SERS of Isotopically Labeled 12C/13C Graphene Bilayer-Gold Nanostructured Film Hybrids: Graphene Layer as Spacer and SERS Probe

Single layer graphene (SLG) is envisaged to improve significantly the substrates for surface-enhanced Raman scattering of planar aromatic molecules as it can ensure a more even enhancement at different places of the substrate. For this purpose, the role of SLG as a spacer in such SERS platforms has to be addressed. Here, we report preparation and Raman spectral probing of hybrid systems constituted by C-13/C-12 bilayer graphene covered by 15 nm thick nanostructured gold. Hybrids with both the C-13 over C-12 layers and in the flipped geometry, and with both the turbostratic and the A-B stacked order have been investigated, and qualitative as well as quantitative information about the enhancement experienced by phonons of the individual graphene layers by the electromagnetic mechanism (EM) of SERS were obtained. In hybrids system under study, the top layer of the isotopically labeled bilayer graphene represents the SLG spacer, while the bottom layer mimics a monolayer of target planar aromatic molecules. Importantly, both the calculation and the experiment based chiefly on comparison of the relative intensity ratio of the clearly distinguished C-13 layer and C-12 layer G mode bands jointly indicate that the enhancement of Raman scattering of the molecular monolayer on SLG spacer by the EM mechanism of SERS will be only 0.7 times lower than that of a monolayer located directly on the nanostructured Au surface.