Isotropic And Anisoropic Silver Nanoparticle Prepared By Light Irradiation Associated With Mechanism Analysis

Noble nanomaterial represented by gold, silver etc.is one of the most frontier research field in modern science, such as material science, micro and nano photonics, biophotoics and so on. Preparation of noble metal nanoparticles with different morphologies is an important area of manipulation of nanoparticles' properties. And with respect to the more stable gold material, silver nano material is always difficult to control its surface morphology. In conventional chemical methods, on the one hand, it is difficult to obtain a regular spherical shape by controlling the growth of crystal faces, on the other hand, the preparation conditions of anisotropic silver nano material which have directional properties are strict and complex. This article is intended using 248 nm excimer laser and continuous light source: mercury lamp and xenon lamp system to irradiate simply prepared precursor colloidal silver nanoparticles to explore new methods for preparing isotropic and anisotropic silver nanoparticles. And at the same time, structural analysis, characterization of the products of the preparation and mechanism of the physical processes are also be studied.This paper is divided into two components, we introduced the preparation of regular isotropic spherical silver nanoparticles using the excimer laser and anisotropic silver nanoparticles prepared using continuous light sources.In the first part, a simple sodium citrate reduction method is used to prepare irregular morphology silver nanoparticles, whose size distribution is in 80-90 nm.Then the nanoparticle sol use irradiated by a 248 nm excimer laser. Regular spherical isotropic particles was prepared. After the preparation TEM, SEM, absorption spectrum, etc. are used to characterize the products' properties to give the best preparation conditions. In characterizing the morphology, the paper presents a quantitative description of the closer degree of nanoparticles to a regular sphere “circularity”. Circularity can be used to visually illustrate the advantages of this preparation method. In the analysis of the mechanism, this paper improved "photothermal- phase change" theory to explain the nature of shape conversion.In the second part, silver nanoparticles prepared by simple chemical reduction is also used as teh precursor sol. But light sources are changed to the continuous light. Mercury lamp system is used to provide UV irradiation and xenon light system to offer visible light. Under different experimental conditions rod and triangular plate-like and other anisotropic silver nanoparticles are prepared. Characterization of the products help us to obtain the optimum parameters for the preparation of different morphologies. To explain the shape transition from irregular to anisotropy, this paper analyzes the mechanism and put forward an evolutionary model, "fragmentation- connection-growth", based on the experimental results.During the above two parts of the work, the products are all used as substrates of surface enhanced Raman scattering experiments to detect their Raman activities. SERS experiments show that both regular spherical and anisotropic silver nanoparticles have unique SERS characteristics. Both of them have the specific absorption and enhancement effects on different groups of the probe molecules.