Electrochemical Deposition and Characterization of Fe₃O₄ Films Produced by the Reduction of Fe(III)-triethanolamine

In this paper, we demonstrate that films of magnetite, Fe3O4, can be deposited by the electrochemical reduction of a Fe(III)-triethanolamine complex in aqueous alkaline solution. the films were deposited with a columnar microstructure and a [100] preferred orientation on stainless steel substrates. In-plane electrical transport and magnetoresistance measurements were performed on the films after they were stripped off onto glass substrates. the resistance of the films was dependent on the oxygen partial pressure. We attribute the increase in resistance in O2 and the decrease in resistance in Ar to the oxidation and reduction of grain boundaries. the decrease in resistance in an Ar atmosphere exhibited first-order kinetics, with an activation energy of 0.2 eV. the temperature dependence of the resistance showed a linear dependence of log(R) versus T-1/2, consistent with tunneling across resistive grain boundaries. a room-temperature magnetoresistance of -6.5% was observed at a magnetic field of 9 T

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

Thesis (Ph. D.)--University of Washington, 2004There 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

Epitaxial Electrodeposition of ZnO on Au(111) from Alkaline Solution: Exploiting Amphoterism in Zn(II)

The amphoteric nature of ZnO is used to produce the material from strongly alkaline solution. The solution pH is lowered globally to produce ZnO powder, and it is lowered locally at a Au(111) surface to produce epitaxial films. ZnO powder is precipitated from a solution of 10 mM Zn(II) in 0.25 M NaOH by simply adding 1 M HNO3 to the solution. For the film electrodeposition, the local pH at the electrode surface is decreased by electrochemically oxidizing the ascorbate dianion. The chemically precipitated ZnO powder grows with a sea urchin-like nanostructure, whereas the electrodeposited films have a columnar structure. ZnO electrodeposited onto a Au(111) single crystal has a ZnO(0001)[101]//Au(111)[10] orientation relationshi

Electrodeposition of Nanometer-Thick Ceria Films by Oxidation of Cerium(III)-acetate

Thin films of ceria were electrodeposited onto Hastelloy substrates by the electrochemical oxidation of Ce(III) acetate complexes. the mode of deposition was dependent on the applied potential. at a potential of + 0.5 V vs. Ag/AgCl, the deposition proceeded by a direct oxidation of Ce(III) to ceria. Films deposited at this potential were smooth and crack-free as observed by SEM. Film thicknesses were determined by X-ray reflectivity and ellipsometry. For a deposition time of 1000 s, the ceria deposited to a thickness of approximately 40 nm and a density of 65%. the deposition exhibited self-limiting growth, with growth rates rapidly decreasing with deposition time. at a higher potential of + 1.1 V vs. Ag/AgCl, the films appear to grow by an indirect mechanism, in which the electrochemical oxidation of water forms O2 which then reacts with Ce(III) to form ceria nanoparticles in the growth solution. It was also shown that nanometer-scale ceria powder could be produced by bubbling the solution with molecular oxygen

Epitaxial Electrodeposition of Chiral CuO Films from Copper(II) Complexes of Malic Acid on Cu(111) and Cu(110) Single Crystals

Chiral films of CuO were anodically electrodeposited onto Cu(111) and Cu(110) single crystals from alkaline solutions of Cu(ii) complexed with the malate ion. The chirality of the film was directed by the chiral solution precursor. X-Ray diffraction pole figures and stereographic projections were used to determine the absolute configuration of the films. CuO films grown on Cu(111) from l-malate had (111) and (311) orientations and the films grown from d-malate had (111) and (311) orientations. CuO films grown on Cu(110) from l-malate had (110) and (311) orientations, whereas the films grown from d-malate deposition bath had (110) and (311) orientations. The CuO films grown from a racemic malate bath showed only the (111) and (111) orientations on Cu(111) and (110) and (110) orientations on Cu(110). Single crystals of l-, d- and dl-bis(malato)copper(ii) dihydrate complexes were synthesized and the structures were determined with X-ray crystallography. The chiral complexes of bis(malato)copper(ii) dihydrate were each found to belong to the monoclinic space group P2 1 whereas the racemic complex belonged to the centrosymmetric P2 1/c space group. The chiral complexes formed coordination polymers along the b-axis, with the carboxyl group from each complex linking to the axial site of an adjacent Cu(ii) complex. In the complex produced from the racemic mixture, no coordination polymers formed. © 2011 The Royal Society of Chemistry

Temperature Dependence of the Relative Rates of Chlorination and Hydrolysis of N2O5 in NaCl-Water Solutions.

We have measured the temperature dependence of the ClNO2 product yield in competition with hydrolysis following N2O5 uptake to aqueous NaCl solutions. For NaCl-D2O solutions spanning 0.0054 M to 0.21 M, the ClNO2 product yield decreases on average by only 43 % from 5 to 25 C. Less reproducible measurements at 0.54 M and 2.4 M NaCl also fall within this range. The ratio of the rate constants for chlorination and hydrolysis of N2O5 in D2O is determined on average to be 1150±90 at 25 C up to 0.21 M NaCl, favoring chlorination. This ratio is observed to decrease significantly at the two highest concentrations. An Arrhenius analysis reveals that the activation energy for hydrolysis is just 3.0±1.5 kJ/mol larger than for chlorination up to 0.21 M, indicating that Cl- and D2O attack on N2O5 have similar energetic barriers despite the differences in charge and complexity of these reactants. In combination with the measured pre-exponential ratio favoring chlorination of {300\ }_{-200}^{+400}, we conclude that the strong preference of N2O5 to undergo chlorination over hydrolysis is driven by dynamic and entropic, rather than enthalpic, factors. Molecular dynamics simulations elucidate the distinct solvation between strongly hydrated Cl- and the hydrophobically solvated N2O5. Combining this molecular picture with the Arrhenius analysis implicates the role of water in mediating interactions between such distinctly solvated species and suggests a role for diffusion limitations on the chlorination reaction

Electrodeposition of Epitaxial Magnetite Films and Ferrihydrite Nanoribbons on Single-crystal Gold

Magnetite (Fe₃O₄), ferrihydrite (Fe 10O14(OH)2), and iron (Fe) films were electrodeposited by cathodic deposition from an alkaline Fe(III)-triethanolamine solution. The electrodeposited phase depended on the applied potential. Magnetite films were electrodeposited from -1.01 to -1.10 V vs Ag/AgCl, whereas ferrihydrite films were deposited from -1.10 to -1.20 V vs Ag/AgCl. Iron deposition occurred at more negative potentials. The polycrystalline films were characterized using X-ray diffraction, scanning electron microscopy, and Mössbauer spectroscopy. Epitaxial magnetite films on low-index gold crystals were produced at three different potentials. X-ray diffraction analysis of the magnetite films deposited at -1.01, -1.05, and -1.10 V vs Ag/AgCl showed [111] oriented films on Au(111) and Au(001). Because of twinning of the 111 planes, the [511] orientation was present in thicker films. Magnetite grew with a [110] orientation on Au(110). At the more negative potentials of -1.10 and -1.20 V vs Ag/AgCl, ferrihydrite deposited with an (1120) orientation. © 2009 American Chemical Society

Recrystallized Arrays of Bismuth Nanowires with Trigonal Orientation

We demonstrate methods to improve the crystalline-quality of free-standing Bi nanowires arrays on a Si substrate and enhance the preferred trigonal orientation for thermoelectric performance by annealing the arrays above the 271.4 °C Bi melting point. The nanowires maintain their geometry during melting due to the formation of a thin Bi-oxide protective shell that contains the molten Bi. Recrystallizing nanowires from the melt improves crystallinity; those cooled rapidly demonstrate a strong trigonal orientation preference