Study Of Surface Enhanced Raman Scattering(SERS) And SERS Enhancement Mechanism Of Doped Semiconductors

Surface enhanced Raman spectroscopy(SERS),as a detection method for studying surface reactions,has the advantages of high sensitivity,high selectivity,low detection requirements and non-destructive properties.SERS substrates developed from the traditional noble metals such as gold,silver,and copper,and have successively developed substrates such as transition metals,semiconductor nanoparticles,and core-shell structure composite nanoparticles.The enhancement ability of semiconductor SERS substrates is generally weak,only about 10³.The electronic structure of semiconductor is closely related to the charge transfer mechanism which supports the semiconductor SERS enhancement mechanism.Doping can modify the electronic properties of semiconductor.Therefore,a new type doped semiconductor nanoparticles was tried as SERS substrate in this study.The indium-doped cadmium oxide(ICO)and antimony-doped tin oxide(ATO)are used as SERS substrates and their enhancement ability and enhancement mechanism influenced by doping contents were explored.The main contents are as follows:(1)Study on enhanced ability and enhanced mechanism of ICO nanoparticles SERS substrate.Cadmium oxide(CdO)and a series of ICO nanoparticles with different doping ratios were synthesized and used as SERS enhanced substrate for the first time.The study showed that the enhancement factor of 4-Mercaptopyridine(4-MPY)adsorbed on ICO nanoparticles SERS substrates can reach 10³.Through the further analysis made on its enhancement mechanism with LSPR of ICO nanoparticles,we observed that the enhancement is attributed to the charge transfer between the probe molecule and the ICO nanoparticles substrate.According to the analysis of the energy level and the electronic structure,a new charge transfer path was proposed for the first time.The free carriers on the conduction bands of the semiconductor are excited by excitation and transferred to the LUMO of molecule.The free carrier in conduction bands determines whether this process can be carried out.And its density also affects the degree of charge transfer,which in turn affects the enhancement ability of the ICO nanoparticle substrate.At the same time,we found that the peak half-width of the SERS spectrum of the probe molecule adsorbed on the ICO nanoparticles substrate is very narrow,indicating that the probe molecule has a high degree of consistency in structure and orientation.(2)Study on enhanced ability and enhanced mechanism of ATO nanoparticles SERS substrate.Tin oxide(SnO₂)and a series of ATO nanoparticles with different doping ratios were synthesized,and used as SERS enhanced substrates for the first time.This study showed that the enhancement factor of 4-mercaptobenzoic acid(4-MBA)adsorbed on ATO nanoparticles SERS substrates can reach to 10³.Through the further analysis of its enhancement mechanism,we attribute the observed enhancement phenomenon to the charge transfer between probe molecule and ATO nanoparticles substrates.Through the analysis of the energy level and electronic structure of ATO nanoparticles,it is found that the charge transfer process is affected by the free carrier density on the semiconductor conduction bands.With low Sb doping of ATO nanoparticles,the charge transfer process is mainly affected by the changes of the bands structure influenced by the free carrier density.With high Sb doping of ATO nanoparticles,the influence of the bands structure is tiny,and the repulsive force between free carriers becomes the main factor affecting the charge transfer process.We also proved that ATO nanoparticles substrate has good reproducibility and stability.The innovation points in this study are mainly attributed as the follows:(1)For the first time,ICO nanoparticles and ATO nanoparticles was used as new type of SERS substrates,their enhancement ability were preliminary verified,and the enhancement mechanism based on charge transfer was discussed;(2)A new charge transfer path between the molecule and the semiconductor was proposed:the free carriers filled in the conduction bands of the semiconductor are excited and transferred to the LUMO of molecules;(3)Through the analysis of the SERS enhancement mechanism of doped semiconductors,it is found that the enhancement ability of doped semiconductors is closely related to the electronic structure,and doped semiconductors could change the energy band and electronic structure by adjusting the doping to obtain the substrate with the best enhancement effect,which embodies the advantages of doped semiconductors as SERS enhanced substrates.