Enhancement of Raman signal of monolayer graphene films using a single optical microsphere-assisted Raman microscopic technique

Abstract

For the first time, we report the enhancement of the Raman scattering signal of monolayer graphene films (MGFs) on Cu foils using a single optical microsphere-assisted Raman microscopic (SOMRM) technique. Initially, the Raman scattering spectra of MGF on Cu foil are recorded using the conventional Raman microscopic (CRM) technique, where the excitation laser is directly focused on the MGFs with the help of a different microscopic objective lens. The obtained spectra are observed to consist of only the low-intensity G and 2D bands but not the D band, known as the disorder or defect band. However, the intensity of all three bands is enhanced significantly using the SOMRM technique. Finally, the numerical investigation is performed on the SOMRM technique to understand the origin of the enhancement of the Raman scattering signal of MGF on the Cu substrates. The role of the substrate for MGF and the radius of the microsphere on the enhancement of the Raman scattering signal of MGFs is also investigated numerically in detail.