Theoretical Study On LSPR Properties And Sensing Performance Of Hexagonal Nanoparticles

Due to the unique local surface plasmon resonance?LSPR?properties,metal nanoparticles show extinction characteristics and the enhancement of local field.Based on these properties mentioned above,metal nanoparticles can be applied in many fields,such as LSPR sensors,nano-waveguide and surface-enhanced raman scattering?SERS?,et al.The sensing performance of the LSPR sensor is denoted with the figure of merit?FOM?,the higher the figure of merit,the better the performance of sensing.The figure of merit is directly related to the full-width at half-maximum?FWHM?of the extinction spectrum and the refractive index sensitivity?RIS?.In order to obtain the better figure of merit,the refractive index sensitivity must be as high as possible,and the full-width at half-maximum of the extinction spectrum must be as narrow as possible.The factors that affect the LSPR properties of metal nanoparticles include material,size,shape,arrangement mode,and refractive index of surrounding media.In recent years,people have made a lot of effort to improve the sensing performance of the metal nanoparticles on various aspects.Both in theoretical calculation and the preparation technology of nanostructure,many remarkable results have been achieved.However,because of lacking the experimental conditions,many nice theoretical results are difficult to realize.This thesis proposed a novel hexagonal metal nanostructure on the basis of the existing experimental results,and studied the LSPR properties and sensing performance using the CST Microwave Studio simulation software.The main work and conclusions of this paper are as follows:1.The vertex angle influence on the LSPR properties and sensing performance of silver hexagram nanoparticles are studied.The simulation results show that the peak wavelength of extinction spectrum has remarkable buleshift and the intensity gradually weakened with the vertex angle increasing fromo20 too140,when the thickness and cross-sectional area of the hexagonal nanoparticles are constant.Vertex angle has great influence on the refractive index sensitivity,but little effect on the full-width at half-maximum of the extinction spectrum.When vertex angle iso30,thegreatest refractive index sensitivity and figure of merit are 1164 nm/RIU and 9.86 RIU^-1,respectively.For the situation with truncated vertices in experiment,the research results display that the figure of merit gradually decreases with the truncation degree of the angle increasing.2.The LSPR properties and sensing performance of sexfoil nanoparticles are studied.The paper calculated the extinction spectrum of sandwich?Ag/Mg F2/Ag?structures firstly,which are easy to achieve in the experiment.The calculation results show that with the thickness of the dielectric layer increasing,long-wavelength peaks blueshift,while short wavelength peaks redshift.Strong near-field coupling of the upper and lower metal layers leads to electric and magnetic field resonances.As the thickness increasing,the electric field resonance gradually increasing,while the magnetic field resonance decreasing.When the thickness of dielectric layer is 80 nm,only a resonance peak appeared in the extinction spectra of sexfoil nanoparticle,and the full-width at half-maximum reduced to the minimum.The obtained refractive index sensitivity and figure of merit are 332 nm/RIU and 3.91 RIU^-1,respectively.Although changing the thickness of the dielectric layer can control the peak wavelength of the LSPR spectrum,the obtained sensing performance is not ideal.To obtain the better figure of merit,we further simulate the extinction spectrum,and research the sensing properties of monolayer Ag sexfoil nanoparticles.After a series of trials to optimize the thickness and shape,the refractive index sensitivity approximates 668nm/RIU,and the greatest figure of merit comes to 14.8 RIU^-1.