Research On Synthesis And Plasmonic Properties Of One Dimensional Au And Ag Nanostructure

A considerable attention from many fields,including physics,material science,energy and biomedical science,has been attracted to the study of noble metal?especially Au and Ag?nanostructures due to their unique optical properties oriented from the surface plasmon resonance?SPR?.Among many nobel metal nanostructures,less attention was paid on Ag nanorods?AgNRs?and ultrafine Au nanowires?AuNWs?contrast to the extensive research of Au nanorods?AuNRs?and Ag nanowires?AgNWs?.Experimental study and theoretical simulation results show that AgNRs is more superior than AuNRs in SPR properties and surface enhanced Raman scattering?SERS?effect,which has potential application in nanoelectronics,biomolecular device,life sciences,photoelectric sensing device,etc.In this dissertation,we will present theoretical analysis and experimental study of AgNRs?including monometallic AgNRs and bimetal Au@AgNRs?,including sample preparation,optical property,SERS and stability.Finite-difference time-domain?FDTD?simulation is also ulitilized to describe the change regulation and analize parameters which affect the SPR properties.Studies on the synthesis and the growth mechanism of ultrafine AuNWs were also carried out.In the dissertation,a simple and effective method is explored to improve the purity of samples with the assistance of surfactants.The main work and related results included in this dissertation are the following:1.Synthesis and plasmonic property of monometallic AgNRs.A facile seed-mediated method is achieved to prepare monometallic AgNRs under an alkalic condition.High purity of monometallic AgNRs are obtained by a simplified purification process.The aspect ratio of monometallic AgNRs can be tuned by changing the amount of seeds.The influences of the reaction conditions were discussed on the yield of AgNRs.The possible growth mechanism of Ag nanostructures was proposed.The SPR and electromagnetic field of monometallic AgNR were studied by FDTD simulations.The SERS was discussed compared with that of AuNRs of the same size.2.Synthesis and plasmonic property of bimetal Au@AgNRs.The Au nanobipyramids?AuNBPs?and Au@AgNRs with different aspect ratios are respectively synthesized by the seed-mediated method.Through anisotropic Ag overgrowth on the surface of the AuNBPs,high-purity Au@AgNRs are obtained by a simplified purification process.The aspect ratio of Au@AgNRs can be tuned by the amount of the AuNBPs and AgNO₃ in the growth solution.The growth mechanism?SPR characteristic and electromagnetic field of Au@AgNRs were investigated.And the influence of AuNBP on the SPR property of Au@AgNR was discussed based on the experimental results and FDTD simulations.The results indicate that the AuNBP core has little effect on the plasma behavior of the Au@AgNR.The unique optical properties and strong electromagnetic effect of Au@AgNRs,along with advantages of superior SERS signal enhancement,which provides a new way for Au@AgNRs to replace the monometallic AgNRs with low-yield and poor-stability.3.The stability of Ag nanorods.Due to the low-purity and unstability of monometallic AgNRs,a method is introduced to synthesize the AgNR@SiO₂ core-shell structure,which improves the stability of the monometallic AgNRs.Meanwhile,the optical properties of the AgNR and AgNR@SiO₂ are studied by FDTD.And the dielectric sensitivity was discussed compared with AuNR of the same size.The stability of Au@AgNRs and monometallic AgNRs stored at room temperature were studied.In addition,the stability of Au@AgNRs were studied comapared with those of AuNRs,AgNRs and AuNBPs under the laser irradiation.Compared with homogeneous AgNRs that have tunable SPR property,the heterogeneous Au@AgNRs not only exhibits high-purity,but also possesses high thermal stability,which shows that Au@AgNRs will be an attractive and promising candidate for plasmonic applications in plasmon-enhanced spectroscopies,bio-molecular detection and plasmon sensor.4.Synthesis of ultrafine Au nanowires?AuNWs?.Ultrafine AuNWs with high yield were synthesized by one-step wet chemical method using oleylamine and oleic acid as solvent,surfactant,and reductant,respectively.By using a simple method of purification,ultrafine AuNWs of² nm in minimum diameter and tens of micrometers in length were obtained.The diameter of ultrafine AuNWs can be tuned by the volume ratio of oleylamine and oleic acid.The possible growth mechanism of Au nanostructures is discussed combined with the influence of the synthesitic parameters?such as reaction temperature and the volume of oleylamine?on AuNWs.And the stability of AuNWs is studied briefly.