Electrochemical deposition into templated architectures has been shown to increase the observed saturation magnetization of a range of magnetic materials (e.g. 1). Here we have created monolayer (2D) and 3D opal-type structures of NiFe (permalloy) and Co by electrodeposition into self-assembled polymer templates. The microstructure and thickness of the resultant macroporous structures is controlled by the electrochemical parameters during nucleation and diffusion-controlled growth. Preferential crystallographic texture is observed – resulting in magnetic anisotropy for Co. The magnetic behaviour is assessed by both conventional bulk magnetometry, and locally using high-resolution Lorentz microscopy in the transmission electron microscope (TEM) - providing new insights into the functional properties of these materials. Hao, F. Q. Zhu, C. L. Chien & P. C. Searson. Fabrication and magnetic properties of ordered macroporous nickel structures. J. Electrochem. Soc. 154, D65-D69, (2007)

ZnO nanotubes were prepared by selective dissolution of electrodeposited nanorods. The effect of solution pH, rod morphology, and chloride ion concentration on the dissolution mechanism was studied. The selective etching was rationalized in terms of the surface energy of the different ZnO crystal faces and reactant diffusion. The nanorod diameter and chloride concentration are the most influential parameters on the dissolution mechanism because they control homogeneous dissolution or selective etching of the (110) and (002) surfaces. Bulk solution pH only has an effect on the rate of dissolution. By accurate control of the dissolution process, the nanomorphology can be tailored, and the formation of rods with a thin diameter (10-20 nm), cavity, or ultra-thin-walled tubes (2-5 nm) can be achieved.

Large area macroporous zinc oxide (ZnO) films have been prepared by colloidal crystal templating on to transparent conducting oxide (TCO) substrates using an electrochemical deposition technique. Characterisation by scanning electron microscopy (SEM) reveals changes in the microstructure of the ZnO films as the template diameter and deposition potential are varied. Analysis by X-ray diffraction (XRD) and UV–vis spectroscopy show that the structural variations do not influence the inherent properties of the ZnO. We attribute the observed microsturctural differences to variations in growth kinetics in response to the applied deposition potential and solution transport phenomena that are controlled by the template dimensions. The optical properties of the structures exhibit two distinct features, originating from the optical band-gap of the ZnO and the photonic band-gap of the ordered macroporous structure.

Electrodeposition of highly crystalline ZnO nanostructures directly onto copper phthalocyanine and pentacene thin films, from aqueous solutions containing zinc nitrate and dissolved oxygen, has been successfully demonstrated for the first time using a two-step electrochemical deposition process. Importantly, surface activation of the molecular thin film substrates by depositing a thin layer of ZnO nanoparticles at high cathodic overpotentials prior to film growth was found to be crucial for achieving a dense coverage of ZnO nanostructures with uniform morphology. The mechanism for ZnO deposition via electroreduction of hydroxide precursor species (oxygen and NO(3)(-) ions) at the organic-electrolyte interface was shown to be analogous to that reported for conventional inorganic and metal electrodes. Comparison of cathodic current density-time curves, measured during deposition, with film orientation and morphology revealed that the cathodic current density and number of nucleation sites are key factors in determining the characteristics of ZnO film growth on organic substrates. Significantly, the CuPc and pentacene films are not damaged or degraded during this process.

Ruddlesden-Popper phases of the general stoichiometry Lnn+1NinO3n+1 are potential solid oxide fuel cell cathodes displaying attractive electronic and ionic conductivities. To ensure long term performance, understanding of the materials degradation mechanisms occurring during operation is vital. One of the key processes in the cathode is the oxygen reduction and incorporation reaction which involves the redox of the transition metal cation species. In order to understand these processes in situ characterisation techniques are required that probe cation oxidation state directly. In this work two cathode materials, La2NiO4+δ and La4Ni3O10−δ, have been investigated by X-ray absorption spectroscopy of the near-edge region (XANES) of the Ni K-edge at room temperature and 650 °C. From these data it has been determined that a polynomial relationship between Ni oxidation state and edge position exists. Further the Ni oxidation state, and hence oxygen non-stoichiometry, was found to reduce on heating under static air for both La2NiO4+δ and La4Ni3O10−δ, implying that ionic conductivity in these materials is significantly affected by Ni valence. This is correlated with previous modelling studies of the defect chemistry of La2NiO4+δ to confirm the nature of the charge compensation mechanism and by extension the mobile species.

The formation of nanoporous gold by open circuit dealloying of 100 nm AgAu foils in nitric acid is investigated in situ and in real time by combining synchrotron small angle X-ray scattering (SAXS) and X-ray diffraction (XRD). The time dependence of the dealloying is followed as a function of acid concentration. For all concentrations, several characteristic dealloying stages are observed. Firstly, there is a fast initial dissolution stage with an increase in surface area due to pore and mound formation; this leads to strain in the nanoporous gold that results from an increase in capillary pressure. After dissolution is complete, there is rapid coarsening of the quasi-periodic, pore-ligament morphology. During this later stage, we deduce strong strain anisotropies that can be explained by preferred crystallographic orientation of ligaments. This rapid coarsening stage is followed by a slow coarsening stage where the SAXS patterns, and hence the quasi-periodic morphology, is self-similar in time. There is a strong correlation between the morphology evolution and strain development, which can be explained by capillary forces.

CeNbO4+delta has been shown to undergo reversible redox processes as a function of both temperature and time. However the associated phase transitions are not fully reversible and this unusual feature is reflected in spectra obtained from near edge X-ray absorption spectroscopy of the Ce L-III edge. Two materials have been studied: CeNbO4.08 and CeNbO4.25 and it is found that the oxidation and reduction rates for these two materials differ significantly and that the thermal history of the material dramatically affects the extent and rate of redox activity. (C) 2009 Elsevier B.V. All rights reserved.

A systematic study of the effect of the zinc oxide (ZnO) electrodeposition parameters (concentration, temperature, potential and pH) on film morphology, thickness, transparency, roughness and crystallographic orientation is presented with the view of producing optimized thin, planar, and continuous ZnO films for photovoltaic applications. Electrochemical measurements of the deposition charge as a function of time are used to understand the mechanism of nucleation and textured growth. Continuous thin films of crystalline ZnO are obtained at temperatures below 100 degrees C without the need for subsequent annealing. The formation of continuous films is favoured by high concentrations of Zn2+ precursor (> 100 mM), high temperature (> 70 degrees C) and low potentials (< -1.1 V/AgAgCl). A low bulk solution pH is shown to be a key factor in obtaining thin continuous films and the crystallographic orientation of these films can also be controlled by the deposition parameters. The importance of orientation and thickness control on device performance is shown by using the electrodeposited films as electron extracting interlayers in a model organic photovoltaic system.

The changes in crystal growth habit of electrodeposited zinc oxide with zinc nitrate concentration are explained by changes in the levels of saturation at the electrode. Three growth regimes are found between 0.5 and 50 mM. For concentrations less than 2 mM, the growth is one-dimensional. Nanorods grow by screw dislocations from the outside inward, no coalescence is observed, and their surface shows pyramid-like features. For concentrations above 20 mM, the growth is two-dimensional. Large levels of supersaturation favor the nucleation on the low indexes faces and large sheets are observed. In the intermediate regime of growth, the growth is pseudo three-dimensional. Nanorods with a conical ends grow initially before coalescing and forming dense films.

We report herein the fabrication of hybrid conjugated polymer/ZnO photovoltaic devices using ZnO nanorod structures prepared by electrodeposition and study the effect of introducing a second metal oxide overlayer using a TiCl4 post-treatment. We use transient absorption spectroscopy, scanning electron microscopy, and photovoltaic device measurements to study the microstructure and charge generation properties of the hybrid films and the performance of the resulting devices. We show how the ZnO nanostructure can be controlled via the nanorod growth conditions and demonstrate that photovoltaic device performance can be optimized by controlling the nanostructure in this way. Moreover, we show that a large increase in photocurrent generation can be achieved by coating the ZnO surface with a thin layer of titanium oxide by treating the ZnO nanostructure with a TiCl4 solution.

A substantial increase in device performance and operational stability in solution processed inverted bulk heterojunction (BHJ) organic photovoltaic devices (OPV) is demonstrated by introducing a zinc oxide (ZnO) interlayer between the electron collecting bottom electrode and the photoactive blend of poly(3-hexylthiophene) (P3HT) and phenyl-C-61-butyric acid methyl ester (PCBM). The structure and morphology of the dense, planar ZnO layers were controlled either by electro-deposition or spray pyrolysis techniques. Metal oxide sandwich OPV devices based on the photoactive blend on an electro-deposited ZnO interlayer with a (100) preferential crystal orientation, and using a tungsten oxide (WOx) interlayer on the opposite electrode, resulted in a remarkable increase in power conversion efficiency with a value of 4.91% under AM1.5 illumination and an external quantum efficiency of 74%. Electro-deposition of the ZnO at low temperature proved to be the most promising method for forming the ZnO interlayers, allowing the highest control of film structure and morphology, as well as leading to significantly improved device efficiency and stability.

ZnO nanostructured films fabricated by electrochemical deposition exhibit a variety of morphologies. Understanding their respective nucleation and growth mechanisms requires in situ techniques. A time-resolved X-ray absorption and fluorescence method is described, which adequately captures both processes and illustrates differences in the growth rates for films deposited at different potentials. In so doing, the new method has significant advantages over a previous method of continually scanning across the near-edge region of the absorption spectrum while the film was being deposited.

In situ synchrotron X-ray absorption was used to study the nucleation and growth of ZnO nanostructures electrochemically deposited from aqueous solutions. A fixed-energy approach was used, which facilitates faster time resolution for systems that are not amenable to transmission measurements and where species-specific information has so far been elusive. Films formed at low potentials (-0.97 V vs Ag/AgCl) show instantaneous nucleation, continued growth, and coalescence of the nanorods. The resultant film is dense with narrow dispersion of rod diameters. At less negative deposition potentials (-0.77 V vs Ag/AgCl), the nucleation is more protracted, resulting in a polydispersed film. In this higher potential region, the growth rates are slower, and there is less evidence of coalescence in the deposited structures, with continued growth along the c-axis only.

We present results of in situ synchrotron X-ray diffraction experiments on electrochemically formed ZnO nanostructured films during their growth on to Au substrates. This allows the evolution of texture to be monitored throughout the deposition process. The results are in good agreement with previous in situ X-ray absorption spectroscopy measurements of growth kinetics and indicate that strong preferred orientation, which is not evident from the microstructure, develops early in the growth process.

ZnO is known to produce a wide variety of nanostructures that have enormous scope for optoelectronic applications. Using an aqueous electrochemical deposition technique, we are able to tightly control a wide range of deposition parameters (Zn 2+ concentration, temperature, potential, time) and hence the resulting deposit morphology. By simultaneously conducting synchrotron x-ray absorption spectroscopy (XAS) experiments during the deposition, we are able to directly monitor the growth rates of the nanostructures, as well as providing direct chemical speciation of the films. In situ experiments such as these are critical to understanding the nucleation and growth of such nanostructures. Recent results from in situ XAS synchrotron experiments demonstrate the growth rates as a function of potential and Zn 2+ concentration. These are compared with the electrochemical current density recorded during the deposition, and the final morphology revealed through ex situ high resolution electron microscopy. The results are indicative of two distinct growth regimes, and simultaneous changes in the morphology are observed. These experiments are complemented by modelling the growth of the rods in the transport-limited case, using the Nernst-Planck equations in 2 dimensions, to yield the growth rate of the volume, length, and radius as a function of time.

ZnO films were grown on polycrystalline Zn foil by cathodic electrodeposition in an aqueous zinc chloride/calcium chloride solution at 80 °C. Variation in the electrochemical parameters resulted in a variation in growth morphology from 1D (nanorods), 2D (‘nanoplates’) to 3D crystal growth. An as-received or mechanically polished substrate proved the most suitable substrate finish and allowed more highly aligned, dense structures to be grown; in contrast, electropolished substrates formed inhomogeneous deposits. Substrate annealing gave rise to large homogenous areas of nanorod deposition. Two-dimensional sheet growth was found to occur in conjunction with nanorods under specific electrochemical conditions. Hexagonal ‘plates’ approximately 50 nm in thickness and several microns in diameter were formed normal to the substrate.

ZnO nano-rods were grown on polycrystalline Zn foil by cathodic electrodeposition in an aqueous zinc chloride/calcium chloride solution at 80°C. Variations in the solution concentration and substrate surface preparation were explored to shed light on the nucleation of the nano-rods. It was found that the nano-rod diameter increased with increasing solution concentration. Rolling striations and native ZnO on the surface of the Zn appeared to enhance nucleation and allowed more highly aligned, dense structures to be grown. By using low solution concentrations (5.0 × 10−4 M ZnCl 2) and non-electropolished Zn substrates, well faceted, hexagonal nano-rod structures of dimension ∼80 nm diameter and >1 µm length were obtained. X-ray studies showed the samples to be highly aligned but containing a Zn-oxychloride impurity phase. Annealing caused the impurity phase to disappear and resulted in the films having a sharp photoluminescence double peak at 380/396 nm.