Diagnostics of aqueous colloids of noble metals by extinction modeling based on mie theory

Abstract

Two-factor dependences of the maximum and half-width of a surface plasmon resonance band on both the average diameter of nanoparticles and the scatter in their particle-size distributions were defined for colloidal silver and gold aqueous solutions based on modeling the extinction effectiveness factor by Mie theory. The obtained three-dimensional surfaces determined the shape of calibration curves used to define the average particle diameters and the scatter in their particle-size distributions from measurements of the maximum and half-width of the surface plasmon resonance band in spectra of the silver and gold colloidal solutions. The calibration curves were correlated with experimental samples of aqueous ultradispersed media containing silver and gold nanoparticles.Keywords: colloidal solutions of noble metals, laser erosion, absorption spectroscopy, transmission electron microscopy, scanning electron microscopy, surface plasmon resonance.Introduction. Nanotechnology, which addresses the production and application of nanostructured materials, is currently undergoing vigorous growth [1]. The field is in need of effective diagnostic methods for the parameters of nanoscale materials in a wide variety of media. A characteristic example of this problem is the study of the properties of metal colloids. Traditional methods of visualizing single minute structures (scanning and transmission electron microscopy and atomic force microscopy) provide in this instance little information because they all require a vacuum in the studied region. The colloid actually ceases to exist after deposition on a substrate. Moreover, as a rule, the location of the visualized nanostructure on the sample surface has a considerable influence on its parameters.Many researchers proposed using a surface plasmon resonance (SPR) band to study ultradispersed metal-containing optical media (at least to determine the average particle size d ). The principal studied factor often turns out to be the spectral position of the SPR band maximum [2-10]. According to seminal work in the study of the interaction of optical radiation with ultradispersed media [11-13], the type of particle material, their size and shape [14], the internal structure (layering, presence of inclusions) [3,9,14], characteristics of the medium environment, ordering of the particles [14,15], and the scatter in the particle-size distribution are among the dominant parameters that affect the spectral shape of the SPR band.Discussions of the spectral position of the SPR band maximum (λ max ) [2, 3, 5-7] mentioned the actual particle material in a certain optical medium and, as a rule, used spherical monolithic particles evenly distributed throughout the medium volume without scatter in the particle-size distribution (i.e., the particle-size distribution scatter σ = 0) as an approximation. We agree with all these assumptions except for the last because they enable a good approximation for an acceptable estimate of to be obtained d . Nullifying the contribution of the particle-size dis...

Predicting the Surface Plasmon Resonance Wavelength of Gold–Silver Alloy Nanoparticles

“…■ THEORETICAL METHODS SPR wavelengths were derived from extinction spectra of monodisperse spherical nanoparticles simulated using Mie theory 2,13 with the software package MiePlot (v4300). 14 While accurate values of dielectric constants of the pure metals are available, 15 this information is scarce for alloys.…”

Two-Step Synthesis of Large Gold–Silver Alloy Nanoparticles via the Combination of Seeded Growth and Citrate Co-reduction

“…UV–vis extinction spectra of gold–silver alloy and pure gold/silver nanoparticles were simulated by software based on Mie theory, , namely, MiePlot (v 4.6) . The dielectric constants of alloy and pure gold/silver nanoparticles were calculated using a reported model. , …”

Investigation of Noble Metals Colloidal Systems Formed by Laser Synthesis at Air

“…In order to determine the spectral shape efficient factor of extinction the approach was used based on the theory of interaction of electromagnetic field with small spherical particles, proposed by Mie [12,13]. This theory is widely used for modeling of the optical characteristics of low-dimensional objects [14,15], it is based on the decomposition of electromagnetic fields interacting with a small particle on vector spherical harmonics, with subsequent calculation of the coefficients of this distribution. The main positions of the approach are presented in [16].…”