Influence of gold nanoholes and nanoslits arrays on Raman spectra and optical reflectance of graphene oxide

We report the effect of gold nanostructured substrates, fabricated by interference lithography technique (IL), on the Raman spectra and optical reflectance of graphene oxide (GO) layers. For purposes of comparison two gold nanostructured substrates, nanoslits (AuNSs) and circular nanoholes (AuNHs) were compared with a non-nanostructured gold substrate. Effects induced by the gold nanostructured substrates are discussed in terms of the I_D/I_G ratio and the FWHM of the G band (FWHM(G)) as a function of the G band intensity (I_G), showing that both I_D/I_G and FWHM(G) parameters are highly sensitive to the number of GO layers (n_GO), which would allow to identify the number of GO layers in a reliable way. Optical reflectance spectra (R(λ)) reveal that plasmons are generated on the surface of nanostructured substrates by the incident radiation. Dips in R(λ) are ascribed as coupling by surface plasmon polaritons described by Bloch waves (BW-SPP). A peak in R(λ) is also observed and it is ascribed to visible radiation produced by Förster resonance energy transfer and Purcell effect. The relevance of these results lies in the possibility of designing colorimetric plasmonic sensors, based on few layers of GO with an excellent control of n_GO and with potential in detection of molecules by fluorescent absorption.