Plasmon Mediated Multiphoton Photoemission Microscopy of Au Nanoholes and Nanohole Dimers

Abstract

Multiphoton photoemission from “nanoholes” and “nanohole dimers” fabricated by nanosphere shadow lithography in a thin Au film are investigated by ultrafast scanning photoionization microscopy (SPIM), which provides detailed information on laser polarization and local electric field enhancement effects for novel 2D plasmonic architectures. The net photoemission signals (at 800 nm) from isotropic nanohole monomers both (i) below (d ≪ λ) and (ii) comparable to (d ≈ λ) the diffraction limit are insensitive to laser polarization, though SPIM images of the larger species clearly reveal strongly enhanced electron emission from nanohole tangent edges perpendicular to incident laser polarization. Fundamentally contrasting behavior is observed for intrinsically anisotropic plasmonic architectures such as nanohole dimers. Specifically, small nanohole dimers reveal enhanced electron emission for λ = 800 nm light polarized perpendicular to the dimer axis, whereas larger nanohole dimers produce optimum electron yields...