Laser Ablation Preparation Of Noble Metal Nano-particles And Their Sers Study

With the development of science and technology, there are many different preparation methods of nanoparticlas. As we know,vapor phase synthetic method,sputtering method,chemical reduction method,laser compositing method and so on are all usual methods to prepare metal nanoparticles. However,because the laser compositing method can well control nanoparticles'uniformity and the scale in the preparing process,it is well used widespread in many fields.In this paper,we use the laser ablation method to prepare noble metal (Ag/Au) nanoparticles in redistilled deionized water,especially the Au shell/Ag core nanoparticles with tunable surface plasma resonance absorption frequency. The preparing processes of Ag/Au nanoparticals with different ablation time and laser energy density were studied. With the measuring tools of transmission electron microscope (TEM) and scanning eletron microscope (SEM),we analyzed the influences of the pulse laser energy density,laser frequency and ablation time to the metal nanoparticles'scaled-size,dispersibility and uniformity. Meanwhile,the ablated Ag/Au plate surface and Ag/Au nanoparticles in laser ablation process were studied at infrared laser wavelength.Surface-enhanced Raman scattering (SERS) is a highly sensitive technique for probing the interfacial phenomena and the behavior of molecules adsorbed on metal nanoparticles surface. In SERS optical spectroscopy, the noble metal Ag/Au nanoparticles can serve as a highly efficient substrate for SERS investigation,but in preveous reports,the SERS substrates,such as Ag and Au nanoparticles,were prepared by chemical reduction methods,these methods are simple and rapid,and the enhanced effects of SERS are are very obvious. However,during the process of producing the metal colloids,the presence of residual oxidation products and extraneous ions in the colloids can cause uncontrolled aggregation and diffusive double layer on the metal nanopartices surface,which will disturb the adsorption behavior between the molecules and the metal surface. All of these will bring out many comples factors for analyzing the physical and chemical mechanism of SERS.In this paper,we ablated Ag/Au plates in redistilled deionized water using pulsed laser and obtained"chemically pure'Ag/Au colloids and metal nanoparticles. No any extraneous ions were imported into the metal colloids during the preparing process. Thus,we could analyze expediently the experimental results. Furthermore, we compared the laser ablated metal surface with other SERS-active substrates and found that the metal surface was a high efficient SERS substrate.