Location: A718, SINANO  

Abstract:  

In the last decades, surface-enhanced Raman scattering (SERS) spectroscopyhas become a versatile vibrational spectroscopic technique with a number of applications in the chemical, material and, in particular, life sciences. In the first part of this talk, I will show our recent work on the use of SERS spectroscopy forprobing the spatial nonlocality effect, which is recently believed to set an ultimate limit of plasmonic near-field enhancement in metallic nanostructures with critical dimensions on the order of a few nanometers or less [1]. I will present our theoretical and experimental investigations on the effect of spatial nonlocality in metal films with controllable surface roughness [2]. In theory, we have used a well-established nonlocal hydrodynamic model to describe the collective motion of conduction electronsand calculate the near-field enhancement atthe surface of silver films. In experiment, we have used the SERS spectroscopic technique to probe indirectly the near-field enhancement factor as a function of surface roughness by measuring the SERS intensity of conformally coated graphene monolayers on a series of silver films. Our results reveal that the spatial nonlocality effect of the metal dielectric response has to be taken into account for more accurate prediction of the SERS enhancement at large surface roughnesses. In the second part of this talk, I will show the use of SERS spectroscopy formonitoring catalytic reaction dynamics provided that plasmonic metal nanoparticles for Raman enhancement are properly integrated with catalytic metals to form a single entity. I will present a facile approach for synthesizing Au@Pt core/shell nanostructures with controllable surface density of sub-5 nm Pt nanoparticles on the surface of Au nanorods. Systematic investigations on both SERS and catalytic activities of the hybrid nanostructures reveal an optimized surface coverage of Pt. More importantly, due to their dual functionalities, the hybrid nanostructures are able to track the Pt-catalyzed reaction in real time by measuring the SERS signals of the reactant, intermediate and final products. 

References: 

[1] C. Ciracì et al, Science 337, 1072 (2012). [2] Y. Zhao et al, Nanoscale 6, 1311 (2014). [3] Z. Y. Bao et al, Bifunctional Au@Pt core-shell nanostructures for in-situ monitoring of catalytic reactions by SERS spectroscopy, accepted by Nanoscale (2014). 

Biography:  

Dang Yuan Lei received his BSc and MPhil degrees, both in Physics, from Northwest University and The Chinese University of Hong Kong in 2005 and 2007, respectively. In October 2008, he went to Imperial College London to conduct his PhD studies, under the supervision of Prof Stefan Maier and in long-term collaboration with Prof Sir John Pendry, and obtained his PhD degree in Physics from Imperial in 2011 with his thesis awarded the prestigious prize “Anne Thorne PhD Thesis Prize”. He is currently an assistant professor in the Department of Applied Physics at The Hong Kong Polytechnic University since September 2012. His main research activities include nanophotonics and nanomaterials studies, with particular interest in surface plasmon-enhanced light-matter interactions at the nanoscale and their applications in energy harvesting, optoelectronic devices and biochemical sensing.