Investigation On Surface-Enhanced Spectroscopy Based On Indium Oxide?In₂O₃? Semiconductor Nanoparticles

Both surface-enhanced Raman spectroscopy?SERS?and surface-enhanced infrared absorption?SEIRA?belong to surface-enhanced spectroscopy,and both of them belong to the vibrational spectrum with good sensitivity,which can provide fingerprint information of monolayer molecules at the surface and interface.Therefore,SERS and SEIRA have outstanding advantages in many aspects such as trace analysis and detection,in situ monitoring,and biochemical molecular analysis.The substrate is necessary for SERS and SEIRA,and the nature of the substrate will limit the applicability fields of SERS and SEIRA.The variety about substrates of SERS has experienced the process from precious metals to transition metals and then to semiconductors.The enhancement factor of semiconductors is far less than that of metals,and have poor reproducibility.However,due to the tunable optical properties and good biocompatibility of semiconductors,it is necessary to continue investing in the researches to make semiconductors take more of their own advantages in SERS.The development of SEIRA is far inferior to that of SERS.The substrates for SEIRA used in the current researches are basically limited to precious metals,which limits the application of SEIRA.In order to promote the development and application of SEIRA,it is necessary to explore the new enhanced substrates of SEIRA.In recent years,indium oxide?In₂O₃?has become one of the most popular transparent conductive oxide materials?TCOs?with good optical properties,such as wide band gap,high free carrier density and stable chemical properties.Therefore,based on In₂O₃ semiconductor nanoparticles,the exploration about SERS for new type of semiconductor substrates was carried out,and their SERS enhancement performance and mechanism were also explored.Indium tin oxide?ITO?with different Sn doping ratios were used as the enhanced substrates for SEIRA,and a preliminary study on the new enhanced substrates was conducted.The main research contents are as follows:a)Investigation of In₂O₃ nanoparticles as a novel substrate for SERS and SERS study of Ag/4-MBA/In₂O₃ interfacial system.In₂O₃ nanoparticles with cubic phase and small particle size were synthesized by high temperature pyrolysis method.And it was first used as a novel SERS substrate.The SERS spectra of molecules such as mercaptobenzoic acid?4-MBA?and p-nonylbenzoic acid?4-HBA?were obtained with laser excitation wavelength were 532,633,and 785 nm.In₂O₃ is confirmed to be a new SERS substrate with good enhancement effect,and the enhancement factor?EF?can reach to 1.22×10⁴.And reproducibility of signal is good.After the analysis that assisted by UV-Vis DRS,UPS and other characterization methods,the enhancement mechanism is attributed to the charge transfer?CT?between the molecule and In₂O₃,and the CT can be excited under the lower energy with laser line is 785 nm.It indicates that In₂O₃ is a promising SERS substrate that excited by near-infrared laser,thus it can extend more SERS research in the near-infrared region and broaden the detectable range of SERS.At the same time,the method of layer-by-layer assembly was used to construct Ag/4-MBA/In₂O₃ structure on the glass slide.And the CT process in this system was discussed by using SERS,which showed the ability of SERS to explore the interfacial CT in optoelectronic devices in the study to improve the material properties.b)Preliminary study on Indium Tin Oxide?ITO?nanoparticles as novel active substrates for SEIRA.ITO nanoparticles with a series of Sn doping ratios were synthesized by high temperature pyrolysis method,and the initial feeding ratios of Sn?x_i?are 0,0.025,0.050,0.075 and 0.100,respectively.They were used as the enhancement substrates,for the first time,to conduct the exploration about SEIRA.The ferrocene dicarboxylic acid?FCA?molecule was used as probe molecule and subjected to SEIRA testing.According to the test,ITO nanoparticles with x_i is 0.050 had the best enhancement effect.It was further explored that the FCA molecules were bonded to the substrate through COO^-.The SEIRA enhancement factor?EF?is 24.What's more,the detectable concentration of solution is as low as 10^-55 mol/L,indicating that the enhancement effect is good.It shows the new type of semiconductor substrate for SEIRA with small size has been successfully obtained,which can provide convenience in situ trace detection in biological aspects.Further more,it can broaden the application scope of SEIRA,and lay a certain foundation for the related research of SEIRA.At the same time,the adsorption behavior of molecules on the surface of ITO was explored by changing the pH of the molecular solution,indicating that SEIRA is a reliable means for the analysis of the molecular state of the surface interface.It also provids an auxiliary means for the study about the effect on the electrode performance of some molecular states modified on the surface of ITO electrode.