Scanning Near-field Optical Microscopy for the Characterization of the Localized Surface Plasmon Resonance of Metallic Nanoparticles

Abstract

Metallic nanoparticles have shown special interest in different areas since they present unique properties, particularly through Surface Enhanced Raman Scattering (SERS) effect with noble metals like Ag and Au being used as substrates to enhance Raman signal. Since the enhancement is quite dependent on morphological and optical nanoparticles' properties, it is extremely important to understand their properties in a deeper way to elucidate the phenomenon of localized surface plasmon resonance (LSPR). Techniques such as Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) are commonly used for nanoparticles' morphology and structure characterization. However, to obtain information about their subwavelength optical properties, Scanning Near-field Optical Microscopy (SNOM) is the technique of choice to provide direct information regarding the LSPR excitation, allowing the correlation between nanoparticles morphology and the enhanced local field. Also, one of the advantages is that this technique can be coupled with Atomic Force Microscopy (AFM), providing at the same time topographical and optical mapping of nanoparticles. In this project, our goal is to investigate systematically different nanoparticles by SNOM technique in order to deep understand how the LSPR is dependent on size, shape, and nature of the metallic nanoparticles.