Size-dependent complex dielectric function of Ni, Mo, W, Pb, Zn and Na nanoparticles

Abstract

This work determines the size dependent metal nanoparticle (NP) dielectric function from a top-down approach using the bulk experimental refractive index as a starting point. Freeelectron damping constant (γ_free) and plasma frequency (ω_p) parameters in the Drude model are calculated for nickel (Ni), molybdenum (Mo), tungsten (W), lead (Pb), zinc (Zn) and sodium (Na) using a method developed in our group. Determined γ_free and ω_p parameters allow to develop an expression that improves the precision in reproducing the discrete metal bulk dielectric function in a wide wavelength range (UV-FIR). The bulk dielectric function is modified for describing the nanometric case by adding size corrective terms for free and bound electrons contributions. As an application of this study we characterize Ni spherical NPs synthesized by ultrafast laser ablation of a solid target in water. Using Mie theory together with the size-dependent dielectric function, we theoretically reproduce its experimental extinction spectrum. From this fitting, composition and size distribution of the particles in the colloidal suspension may be derived. Transmission electron microscopy (TEM) results agree with the sizes and structure derived from optical extinction spectroscopy (OES).