Optics of nanoparticles: Substrate, size and interface effects

We present recent theoretical and experimental studies of the optical properties of single noble metal nanoparticles and their dimers located near a substrate. The presence of a substrate or adjacent polarized particle influences the local field acting on the particle, leading to a shift in the extinction of light due to localized plasmon excitation (red or blue depending on the polarization of the applied field). We derive analytical expressions for the components of the effective dipole polarizability tensor of a dimer of spheres located near a plane substrate. We use the results to study the experimentally observed red and blue shifts of the plasmon resonance of the dimer as a function of the distance between the particles, and between the particles and the substrate. We present numerical modeling of the local near field distribution of the resonantly excited dimers of the noble metal nanoparticles near a substrate. We discuss recent results of experimental and theoretical investigations of TiN nanoparticles, which were produced by a laser ablation-evaporation technique followed by adiabatic expansion. We present their compositional and structural characterization using secondary ion mass spectrometry (SIMS), electron energy loss spectrometry (EELS) and X-ray diffraction (XRD). Transmission electron microscopy (TEM) analysis shows that TiN nanoparticles exhibit cuboid shapes. Optical transmission spectra of the TiN nanoparticles deposited on a quartz substrate indicate a pronounced plasmon resonance around 1.7 eV. The experimental optical extinction spectra of different samples were modeled using Mie theory calculations. The dielectric function of bulk TiN was modified to account for size and interface damping of the surface plasmon resonance. Due to the distinct absorption band, TiN may be used as a color pigment. The dependence of the color stimulus on the extinction cross section as well as on the product of the particle concentration and the sample thickness were examined.We discuss the interface decay channel of the surface plasmon resonance in metallic clusters embedded in a matrix. This non-classical broadening effect is caused by adsorbate induced local density of states near the Fermi level of the cluster. We study theoretically the broadening effect for realistic small noble metal clusters. The broadening of the surface plasmon resonance caused by the interface decay channel is significantly influenced by interband transitions in the metallic cluster. Finally we discuss the influence of electronic interband transitions on the surface plasmon excitations in metallic nanoparticles. We derive expressions for the resonance frequency and bandwidth of the light absorption cross section of noble metal nanoparticles, taking into account interband transitions in the dielectric function. We propose a simple method for determining the width of the plasmon resonance based on an analysis of the dielectric permittivity of the constituent metal.