Double potential step chronoamperometry at microdisk electrodes: simulating the case of unequal diffusion coefficients

An efficient approach to the simulation of the double potential step chronoamperometry at a microdisk electrode based on an exponentially expanding time grid and conformal mapping of the space is presented. The dimensionless second potential step flux data are included as a function of the first potential step duration and the ratio of the diffusion coefficients of the reacting species allowing instant analysis of the experimental double potential step chronoamperograms without a need for simulation. The values of the diffusion coefficients are determined for several test systems and found to be in good agreement with existing literature data. (C) 2004 Elsevier B.V. All rights reserved.

Electroreduction of Chlorine Gas at Platinum Electrodes in Several Room Temperature Ionic Liquids: Evidence of Strong Adsorption on the Electrode Surface Revealed by Unusual Voltammetry in Which Currents Decrease with Increasing Voltage Scan Rates

Voltammetry is reported for chlorine, Cl-2, dissolved in various room temperature ionic liquids using platinum microdisk electrodes. A single reductive voltammetric wave is seen and attributed to the two-electron reduction of chlorine to chloride. Studies of the effect of voltage scan rate reveal uniquely unusual behavior in which the magnitude of the currents decrease with increasing scan rates. A model for this is proposed and shown to indicate the presence of strongly adsorbed species in the electrode reaction mechanism, most likely chlorine atoms, Cl*((ads)).

Investigating the Mechanism and Electrode Kinetics of the Oxygen vertical bar Superoxide (O-2 vertical bar O-2(center dot-)) Couple in Various Room-Temperature Ionic Liquids at Gold and Platinum Electrodes in the Temperature Range 298-318 K

The reduction of oxygen was studied over a range of temperatures (298-318 K) in n-hexyltriethylammonium bis(trifluoromethanesulfonyl)imide, [N-6,N-2,N-2,N-2][NTf2], and 1-butyl-2,3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [C(4)dmim][NTf2] on both gold and platinum microdisk electrodes, and the mechanism and electrode kinetics of the reaction investigated. Three different models were used to simulate the CVs, based on a simple electron transfer ('E'), an electron transfer coupled with a reversible homogeneous chemical step ('ECrev') and an electron transfer followed by adsorption of the reduction product ('EC(ads)'), and where appropriate, best fit parameters deduced, including the heterogeneous rate constant, formal electrode potential, transfer coefficient, and homogeneous rate constants for the ECrev mechanism, and adsorption/desorption rate constants for the EC(ads) mechanism. It was concluded from the good simulation fits on gold that a simple E process operates for the reduction of oxygen in [N-6,N-2,N-2,N-2][NTf2], and an ECrev process for [C(4)dmim][NTf2], with the chemical step involving the reversible formation of the O-2(center dot-)center dot center dot center dot [C(4)dmim](+) ion-pair. The E mechanism was found to loosely describe the reduction of oxygen in [N-6,N-2,N-2,N-2][NTf2] on platinum as the simulation fits were reasonable although not perfect, especially for the reverse wave. The electrochemical kinetics are slower on Pt, and observed broadening of the oxidation peak is likely due to the adsorption of superoxide on the electrode surface in a process more complex than simple Langmuirian. In [C(4)dmim][NTf2] the O-2(center dot-) predominantly ion-pairs with the solvent rather than adsorbs on the surface, and an ECrev quantitatively describes the reduction of oxygen on Pt also.

Evaluation of a simple disposable microband electrode device for amperometric gas sensing

We report a simple and facile methodology for constructing Pt (6.3 mm x 50 mu m) and Cu (6.3 mm x 30 mu m) annular microband electrodes for use in room temperature ionic liquids (RTILs) and propose their use for amperometric gas sensing. The suitability of microband electrodes for use in electrochemical analysis was examined in experiments on two systems. The first system studied to validate the electrochemical responses of the annular microband electrode was decamethylferrocene (DmFc), as a stable internal reference probe commonly used in ionic liquids, in [Pmim][NTf2], where the diffusion coefficients of DmFc and DmFc(+) and the standard electron rate constant for the DmFc/DmFc(+) couple were determined through fitting chronoamperometric and cyclic voltammetric responses with relevant simulations. These values are independently compared with those collected from a commercially available Pt microdisc electrode with excellent agreement. The second system focuses on O-2 reduction in [Pmim][NTf2], which is used as a model for gas sensing. The diffusion coefficients of O-2 and O-2(-) and the electron transfer rate constant were again obtained using chronoamperometry and cyclic voltammetry, along with simulations. Results determined from the microbands are again consistent to those evaluated from the Pt microdisc electrode when compared these results from home-made microband and commercially available microdisc electrodes. These observations indicate that the fabricated annular microband electrodes are suitable for quantitative measurements. Further the successful use of the Cu electrodes in the O-2 system suggests a cheap disposable sensor for gas detection. (C) 2013 Elsevier B.V. All rights reserved.

One-Electron Reduction of 2-Nitrotoluene, Nitrocyclopentane, and 1-Nitrobutane in Room Temperature Ionic Liquids: A Comparative Study of Butler–Volmer and Symmetric Marcus–Hush Theories Using Microdisk Electrodes

The voltammetry for the reduction of 2-nitrotoluene at a gold microdisk electrode is reported in two ionic liquids: trihexyltetradecylphosphonium tris(pentafluoroethyl)trifluorophosphate ([P-14,P-6,P-6,P-6][FAP]) and 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([Emim][NTf2]). The reduction of nitrocyclopentane (NCP) and 1-nitrobutane (BuN) was investigated using voltammetry at a gold microdisk electrode in the ionic liquid [P-14,P-6,P-6,P-6][FAP]. Simulated voltammograms, generated through the use of ButlerVolmer theory and symmetric MarcusHush theory, were compared to experimental data, with both theories parametrizing the data similarly well. An experimental value for the Marcusian parameter, 1 was also determined in all cases. For the reduction of 2-nitrotoluene, this was 0.5 +/- 0.1 eV in both solvents, while for NCP and BuN in [P-14,P-6,P-6,P-6][FAP], it was 2 +/- 0.1 and 5 +/- 0.1 eV, respectively. This is attributed to the localization of charge on the nitro group and the primary nitro alkyls increased interaction with the environment, resulting in a larger reorganization energy.

Generic SoC QR Array Processor for Adaptive Beamforming

A generic architecture for implementing a QR array processor in silicon is presented. This improves on previous research by considerably simplifying the derivation of timing schedules for a QR system implemented as a folded linear array, where account has to be taken of processor cell latency and timing at the detailed circuit level. The architecture and scheduling derived have been used to create a generator for the rapid design of System-on-a-Chip (SoC) cores for QR decomposition. This is demonstrated through the design of a single-chip architecture for implementing an adaptive beamformer for radar applications. Published as IEEE Trans Circuits and Systems Part II, Analog and Digital Signal Processing, April 2003 NOT Express Briefs. Parts 1 and II of Journal reorganised since then into Regular Papers and Express briefs

Magnetic and electrode structure design for a new EBIT

Electron beam trajectory simulations have been performed to design a new electron beam ion trap. The design of the magnet and electrode structures was optimized based on the results of the simulations. (C) 2003 Elsevier Science B.V. All rights reserved.

The basis for the formation of stable metal clusters on an electrode surface

Metal nanoclusters can be produced cheaply and precisely in an electrochemical environment. Experimentally this method works in some systems, but not in others, and the unusual stability of the clusters has remained a mystery. We have simulated the deposition of the clusters using classical molecular dynamics and studied their stability by grand-canonical Monte Carlo simulations. We find that electrochemically stable clusters occur only in those cases where the two metals involved form stable alloys.

Photodiodes array as potential diagnostic for measuring short bursts of K-alpha radiation from Ti targets irradiated with 45 fs laser pulses

We report on a study comparing absolute K-alpha yield from Ti foils measured with a calibrated system of an X-ray CCD coupled to a curved LiF Von-Hamos crystal spectrometer to the difference in the signals measured simultaneously with two similar photodiodes fitted with two different filters. Our data indicate that a combination of photodiodes with different filters could be developed into an alternative and inexpensive diagnostic for monitoring single shot pulsed emission in a narrow band of X-ray region.

The complex array of bradykinin-related peptides (BRPs) in the peptidome of pickerel frog (Rana palustris) skin secretion is the product of transcriptional economy.

Previous peptidomic analyses of the defensive skin secretion from the North American pickerel frog, Rana palustris, have established the presence of canonical bradykinin and multiple bradykinin-related peptides (BRPs). As a consequence of the multiplicity of peptides identified and their diverse primary structures, it was speculated that they must represent the products of expression of multiple genes. Here, we present unequivocal evidence that the majority of BRPs (11/13) identified in skin secretion by the peptidomic approach can be generated by differential site-specific protease cleavage from a single common precursor of 321 amino acid residues, named skin kininogen 1, whose primary structure was deduced from cloned skin secretion-derived cDNA. The organization of skin kininogen 1 consists of a hydrophobic signal peptide followed by eight non-identical domains each encoding a single copy of either canonical bradykinin or a BRP. Two additional splice variants, encoding precursors of 233 (skin kininogen 2) or 189 amino acid residues (skin kininogen 3), were also cloned and were found to lack BRP-encoding domains 5 and 6 or 4, 5 and 6, respectively. Thus, generation of peptidome diversity in amphibian defensive skin secretions can be achieved in part by differential protease cleavage of relatively large and multiple-encoding domain precursors reflecting a high degree of transcriptional economy.

Toward Self-Assembled Ferroelectric Random Access Memories: Hard-Wired Switching Capacitor Arrays with Almost Tb/in.2 Densities

We report on the successful fabrication of arrays of switchable nanocapacitors made by harnessing the self-assembly of materials. The structures are composed of arrays of 20-40 nm diameter Pt nanowires, spaced 50-100 nm apart, electrodeposited through nanoporous alumina onto a thin film lower electrode on a silicon wafer. A thin film ferroelectric (both barium titanate (BTO) and lead zirconium titanate (PZT)) has been deposited on top of the nanowire array, followed by the deposition of thin film upper electrodes. The PZT nanocapacitors exhibit hysteresis loops with substantial remnant polarizations, while although the switching performance was inferior, the low-field characteristics of the BTO nanocapacitors show dielectric behavior comparable to conventional thin film heterostructures. While registration is not sufficient for commercial RAM production, this is nevertheless an embryonic form of the highest density hard-wired FRAM capacitor array reported to date and compares favorably with atomic force microscopy read-write densities.

Australia Telescope Compact Array 1.2cm Observations of the Massive Star Forming Region G305.2+0.2

We report on Australia Telescope Compact Array observations of the massive star-forming region G305.2+0.2 at 1.2 cm. We detected emission in five molecules towards G305A, confirming its hot core nature. We determined a rotational temperature of 26 K for methanol. A non-local thermodynamic equilibrium excitation calculation suggests a kinematic temperature of the order of 200 K. A time-dependent chemical model is also used to model the gas-phase chemistry of the hot core associated with G305A. A comparison with the observations suggest an age of between 2 × 104 and 1.5 × 105 yr. We also report on a feature to the south-east of G305A which may show weak Class I methanol maser emission in the line at 24.933 GHz. The more evolved source G305B does not show emission in any of the line tracers, but strong Class I methanol maser emission at 24.933 GHz is found 3 arcsec to the east. Radio continuum emission at 18.496 GHz is detected towards two H ii regions. The implications of the non-detection of radio continuum emission towards G305A and G305B are also discussed.

Electrode field penetration: A new interpretation of tunneling currents in barium strontium titanate (BST) thin films

This paper shows that penetration of the applied electric field into the electrodes of a ferroelectric thin film capacitor produces both an interfacial capacitance and an effective mechanism for electron tunneling. The model predictions are compared with experimental results on Au-BST-SrRuO3 capacitors of varying thicknesses, and the agreement is excellent.

The effect of tungsten trioxide thin films at ferroelectric-electrode boundaries on fatigue behaviour

A conventional thin film capacitor heterostructure, consisting of sol-gel deposited lead zirconium titanate (PZT) layers with sputtered platinum top and bottom electrodes, was subjected to fatiguing pulses at a variety of frequencies. The fatigue characteristics were compared to those of a similarly processed capacitor in which a ~20nm tungsten trioxide layer had been deposited, using pulsed laser deposition, between the ferroelectric and upper electrode. The expectation was that, because of its ability to accommodate considerable oxygen non-stoichiometry, tungsten trioxide (WO3) might act as an efficient sink for any oxygen vacancies flushed to the electrode-ferroelectric boundary layer during repetitive switching, and hence would improve the fatigue characteristics of the thin film capacitor. However, it was found that, in general, the addition of tungsten trioxide actually increases the rate of fatigue. It appears that any potential benefit from the WO3, in terms of absorbing oxygen vacancies, is far outweighed by it causing dramatically increased charge injection in the system.