An Experimental Investigation On The Preparation Of Ag Nanoparticles By Femtosecond Laser Ablation

In recent years, nanomaterials have been exploited for the extensively potential applications in many fields, such as optics, electronics, magnetics, biomedicine, sensing, due to their unique surface effect, volume effect and quantum effect that are different from macroscopic bulk phases. Because of these properties, more and more people have been attracted to devote themselves into this field. Among all kinds of nanomaterials, gold(Au) and silver(Ag) nanomaterials which have fascinating optical and electrical properties, have been the subjects of a large number of studies for fundamental interests and practical applications. The peculiar properties of nanomaterials are determined by their size, morphology, composition, crystalline and assemble structures,thereby size-controlled and morphology-controlled preparation of nanomaterials is very important. At present, various synthesis methods for Au and Ag nanoparticles have been reported, as we know,vapor phase synthetic method,sputtering method,chemical reduction method,laser ablation method and so on are all usual methods to prepare metal nanoparticles. However, because the laser ablation method can well control nanoparticles'size and the morphology in the preparing process, it is well used widespread in many fields.In this paper, the noble metal(Ag) nanoparticles were prepared by focusing femtosecond laser pulses on the solid samples in aqueous solutions. The shapes of ablation craters on the Ag surface have been determined by scanning eletron microscope (SEM). The size and morphology of the produced Ag nanoparticles were measured by transmission electron microscope (TEM). The absorbance spectra were measured by UV–visible(UV–Vis) spectrophotometer. The Line width ,line shift and the line intensity of the measured surface plasmon resonance (SPR) spectrum were obtained. The effects of pulse laser energies and the interaction time interval between laser and Ag target surface on the morphology, size and its distribution, and the concentration of the produced Ag nanoparticles were investigated.This paper is divided into three chapters. In chapter one, we introduced the basic concepts, properties and the research development of the nanomaterials. The applications, synthesis methods, Characterization methods of nanoparticles were also summarized in detail. In chapter two, we mainly introduced the setup and measurement methods of this experiment in which Ag nanoparticles were prepared by ablating a solid Ag target submerged in redistilled water by femtosecond pulse laser. The size, morphology, uniformity and spatial dispersity of Ag nanoparticles was studied by different ablation time interval and different laser energy. At the same time, the stability of Ag colloids and the craters of Ag target were investigated. The results show that generated Ag nanoparticles are spherical, the average diameter and distribution of Ag nanoparticles is increased with the increase of ablation energy. the average diameter and distribution region of Ag nanoparticles is decreased and the spatial dispersity of Ag nanoparticles is better with the increase of the laser ablation time interval. Ag colloids produced in the solution are prone to gather after a few days and Ag target surface ablated by laser has nanometer level ablation craters. In chapter three, Ag nanoparticles were prepared by ablating a Si target immerged AgNO₃ solution by femtosecond laser. we analyzed the influence of the different ablation time interval and the different concentrations of AgNO₃ solutions on the size and the morphology of the produced Ag nanoparticles. The results show that generated Ag nanoparticles are spherical, the size keeps unchanged with the increase of laser energy, ablation time interval and the concentration of AgNO₃ solution. But the concentration of Ag nanoparticles increases firstly and then decreases.