Modeling the optical properties of metal nanoparticles and metal-molecule systems

Open Access
Author:
Ewusi-Annan, Ebo
Graduate Program:
Chemistry
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 26, 2010
Committee Members:
  • Lasse Jensen, Thesis Advisor
Keywords:
  • plasmons
  • nanoparticles
  • Drude
  • Drude-Lorentz
  • PIM
Abstract:
In this thesis, we address two problems pertaining to light interacting with metal nanoparticles and metal-molecule systems. In the first project, we extract the dielectric functions of noble metal alloys (Au/Ag and Au/Cu) by fitting the experimental absorbance spectra using a Drude term and Lorentz oscillators to describe the dielectric functions. We are able to extract the dielectric functions successfully but we are unable to find any meaningful relationship between the fitted dielectric functions parameters for both alloy systems considered. In the second project, we calculate the the polarizabilities and hence absorption cross sections of metals and metal-molecule nanoparticles using the polarizabilty interaction model. We investigate the effect of shape and size on the absorption cross sections of silver (Ag) clusters of different motifs i.e icosahedra, ino decahedra, Marks decahedra and cuboctahedra. We show that the absorption cross sections increase with size for all the motifs. However the peak positions of the icosahedra and cuboctahedra clusters are the same while that of the ino and Marks decahedra blue shift with increase in size. We also investigate how the arrangement of adsorbed molecules on a cluster as well as the shape of the cluster affects the plasmon peak or absorption cross section evolution of the cluster. We find that the arrangement of the adsorbed molecules affects the way the plasmon peak evolves even though both types of arrangements considered converged to the same plasmon peak when the cluster was completely covered with molecules. We also show that the shape of the cluster influences the intermediate cluster-molecules plasmon peaks as they evolve.