中研院原分所演講公告
Speaker: Dr. Wei-Shun Chang (Dept. of Chemistry, Rice University, USA)
Contact: Dr. Jung-Chi Liao 廖仲麒博士
Plasmonic nanostructures have attracted significant attention because of their unique optical properties arising from localized surface plasmon resonances (LSPR). Due to the high optical sensitivity of LSPR to size, shape, electron density, and local environments, it is possible to probe the physical and chemical processes on nanoparticles by monitoring their spectral change of LSPR. However, the inhomogeneous broadening caused by the size and shape heterogeneities in chemically synthesized nanoparticles impedes the detailed spectroscopic information in conventional ensemble measurements. In addition, optical characterization is usually performed using scattering methods, or extinction, which is the sum of absorption and scattering. Separate measurements of the absorption and scattering are important as absorption determines nanoparticle heating and hot electron generation, while scattering represents the strength of nanoparticle antenna. Single-nanoparticle spectroscopy resolves the obstacles of sample heterogeneity.
In this talk, I will present a new technique to separately measure steady-state absorption and scattering spectra on single gold nanospheres, nanorods and particle clusters. A comparison of the absorption spectra to the scattering spectra of the same individual gold nanoparticles reveals a small blueshift of the absorption spectra. This small blueshift might be originated from the interband transition of the materials. In contrast, the absorption deviates significantly from the scattering for the nanoparticle clusters due interference of bright and dark modes giving rise to a Fano resonance. I will further discuss using spectro-electrochemical microscopy to probe electrochemical processes on single plasmonic nanoparticles. I will demonstrate how the optical properties of LSPR response to capacitive charging, ion adsorption and redox reactions at single particle level. We found that the sensing sensitivity depends on the morphology and the geometry of nanoparticles.