Non-ohmic Behavior Research Articles

Mechanism of non-Ohmic conduction in a single Y3Fe5O12 nanofiber

We present a strong non-Ohmic transport characteristic in an individual Y3Fe5O12 (YIG) nanofiber at low temperature. The structural characterization reveals that the nanofiber consists of a multitude of nanoparticles stacked along the nanofiber axis. The non-Ohmic conductive behavior manifests itself by a strong input current dependence and the nonlinear I–V curves with a critical temperature around 160 K. The current measured at temperatures lower than 160 K follows the Simmons tunneling model, and the tunneling through the grain boundary is proposed to interpret the non-Ohmic feature in an individual YIG nanofiber. However, the observed resistance follows a T−1/4 variation in the high temperature range (> 160 K), suggesting a variable range hopping conduction.

On the behavior of a water electrolysis cell in a DC circuit

The electrolysis of water using a DC circuit is a familiar physical science experiment and the empirical details of the process, especially in terms of the chemistry, are well known. There are however, long-standing questions in regard to the specific role played by the circuit itself and the electrolyte. Recent empirical studies of an electrolysis cell as a circuit element have revealed what we see as clues towards understanding the cell’s behavior electrodynamically (Shen M et al 2011 Int. J. Hydrog. Energy 36 14335; Sun C-W and Hsiau S-S 2018 J. Electrochem. Sci. Technol. 9 99). For example, the cell is observed to be non-conductive below a threshold in the difference of potential, and once it becomes conductive the current is proportional to the difference between the applied voltage and the threshold, not the applied voltage. This type of non-Ohmic behavior guides our modeling of the cell in two steps. The first is the analysis of an equivalent circuit that captures the observed behavior. The second is an examination of the charge distributions within the double layers near the electrodes that polarize the cell. This polarization renders the cell non-conductive below the threshold, and its lingering effects explain the overall non-Ohmic behavior once conduction is possible. In addition, the energy transfer process required to power the cell, we find, is suggestive of non-classical (i.e. quantum mechanical) mechanisms.

Self-heating controlled current–voltage and noise characteristics in graphene

Pulsed current–voltage characteristics have been measured for epitaxial SiC graphene under controlled lattice temperature conditions. The monolayer and AB stacked bilayer graphene is dry transferred on SiO2. The measured characteristics of two-terminal samples with coplanar electrodes demonstrate non-ohmic behaviour up to intermediate-high fields. At high currents thermal effects come into play and soft damage of the samples takes place. Bilayer graphene samples withstand 20 kV cm−1 electric field when few nanosecond voltages pulses are applied. The results are treated in terms of hole drift velocity estimated from the data on current under the assumption of uniform electric field and constant hole density. The highest velocity of ∼3.5–5 × 106 cm s−1 (∼1.5 × 107 cm s−1) is estimated for the bilayer (monolayer) graphene. The velocity results are interpreted with hot phonons. High frequency noise is measured at 10 GHz for the monolayer graphene and the associated shot noise is resolved.

Anomalous vortex liquid in charge-ordered cuprate superconductors

The interplay between charge order and d-wave superconductivity in high-[Formula: see text] cuprates remains an open question. While mounting evidence from spectroscopic probes indicates that charge order competes with superconductivity, to date little is known about the impact of charge order on charge transport in the mixed state, when vortices are present. Here we study the low-temperature electrical resistivity of three distinctly different cuprate families under intense magnetic fields, over a broad range of hole doping and current excitations. We find that the electronic transport in the doping regime where long-range charge order is known to be present is characterized by a nonohmic resistivity, the identifying feature of an anomalous vortex liquid. The field and temperature range in which this nonohmic behavior occurs indicates that the presence of long-range charge order is closely related to the emergence of this anomalous vortex liquid, near a vortex solid boundary that is defined by the excitation current in the [Formula: see text] 0 limit. Our findings further suggest that this anomalous vortex liquid, a manifestation of fragile superconductivity with a suppressed critical current density, is ubiquitous in the high-field state of charge-ordered cuprates.

Induced Maxwell\u2013Chern\u2013Simons effective action in very special relativity

In this paper, we study the one-loop induced photon’s effective action in the very special relativity electrodynamics in (2+1) spacetime (hbox {VSR}–hbox {QED}_{3}). Due to the presence of new nonlocal couplings resulting from the VSR gauge symmetry, we have additional graphs contributing to the langle AArangle and langle AAA rangle amplitudes. From these contributions, we discuss the VSR generalization of the Abelian Maxwell–Chern–Simons Lagrangian, consisting in the dynamical part and the Chern–Simons-like self-couplings, respectively. We use the VSR–Chern–Simons electrodynamics to discuss some non-Ohmic behavior on topological materials, in particular VSR effects on Hall’s conductivity. In the dynamical part of the effective action, we observe the presence of a UV/IR mixing, due to the entanglement of the VSR nonlocal effects to the quantum higher-derivative terms. Furthermore, in the self-coupling aspect, we verify the validity of the Furry’s theorem in the {hbox {VSR}}–hbox {QED}_{3} explicitly.

Low Field Vertical Charge Transport in the Channel and Buffer Layers of GaN-on-Si High Electron Mobility Transistors

Substrate ramps and stepped stress transient measurements are applied to study vertical charge transport mechanisms in GaN-on-Si power HEMTs. By choosing appropriate bias points for substrate stress it is possible to single out the dominant charge transport mechanism: at low negative biases transport through carbon-doped GaN manifests itself in negative (decreasing) current transients with apparent activation energy (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> ) = 0.29 eV, while at larger negative voltages transport through unintentionally doped GaN is characterized by positive (increasing) current transients (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> = 0.38 eV). We present experimental evidence for 3D variable range hopping taking place in C-doped GaN and 1D hopping along the dislocations in unintentionally doped GaN. By investigating transients obtained from bidirectional voltage steps of 10 V potential difference in the range 0 to -140 V, we observe that hopping transport through dislocations shows non-Ohmic behavior at low substrate biases, which manifests itself in a time constant τ strongly dependent on bias. We propose that this can be explained by the existence of a diode junction between the dislocation core and the 2D electron gas (2DEG).

Percolation Conduction of Carbon Nanocomposites.

Carbon nanocomposites present a new class of nanomaterials in which conducting carbon nanoparticles are a small additive to a non-conducting matrix. A typical example of such composites is a polymer matrix doped with carbon nanotubes (CNT). Due to a high aspect ratio of CNTs, inserting rather low quantity of nanotubes (on the level of 0.01%) results in the percolation transition, which causes the enhancement in the conductivity of the material by 10–12 orders of magnitude. Another type of nanocarbon composite is a film produced as a result of reduction of graphene oxide (GO). Such a film is consisted of GO fragments whose conductivity is determined by the degree of reduction. A distinctive peculiarity of both types of nanocomposites relates to the dependence of the conductivity of those materials on the applied voltage. Such a behavior is caused by a non-ideal contact between neighboring carbon nanoparticles incorporated into the composite. The resistance of such a contact depends sharply on the electrical field strength and therefore on the distance between neighboring nanoparticles. Experiments demonstrating non-linear, non-Ohmic behavior of both above-mentioned types of carbon nanocomposites are considered in the present article. There has been a model description presented of such a behavior based on the quasi-classical approach to the problem of electron tunneling through the barrier formed by the electric field. The calculation results correspond qualitatively to the available experimental data.

Influence of MCO3 (M=Ca, Sr, Ba)-doping on the non-ohmic properties of the ceramic varistor system SnO2–Co3O4–Cr2O3–Nb2O5

In this study, the influence of the addition of calcium, strontium and barium carbonates on the microstructure and the electrical properties of the SnO2–Co3O4–Cr2O3–Nb2O5 ceramic varistor system was investigated. The powder mixtures were previously studied by thermogravimetric analysis and differential scanning calorimetry showing the decomposition of carbonates into CaO, SrO, and BaO below 1000 °C. Then, green tablets were obtained and sintered at 1350 °C for 1 h under an ambient atmosphere. Later characterization by X-ray diffraction demonstrates a systematic increase on the lattice parameters as CaCO3 SrCO3, and BaCO3 were added. Scanning Electron Microscopy reveals a decreasing tendency for the average grain size. The electrical performance was evaluated in terms of electrical breakdown field (Eb) and non-linear coefficient (α). Although all the samples exhibited non-ohmic electrical behavior, the SrCO3-doped ceramic showed the highest non-linear coefficient (α = 10) compared to those doped with CaCO3 or BaCO3. A defect model is proposed to explain the way that Ca2+, Sr2+, or Ba2+ incorporates into SnO2 lattice.

Dielectric and non-ohmic analysis of Sr2+ influences on CaCu3Ti4O12-based ceramic composites

In this study, CaCu3Ti4O12 ceramic composites were prepared through solid-state reaction by adding Sr2+ and removing Cu2+. Application of the Rietveld method and structure refinement revealed the presence of pure CaCu3Ti4O12 (CCTO) phase for x = 0.00 and Sr0.75Ca0.25TiO3 (SCTO) phase for sample x = 3.00. The other samples presented a mixture of both phases. The sample microstructures showed that increasing the amount of SCTO phase led to the formation of cubic CCTO grains. The x = 0.15 sample presented giant dielectric permittivity results, 3.28 × 105, associated with increased grain size and greater grain boundary capacitance, thus indicating it could be a promising material for class III capacitors. On the other hand, greater presence of the SCTO phase displayed potential non-ohmic behavior, as seen with sample x = 2.70, which has a high nonlinear coefficient (α ∼ 30.0) and low current leakage, (IL ∼ 9.0 μA).

Tribological Evaluation of Electrical Resistance of Lubricated Contacts

Abstract We report a tribo-electrochemical configuration to conduct in situ measurement of electrical conductivity and thickness of lubricating oils against friction. Results showed the non-ohmic behavior of a lubricating film in the hydrodynamic regime. Properties of lubricants and testing conditions are factors affecting the performance. The approach reported here opens windows for future investigation in the fundamentals of lubrication and alternative design of next-generation lubricants.

Lipid Hydroperoxidation Effect on the Dynamical Evolution of the Conductance Process in Bilayer Lipid Membranes: A Condition Toward Criticality.

Cell membranes are one of the main targets of oxidative processes mediated by reactive oxygen species (ROS). These chemical species interact with unsaturated fatty acids of membrane lipids, triggering an autocatalytic chain reaction, producing lipid hydroperoxides (LOOHs) as the first relatively stable product of the ROS-mediated lipid peroxidation (LPO) process. Numerous biophysical and computational studies have been carried out to elucidate the LPO impact on the structure and organization of lipid membranes. However, although LOOHs are the major primary product of LPO of polyunsaturated fatty acids (PUFAs), to the best of our knowledge, there is no experimental evidence on the effects of the accumulation of these LPO byproducts on the electrical properties and the underlying dynamics of lipid membranes. In this work, bilayer lipid membranes (BLMs) containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocoline (POPC) with increasing hydroperoxidized POPC (POPC-OOH) molar proportions (BLMPC/PC-OOH) are used as model membranes to investigate the effect of LOOH-mediated LPO propagation on the electrical behavior of lipid bilayers. Voltage-induced ion current signals are analyzed by applying the fractal method of power spectrum density (PSD) analysis. We experimentally prove that, when certain LOOH concentration and energy threshold are overcome, oxidized membranes evolve toward a critical state characterized by the emergence of non-linear electrical behavior dynamics and the pore-type metastable structures formation. PSD analysis shows that temporal dynamics exhibiting "white" noise (non-time correlations) reflects a linear relationship between the input and output signals, while long-term correlations (β > 0.5) begin to be observed closely to the transition (critical point) from linear (Ohmic) to nonlinear (non-Ohmic) behavior. The generation of lipid pores appears to arise as an optimized energy dissipation mechanism based on the system's ability to self-organize and generate ordered structures capable of dissipating energy gradients more efficiently under stressful oxidative conditions.

The genuine ac-to-dc proton conductivity crossover of nafion and polymer dielectric relaxations as a fuel cell polarization loss

The non-ohmic behavior of Nafion electrical properties, i. e., the thickness and potential dependent conductivity, was studied in the impedance, dielectric and conductivity representations with the use of a special through-plane sample-holder in a 4-probe array. Such measurements allowed identifying the genuine ac-to-dc conductivity crossover frequency in Nafion, which occurs for f < 10-1 Hz. In addition, the minimization of the interfacial electrode/ionomer polarizations with the 4-probe setup permitted the determination of the bulk dc conductivity and dielectric constant of Nafion, which are σ ~ 0.03 Scm-1 and ε′ ~ 106 (T = 40 °C and RH = 100%), respectively. The colossal dielectric constant is shown to increase the Debye length of the electric double layer to values comparable to the membrane thickness. Therefore, the exponential increase of the proton conductivity with increasing both membrane thickness and electric potential are a result of canceling out the non-linear effects of electric double layer caused by the high dielectric permittivity of Nafion. The ac-to-dc conductivity crossover in H2/O2 fuel cell impedance curves takes place for f < 100 Hz and matches with the ex situ impedance spectroscopy study in excellent agreement, revealing a striking result: the potential dependent conductivity of Nafion requires extra fuel cell overpotential to overcome the electrode/ionomer interfacial polarization representing an additional polarization loss to polymer electrolyte fuel cells.

Effect of the boron-to-nitrogen ratio on leakage current characteristics of boron nitride films prepared by surface-wave plasma enhanced chemical vapor deposition

Sp2-bonded boron nitride (BN) films with different B-to-N ratios are deposited on Si and Ni substrates at an ion impact energy of around 50 eV by surface-wave plasma enhanced chemical vapor deposition. The overall crystallinity and order of sp2 bonding structure are almost retained with increasing BF3/N2 gas flow ratio in the plasma, while the B-to-N ratio in the film is varied from 0.89 to 0.96. The electrical resistivity of the films measured at room temperature for Ni-BN-Ni structures shows a large increase up to the order of 1010 Ω cm when the B-to-N ratio in the film is increased closer to the stoichiometry due to a lower density of defect states related to the boron vacancy. The characteristics of leakage current vs. applied bias voltage show Ohmic behavior at low fields and non-Ohmic behavior governed by the thermionic emission mechanism at high fields for any B-to-N ratio.

Impact of Current and Temperature on Extremely Low Loading Epoxy-CNT Conductive Composites.

Carbon nanotube (CNT) conductive composites have attracted significant attention for their potential use in applications such as electrostatic dissipation and/or electromagnetic interference shielding. The focus of this work is to evaluate resistivity trends of extremely low loading (<0.1 wt%) epoxy-CNT composites that lack a connected CNT network, but still present electrical conductivity values appropriate for those uses. The impact of current, temperature, and cycle life on electrical properties are here identified and tied to possible performance limits. At extremely low loadings, the CNT content is not sufficient to form a completely interconnected grid, thus, electrons must travel through insulating media. While still in the semi-conductor range, resistivity values are observed to decrease with increasing direct current and demonstrate a non-ohmic behavior. CNT epoxy composites were subjected to elevated currents and/or temperatures over diverse periods of time to examine impacts on resistivity. Microstructural analyses of composite samples were conducted to observe signs of damage for specimens taken to extreme temperatures/currents. An understanding of the electrical conductivity characteristics of extremely low loading epoxy-CNT composites and their failure mechanisms will aid in understanding risks associated with their use in challenging environments that may include high temperatures, high currents, and/or high frequencies.

Evidence of charge density wave transverse pinning by x-ray microdiffraction

Incommensurate charge density waves (CDW) have the extraordinary ability to display non-Ohmic behavior when submitted to an external field. The mechanism leading to this nontrivial dynamics is still not well understood, although recent experimental studies tend to prove that it is due to solitonic transport. Solitons could come from the relaxation of the strained CDW within an elastic-to-plastic transition. However, the nucleation process and the transport of these charged topological objects have never been observed at the local scale until now. In this paper, we use in situ scanning x-ray microdiffraction with micrometer resolution of a ${\mathrm{NbSe}}_{3}$ sample designed to have sliding and nonsliding areas. Direct imaging of the charge density wave deformation is obtained using an analytical approach based on the phase gradient to disentangle the transverse from the longitudinal components over a large surface $(90\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\text{m})$. We show that the CDW dissociates itself from the host lattice in the sliding regime and displays a large transverse deformation, ten times larger than the longitudinal one and strongly dependent on the amplitude and the direction of the applied currents. This deformation continuously extends across the macroscopic sample dimensions, over a distance 10 000 times greater than the CDW wavelength despite the presence of strong defects while remaining strongly pinned by the lateral surfaces. This two-dimensional quantitative study highlights the prominent role of the shear effect, which should be significant in the nucleation of solitons.

Complex electrical spiking activity in resistive switching nanostructured Au two-terminal devices

Networks of nanoscale objects are the subject of increasing interest as resistive switching systems for the fabrication of neuromorphic computing architectures. Nanostructured films of bare gold clusters produced in gas phase with thickness well beyond the electrical percolation threshold, show a non-ohmic electrical behavior and resistive switching, resulting in groups of current spikes with irregular temporal organization. Here we report the systematic characterization of the temporal correlations between single spikes and spiking rate power spectrum of nanostructured Au two-terminal devices consisting of a cluster-assembled film deposited between two planar electrodes. By varying the nanostructured film thickness we fabricated two different classes of devices with high and low initial resistance respectively. We show that the switching dynamics can be described by a power law distribution in low resistance devices whereas a bi-exponential behavior is observed in the high resistance ones. The measured resistance of cluster-assembled films shows a scaling behavior in the range of analyzed frequencies. Our results suggest the possibility of using cluster-assembled Au films as components for neuromorphic systems where a certain degree of stochasticity is required.

Palladium forms Ohmic contact on hydrogen-terminated diamond down to 4 K

A hydrogen-terminated diamond (H-terminated diamond) surface supports a two-dimensional (2D) p-type surface conductivity when exposed to the atmosphere, as a result of the surface transfer doping process. The formation of reliable Ohmic contacts that persist to cryogenic temperature is essential for the exploration of quantum transport in the diamond 2D conducting channel. Herein, the contact properties of Pd on H-terminated diamond have been fully investigated down to 4 K using transmission line method measurements. Pd is shown to form an Ohmic contact on H-terminated diamond with linear I–V characteristics and low specific contact resistance in the range of (8.4 ± 1) ×10−4 Ω·cm2 to (1.3 ± 0.2) ×10−3 Ω·cm2 for the temperature range of 300 K–4 K. This is in stark contrast to reference devices with Au/Pt/Ti contacts, which exhibit a significant temperature dependence and non-Ohmic behavior at low temperature. Using 2D thermionic emission theory, a negative Schottky barrier height (SBH), − 23 ± 1 meV, between Pd and H-terminated diamond has been determined, in comparison to a positive SBH of 42 ± 1 meV for the Au/Pt/Ti/H-terminated diamond interface. These results show that Pd serves as an excellent candidate for forming reliable Ohmic contacts on H-terminated diamond for enabling precise electrical transport measurements at cryogenic temperature.

Observation of Anomalous Non-Ohmic Transport in Current-Driven Nanostructures

Sufficiently large electric current applied to metallic nanostructures can bring them far out-of-equilibrium, resulting in non-Ohmic behaviors characterized by current-dependent resistance. We experimentally demonstrate a linear dependence of resistance on current in microscopic thin-film metallic wires at cryogenic temperatures, and show that our results are inconsistent with common non-Ohmic mechanisms such as Joule heating. As the temperature is increased, the linear dependence becomes smoothed out, resulting in the crossover to behaviors consistent with Joule heating. A plausible explanation for the observed behaviors is the strongly non-equilibrium distribution of phonons generated by the current. Analysis based on this interpretation suggests that the observed anomalous current-dependent resistance can provide information about phonon transport and electron-phonon interaction at nanoscale. The ability to control the properties of phonons generated by current can lead to new routes for the optimization of thermal properties of electronic nanodevices.

Atypical electrical behavior of few layered WS2 nanosheets based platform subject to heavy metal ion treatment

We herein report an atypical electrical behavior of WS2 nanosheets drop casted on Cu electrodes. The addition of heavy metal ions on this platform results in non-ohmic behavior, accompanied by a dramatic rise of current. Additionally, this atypical behavior is found to be reversible. The proposed platform regains its ohmic behavior upon removal of these ions from the nanosheets. It is envisioned that this unusual characteristic will pave way for more research in the field of sensing as well as in relevant fields.

Design, Simulation and Fabrication of Highly Sensitive Cooled Silicon Bolometers for Millimeter-Wave Detection

This paper reports our results on the electrothermal modeling of cryogenic silicon bolometers with pixel pitches of 500 and 1200 µm designed for cosmic microwave background polarimetric observation in 0.6 mm and 1.5 mm bands. These detectors should provide a high responsivity, typically around 10$^{11}$ V/W, and a very low noise equivalent power (NEP) of 10$^{−18}$ W/Hz$^{1/2}$ between 50 and 100 mK. They are based on doped silicon thermometers, which exhibit a nonohmic behavior described by the “hot electron model” (HEM) at very low temperature under high bias currents. We compare this model to the experimental characterization of these thermometers at cryogenic temperatures to confirm that the HEM is governing their electrical characteristics and their sensitivity at very low temperature. Finally, this model is used to derive the simulated responsivity and NEP performances of the pixels under weak and moderate optical power illumination.