Study On Self-formation And SERS Performance Of Ag/Ag-Zr Granular Film On Flexible Substrates

Silver（Ag）nanoparticles and silver alloy thin films have become the preferred materials as surface enhanced Raman scattering（SERS）substrates due to their outstanding surface plasmon resonance characteristics,which are widely used in biomedicine,food safety,environmental monitoring,materials science and other fields.How to prepare the SERS substrate with good performance,uniform structure and appropriate price is one of the most critical research topics in the field of SERS technology.In this paper,the composite structure of Ag particles/Ag-Zr alloy films was prepared on three substrates by magnetron sputtering.A new type of SERS substrate with excellent performance was prepared by combining the Ag particles with high SERS sensitivity and the Ag alloy films with good repeatability.The effects of film thickness,Zr content and annealing temperature for the formation of particles and the properties of alloy film were studied.The mechanism of polyhedral pure Ag particles self-growing on the film surface was analyzed.The enhancement effect of the composite structure of Ag film/Ag particle/Ag-Zr film as SERS substrate with Rhodamine（R6G）as probe molecule was characterized.The main work is as follows:1.The Ag-Zr films deposited on PI substrates by composite target and double target co-sputtering show Ag（111）preferred growth.The diffraction peak of Ag（111）in XRD patterns shifts to a high angle,indicating that there is residual compressive stress in Ag-Zr films.2.The surface of Ag-Zr alloy films deposited on PI substrate by composite target sputtering is smooth and does not grow particle.After annealing at a certain temperature,a large number of polyhedral single crystal silver particles with uniform distribution are grown on the alloy film surface,and the Ag particle ranges from dozens of nanometers to about 1μm.The results show that the size and quantity of Ag particles can be controlled by changing the film thickness,Zr content and annealing temperature.3.Ag-Zr alloy films with different Zr content and film thickness were prepared on PI substrate by double target co-sputtering.At room temperature,a large number of single crystal Ag nanoparticles were formed on the surface of some Ag-Zr films.The main influencing factors of particle size and quantity are Zr content,film thickness and annealing temperature.The as-deposited Ag-Zr films obtained by double target co-sputtering does not exist any particles,when Zr content is less than 5.6%.The number of Ag nanoparticle self-formed on the Ag-Zr film surface increased gradually,When the Zr content increased from 5.6%to 21.7%,especially the Ag particles on the surface of 45 nm thickness Ag-21.7%Zr film were the same size,and there were nanometer gaps between adjacent particles and were not particle agglomeration.The size and quantity of particles on the surface of 45 nm thick Ag-30.1%Zr film decreased obviously,when Zr content increased to 30.1%.4.Formation mechanism of pure Ag particles:Since Ag grains and Zr grains can inhibit each other’s growth during the annealing process,Ag atoms along the surface and grain boundaries diffused on the alloy film surface formed polyhedral pure Ag particles,driven by the release of thermal and residual stress and the heat action,in order to reduce the system energy.5.The Ag nano-particles formed on the film surface and Ag-Zr alloy film form a new type of Ag film/Ag Zr particle film,covering an ultra-thin pure Ag film on the surface of the granular film can effectively improve the SERS performance.In particular,the 26-nm-thick Ag film deposited on the surface of the 23 thickness Ag-21.78%Zr granular film annealed at 260℃,which can accurately detect the lowest concentration of rhodamine solution up to 5×10^-15M.The enhancement factor is1.1985×10¹⁴.It has good repeatability.The excellent SERS activities of Ag film/Ag Zr particle film are attributed to a large number of SERS"hot spots"produced by the evenly distributed,monodisperse Ag nanoparticles well combined with the film and narrow nanoscale gaps.