Fig. 2: Graphene as model surface to probe surface-sensitive Raman scattering by nanoporous Au membranes.

a Sample schematic where a graphene flake on a 300 nm SiO₂ on Si substrate is partially covered by a PAuM. Raman spectra of the bare graphene (black, reference) compared to spectra from graphene plus PAuM for (b, green) 532 nm, (c, red) 660 nm, and 785 nm (d, purple) excitation. The background in b–d stems from gold luminescence with a modulation due to etaloning for 532 nm. e First-order Silicon Raman peak with PAuM for 532 nm (green), 660 nm (red), and 785 nm (purple) normalized and compared to the corresponding reference Raman spectra (black) without PAuM. The spectra for each wavelength are offset for clarity. f Microscope image of graphene flake (dashed turquoise) partially covered by PAuM (yellow). × (with PAuM) and # (reference) mark the locations of the spectra shown (b–e). The dashed line marks the location of the spatial profile shown in j. Spatial Raman maps of the graphene 2D mode for g 532 nm, h 660 nm, and i 785 nm excitation. For each excitation wavelength, the intensity is normalized to the 2D intensity of bare graphene reference with interference effect taken into account. j Spatial profile of the normalized silicon Raman intensity along a horizontal line (dashed in f) through the locations x and # as indicated in f for all three excitation wavelengths. The arrow marks the edge of the PAuM. The scale bar in f–i is 2 μm.