| It is well known that the localized electric field strength of surface enhanced Raman scattering(SERS)substrates can be enhanced through the surface plasmon effect introduced by some noble metallic nanostructures.As a result,the SERS performance could be eventually significantly improved.However,the applications of such substrates in the fields of biomedical,food safety and environmental protection have been limited due to the low stability and sensitivity of the SERS hotspots offered by the noble metallic nanoparticles or rough metal films.The combination of noble metallic nanoparticles with a silicon-based material with good biocompatibility and facile texture tunability is a potential strategy to improve the stability and sensitivity of the SERS substrates.In this dissertation,silver/pyramid silicon(Ag/PSi)and silver/porous silicon(Ag/Po Si)substrates were firstly prepared by a wet chemical method as an experimetnal foundation for the combination of porous pyramid silicon substrate and silver nanoparticles.The experimental results indicate that the Ag/PSi substrate could reveal good SERS performance reflecting by the high SERS enhancement factor of 4.3×105 and the low limit of detection of 10-9 M for R6G molecules.On the other hand,the optimized Ag/Po Si substrate also show SERS porformance with the enhancement factor of 2.0×103.Based on the research regarding Ag/PSi and Ag/Po Si substrates,the novel silver/porous pyramidal silicon(Ag/PPSi)active substrates were successfully prepared.Such substrates are composed of porous pyramidal silicon,which takes advantage of the large specific surface area of porous silicon and the regular array structure of pyramidal silicon,and Ag nanoparticles,and therefore could show better SERS detection sensitivity.Indeed,the experimental results show that the SERS enhancement factor and the limit of detection of the Ag/PPSi substrate for R6G molecules can up to 1.1×106 and down to 10-10 M,resepecitively.Furhtermore,the Raman examinations on the Ag/PPSi substrate excited by multiple incident angles indicate that the substrate could be excited in a wide incident direction range,so that the substrate reveal better practical detection adaptability.In addition,the finite element simulations show that the average near-filed enhancement factor of Ag/PPSi substate will increase with the increasing of size and distribution density of the Ag nanoparticles in the beginning,and then decreases sicne the coupling structure will be more complicated by changing from isolated Ag with Si to Ag dimer with Si.The maximum average near-filed enhancement factor with magnitude of 108 can be reached when the substrate with Ag dimer structure containing particle radius and gap of 52 and 20 nm,respectively.Finally,the silver/silicon nanowires(Ag/Si NWs)composites were successfully fabricated.The calculations based on the SERS characterizations indicate that Ag/Si NWs could show SERS porformance with the enhancement factor of 3.0×103,which is one order of magnitude higher than the value calculated by the finite element simulation.Such deviation could be due to the distribution of Ag nanoparticles on the Si nanowires.Indeed,the finite element simulations show that the critical coupling gap of the Ag dimer on Si nanowire is about 24 nm.In this case,the average near-filed enhancement factor of the composite is five orders of magnitude higher than that of the structure of single Ag nanoparticle on Si nanowire,reaching the order of 107,which can be attributed to the strong localized surface plasmon coupling happenning at the dimer gap. |
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