Nonlinear Current-voltage Characteristics Research Articles

Physical reservoir application of random network of gold nanoparticles fabricated by multi-step immersion in gold colloidal solution

Abstract We fabricated a random network of gold nanoparticles (RN-GNPs) over 12 NiCr/Au electrodes by using a multi-step immersion method, where a sample was immersed in a gold colloid solution three times. 
Nonlinear current-voltage characteristics due to the Coulomb blockade were observed at 77 K. 
For demonstration of physical reservoir applications, input-output characteristics of the RN-GNPs were also measured in a one-input, nine-output terminal configuration. 
Distorted output voltage waveforms were obtained for a sinusoidal voltage input of 100 Hz. 
The higher-order harmonic components were confirmed in the frequency spectra of the outputs. 
The waveform reconstruction task and short-term storage capacity estimation were performed by an echo state network model with ridge regression and linear regression, respectively.

Proton Coulomb Blockade Effect Involving Covalent Oxygen-Hydrogen Bond Switching.

Instead of the canonical Grotthuss mechanism, we show that a knock-on proton transport process is preferred between organic functional groups (e.g., -COOH and -OH) and adjacent water molecules in biological proton channel and synthetic nanopores through comprehensive quantum and classical molecular dynamics simulations. The knock-on process is accomplished by the switching of covalent O─H bonds of the functional group under externally applied electric fields. The proton transport through the synthetic nanopore exhibits nonlinear current-voltage characteristics, suggesting an unprecedented proton Coulomb blockade effect. These findings not only enhance the understanding of proton transport in nanoconfined systems but also pave the way for the design of a variety of proton-based nanofluidic devices.

Stand-alone PV-SOFC-battery power system based on ANFIS controller for electric vehicle charging

Purpose This study aims to offer a hybrid stand-alone system for electric vehicle (EV) charging stations (CS), an emerging power scheme due to the availability of renewable and environment-friendly energy sources. This paper presents the analysis of a photovoltaic (PV) with an adaptive neuro-fuzzy inference system (ANFIS) algorithm, solid oxide fuel cell (SOFC) and a battery storage scheme incorporated for EV CS in a stand-alone mode. In previous studies, either the hydrogen fuel of SOFC or the irradiance is controlled using artificial neural network. These parameters are not controlled simultaneously using an ANFIS-based approach. The ANFIS-based stand-alone hybrid system controlling both the fuel flow of SOFC and the irradiance of PV is discussed in this paper. Design/methodology/approach The ANFIS algorithm provides an efficient estimation of maximum power (MP) to the nonlinear voltage–current characteristics of a PV, integrated with a direct current–direct current (DC–DC) converter to boost output voltage up to 400 V. The issue of fuel starvation in SOFC due to load transients is also mitigated using an ANFIS-based fuel flow regulator, which robustly provides fuel, i.e. hydrogen per necessity. Furthermore, to ensure uninterrupted power to the CS, PV is integrated with a SOFC array, and a battery storage bank is used as a backup in the current scenario. A power management system efficiently shares power among the aforesaid sources. Findings A comprehensive simulation test bed for a stand-alone power system (PV cells and SOFC) is developed in MATLAB/Simulink. The adaptability and robustness of the proposed control paradigm are investigated through simulation results in a stand-alone hybrid power system test bed. Originality/value The simulation results confirm the effectiveness of the ANFIS algorithm in a stand-alone hybrid power system scheme.

P-type π-conjugated BTPDS-8 organic molecule for broadband hybrid photodetector with organic/inorganic heterostructure

A novel p-type π-conjugated organic small molecule 3,7-bis(4-([2,2′:6′,2''-terpyridin]−4′-yl)phenyl)− 5H-dibenzo[a,d][7]annulen-5-one (named as BTPDS-8) in which terpyridinyl units are linked to the dibenzosuberenone backbone by a phenyl bridge was successfully synthesized in four reaction steps. The synthesized organic material BTPDS-8 was fully characterized using 1H NMR, 13C NMR, IR, and HRMS spectroscopy techniques. Then, eleven BTPDS-8/Si heterojunctions were fabricated having non-linear current-voltage characteristics. Among these devices, the one with the highest rectification ratio (with 8.43 ×105) was analyzed in detail under UV and IR light as well as different intensities of visible light. Experimental results showed that the device has good photoresponse performance under any light source in addition to self-driven mode characteristics. It was observed that the saturation current and barrier height increased, and the ideality factor decreased, depending on the light intensity under visible light. Photocurrent, on/off ratio, responsivity, detectivity and NPDR were calculated from the optical measurements. The broad spectrum photoresponse of the BTPDS-8/Si heterojunction from UV to IR demonstrated that the device has the potential to be used as a broadband photodetector. The best performance was obtained under 850 nm IR light. The detectivity values under IR light were 1.22 × 1010 Jones and 7.53 × 109 Jones for V= 0.0 volts (self-driven mode) and V= −2.0 volts, respectively.

Moving Crystal Phases of a Quantum Wigner Solid in an Ultra-High-Quality 2D Electron System.

In low-disorder, two-dimensional electron systems (2DESs), the fractional quantum Hall states at very small Landau level fillings (ν) terminate in a Wigner solid (WS) phase, where electrons arrange themselves in a periodic array. The WS is typically pinned by the residual disorder sites and manifests an insulating behavior, with nonlinear current-voltage (I-V) and noise characteristics. We report here measurements on an ultralow-disorder, dilute 2DES, confined to a GaAs quantum well. In the ν<1/5 range, superimposed on a highly insulating longitudinal resistance, the 2DES exhibits a developing fractional quantum Hall state at ν=1/7, attesting to its exceptional high quality and dominance of electron-electron interaction in the low filling regime. In the nearby insulating phases, we observe remarkable nonlinear I-V and noise characteristics as a function of increasing current, with current thresholds delineating three distinct phases of the WS: a pinned phase (P1) with very small noise, a second phase (P2) in which dV/dI fluctuates between positive and negative values and is accompanied by very high noise, and a third phase (P3) where dV/dI is nearly constant and small, and noise is about an order of magnitude lower than in P2. In the depinned (P2 and P3) phases, the noise spectrum also reveals well-defined peaks at frequencies that vary linearly with the applied current, suggestive of washboard frequencies. We discuss the data in light of a recent theory that proposes different dynamic phases for a driven WS.

Electric-field modulation of the charge-density-wave quantum condensate in h-BN/NbS3 quasi-2D/1D heterostructure devices

We report on the field-effect modulation of the charge-density-wave quantum condensate in the top-gated heterostructure devices implemented with quasi-one-dimensional NbS3 nanowire channels and quasi-two-dimensional h-BN gate dielectric layers. The charge-density-wave phases and collective current in quasi-1D NbS3 nanowires were verified via temperature dependence of the resistivity, non-linear current–voltage characteristics, and Shapiro steps that appeared in the device response under radio frequency excitation mixed with the DC bias. It was demonstrated that the electric field of the applied gate bias can reversibly modulate the collective current of the sliding charge-density-wave condensate. The collective current reduces with more positive bias, suggesting a surface effect on the condensate mobility. The single-particle current, at small source–drain biases, shows small-amplitude fluctuation behavior, attributed to the variations in the background potential due to the pinned or creeping charge-density-wave condensate. The knowledge of the electric-field effect on the charge density waves in quasi-1D NbS3 nanowires is useful for potential electronic applications of such quantum materials.

Evaluation of Contactless Identification Card Immunity against a Current Pulse in an Adjacent Conductor

This paper analyses the possibility of damaging and destroying an identification chip of the Mifare type in a frequently used contactless identification card of size ID-1, following the standard ISO/IEC 7810 (i.e., with dimensions 85.60 × 53.98 × 0.76 mm), using the magnetic field of an adjacent conductor in which a current pulse of a defined shape and amplitude is flowing. For analysis purposes, the nonlinear current–voltage characteristic of the Mifare chip voltage limiter was measured and approximated, and the mutual inductance of the straight conductor and the rectangle coil antenna in the card was calculated. Next, a mathematical analysis was conducted based on the description of the equivalent electrical circuit by the differential equations. The results of the mathematical analysis were verified by a simulation in the free simulation software Micro-Cap 12. The peak value of the current pulse that can damage the Mifare chip was measured by a combination wave generator. Based on these measurements and the chip characteristics, the energy capable of destroying the chip was calculated. The characteristics of chip damage were determined using a comparison of the resonant characteristics of undamaged and damaged RFID cards with Mifare chips.

Superconducting nonlinear transport in optically driven high-temperature K3C60

Optically driven quantum materials exhibit a variety of non-equilibrium functional phenomena, which to date have been primarily studied with ultrafast optical, X-Ray and photo-emission spectroscopy. However, little has been done to characterize their transient electrical responses, which are directly associated with the functionality of these materials. Especially interesting are linear and nonlinear current-voltage characteristics at frequencies below 1 THz, which are not easily measured at picosecond temporal resolution. Here, we report on ultrafast transport measurements in photo-excited K3C60. Thin films of this compound were connected to photo-conductive switches with co-planar waveguides. We observe characteristic nonlinear current-voltage responses, which in these films point to photo-induced granular superconductivity. Although these dynamics are not necessarily identical to those reported for the powder samples studied so far, they provide valuable new information on the nature of the light-induced superconducting-like state above equilibrium Tc. Furthermore, integration of non-equilibrium superconductivity into optoelectronic platforms may lead to integration in high-speed devices based on this effect.

Development of Flexible Semiconductors Based on g-C3N4/Cu2O P–N Heterojunction for Triboelectric Nanogenerator Application

This research aims to develop flexible semiconductors for triboelectric nanogenerator (TENG) applications. The sample powders of graphitic carbon nitride (g-C3N4) and copper (I) oxide (Cu2O) as N-type and P-type semiconductors, respectively, were synthesized. The semiconductors were prepared to be a composite film with alginate. The structure, morphology, and purity of the N- and P-type semiconductors were characterized using X-Ray diffraction and scanning electron microscopy techniques. Through the optical characterization, the N-type semiconductor showed the calculated energy band gap of 2.80 eV, while the P-type semiconductor was 1.90 eV. The P–N junction property of prepared samples was confirmed using a nonlinear current–voltage characteristic. After that, two flexible semiconductors were frictional paired for TENG. Through a vertical contact-separation mode, the P–N junction-based TENG produced a maximum output voltage and current of 3.90 V and 0.44 µA, respectively, with a maximum output power of 0.35 µW at 10 MΩ. In summary, the present work achieved the preparation of flexible P- and N-type semiconductors. The feasibility to harvest the mechanical energy was demonstrated in the TENG configuration. This idea is crucial for the future development of flexible harvesting/sensing devices using a novel concept.

Role of ZnMn2O4 phase in formation of varistor characteristics in ZnO:Mn ceramics

The samples ZnO:Mn were prepared using the conventional solid-state technique. To dope them with manganese, we used water solutions of MnSO4 and MnCl2. The properties inherent to both types of the obtained ceramics have been compared. It was found that the former demonstrated nonlinear current-voltage characteristics, whereas those of the latter were, in fact, linear. The analysis of EPR, diffuse reflectance and Raman spectra obtained for prepared ceramics allowed concluding that, in the samples doped with MnSO4, formation of Mn-related phase, namely, ZnMn2O4 spinel occurred at ZnO grain boundaries under sintering. It has been ascertained that a thin layer of this substance separates adjacent ZnO grains, which provides appearance of the back-to-back Schottky barriers at grain boundaries and “varistor behavior” of current-voltage characteristics.

Pure edge-contact devices on single-layer-CVD-graphene integrated into a single chip

We present a simple and cost-effective fabrication technique for on-chip integration of pure edge contact two-terminal (2T) and Graphene field effect transistor (GFET) devices with low contact resistance and nonlinear characteristics based on single-layer chemical-vapor-deposited (CVD) graphene. We use a smart print-based mask projection technique with a 10X magnification objective lens for maskless lithography followed by thermal evaporation of the contact material Cr-Pd-Au through three different angles (90° and ± 45°) using a customized inclined-angle sample-holder to control the angle during normal incidence evaporation for edge-contact to graphene. Our fabrication technique, graphene quality, and contact geometry enable pure metal contact to 2D single-layer graphene allowing electron transport through the 1D atomic edge of graphene. Our devices show some signatures of edge contact to graphene in terms of very low contact resistance of 23.5 Ω, the sheet resistance of 11.5 Ω, and sharp nonlinear voltage-current characteristics (VCC) which are highly sensitive to the bias voltage. This study may find application in future graphene-integrated chip-scale passive or active low-power electronic devices.

Gated ion transport in disjoint carbon nanotubes by a water bridge

Nanofluidic ion transport in carbon nanotubes (CNTs) has numerous applications, including membrane separation, energy conversion, and ionic circuits. To imitate the natural gated ion channel systems, CNTs require a more complex structure beyond a single intact tube. In this study, we present molecular dynamics simulations demonstrating the gated ion transport in two disjoint CNTs with a nanogap. The observation of nonlinear current-voltage characteristics, featuring onset and plateau voltages for ion transport, indicates that the nanogap serves as a gate. Ions cannot transport through the disjoint CNTs below the onset voltage. Interestingly, a water bridge forms occasionally within the nanogap above the onset voltage, allowing ions to transport through coupling with water molecules. Above the plateau voltage, a stable water bridge forms and ions can transport in disjoint CNTs with the same efficiency as in the intact CNT. The formation of water bridges is due to that the electric stress on polarized water molecules near the nanogap overcomes the surface tension. Furthermore, the gated ion transport behavior is dependent on the nanogap length, CNT diameter, and CNT wettability, but not on the ion concentration. This work offers a viable approach for developing CNT-based nanofluidic devices with finely tuned ion transport efficiency.

Collective Transport for Nonlinear Current-Voltage Characteristics of Doped Conducting Polymers.

Origin of nonlinear transport phenomena in conducting polymers has long been a topic of intense controversies. Most previous knowledge has attributed the macroscopic nonlinear I-V characteristics to individual behaviors of elementary resistors in the network. In this Letter, we show via a systematic dimensionality-dependent transport investigation, that understanding the nonlinear transport in conducting polymers must include the collective transport effect in a percolation network. The possible mediation of percolation threshold p_{c} by controlling the samples' dimensionality unveiled the collective effect in growth of percolation paths driven by electric field, enabling us to draw a smooth connection between two typically observed nonlinear phenomena, dissipative tunnelinglike and threshold-limited transport, which have been controversial for years. The possible microscopic origins of the collective transport are discussed within the Coulomb blockade theory.

Electrical properties of tin oxide based varistors with PbO addition in humid air

In order to decrease the humidity sensitivity of SnO2–Co3O4–Nb2O5–Cr2O3 varistor ceramics, lead oxide was added and the electric characteristics of synthesized materials with the PbO concentration of 0, 0.1, 0.5, 0.7, 1 and 2 mol.% in the air with relative humidity of 10–86% were investigated. All tested samples have non-linear current–voltage characteristics with large values of the nonlinearity coefficient of 38–51. The optimal concentration of PbO addition in ceramics is 0.5–0.7 mol.%. The addition of such quantity of lead oxide to the ceramics leads to the decrease of the breakdown electric field up to 4390 V/cm and the humidity sensitivity coefficient up to 172. The increase of the PbO concentration provides the increase of the electrical conductivity of samples at low fields. The barrier mechanism of electrical conductivity of the studied ceramics is proved by the obtained values of potential barrier heights of 0.85–0.90 еV on the SnO2 crystallite boundaries.

Enhanced UV photo-detection properties of graphene oxide incorporated transparent TiO2 thin films in Schottky configuration

Here we report the modification of UV photo-response characteristics of solution processed transparent titanium dioxide-graphene oxide (TiO2-GO) nanocomposite thin films measured in metal-semiconductor (MS) Schottky junction configuration with the variation of GO content. Optical characterizations confirm the GO induced modification of optical band gap of TiO2 thin films of average thickness ∼100 nm without compromising the transparency in the visible range of electromagnetic spectrum. The nonlinear current-voltage characteristics with rectifying nature for TiO2-GO nanocomposite thin films with silver electrode indicate the formation of MS Schottky junction. The UV response characteristics like photocurrent, photo response times of the fabricated MS junctions improve significantly with the GO content in host TiO2 matrix when measured under UV light of wavelength ∼365 nm. The enhanced photocurrent (Iph) with reduced rise (tON) and recovery time (tOFF) of photo response is attributed to the GO induced modification of space charge region, passivation of interface defect states for betterment of charge carrier transport and less recombination of photo-generated charge carriers. Impedance spectra measured for nanocomposite thin films under dark and illumination confirm the modification of grain-boundary/interface to enhance the charge transport mechanism.

Amorphous ITZO-Based Selector Device for Memristor Crossbar Array

In the era of digital transformation, a memristor and memristive circuit can provide an advanced computer architecture that efficiently processes a vast quantity of data. With the unique characteristic of memristor, a memristive crossbar array has been utilized for realization of nonvolatile memory, logic-in-memory circuit, and neuromorphic system. However, the crossbar array architecture suffers from leakage of current, known as the sneak current, which causes a cross-talk interference problem between adjacent memristor devices, leading to an unavoidable operational error and high power consumption. Here, we present an amorphous In-Sn-Zn-O (a-ITZO) oxide semiconductor-based selector device to address the sneak current issue. The a-ITZO-selector device is realized with the back-to-back Schottky diode with nonlinear current-voltage (I-V) characteristics. Its nonlinearity is dependent on the oxygen plasma treatment process which can suppress the surface electron accumulation layer arising on the a-ITZO surface. The a-ITZO-selector device shows reliable characteristics against electrical stress and high temperature. In addition, the selector device allows for a stable read margin over 1 Mbit of memristor crossbar array. The findings may offer a feasible solution for the development of a high-density memristor crossbar array.

Transient conduction of ZnO varistors under moderate time-varying voltages: Dynamics of interfacial charges of the double Schottky barrier

ZnO varistors are widely employed for overvoltage protections and surge absorptions due to their excellent nonlinear current–voltage characteristics originating from double Schottky barriers (DSBs). In most cases, they are operating under moderate ac voltages, while calculating the transient current responses of DSBs remains a challenge, impeding the development of condition assessments. In this paper, a transient conducting model for the DSB is proposed by quantifying the charge trapping processes of the interface states. The DSB is found to quickly reach a quasi-steady state, where the interfacial charge stabilizes with only small modulations at a relatively high level above the dc equilibrium value, even though the applied ac voltage varies in time and polarity. This is the result of efficient charge trapping and slow de-trapping by grain boundary interface states. For charge compensation under the time-varying voltage, the width of the two depletion regions of the DSB shows periodic changes. The proposed model is validated by a satisfying agreement between experimentally measured current responses and simulation results of ZnO varistors. The findings of this study provide a perspective on investigating the time-varying conducting systems and open avenues for condition assessments of nonlinear conducting devices.

Optimal Design of Fuzzy Controller for Photovoltaic Maximum Power Tracking Using Particles Swarm Optimization Algorithm

Solar panels have non-linear current-voltage characteristics and a specified maximum power point, which depends on environmental factors like the solar radiation and ambient temperature. The voltage-power curve of the photovoltaic system has multiple peaks under different atmospheric conditions that reduce the efficiency of the maximum power tracking techniques. This paper proposes an optimal design of a fuzzy controller using particle swarm optimization algorithm to track the maximum power point of a photovoltaic system operating under different conditions to improve its performance. The proposed system optimizes the particle swarm to produce an optimal working coefficient, which varies with photovoltaic parameters to extract maximum power. Results of simulations – performed using the MATLAB software - show the advantages of the proposed method, namely the ability to track the maximum power point in a short time and maintain the output waveform despite the relatively high variations in environmental conditions.

ZnO varistors with low leakage current and high stability arrester with Ga doping

The insulation level of power equipment in power system is based on the overvoltage protection level of metal oxide arrester represented by zinc oxide valve blade. Owing to its superior nonlinear voltage current characteristics and surge energy absorption capacity, ZnO varistor is widely used as the core component of power system arrester. The electrical characteristics of ZnO varistors are determined by their complex microstructures and grain boundary characteristics. Therefore, to further improve the insulation level of power grid equipment, doping is required to further improve the grain boundary characteristics of ZnO varistors. In order to obtain more stable ZnO varistors, the stability characteristics of Ga doped ZnO varistors are investigated. The microstructural and electrical characteristics of the obtained experimental samples are tested by scanning electron microscope, voltage current nonlinear characteristics, capacitance voltage characteristics, X-ray diffraction spectrum, energy spectrum scanning, dielectric loss, and AC acceleration aging. The experimental results show that with the further increase of gallium doping, gallium ions occupy the vacancies on the zinc oxide lattice, increasing the interface state density, and improving the Schottky barrier height. On the one hand, the leakage current density of ZnO varistor is reduced, on the other hand, the migration of free electrons in the depletion layer is suppressed, and the stability of ZnO varistor in the high charge rate environment is improved. Aluminum ions are dissolved into the ZnO lattice to generate a large number of free electrons, thereby reducing the resistivity of ZnO grains, which can effectively reduce the residual voltage ratio of ZnO varistor when large current passes through it. When the doping amount of Ga reaches 0.6%, the leakage current is 0.84 μA/cm&lt;sup&gt;2&lt;/sup&gt;, the residual voltage ratio is 1.97, the nonlinear coefficient is 66, and the Schottky barrier height is 1.81 eV. At 115 ℃, AC accelerated aging voltages of 87% &lt;i&gt;E&lt;/i&gt;&lt;sub&gt;1 mA&lt;/sub&gt;, 89% &lt;i&gt;E&lt;/i&gt;&lt;sub&gt;1 mA&lt;/sub&gt; and 91% &lt;i&gt;E&lt;/i&gt;&lt;sub&gt;1 mA&lt;/sub&gt; are applied to the test sample separately. The aging time is 1000 h, and the aging coefficients are 0.394, 0.437 and 0.550 separately. This research will help to further improve the protection level of zinc oxide surge arresters, achieving the deep limitation of grid overvoltage, and improving the security and stability of power systems.

Effect of surfactant-assisted hierarchical growth of cupric oxide-hydroxyapatite nanocomposite on the dielectric and electrical transport behavior

The current biomedical appliances require nano biomaterials with promising dielectric and transport properties. For this purpose, expensive, complicated instrumentations or time-consuming synthesis procedures, reducing acceptability of the developed materials, must be excluded. Therefore, for an effective solution to these challenges, proper scaling of electrical properties of nontoxic bioceramics is necessary by choosing eco-friendly surfactant-assisted synthesis methods. The present paper reports Polyvinylpyrrolidone-assisted hydrothermal synthesis of cupric oxide-hydroxyapatite nanocomposite (CuO-HAp-PVP) with crystallite size 25 nm. As observed by electron microscopy, the uniaxial growth of the CuO-HAp-PVP nanostructures elucidate novel flower-like aggregation. The nano-metric attachments of CuO phases are observed on the mesoporous surface (specific area of ∼17.7 m2/g obtained from Brunauer–Emmett–Teller study). The polymeric surfactant-mediated amorphous phases generate internal heterojunctions influencing the polarization process. The dielectric behavior [permittivity ∼6 × 103] and ionic conductivity of the nanocomposite are hence improved. Trap state-dependent bulk carrier conduction is observed by the nonlinear current-voltage characteristics.