Nanosphere Lithography: Surface Plasmon Resonance Spectrum of a Periodic Array of Silver Nanoparticles by Ultraviolet−Visible Extinction Spectroscopy and Electrodynamic Modeling

Abstract

In this paper we measure the optical extinction spectrum of a periodic array of silver nanoparticles fabricated by nanosphere lithography (NSL) and present detailed comparisons of the results with predictions of electrodynamic theory. The silver nanoparticles are small (∼100 nm) compared to the wavelength of light but too large to have their optical properties described adequately with a simple electrostatic model. We make use of the discrete dipole approximation (DDA), which is a coupled finite element method. With the DDA one can calculate the extinction of light as a function of wavelength for particles of arbitrary size and shape. We show that NSL-fabricated Ag nanoparticles can be modeled without adjustable parameters as truncated tetrahedrons, taking their size and shape parameters directly from atomic force microscopy (AFM) measurements and using literature values of the bulk dielectric constants of silver. These AFM measurements are presented as part of this paper, and the resulting theoretical li...