Synthesis And Optical Properties Of Low Density Gold-silica Complexes

In the process of strong laser and material interaction, the simulation results offluid mechanics show that the low density metal （such as Au, Pb） used as targetmaterials maybe effectively enhance laser absorption rate and X-ray reflectivity, andreduce the wastage of the radiant energy. Therefore, low density materials haveattracted more attention. In this paper, low density materials composed of Au andSiO₂were synthesized by nanotechnology and the optical properties have beensystematically studied.Firstly, gold nano-particles （AuNPs） were prepared using an improved chemicalreduction method. In order to control the morphology of AuNPs, the amount ofsodium citrate used as reducing agent was adjusted in the reaction process. The resultsshow that size distribution of AuNPs was in10nm-50nm, and the monodispersity wasgood.Secondly, gold coated amorphous silica （Au@SiO₂） particles were successfullysynthesized by the modified chemical coating method, in which polyvinylpyrrolidone（PVP） was used to modify the surface of AuNPs. The effect of silica shell thicknesson the local surface plasmon resonance （LSPR） of AuNPs was discussed. Our resultsfound that the absorption peak has an evidence red shift as shell thickness increased.Thirdly, photonic crystal film of Au@SiO₂particles was fabricated by usingisothermal heating evaporation induced self-assembly （IHEISA）. The correlationsbetween the experimental parameters and the structure of colloidal crystal wasdiscussed. Our results show that the photonic crystal quality strongly dependent onthe heat treatment temperature. Photonic band gap has a blue shift with increase ofheat treatment temperature. The intensity of the LSPR in the film is larger than that indispersion because of the interaction of LSPR among the ordered structure.Finally, the monodisperse Au@SiO₂particles were compressed in the mold. Inorder to obtain the block with different density, varied amount of polystyrene （PS）spheres was added during compressing process. At last, the low density material wassuccessfully synthesized （the minimum density up to368mg/cm³） by removing PSspheres at a high temperature.