We dispersed silver nanospheres of diameter 5nm in a homogeneous binder. Films were spin-coated on glass substrates. The transmission spectra of such films are measured as particle concentration is varied. The transmission spectra show deeper and wider minima in the shorter wavelength side as the concentration of nanoparticles increase. This might be explained by the formation of aggregates of nanoparticles and the coherent interaction among the constituent elements of the aggregates. The coherent interaction can include coupling among the localized surface plasmon resonance (LSPR) modes of individual particles. To explain the dependence of transmission spectra on the concentration of particles we computed the scattering properties of particle aggregates. The scattering properties of a single spherical particle can be computed analytically using Mie theory. No analytical computation method is available for aggregates of nanoparticles. Numerical methods, like finite-difference time-domain (FDTD) method can be used. We computed the scattering properties of aggregates of silver nanospheres using a monochromatic version of recursive convolution finite-difference time-domain (RC-FDTD) method. In contrast with the conventional broadband RC-FDTD [3], the monochromatic version allows one to use the handbook values of permittivity of the material of the particles at every simulation wavelength. The algorithm employs the 1st order Drude model to make it stable for metals with negative real part of permittivity. The particle-aggregates are generated using a random number generator that distributes nanospheres uniformly throughout a larger sphere made of the homogeneous binder medium.

Date Published: 28 August 2014
PDF: 4 pages
Proc. SPIE 9170, Nanoengineering: Fabrication, Properties, Optics, and Devices XI, 91700M (28 August 2014); doi: 10.1117/12.2062483

Published in SPIE Proceedings Vol. 9170:
Nanoengineering: Fabrication, Properties, Optics, and Devices XI
Eva M. Campo; Elizabeth A. Dobisz; Louay A. Eldada, Editor(s)