Induced Conductivity Changes Research Articles

Gas-Sensing Performance of Metal Oxide Heterojunction Materials for SF6 Decomposition Gases: A DFT Study.

The online monitoring of GIS equipment can be realized through detecting SF6 decomposition gasses. Metal oxide heterojunctions are widely used as gas-sensing materials. In this study, the structural and electrical properties of In2O3-ZnO and TiO2-ZnO heterojunctions were analyzed based on density functional theory calculations. After heterojunction structural optimization, the electrical conductivity of these two heterojunctions was enhanced compared to each intrinsic model, and the electrical conductivity is ranked as follows: In2O3-ZnO heterojunction > TiO2-ZnO heterojunction. The gas-sensing response of these two heterojunctions to four SF6 decomposition gasses, H2S, SO2, SOF2, and SO2F2, was investigated. For gas adsorption systems, the adsorption energy, charge transfer, density of states, charge difference density, and frontier molecular orbitals were calculated to analyze the adsorption and gas-sensing performance. For gas adsorption on the In2O3-ZnO heterojunction surface, the induced conductivity changes are in the following order: H2S > SO2F2 > SOF2 > SO2. For gas adsorption on the TiO2-ZnO heterojunction surface, H2S and SOF2 increase conductivity, and SO2 and SO2F2 decrease conductivity.

Conversion from memory to threshold resistance switching behavior by modulating compliance current

The volatile and nonvolatile resistance switching (RS) characteristics can be, respectively, used for the selector and memristor, which have received much attention. Thus, it is essential to find a simple and effective method to control the specific RS behavior of NbOx materials due to the co-occurrence of memory RS and threshold RS behaviors. Here, the NbOx film with a thickness of 100 nm was prepared by magnetron sputtering at 80 °C. The tungsten steel tip/NbOx/Pt device exhibited the co-existence of memory RS and threshold RS behaviors. By properly regulating compliance current (Icc), the specified memory and threshold RS behaviors were observed: the memory RS behavior occurred with an Icc of 5 mA, the threshold RS behavior occurred with an Icc of 10 mA, and integrated one selector-one-RRAM (resistive random access memory) (1S1R) RS behavior occurred with an Icc of 50 mA. Moreover, individual RS behavior showed good performance, e.g., good stability of memory RS, good repeatability and concentrated voltage distribution of threshold RS. The memory RS behavior occurred mainly due to the formation and fracture of oxygen vacancy conductive filaments (CFs). Meanwhile, mediated by local Joule heating, thermally induced conductivity change was responsible for the threshold RS behavior. Under an Icc of 50 mA, the oxygen vacancy CFs and a thermally induced conductivity change triggered the 1S1R RS behavior, which significantly suppressed the leakage current in RRAM 3D integrated structures. This work provides an efficient and convenient method for modulating and obtaining the desired RS behavior and better understanding the conversion mechanism between them.

Thermal Conductivity of Amorphous NbOx Thin Films and Its Effect on Volatile Memristive Switching.

Metal-oxide-metal (MOM) devices based on niobium oxide exhibit threshold switching (or current-controlled negative differential resistance) due to thermally induced conductivity changes produced by Joule heating. A detailed understanding of the device characteristics therefore relies on an understanding of the thermal properties of the niobium oxide film and the MOM device structure. In this study, we use time-domain thermoreflectance to determine the thermal conductivity of amorphous NbOx films as a function of film composition and temperature. The thermal conductivity is shown to vary between 0.86 and 1.25 W·m-1·K-1 over the composition (x = 1.9 to 2.5) and temperature (293 to 453 K) ranges examined, and to increase with temperature for all compositions. The impact of these thermal conductivity variations on the quasistatic current-voltage (I-V) characteristics and oscillator dynamics of MOM devices is then investigated using a lumped-element circuit model. Understanding such effects is essential for engineering functional devices for nonvolatile memory and brain-inspired computing applications.

Deterministic and Stochastic Cellular Mechanisms Contributing to Carbon Monoxide Induced Ventricular Arrhythmias.

Chronic exposure to low levels of Carbon Monoxide is associated with an increased risk of cardiac arrhythmia. Microelectrode recordings from rat and guinea pig single isolated ventricular myocytes exposed to CO releasing molecule CORM-2 and excited at 0.2/s show repolarisation changes that develop over hundreds of seconds: action potential prolongation by delayed repolarisation, EADs, multiple EADs and oscillations around the plateau, leading to irreversible repolarisation failure. The measured direct effects of CO on currents in these cells, and ion channels expressed in mammalian systems showed an increase in prolonged late Na+, and a decrease in the maximal T- and L-type Ca++. peak and late Na+, ultra-rapid delayed, delayed rectifier, and the inward rectifier K+ currents. Incorporation of these CO induced changes in maximal currents in ventricular cell models; (Gattoni et al., J. Physiol., 2016, 594, 4193–4224) (rat) and (Luo and Rudy, Circ. Res., 1994, 74, 1071–1096) (guinea-pig) and human endo-, mid-myo- and epi-cardial (O’Hara et al., PLoS Comput. Biol., 2011, 7, e1002061) models, by changes in maximal ionic conductance reproduces these repolarisation abnormalities. Simulations of cell populations with Gaussian distributions of maximal conductance parameters predict a CO induced increase in APD and its variability. Incorporation of these predicted CO induced conductance changes in human ventricular cell electrophysiology into ventricular tissue and wall models give changes in indices for the probability of the initiation of re-entrant arrhythmia.

Tethered Bilayer Lipid Membranes to Monitor Heat Transfer between Gold Nanoparticles and Lipid Membranes.

Here we report a protocol to investigate the heat transfer between irradiated gold nanoparticles (GNPs) and bilayer lipid membranes by electrochemistry using tethered bilayer lipid membranes (tBLMs) assembled on gold electrodes. Irradiated modified GNPs, such as streptavidin-conjugated GNPs, are embedded in tBLMs containing target molecules, such as biotin. By using this approach, the heat transfer processes between irradiated GNPs and model bilayer lipid membrane with entities of interest are mediated by a horizontally focused laser beam. The thermal predictive computational model is used to confirm the electrochemically induced conductance changes in the tBLMs. Under the specific conditions used, detecting heat pulses required specific attachment of the gold nanoparticles to the membrane surface, while unbound gold nanoparticles failed to elicit a measurable response. This technique serves as a powerful detection biosensor which can be directly utilized for the design and development of strategies for thermal therapies that permits optimization of the laser parameters, particle size, particle coatings and composition.

Anomalous Broadband Spectrum Photodetection in 2D Rhenium Disulfide Transistor

Abstract2D transition metal dichalcogenide (TMD)‐based phototransistors generally work under photoconductive, photovoltaic, or photogating mode, in which photocarriers are generated from band‐to‐band excitation. Nevertheless, due to the relatively large bandgap, most TMD phototransistors working under these modes are restricted in visible spectrum. Here, photodetection in 2D multilayer rhenium disulfide (ReS2) transistor via bolometric mode, which relies on light heating induced conductance change instead of band‐to‐band photoexcitation is reported, making it possible for sub‐bandgap photon detection. The bolometric effect induced photoresponse is first revealed by an anomalous sign switching of photocurrent from positive to negative while increasing gate voltage under visible light, which is further validated by the temperature dependent electrical transport measurements. The phototransistor exhibits remarkable photoresponse under infrared regime, beyond the optical bandgap absorption edge of the ReS2 flake. Additionally, it demonstrates a low noise equivalent power, less than 5 × 10−2 pW Hz−1/2, which is very promising for ultra‐weak light detection. Moreover, the response time is below 3 ms, nearly 3–4 orders of magnitude faster than previously reported ReS2 photodetectors. The findings promise bolometric effect as an effective photodetection mode to extend the response spectrum of large bandgap TMDs for novel and high‐performance broadband photodetectors.

Numerical and experimental study of radiation induced conductivity change of carbon nanotube filled polymers

Measuring the conductivity changes of sensing materials to detect a wide range of radiation energy and dosage is one of the major sensing mechanisms of radiation sensors. Carbon nanotube (CNT) filled composites are suitable for sensing radiation because of the extraordinary electrical properties of CNTs and the CNT-network formed inside the polymer matrix. Although the use of CNT-based nanocomposites as potential radiation sensing materials has been widely studied, there is still a lack of theoretical models to analyze the relationship between electrical conductivity and radiation dosages. In this article, we propose a 3D model to describe the electrical conductivity of CNT-based nanocomposites when being irradiated by ionizing radiation. The Monte Carlo method has been employed to calculate radiation intensity, CNT concentration and alignment’s influence on the electrical conductivity. Our simulation shows a better agreement when CNT loading is between the percolation threshold and 3% volume fraction. Radiation experiments have been performed to verify the reliability of our model to illustrate a power function relationship between the electrical conductivity of a CNT-filled polymer and radiation intensity. In addition, the predicted alignment to obtain the best sensitivity for radiation sensing has been discussed to help with CNT-network building in the fabrication process.

Transient and persistent current induced conductivity changes in GaAs/AlGaAs high-electron-mobility transistors

We report the observation of a current induced change of the low temperature conductivity of two-dimensional electron gases in GaAs/AlGaAs-high-electron-mobility transistors. By applying voltage pulses on the ohmic contacts of a Hall bar-mesa-structure, both sheet-carrier-density n2D and electron mobility μ are decreased. At temperatures below 50 K, a persistent change combined with a partial transient recovery of n2D has been observed. The transient behaviour and the lateral spreading of the effect are studied. Moreover, a temperature dependent investigation has been done in order to get insight into the addressed defect energy levels. A model based on the phenomenology of the effect is proposed. The observed effect is not a permanent degradation as the original carrier concentration can be restored by warming up the sample to room temperature and recooling it.

Direct observation of lithium-ion transport under an electrical field in LixCoO2 nanograins.

The past decades have witnessed the development of many technologies based on nanoionics, especially lithium-ion batteries (LIBs). Now there is an urgent need for developing LIBs with good high-rate capability and high power. LIBs with nanostructured electrodes show great potentials for achieving such goals. However, the nature of Li-ion transport behaviors within the nanostructured electrodes is not well clarified yet. Here, Li-ion transport behaviors in LixCoO2 nanograins are investigated by employing conductive atomic force microscopy (C-AFM) technique to study the local Li-ion diffusion induced conductance change behaviors with a spatial resolution of ~10 nm. It is found that grain boundary has a low Li-ion diffusion energy barrier and provides a fast Li-ion diffusion pathway, which is also confirmed by our first principles calculation. This information provides important guidelines for designing high performance LIBs from a point view of optimizing the electrode material microstructures and the development of nanoionics.

Continuous Dynamic Photostimulation - inducing defined, in-vivo-like fluctuating stimuli with Channelrhodopsins

Event Abstract Back to Event Continuous Dynamic Photostimulation - inducing defined, in-vivo-like fluctuating stimuli with Channelrhodopsins Andreas Neef1*, Ahmed ElHady1, Jatin Nagpal2, Kai Broking2, Ghazaleh Afshar2, Theo Geisel1, 2, Ernst Bamberg3, Ragnar Fleischmann2, Walter Stühmer1, 4 and Fred Wolf1, 2 1 BCCN Göttingen, Germany 2 MPI DS, Germany 3 MPI Biophysics, Germany 4 MPI Experimental Medicine, Germany Central neurons typically operate in a noise driven regime: thousands excitatory and inhibitory synapses give rise to a constantly fluctuating conductance. Its statistic is similar to low-pass filtered white noise conductance that can be parameterized by is average, standard deviation and correlation time. An understanding of action potential generation and encoding in the noise driven regime requires the detection of action potential times during stimulation with defined time dependent conductance. Channelrhodopsin variants, expressed in neurons have been almost exclusively used to drive action potentials by illumination with very brief, intense light flashes; effectively imprinting action potential patterns, that are largely independent of the neurons intrinsic response properties. Using the only known weakly inactivating channelrhodopsin variant ChIEF under continuously fluctuating illumination by an LED, we achieve a defined, reproducible conductance modulation that mimicks the naturally occurring synaptic inputs . Cultured hippocampal neurons subjected to this continuous dynamic photostimulation (CoDyPs) generate seemingly random, but reproducible patterns of action potentials, even in experiments lasting several hours. Within the range of illumination intensities used (up to 0.3 mW/µm²) the induced conductance change can be predicted, up to a factor describing the number of expressed ChIEF-Molecules, by convolution of the light signal with the light-conductance transfer function of ChIEF. This Transfer function was determined from light-induced currents, recorded in voltage clamped cultured cells (HEK-293), transiently expressing ChIEF. It resembles the transfer function of a simple single pole low-pass filter with a corner frequency of 20-25 Hz. Together with non-invasive action potential detection by extracellular electrodes, CoDyPs lays the foundation for very long-lasting studies of action potential generation in a fluctuation driven regime. This promises to allow the measurement of dynamical response properties and the respective cut-off frequencies from individual neurons. It might also prove a useful addition to conventional flash-evoked imprinting of action potential patterns for in-vivo experiments. Figure 1 Acknowledgements Supported by funding through BFNT and BCCN Göttingen Keywords: channelrhodopsin, dynamic gain, Neurons, networks and dynamical systems, neurotechnology, optogenetics Conference: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011, Freiburg, Germany, 4 Oct - 6 Oct, 2011. Presentation Type: Poster Topic: neurons, networks and dynamical systems (please use "neurons, networks and dynamical systems" as keywords) Citation: Neef A, ElHady A, Nagpal J, Broking K, Afshar G, Geisel T, Bamberg E, Fleischmann R, Stühmer W and Wolf F (2011). Continuous Dynamic Photostimulation - inducing defined, in-vivo-like fluctuating stimuli with Channelrhodopsins. Front. Comput. Neurosci. Conference Abstract: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011. doi: 10.3389/conf.fncom.2011.53.00045 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Aug 2011; Published Online: 04 Oct 2011. * Correspondence: Dr. Andreas Neef, BCCN Göttingen, Göttingen, Germany, aneef@gwdg.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Andreas Neef Ahmed ElHady Jatin Nagpal Kai Broking Ghazaleh Afshar Theo Geisel Ernst Bamberg Ragnar Fleischmann Walter Stühmer Fred Wolf Google Andreas Neef Ahmed ElHady Jatin Nagpal Kai Broking Ghazaleh Afshar Theo Geisel Ernst Bamberg Ragnar Fleischmann Walter Stühmer Fred Wolf Google Scholar Andreas Neef Ahmed ElHady Jatin Nagpal Kai Broking Ghazaleh Afshar Theo Geisel Ernst Bamberg Ragnar Fleischmann Walter Stühmer Fred Wolf PubMed Andreas Neef Ahmed ElHady Jatin Nagpal Kai Broking Ghazaleh Afshar Theo Geisel Ernst Bamberg Ragnar Fleischmann Walter Stühmer Fred Wolf Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. 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A study on the feasibility of wrist pulse determination using electrical impedance measurement

The results presented in the present paper are concentrated on the determination of pulse using electrical impedance method at the wrist level. The electric field distribution in an arm segment was estimated by simulation of the electric field changes due to conductivity modifications determined by pulse. It was found that the motion induced conductivity changes, due to arm geometry deformation, are similar in magnitude with the blood related changes. The simulation data was validated in an experiment using a simple test circuit. The data ranges of pulse induced changes of conductivity prove the feasibility of the application of the method in practice. Additional work is necessary to device a method to eliminate motion artefacts by appropriate digital signal processing.

Effect of photon irradiation on conductivity of nanoscale yttria-doped zirconia thin films

The effect of photon irradiation on high temperature conductivity of nanoscale yttria-doped zirconia thin films is reported. Nanoscale films show substantial decrease in total conductivity (as high as ∼40%) during ultraviolet (UV) irradiation, while the conductivity of bulk single crystals shows negligible changes. The UV induced conductivity changes are rapid and reversible and activation energies for ion migration remain unaffected. The reduction in conductivity may arise from changes in effective oxygen vacancy concentration. Such UV-influenced alteration of electrical properties offers an elegant route to tailor surface catalytic activity of oxygen ion and mixed conductors used in various solid-state devices.

Nonlinear current–voltage relationship of the plasma membrane of single CHO cells

The application of electric field pulses to Chinese Hamster Ovary (CHO) cells causes membrane electroporation (MEP). If a voltage or current ramp is applied to the cellular membrane of a single CHO cell, the membrane conductance increases nonlinearly with field strength reaching saturation. In particular, the kinetics of the induced conductance changes represents the data basis for the interpretation in terms of underlying structural changes. The current/voltage characteristic is found to be continuous, but displays occasionally a sharp increase in the conductance. The step-like increases are interpreted to reflect the formation of one (or more) larger pore(s). The analysis of current clamp data yields pores of radius ( r p) in the range of 2.5 ≤ r p/nm ≤ 20; the pores of the voltage clamp data are in the range of 2.5 ≤ r p/nm ≤ 55. The larger pores occur predominantly during hyperpolarising and less frequently during depolarising conditions, respectively. The different kinetics of pore formation in the hyperpolarising condition, where the inward field increases, and the depolarising condition, where the inward field first decreases and then increases in the opposite direction, suggests structural asymmetry with respect to the direction of the electric membrane field. At the required higher voltage, the effect of the resting potential is negligibly small.

Experimental and numerical investigation of crack closure measurements with electrical potential drop technique

Crack closure measurements during fatigue crack propagation using the electrical potential drop (PD) technique is evaluated using a combination of experiments and simulations. From finite element simulations it is shown that variations in the potential drop value over a fatigue cycle can be explained by crack closure and strain induced conductivity changes. It is also demonstrated that closure measurements made with PD are consistent with closure observations made from in situ SEM observations of crack closure. Finally, it was observed that closure measurements made by a compliance-based measuring technique gave a somewhat lower opening load as compared to the PD-measurement.

MEMS sensor material based on polypyrrole–carbon nanotube nanocomposite: film deposition and characterization

Conductive polymer-based nanocomposite has been utilized as a MEMS sensing material via a one-step, selective on-chip deposition process at room temperature. A doped polypyrrole (PPy) variant synthesized by incorporating multi-walled carbon nanotube (MWCNT) into electropolymerized PPy has been shown to improve the sensing performance utilizing a two-terminal, micro-gap chemiresistor architecture. The dodecylbenzenesulfonate (DBS)-doped PPy–MWCNT nanocomposites are found to be responsive to oxidants, such as hydrogen peroxide (H2O2), and this effect can be extended to glucose detection using H2O2 as a proxy material. The oxidant sensing effect is demonstrated by subjecting a glucose oxidase (GOx)-laden PPy–MWCNT nanocomposite film to various concentrations of glucose solution. Such PPy–MWCNT nanocomposite, when applied in a chemiresistor configuration, obviates the need for reference electrode and electron mediators, by measuring the direct and reversible, oxidation–reduction induced conductivity change. Experimentally, GOx-laden, doped PPy–MWCNT is tested to be sensitive to glucose concentration up to 20 mM, which covers the physiologically important range for diabetics of 0–20 mM.

Simultaneous detection of atmosphere induced mass and conductivity variations using high temperature resonant sensors

A sensor concept is presented which enables detection of conductivity and mass related changes induced in gas sensitive films deposited onto the surface of high temperature crystal microbalances with special electrode design. This unique superposition of effects on resonant frequency increases the selectivity of high temperature resonant gas sensors while retaining the simplicity of a single data acquisition technique, i.e. resonant frequency measurement. Environmental induced conductivity changes of sensor films alter the effective resonator electrode size and therefore the average mass sensitivity. Using this concept, the ability of such a sensor to distinguish between H 2 and CO is demonstrated.

A Comparison Between Potapof's and Pride's Equations for Seismoelectric Waves

AbstractPotapof's equations for the first and the second types of seismoelectric effects are analyzed. The first type of seismoelectric effect refers to elastic wave induced conductivity change. When no macroscopic static electric field exists, Potapof's equations reduced to equations for the second type of seismoelectric effect, which is also described by Pride's equations. Comparison is made between these two sets of equations. When ignoring the coupling between elastic and electromagnetic field, both the Pride's and the Potapof's equations reduce to equations for poroelasticity. The elastodynamical parameters in Potapof's equations are explained with well‐known parameters in Biot's theory for elastic waves. By comparison to Biot theory, it is clear that in Potapof's equations the mass coupling between fluid and solid frame is ignored. The square of porosity is erroneously taken as porosity in the viscous damping term, which may lead to exaggerated amplitudes of the elastic wave and its converted electric wave. And there is an error in the boundary condition about fluid filtration across the interface, which influence the study on the behavior of reflection and refraction of the seismoelectric waves on boundaries.

Proposal of controlled NOT gate using FQHE system and observation of large life time of laser triggered conductance change in LaSrCuO film with localization

According to a theoretical proposal denoting large decoherence time in fractional quantum Hall effect (FQHE) system, we studied the CO 2 laser irradiation effect on the La 1.95Sr 0.05CuO 4− δ film, whose electronic behavior is supposed to be described by FQHE caused by the unique zero-point oscillation of Cu electron. The irradiation induced conductivity change at room temperature shows the switching of hysteretic behavior triggered by the laser light. The effect remains after the irradiation for several days. The long life time can be explained by the large decoherence time of FQHE system, which is necessary for the feasibility of quantum computing.

Ultrafast Laser Induced Conductive and Resistive Transients inLa0.7Ca0.3MnO3: Charge Transfer and Relaxation Dynamics

Pulsed laser excitation induced conductance changes in colossal magnetoresistance material ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ were studied on the picosecond time scale. A two-component signal was seen consisting of a fast positive transient associated with the paramagnetic insulating state and a slower negative signal associated with the ferromagnetic metallic state. The fast component corresponds to the photoionization of the Jahn-Teller small polaron. The slow component is explained in terms of the reduced carrier mobility due to photogenerated magnetic excitations.

Optically Induced Conductivity Changes in Amorphous Silicon: A Historical Perspective

ABSTRACTA historical perspective of the discovery of optically induced changes in amorphous silicon is presented in this paper from my personal point of view. It includes the story of how Chris Wronski and I discovered the effect, the key elements in our R&D environment that lead to our quick realization that the effect was reversible and reproducible, how our research environment supported the rapid publication of our first paper, and a brief look at the effect from today's perspective.