Current Enhancement Effect Research Articles

3D-Printed Microfluidics System Coupled with Electrochemical pH Control for Enhanced Chlorine Detection

In this work we present the design of a novel technique for amplifying chlorine detection via a reusable microfluidics platform for use with electrochemical sensors. This platform enables experiments to be performed in hydrodynamic conditions, utilising convection as a secondary mode of mass transport for the analyte. All experiments have also been corroborated using COMSOL Multiphysics simulations. The platform is constructed using 3-D printing, which has been used for macroscale electrode microfluidics previously [1]. However, the sensors utilised herein are of the ultramicro scale with complex geometry. This geometry allows bipotentiostatic electrochemistry to be utilised enabling localised electrochemical pH control. This effect, while studied in quiescent conditions, remains poorly understood in hydrodynamic conditions at this scale, though has been investigated at the macroscale.[2] By utilising these two phenomena in tandem, we demonstrate, both experimentally and through simulations, the feasibility of this coupling at the ultramicro scale. Initially we demonstrate operability using ferrocene monocarboxylic acid to electrochemically characterise our sensors, under various controlled flowrates. A highly linear relationship was observed between the cubic root of flowrate in uL/min and the observed current at the working electrode. This cubic root relationship follows the expected theory when compared to the Levich equation as demonstrated by Rees et al [3]. Next we demonstrated the impact of flowrate on electrochemical pH control. This was done using the location of the gold oxide reduction peak, which has been shown to be indicative of local pH by Seymour et al [4]. We observed a visible shift in the location of this peak, with a set potential bias applied, once a flowrate was applied. This potential shift when compared to the static counterpart suggests that electrochemical pH control is less efficient under flow conditions, as expected when compared to the COMSOL simulations. However, this loss of efficiency can be compensated for as demonstrated by our work. By simply adjusting the potential bias as required, the gold oxide reduction peak can be shifted back to its initial location, meaning the desired local pH has been achieved. This compensated potential was then used for pH controlled detection of hypochlorous acid. The previously mentioned cubic root relationship was also demonstrated for the detection of a set concentration of hypochlorous acid under varying flow conditions. We report a near 30-fold enhancement of signal for a set concentration of hypochlorous acid, in water samples, when high flow is applied. Crucially, this enhancement was obtained while electrochemically regulating the local pH. Furthermore, the high linearity of the current enhancing effect of increasing flowrate is demonstrated. In boosting the signal, lower limits of detection can be obtained before signals are lost to background noise. Figure 1 Hypochlorous acid detection in static and high flow conditions. Inset shows the activity of static scans in greater detail

Measurement of the C12A7:e- thermionic emission enhancement due to photon exposure

In this work, a test set-up device is designed, developed and manufactured to perform a direct measurement of the current emission enhancement that the photon absorption can bring to the thermionic emission in a Photon-Enhanced Thermionic Emission Device (PETED) where the C12A7:e- electride is used as the semiconductor due to its low work function value of 2.4 eV. Even though the measured thermionic emission starts at low operational temperatures, obtaining for example a current density emission of 5 mA/cm2 at 500 °C, there is barely an increase of 1% in the current emission when the device is exposed to a source of photons. This effect is mainly due to the presence of a dielectric layer at the material surface, which acts as a barrier, reduces the current enhancement effect from photon excitation, and drives to a limited efficiency of 27 μA/cm2/W.

Lowering Electrocatalytic CO2 Reduction Overpotential Using N-Annulated Perylene Diimide Rhenium Bipyridine Dyads with Variable Tether Length

We report the design, synthesis, and characterization of four N-annulated perylene diimide (NPDI) functionalized rhenium bipyridine [Re(bpy)] supramolecular dyads. The Re(bpy) scaffold was connected to the NPDI chromophore either directly [Re(py-C0-NPDI)] or via an ethyl [Re(bpy-C2-NPDI)], butyl [Re(bpy-C4-NPDI)], or hexyl [Re(bpy-C6-NPDI)] alkyl-chain spacer. Upon electrochemical reduction in the presence of CO2 and a proton source, Re(bpy-C2/4/6-NPDI) all exhibited significant current enhancement effects, while Re(py-C0-NPDI) did not. During controlled potential electrolysis (CPE) experiments at Eappl = -1.8 V vs Fc+/0, Re(bpy-C2/4/6-NPDI) all achieved comparable activity (TONco ∼ 25) and Faradaic efficiency (FEco ∼ 94%). Under identical CPE conditions, the standard catalyst Re(dmbpy) was inactive for electrocatalytic CO2 reduction; only at Eappl = -2.1 V vs Fc+/0 could Re(dmbpy) achieve the same catalytic performance, representing a 300 mV lowering in overpotential for Re(bpy-C2/4/6-NPDI). At higher overpotentials, Re(bpy-C4/6-NPDI) both outperformed Re(bpy-C2-NPDI), indicating the possibility of coinciding electrocatalytic CO2 reduction mechanisms that are dictated by tether-length and overpotential. Using UV-vis-nearIR spectroelectrochemistry (SEC), FTIR SEC, and chemical reduction experiments, it was shown that the NPDI-moiety served as an electron-reservoir for Re(bpy), thereby allowing catalytic activity at lower overpotentials. Density functional theory studies probing the optimized geometries and frontier molecular orbitals of various catalytic intermediates revealed that the geometric configuration of NPDI relative to the Re(bpy)-moiety plays a critical role in accessing electrons from the electron-reservoir. The improved performance of Re(bpy-C2/4/6-NPDI)dyads at lower overpotentials, relative to Re(dmbpy), highlights the utility of chromophore electron-reservoirs as a method for lowering the overpotential for CO2 conversion.

The Influence of Electric Field Intensity and Particle Length on the Electrokinetic Transport of Cylindrical Particles Passing through Nanopore.

The electric transport of nanoparticles passing through nanopores leads to a change in the ion current, which is essential for the detection technology of DNA sequencing and protein determination. In order to further illustrate the electrokinetic transport mechanism of particles passing through nanopores, a fully coupled continuum model is constructed by using the arbitrary Lagrangian–Eulerian (ALE) method. The model consists of the electric field described by the Poisson equation, the concentration field described by Nernst–Planck equation, and the flow field described by the Navier–Stokes equation. Based on this model, the influence of imposed electric field and particle length on the electrokinetic transport of cylindrical particles is investigated. It is found firstly the translation velocities for the longer particles remain constant when they locate inside the nanopore. Both the ion current blockade effect and the ion current enhancement effect occur when cylindrical particles enter and exit the nanopore, respectively, for the experimental parameters employed in this research. Moreover, the particle translation velocity and current fluctuation amplitude are dominated by the electric field intensity, which can be used to adjust the particle transmission efficiency and the ion current detectability. In addition, the increase in particle length changes the particle position corresponding to the peak value of the ion current, which contributes to distinguishing particles with different lengths as well.

Hole Injection Enhancement of MoO3/NPB/Al Composite Anode**Supported by the National Natural Science Foundation of China under Grant Nos 11874007 and 11574049.

An ultra-thin molybdenum(VI) oxide (MoO3) modification layer can significantly improve hole injection from an electrode even though the MoO3 layer does not contact the electrode. We find that as the thickness of the organic layer between MoO3 and the electrode increases, the hole injection first increases and it then decreases. The optimum thickness of 5 nm corresponds to the best current improvement 70%, higher than that in the device where MoO3 directly contacts the Al electrode. According to the 4,4-bis[N-(1-naphthyl)-N-phenyl-amino] biphenyl (NPB)/MoO3 interface charge transfer mechanism and the present experimental results, we propose a mechanism that mobile carriers generated at the interface and accumulated inside the device change the distribution of electric field inside the device, resulting in an increase of the probability of hole tunneling through the injection barrier from the electrode, which also explains the phenomenon of hole injection enhanced by MoO3/NPB/Al composite anode. Based on this mechanism, different organic materials other than NPB were applied to form the composite electrode with MoO3. Similar current enhancement effects are also observed.

Molecular Interactions between Kv4.3 and DPP6 - The Biochemical Anatomy of Idiopathic Ventricular Fibrillation

The molecular basis of idiopathic ventricular fibrillation (IVF) is poorly understood. Previously, we identified crucial role of DPP6, a Kv4.3-associating β-subunit, in Purkinje fiber Ito and gene variants causing DPP6 gain-of-function in IVF. This study investigated the molecular basis of Kv4.3-DPP6 interaction, about which little is known. A computational model of the Kv4.3-DPP6 interaction (using AutoDock Vina) predicted that the N-terminus and some charged regions of DPP6 might interact with the N-terminus and 3 positively charged residues of Kv4.3. The predictions were verified in a patch-clamp study of wildtype and engineered mutant proteins expressed in HEK cells. Wildtype Kv4.3 showed substantial current enhancement upon co-expression with DPP6 after 48 hrs, as previously reported. Deletion of 5 amino acids in the Kv4.3 N-terminus decreased the peak-current density compared to wildtype Kv4.3 but did not prevent current-enhancement by wildtype DPP6, suggesting that this region of Kv4.3 N-terminus is not essential for interaction with DPP6. Neutralization of the 3 positively charged amino acids in the Kv4.3 N-terminus by alanine mutation enhanced the DPP6-induced current-increase. On the other side, deletion of the N-terminal region of DPP6 prevented its current-enhancing effect on Kv4.3. Neutralization of either positively or negatively charged regions in DPP6 significantly attenuated its ability to increase current density when co-expressed with wildtype Kv4.3. We conclude that Kv4.3 interacts with DPP6 via docking involving the DPP6 N-terminus, and that crucial charged amino acids on both Kv4.3 and DPP6 strongly affect the interaction. However, the opposite effects of charge neutralization in the Kv4.3 and DPP6 N-termini argue against a simple electrostatic interaction. These results provide insights into the biochemical anatomy of IVF and may help to develop effective molecularly-targeted blockers for patients with IVF-inducing DPP6 gain-of-function.

Probing Binding Sites and Mechanisms of Action of an IKs Activator by Computations and Experiments

The slow delayed rectifier (IKs) channel is composed of the KCNQ1 channel and KCNE1 auxiliary subunit, and functions to repolarize action potentials in the human heart. IKs activators may provide therapeutic efficacy for treating long QT syndromes. Here, we show that a new KCNQ1 activator, ML277, can enhance IKs amplitude in adult guinea pig and canine ventricular myocytes. We probe its binding site and mechanism of action by computational analysis based on our recently reported KCNQ1 and KCNQ1/KCNE1 3D models, followed by experimental validation. Results from a pocket analysis and docking exercise suggest that ML277 binds to a side pocket in KCNQ1 and the KCNE1-free side pocket of KCNQ1/KCNE1. Molecular-dynamics (MD) simulations based on the most favorable channel/ML277 docking configurations reveal a well-defined ML277 binding space surrounded by the S2-S3 loop and S4-S5 helix on the intracellular side, and by S4–S6 transmembrane helices on the lateral sides. A detailed analysis of MD trajectories suggests two mechanisms of ML277 action. First, ML277 restricts the conformational dynamics of the KCNQ1 pore, optimizing K+ ion coordination in the selectivity filter and increasing current amplitudes. Second, ML277 binding induces global motions in the channel, including regions critical for KCNQ1 gating transitions. We conclude that ML277 activates IKs by binding to an intersubunit space and allosterically influencing pore conductance and gating transitions. KCNE1 association protects KCNQ1 from an arrhythmogenic (constitutive current-inducing) effect of ML277, but does not preclude its current-enhancing effect.

A signal-on electrochemical biosensor for sensitive detection of silver ion based on alkanethiol–carbon nanotube-oligonucleotide modified electrodes

A simple, signal-on electrochemical biosensor for sensitive detection of Ag+ was developed based on the three components of alkanethiol, single-walled carbon nanotube (SWNT) and silver ion-specific oligonucleotide (SSO) layer-by-layer modified electrode where square wave voltammetry (SWV) response of K3[Fe(CN)6] at the modified electrode was used for signal transduction. A gold electrode was first assembled with 1-dodecanethiol (C12H25SH) monolayer to which SWNTs were attached. The SWNT surfaces were further noncovalently bound with SSO probes to obtain the sensor interface. The negatively charged SSO probe acts as a physical obstacle and electrostatic repulsion barrier to block the SWNT-mediated long-distance electron transfer of K3[Fe(CN)6] across the –SC12H25 monolayer. Upon Ag+ binding, the SWNT surface-bound SSO probe forms an unimolecular duplex through C–Ag+–C interaction-mediated intramolecular hybridization and departs from the SWNT surface, resulting in decreased electron transfer resistance and increased SWV current of K3[Fe(CN)6] at the modified electrode. This current enhancement effect provides a signal-on mechanism for sensitive transduction of Ag+ recognition and the resulted current increase is linear with the logarithmic concentration of Ag+ from 2.0nM to 100nM. The developed biosensor was highly selective and its practical applicability in tap water was also tested with a satisfactory result.

A Point Mutation that Impairs the Omega-3 Fatty Acid Sensitivity of Human Slo1 BK Channels

Docosahexaenoic acid (DHA), a long-chain omega-3 fatty acid with a 22 carbon chain, directly activates large-conductance calcium- and voltage-gated Slo1 BK channels with an EC50 = ∼500 nM and lowers blood pressure when injected into anesthetized mice (Hoshi et al. 2013 Proc Natl Acad Sci U S A. 110, 4816-21). The stimulatory action of DHA is observed in excised patches and reversible, suggesting that DHA directly interacts with the channel protein. Here we examined the molecular elements within Slo1 critical for the action of DHA. Unlike the clear stimulatory effect of DHA on human Slo1 (hSlo1) channels, we found that Drosophila Slo1 (dSlo1) channels expressed in mammalian cells were not stimulated by DHA, up to 10 μM. Prompted by this finding, we generated a series of chimeric dSlo1-hSlo1 channels and identified a single residue in S6 critical for the stimulatory effect of DHA on hSlo1. With the the human-to-Drosophila mutation Y318S, the current-enhancing effect of DHA on hSlo1, hSlo1+ β1 and hSlo1+β4 channels was severely impaired. The converse Drosophila-to-human mutation S332Y, however, failed to introduce sensitivity to DHA in dSlo1. Interestingly, the hSlo1 mutation Y318S altered the hSlo1+β1 channel sensitivity to 22- and 20-carbon omega-3 fatty acids but did not affect the response to alpha-linolenic acid with a 20-carbon chain or the omega-6 fatty acid arachidonic acid with a 20-carbon chain. Y318 in hSlo1 S6 is thus a critical determinant of the channel's sensitivity to select fatty acids. Supported in part through the NIH, DFG FOR 1738, and Shanghai Science and Technology Commission.

Differential Effects of PIP2 on Slo1 BK Channels with Different β Subunits

Phosphatidylinositol 4, 5-bisphosphate (PIP2) regulates numerous ion channels, including large-conductance Ca2+- and voltage-dependent K+ (BK) channels (Vaithianathan et al. 2008, J Gen Physiol 132:13-28). We examined the molecular and biophysical mechanisms of the current-enhancing effect of PIP2 on human Slo1 BK channels with different auxiliary subunits heterologously expressed in HEK cells. In the absence of auxiliary subunits, PIP2 (10 μM) isolated from bovine brain applied to the cytoplasmic side inhibited currents through Slo1 channels recorded without Ca2+ by shifting GV curve by 17.8±1.7 mV and decelerated the activation kinetics at positive voltages. In contrast, PIP2 markedly increased currents through Slo1+β1 and Slo1+β4 channels by shifting the GV curves by −45.5±2.2 mV and −34.0±2.9 mV, respectively. PIP2 accelerated the macroscopic activation kinetics at positive voltages and decelerated the macroscopic deactivation kinetics at negative voltages. The current-enhancing effect of PIP2 on Slo1+β1 was observed at negative voltages and also in 100 μM Ca2+. For Slo1+β2 with a deletion in the β2 N terminus to remove inactivation (Δ2-32) the GV shift by PIP2 was significantly smaller (−28.9±2.3 mV) than that observed with Slo1+β1. PIP2 had no effect on the deactivation kinetics of Slo1+β2Δ2-32 channels. Measurements using chimeric β1-β2 subunits show that the second transmembrane domain and the C terminus of β1 are important for the large electrophysiological changes in Slo1+β1 channels caused by PIP2. Supported in part through the NIH, DFG HE 2993/8, and Shanghai Science and Technology Commission.

Explanation of the Rugged LDMOS Behavior by Means of Numerical Analysis

In this paper, a numerical investigation on the behavior of a rugged LDMOS transistor operating in the high current-voltage pulsed regime is carried out with the aim of clarifying the physical origin of the current enhancement that is visible in the output characteristics at high drain and gate biases. The investigation shows that the output characteristics are significantly affected by the quasi-saturation effect at low drain voltages. The impact-ionization rate in the drain extension at high drain voltages reduces the series resistance of the drift region and, hence, raises the electrostatic potential near the channel end, thus driving the intrinsic MOSFET into a saturation condition. The analysis provides a clear insight on the quasi-saturation and current enhancement effects, which is instrumental for the development of compact models that are particularly useful for circuit-design tools.

The acrylamide (S)-1 differentially affects Kv7 (KCNQ) potassium channels

The family of Kv7 (KCNQ) potassium channels consists of five members. Kv7.2 and 3 are the primary molecular correlates of the M-current, but also Kv7.4 and Kv7.5 display M-current characteristics. M-channel modulators include blockers (e.g., linopirdine) for cognition enhancement and openers (e.g., retigabine) for treatment of epilepsy and neuropathic pain. We investigated the effect of a Bristol–Myers Squibb compound ( S)- N-[1-(3-morpholin-4-yl-phenyl)-ethyl]-3-phenyl-acrylamide [(S)-1] on cloned human Kv7.1–5 potassium channels expressed in Xenopus laevis oocytes. Using two-electrode voltage-clamp recordings we found that (S)-1 blocks Kv7.1 and Kv7.1/KCNE1 currents. In contrast, (S)-1 produced a hyperpolarizing shift of the activation curve for Kv7.2, Kv7.2/Kv7.3, Kv7.4 and Kv7.5. Further, the compound enhanced the maximal current amplitude at all potentials for Kv7.4 and Kv7.5 whereas the combined activation/block of Kv7.2 and Kv7.2/3 was strongly voltage-dependent. The tryptophan residue 242 in S5, known to be crucial for the effect of retigabine, was also shown to be critical for the enhancing effect of (S)-1 and BMS204352. Furthermore, no additive effect on Kv7.4 current amplitude was observed when both retigabine and (S)-1 or BMS204352 were applied simultaneously. In conclusion, (S)-1 differentially affects the Kv7 channel subtypes and is dependent on a single tryptophan for the current enhancing effect in Kv7.4.

Microwave enhanced electroanalysis of formulations: processes in micellar media at glassy carbon and at platinum electrodes

The direct electroanalysis of complex formulations containing alpha-tocopherol (vitamin E) is possible in micellar solution and employing microwave-enhanced voltammetry. In the presence of microwave radiation substantial heating and current enhancement effects have been observed at 330 microm diameter glassy carbon electrodes placed into a micellar aqueous solution and both hydrophilic and highly hydrophobic redox systems are detected. For the water soluble Fe(CN)(6)(3-/4-) redox system in micellar aqueous solutions of 0.1 M NaCl and 0.1 M sodium dodecylsulfate (SDS) at low to intermediate microwave power, thermal effects and convection effects are observed. At higher microwave power, thermal cavitation is induced and dominates the mass transport at the electrode surface. For the micelle-soluble redox systems tert-butylferrocene and 2,5-di-tert-butyl-1,4-benzoquinone, strong and concentration dependent current responses are observed only in the presence of microwave radiation. For the oxidation of micelle-soluble alpha-tocopherol current responses at glassy carbon electrodes are affected by adsorption and desorption processes whereas at platinum electrodes, analytical limiting currents are obtained over a wide range of alpha-tocopherol concentrations. However, for the determination of alpha-tocopherol in a commercial formulation interference from proteins is observed at platinum electrodes and direct measurements are possible only over a limited concentration range and at glassy carbon electrodes.

Current enhancement with alternating gate voltage in the Coulomb-blockade regime of a single-wall carbon nanotube

We investigated the current–voltage characteristics of a carbon nanotube in a single electron transistor structure with alternating gate voltage. A continuous current enhancement effect with increasing frequency of the applied gate voltage up to 13 MHz is reported. Assuming that I=nef, more than 1000 electrons are driven to flow across the source–drain channel at VDS=100 mV, 13 MHz of gate voltage (Vp-p=2 V) and T=1.8 K. The continuous current enhancement is explained by the broadening effect of the discrete energy levels of the finite-length carbon nanotube.

Current enhancing effect of poly[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium] films on the electrode reaction of anthraquinonedisulfonate

Abstract The charge transfer rate for anthraquinonedisulfonate reduction at electrodes modified with poly[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium] chloride films was determined as a function of the electrode potential, solution pH, and solvent composition by electrochemical impedance spectroscopy. The polycationic film reduced the apparent heterogeneous rate constant of the redox reaction by about two orders of magnitude relative to a naked electrode. This decrease resulted from strong binding of the reacting species to the polymer and a repulsive interaction between the reacting species in the film. On the other hand, the polycationic film extracted a large amount of anthraquinonedisulfonate from an aqueous solution: the partition coefficient amounted to as much as 7×104. Because of the resulting large increase in the voltammetric current of the redox reaction, the polymer-modified electrodes enabled us to determine traces of the redox species.

Separable effects of human Kvbeta1.2 N- and C-termini on inactivation and expression of human Kv1.4.

1. The Kvbeta subunits of voltage-gated K+ channels alter the functional expression and gating of non- or slowly inactivating Kvalpha1 subunits via two separate domains. To determine how Kvbeta subunits modulate a rapidly inactivating Kvalpha1 subunit, we did two-microelectrode voltage clamp experiments on human Kv1.4 voltage-gated K+ channels expressed heterologously in Xenopus oocytes. In addition we tested a slowly inactivating mutant of Kv1.4 lacking amino acids 2-146 of the N-terminal alpha-ball domain (Kv1. 4DeltaN2-146). Kv1.4 or Kv1.4DeltaN2-146 were co-expressed with either rat Kvbeta2 or human Kvbeta1.2. To separate domain effects, we also used a mutant of Kvbeta1.2 lacking the unique 79 amino acid N-terminal beta-ball domain (Kvbeta1-C). 2. For the mutant Kv1.4DeltaN2-146 we found that Kvbeta1-C or Kvbeta2 increased current amplitude without altering activation or inactivation. By contrast Kvbeta1.2 produced rapid inactivation and slowed deactivation due to block produced by the beta-ball. The beta-ball also increased the rate of C-type inactivation in 5 mM, but not 50 mM, external K+ consistent with an effect of blockade on K+ efflux. 3. For Kv1.4, Kvbeta1-C produced a voltage-independent increase in the rate of inactivation and shifted the inactivation curve to more hyperpolarized potentials, but had no effect on deactivation. Kvbeta1-C, Kvbeta2 and Kvbeta1.2 slowed recovery from inactivation similarly, thereby excluding involvement of the beta-ball. Kvbeta1.2 produced an additional more rapid, voltage-dependent component of inactivation, significantly reduced peak outward current and shifted steady-state inactivation towards hyperpolarized potentials. 4. Yeast two-hybrid studies showed that alpha-beta interaction was restricted to the N-terminus of Kv1.4 and the C-terminus of Kvbeta1. 2 or Kvbeta2. Direct interaction with the alpha-ball did not occur. Our interpretation is that Kvbeta1-C and Kvbeta2 enhanced N-type inactivation produced by the Kv1.4 alpha-ball allosterically. 5. We propose that Kvbeta1.2 has three effects on Kv1.4, the first two of which it shares with Kvbeta2. First, Kvbeta1-C and Kvbeta2 have a current-enhancing effect. Second, Kvbeta1-C and Kvbeta2 increase block by the alpha-ball allosterically. Third, the beta-ball of Kbeta1.2 directly blocks both Kv1.4 and Kv1.4DeltaN2-146. When both alpha- and beta-balls are present, competition for their respective binding sites slows the block produced by either ball.

Field emission from an elliptical boss: Exact and approximate forms for area factors and currents

Field emission from metallic or semiconductor tips, in comparison to planar surfaces, is complicated by current enhancement effects and changes in the image charge. It is shown that the approximations typically used for the calculation of the transmission coefficient, namely, a ‘‘linearized’’ Wentzel–Kramers–Brillouin approach and methods based upon the Fowler–Nordheim approach, are inappropriate for small spherical surfaces but adequate for elliptical surfaces. The derivation of the approximate approaches is given, as well as a simple analytical formula for the average emitting area, which may be derived based on the Fowler–Nordheim equation. By use of the elliptical approximation for the tip geometry, a simple scale factor is sufficient to deal with spherical and pointed tips.

Field emission from an elliptical boss: Exact versus approximate treatments

Field emission from tips, in comparison to planar surfaces, is complicated by current enhancement effects and changes in the image charge. We show that the approximations typically used for the calculation of the transmission coefficient are inappropriate for small spherical surfaces but adequate for elliptical surfaces. A simple analytical formula for the average emitting area may be derived based on the Fowler–Nordheim equation under conditions of field emission. By use of the elliptical approximation, a simple scale factor is sufficient to deal with spherical and pointed tips.

Defect size dependence of critical current density enhancement for irradiated YBa 2Cu 3O 7−δ

The effects of 100 MeV electron (to 3.6×10 18 cm −2) and fast neutron irradiation (to 4.0 × 10 18 cm −2) on the superconducting properties of melt-textured YBa 2Cu 3O 7-σ is studied experimentally. By comparing the critical current enhancement effects normalized to the total atomic displacement damage, it is found that the enhancement depends heavily on the type and energy of radiation and on the beam direction with respect to the crystal. Fast neutron irradiation is more effective than 100 MeV electron irradiation (along the c-axis) in enhancing the critical current, and electron irradiation along the c-axis is more effective than electron irradiation along the a, b-plane. A model based on defect size is proposed to interpret the effects.

Properties of plasma-deposited Si-rich silicon nitride films in current enhancement injectors

Si-rich silicon nitride (SiNx:H) film deposited on top of thermal SiO2 has been found to give rise to current enhancement through the double-layer sandwich structure similar to the injector device based on Si-rich SiO2 [DiMaria et al., J. Appl. Phys. 51, 2722 (1980)]. In this paper, the properties of the SiNx:H film, deposited by the plasma-enhanced chemical vapor deposition technique and its injector structure, are reported. It has been found that the as-deposited film is amorphous, but subsequent annealing done at 900–1100 °C leads to the crystallization of the excess Si in the material. For injector structures made of moderately Si-rich films, the current enhancement effect does not depend strongly on the film composition and the subsequent heat treatment. For samples made of very Si-rich films, however, the post-metallization anneal step (at 400 °C) causes the as-deposited SiNx:H film to react strongly with the gate Al. This lowers the crystallization temperature of the excess Si very significantly, and also supresses the current enhancement in the corresponding injector structure. Possible mechanisms are discussed. The cyclability of the injector structure, in particular, charge trapping and degradation of the underlying SiO2 layer as a result of current injection, is also discussed.