Quantitative PEEM and Raman Study of Nanorough Au SERS-Active Substrates for Molecular Sensing Applications

Surface-enhancedRaman scattering (SERS) is a well-establishedsurface-sensitive technique for detecting trace amounts of molecularanalytes. While the impact of surface singularities on plasmonic materialshas been widely studied, the fabrication of cost-effective, efficientSERS substrates remains a challenge. In this paper, we present thestudy of large-area nanorough Au SERS-active substrates, elaborated by thermal evaporation deposition by photoemission electron microscopy(PEEM), a high-resolution near-field mapping technique, to accessthe statistical properties of the hot-spot distribution. We experimentallydemonstrate that the near-field PEEM and far-field Raman statisticalsignatures of nanorough Au surfaces are quantitatively correlatedwhen used for molecular sensing. The maximum of the SERS signal ofthiophenol (TP) molecules diluted to 10(-6) M is observednear the film percolation threshold for which the hot-spot densityis maximum. Finally, SERS measurements from solutions of TP, crystalviolet, and rhodamine B molecules at 10(-8) M demonstratedthe sensitivity of our substrates for molecular sensing.