Ordered Array of Metal Particles on Semishell Separated with Ultrathin Oxide: Fabrication and SERS Properties

Xianglin Li,Alfred Tok,Chiew Tan,Zexiang Shen,Zhiwei Wang

doi:10.3390/coatings9010020

Abstract

Metal particles in gap cavities provide an interesting system to achieve hybrid local surface plasmon modes for local field enhancement. Here, we demonstrate a relatively simple method to fabricate Ag nanoparticles positioned on Ag semishells separated by a thin (~5 nm) dielectric layer. The obtained structure can provide strong local electric field enhancement for surface-enhanced Raman scattering (SERS). The fabrication of the ordered array structure was realized by nanosphere self-assembly, atomic layer deposition, and metal thin-film dewetting. Numerical simulation proved that, compared to the conventional metal semishell arrays, the additional Ag particles introduce extra hot spots particularly in the valley regions between adjacent Ag semishells. As a result, the SERS enhancement factor of the metal semishell-based plasmonic structure could be further improved by an order of magnitude. The developed novel plasmonic structure also shows good potential for application in plasmon-enhanced solar water-splitting devices.

Highlights

As a powerful spectroscopic technique, surface-enhanced Raman scattering (SERS) has found increased applications in various fields, including analytical chemistry, life sciences, medical sciences, and food safety [1,2,3,4,5,6,7,8,9]
We demonstrate a facile and scalable fabrication process based on nanosphere monolayer assembly and atomic layer deposition to achieve an array structure with metal particles on semishell (PoSS) for SERS application
Our results demonstrate the usefulness of nanosphere self-assembly and atomic layer deposition (ALD) in fabricating plasmonic nanostructures for applications in biomedical sciences and surface plasmon-enhanced solar water-splitting devices

Summary

Introduction

As a powerful spectroscopic technique, surface-enhanced Raman scattering (SERS) has found increased applications in various fields, including analytical chemistry, life sciences, medical sciences, and food safety [1,2,3,4,5,6,7,8,9]. One major challenge in making SERS a general analytical tool lies in the fabrication of noble metal nanostructure substrates with large and reproducible Raman enhancements over a wide sampling area, using ideally less costly, high-throughput methods [4,10,11,12,13,14,15,16]. Metal semishell array substrates have been widely employed in many SERS-based biosensing applications in complex media [27,28]. These semishell array substrates consist of ordered nanogaps between the spheres, which create plasmonic features with good control and tunability compared to random metal structures [29]. This is because in most of these conventional metal array nanostructures, there are only limited number of plasmonic ‘hot spots’ contributing to the overall SERS signal, and the metal gap size is still generally very large

Methods

Results

Conclusion