Controllable Construction And Optical Properties Of Multilayer Gold Nanosphere Arrays

Precious metal nanoparticles have the characteristics of surface plasmon polaritons,which greatly enhance the interaction between light and matter and become an important branch of nano-materials research.The surface plasmon characteristics of metal nanoparticles are closely related to the composition of the material,the shape and size of the structure,and the coupling between particles will also cause changes in the local electromagnetic field and extinction cross section.Therefore,the macro-optical properties of noble metal nanoparticles can be designed by adjusting their microstructure.According to the above foundation,this paper chooses gold with better comprehensive performance as the material,explores the construction scheme of gold nanospheres multilayer close-packed array from the preparation of gold nanospheres,and studies the optical properties of single-layer and double-layer arrays of gold nanospheres,so as to explore the relationship between the microstructure and optical properties of gold nanospheres multilayer array films.The research work is summarized as follows:(1)Preparation of gold nanospheres and construction of monolayer and multilayer arrays of gold nanospheres.Gold nanospheres with an average size of 49 nm-176 nm were successfully prepared by polyol reduction method.The size of gold nanospheres can be adjusted by adjusting the reaction temperature and other conditions.The morphology and spectral characterization of the samples show that they have a good spherical structure.Based on the preparation of gold nanospheres solution,a single-layer periodic array of gold nanospheres was prepared by gas-liquid interface self-assembly,which was transferred to quartz glass and monocrystalline silicon substrate to form a single-layer array of gold nanospheres.After the monolayer array is naturally dried,it can be transferred again(many times)as a substrate to prepare a double-layer(multi-layer)periodic array of gold nanoparticles.(2)The optical properties of periodic arrays of single-layer gold nanospheres were studied.The results show that the dipole resonance peak of particles in solution becomes an inconspicuous weak peak in the close-packed array.In the smaller gold nanosphere monolayer array,the reflection spectrum presents a reflection peak.The reflection peak wavelength of the monolayer array constructed by 49 nm particles is 857 nm,and the reflection peak intensity is 47.7%.When the particle size increases to 69 nm,the reflection peak wavelength of the array is 985 nm and the intensity is61.9%,and the reflection peak is redshifted and enhanced.When the particle size of the array becomes larger,the light reflection in the near infrared band gradually increases.When the particle size reaches137 nm,the array presents continuous light reflection in the near infrared band,and the light reflection at the near infrared wavelength of 1000 nm and 2000 nm is 62% and 62.6% respectively.This strong continuous reflection reflects the characteristics of some gold films.In terms of light absorption,with the increase of the size of the building particles,the light absorption in ultraviolet band and near infrared band is gradually enhanced,and the absorption edge caused by interband transition near the wavelength of 500 nm becomes clear.(3)The optical properties of double-layer gold nanosphere arrays were studied.The research results of x-x double-layer array with the same particle size show that with the adjustment of the particle size from 49 nm to 176 nm,the scattering peak of the array shifts from 770 nm to 1340 nm,and the absorption peak shifts from 876 nm to 1935 nm.On this basis,the research results of x-y array with two kinds of diameter particles show that the difference of particle size between the upper layer and the lower layer has a significant influence on the absorption peak intensity.The absorption peak intensity of the x-y array with 137 nm particles as the lower layer and 49 nm particles as the upper layer is 74.4%,which is 33.4% higher than that of the array with 137 nm particles on the upper and lower layers.These results show that the scattering(absorption)peak position and absorption peak intensity can be adjusted by adjusting the size of the upper and lower layers of gold nanosphere arrays.(4)The photothermal conversion of single-layer and double-layer arrays of gold nanospheres in near infrared band was studied.Under the fixed power of 980 nm laser,the temperature rise of double-layer 69 nm gold nanosphere array with absorption peak in near infrared band is 2.3 °C higher than that of single-layer 69 nm gold nanosphere array.With similar absorption peakposition,the temperature rise of the x-y array with 49 nm particles as the upper layer and 103 nm particles as the lower layer increased by 9.3 °C.This shows that the infrared absorption peak of the double-layer gold nanosphere array can improve its photothermal conversion ability,and the intensity of the absorption peak can be adjusted by combining the size of the constructed particles,which is beneficial to the photothermal application of the near-infrared biological window.