P. N. Bartlett

The preparation and characterisation of H1-e palladium films with a regular hexagonal nanostructure formed by electrochemical deposition from lyotropic liquid crystalline phases

The hexagonal (H1) lyotropic liquid crystalline phases of C16EO8 (octaethyleneglycol monohexadecyl ether) and Brij® 56 non-ionic surfactants have been used to template the electrochemical deposition of nanostructured palladium films. The resulting H1-e palladium films were characterised by SEM, TEM and X-ray. The films contain regular hexagonal arrays of cylindrical pores separated by palladium walls with a centre to centre distance of 5.8 nm. Electrochemical studies show that these films have very high surface areas of the order of 91 m2 g−1. Studies of the hydrogen evolution reaction on these H1-e palladium films in acid show that the formation of adsorbed hydrogen can be readily distinguished because of the high surface area to volume ratio of the films (of the order of 107 cm2 cm−3). Hydrogen insertion into the palladium films is fast and the formation of both the α and β-hydride phases is observed in the voltammetry at potentials which are similar to those reported for bulk palladium. The electrodes are stable towards repeated cycling to form the β-hydride phase showing that the hydrogen insertion and concomitant lattice expansion does not destroy the H1 nanostructure.

Sculpted substrates for SERS.

Sculpted SERS-active substrates are prepared by assembling a closed packed monolayer of uniform polystyrene colloidal particles (diameter 350 to 800 nm) onto an evaporated gold surface and then electrodepositing gold through this template to produce films with controlled thicknesses, measured as fractions of the sphere diameter, d. The resulting surfaces consist of a regular hexagonal array of interconnected spherical cross-section dishes. The role of localised plasmons in determining the SERS enhancement factor obtained for benzene thiol adsorbed onto the surfaces is then investigated by correlation of the UV-visible reflectance spectra, 400 to 900 nm, measured at the same positions on the substrate surfaces, with the SERS spectra. The results are interpreted in terms of the relative contributions of plasmons that are free to propagate across the top surface and those trapped within the dishes of the sculpted surface.

An accurate microdisc simulation model for recessed microdisc electrodes

Abstract This study concentrates on an accurate determination of the chronoamperometric response for shallow and deep recessed microdiscs. Diffusion to the recessed microdisc is simulated using the finite element method (FEM). The deviation of the chronoamperometric response for a recessed microelectrode from that for the corresponding inlaid microelectrode can be significant depending on the recess depth. This is noted in terms of the magnitude of the chronoamperometric response and the shape of the chronoamperometric curves. We find cottrellian current decay for deep recess microdiscs at short times “switching” to steady-state behaviour at long times. This switch over in behaviour becomes sharper as the depth of the recess increases. The deviation of the recessed microdisc response from previously proposed approximate expressions is also discussed, with emphasis on the significant deviations for shallow recess microdiscs. The simulation model developed here is accurate yielding transient and steady state values. Approximate analytical expressions which can be used to calculate the transient and steady state responses for recessed microdisc electrodes are presented.

The oxidation of β-nicotinamide adenine dinucleotide (NADH) at poly(aniline)-coated electrodes. Part II. Kinetics of reaction at poly(aniline)-poly(styrenesulfonate) composites

Poly(aniline)–poly(styrenesulfonate) composite-coated glassy carbon electrodes are shown to produce a stable, reproducible amperometric response to NADH in citrate–phosphate buffer at pH 7. These responses have been studied as a function of electrode potential, film thickness and both NADH and NAD+ concentration. The results show that the oxidation of NADH occurs throughout the whole of the film and that NAD+, the reaction product, reversibly inhibits the reaction. Rate constants for the different processes have been obtained by kinetic modelling and compared with those previously determined for poly(aniline)–poly(vinylsulfonate) films. Preliminary comparisons imply that diffusion within ‘pores’ in these poly(aniline) composite matrices is important in determining the magnitude of the amperometric responses.

The fabrication of plasmonic Au nanovoid trench arrays by guided self-assembly

Plasmonic devices, which will enable on chip optical communication, rely on the interaction of light with free charges, and are key to optical sensing and waveguiding [1]. In previous work [2, 3], we have shown that spherical nanoscale voids in metal possess different, and potentially more useful, plasmonic modes than nanoscale metal particles. However, only by making linear arrays of such nanovoid structures it is possible to guide plasmons in specific geometric directions and fabricate plasmon waveguides which will enable on chip optical communication. In this work, single and multilayer arrays of gold voids have been fabricated through self assembly of sub-micron polystyrene spheres in V-shaped trenches in silicon, followed by selective area electrodeposition. Angle-dependent dispersion characteristics reveal the existence of localized plasmons. This is the first experimental evidence of linear plasmon arrays in templated self assembled structures.

Electrochemistry and contact angle measurements on polymer films of ω-(3-pyrrolyl)-alkanoic acids in aqueous solution

Films of poly(3-(pyrrolyl)-carboxylic acid), poly(3-(pyrrolyl)-butanoic acid) and poly(3-(pyrrolyl)-pentanoic acid) were prepared by electrochemical polymerisation of the monomers in acetonitrile. All three give stable voltammetry in aqueous solutions. In the case of poly(3-(pyrrolyl)-carboxylic acid) and poly(3-(pyrrolyl)-butanoic acid) this voltammetry is pH dependent. Measurement of the advancing contact angle using buffered solutions of different pH is shown to be a sensitive technique for the characterisation of the surfaces of these conducting polymer films. These contact angle titrations provide information about the acidity of the carboxylic acid groups at the surface of the polymer film. We find that the surface acid groups are about 1.5 pK(a) units less acidic than simple carboxylic acids in solution but that the pH titration curves are not broadened as is usually observed for surface bound carboxylate groups. (C)2000 Elsevier Science S.A. All rights reserved.

Electrodeposition of the bismuth-based superconductor Bi2Sr2CaCu2O8 + δ

Abstract Precursor films for Bi-Sr-Ca-Cu superconductors have been prepared by employing a reproducible electrochemical technique. Thick films (> 1 μm ) were routinely electrodeposited, within a controlled environment, onto polished Ag substrates, from a non-aqueous solution containing the relevant dehydrated nitrate salts. The as-deposited films were analysed using energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). Heat treated as-deposited films yielded almost single phase, highly c -axis aligned, Bi 2 Sr 2 CaCu 2 O 8 + δ superconductors, with a superconducting onset transition temperature, T c , of 87 K.

Towards the electrochemical manufacture of superconductor precursor films in the presence of an ultrasonic field

Abstract Films of TI-Pb-Sr-Ca-Cu superconductor precursor material have been synthesised. The films were electrodeposited onto polished Ag substrates, with and without the presence of an ultrasonic field in the solution, by applying a pulsed potential sufficiently large to cause reduction of the appropriate metallic cations. The deposition solution was composed of dehydrated metallic nitrate salts dissolved in dimethylsulfoxide. The morphology, and the compositions, of the films were analysed using scanning electron microscopy and emission dispersive spectroscopy respectively. Deposition in the presence of the ultrasonic field showed an increased deposition current, by a factor of 4, caused by mass transfer enhancements as a result of cavitation effects produced by the ultrasonic irradiation of the solution. These films were denser compared with those deposited without the presence of the ultrasound, displaying a void percentage of around 45%, and also displayed greater morphological homogeneity.

Fabrication of plasmonic Au nano-void trench arrays by guided self-assembly

Plasmonic devices, which will enable on chip optical communication, rely on the interaction of light with free charges, and are key to optical sensing and waveguiding [1]. In previous work [2, 3], we have shown that spherical nanoscale voids in metal possess different, and potentially more useful, plasmonic modes than nanoscale metal particles. However, only by making linear arrays of such nanovoid structures it is possible to guide plasmons in specific geometric directions and fabricate plasmon waveguides which will enable on chip optical communication. In this work, single and multilayer arrays of gold voids have been fabricated through self assembly of sub-micron polystyrene spheres in V-shaped trenches in silicon, followed by selective area electrodeposition. Angle-dependent dispersion characteristics reveal the existence of localized plasmons. This is the first experimental evidence of linear plasmon arrays in templated self assembled structures.

Transport mechanisms at Ni-Si Schottky barriers for spin injection

Spin injection from a magnetic metal into a semiconductor requires spin conservation during the transport of electrons. It is particularly interesting because it allows the integration of magnetic devices with microelectronics. The conductivity mismatch problem has been shown to prevent ohmic contacts from being used for spin injection. Instead, Schottky barriers and ferromagnet/insulator/semiconductor contacts have been proposed. It has been shown that electrodeposition is a promising technique for Ni-Si Schottky barriers. In this digest, the transport mechanisms in electrodeposited Ni-Si Schottky barriers are studied. Moderately doped Si shows a high quality Schottky barrier with ultra low reverse leakage and domination of thermionic emission. Tunneling takes over for highly doped Si, giving leakage-free thermionic field emission in reverse bias.