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

TL;DR

This study uses near-field optical imaging with a gold tip and atomic force microscopy to investigate plasmon resonance and luminescence, revealing strong tip-surface coupling and high-resolution surface characterization.

Contribution

It introduces a novel experimental setup combining spectroscopy and AFM to analyze plasmonic properties and luminescence at nanometer scales on gold surfaces.

Findings

Strong optical coupling affects luminescence parameters.

Luminescence fluctuations relate to plasmonic properties.

Achieves ~20 nm spatial resolution in near-field imaging.

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.