| Since the Surface-enhanced Raman scattering?SERS?has been discovered,it has become a powerful tool for environmental monitoring,food safety,military science,and life sciences,because its high sensitivity,high resolution and low cost.The SERS can effectively solve the prombles of traditional Raman spectroscopy,such as low sensitivity and fluorescence interference.With the development of nanotechnology,the preparation of SERS substrates with high reproducibility,high reproducibility,high stability,high sensitivity,large area,low cost,and simple process become more and more promising.The metal nano-islands prepared by the dewetting of the metal film have a good performance in SERS enhancement,repeatability and reproducibility.It has benn widely used in SERS substrates,because of their simple preparation process,low cost,and large-area preparation.However,there are two scientific problems about the metal nano-island:?1?The correlation between the dewetting conditions of metal nano-island and SERS enhanced properties is not clear;?2?Due to the principle of metal film dewetting,it is difficult to control the spacing between the nano-islands within a small range.Thus,the SERS enhancement capability of metal nano-islands always is lower than other SERS substrates.In this thesis,aiming at the above scientific problems,we will focus on the metal nano-island.The formation of metal nano-islands and its SERS enhancement properties were studied.Meanwhile,metal nano-islands are modified in different dimensions to improve its SERS enhancement factor.The modifications of nano-islands are divided into three different levels:two-dimensional nanoparticle modification,three-dimensional nanoparticle modification and nano-film modification,corresponding to nano-filled nano-island SERS substrate,three-dimensional nanoisland-graphene-nanoisland structure and the silver-film coupled nano-island structure.All those substrates have achieved ultra-high detection sensitivity at a low cost and simple process.The specific research contents are as follows?1?The formation of silver nano-islands and the effect of annealing temperature on the SERS enhancement ability of the substrate have been studied by theoretically and experimentally.The dewetting process of silver film on the surface of the substrate was studied experimentally.The diameter,spacing and contact angle of the silver nano-island in the surface diffusion-limited temperature range were theoretically analyzed,and the relationship with temperature was obtained.COMSOL Multiphysics simulation software was used to investigate the electromagnetic field enhancement of substrate.Finally,the consistency between the simulation and the experiment is proved by comparing the results obtained by the simulation with experiment.?2?The nanoisland substrate was modified in two dimension.First substrate is prepared by self-assembling of Ag nanoparticles into the nanogaps of Ag nano-islands.The silver sol was prepared by the classical Lee–Meisel method.The morphology of the substrate was investigated.With R6G solution as the object,the experiment proved that the substrate has an enhancement factor of up to 1.2×108.The deposition process of silver nanoparticles on the silver nano-island substrate was analyzed in detail,and the relative standard deviation of the substrate was as low as 13.2%.The enhancement mechanism of the substrate was analyzed by COMSOL Multiphysics simulation software.It was proved that the silver sol can increase the electromagnetic field enhancement ability of the substrate by 447 times.Theoretically,enhancement factor of substrate can be 1010.At the same time,another nano-filled substrate was prepared by secondary deposition of an Ag film,which was also demonstrated with a SERS enhancement of up 10-7.?3?The performance of three-dimensional metal nanoparticle-graphene-metal nanoparticle composite substrate was systematically studied,which corresponds to the the nanoisland substrate modified in three dimension.A 3D AG-G-AG SERS substrate with twice annealings,a 3D AG-G-AG SERS substrate with once annealing and an 3D AG-G-AU SERS substrate with once annealing were prepared.Graphene was prepared by CVD method and characterized.With R6G solution as the object,experiments have shown that the SERS enhancement factor of the substrate reaches 2.7×109,which achieves an ultra-low solution concentration detection of 10-14 M.The enhancement mechanism of the substrate was analyzed by COMSOL Multiphysics simulation software,which indicates the maximum electric field enhancement was 191 times.At the same time,a 3D AG-G-AG SERS substrate with once annealing was prepared in a simpler process,demonstrating that a SERS substrate with an enhancement factor of1.4×109 can be prepared by one annealing.Then,the upper silver nano-island was replaced by gold nano-island.The experiment proved that the double-annealed 3D AG-G-AU SERS substrate has superior SERS stability.After being placed in the air for3 months,the SERS enhancement only decreased by 10%.?4?The application of self-encapsulation techniques in SERS was studied.The basic principle and characteristics of self-encapsulation technology were analyzed.The silver film with controlled thickness of Al2O3 was prepared by annealing Ag/Al bilayer metal film under ultra-low oxygen conditions.The silver film was characterized by SEM,which proved that the self-encapsulated silver film maintained its continuity after annealing.By the ellipsometer,experiments have shown that the thickness of the Al2O3package can be controlled by the annealing temperature in the range of 4-22 nm.The Ag film-coupled Ag nano-island structure was prepared by deweting of silver film on the surface of Al2O3,and its morphology was characterized.The near-field and far-field simulations of the fabricated structures were carried out by COMSOL Multiphysics simulation software.It is proved that the silve film-coupled silver nano-island substrate can effectively generate SERS enhancement in both near-field and far-field.Finally,with R6G as the probe molecule,experiment has shown that the substrate enhancement factor can reach 6.2×108.Therefore,this paper has improved the SERS enhancement ability of silver nanoislands by modifying the silver nanoislands in different dimensions.We found that the preparation process of the two-dimensional modified substrate is the simplest,and the three-dimensional modified substrate has the strongest Raman enhancement effect,while the silver-modified nano-island substrate is more suitable for large-scale production.The different modification methods can be used for different applications.. |
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