Plasmon-Enhanced Raman Scattering by Multilayered Graphene at the Micro- and Nanoscale: SERS and TERS Analysis

Abstract

This work is devoted to the study of plasmon-enhanced Raman scattering by the fundamental vibrational modes of multilayered graphene films. The film thickness was ∼3.5 nm, which corresponds to ∼10 monolayers. Multilayered graphene films were placed on a plasmonic substrate consisting of arrays of gold nanodisks (50–250 nm in diameter). Surface-enhanced Raman scattering by the main vibrational modes of multilayered graphene film placed on an array of Au nanodisks of various sizes was implemented. The measurements were performed at excitation wavelengths of 532, 638, and 785 nm. A resonant SERS enhancement of the main vibrational modes of multilayered graphene by a factor of 25 was achieved for nanodisks with a diameter of 103 nm upon excitation at 638 nm. A stronger local enhancement of Raman scattering in multilayered graphene (by a factor of 50) placed on Au nanodisk array is achieved using gap-mode tip-enhanced Raman scattering (gap-mode TERS). Nanofolds in the graphene film appeared due to the corrugated surface of the plasmonic substrate were visualized with nanometer spatial resolution. It is shown that the frequency positions of G and 2D modes of nanofolds decrease with respect to the corresponding values in flat multilayered graphene manifesting mechanical stresses in the nanofolds up to 0.7%. The results obtained shed light on the effects of the interaction of multilayered graphene with metal nanostructures and are important in creating hybrid metal/graphene plasmonic substrates.