Comparative Study On Several Surface-enhanced Raman Scattering Active Substrates

Surface-enhanced Raman spectroscopy?SERS?is a molecular vibrational spectrum that reflects the rich fingerprint information of molecular structures.Now,it has been widely used in many fields as a crucial routine analysis tool,such as chemistry,physics,materials,biology,medicine,environment and safety and so on.At present,there are two main enhancement mechanism for SERS that are generally accepted.They are Electromagnetic Enhancement Mechanism and Chemical Enhancement Mechanism.The former is due to the excitation of the substrate by laser and resulting in Surface Plasmon Resonance?SPR?effect.At the same time,it will generate a strong electromagnetic field and the Raman signal of adsorbate will get a huge enhancement.The latter is due to the structure of compound which is consist of adsorbates and substrates.There is some mode of charge transfer and the Raman signal of adsorbed molecules will be enhanced by this process.For the SERS effect,the substrate properties are undoubtedly important,and excellent substrate with the following advantages: 1.High sensitivity;2.Stability and repeatability;3.Selectivity and compatibility;4,Simple preparation.At present,the material of substrate can be divided into the following categories: 1.Noble metals and transition metal substrate;2.semiconductor substrate;3.Carbon material substrate;4.Composite material substrate.Each SERS active substrate has its superior performance and the corresponding enhancement mechanism and it requires us to explore the physical and chemical properties of the substrate material and related enhancement mechanism in detail.The work of this thesis will be divided into following three contents:1.The preparation of silver sol was explored by method of Lee-Meisel,and the formation of silver sol was explored by the method of UV absorption spectroscopy.The silver nanoparticles with different particle sizes were effectively synthesized by controlling the temperature at the nucleation stage.Meanwhile,the range of surface plasmon of silver nanoparticles is adjusted.In addition,silver nanoparticles with different sizes were used as SERS reinforcement substrates and 4-MBA was employed as probe molecules to explore the SERS effect of different sizes of silver nanoparticles.In the end,we determined the optimal size of silver nanoparticles and analyzed relevant reasons.2.In this work,we employed TiO₂-4-MBA and TiO₂-4-MBA-Ag systems by using 4-MBA as the probe molecule,respectively.Two systems were prepared from different sizes of TiO₂ nanocrystals and we gained different SERS signals at the laser wavelength of 532 nm,633nm,785 nm and then explored the enhancement effect and enhancement mechanism of large scale TiO₂ systems.In addition,we discovered the reasons behind the variation.3.We employed solvent method to synthesis nanocrystals which is used SERS substrate and 4-MBA,PATP and Mpy are respectively seleced as probe molecules to exoplore SERS effect of galena substrate.In addition,Ag-probe molecule-PbS composite substrates was constructed to further explore the SERS effect and its enhancement mechanism.