Journal of Nano Research Vol. 3

Abstract: Metallic silver particles in the nanometer size range were obtained in SiO2 matrix by the reduction of AgNO3 with the non-ionic diblock copolymer (Brij 58). Hexagonal mesostructured sol-gel films were synthesized by dip-coating method using the surfactant Brij58 to produce channels into the film, which house the silver nanoparticles. Optical properties of the metallic nanoparticles were studied by UV-Vis spectroscopy, TEM and HRTEM images. The experimental absorption spectrum of the metallic silver nanoparticles exhibits an absorption band located at 438 nm and a shoulder at longer wavelength. The TEM images show randomly distributed silver nanoparticles (Type I) along with some oriented as long line (Type II). Both distributions exhibit a silver oxide shell around of them. The second shell covering the silver core - silver oxide shell system is related to the surfactant. The optical absorption spectrum was modelled using the Gans theory. The fit shows two main contributions related to metallic silver nanoparticles with different axial ratios, and surrounding of a dielectric medium with high refractive index. Presence of the high refractive index silver oxide shell was confirmed by X-ray diffraction technique. The contributions of silver core and silver oxide shell play important roles in the optical properties of the films.

Abstract: Sol-gel silica films containing gold ions were prepared with and without citric acid (capping agent). Heat treatment of these films in hydrogen atmosphere (reducing agent) leads to the formation of gold nanoparticles. The experimental optical spectra of the gold nanoparticles prepared with citric acid revealed a surface plasmon resonance band located at 585 nm. Transmission electronic microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) measurements revealed the formation of prolate gold nanoparticles (6.4 nm of average diameter) and aggregates dispersed in silica matrix. On the other hand, gold nanoparticles in sol-gel silica films prepared without citric acid exhibited a splitting in surface plasmon resonance band for the prolate gold nanoparticles with an average size <12 nm. On further annealing the samples in oxygen atmosphere, the gold nanoparticles prepared with citric acid exhibited high stability in contrast to the samples prepared without citric acid. This stability probably depends on the formation of a microporous structure of silica produced by the citric acid. The optical properties of the metallic nanoparticles were modeled using Gans theory.

Abstract: Nanocrystalline CaTiO3 powders doped with Fe2O3 have been prepared using a soft chemical route. Precipitation of CaTiO3 nanocrystals has been studied by monitoring the exothermic peak in their DSC spectra. The crystal growth temperature of the samples depends on the concentration of iron. Surface morphology, crystal structure, optical and electrical properties of the nanostructures are investigated. X-ray diffraction study shows that the as-prepared powders are amorphous in nature and CaTiO3 phase formation starts at around 500 0C. Rietveld analysis revealed that the particle size of iron substituted CaTiO3 is in nanometer range. Optical bandgap of the nanostructures varies from 4.3 to 3.7 eV for the variation of iron concentration from 0.05 to 0.2 mole %.