Modulation Of Localized Surface Plasmon Resonance Absorption With Nano Cu@Ag Composite

Localized Surface Plasmon Resonance（LSPR）is a phenomenon in which light interacts with nano-sized metal particles.By adjusting the size,morphology,shell structure and physical and chemical properties of the background medium of metal nanomaterials to control the absorption spectrum,nano-photonic devices with various functions are designed,which has a wide application potential in the fields of spectrum control,sensing and monitoring,solar cells and medical imaging.Compared with Au,Ag and other precious metals,Cu material has been widely concerned in recent years due to its abundant reserves and excellent optical properties.However,at present,the optical properties of Cu nanostructure are mostly controlled by changing the morphology,so the spectral range of LSPR is narrow.In order to expand the dimension and scope of optical property regulation of Cu-based nanomaterials,the paper designed and fabricated Cu elements with different dimensions by combining theoretical simulation and experiment,and discussed the LSPR regulation law of size and morphology on nano Cu.The effect of Cu/Ag ratio on LSPR optical absorption of Cu@Ag composite metal with different structure was investigated.（1）The finite-difference time-domain（FDTD）method was used to establish a Cu nanosphere model,and the effects of size and array spacing on the LSPR characteristic absorption spectra of Cu nanospheres were simulated.The results show that the characteristic absorption of LSPR was red-shift with the increase of the diameter of Cu nanospheres in the range of 75-300 nm.The blue-shift of LSPR characteristic absorption occurs when Cu nanosphere array spacing increases.In this paper,the corresponding size of Cu nanospheres was prepared by hydrothermal method,and their LSPR characteristic absorption was studied.The experimental results were consistent with the simulation trend,and the absorption spectrum can be adjusted from 582-599 nm.（2）The regulation mechanism of LSPR characteristic absorption on one-dimensional Cu nanowires was simulated and experimentally studied.The effects of the diameter,spacing and background dielectric environment（deionized water,ethanol and n-hexane）on the LSPR characteristic absorption of Cu nanowires were investigated.The results show that in the range of 75-300 nm,with the increase of the diameter of Cu nanowires,the LSPR characteristic absorption spectrum can red-shift from 568 to 630 nm,and the intensity of characteristic peak increases simultaneously.Different from Cu nanospheres,the spacing of Cu nanowires has little effect on their LSPR spectra,which can be ignored.The LSPR characteristic absorption peak of Cu nanowires was red-shift with the increase of refractive index in the surrounding dielectric environment.The reason was that due to the increase of dielectric constant,the polarization electric field caused by the effective electric field is weakened,and finally leads to the reduction of internal electron recovery force,resulting in the red shift of absorption peak（3）This paper explored the regulation mechanism of LSPR characteristic absorption of two-dimensional Cu nanosheets,and studied the LSPR spectra of triangular and hexagonal Cu nanosheets with different sizes and thicknesses.The simulation results show that the triangular and hexagonal Cu nanosheets have a wider spectrum range.When the side length of triangular Cu nanosheets increases from 30 to 400 nm,its LSPR characteristic absorption peak red-shifts from 661 to1058 nm.When the side length of hexagonal Cu nanosheets increases from 30 to 70 nm,its LSPR characteristic absorption peak red-shift from 624 to 812 nm.In the experiment,due to the stacking effect of the nanosheet,the corresponding absorption spectrum range was smaller than the simulation result,because the increase of the thickness of the two-dimensional Cu nanosheet will lead to the obvious blue-shift of the LSPR characteristic absorption peak.Therefore,fully disperses the nanosheets and prevents stacking effect was an effective method to expand the regulation range of the LSPR characteristic absorption spectrum of Cu nanosheets.（4）Ag nanospheres were deposited on Cu nanospheres,nanowires and nanosheets by sacrificial template method,and Cu@Ag nanomaterials with different Cu/Ag ratios are grown.The regulation mechanism of structure and composition on LSPR characteristic absorption peaks of Cu@Ag nanomaterials was studied.The results show that when the Cu/Ag ratio is greater than 1:0.16 or less than 1:3,the characteristic absorption peak of LSPR was single.When the Cu/Ag ratio was in between,the characteristic absorption peak of LSPR was dipole and quadrupole,and the maximum wavelength of LSPR was 648 and 650 nm,respectively.Due to the anisotropy of Cu@Ag nanosheets and the influence of plasma hybridization mechanism,the characteristic absorption peak position of LSPR was different from that of Cu@Ag nanospheres and nanowires.When the Cu/Ag ratio were 1:0.5 and1:1,Cu@Ag nanosheets have three peak responses.By controlling the Cu/Ag ratio,the control range of triangular Cu@Ag nanosheets and hexagonal Cu@Ag nanosheets can reach 260-595 nm and 339-795 nm,respectively.Therefore,compared with single metal,multi-dimensional Cu@Ag composite metal can expand the spectrum control range of LSPR to a greater extent.