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

Abstract

This 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

“…Our experimental setup has been described in a previous publication . Basically, we performed TERS measurements with homemade etched gold tips with a 632.8 nm laser excitation.…”

“…Our experimental setup has been described in a previous publication. [20] Basically, we performed TERS measurements with homemade etched gold tips with a 632.8 nm laser excitation. The typical optical resonance of such tips reported in the literature is located between 600 and 800 nm, [21,22] which is in good agreement with our laser excitation.…”

Optical near-field mapping of plasmonic nanostructures prepared by nanosphere lithography

“…Mitutoyo MPlan Apo 100× objective placed under a 65° inclination was used to focus the laser onto a gold tip. A schematic of the experimental setup can be found elsewhere [ 37 ]. The elastically backscattered signal detected by a PMT was studied here.…”

Topography-induced variations of localized surface plasmon resonance in tip-enhanced Raman configuration

“…[6] aSNOM combines the high spatial resolution of conventional scanning probe microscopy (SPM) with the high sensitivity of surface enhanced optical analysis. [7,8] In our previous work, we used aSNOM to image changes in average refractive index of a variety of materials at the nanoscale. These studies were performed with a plasmonic gold tip in TERS configuration.…”

“…The first contribution is the luminescence of the gold tip, which is an intrinsic property that can be attributed to the gold inter-band d-sp transitions. [8,12,13] This gold luminescence has a broad feature extending to high wavenumbers, broad enough to be considered locally flat within the spectral range of interest. The second contribution is the LSPR that results from a large number of free electrons oscillating collectively at the tip apex following its excitation by the incident laser.…”