Dependence of the localized surface plasmon resonance of noble metal quasispherical nanoparticles on their crystallinity-related morphologies This paper develops a novel method for simultaneously determining the plasma frequency x P and the damping constant c f ree in the bulk damped oscillator Drude model, based on 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 x p (0.5%-1.6%) and for c f ree (3%-8%), which are smaller than those reported in the literature. These small uncertainties in x p and c f ree 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 x p and c f ree 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 contributions. 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 Transmission Electron Microscopy (TEM). V C 2014 AIP Publishing LLC.

Synthesis of nickel (Ni) nanoparticles (NPs) suspensions was performed using a 120 femtosecond (fs) pulse laser to ablate a Ni solid target in n-heptane and water.Analysis of structure, configuration and sizing was carried out using different independent techniques such as Optical Extinction Spectroscopy (OES), Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM) and Electron Diffraction (ED), which yield interrelated information.AFM microscopy allows determining the spherical shape and size distribution of the NPs in the obtained colloids while TEM provides knowledge about shape, structure and size distribution. ED allows identification of the different metal and metal oxide composition as well as their crystallographic phase. On the other hand, OES gives information related to size distribution, structure, configuration and composition.Interpretation of these spectra is based on Mie theory which, in turn, depends on Ni dielectric function. For NPs radii smaller than 3 nm, size-dependent free and bound electron contributions to the dielectric function must be considered. To account for the full size span, complete Mie expansion was used for optical extinction cross-section calculations. A theoretical analysis of the dependence of plasmon resonance of bare core and core-shell Ni NPs with core size and shell thickness provide insight about their spectroscopic features.For n-heptane, species like bare core Ni and hollow Ni NPs are found in the colloid, being the latter reported for the first time in this work. Instead, for water, the colloid contains hollow nickel NPs and nickel oxide in different core-shell configurations: Ni-NiO and NiO-Ni, being the latter also reported for the first time in this paper. In both cases, size distribution agrees with that derived from TEM and AFM analysis. The formation of the oxide species is discussed in terms of oxidation-reduction processes during ablation. Possible mechanisms for the formation of hollow species are proposed.

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).