Nanoscale Dielectric Function of Fe, Pt, Ti, Ta, Al, and V: Application to Characterization of Al Nanoparticles Synthesized by Fs Laser Ablation

Abstract

Development and applications of new nanomaterials and nanocomposites that include metal nanoparticles have received much attention in the last years. However, there are relatively few studies concerning basic physical characteristics of the dielectric function at the nanoscale, which is needed for predicting their optical and plasmonic response. The size-dependent complex dielectric function of metal Fe, Pt, Ti, Ta, Al, and V nanoparticles (NPs) is calculated for the first time for an extended wavelength range from UV to FIR, based on experimental bulk complex refractive index measurements in the mentioned range at room temperature. Calculation is based on a Btop-down^approach, based on a stepwise modification of the Drude model. Bulk plasma frequency (ω p ) and damping constant (γ free ) in this model are determined using a method that improves the relative uncertainties in their values and provide an insight about the wavelength range over which the metal may be considered Drude like. Validation of ω p and γ free values is demonstrated by the improved accuracy with which the experimental bulk dielectric function is reproduced. For nanometric and subnanometric scales, dielectric function is made size dependent considering sizecorrective terms for free and bound electron contributions to the bulk dielectric function. These results are applied to analyze the synthesis of Al NP suspensions using a 120-fs pulse laser to ablate an Al solid target in n-heptane and water. The presence of Al, Al-Al 2 O 3 , and air-Al core-shell structures is also reported for the first time in these type of colloids. Analysis of the structure, configuration, sizing, and relative abundance was carried out using optical extinction spectroscopy (OES). Sizing results are compared with those provided by atomic force microscopy (AFM) studies.

Determination of thickness-dependent damping constant and plasma frequency for ultrathin Ag and Au films: nanoscale dielectric function

“…Within the Drude model approach, it is important then to determine the size dependent damping constant and plasma frequency optical constants for studies related to photonics, 11 plasmonics, 12,13 clusters of NPs 14 and characterization of nanostructures by Optical Extinction Spectroscopy. [15][16][17][18][19][20][21] Knowledge derived from these studies may be used for on-demand design of devices for specific applications.…”

Nonlocal and Size-Dependent Dielectric Function for Plasmonic Nanoparticles

“…This can be attributed to two effects. First of all, their imaginary part of the interband contribution due to size-dependent effects is not negligible in the spectral region of surface plasmon polariton resonance [14,15]. Second, nonlocal effects due to the scattering of the conduction electrons arise as the nanoparticle size is decreased, relative to metal films [39,40].…”

“…Therefore, in order to overcome this difficulty in a classical mean free path approach, a more reasonable alternative way for describing size-dependent dielectric functions is needed by considering the dominated conditions and a scope of the contributions of intraband transitions (free electrons) and interband transitions (bound electrons). Herein, according to previous studies about suitable modification of the bulk complex dielectric function for free and bound electrons within metallic nanoparticles [14][15][16], the full size-corrected dielectric function can be written as the sum of three terms:…”

“…Recent studies have shown a theoretical method with a suitable modification of the bulk complex dielectric function for free and bound electrons within metallic nanoparticles [14][15][16][17][18][19], for the determination of plasma frequency, damping constants, and size distributions of noble metal nanoparticles, such as gold, silver and copper; in addition, the corresponding optical characterization deduced by Mie's theory has been tested to fit full UV-Vis experimental extinction spectra. The above theoretical framework follows the idea of Kreibig and von Fragstein [20], who considered that the augmentation of the damping constant in the Drude model results from additional collisions of free electrons with the particle boundary, as well as the idea of Inouye et al [21], who took into account the interband transitions of bound electrons for the complex dielectric function.…”

“…Under this theoretical framework, the significant finite-size effects of optical properties for metallic nanoparticles can be expected to be observed below a certain limited size range (e.g., valid restriction of 20 nm drawn from Refs. [14,15]).…”