电路及器件、以及新型柔性氢气传感器的研制等研究方向上均取得了创新性科研成果。已在权威国际刊物如Science、Nature Nanotechnology、Adv. Mater.、Nano Letters、JACS等上发表学术论文80余篇，其中第一作者及通讯作者论文40篇。这些论文中影响因子大于6的有35篇，共被国际同行他引7000多次。
2000-2010年全球材料学家排名100位（Thomson Reuters统计）第5名。
Abstract:
Nanoparticles made of noble metals such as silver and gold exhibit strong optical absorption due to their surface plasmon resonance (SPR) that corresponds to the collective oscillation of surface conduction electrons in response to the incident electromagnetic waves. As the nanoparticles are smaller than 20 nm the interfacial quantum effect may take place to influence the SPR of the nanoparticles.For example, the monodispersed silver nanoparticles synthesized via a well-defined chemical reduction process exhibit an exceptional size-dependence of SPR peak positions: as particle size decreases from 20 nm the peaks blue-shifts but then turns over near ~12 nm and strongly red-shifts. Theoretic modeling and calculations reveal that the surface chemistry corresponding to the interactions between the capping molecules and the surface silver atoms in the nanoparticles become pronounced in determining their optical properties because the surface silver atoms represent a significant fraction of the total number of atoms in small nanoparticles.Such surface chemistry reduces the density of conduction band electrons (i.e., free electrons) in the surface layer of metal atoms, thus consequently influences the frequency-dependent dielectric constant of the metal atoms in the surface layer and the overall SPR absorption spectrum. Another class of hybrid silver-gold nanoparticles will also be discussed. The coupling between the SPR of the silver and gold components leads to very interesting optical signals that can be interpreted with classical plasmonics in combination with a quantum-corrected model.A comprehensive understanding of the relationship between interfacial coupling/chemistry and optical properties will be beneficial to exploit new applications of small colloidal metal nanoparticles, such as colorimetric sensing, electrochromic devices, surface enhanced spectroscopies, and photocatalysis.
This work was performed at the Center for Nanoscale Materials, a U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences User Facility under Contract No. DE-AC02-06CH11357.
