Mapping Hot-Spots in Hexagonal Arrays of Metallic Nanotriangles with Azobenzene Polymer Thin Films

Abstract

Metallic nanotriangles arranged in a hexagonal lattice are common nanostructures used for surface-enhanced Raman spectroscopy. Such structures, generally made by nanosphere lithography or electron beam lithography (EBL), exhibit localized surface plasmon resonance (LSPR) at the junctions between two facing nanotriangles. Localized and efficient enhancement of the electromagnetic field is expected when light with the matching LSPR frequency is impinging the sample. Herein, first, we report modeling of the electromagnetic field for both gold and silver structures, made by EBL, when irradiated with a linearly polarized beam at 532 nm. The total and the polarized components are calculated using the finite-difference time domain method. Second, using atomic force microscopy and a photosensitive polymer that undergoes surface deformation upon irradiation, we map the LSPR (hot-spots) over these metallic arrays.