CONICET | Buscador de Institutos y Recursos Humanos

Optical properties of metal nanostructures have generated a great scientific interest during the last years due to their broad prospects in nanoscience and nanotechnology. These properties have a strong dependence on the metal dielectric function, its size, shape and surrounding environment. For noble metals, the dielectric function of nanosized particles has been studied with detail, while other metals with potential applications have not studied yet.This work determines size dependent metal nanoparticle (NP) dielectric function based in a ?top-down? approach using the bulk Drude model as a first approximation. For this aim, the free-electron damping constant (γ_free) and plasma frequency (ω_p) Drude parameters are calculated using a method that lifts the usual approximation ω >> γ_free, which restricts the frequency values to the UV range. These calculations are made for nickel (Ni), molybdenum (Mo), tungsten (W), lead (Pb), zinc (Zn) and sodium (Na).With the values of these parameters, the expression for the bulk dielectric function may be modified introducing size-dependent corrections that allow the size-dependent complex dielectric function to be written as the sum of three terms: the experimental bulk dielectric function, a size corrective term for free electrons and other for bound electrons. Based on this expression, the behavior of the extinction spectra of metal particles in the nanometric and subnanometric radius range can be studied using the Mie theory.Finally, the theoretical analysis is applied to fit experimental extinction spectrum of Ni spherical nanoparticles (NPs) synthesized by ultrafast laser ablation of a solid target in water, and characterize the composition and size distribution of the particles in the colloidal suspension. Transmission Electron Microscopy (TEM) results agree with the sizes and structure obtained by Optical Extinction Spectroscopy (OES) of the NPs generated.