The Controllable Preparation And SERS Effect Of Alloy Nanoparticles/Silver Nanowires

Surface-enhanced Raman scattering(SERS)technology has the characteristics of high efficiency,sensitivity and high resolution.The research of SERS technology focuses on the composition and structure of substrate materials.The solid-state ionics method can realize the controllable preparation of metal nanomaterials by changing the magnitude and direction of the impressed current,but its growth mechanism is still unclear.In this paper,Rb Ag₄I₅ was selected as the fast ionic conductor films and metal nanostructures were prepared with different metal electrodes by the solid-state ionics method combined with the vacuum thermal evaporation process to investigate the growth mechanism of the solid-state ionics method.Ag nanowires(Ag NWs)were prepared by changing the intensity of impressed current and used as SERS substrates.The effects of different impressed currents on the surface morphology of Ag NWs and the effect of surface morphology on the SERS performance of Ag NWs were discussed.The process parameters for most excellent SERS performance was determined.The different alloy nanoparticles were evaporated on the surface of Ag NWs with excellent SERS performance,the effect of alloy nanoparticles on the SERS performance of Ag NWs was explored and the SERS enhancement mechanism was further analyzed.The specific research contents of the paper are as follows:(1)The metal nanostructures were prepared with Cu,Ag and Au as metal electrodes and Rb Ag₄I₅ conductor films at the 5?A impressed currents by solid-state ionics method.By analyzing its morphology and composition,it was found that the composition of the metal nanostructure was pure Ag,Ag NWs were closely arranged with each other and numerous Ag nanoparticles(Ag NPs)with diameters of 40-70 nm were attached to the surface of Ag NWs.The Cu and Au elements appeared in Rb Ag₄I₅ films when Cu and Au were used as metal electrodes to prepare Ag NWs.It was analyzed that the Rb Ag₄I₅ films conduct ions by ion exchange,the difference of ion radius caused distortion in the crystal structure of Rb Ag₄I₅ in the process of ion exchange,resulting in the gradual loss of the ability to conduct ions in the Rb Ag₄I₅ films.The macroscopic morphology of Ag NWs prepared at the 2 and 8?A impressed currents was analyzed by fractal dimension when Ag was used as the metal electrode.The fractal dimension of Ag NWs showed a tendency to increase and then decrease with the increase of current intensity due to the irregular electrode interface and the apical growth advantage.(2)The microscopic morphology of Ag NWs prepared with Ag as the metal electrode at 2,5 and 8?A impressed currents shown that the average diameter of Ag NWs decreased with increasing current intensity,which were used as SERS substrates detect the probe molecules of Crystal Violet(CV),Basic Fuchsin 9(BF),Acid Orange II(AO?)and Alkali blue 6B(AB 6B)were selected as the probe molecules.The Ag NWs prepared at 5?A impressed currents was obtained with the limit concentrations of 10^-14 mol/L,10^-11 mol/L,10^-7 mol/L and 10^-7 mol/L for the detection of CV,BF,AO?and AB 6B,respectively,which were three to four orders of magnitude lower than the limiting concentrations of Ag NWs prepared at 2 and 8?A impressed currents for detecting the same probe molecules.It was concluded that the microscopic morphology of the Ag NWs prepared at different impressed currents differed significantly,which leads to the significant differences in the SERS performance.The Ag NWs prepared at 5?A impressed currents were more closely arranged with each other compared to those prepared at 2and 8?A impressed currents,numerous Ag NPs attached to the surface of Ag NWs and the synergistic effect of the plasma excitations between Ag NPs and Ag NWs provide strong local electromagnetic fields and adsorption points for the probe molecules,which make the Ag NWs exhibit excellent SERS activity.(3)Four alloy nanoparticles of Au-Ag,Au-Cu,Ag-Cu with a mass ratio of 1:1 and Au-Ag-Cu with a mass ratio of 1:1:1 were vaporized on the surface of Ag NWs prepared at 5?A impressed current by vacuum thermal evaporation process,respectively.It was found that more nanoparticles were attached to the surface of the tightly arranged Ag NWs by characterizing the microscopic morphology.When they were used as SERS substrates detect CV,BF,AO?and AB6B,Au-Ag alloy nanoparticles/Ag nanowires(Au-Ag alloy nanoparticles/Ag NWs,Au-Ag ANPs/Ag NWs)had the most excellent SERS performance with the limit concentrations of 10^-16mol/L,10^-13 mol/L,10^-7 mol/L and 10^-9 mol/L for the detection of probe molecules,respectively.In order to explore the effect of the composition ratio of Au-Ag ANPs on the SERS performance of Ag NWs,Au-25Ag ANPs and Ag-25Au ANPs were prepared at mass ratios of 3:1 and 1:3 and deposited on the surface of Ag NWs.The limiting concentrations of their detection probe molecules is one to two orders of magnitude higher than that of Au-Ag ANPs/Ag NWs as SERS substrate detection probe molecules,so Au-Ag ANPs/Ag NWs have the most excellent SERS performance.It was analyzed that the SERS performance of Au-Ag ANPs/Ag NWs was determined by the combination of the free electron density provided by Au and the SERS activity provided by Ag.The SERS activity of Au-Ag ANPs is most excellent,and the random distribution of nanoparticles leads to a significant increase in the surface concentration of probe molecules and accelerates the transfer between charges when the mass ratio of Au and Ag is 1:1.In this paper,the growth mechanism of metal nanostructures prepared by solid-state ionics method is explored,which provides the reference for the preparation of metal nanomaterials.Metal nanostructured SERS substrates with ultra-high sensitivity were prepared by solid-state ionics method and vacuum thermal evaporation process,which provides the technical support for trace analysis in food and environmental fields.