A near field optical image of a gold surface: a luminescence study

International audienceThis paper addresses recent experimental findings about luminescence of a gold tip in near-field interaction with a gold surface. Our electrochemically etched gold tips show a typical, intrinsic luminescence that we exploit to track the plasmon resonance modeled by a Lorentzian oscillator. Our experimental device is based on a spectrometer optically coupled to an atomic force microscope used in tuning fork mode. Our measurements provide evidence of a strong optical coupling between the tip and the surface. We demonstrate that this coupling strongly affects the luminescence (Intensity, wavelength and FHWM) as a function of the tip position in 2D maps. The fluctuation of these parameters is directly related to the plasmonic properties of the gold surface and is used to qualify the optical near field enhancement (which subsequently plays the predominant role in surface enhanced spectroscopies) with a very high spatial resolution (typically around 20 nm). We compare these findings to the independently recorded near-field scattered elastic Rayleigh signal

Relation between plasmonic tip emission and electromagnetic enhancement evidenced in tip-enhanced Raman spectroscopy

International audienceWe report tip-enhanced Raman spectroscopy measurements of single wall carbon nanotubes deposited on a barium titanate substrate. The tip-enhanced Raman spectroscopy mappings demonstrate that the evolution of the gold tip enhanced luminescence is strongly correlated with the intensity of the Raman modes from the single wall carbon nanotubes and the substrate. As the tip emission is directly related to the plasmonic properties of the nanoantenna at the apex of the tip, it is possible to compare the frequency and intensity of each vibrational mode with the electromagnetic enhancement model. We find a very good agreement between all these parameters confirming the essential role of the electromagnetic enhancement mechanism in surface enhanced spectroscopy

High resolution scanning near field mapping of enhancement on SERS substrates: comparison with photoemission electron microscopy

International audienceThe need for a dedicated spectroscopic technique with nanoscale resolution to characterize SERS substrates pushed us to develop a proof of concept of a functionalized tip–surface enhanced Raman scattering (FTERS) technique. We have been able to map hot spots on semi-continuous gold films; in order to validate our approach we compare our results with photoemission electron microscopy (PEEM) data, the complementary electron microscopy tool to map hot spots on random metallic surfaces. Enhanced Raman intensity maps at high spatial resolution reveal the localisation of hotspots at gaps for many neighboring nanostructures. Finally, we compare our findings with theoretical simulations of the enhancement factor distribution, which confirms a dimer effect as the dominant origin of hot spots