CONICET | Buscador de Institutos y Recursos Humanos

This paper develops a novel method for simultaneously determining the plasma frequency ω_P and the damping constant γ_free in the bulk damped oscillator Drude model, based on the experimentally measured real and imaginary parts of the metal refractive index in the IR wavelength range, lifting the usual approximation that restricts frequency values to the UV - deep UV region. Our method was applied to gold, silver and copper, improving the relative uncertainties in the final values for ω_p (0.5 ? 1.6 %) and for γ_free (3 ? 8 %), which are smaller than those reported in the literature. In a ?top-down? approach, these small uncertainties in ω_p and γ_free determination yield a much better fit of the experimental complex dielectric function. For the case of nanoparticles (Nps), a series expansion of the Drude expression (which includes ω_p and γ_free determined using our method), enables size-dependent dielectric function to be written as the sum of three terms: the experimental bulk dielectric function plus two size corrective terms, one for free electron and the other for bound-electron contribution. Finally, size distribution of nanometric and subnanometric gold Nps in colloidal suspension was determined through fitting its experimental optical extinction spectrum using Mie theory based on the previously determined dielectric function. Results are compared with size histogram obtained from TEM microscopy.

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