Controllable Preparation And Formation Mechanism Of Metal Nanoparticles Used For Surface Enhanced Raman Scattering Substrate

Nowadays,metal nanoparticles have attracted wide attention used for surface enhanced Raman scattering(SERS)substrate due to their high sensitivity,stability and biocompatibility.The performance of SERS substrate is closely related to the diameter and gap of nanoparticle.Therefore,the controllable preparation of metal nanoparticle can lay the foundation for the wide application of SERS substrate in various fields.In this work,the Ag nanoparticle(Ag NPs)and Au NPs deposited by magnetron sputtering combining annealing were prepared and used as SERS substrates.The Ag film deposited by magnetron sputtering was treated by within-situ annealing and ex-situ rapid thermal annealing,and we performed a comparison study on the surface topography evolutions and agglomeration mechanisms of Ag films under the two thermal annealing method.The Ag NPs deposited by magnetron sputtering following by rapid thermal annealing were prepared as SERS substrate.Moreover,we also researched the evolution of Au film under different annealing temperature,and a thermodynamic model is adopted to explain the shape transition.The simple physical approach to prepare regular hexagonal Au NPs with sharp edges exhibits a SERS effect with high enhancement.The main results of the experiment are as follows:1.The in-situ(the heating rate is 0.33℃/s,1.0×10-5 Pa)annealed Ag films agglomerate via voids nucleation followed by the fractal growth of voids,which leads to the appearance of large small-sized nanoparticle.Moreover,we found that the critical void radius upon which the void growth is favored decreases with increasing the annealing temperature.For the case of rapid annealing(the heating rate is100℃/s,N2),the agglomeration of Ag films follows the grain boundary grooving mechanism due to the rather high heating rate.Compared with the in-situ heating process,the rapid annealing treatment allows a more uniform size distribution of the nanoparticles.2.Based on the method of uniform Ag NPs by magnetron sputtering following thermal rapid annealing,the optimized parameters for Ag NPs were confirmed by the theoretical and experimental results.The function relationship between the size,gap of NPs and the thickness of Ag films guides the obtainment of SERS substrate with optimized size.Moreover,the Ag NPs with optimized size and gap present high reproducibility and uniformity as SERS substrates.3.The shape evolution process of Au nanoparticles with the aspect ratio from 1.8,1.2 to 1.0 under different annealing temperature was studied,and a thermodynamic model is adopted to explain the shape transition.When the annealing temperature is 900℃,the Au nanoprisms with regular hexagonal shape was successfully prepared.4.Au nanoprisms with sharp edges as SERS substrate,coating of these Au nanoprisms with graphene cause them to exhibit a SERS enhancement of 60 fold.This is the first demonstration of a physical approach to fabricate regular hexagonal Au nanoprisms that exhibit a SERS effect with high enhancement.The local field distribution of a series of Au nanoprisms with different sizes was simulated to better understand their SERS performance.And the theoretical results are in agreement with the experimental results.