Research On Farication And Plasmonic Coupling Of Nanocomplex And Nanocavity Based On Au Nanostructures

A considerable attention from many fields has been attracted to the study of noble metal nanostructures due to their unique optical properties oriented from the surface plasmon resonance(SPR)effect.This SPR properties can be tuned by particle size,morphology,chemical composition,and surrounding environment.In recent years,various monodispersed noble metal nanostructures,especially for gold and silver nanorods,have been widely investigated for their tunable SPR property and promising applications in the fields of waveguild,photothermal therapy,biochemical detecting and sensing.Contrast to the explosion of plasmonic nanoparticle monomer,more attention was paid on the hollow nanoframe,multilayer nanostructures and assembly system for their improved properties and high stabilities.This plasmonic nanocavitis have an advantage to concentrate the optical energy in a subwavelength range of metallic surface,which lead to a significant enhancement of localized field and generate hot electron-hole pair.Based on the as-prepared isolated high-purity noble metal nanoparticles(such as nanobipyramids,nanorods and nanoplates),we carried out the fabrication and properties study on the alloyed nanostructures and nanostructures enriched with nanogaps and nanocavities.The SPR of the obtained nanostructures can be controlled over a large spectra region,which agree well with the FDTD simulations.The main results are list as following.1.Monodisperse anisotropic gold nanocrystals and SPR properties were synthesized.Monodisperse anisotropic gold nanocrystals,including Au nanorods(NRs),nanobipyramids(NBPs)and nanoplates(NPs),are fabricated by seed-mediated method.Effects of reaction conditions involving reagents and aged temperature in seed solution on crystalline structures(single and twin crystals)are investigated.Moreover,reagents parameters employed in the growth solution also offer valuable insight into the anisotropic growth.The as-prepared nanostructures are purified by centrifugation or precipitation methods to remove nanospheres.Combined with FDTD simulation,the dependence of SPR on structural configurations is explored.2.Alloyed Au-Ag nanorods with high aspect ratios were achieved by annealing Au nanobipyramids directed-Au@Ag core-shell NRs.The core-shell NRs are encapsulated within mesoporous silica outer-shells to avoid the fusion or aggregation in the subsequent treatments.The SPR modes of alloyed Au-Ag NRs can be tuned in a wide spectral region of 400–2000 nm by controlling the aspect ratio and the composition ratio(Ag/Au).The final products are selective for carrier gas conditions(N₂,Air and O₂).As the annealing temperature increases from 400°C to450°C,annealing Au@Ag core-shell NRs with high aspect ratio would transform into fully alloyed Au-Ag NRs from partially alloyed Au-Ag NRs.The stability of rod-like structure is improved with alloying of Au and Ag.To explore the chemical stability of NRs,core-shell and alloyed NRs are incubated into etchant solution.Au@Ag core-shell NRs would decay into nanobipyramids,while the alloyed NRs would maintain the rod-like structure.Additionally,fully alloyed NRs also present much better thermal stability than Au@Ag core-shell NRs under high temperatures up to 600°C in air.Benefiting from excellent structural and chemical stabilities,surface-enhanced Raman scattering effect based on alloyed NRs is stable in harsh environment.The obtained nanostructures can also be served as drugs carries.Perfect photo-thermal effect induced by the particular SPR of alloyed NRs can improve the release efficiency of drugs.3.Different types of Au NRs assemblies(end-to-end and side-by-side)were achieved by molecular modification on the surfaces(3-mercaptopropionic acid and tetrahydrofuran).Notablly,when the surfaces of structures possess low concentration of surfactant,Au NRs will contact one with around the particles.FDTD simulation are applied into investigate the SPR properties and localized field of assemblies.The optical properties of Au NR assemblies can be precisely tailored by different configurations,red-or blue-shifting with different assembled types,numbers,and gap sizes.For assemblies,the interaction of adjacent nanoparticles can give rise to novel resonance modes and strong localized field enhancements.When one of the interactive surfaces is curved,an additional plasmon resonance can be stimulated under the polarization of incident light along the gap.Moreover,the releationship of optical responses for Au naonoplate dimers with gap distance and offset is also explored.New SPR modes can be induced with symmetry breaking.4.A novel“matrioska”nanocavity structures composed of Au nanorod(Au NR)within nanobox(Au NB)were fabricated by a two-step wet-chemical method,incluing overgrowth of Ag on Au NRs and replacement reaction between Ag and HAu Cl₄.The exploration on optical properties and field distributions of nanocavity structure composed of Au NR within Au NB is carried out via finite-difference time-domain(FDTD)simulation.The multiple SPR modes of optical spectrum for nanocavity are caused by the strong interaction between Au NR-core and Au NB-shell when the incident light is perpendicular or parallel to the long axis of Au box/rod nanocavity(Au BRC).The SPR modes are known as dipole-dipole bonding resonance mode in lower-energy region and antibonding resonance mode in higher-energy region.Additionally,the localized field of inner core is remarkable enhanced due to the confined effect of external shell.