Study Of Radiative Properties Of Gold And Silver Nano-Particles Using Finite Difference Time Domain(FDTD) Method

In the field of nano-scale particles,optical nanoparticles（NPs）are those nanostructures constructed to accurately transfer free propagating optical radiation to localized energy.Many advancements have been made in this area by many scholars.However,many researches focused on experimental studies rather than numerical studies,especially on spectral radiative properties of complex gold and silver nanostructures.Therefore,numerical simulation was used to extensively study on spectral radiative properties of metallic NPs of novel shapes and morphology and their surface enhancement by controlling their specific parameters.The paper starts with the radiative properties of a single nanoparticle with or without considering the shape effects for comparison with Mie theoretical solution.The study then metamorphosed to coupled NPs and generalized to multilayered structures based on FDTD method.In the analysis of the design and optimization of electrically connected gold NPs with geometrical,shapes and dimensional control,it was first seen from the analysis of unconnected gold nano rod dimer that there is increasing redshift for decreasing separation distance between the two-nano rod,which shows that near-field induced coupling of two-nano rod arms.The bigger the gap in-between the charges are,the lower the restoring force tends to be.This result has shown that in practice,it is best to obtain lower separation distance between the nano rods,which is the major challenges faced in the fabrication of efficient nano antennas.To deeply understand the effects of the tunable extinction spectral for bowtie nanostructure as a function of junction ring inner radius reduction,detailed numerical calculation describing the control of the inner radius of nano ring place at the junction of bowtie nanoparticle was made,in the calculation dipole-dipole strong coupling effect was notice in the bowties that result to a stronger electric field in the hot spot and also a redshift of the plasmon resonance as well as concentration of the near-field in the hot spot.This indicates that when bowtie nano antenna arrays are electrically connected with rings at the junction the inner radius of the ring must be close to the outer ring radius in other to give a good output when in use as an optical sensing device,as the device is useful when the designer what to focus on the dipole response.A novel Sierpinski NPs were developed via coordinated multiple coupling.The study numerically exhibits that integrate design and application of different optical coupling effects can bring about the increased tunability in the spectral response and automatically enhanced electromagnetic field.The results show that Sierpinski NPs show an exceptional enhancement and electric field localization when correlated with a regular bowtie nanoparticle.This is because of the increase in density of the near fields generated in the cavities for the designs,which shows amaze bigger region on the metal surface,even when the region on the metal decreased after each fractalization.These enhanced localized fields on the fractal nanoparticle provide an avenue for efficient surface-enhanced Raman spectroscopy（SERS）substrates.The study also presents a qualitative investigation on the effect of conductive bridge across Ag Si O₂ core-shell nanoparticle with nano wire junction,and how it will influence the radiative properties of the system.It is found that the spectrum shows a strong near field in the direction of polarization,the reciprocating near-field circulation at the direction of polarization shows its remarkable characteristic feature,this near-field characteristic is very important in applications such as SERS.Furthermore,it is observed that profile of the plasmon band is completely dependent on the layers;this assertion is taken from the information gotten from the three particular layers tested.Also,through simultaneously increasing the length of the rectangular nanowire conductive bridge in which the distance（d）is constantly fixed at 22 nm and L varies from 17 nm–2 nm which give 2.5 nm,5 nm,7.5 nm,and 10 nm separation gap respectively,at this the spectral absorption spectrum of the core-shell structure of this band witness the addition of a second band grows when the junction dimensions were kept at optimal values L=17 nm to 2 nm and the distance between the core-shells at constant d=22 nm.It is found that applying the principles of conductive-bridged nanowire as explained can play an important part in tuning the spectral responses of plasmonic core-shell nanostructures for sensing and designing artificial molecules.