Research On Composite Nanostructures Based On Low-Dimensional Nanomaterials And Hyperbolic Metamaterial For Sers Application

Surface-enhanced Raman scattering（SERS）is a powerful spectroscopic technique that is capable of detecting the fingerprint of single molecules,by amplifying the Raman signal up to10¹² times.In recent years,3D multilayer hyperbolic metamaterial（HMM）substrates have unique potential in SERS due to their tunable spectral ranges and plasma collective response.HMMs are an important class of artificial anisotropic materials that are composed of alternating layers of metal and dielectric materials.The multilayer HMM has received special consideration owing to the support of different propagating modes such as surface plasmonic polaritons（SPP）and bulk plasmon polaritons（BPP）.However,for multilayer HMM,the internally propagating modes（especially BPP）are highly domain-limited and cannot propagate to the far field,so the excitation of these propagating modes in HMM needs to satisfy the wave vector matching condition,and the general incident laser light cannot complete the wave vector requirement.The electric field outside the HMM structure also undergoes rapid decay owing to the field localization effect,which cannot meet the needs of SERS applications.To solve these problems,an external coupling structure is necessary to be designed and combined with HMM to enable the excitation of propagating modes inside the HMM.Therefore,this thesis aims to address this issue and focused on designing external plasmonic nanoparticles（AgNPs,graphene-covered AgNPs,and Ag-decorated Zn Se）for HMM to enable the excitation of propagating modes inside the HMM.Therefore,we design different composite structures AgNPs/HMM,graphene-covered AgNPs/HMM,and Ag-decorated Zn Se/HMM,and study their SERS behavior.The numerical COMSOL simulation and Raman experiments were employed to assess the performance of these composite SERS substrates.The results demonstrated that the combination of external plasmonic nanoparticles with HMM boosted the hot spot zone,resulting in a significantly enhanced local electromagnetic field of these composite nanostructures.The uniform AgNPs were synthesized through chemical synthesis or magnetron sputtering annealing methods,and the deposition of the multilayer HMM comprising Au/Al₂O₃ layers was carried out using vacuum thermal evaporation.By combining simulation design with experimental preparation,we successfully prepared composite SERS substrates with enhanced SERS signal and verified their performance by detecting various organic molecules,including rhodamine 6G,malachite green,crystal violet,etc.In summary,this work can be summarized as follows:（1）A composite SERS structure,made of a monolayer of AgNPs and multilayer HMM（AgNPs/HMM）,was successfully fabricated.When AgNPs were combined with HMM,it was found that the hot spots were boosted.The COMSOL simulations confirmed that the excellent SERS behavior was due to highly populated hotspots with very small gaps（～10 nm）.The AgNPs and multilayer HMM structure are coupled to produce different propagating modes,including SPPs,and BPPs,resulting in the enhanced SERS performance of the composite structure.Consequently,the composite substrate exhibited excellent SERS sensitivity for crystal violet and rhodamine 6G solutions,reaching a minimum detection limit of 10^-12 M.Moreover,the proposed composite SERS substrate was successfully applied for the in-situ detection of melamine in milk and is expected to have practical applications in the fields of medicine,biotechnology,and food safety detection.（2）A flexible composite SERS structure was designed by combining graphene-covered AgNPs and HMM（Gr-Ag/HMM）.The graphene films were synthesized via chemical vapor deposition,while uniform AgNPs were deposited on the graphene films through magnetron sputtering annealing methods.It was found that the hot spots were boosted when the graphene-covered AgNPs were introduced with HMM.Further analysis using COMSOL simulation confirmed the significant enhancement in SERS performance is due to the presence of graphene,which created a densely populated hot spot zone in the nanogap area.Furthermore,the proposed composite Gr-Ag/HMM structure was applied to the quantitative detection of thiram residue in the soil,demonstrating its potential for practical applications in environmental protection and food safety fields.（3）A recyclable composite SERS structure,composed of Ag-decorated ZnSe nanowires and HMM（Ag-Zn Se/HMM）,was designed.The Zn Se nanowires SERS substrates were synthesized via chemical vapor deposition and compared to pure Zn Se nanowires,the Ag-Zn Se/HMM composite structure showed a significant enhancement in SERS performance.This enhancement can be attributed to the Ag-decorated Zn Se nanowires that act as an external coupling structure for the HMM,which induces different propagating modes（SPPs,BPPs）within the HMM.The SERS behavior of the proposed composite structure was assessed using rhodamine6G,malachite green,and adenosine,which showed outstanding stability and a sensitivity limit of10^-12 M.To evaluate the recyclability of SERS substrates,Raman mapping was performed using visible light to photo-catalytically degraded the rhodamine 6G and malachite green molecules.The bifunctional composite structure not only offers a unique way of boosting SERS efficiency but is also considerable for photocatalytic behavior.