Plasmon-induced Hot Electrons Influenced by Electric Field

Abstract

The plasmonic nanostructures have attracted particular attention due to their superior ability to capture and modulate light in ultraviolet-visible and near-infrared range, by changing the size, morphology, and the composition of nanostructures. Especially in plasmon-driven chemical reactions, plasmon-induced hot electrons (HEs) can be transferred from the surface of metal nanostructures to the lowest unoccupied molecular orbital (LUMO) of the adsorbate molecule or the conduction band of the semiconductor to achieve catalytic reaction. Therefore, how to improve the excitation efficiency of HEs has become a key problem to be solved urgently. In this paper, 120 nm Ag nanoparticles (NPs) were synthesized by seed growth method using 45 nm Au as seed. Subsequently, (3-aminopropyl)trimethoxysilane as coupling agent and sodium silicate as the silicon source were used to prepare the shell-isolated Ag NPs with 2~3 nm SiO2 shell (Ag SHINs). Finally, Ag SHINs were modified with poly(allylamine hydrochloride), then small Au (ca. 15 nm) as satellites were electrostatic self-assembled onto the surface of Ag SHINs to form a 3D Ag SHINs-Au superstructure. Using p-aminothiophenol (pATP) as probe molecule, in-situ surface-enhanced Raman spectroscopy (SERS) was employed to real-timely monitor the catalytic reaction processes from pATP to DMAB, using 532, 638, and 785 nm lasers for excitation, respectively. The results showed that the highest conversion efficiency was achieved when 638 nm laser was applied. In addition, the reaction rate under 785 nm excitation was faster than that under exposure to 532 nm laser. Then, we used three dimensional (3D) finite-difference time-domain (FDTD) to simulate the electric field distribution of 3D Ag SHINs-Au superstructure. The electric field simulation results are consistent with the experimental results. In consequence, the stronger the electric field intensity, the higher the HEs excitation efficiency. On the other hand, the intra-band transitions produce HEs more efficiently than inter-band transitions. Therefore, this study is helpful for understanding how the electric field intensity affect the excitation efficiency of the HEs.