Electron Current Flow Research Articles

Synthetic Biology: A Unifying View and Review Using Analog Circuits.

We review the field of synthetic biology from an analog circuits and analog computation perspective, focusing on circuits that have been built in living cells. This perspective is well suited to pictorially, symbolically, and quantitatively representing the nonlinear, dynamic, and stochastic (noisy) ordinary and partial differential equations that rigorously describe the molecular circuits of synthetic biology. This perspective enables us to construct a canonical analog circuit schematic that helps unify and review the operation of many fundamental circuits that have been built in synthetic biology at the DNA, RNA, protein, and small-molecule levels over nearly two decades. We review 17 circuits in the literature as particular examples of feedforward and feedback analog circuits that arise from special topological cases of the canonical analog circuit schematic. Digital circuit operation of these circuits represents a special case of saturated analog circuit behavior and is automatically incorporated as well. Many issues that have prevented synthetic biology from scaling are naturally represented in analog circuit schematics. Furthermore, the deep similarity between the Boltzmann thermodynamic equations that describe noisy electronic current flow in subthreshold transistors and noisy molecular flux in biochemical reactions has helped map analog circuit motifs in electronics to analog circuit motifs in cells and vice versa via a `cytomorphic' approach. Thus, a body of knowledge in analog electronic circuit design, analysis, simulation, and implementation may also be useful in the robust and efficient design of molecular circuits in synthetic biology, helping it to scale to more complex circuits in the future.

Fano resonances in the conductance of graphene nanoribbons with side gates

The control of side gates on the quantum electron transport in narrow graphene ribbons of different widths and edge types (armchair and zigzag) is investigated. The conductance exhibits Fano resonances with varying side gate potential. Resonant and antiresonant peaks in the conductance can be associated with the eigenstates of a closed system, and these peaks can be accurately fitted with a Fano line shape. The local density of states (LDOS) and the electron current show a specific behavior at these resonances, which depends on the ribbon edge type. In zigzag ribbons, transport is dominated by intervalley scattering, which is reflected in the transmission functions of individual modes. The side gates induce $p\ensuremath{-}n$ interfaces near the edges at which the LDOS exhibits peaks. Near the resonance points, the electron current flows uniformly through the constriction, while near the antiresonances it creates vortices. In the armchair ribbons the LDOS spreads in areas of high potential, with current flowing near the edges.

Effects of Current Collector Positions on Temperature and Reactive Current Distributions in a Micro-Tubular Solid Oxide Electrolysis Cell

1. IntroductionSolid oxide electrolysis cells (SOECs) are devices which can generate hydrogen from high temperature steam by electrolysis techniques. For a micro-tubular SOEC, a current collector position affects the temperature and the reactive current distributions, and these distributions affect performance and durability. Understanding the distributions is important, however, researching the distributions by only experimental methods is difficult because of thin components, small radius and high operating temperature. Therefore, combining the experiment and numerical analysis is better way to understand phenomena in the SOEC.In this study, the latter method is mainly reported. the two-dimensional tubular model of micro-tubular SOEC based on heat, mass and electric charge transfers was developed. The results of numerical analysis were compared with experimental data of micro-tubular SOEC. In addition, the conditions of co-flow and counter-flow were calculated and compared for the temperature distributions. Here, the co-flow means electron current flow is in parallel with gas flow. The counter-flow means electron current flow face gas flow. In this report, the anode gas flow is in parallel with the cathode gas flow.2. Numerical model and analytic conditionsIn the model, heat, mass and electric charge transfers were calculated simultaneously. Heat and mass transfers were calculated as two-dimensional models. On the other hand, the electronic charge transfer in anode electrode (the outside of the cylinder) and all ionic charge transfer were calculated as quasi-two-dimensional models to reduce computation time. The quasi-two-dimensional models mean that one-dimensional models for radius direction were lined up to direction of length. Electronic charge transfers in the cathode electrode (the inside of the cylinder) were calculated as two-dimensional models.The anode electrode was mixed material of nickel (Ni) and yttrium stabilized zirconium (YSZ). The electrolyte was YSZ. The cathode electrode was mixed material of lanthanum strontium manganite (LSM) and YSZ. Current collectors were platinum (Pt). The thicknesses of anode electrode, electrolyte and cathode electrode were 200um, 20um and 20um, respectively. Supplied anode gas was mixed gas of hydrogen and steam (hydrogen/steam ratio = 1). Supplied cathode gas was air. The operating temperature was 1123K. Experiments for micro-tubular SOEC were carried out under the similarly conditions.3. Results and discussionsFig. 1 shows the relationship between current density and overpotential. Fig. 2 shows the relationship between overpotential and temperature change. In Fig. 1 and 2, both experimental data and results of numerical analysis are shown. In Fig. 2, experimental data and the results of numerical analysis is different, however, tendency of temperature changes was similar. In the part of lower overpotential, temperature changes were negative because of heat absorption with electrolysis reaction. On the other hand, in the part of higher overpotential, temperature changes were positive because amount of heat generation from overpotential was higher than that of heat absorption.Fig. 3 is temperature distributions in a micro-tubular SOEC. Fig. 3(a) is positions of SOEC’s components. The current collector at the cathode was located at z = 4.0cm. Fig. 3(b) shows the distribution with co-flow condition. Fig.3(c) shows the distributions with counter-flow conditions. The maximum temperature change of co-flow condition was larger than that of counter-flow because the reactive current of the cathode was concentrated to the current collector side of the reactive area. The reactive area is range that z position is from 1.0cm to 3.0cm.

A current-driven electromagnetic mode in sheared and toroidal configurations

The induced electric field in a tokamak drives a parallel electron current flow. In an inhomogeneous, finite beta plasma, when this electron flow is comparable to the ion thermal speed, the Alfvén mode wave solutions of the electromagnetic gyrokinetic equation can become nearly purely growing kink modes. Using the new ‘low-flow’ version of the gyrokinetic code GS2 developed for momentum transport studies (Barnes et al 2013 Phys. Rev. Lett. 111 055005), we are able to model the effect of the induced parallel electric field on the electron distribution to study the destabilizing influence of current on stability. We identify high mode number kink modes in GS2 simulations and make comparisons to analytical theory in sheared magnetic geometry. We demonstrate reassuring agreement with analytical results both in terms of parametric dependences of mode frequencies and growth rates, and regarding the radial mode structure.

階層化高分子組織体を用いた電子機能材料

The most efficient electric devices in nature will be the light harvesting system in biological membrane. Photosensitive proteins complex, such as photosystem I (PS I), photosystem II (PS II), and electron transport proteins complex such as cytochrome were hierarchically assembled in the bilayer membrane based on their redox potentials. Electrons, which were produced by photoinduced electron transfer in PS II are unidirectionally transferred to cytochrome b6f then PS I following the potential gradient in the membrane. We can produce similar hierarchical molecular assemblies using the Langmuir-Blodgett (LB) technique. The unidirectional electron current flow has been achieved in hierarchical assembled LB films to produce efficient light-energy conversion devices. In this paper, we prepare hierarchical assembled polymer films using the LB technique. It has been reported that poly (N-dodecylacrylamide) forms a stable polymer monolayer “polymer nanosheets” at the air-water interface. Several electrofunctional polymer nanosheets were assembled in a tailor-made manner to achieve the unidirectional electron transfer. We applied the unidirectional electron transfer to produce other unique electrofunctional devices such as molecular memory and mutli-color electrochromism. The results indicate that we can produce unique electric devices by not just mimicking functions in nature but extracting the essence of their functions and applying them.

Lattice dependent motion of voids during electromigration

The influence of the crystal lattice configuration to electromigration processes, e.g., void formation and propagation, is investigated in suitable test structures. They are fabricated out of self-assembled, bi-crystalline Ag islands, grown epitaxially on a clean Si(111) surface. The μm-wide and approximately 100 nm thick Ag islands are a composition of a Ag(001) and a Ag(111) part. By focused ion beam milling, they are structured into wires with a single grain boundary, the orientation of which can be chosen arbitrarily. In-situ scanning electron microscopy (SEM) allows to capture an image sequence during electrical stressing and monitors the development of voids and hillocks in time. To visualize the position and motion of voids, we calculate void maps using a threshold algorithm. Most of the information from the SEM image sequence is compressed into one single image. Our present electromigration studies are based on in-situ SEM investigations for three different lattice configurations: Ag(001) (with electron current flow in [1¯1¯0] direction), Ag(111) (with electron current flow in [112¯] direction), and additionally 90∘ rotated Ag(111) (with electron current flow in [1¯10] direction). Our experimental results show that not only the formation and shape but also the motion direction of voids strongly depends on the crystal orientation.

Imaging topologically protected transport with quantum degenerate gases

Ultracold and quantum degenerate gases held near conductive surfaces can serve as sensitive, high resolution, and wide-area probes of electronic current flow. Previous work has imaged transport around grain boundaries in a gold wire by using ultracold and Bose-Einstein condensed atoms held microns from the surface with an atom chip trap. We show that atom chip microscopy may be applied to useful purpose in the context of materials exhibiting topologically protected surface transport. Current flow through lithographically tailored surface defects in topological insulators (TI)---both idealized and with the band-structure and conductivity typical of Bi$_{2}$Se$_{3}$---is numerically calculated. We propose that imaging current flow patterns enables the differentiation of an ideal TI from one with a finite bulk--to--surface conductivity ratio, and specifically, that the determination of this ratio may be possible by imaging transport around trenches etched into the TI's surface.

Structural change of ion-induced carbon nanofibers by electron current flow

A graphite foil was irradiated with argon (Ar+) ions to fabricate conical structures with a carbon nanofiber (CNF) on top of the structure. The field emission (FE) properties of one-dimensional individual CNF-tipped cones that had been fabricated were carefully measured by in situ transmission electron microscopy (TEM) facilities. The highest FE current, 550 nA, was observed in the current-voltage (I-V) measurement of a single CNF. Almost no degradation in I-V properties were detected during the reliability test after 30 min. TEM images indicated that the CNF was amorphous in nature initially, and that the electron current flow in the FE process induced the dramatic change in the crystalline structure of both the CNF and of the tip region of the basal cone part. After performing the FE process, the crystalline structures of the amorphous CNFs were transformed into ring-shaped graphene layers, whereas nanodiamond like nanoparticles formed in the outer layer of the tip region of the basal cone. The structural changes induced can be attributed to Joule heating under the high electric field.

Electron flow stability in magnetically insulated vacuum transmission lines

We evaluate the stability of electron current flow in high-power magnetically insulated transmission lines (MITLs). A detailed model of electron flow in cross-field gaps yields a dispersion relation for electromagnetic (EM) transverse magnetic waves [R. C. Davidson et al., Phys. Fluids 27, 2332 (1984)] which is solved numerically to obtain growth rates for unstable modes in various sheath profiles. These results are compared with two-dimensional (2D) EM particle-in-cell (PIC) simulations of electron flow in high-power MITLs. We find that the macroscopic properties (charge and current densities and self-fields) of the equilibrium profiles observed in the simulations are well represented by the laminar-flow model of Davidson et al. Idealized simulations of sheared flow in electron sheaths yield growth rates for both long (diocotron) and short (magnetron) wavelength instabilities that are in good agreement with the dispersion analysis. We conclude that electron sheaths that evolve self-consistently from space-charged-limited emission of electrons from the cathode in well-resolved 2D EM PIC simulations form stable profiles.

Statistics of radiation emitted from a quantum point contact

We analyze the statistics of the electromagnetic radiation emitted from electrons pushed through a quantum point contact. We consider a setup implemented in a two-dimensional (2D) electron gas where the radiation manifests itself in terms of 2D-plasmons/photons emitted from electrons scattered at the point contact. The bosonic statistics of the photons compete with the fermionic statistics of the electrons; as a result, the quantum point contact emits nonclassical radiation with a statistics which can be tuned from bunching to anti-bunching by changing the driving voltage. Our perturbative calculation of the irreducible two-photon probability correlator provides us with information on the statistical nature of the emitted photons and on the underlying electronic current flow.

High-output current-perpendicular to the plane giant magnetoresistance sensor with synthetic-ferrimagnet free layer and enhanced spin-torque critical currents

It is shown that the maximum stable output of a current-perpendicular to the plane giant magnetoresistance sensor is increased significantly by using a synthetic-ferrimagnet free layer, provided the electron current flows from free layer to reference layer. This free layer allows a larger magnetoresistance ratio for a given free layer magnetic moment, and in addition results in a greater than threefold increase in the critical current, above which spin-torque instability of the free layer occurs. In read heads with net free layer moments equivalent to only 4.5 nm of Ni80Fe20, this effect is shown to result in sustainable sense current densities above 2×108 A/cm2.

ELECTRICAL RESISTANCE OF CRACK-FREE GaN/AlN HETEROSTRUCTURE GROWN ON Si(111)

This paper presents the electrical resistance of crack-free n-GaN/AlN/n-Si(111) diodes in relation to the temperature of the Al effusion cell for the growth of AlN intermediate layer (348 nm thickness) using radio-frequency molecular beam epitaxy (RF-MBE). The thickness of the unintentionally doped n-type GaN thin film is in the range of 63–100 nm. Aluminium (300 nm thickness) was sputtered onto the n-type GaN through a metal mask, followed by the 100 nm thick titanium (Ti) capping layer to obtain an ohmic contact. The back contact was created on the back surface of the Si substrate by evaporating indium (In) followed by thermal annealing at 400°C. We will consider the above as a device on an n-type Si(111) substrate, where the electron current flows from the Si substrate to the n-type GaN top layer. It was found that the current–voltage (I–V) characteristics depend on the various deposition temperature of the Al effusion cell for the growth of the AlN intermediate layer. In the forward bias region, where the electrons flow from Si(111) to the GaN top layer, we observe a threshold voltage of approximately 0.5 V for turning on a high current. The order of differential resistance magnitude was nearly a constant in the voltage range of 1.0 to 3.0 V.

Nonlinear electron magnetohydrodynamics physics. III. Electron energization

Wave-particle interactions of low-frequency whistler modes with wave magnetic fields exceeding the ambient field are investigated experimentally. These highly nonlinear modes are excited with magnetic loop antennas in a large magnetized afterglow plasma. While the nonlinear wave properties are described elsewhere, the present paper focuses on the modification of the electron distribution function by the whistler waves. When the electron current flows in regions of magnetic nulls, such as in spheromak and field-reversed configurations (FRCs), strong electron energization is observed. When the whistler modes are created by electron Hall currents, such as in whistler mirrors, no significant energization occurs. The electron temperature can be raised locally by an order of magnitude. Non-Maxwellian distributions with energetic tail electrons are observed. Electron energization to ≳10eV produces visible light emission whose time and space dependence is mapped. The light source travels with the subthermal speed of whistler spheromaks. When counterpropagating spheromaks collide, the resultant FRC produces strong local heating and light which dissipates its free magnetic energy.

Localization of plasma in the extended hollow cathode of a ribbon-electron-beam plasma source at forevacuum pressures

The results of a study of the plasma density distribution in the slit aperture of a right-angled extended hollow cathode used in a ribbon-electron-beam plasma source operating at forevacuum pressures (1–10 Pa) are presented. It is shown that a local peak of plasma density appears in some region of the slit aperture as the slit width is decreased. This results in the appearance of a region of increased current density when the ribbon beam forms. The uniformity of the beam current density distribution is additionally disturbed by the reverse ion flow whose effect on the emission properties of the plasma is significant in the region of elevated pressure. A model which describes the development of plasma density nonuniformity in a hollow cathode is proposed which is based on the idea that the electron current flows predominantly through the slit aperture regions that are associated with local openings of the cathode layer ion sheaths.

Study of the influence of the molecular organization on single-layer OLEDs’ performances

We have synthesized three new silole derivatives with incrementally flexible structure to tune their packing ability and therefore study the influence of the molecular organization in single-layer OLEDs. This architecture was chosen since the absence of organic layers interfaces allows a better evaluation of the role of the molecular arrangement in the active layer. The examination of the EL properties gives evidences of the prominent role of the molecular organization on the OLED efficiency. A crystalline-like organization of the molecules allows high current density but low luminance efficiency since an excessive electron current flow is involved compared to the hole one, and the recombination rate is poor. On the contrary, disordered assemblies of molecules allows better performances by avoiding unfavourable π-stacking, while keeping good intermolecular orbital overlaps to support charge carrier transport.

Electromagnetic interchange-like mode and zonal flow in electron-magnetohydrodynamic plasma

A numerical simulation of the nonlinear state of interchange instability associated with electron inertia in an unmagnetized plasma is studied. It is shown that a self-consistent sheared transverse electron current flow is generated due to nonlinear mechanisms. This zonal flow can reduce the growth rate of the magnetic interchange-like instability and reach a steady state. The zonal flow generation mechanisms are discussed by truncated Fourier mode representation. In the truncated model, three mode equations are considered that have an exact analytic solution that matches well with the numerical solution. The effect of different boundary conditions in such investigations is also discussed.

Observation of Electroluminescence and Photovoltaic Response in Ionic Junctions

Electronic devices primarily use electronic rather than ionic charge carriers. Using soft-contact lamination, we fabricated ionic junctions between two organic semiconductors with mobile anions and cations, respectively. Mobile ionic charge was successfully deployed to control the direction of electronic current flow in semiconductor devices. As a result, these devices showed electroluminescence under forward bias and a photovoltage upon illumination with visible light. Thus, ionic charge carriers can enhance the performance of existing electronic devices, as well as enable new functionalities.

Effect of contact metallization on electromigration reliability of Pb-free solder joints

The effect of underbump metallization (UBM) on electromigration (EM) lifetime and failure mechanism has been investigated for Pb-free solder bumps of 97Sn3Ag composition in the temperature range of 110–155°C. The EM lifetime of the SnAg Pb-free solders with either Cu or Ni UBM was found to be better than the eutectic SnPb (63Sn37Pb) solders but worse than high-Pb (95Pb5Sn) solders. In the test temperature range, the EM lifetimes were found to be comparable for Cu and Ni UBMs but with different activation energies: 0.64–0.72eV for Cu UBM and 1.03–1.11eV for Ni UBM. EM failure was observed only in solder bumps with electron current flow from UBM to the substrate. Failure analysis revealed that EM damage was initiated by the formation of intermetallic compounds (IMC) at the UBM∕solder interface which was found to be significantly enhanced by mass transport driven by the electron current. Under EM, the continued growth of IMC with the dissolution of the UBM and the accumulation of Kirkendall voids resulted in the formation of interfacial cracks and eventual EM failure of the solder bump. For Ni UBM, the IMC formation was dominated by the Ni3Sn4 phase while for Cu UBM, a bilayer of Cu3Sn∕Cu6Sn5 was found. Void formation at the Cu6Sn5∕solder interface was found to be important in controlling the EM lifetime of the Cu UBM solder.

Type-I superconductivity and neutron star precession

Type-I proton superconducting cores of neutron stars break up in a magnetic field into alternating domains of superconducting and normal fluids. We examine two channels of superfluid-normal fluid friction where (i) rotational vortices are decoupled from the nonsuperconducting domains and the interaction is due to the strong force between protons and neutrons; (ii) the nonsuperconducting domains are dynamically coupled to the vortices and the vortex motion generates transverse electric fields within them, causing electronic current flow and Ohmic dissipation. The obtained dissipation coefficients are consistent with the Eulerian precession of neutron stars.

Effect of Current Direction on the Reliability of Different Capped Cu Interconnects

AbstractThe reliability of Cu M1-V1-M2-V2-M3 interconnects with SiN and CoWP cap layers was investigated. Similar to previously reported results, the reliability of CoWP capped structures is much better than identical SiN capped structures. However, it was also observed that the reliability of CoWP capped interconnects was independent of the direction of electrical current flow. This phenomenon is different from what was observed for SiN capped structures, where M2 lines with electron current flow in the upstream configuration (“via-below”) have about three times larger median-time-to-failure than identical lines in the downstream configuration (“viaabove”). This is because the Cu/SiN interface is the preferential void nucleation site and provides the fastest diffusion pathway in such an architecture. Failure analysis has shown that fatal partially-spanned voids usually had formed directly below the via for “via-above” configuration, and fully-spanned voids occurred in the lines above the vias for “via-below” configuration.On the other hand, failure analysis for CoWP-coated Cu structures showed that partiallyspanned voids below the via do not cause fatal failures in the downstream configuration. This is because the CoWP layer is conducting, and thus able to shunt current around the void. As a result, a large fully-spanning void is required to cause a failure, just like the upstream configuration. Thus the lifetime of an interconnect with a conducting cap layer is independent of whether the current is flowing upstream or downstream.