Surface-Enhanced Raman Spectroscopy on Hybrid Graphene/Gold Substrates near the Percolation Threshold.

Dmitry E Tatarkin,Georgy A Ermolaev,Aleksey V Arsenin,Sergey M Novikov,Dmitry I Yakubovsky,Valentyn S Volkov,Yury V Stebunov,Artem A Voronov

doi:10.3390/nano10010164

Abstract

Graphene is a promising platform for surface-enhanced Raman spectroscopy (SERS)-active substrates, primarily due to the possibility of quenching photoluminescence and fluorescence. Here we study ultrathin gold films near the percolation threshold fabricated by electron-beam deposition on monolayer CVD graphene. The advantages of such hybrid graphene/gold substrates for surface-enhanced Raman spectroscopy are discussed in comparison with conventional substrates without the graphene layer. The percolation threshold is determined by independent measurements of the sheet resistance and effective dielectric constant by spectroscopic ellipsometry. The surface morphology of the ultrathin gold films is analyzed by the use of scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the thicknesses of the films in addition to the quartz-crystal mass-thickness sensor are also measured by AFM. We experimentally demonstrate that the maximum SERS signal is observed near and slightly below the percolation threshold. In this case, the region of maximum enhancement of the SERS signal can be determined using the figure of merit (FOM), which is the ratio of the real and imaginary parts of the effective dielectric permittivity of the films. SERS measurements on hybrid graphene/gold substrates with the dye Crystal Violet show an enhancement factor of ~105 and also demonstrate the ability of graphene to quench photoluminescence by an average of ~60%.

Highlights

Surface-enhanced Raman spectroscopy (SERS) [1,2,3,4] is a powerful and highly selective tool that allows researchers to identify chemical compounds and determine the structure of materials and molecules based on their specific vibration bonds
We focus on a comprehensive analysis of ultrathin gold films with thicknesses close to the percolation threshold, deposited on SiO2/Si wafers with and without a single-layer CVD graphene for SERS applications
We demonstrated that the thickness of the deposited gold films measured by atomic force microscopy (AFM) and sensor values can vary significantly

Summary

Introduction

Surface-enhanced Raman spectroscopy (SERS) [1,2,3,4] is a powerful and highly selective tool that allows researchers to identify chemical compounds and determine the structure of materials and molecules based on their specific vibration bonds. One of the easiest and cheapest methods for the fabrication of large-area SERS substrates relies on the usage of semi-continuous metal films near the percolation threshold [20,21,22], the critical point at which individual metal clusters start forming connected structures across the substrate domains [20,23,24]. The concentration of such hot spots (along with the average value of the SERS signal gain) is expected to be maximal near the percolation threshold [22,25]. The interest in graphene is mainly due to its biocompatibility and ability to quench photoluminescence [32,33]

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Results

Conclusion