Papers by Author: James H. Dickerson

Abstract: The electrophoretic deposition of TiO₂ iron oxide nanocrystal monolayers from stable, mixed colloidal suspensions by electrophoretic deposition using non polar solvents is reported. The selective deposition of TiO₂ was accomplished by controlling the mobility of the nanocrystals and the voltage during electrophoretic deposition. The effect of the electrophoretic deposition processing parameters (voltage and particle mobility) on the promotion and suppression of nanocrystal deposition was investigated.

Abstract: Electrophoretic current densities and nanoparticle densities were measured during and after the electrophoretic deposition of iron oxide nanoparticles and were compared to infer the relationship between the quantity of deposited nanoparticles and the measured current. This information led to an assessment of the primary contributors to the measured current during non-polar solvent-based electrophoretic deposition. Such information was employed to monitor and to control sub-monolayer growth of nanoparticle films. Subsequently, the average charge magnitude of each suspended colloidal nanoparticle was calculated to be ±3.2 ± 0.3 electron charges.

Abstract: Colloidal sol-gel is a common method used for the preparation of stable and homogeneous sols and thin films. The nanoparticulate sols can be easily deposited by EPD, which is a versatile technique for producing denser and thicker coatings than those produced by other techniques like dipping. A complete characterization of the sols, such as colloidal stability and electrophoretic mobility, which can be determined through zeta potential measurements, as well as the influence of deflocculants in the surface properties, is needed before using electrophoretic deposition. In this work, we have prepared sols of TiO₂ with an alkoxide:water molar ratio of 50:1 and Eu (III) doped-TiO₂ (2 mole % Eu (III)) using as precursors titanium (IV) isopropoxide and europium (III) acetate hydrate, respectively. The stability of the particulate sols was studied in terms of conductivity, zeta potential and viscosity evolution. Anatase stable sols, after peptization and without the use of any additive, were deposited on stainless steel substrates by electrophoretic deposition under both constant current and constant voltage conditions. Using different intensities and deposition times we have obtained thin films with different features (thicknesses and morphology) and different optical properties. The presence of europium (III) increases particle size, viscosity and peptization time and decreases the band gap of TiO₂.

Abstract: The electrophoretic deposition of polystyrene/divinylbenzene (PS/DVB) star polymer-europium sulphide (EuS) nanocomposite films from a colloidal suspension is reported. Liquid suspension, containing both the PS/DVB star polymer and EuS nanocrystals were prepared by separately injecting dichloromethane (DCM) based solutions of EuS nanocrystals and of the star polymers, respectively, into a stratified liquid combination of hexane and DCM. Scanning electron microscopy illustrates images of the dependence of surface morphology on nanocrystal concentration of the PS/DVB-EuS star polymer film. These polymer-encased nanocrystal films may be a more practical option for the fabrication of magneto-optical thin film devices, such as optical switches, optical isolators, and optical memories.