Understanding Electromagnetic Interactions and Electron Transfer in Ga Nanoparticle–Graphene–Metal Substrate Sandwich Systems

Yael Gutiérrez,Fernando Moreno,April S Brown,Maria M Giangregorio,Maria Losurdo

doi:10.3390/app9194085

Abstract

Plasmonic metal nanoparticle (NP)–graphene (G) systems are of great interest due their potential role in applications as surface-enhanced spectroscopies, enhanced photodetection, and photocatalysis. Most of these studies have been performed using noble metal NPs of silver and gold. However, recent studies have demonstrated that the noble metal–graphene interaction leads to strong distortions of the graphene sheet. In order to overcome this issue, we propose the use of Ga NPs that, due to their weak interaction with graphene, do not produce any deformation of the graphene layers. Here, we analyze systems consisting of Ga NP/G/metal sandwich coupling structures, with the metal substrate being, specifically, copper (Cu) and nickel (Ni), i.e., Ga NP/G/Cu and Ga NPs/G/Ni. We experimentally show through real-time plasmonic spectroscopic ellipsometry and Raman spectroscopy measurements of the quenching of the Ga NP localized surface plasmon resonance (LSPR) depending on the wetting of the graphene by the Ga NPs and on the electron transfer through graphene. Theoretical finite-difference time-domain (FDTD) simulations supportively demonstrate that the LSPR in such sandwich structures strongly depends on the contact angle of the NP with graphene. Finally, we also provide evidence of the electron transfer from the Ga NPs into the graphene and into the metal substrate according to the work function alignments. These considerations about the contact angle and, consequently, geometry and wetting of the metal NPs on graphene, are useful to guide the design of those plasmonic systems to maximize electromagnetic enhancement.

Highlights

Several plasmonic metal nanoparticle–graphene systems have been reported in the literature for applications in surface-enhanced Raman spectroscopy (SERS) [1,2], photodetection [3], enhanced biosensing, and photocatalysis, among others
We demonstrate that there is no appearance of surface plasmon resonances in the work-function asymmetric graphene–metal sandwich systems, and we theoretically show that this process strongly depends on the contact angle between the metal NPs and the G/metal substrate, a parameter determined by the interfacial free energy between the nanoparticle and the graphene layer
Ga nanoparticles (Ga NPs) were deposited on chemical vapor deposition (CVD) graphene grown on Cu and Ni substrates

Summary

Introduction

Several plasmonic metal nanoparticle–graphene systems have been reported in the literature for applications in surface-enhanced Raman spectroscopy (SERS) [1,2], photodetection [3], enhanced biosensing, and photocatalysis, among others. In analyzing this literature, the use of pristine graphene (G) or graphene oxide (GO) should be noted [4,5], the latter always presenting some defects and some oxygen functional groups such as COOH, COH, and COH at the reduced graphene oxide surface. Most of these systems rely on noble plasmonic metals such as gold (Au) and silver (Ag), and again, in comparing literature in the field of graphene-plasmonic Au NPs, attention should be paid to whether

Methods

Results

Conclusion