Large-area and clean graphene transfer on gold-nanopyramid-structured substrates: implications for surface-enhanced Raman scattering detection

The transfer of large-area and clean graphene to arbitrary substrates, especially to those with raised nanostructures, represents a great challenge. Polymer-based supporting layers generally lead to organic residues, while graphene transfer using alternative supporting materials like paraffin suffers from breaking and thus limits the transfer area. We demonstrated an improved poly(methyl methacrylate) (PMMA)/paraffin double layer, enabling the large-area transfer of graphene with high cleanliness and high coverage (81%) onto gold nanopyramid (AuNP)-structured substrates. The impact of supporting layers including single PMMA or paraffin and mixed PMMA/paraffin was clarified. The properties of graphene on AuNPs were theoretically and experimentally examined in detail. Raman spectra show a polarization-dependent D peak due to the folding of large-curvature graphene. The graphene on AuNPs shows a slightly tensile strain and provides extra surface-enhanced Raman scattering (SERS) with an enhancement factor of ∼20 times. These findings open a pathway to extend the applications of transferred graphene on raised nanostructures in many fields, such as SERS detection, catalysis, biosensors, light-emitting diodes, solar cells, and advanced transparent conductors.