Study On The Preparation And Raman Enhancement Of Silver Nanostructure Arrays Obtained From V-Shaped Porous Alumina Template

Because of the excellent optical properties,metal nanostructures are widely applied in biochemical sensing,plasmon enhanced light harvesting,etc.With the continuous advancement and innovation of nanotechnology,people can fabricate metal nanostructures with various shapes and sizes,and effectively control their optical properties.Ag is a noble metal material with excellent plasmonic properties,which has a low loss in the visible and near-infrared light regions.Therefore,it is of great significance to study the preparation,optical properties and application of Ag nanostructures in surface-enhanced Raman spectroscopy.Based on the investigation on the growth characteristics of new type of silver nanostructures,this work focuses on the enhanced Raman properties of different silver nanostructure arrays.In this paper,Ag nanostructure arrays were prepared by combining ordered V-shaped porous alumina templates with physical vapor deposition techniques including thermal evaporation and ion sputtering.Furthermore,the optical properties and the applications in surface-enhanced Raman spectroscopy of the prepared arrays were explored.The main research results are as follows.1.Large-area ordered Ag hollow cone arrays and three-dimension distributed Ag nanoparticle arrays were fabricated on V-shaped porous alumina templates by thermal evaporation,and the SERS properties of the fabricated arrays were measured.It shows that the silver hollow cone can act as an optical cavity which effectively confine and focus the incident light,and generate an enhanced electric field in the cavity.Thus,enhanced Raman signals of the molecules adsorbed on the surface can be realized.The enhancement factor for R6G is about 3.8×10~5.Moreover,the 3D-distributed Ag nanoparticle arrays,combining the focusing effect of optical cavity with the localization effect of nanogap,form stronger localized electric field and thus better SERS performance.The enhancement factor for R6G was up to 2.2×10~7.In addition,the reproducibility of this SERS substrates was further improved due to the high-density distribution of the electromagnetic hot spots,and the relative standard deviation of the Raman signals is as low as about 5%.2.Annealing was carried out on the above-mentioned samples,the structural change and its influence on SERS performance were investigated.It shows that annealing degenerated the activity of the SERS substrate.This can be attributed to the increased interparticle spacing,weakened electric field and decreased hot spot density due to the aggregation of smaller silver nanoparticles in V-shaped holes under annealing.3.Ordered Ag cone array was obtained by successively spinning,curing and peeling off a layer of PDMS on the prepared Ag hollow cone array,and its SERS performance was measured.The results show that the Ag cone array with larger height presents higher SERS activity,which can be attributed to the more intense localized electric field due to the lightning rod effect.