Synthesis Of Infrared Surface Plasmon Nanomaterials And Corresponding Explorations In The Surface Enhanced Infrared Absorption Spectroscopy

Surface Enhanced Infrared Absorption(SEIRA)is an important means of spectral detection.Since the technology was discovered in 1980,people have been trying to promote it to be capable of single molecular analysis and detection.Initially,the enhanced substrate of SEIRA is a metal island film,but because of its uncontrollable appearance and its own limitations,SEIRA development has encountered a bottleneck.With the proposal of resonance SEIRA and the advancement of technology,SEIRA has entered a new period of rapid development,researchers use electron beam lithography(EBL),focused ion beam(FIB),and nanosphere lithography to prepare metal nano-antenna substrates,such as nano-arrays,nano-gap and nano-tips to reduce the detection limit.Therefore,a variety of SEIRA substrates have been continuously proposed,and the enhancement effect has been continuously improved.However,the equipment used for substrate preparation is becoming more and more expensive,the substrates prepared are more and more complicated,and the difficulty of preparation is increasing.Therefore,it is extremely important to seek a substrate with simple preparation and good enhancement effect for the promotion and application of SEIRA.Colloidal gold nanowires are synthesized by the colloidal method,and the longitudinal SPR mode can be tuned in a relatively wide infrared region,which is an excellent material for SEIRA.But at the same time,the carrier concentration of noble metal materials cannot be adjusted due to their natural properties,unlike counterpart,the carrier concentration of semiconductor materials can be increased by several orders of magnitude by doping.In addition,due to the large number of carriers generated by doping,the doped metal oxide exhibits metal-like behavior,so the conductive metal oxide nanocrystals can achieve localized surface plasmon resonance(LSPR).And unlike metal nanomaterials,which can only be tuned by changing the size and morphology of nanoparticles,doped metal oxides can also be tuned by changing the doping element and doping concentration.This thesis focuses on the application of colloidal gold nanowires(Au NWs)in SEIRA,and explores the properties of cerium-doped indium oxide(Ce:In₂O₃)nanoparticles,as a potential type of infrared surface plasmon nanomaterials.The main research contents of this manuscript are as following:1.Preparation,characterization of Au NWs colloidal solution and selection of SEIRA signal molecules(Chapter 2).Au NWs with a specific length were prepared by the colloidal method,with an average diameter and length of 1.8±0.21 nm and 166±36.54 nm,respectively,and the size was relatively uniform.The spectra of Au NWs growth process show that the energy of its longitudinal SPR peak is opposite to its aspect ratio.And then finding suitable molecules as signal molecules of SEIRA for further observation and application.As a ligand molecule on the surface of Au NWs,Oleamine(OA)has natural advantages,and it does not overlap with the IR signals of other molecules in the 721 cm^-1IR absorption vibration peak,which is the top choice as a SEIRA signal molecule.2.The Au NWs colloidal solution was used as the enhanced substrate for SEIRA,and the enhancement factor(EF)was measured and calculated(Chapter 3).Using the colloidal Au NWs synthesized in Chapter 2 as the enhancement substrate,the OA molecules were successfully enhanced,and the entire enhancement factor was 151without any treatment.After removing free OA molecules that do not contribute to SEIRA in the solution,the surface enhancement factor of Au NWs(enhancement effect on surface OA molecules)is about 5.29×10⁴.If only the effective enhancement at both ends of the nanowire is considered,the local enhancement factor can be estimated as 4.96×10⁶,which is similar to the square of increased electromagnetic field intensity calculated by the FDTD simulation.3.Preparation and performance evaluation of Ce:In₂O₃nanoparticles with different doping levels(Chapter 4).Ce:In₂O₃nanoparticles were prepared by colloidal method,and nanoparticles with different doping levels and morphology mainly composed by cubes with size of about 20 nm were obtained by adjusting the content of cerium precursor in the reaction.In addition,as the particle doping level increases,its LSPR peak shifts to the high energy region.The performance of the material is evaluated by LSPR data and the value of Quality factor(Q-factor)and comparing them with other doped oxides The LSPR of Ce:In₂O₃nanoparticles with a doping level of 5.19%has an FWHM of 55 me V and a Q-factor of 4.8,to our knowledge,which is the narrowest of the LSPRs of the doped metal oxides within similar resonance energy range,and could potentially play an important role in the application of signal enhancement for specific vibration modes.