Polarity Of Bias Voltage Research Articles

Dynamically Tunable Localized Surface Plasmon Resonance in Self‐Assembled SrCoOx‐Au Vertically Aligned Nanocomposite Thin Films

AbstractWhile the physical principles for regulating localized surface plasmon resonance (LSPR) are well established, dynamically tuning the LSPR in a given material post synthesis remains challenging. Herein, this study demonstrates a strategy for dynamically tuning the LSPR of Au nanostructures by selectively altering the dielectric environment. Au is integrated with an electrochemically gatable oxide, i.e., SrCoOx (SCO), into vertically aligned nanocomposite thin films via a self‐assembly growth mechanism, where Au develops into nanopillars embedded in the SCO matrix. By selectively controlling the tri‐state phase transitions of SCO matrix via varying the bias voltage polarity in ionic liquid gating (ILG), the LSPR behavior of Au nanopillars can be dynamically tuned. Specifically, gating with a negative bias fully suppresses the LSPR, while a positive bias leads to a continuous blueshift of the LSPR wavelength upon increasing the ILG duration. This work not only opens new directions for the dynamic control of LSPR of noble metal nanostructures, but also offers insight to the voltage control of multifunctionalities via structural and physical intercoupling between different phases in self‐assembled nanocomposites.

Binary and ternary logic-in-memory using nanosheet feedback field-effect transistors with triple-gated structure

In this study, we demonstrate binary and ternary logic-in-memory (LIM) operations of inverters and NAND and NOR gates comprising nanosheet (NS) feedback field-effect transistors (FBFETs) with a triple-gated structure. The NS FBFETs are reconfigured in p- or n-channel modes depending on the polarity of the gate bias voltage and exhibit steep switching characteristics with an extremely low subthreshold swing of 1.08 mV dec–1 and a high ON/OFF current ratio of approximately 107. Logic circuits consisting of NS FBFETs perform binary and ternary logic operations of the inverters and NAND and NOR gates in each circuit and store their outputs under zero-bias conditions. Therefore, NS FBFETs are promising components for next-generation LIM.

Dependence of Sensitivity, Derivative of Transfer Curve and Current on Bias Voltage Magnitude and Polarity in Tunneling Magnetoresistance Sensors.

The sensitivity of tunneling magnetoresistance sensors is an important performance parameter. It depends on the derivative of resistance versus magnetic field (transfer curve) and the current and is expressed as the product of the two factors. Previous research has demonstrated that the bias voltage has a significant impact on the sensitivity. However, no research has been conducted into the dependence of current and the derivative on bias voltage magnitude and polarity, and their contribution to the sensitivity. Thus, this paper investigates the dependence of sensitivity, derivative of resistance versus magnetic field curve and current on bias voltage magnitude and polarity in CoFeB/MgO/CoFeB-based tunneling magnetoresistance sensors with weak, strong and no voltage-controlled perpendicular magnetic anisotropy modification. It demonstrates that the sensitivity dependence on bias voltage for sensors with voltage controlled magnetic anisotropy modification showed no saturation up to 1 V. Moreover, the sensitivity asymmetry with respect to bias polarity changed significantly with bias, reaching a ratio of 6.7. Importantly, the contribution of current and the derivative of resistance versus magnetic field curve to the sensitivity showed a crossover. The current dominated the bias dependence of sensitivity below the crossover voltage and the derivative above the voltage. Furthermore, the crossover voltage in sensors without voltage controlled magnetic anisotropy modification did not depend on polarity, whereas in sensors with voltage controlled magnetic anisotropy modification, it appeared at significantly higher voltage under positive than negative polarity.

Scaling of Time-Dependent Tunneling Current in Terahertz Scanning Tunneling Microscopes

Terahertz scanning tunneling microscopy (THz-STM) has enabled spatiotemporal imaging with femtosecond temporal resolution and angstrom spatial resolution. In THz-STMs, the junction bias is modulated by coupling THz pulses, which results in transient voltage bias and extremely high transient tunneling currents. In order to have efficient imaging of the sample surface, it is important to understand the nonlinear tunneling current response and its parametric dependence. In this work, we theoretically investigate the basic scaling of rectified electrons in a THz-STM junction. We use a self-consistent quantum model that includes both space-charge potential and exchange-correlation potential, which were ignored in previous studies. Since THz-STMs are operated at high transient voltage in field emission regime, the effects of exchange-correlation potential become crucial. We validate our calculation with recently reported experimental data and investigate the rectification property of the tip-sample junction for different parameters. We find that the time-dependent tunneling current and the electron transport can be manipulated by varying the dc bias voltage (polarity, amplitude), incident THz field (polarity, shape, peak amplitude), work functions of STM tip and sample---especially their difference $\mathrm{\ensuremath{\Delta}}W$, and the tip-sample separation. Our study provides an important framework that can be used in the future to characterize, control, and improve THz-induced currents and probing techniques at the nanometer scale over subpicosecond time periods.

Evidence of cluster dipole states in germanium detectors operating at temperatures below 10 K

By studying charge trapping in germanium detectors operating at temperatures below 10 K, we demonstrate for the first time that the formation of cluster dipole states from residual impurities is responsible for charge trapping. Two planar detectors with different impurity levels and types are used in this study. When drifting the localized charge carriers created by α particles from the top surface across a detector at a lower bias voltage, significant charge trapping is observed when compared to operating at a higher bias voltage. The amount of charge trapping shows a strong dependence on the type of charge carriers. Electrons are trapped more than holes in a p-type detector, while holes are trapped more than electrons in an n-type detector. When both electrons and holes are drifted simultaneously using the widespread charge carriers created by γ rays inside the detector, the amount of charge trapping shows no dependence on the polarity of bias voltage.

Design of an Aerospace Langmuir Probe Volt-ampere Characteristic Load Simulator

The development process of space Langmuir probe needs to complete a large number of tests and calibration tests on the ground. Due to the long calibration period, complexity and high cost of plasma environment calibration, calibration tests are usually carried out after the instrument has been developed, in order to conduct preliminary tests on Langmuir probe during the instrument development process to verify the performance, as well as to save the cost of calibration tests and increase the reliability of the instrument, An advanced spatial Langmuir probe volt-ampere(I-V) load simulator was designed in this paper. Based on the positive and negative polarity of the external bias voltage, the I-V characteristic curve of the Langmuir probe was divided into positive and negative characteristic curves, which were realized by the combination of the output characteristic curves of NPN and PNP transistors, and the diode switching selectivity. The laboratory test results were consistent with the theoretical curve, verifying the validity and compliance of the design, which can play an important role in supporting the development of the space Langmuir probe and the calibration of the plasma environment.

Nanoscale Impact Ionization and Electroluminescence in a Biased Scanning-Tunneling-Microscope Junction

Electroluminescence from a p-type GaAs(110) surface was induced by tunneling electrons in a scanning tunneling microscope under both polarities of bias voltage. The optical spectra exhibit a polarity-independent luminescence peak at 1.47 eV resulting from the exciton recombination. However, the quantum yield of photon emission at negative bias voltage is two orders of magnitude weaker than that at positive bias voltage. Moreover, the luminescence at negative bias voltage shows the linear dependence of bias voltage, distinct from the rapid rise due to resonant electron injection at positive bias. Furthermore, the threshold bias voltage for electroluminescence at negative bias is nearly twice the bandgap of GaAs, not simply satisfying the energy conservation for the creation of an electron-hole pair. Through theoretical calculation, we propose an impact ionization model to nicely explain the newly observed electroluminescence at negative bias voltage. We believe that this mechanism of impact ionization could be readily applied to other nanoscale optoelectronics including 2D semiconductors and 1D nanostructures.

Polarity reversal of resistance response to trace H2 gas in the air between asymmetrically shaped electrodes on rutile-TiO2 single crystal

We investigated the resistance response to trace hydrogen gas in the air between the asymmetrically shaped point contact- (Pt tip) and plane contact- (Al thin-film) electrodes formed in-plane on a rutile TiO2 single crystal at 673 K. It was found that the polarity of the resistance response, that is, the increase or the decrease of the resistance by exposing to hydrogen, reverses depending on the bias voltage polarity. This reversal mechanism of the resistance response was analyzed from the electrical conduction properties and the depth profile of the oxygen tracer (18O) in the electric field-induced diffusion. The central mechanism is proposed to be the oxygen transfer reaction at the Pt/TiO2 interface, accompanied by the modulation of the positively charged-oxygen vacancy concentration, thus the resistance between the two terminals. It is also proposed that the proton hinders the transfer reaction at the interface; and hence, the resistance increases by exposing to hydrogen with biasing the positive voltage to the Pt tip electrode. The application of this reversal of the resistance response for separating hydrogen and ethanol in the trace gas sensing is discussed, which is quite limited for a conventional semiconductor gas sensor.

Bias-dependent tunneling anisotropic magnetoresistance in antiferromagnetic Pd-doped FeRh-based junctions

We report the bias-dependent tunneling anisotropic magnetoresistance (TAMR) in antiferromagnetic α′-Fe(Rh0.98Pd0.02)/MgO/γ-Fe(Rh0.98Pd0.02) junctions. The TAMR effect is driven by the antiferromagnetic-ferromagnetic phase transition of α′-Fe(Rh0.98Pd0.02) and concomitantly large variation of the density of states (DOS) near the Fermi level. It exhibits polarity reversion behavior with increasing bias voltage, i.e., negative and positive polarities for low and high bias voltages, respectively. Such bias-dependent TAMR is comprehended by first-principle calculations, where a crossing point and subsequent magnitude-reversion emerge between the DOS of antiferromagnetic and ferromagnetic phases of α′-Fe(Rh0.98Pd0.02). Harnessing the tunneling behavior by a feasible bias voltage in an antiferromagnet-based junction is a frontier of great promise in antiferromagnet spintronics.

Bias Voltage Dependence of Sensing Characteristics in Tunneling Magnetoresistance Sensors.

One of the characteristic features of tunneling magnetoresistance (TMR) sensors is a strong influence of bias voltage on tunneling current. Since fundamental sensing characteristics of the sensors are primarily determined by the tunneling current, the bias voltage should impact these characteristics. Previous research has indeed showed the influence of the bias voltage on the magnetic field detection and sensitivity. However, the effect has not been investigated for nonlinearity and hysteresis and the influence of bias voltage polarity has not yet been addressed. Therefore, this paper systematically investigates the dependence of field sensitivity, nonlinearity, hysteresis and magnetic field detection of CoFeB/MgO/CoFeB-based magnetoresistance sensors on bias voltage magnitude and polarity. The sensitivity and field detection of all sensors improved significantly with the bias, whereas the nonlinearity and hysteresis deteriorated. The sensitivity increased considerably (up to 32 times) and linearly with bias up to 0.6 V. The field detection also decreased substantially (up 3.9 times) with bias and exhibited the minimum values for the same magnitude under both polarities. Significant and linear increases with bias were also observed for nonlinearity (up to 26 times) and hysteresis (up to 33 times). Moreover, not only the voltage magnitude but also the polarity had a significant effect on the sensing characteristics. This significant, linear and simultaneous effect of improvement and deterioration of the sensing characteristics with bias indicates that both bias voltage magnitude and polarity are key factors in the control and modification of these characteristics.

Квазісинхронна термокомпенсація в іонометрії із застосуванням ІСПТ. Частина 2: Практична реалізація

This paper is a continuation of the previously published work by the same authors, where general principles of the ionometric transducer design utilizing solid-state ion-sensitive electrodes (ion-sensitive field effect transistors, ISFETs) that can simultaneously serve as temperature sensors were laid out. In that part of the work, a possibility of using such transducer as a basis for ionometric device that performs automatic compensation of the temperature dependence of electrode potential without the need for a dedicated thermometric measuring path in the device structure was demonstrated with the circuit simulation results. Combination of the two functions (ionometric and thermometric) in a single sensor is achieved by separating the sensor operation modes in time, and dynamically switching between them by controlling the ISFET bias voltage. In the present part, a practical implementation of the secondary transducer for ionometric sensors based on ISFET is considered and described. The proposed transducer provides the possibility of programmatic control of the ISFET bias voltage magnitude and polarity, thus allowing to use the ISFET as a temperature sensor. Consecutive switching between ionometric and thermometric modes of sensor operation, along with subsequent algorithmic processing of the obtained data by a microprocessor incorporated into the transducer structure, allows to compensate the temperature dependence of the ISFET electrode potential. Circuit diagrams for the main components of transducer — namely, the programmable voltage source for ISFET biasing and the transimpedance amplifier for the sensor output readout — are presented, as well as the experimental estimation of the ISFET sensor thermometric properties and the efficiency of thermocompensation.

Local electrical degradations of solid-state electrolyte by nm-scale operando imaging of ionic and electronic transports

We report on degradation mechanisms of solid-state electrolyte (SSE) based on insights from nm-scale ionic conduction and electronic leakage for solid-state batteries. The significantly different local degradations revealed by nm-scale ionic and electronic transport imaging demonstrate the need for this nm-scale investigation. State-of-the-art lithium-ion conductive glass ceramic (Li2O–Al2O3–SiO2–P2O5–TiO2-GeO2) SSE shows at least two types of degradations spatially separated within the SSE, namely: (1) ionic conduction blocking and slight electronic leaking and (2) highly electronic shunting. Degradation was significantly suppressed by application of a Li-containing polyacrylonitrile thin coating on both sides of the ceramic SSE. With this coating, the ionic conduction was not reduced by the extensive cycling; instead, it improved slightly, although accompanied by a slight increase in electronic leaking. Our nm-scale transport imaging was achieved using an atomic force microscopy (AFM)-based half-cell setup and a logarithmic-scale amplifier with current sensitivity down to the fA (10−15 A) range. This half-cell setup consisting of an AFM-probe/SSE/Li structure can distinguish the ionic from the electronic current by flipping the bias-voltage polarity. This nm-scale operando imaging opens up novel characterization of ionic and electronic transport in the field of solid-state batteries.

Temperature dependence of tunneling current in Pt/Nb:SrTiO3 Schottky junction

We investigate temperature-dependent electrical properties of Pt/Nb:SrTiO3 Schottky junctions by measuring current–voltage and capacitance–voltage curves at various temperatures (20 K–300 K). Interestingly, the Schottky junctions have shown different temperature dependences of resistance according to the polarity of bias voltage: insulating behaviors are displayed in the positive bias branch, while metallic behaviors are observed in the negative bias branch. These behaviors can be ascribed to Schottky barrier modulation that arises from the temperature and field dependences of dielectric permittivity of SrTiO3. The modulation of the barrier profile determines anomalous tunneling current in the negative bias branch as a function of temperature. These comprehensive analyses could not only reveal the rich physics of the Pt/Nb:SrTiO3 Schottky junction but also enhance our understanding for high dielectric materials.

Qualitative Analysis of Chaotic Behaviour in a Plasma System

To analyze a physical plasma system, qualitative analysis methods should be applied first. Plasma systems components like the plasma source itself and its diagnostic tools must be studied to find out how these components interact to yield results describing the actual plasma system behaviour. For example, immersing a basic electric diagnostic instrument, such as the Langmuir probe, in a thermionically produced plasma source to measure plasma characteristic parameters constitutes a plasma system. When a time-sweep of the probe bias voltage is applied to the probe tip, plasma charge current is collected between the two probe bias voltage polarities. The resulting so-called I-V characteristics curve resembles the logistic curve proposed, previously, by Verhulst. The Verhulst logistic model curve described how population grow relative to available resources and formed the basis of modern chaos theory. In this letter, accounting for plasma charges population growth (or decay) as well as how they are sustained in a plasma system is discussed qualitatively. This is done without bearing additional assumptions as to the physical composition of the plasma charge itself. In addition, the findings here should modify the approach in interpreting Langmuir probe trace data that used before, only, an exponential fit to model the plasma charge current vs. probe bias voltage data. This allows for more fitting models to be implemented to analyze the behaviour of a variety of plasma systems.

Effect of Functional Group on Electrical Switching Behaviour of an Imidazole Derivative in Langmuir‐Blodgett Film

AbstractHere we report the design and synthesis of an imidazole derivative namely 1‐benzyl‐2,4,5‐triaryl imidazole (compound 2) and its switching behaviour assembled onto Langmuir‐Blodgett (LB) films. Monolayer characteristic of compound 2 at the air‐ water interface has been studied by surface pressure vs area per molecule (π – A) isotherm, hysteresis analysis and in‐situ Brewster Angle Microscopy (BAM). These studies indicated the formation of stable floating Langmuir film at the water subphase. Atomic Force Microscopy (AFM) investigation confirmed the successful deposition of the Langmuir film onto solid substrate. Device consisted of 60 layers LB films of 2 showed resistive bipolar switching behaviour irrespective of the first applied bias voltage polarity. Observed bipolar switching has been explained in terms of reduction – oxidation process. Due to the presence of strong reducible group (C=N) in the imidazole core, reduction – oxidation process takes place easily during bias. Presence of sharp reduction and oxidation peaks in the Cyclic Voltammetry (CV) measurement of 2 also supported this hypothesis. Presence of benzyl group with the imidazole core played the crucial rule in the reduction – oxidation process and hence the switching behaviour. When benzyl group was replaced by a ‘–H’ then bipolar switching was not observed. In that case oxidizable group N – H opposed the reduction process during bias. This type of bipolar switching is very promising for future technological applications in organic electronics.

Regularly-swelling plumes generated in atmospheric pressure argon plasma jet excited by a biased sinusoidal voltage

Far different from conical plumes, regularly-swelling plumes are generated in an atmospheric pressure argon plasma jet excited by a biased sinusoidal voltage at low frequency. Depending on the polarity of bias voltage, the plumes with periodic swells can be solid or hollow. Results indicate that discharge initiates once per voltage cycle, which appears in the negative and positive half cycles for the solid and hollow plumes, respectively. By fast photography, it is found that streamers are involved propagating downstream of the argon flow for the two plumes. Transversely, the streamer diffuses for the solid plume, while it propagates only in the flow periphery for the hollow plume. Due to a high field, intense discharges near the nozzle provide the following swell positions with active species, which can remarkably enhance the discharges there and induce the swells. This formation mechanism of periodic swells is verified through investigating the distance of two adjacent swells as a function of gas flow rate and driving frequency. Moreover, spatial distributions of excited electron temperature and streamer propagation velocity are qualitatively explained based on the mechanism.

The effect of electric field on a fullerene molecule on a metal surface by a nano STM tip

Applying bias voltage generates the electric field between the sample and the probe tip of the scanning tunneling microscopy (STM). At the tunneling distance, individual fullerene molecule on a metal surface can be induced to diffuse into the region beneath the tip or desorb by the field strength. Finite Element Method Magnetics (FEMM) simulations were performed to investigate the electric field effect on a C60 molecule on a finite metal surface with a metallic STM tip. The field gradient has been simulated to study the effect of tip-apex size, 10, 30 and 50 nm and bias voltage, from +1.7 V to +4.8 at the calculated tunneling distance. This model appropriately defines the field strength just over the fullerene molecule as ∼6.8×109 V/m at +4.4 V and then exponentially decays with increasing radial distance from the tip about 69% in a range of 5 nm. Similar trends are obtained in between the molecule and surface gap but the field strength is enhanced by 2.5 times higher than the field over the C60 molecule with an effective range of 1 nm. The effective range of the field is enhanced by the bias voltage and the tip radii. For both the tip-molecule and molecule-sample gap, the E-field strengths show a linear increase with varying the bias voltage up to a maximum ∼17×109 V/m which is less than the threshold strength to yield a field evaporation of the surface adatoms. Independent from bias voltage polarity, the molecule can be diffused preferentially towards the tip-apex up to +3.0 V without thermal decomposition. Above +5.0 V voltage pulse, the desorption of the molecule is possible in the presence of the E-field. The van der Waals force with a range of 12–15 Å does not provide sufficient energy to induce either diffusion or desorption of the molecule.

Resistive switching device with highly asymmetric current–voltage characteristics: a solution to backward sneak current in passive crossbar arrays

With the view towards future non-volatile random access memories that can be integrated at a large scale, extensive study on resistive switching (RS) devices arranged in a crossbar array is currently underway. Although the crossbar array architecture offers relatively simple and acceptable scalability, the presence of sneak current is recognized as a critical issue that needs to be resolved at device level. In addressing this issue, we demonstrate a new type of RS device fabricated by combining graphene oxide (G–O) and zinc oxide (ZnO) with highly asymmetric current–voltage (I–V) characteristics depending on the polarity of bias voltage. The distinctive highly asymmetric I–V characteristics result from the presence of a hetero-junction interface formed between the G–O and ZnO layers. This hetero-junction manifests resistance in the range of GΩ under both forward and reverse bias voltage when the device is in the OFF state, in contrast, when the device is in the ON state, it exhibits resistance in the range of MΩ or kΩ under forward bias and GΩ under reverse bias. We propose to employ demonstrated RS devices with highly asymmetric I–V characteristics to mitigate adverse effects of the sneak current.

Katherine: Ethernet Embedded Readout Interface for Timepix3

The Timepix3—the latest generation of hybrid particle pixel detectors of Medipix family—yields a lot of new possibilities, i.e. a high hit-rate, a time resolution of 1.56 ns, event data-driven readout mode, and the capability of measuring the Time-over-Threshold (ToT - energy) and the Time-of-Arrival (ToA) simultaneously. This paper introduces a newly developed readout device for the Timepix3, called "Katherine", featuring a Gigabit Ethernet interface. The primary benefit of the Katherine is the operation of Timepix3 at long distance (up to 100 m) from computer or server, which is advantageous for the installation at beam lines, where the access is difficult or where radiation levels are too high for human interventions. The maximal hit-rate is limited by the bandwidth of the Ethernet connection (peer-to-peer connection; up to 16 Mhit/s). Since the Katherine interface is equipped with a processor of high computational power (ARM Cortex-A9 dual-core processor), it permits the use as a stand-alone (autonomous) radiation detector. The key features of the device are described in detail. These are the implemented high voltage power supply offering both polarities of bias voltage (up to ± 300 V), the automatic data sending to a sever via SSH, the automatic compensation of ToA values from columns with shifted matrix clock, etc. A dedicated control software was developed, which can be used for the detector preparation (sensor equalization, the DACs dependency scan, and the THL scan) and measurement control. Measured energy spectra from photon fields are shown.

Asymmetric Tunable Photonic Bandgaps in Self‐Organized 3D Nanostructure of Polymer‐Stabilized Blue Phase I Modulated by Voltage Polarity

AbstractElectrically responsive photonic crystals represent one of the most promising intelligent materials for technological applications in optoelectronics. In this research, a polymer‐stabilized blue phase (PSBP) I film with the self‐organized 3D nanostructure is fabricated, and an electrically tunable photonic bandgap (PBG) is achieved. Interestingly, the large‐scale shift of the PBG covering the entire visible spectrum is found to be asymmetric and can be modulated by the polarity and magnitude of bias voltage. Moreover, to demonstrate the usability in optical devices, blue phase lasers are developed by doping the PSBP material with fluorescent dyes. And mirrorless lasing emission with electrically tunable wavelength is observed. This self‐assembled soft material is prospective to produce large‐scale electrically responsive photonic crystals in facile fabrication process and has enormous potential applications in intelligent optoelectronic devices, such as 3D tunable lasers, reflective full‐color displays, or photonic integrated circuits.