Nonlinear Electrical Properties Research Articles

Twist angle dependence of graphene-stacked junction characteristics

Vertically stacked graphene diodes are fabricated using epitaxially grown graphene with twist angles ranging from 0° to 30°. Their switching behavior and negative differential conductance are observed at all the measured angles. The junction conductance in the initial state does not indicate clear angle dependence and is almost constant, i.e. 231 μS for all devices. The junction conductance in the high-bias region exhibits a steep peak at 12°. The on/off ratio of the stacked junction diode indicates a maximum value of 142 at 12°. Therefore, the fabricated stacked graphene device with a simple structure exhibits strong nonlinear electrical properties and negative differential conductance at all twist angles. The on/off ratio of the stacked junction diodes is controlled by the twist angle between two single-crystal graphene layers.

Giant permittivity response and enhanced nonlinear electrical properties in a novel perovskite-like ceramic with multiple elements

Copper calcium titanate (CaCu3Ti4O12, CCTO) ceramics are receiving a great deal of attention for advanced electronic and energy storage device applications owing to their giant permittivity response and good temperature stability. However, the development and real applications of CCTO ceramics are generally restricted by their large dielectric loss and low breakdown electric field strength. In the present study, a novel type of perovskite-like Na1/3(Ca1/2Sr1/2)1/3(Bi1/2Y1/2)1/3Cu3Ti4O12 (NCSBYCTO) ceramics were designed via multiple elements strategy based on the high-entropy concept. Consequently, all the NCSBYCTO ceramics present a giant permittivity response (103∼104), good stability of temperature and frequency, and remarkable relaxation characteristics, especially the NCSBYCTO ceramic sintered at 1050 °C exhibits a relative balance between the giant permittivity of about 7.0 × 103–9.5 × 103 and the lower dielectric loss of approximately 0.043–0.294 at a frequency range of 104–106 Hz under room temperature. Furthermore, all the NCSBYCTO ceramics present an obvious nonlinear characteristic. More encouragingly, a higher breakdown field strength of around 2552.56 V/cm accompanied by a larger nonlinear coefficient of about 6.48 is achieved in the NCSBYCTO ceramic sintered at 1070 °C. A significant electrical heterogeneity structure and electron defect structure induced by the existence of mixed-valence Cu+/Cu2+ and Ti3+/Ti4+ are also found in the NCSBYCTO ceramics. The giant permittivity response, low dielectric loss and improved nonlinear properties can be considered the synergistic effect of the defect mechanism and the internal barrier layer capacitor model. This finding offers a route for designing giant permittivity ceramics with brilliant dielectric properties and nonlinear behaviors, which is expected to benefit dual-functional device applications of capacitors and varistors.

Global imaging for polarization resolved second harmonic generation of WS2 monolayers

Second-harmonic generation (SHG) is a nonlinear optical effect enhanced by broken crystallin symmetry and is very sensitive to electronic structures. SHG has recently been applied to two-dimensional transition metals dichalcogenides (2D-TMDs). 2D-TMDs have been the focus of much recent research due to their ultrathin scale, high quantum confinement, and energy gap toning ability that results in unique linear or nonlinear optical and electrical properties. WS2 monolayers are well-known 2D TMDs with strong SHG. They have attracted a great deal of interest due to their potential applications in fundamental material characterization and nanophotonic device development. In this study, we grew WS2 monolayers using the chemical vapor deposition (CVD) technique and characterized them with Raman and photoluminescence (PL) spectroscopy. The intense direct excitonic peak A at 630 nm was identified in the PL spectra, while the Raman spectra exhibited the two distinctive modes A1g (at 418 cm−1) and E2g (at 356 cm−1). The monolayers were pumped by an 830 nm circularly polarized and defused pulsed laser to produce the SHG image. global one-shot SH images for different growth shapes were obtained and crystalline domains were identified using polarization-resolved second-harmonic generation imaging (PRSHGI). The defect level was observed to clearly enhance the SHG signal following the increase in broken crystalline centrosymmetric and relaxing the optical selection roles at the valley degree of freedom.

Tuning enhanced dielectric properties of (Sc3+–Ta5+) substituted TiO2 via insulating surface layers

In this study, we achieved significantly enhanced giant dielectric properties (EG-DPs) in Sc3+–Ta5+ co-doped rutile-TiO2 (STTO) ceramics with a low loss tangent (tanδ ≈ 0.05) and high dielectric permittivity (ε′ ≈ 2.4 × 104 at 1 kHz). We focused on investigating the influence of insulating surface layers on the nonlinear electrical properties and the giant dielectric response. Our experimental observations revealed that these properties are not directly correlated with the grain size of the ceramics. Furthermore, first-principles calculations indicated the preferred formation of complex defects, specifically 2Ta diamond and 2ScVo triangular-shaped complexes, within the rutile structure of STTO; however, these too showed no correlation. Consequently, the non-Ohmic properties and EG-DPs of STTO ceramics cannot be predominantly attributed to the grain boundary barrier layer capacitor model or to electron-pinned defect-dipole effects. We also found that the semiconducting grains in STTO ceramics primarily arise from Ta5+, while Sc3+ plays a crucial role in forming a highly resistive outer surface layer. Notably, a significant impact of grain boundary resistance on the nonlinear electrical properties was observed only at lower co-dopant concentrations in STTO ceramics (1 at%). The combination of low tanδ values and high ε′ in these ceramics is primarily associated with a highly resistive, thin outer-surface layer, which substantially influences their non-Ohmic characteristics.

Microstructure and nonlinear electrical properties in Na2CO3-ZnO varistor ceramics

Herein, (1-x)ZnO + xNa2CO3 (x = 0, 0.5, 1.0, and 1.5 mol%) varistor ceramics were prepared via conventional solid-state sintering at a low sintering temperature of 900 ℃. The microstructure and electrical properties of these varistor ceramics were systematically investigated as a function of Na2CO3 concentration. Results revealed that the prepared varistor ceramics exhibit the hexagonal structure without a secondary phase. The increase of Na2CO3 concentration promotes the ZnO grain growth. Owing to an increasement in the barrier height at the grain boundaries, the nonlinear electrical properties of the ceramics considerably improve with increasing Na2CO3 concentration. The optimal composition of 98.5 mol%ZnO + 1.5 mol%Na2CO3 corresponds to a nonlinear coefficient of 3.55, leakage current density of 450 μA/cm2, breakdown strength of 241.2 V/mm, and barrier height of 0.57 eV. Moreover, the dielectric properties of the varistor ceramics are considerably affected by Na2CO3 concentration.

Tweaks to intrinsic point defects in ZnO ceramics via MnCO3 and their effect on electrical properties

Transition metal elements are necessary dopants in ZnO ceramics to improve electrical properties by defects engineering. In the present study, the tweaking effect of MnCO3 on the intrinsic point defects, i.e., the zinc interstitial and the oxygen vacancy, are investigated to optimize electrical properties of ZnO ceramics. After analyzing microstructure and dielectric response, it was found that Mn2+ was further oxidized to Mn4+ during sintering and Mn4+ solved into ZnO grains and inhibited the formation of the intrinsic point defects. On the other hand, due to the increase of the interface states contributed by Mn separation at grain boundaries, the barrier width broadened to keep charge neutrality. As a result, although the barrier height decreased from 0.68 eV to 0.54 eV as MnCO3 content increased from 0 mol% to 0.63 mol%, the nonlinear electrical properties were enhanced, that is, the breakdown field increased from 188.47 V/mm to 234.82 V/mm, the nonlinear coefficient increased from 12.87 to 74.76, and the leakage current density decreased from 22.08 μA/cm2 to 0.04 μA/cm2. Combined with the stability during DC aging tests, it is suggested that the optimal content of MnCO3 is 0.38 mol%. The study also indicates that the barrier width is a sensitive parameter in optimizing electrical properties of ZnO ceramics, instead of the sole focus on higher barrier height.

Actin Paracrystals Display Double Schottky Diode‐Like Electrical Behavior

AbstractActin filaments are abundant intracellular polymers implicated in cell motility and contraction. Actin also forms paracrystalline structures under various conditions, including exposure to lanthanides and other high ionic strength conditions. Here the electrical properties of purified actin paracrystals induced by either MgCl2 or GdCl3 are tested. Tight electrically seal‐voltage‐clamped crystals display strong rectification with a nonlinear conductance under symmetrical and biionic conditions, including 20 mm GdCl3/140 mm KCl and 10 mm MgCl2/140 mm KCl. Rectification is observed in symmetrical ionic conditions with positive‐to‐negative conductance ratios ranging from 4.18 to 9.00 nS. The current‐to‐voltage relationships can be fitted with theoretical double Schottky equations and resemble the behavior of semiconducting nanotubes. The highly nonlinear electrical properties of paracrystalline actin arrays may help explain the physiology of actin‐rich cellular compartments, such as stereocilia of the cochlea and neuronal dendritic spines also suggest potentially relevant nano‐technological properties of this protein.

Learning in ensembles of proteinoid microspheres.

Proteinoids are thermal proteins which form microspheres in water in the presence of salt. Ensembles of proteinoid microspheres exhibit passive nonlinear electrical properties and active neuron-like spiking of electrical potential. We propose that various neuromorphic computing architectures can be prototyped from the proteinoid microspheres. A key feature of a neuromorphic system is a learning. Through the use of optical and resistance measurements, we study mechanisms of learning in ensembles of proteinoid microspheres. We analyse 16 types of proteinoids study and their intrinsic morphology and electrical properties. We demonstrate that proteinoids can learn, memorize and habituate, making them a promising candidate for novel computing.

Enhanced nonlinear conductivity of silicone rubber composites with hybrid graphene and alumina for cable accessory

The electric field distortion and charge accumulation in cable accessories are still challenges for high voltage direct current transmission (HVDC). Using silicone rubber (SR) based materials with nonlinear conductivity properties can ameliorate these problems in cable accessories. Herein, SR composites with hybrid filler network were prepared by adding graphene (G; 0.25 phr) and alumina particles (Al2O3; 5–40 phr) to SR to obtain good nonlinear conductivity and relative high breakdown strength, along with thermal conductivity. The SEM results showed that graphene was well dispersed between Al2O3 particles and a hybrid filler network was constructed in the SR matrix. The G/Al2O3/SR composites exhibited favorable nonlinear electrical conductivity properties and thermal conductivity properties while sustaining high breakdown strength under different electrical and temperature field. The non-linear conductivity α of the 0.25G/40Al2O3/SR composite reached 6.68 at 23 °C, whereas the breakdown field strength E0 of 49.1 kV/mm could comparable to that of pure SR. Moreover, the thermal conductivity of 0.25G/30Al2O3/SR was 0.28 Wm−1K−1 at 23 °C, which increased by 114.98% compared to pure SR. This work suggests the promising application of G/Al2O3/SR composites as cable accessory.

Nondestructive characterization of grain boundary Z‐directional lateral surface in ZnO using nanorobot combined with SEM

AbstractDifferent from focusing on grain boundary upper surface in plane X–Y, a unique approach of nanorobot‐based nondestructive characterization of grain boundary Z‐directional lateral surface within bulk ZnO ceramic can be creatively developed under scanning electron microscope (SEM). By rolling‐over bulk ZnO, two‐dimensional profiles and grain boundaries in Z‐directional lateral surfaces have been imaged in plane Y–Z and individually electrically characterized nondestructively. Experiments demonstrate that it is feasible to realize nondestructive characterization of grain boundary Z‐directional lateral surface structures and electrical properties using nanorobot combined with SEM. Relative height differences between grain boundaries within Z‐directional lateral surface can characterize the relative position relationships. Z‐directional lateral surface structures can further extend irregular grain boundary lengths in plane Y–Z to interpret surface effects of nonlinear electrical properties. Relative minor electrical reactive effects in grain indicate grain boundary dominate in nonlinear macroscopic electrical properties. Furtherly, it can be advanced to promote a nondestructive characterization of grain boundary.

Resistive-switching behavior in stacked graphene diode

In this study, stacked graphene diodes were fabricated via direct bonding using single-crystal graphene on a SiC substrate. Switching and S-shaped negative resistance were observed in the junction electrical properties measured via the 4-terminal configuration. The high-resistance state switched to the low-resistance state after applying a maximum junction voltage of ∼10 V. In the high-bias voltage region, the junction voltage decreased from the maximum junction voltage to a few volts, indicating a negative resistance. In the high-resistance state, junction conductance was nearly constant at 0.13 mS. Electrical conductance in the high-bias region was expressed using an exponential function with an exponent of −1.26. Therefore, the fabricated stacked graphene diode with a simple device structure demonstrated strong nonlinear electrical properties with negative differential conductance.

Surface treated ZnO whisker optimizing the comprehensive performance of the self-adaptive dielectrics

The application of self-adaptive dielectrics (SADs) is a promising approach to enhancing the insulation performance as well as downsizing of most high voltage apparatus. Beside nonlinear electrical property, good thermal and mechanical performances of SADs are also expected. However, heavy load of functional fillers often leads to poor elasticity of traditional SADs and it is a challenge to decrease filler concentration while ensuring satisfied thermal and nonlinear electrical conductivity. In this paper, tetrapod-shaped ZnO whisker coated with oxides shell and its silicone rubber composites have been manufactured. The core-shell interface equips the ZnO whisker with nonlinear conducting behavior and the composites also exhibit similar self-adaptive electrical property like traditional SADs. Due to the relative large respect ratio, the coated whisker can reduce the filler concentration to about 10 vol% which guarantees good mechanical property of the material. The thermal conductivity of the composites and traditional SADs are compared and an optimized filler concentration range considering comprehensive property of the composite is obtained. This work is helpful to design smart composites to self-adaptively control high electrical field of electrical and electronic devices and increase their stability and durability.

Effect of Nb2O5 on ZnBiMnO varistor ceramic prepared by solid-state sintering at 850°C

Nb 2 O 5 is a commonly used donor dopant for ZnO-based varistor ceramics, but its effect, especially on the low-temperature sintered ZnO varistor ceramics, is not fully understood. To provide a possible answer to this problem, ZnO–Bi 2 O 3 –MnCO 3 (ZnBiMnO) based varistor ceramics with 0.05%–0.3% (in mole ratio) Nb 2 O 5 were fabricated by solid-state sintering at 850 °C for 3 h. Their microstructure and nonlinear electrical properties were studied by XRD, SEM and the standard current-voltage (I–V) tests to reveal the effect of Nb 2 O 5 . With the increase of Nb 2 O 5 from 0.05 mol% to 0.3 mol%, more solid Bi 5 Nb 3 O 15 inter-granular particles form within the ceramic during sintering, thereby decreasing the Bi-rich liquid phase. As a result, the average size of ZnO grain decreases from 4.35 μm to 1.67 μm. This microstructural change leads to the increase of the breakdown voltage in the range of 821 V/mm to 1851 V/mm. The ZnBiMnO varistor ceramic with 0.1 mol% Nb 2 O 5 shows the best nonlinear properties. The optimum nonlinear coefficient is 35.81, the breakdown voltage is 907.51 V/mm, and the leakage current is 7.72 μA/cm 2 . The result of this study provides a promising candidate material for manufacturing the multilayered low-voltage varistor that may use Ag, Ni or even Cu as the inner electrodes.

Computational study of non-linear optical and electrical properties of 1,3-dinitropyrene

Computational study of non-linear optical and electrical properties of 1,3-dinitropyrene

Logics in Fungal Mycelium Networks

The living mycelium networks are capable of efficient sensorial fusion over very large areas and distributed decision making. The information processing in the mycelium networks is implemented via propagation of electrical and chemical signals en pair with morphological changes in the mycelium structure. These information processing mechanisms are manifested in experimental laboratory findings that show that the mycelium networks exhibit rich dynamics of neuron-like spiking behaviour and a wide range of non-linear electrical properties. On an example of a single real colony of Aspergillus niger, we demonstrate that the non-linear transformation of electrical signals and trains of extracellular voltage spikes can be used to implement logical gates and circuits. The approaches adopted include numerical modelling of excitation propagation on the mycelium network, representation of the mycelium network as a resistive and capacitive network and an experimental laboratory study on mining logical circuits in mycelium bound composites.

Core-double-shell structured BT@TiO2@PDA and oriented BNNSs doped epoxy nanocomposites with field-dependent nonlinear electrical properties and enhancing breakdown strength

Field-grading polymer nanocomposites have drawn significant attention in high voltage electrical industries due to their excellent nonlinear conductive or dielectric properties. But composites with both nonlinear properties are rarely reported, and desirable nonlinear performance associated with excess fillers in the composite is at the expense of electric breakdown strength. In this work, BaTiO3 nanoparticles were decorated successively using double-shell layers of TiO2 and polydopamine, which are developed as novel nanofillers (BT@TiO2@PDA) for field-grading applications. Subsequently, BNNSs were prepared by liquid phase exfoliation, serving as the inhibitor of breakdown phase growth in the composites. Finally, novel epoxy nanocomposites (EP/BT@TiO2@PDA-OB) with BT@TiO2@PDA and oriented BNNSs were fabricated by a simple hot-pressing method. Results show that the hierarchically designed nanoparticles can make the composites possess not only nonlinear dielectric properties due to high εr of BT and improved interfacial polarization, but also nonlinear conductive properties resulted from the organic semiconductor PDA shell. Nonlinear effective medium theory (EMT) was utilized to explain the nonlinear dielectric properties, and the hopping transport model considering Pool-Frenkel effect was applied to explain the nonlinear conductive properties. In addition, electric breakdown tests reveal that EP/BT@TiO2@PDA-OB has significantly enhanced breakdown strength (45.7 kV/mm) as compared to that of pristine epoxy resin (29.4 kV/mm) and EP/BT@TiO2@PDA-RB (randomly dispersed BNNSs, 36.2 kV/mm). It is expected that these results can open new avenues for the design of novel composites with both nonlinear conductive properties and dielectric properties as well as high breakdown strength.

Current Progress on Power Management Systems for Triboelectric Nanogenerators

This article presents a review on the development of power management systems (PMSs) for triboelectric nanogenerators (TENGs). The TENG is the most recent technology to harvest ambient mechanical energy from the environment and human activities. Its invention was motivated by the prospect of building self-powered systems. The TENG has several appealing advantages, such as high power density, high voltage output, high efficiency at low frequency, and low cost. However, due to the TENG's unique nonlinear electrical property and capacitive behavior, the development of its PMS has presented great challenges as compared to other energy harvesters. The objective of PMS design has evolved from boosting the peak output power, to increasing the energy stored in a capacitor, and to increasing the steady-state output power of a resistive load by using a power converter. Driven by the need to build self-powered systems, the switches in the TENG PMS have evolved from active switches to passive switches. The past decade has witnessed exciting breakthroughs in the development of TENG PMS, yet there are still unlimited opportunities in exploring TENG's energy generation mechanism and vast potential in boosting energy extraction from the TENG by designing effective power converter topologies.

Flexible Piezoelectric Nanogenerators Based on One-Dimensional Neutral Coordination Network Composites

Metal–organic coordination polymers are modular systems whose structures can be modified in numerous ways to introduce and influence non-linear optical and electrical properties. However, their full potential as piezoelectric nanogenerators for self-powered electronics is yet to be uncovered. Here, we report a Zn(II)-based ferroelectric one-dimensional coordination network {[Zn(L1)(bpy)]·(H2O)1.5}∞ (1) derived from a flexible dicarboxylate ligand [PhPO(NH-(C6H4COOH))2] (L1H2) and 2,2′-bipyridine as a co-ligand. The origin of polarization in 1, despite its neutral structure, is due to the polyhedral distortions around the Zn(II) center as revealed by ab initio calculations. The presence of polarizable domains was visualized by piezoresponse force microscopy (PFM) experiments. Also, from the PFM studies, a sizable converse piezoelectric coefficient (d33) value of 19.4 pm/V was noticed for 1, which is unprecedentedly high for the class of neutral-network coordination polymers. Furthermore, flexible composite devices comprising a thermoplastic polyurethane (TPU) polymer with different weight percentages (wt %) of 1 were prepared and examined for application as piezoelectric nanogenerators. Notably, the champion device of this series (poled 5 wt % 1-TPU composite) exhibits a highest open-circuit voltage of 5.6 V and power density output of 14.6 μW/cm2.

Investigation of microstructural evolution and suitable potential barrier model for non-linear electrical response of Sr and Nb co-doped CaCu3Ti4O12 ceramics

This work reported about impact of co-doping on structural and non-linear electrical property of CaCu 3 Ti 4 O 12 (CCTO) ceramics with composition Ca 0·95 Sr 0·05 Cu 3 Ti 3·94 Nb 0·06 O 12 prepared by solid state reaction technique. Rietveld refinement of X-ray diffraction data was performed to analyse various parameters for its structure exploration. Microstructure and compositional information of prepared ceramic was determined by SEM, EDX and elemental mapping. The grain size was found 2.32 μm with the use of ImageJ software on SEM images. The identical Raman mode were observed in present doped CCTO ceramics comparative to that reported for pure CCTO in Raman spectroscopy. The resistivity of prepared sample reveals NTC behaviour of the ceramic. The parameters; non-linear coefficient (α = 1.86), breakdown electric field (E b = 191.56V/cm) and leakage current (I = 0.44 mA) were obtained by current voltage measurement at room temperature (RT∼303K). The detail comparative study of various barrier models was carried out and found Schottky barriers as most suited model for potential barrier at grain boundaries in the present system. • Ca0·95Sr0·05Cu3Ti3·94Nb0·06O12 ceramic was synthesized using Solid State Reaction method. • Structural Properties were investigated by XRD, SEM, Raman and FT-IR spectroscopy. • Schottky emission model was found most suitable for non-linear electrical response of prepared ceramics. • The value of nonlinear coefficient and Breakdown field suggest it was suitable for low voltage application. • The present sample exhibits good NTC behaviour at low DC voltage and found useful for varistor and thermistor application.

Enhanced dielectric response and non-Ohmic properties of Ge-doped CaTiO3/CaCu3Ti4O12

ABSTRACT We present a method for increasing the dielectric constant of CaTiO3/CaCu3Ti4O12 (CTO/CCTO) composites and retaining a low-loss tangent (tanδ) by doping with Ge dopant. The Ge-doped CTO/CCTO composites were fabricated using a one-step processing method. The phase composition and microstructure analyses confirmed the existence of CTO and CCTO phases, in which Ge doping ions can be substituted into both phases. The mean grain sizes of the two phases were slightly reduced by decreasing the porosity. Doping the CTO/CCTO with Ge doping ions resulted in a high dielectric constant by ~ two times, while a very low tanδ value of ~0.01 did not change. Furthermore, the dielectric constant changed by less than ±15% in the temperature range of −60 – 150°C. The nonlinear current density–electric field properties of CTO/CCTO can also be enhanced. Impedance spectroscopy showed a heterogeneous microstructure with enhanced grain boundary properties after doping with Ge dopants, giving rise to enhanced nonlinear electrical properties. The decreased grain resistivity due to Ge substitution is confirmed to originate from the increase in the Ti3+/Ti4+ ratio, which was analyzed using X–ray photoelectron spectroscopy .