Synthesis of silver nanostructure on gold nanoparticle using near field assisted second harmonic generation

Takashi Yatsui,Felix Brandenburg,Olivier Soppera,Benjamin Leuschel

doi:10.1038/s41598-021-84944-w

Abstract

By using gold (Au) nanoparticles (NPs) as an optical near-field source under far-field illumination in combination with a silver (Ag) ion solution containing a photoinitiator, we coated Ag on Au NPs using a near-field (NF)-assisted process. We evaluated the change in the size of the NPs using transmission electron microscopy. Evaluation of the synthesized Ag volume over illumination power confirmed the squared power dependence of the NP volume with illumination using 808 nm light, i.e., a wavelength longer than the absorption edge wavelength of the photoinitiator molecules. The rate of volume increase was much lower than the plasmonic field enhancement effect. Therefore, the squared power dependency of the volume increase using a wavelength longer than the absorption edge wavelength originated from NF-assisted second-harmonic generation and the resulting excitation.

Highlights

By using gold (Au) nanoparticles (NPs) as an optical near-field source under far-field illumination in combination with a silver (Ag) ion solution containing a photoinitiator, we coated Ag on Au NPs using a near-field (NF)-assisted process
Because photochemical reactions are based on the photoexcitation of molecules, the wavelength employed for the photochemical reaction should be shorter than the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap (HLG) wavelength
The optical near-field (ONF) can excite dipole forbidden transitions of various m olecules[6] via intermediate states inside the HLG, making it possible to utilize wavelengths longer than the HLG wavelength. By harnessing such properties of the ONF, we have improved the efficiency of photochemical reactions, including those involved in H 2 generation9, CO2 reduction10,11, photolithography[12], and photodimerization[13] using wavelengths longer than the HLG wavelength, which expands the possibilities for excitation of resonant transitions demonstrated in other works[14,15,16]

Summary

Introduction

By using gold (Au) nanoparticles (NPs) as an optical near-field source under far-field illumination in combination with a silver (Ag) ion solution containing a photoinitiator, we coated Ag on Au NPs using a near-field (NF)-assisted process. ∂E ∂r is not zero for nanoscale materials In such a system, the ONF inherently achieves strong second-harmonic generation (SHG) without intense light illumination because the ONF breaks the selection rules of SHG7,8. The ONF can excite dipole forbidden transitions of various m olecules[6] via intermediate states inside the HLG, making it possible to utilize wavelengths longer than the HLG wavelength By harnessing such properties of the ONF, we have improved the efficiency of photochemical reactions, including those involved in H 2 generation9, CO2 reduction10,11, photolithography[12], and photodimerization[13] using wavelengths longer than the HLG wavelength, which expands the possibilities for excitation of resonant transitions demonstrated in other works[14,15,16]. It is possible to utilize a wavelength longer than the HLG wavelength, phenomena associated with far-field (FF) properties were observed—such as changes in the p hotocurrent[9] or absorption s pectra10,11,13—and to date there remains no direct proof of the ONF effect. Transmission electron microscopy (TEM) is employed to obtain direct proof of the ONF-based reaction by measuring the change in size of nanostructures at the atomic level

Methods

Results

Conclusion