Sol electrophoretic growth of oxide nanostructures: synthesis, properties and modeling

Abstract

There is great interest in the ability to form oxide (especially complex oxide) nanorods, given the number of functional properties exhibited by oxide materials. This research examines the template-based growth of nanorods of several oxide ceramics, formed by means of a combination of sol-gel processing and electrophoretic deposition. While sol electrophoretic deposition has been known for some time as a technique for formation of films, this work pioneers its use for the formation of nanorods.Both single metal oxides (TiO2, SiO2) and complex oxides (BaTiO3, Sr2Nb2O7, and Pb(Zr0.52Ti0.48)O3) have been grown by this method. Uniformly sized nanorods of about 45--200 nm in diameter and 10--60 mum in length were grown over large areas with near unidirectional alignment. Desired stoichiometric chemical composition and crystal structure of the oxide nanorods was readily achieved by an appropriate procedure of sol preparation, with a heat treatment for crystallization and densification. A systematic study of the influence of the several processing parameters was undertaken to determine optimal processing conditions. Preliminary property measurements for several oxide nanorod systems are also reported.In addition, this work presents and discusses the formation and properties of silica and titania nanorods encapsulated with a thin gold shell. Nanorods of silica and titania ∼10 mum in length and with diameters ∼90--200 nm are made by combining sol-gel electrophoresis with a suitable template. After removing the template at high temperature, the surface of the rods is re-hydrolyzed by heating in water. 3-Aminopropyltrimethoxysilane is reacted with the surface hydroxyl groups, self-assembling amine functionality on the surface of the rods. These groups act as anchoring sites for the gold, which forms a thin shell around the oxide nanorod. UV-vis absorbance spectra of these samples are analyzed to determine the relationships between shell thickness, core size, core material and properties.