Research On Surface Enhanced Raman Scattering Of Ag NWs-WS₂（MoS₂） Composite Structure

Surface enhanced Raman scattering（SERS）is a simple and efficient spectral analysis technology,especially in the detection of small molecules.Therefore,it is widely used in the detection and exploration of micro substances in the fields of materials,biology and chemistry.However,an important factor affecting the development of this technology is how to obtain SERS substrate with high sensitivity,simple preparation process and good reproducibility.In view of the local surface plasmon resonance（LSPR）effect of noble metal nano materials（gold or silver）,many"hot spots"can be generated to enhance Raman signals,which are often used as SERS substrate materials.In recent years,two-dimensional transition metal dichalcogenides,especially tungsten disulfide（WS₂）and molybdenum disulfide（Mo S₂）,are excellent carrier materials and can also be used as SERS substrate materials because of their excellent photoelectric properties,strong adsorption and large specific surface area.This paper will effectively combine the SERS effect of precious metals and two-dimensional material substrates to construct the composite structure of precious metal silver nanowires（Ag NWs）and WS₂（Mo S₂）,hoping to obtain SERS substrates with high sensitivity,good repeatability and strong stability.The main research contents are as follows:（1）Ag NWs with smooth surface and controllable diameter of 100-700 nm were successfully prepared by polyol reduction method and seed method.WS₂ films with different layers were successfully prepared by low pressure chemical vapor deposition.The effects of growth temperature,carrier gas flow rate and mass ratio of precursors on WS₂ film and the auxiliary effect of sodium chloride on WS₂ growth were studied.Under the optimal growth conditions,a triangular monolayer WS₂ with a size of 90μm could be obtained.In addition,triangular Mo S₂ with good morphology and controllable layers was prepared by adjusting different growth parameters（carrier gas flow,the quality of S powder,the growth temperature of Mo O₃,etc.）by chemical vapor deposition,in which the maximum side length was 26.2μm.（2）A novel SERS active substrate was designed,that is,two side-by-side Ag NWs were placed on the surface of triangular layered WS₂ to form Ag NWs-WS₂ nanocomposite structure.Using rhodamine（R6G）as the probe molecule,the Raman signals on the simple Ag NWs,WS₂ and Ag NWs-WS₂ composite structures were compared and studied.The results showed that compared with pure Ag NWs,the Raman signal enhancement of R6G at613 cm^-1 can be increased by six times,indicating that the designed Ag NWs-WS₂ composite structure had excellent SERS ability.In addition,the dependence of SERS intensity of the composite structure on the polarization angle of incident light（sin function relationship）was studied.Finally,the distribution and size of surface plasma electric field of Ag NWs and Ag NWs-WS₂ on Si O₂ substrate were compared by finite element method,which showed that the strong SERS of the composite structure could be attributed to the hot spot effect of electric field.At the same time,the effects of the wavelength of incident light,the thickness of WS₂and the spacing between Ag NW_S on the maximum electric field intensity were also analyzed.（3）The SERS substrate of Ag NWs-Mo S₂ composite structure was designed and constructed,and the strong SERS ability and polarization dependence of the composite structure substrate were verified by experiments.The experimental results showed that the Raman signal enhancement intensity of the composite structure substrate on R6G molecule was five times higher than that of pure Ag NWs,indicating that the composite structure played a significant role as SERS active substrate.In addition,the dependence of Ag NWs-Mo S₂composite structure substrate on the polarization state of incident light was consistent with that of Ag NWs-WS₂ substrate.Based on the finite element method,the surface plasma electric field distribution of Ag NWs and Ag NWs-Mo S₂ on Si O₂ substrate was compared.It was found that the total electric field intensity distributed on Ag NWs-Mo S₂ is twice that of Ag NWs.At the same time,the influence of the wavelength of the incident light on the maximum electric field intensity is discussed.The results showed that when it reached 630nm,the maximum electric field intensity could be achieved.