Polarization- and Wavelength-Dependent Shell-Isolated-Nanoparticle-Enhanced Sum-Frequency Generation with High Sensitivity
Yuhan He, He Ren, En‐Ming You, Petar M. Radjenovic, Shi‐Gang Sun, Zhong‐Qun Tian, Jian‐Feng Li, Zhaohui Wang
Abstract
Sum-frequency generation (SFG) spectroscopy is a highly versatile tool for surface analysis. Improving the SFG intensity per molecule is important for observing low concentrations of surface species and intermediates in dynamic systems. Herein, Shell-Isolated-Nanoparticle-Enhanced SFG (SHINE-SFG) was used to probe a model substrate. The model substrate, p-mercaptobenzonitrile adsorbed on a Au film with SHINs deposited on top, provided an enhancement factor of up to 10^{5}. Through wavelength- and polarization-dependent SHINE-SFG spectroscopy, the majority of the signal enhancement was found to come from both plasmon enhanced emission and chemical enhancement mechanisms. A new enhancement regime, i.e., the nonlinear coupling of SHINE-SFG with difference frequency generation, was also identified. This novel mechanism provides insight into the enhancement of nonlinear coherent spectroscopies and a possible strategy for the rational design of enhancing substrates utilizing coupling processes.