Studying The Scattering Properties Of Gold And Silver Nanoparticles

Noble metal nanoparticles, such as silver and gold nanoparticles, have been widely investigated, because their unique chemical and physical properties in the filed of optics, electronics, magnetism, and catalysis, which are strongly size and shape dependent. For the case of their optical properties, noble metal nanoparticles with different size and shape possess distinct scattering and absorption properties, giving a variety of characteristic surface plasmon resonance (SPR) properties. In order to investigate their scatting property, In 1908,Mie presented a solution to Maxwell's equation that describes the extinction spectra of spherical particles of arbitrary size. Mie's solution remains of great interest to the day, it is the only simple, exact solution to Maxwell's equation that is relevant to particles. In addition, most of the standard colloidal preparations yield particles that are approximately spherical, and most of the optical methods for characterizing nanoparticles spectra probe a large ensemble of these particles. This leads to results that can be modeled reasonably well using Mie-theory. More recently, new lithographic techniques as well as improvements to classical wet chemistry methods have made it possible to synthesize noble metal nanoparticles with a wide range of sizes, shapes, and dielectric environments. There has been growing interest in characterizing the optical properties that are made using lithographic methods such as nanosphere lithography, e-beam lithography, and other methods, which produce well-defined sizes and nonspherical shapes without aggregation. In addition, variations on classical wet chemistry techniques have been developed that give high yields of nonspherical particles. The modern generation of metal nanoparticle science, including applications to medical diagnostics and nanooptics, have provided new challenges for theory. All of these factors motivate the need for theory that can describe the electrodynamics of nanoparticles of arbitrary shape and size subject to a complex external dielectric environment.In this feature article, First, We choose silver nanoparticles as the object and synthesized two kinds of silver nanoparticles, in shape of triangle, disk-like with controllable size and described their properties of extinction by uv-vis spectrometer. Secondly, in order to study the scatting properties of synthesized silver nanoparticles, we measured their properties making use of experiments. Furthermore, we give a brief description of modern numerical techniques that can treat arbitrary particles and environments, and then, we describe applications of these techniques to problems of recent interest, using a method known as the discrete dipole approximation (DDA).Our applications include studies of the particle size and shape dependence of absorption,extinction and scattering coefficients, which can be directly compared with experiments. There are mainly there aspects in this thesis listed as follow:1. Synthesis of triangular and circle silver nanoplates.Triangluar silver nanoplates were synthesized by irradiating the growth solution, which contained silver nanoseeds, silver cations, and citrate anions. The sodium lamp was chosen as the light source. The citrate anions in the system acted as both reducing agents and stabilizers. the silver nanodisks were synthesized by a thermal etching method, in which the triangular nanoplates were used as theprecursors. This process occured under a certain molar ration between silver cations and citrate anions.2. Studying the scattering properties of nanoparticles via experiment.Triangular and circle silver nanoplates were monitored by the UV-vis spectrometer. Their extinction and scattering coefficients was obtained by resonance light scatting technique and an integrating sphere detector, which were made by reviews and simple remarks on application of the technique.3. Studying the scattering properties of nanoparticles via numerical techniques– the discrete dipole approximation (DDA).A theoretical approach, where is used to account for the trends in the measured cross sections. The nanoparticles were treated as an induced dipole for which the dipolar polarizability is calculated based on triangular and circle silver nanoplates in the dielectric medium surrounding them.We believe that this study can be very useful to determine and optimize some of the physical properties nanoparticles by controlling their shape and size ,to motiviate future measures of scattering spectra of nanoparticles.