Study On SERS Enhancement Mechanism Of Ordered Metal-semiconductor Composites

Surface-Enhanced Raman Scattering（SERS）refers to the phenomenon that the Raman spectrum signal of a molecule that is physically or chemically adsorbed on the surface of a nano-active substrate is greatly enhanced.With its advantages of high sensitivity,high selectivity and non-destructive testing,it has been widely used in the detection of surface/interface.This paper combines self-assembly template technology and magnetron sputtering technology,combining the advantages of metals and semiconductors,to build a highly ordered,controllable,and stable metal-semiconductor composite SERS active substrate.The SERS enhancement mechanism was studied.The main research content has the following three parts:1.The Ag-FeS nanocap film was fabricated on a 200 nm polystyrene colloidal particles（PSCP）array by magnetron sputtering.The sputtering power of FeS was adjusted to control the structural parameters of the Ag-FeS nanocap film,the intensity and coupling degree of the surface plasmon resonance（SPR）of the array structure can be adjusted.During the sputtering process,the Ag film was separated into Ag islands partially covered by FeS,and strong coupling occurred between FeS and the separated Ag islands,which leaded to the SERS phenomenon.The methylene blue（MB）molecules adsorbed on the nanocap film were used to study the SERS enhancement mechanism.The calculation result of enhancement factor（EF）was as high as 1.8×10⁶.The influence of the changes in the shape and structure of the thin film array on the SERS effect was discussed.2.The structured Ag/FeS/4-MBA system was changed the FeS film thickness to achieve Ag SPR regulation,and the SERS enhancement mechanism of the interaction between FeS and Ag was explored,and revealed the contribution of SPR to charge transfer（CT）.The CT mechanism model was constructed according to the energy level distribution of different materials.In order to measure the contribution of CT to SERS enhancement,charge transfer degree（ρCT）in a layer-by-layer sputtering system was calculated using selected SERS spectra obtained at different excitation wavelengths.By adjusting the excitation wavelength,the separation of electron/hole pairs at the interface was promoted,thereby inducing the CT process between the semiconductor and the molecule,and maximizing the enhancement of SERS.3.Ag and ZnS were combined to form a new（Ag）_x（ZnS）_ycomposite system.The band gap distribution changes caused by the carrier density change in the system are studied.By changing the relative ratio of Ag and ZnS,the carrier density could be adjusted.The band gap distribution changes caused by the carrier density changes were studied,and it was found that the adjustment of the ZnS content makes the carrier density and the band gap position decrease regularly.There was a good linear relationship between the intensity ratio of the b₂peak and the a₁peak in the SERS spectra and the carrier density,which intuitively showed that as the carrier density decreases,its CT contribution gradually became dominant in the system.The fitted data clearly showed that the change of the carrier density was helpful to improve the electron separation and transmission efficiency,and improved the semiconductor SERS enhancement capability.