Generation of an ordered layer of silver nanoparticles in mesostructured dielectric films

Abstract : Mesostructured organic–inorganic silica films containing AgNO3 are used as template to form ordered and dense layers of silver nanoparticles embedded in a dielectric matrix. The hybrid silica films are mesostructured by a triblock copolymer polyethylene oxide-polypropylene oxide-polyethylene oxide ((PEO)106(PPO)70(PEO)106, F127) and contain the silver precursor (AgNO3) which is dissolved directly in the silica sol prior to deposition. The films are reacted with a sodium borohydride solution (NaBH4), which leads to the formation of a plane ordered network of silver oblate nanoparticles with a narrow size distribution located just below the film surface, and observed by Transmission Electron Microscopy (TEM). The minor and major axis lengths are equal to 5.3 ± 0.5 and 7.2 ± 0.6 nm, respectively. The characterization of the mesostructured film before and after the reductive treatment evidences that silver particles grow in place of copolymer micelles in the upper layer of the mesostructured thin film. Rutherford Backscattering Spectrometry (RBS) measurements support the hypothesis that silver ions initially dispersed in the film volume migrate toward the film surface to form the monolayer of silver nanoparticles, organized and stabilized by the copolymer micelles in the film. IR and ellipsometric measurements are used to characterize the changes in the hybrid copolymer-silica matrix.