Control And Application Of Metal Surface Plasmon Polaritons And Its Spectral Enhancement

Metallic micro-nanostructures have potiential applications in the fields of newly photoelectric materials,biomedicine,and environmental and food detections because of their surface plasmon resonance（SPR）.SPR arising from metallic micro-nanostructures is strongly affected by their size,morphology,composition,arrangement,and ambient medium,for which a large electromagnetic field is generated to improve the optical signals.In this thesis,Au nanoparticle（Au NP）arrays with various nanoparticle sizes were prepared by self-assembly of block copolymer thin films in combination with solution growth.Through compounding Au NPs with shape memory polyurethane（SMPU）and Ag nanowires（Ag NWs）,the structural paramaters such as size,composition,and structural unit distance were tuned to regulate the SPR and its spectral enhancement.Taking advantages of its spectral enhancement,the application of patterned Au NP arrays in anti-counterifeiting was investigated.Based on self-assembly of block copolymer thin films,we chose diblock copolymer polystyrene-block-poly（4-vinyl pyridine）（PS-b-P4VP）,designed two routes to prepare Au NP arrays on the silicon wafer,and investigated the effect of the molecular weight of PS-b-P4VP on Au NP arrays.The results indicated that the particle density of Au NP arrays decreased with the increase of the molecular weight of PS-b-P4VP,whereas the particle size decrease with the decrease of the molecular weight of the P4VP block in PS-b-P4VP.In combination with solution growth,Au NP arrays prepared by self-assembly of block copolymer thin films were used as the seed layer and immersed in the growth solution for further growth.Au NP arrays with various nanoparticle sizes were obtained by the control of growth time,and their surface-enhanced Raman scaterring（SERS）activities were studied.The results showed that the SERS activity of Au NP arrays improved with the increase of nanoparticle size.When the nanoparticle size was fixed at about 53 nm,the detection limit of Au NP arrays was 10^-6 M for malachite green with an excellent reproducibility.To tune the structural unit distance in metallic micro-nanostrucutres for further intelligent control of SPR,Au NP arrays were incorporated into SMPU substrates to serve as flexible materials for tunable localized surface plasmon resonance（LSPR）.Au NP arrays prepared by self-assembly of block copolymer thin films were transferred from rigid silicon wafers onto flexible SMPU substrates with ultrasonic treatment rather than peeling off directly.The resultant Au NP array SMPU films had excellent mechanical properties and stable thermodynamic properties.The LSPR arising from Au NP arrays increased by negative bending on SMPU substrates,whereas the LSPR decreased by positive bending.Besides,upon uniaxial tension,the vertical LSPR increased first then decreased,whereas the parallel LSPR is similar,which resulted in the overall LSPR of Au NP arrays increasing first and then decreasing with the mechanical uniaxial tension of SMPU.Moreover,the resultant Au NP array SMPU films exhibited excellent flexibility,stability,and homogeneity in practical SERS application.The fabrication of flexible SERS substrates for sensitive detection on uneven or irregular surfaces has been challenging.We demonstrated a flexible dual plasmonic SERS（FDPS）substrate rationally constructed using Au NP arrays/aligned Ag NWs and elastic polyurethane（PU）.It exhibited high sensitivity(detection limit of 10^-8 M for melamine and10^-10 M for malachite green)and excellent reproducibility.The well-designed structure of Au NP arrays/aligned Ag NWs fabricated using the self-assembly of block copolymer thin films and oil–water–air interfacial assembly successfully enhanced the electromagnetic field through plasmonic coupling.In addition,the FDPS substrate retained a high SERS sensitivity after exposure to air at room temperature for 30 days because of the high stability of Au NP arrays and antioxidation characteristic of the PU covered on the aligned Ag NWs.Even after undergoing stretching,bending,and twisting for 100 cycles,the FDPS substrate maintained a stable SERS activity owing to the introduction of the elastic PU.Metallic micro-nanostructures show their potential values in encryption and anti-counterfeiting because of their SPR.Patterned Au NPs were constructed by the skillful combination of self-assembly of block copolymer thin films with shadow mask lithography to provide a simple and universal approach for large-area fabrication of patterned nanostructures.The Au NP arrays pattern became visible by increasing the nanoparticle size.A SERS-based physical unclonable function（PUF）security label with a large encoding capacity was fabricated by depositing malachite green on the surface.The broadening of the size distribution of the Au NPs after their growth and the increased disorder in their arrangement conferred the security label with unique and unclonable characteristics.The as-prepared optical PUF security label was read out by a confocal Raman spectrometer to extract binary codes,which were then authenticated through comparison.In this thesis,Au NP arrays were incorporated into SMPU,and the adjacent distance was tuned upon stimuli-responsive deformation to study the relationship between structural units and SPR,which lays the foundation for the precise control of SPR in the future.Meanwhile,a FDPS substrate was rationally designed and constructed using Au NP arrays/aligned Ag NWs and elastic PU,which demonstrates a potential application of SERS detection under practical conditions for irregular surfaces and may be helpful in the development of flexible sensors.In addition,based on SERS originating from metallic micro-nanostructures,patterned Au NP arrays prepared by the combination of self-assembly of block copolymer thin films with shadow mask lithography were used as optical PUF anti-counterfeiting labels,which provides more possibility for their further applications.