讲座题目：Direct visualization of Interface Plasmon in Pseudo One-dimensional Si/SiO2 core-shell Nanostructures

报告人：Quan Li

时 间：8月24日（周二）上午10:00~11:30 
地 点：化学楼A713会议室
主持人：侯仰龙（特聘研究员）

报告内容摘要：
      The interface Plasmon (IP) of Si-based nanostructures (which surface is always covered by a layer SiO2) has aroused much interest for potential applications in optoelectronic and energy conversion devices.  One dimensional Si/SiO2 nanostructures start to draw more and more research attention, due to the proposal of IP energy tuning by varying the size and the aspect ratio of the nanostructures, and via plasmon coupling among individual nanostructures. Consequently, understanding on the evolution of IP as a function of the size/aspect ratio and the possible coupling of the nanostructures, as well as the spatial distribution of specific IP modes are of great importance.
      In the present work, the interface plasmon dependence on the size and aspect ratio of the Si/SiO2 core shell nanostructures have been investigated using electron energy loss spectroscopy (EELS)-related techniques under parallel illuminations, which results are comparable to those obtained by optical methods.  Elongation from a perfect spheroid Si/SiO2 core-shell nanoparticle results in splitting of the IP modes to a transverse and a longitudinal branch.  The longitudinal IP mode red shifts with the aspect ratio increase of the nanostructure due to the longer charge separations along the long axis of the nanostructure.   Retardation effect comes into play in longer nanostructures, and the corresponding charge distribution in such a nanostructure is revealed by the uniform intensity along the longitudinal direction of the long Si/SiO2 nanocable in the energy filtered image.  The small diameter of the nanostructure determines the dominance of the longitudinal mode in the IP oscillation. Assembly of the Si nanoparticles into one-dimensional particle chains leads to interaction between the adjacent nanoparticles, which can also induce the splitting of the interface plasmon into transverse and longitudinal polarizations.  In addition, such coupling causes spatial re-distribution of the IP intensity, leading to local field enhancement in-between the two nanoparticles.  By controlling the growth of Si nanostructures into different morphologies, we demonstrate that the material’s optical properties can be manipulated.

报告人简介：
     Dr. Quan Li received a B.S. degree in chemistry at 1997 and a Ph.D. degree of Materials Science and Engineering in Northwestern University. She is crurrently an associate professor in the department of physics in The Chinese University of Hong Kong. Her research interests include Materials for clean energy solutions, and nanomaterials for biology-related applications.