Formation Of Conducting Channels Research Articles

Field Ion Microscopy of Tungsten Nano-Tips Coated with Thin Layer of Epoxy Resin

This paper presents an analysis of the field ion emission mechanism of tungsten–epoxy nanocomposite emitters and compares their performance with that of tungsten nano-field emitters. The emission mechanism is described using the theory of induced conductive channels. Tungsten emitters with a radius of 70 nm were fabricated using electrochemical polishing and coated with a 20 nm epoxy resin layer. Characterization of the emitters, both before and after coating, was performed using electron microscopy and energy-dispersive X-ray spectroscopy (EDS). The Tungsten nanocomposite emitter was tested using a field ion microscope (FIM) in the voltage range of 0–15 kV. The FIM analyses revealed differences in the emission ion density distributions between the uncoated and coated emitters. The uncoated tungsten tips exhibited the expected crystalline surface atomic distribution in the FIM images, whereas the coated emitters displayed randomly distributed emission spots, indicating the formation of induced conductive channels within the resin layer. The atom probe results are consistent with the FIM findings, suggesting that the formation of conductive channels is more likely to occur in areas where the resin surface is irregular and exhibits protrusions. These findings highlight the distinct emission mechanisms of both emitter types.

2D electrodeposition assembly of Cu/Cu2O nanoarrays for low temperature H2S sensing

Ultra-sensitive hydrogen sulfide (H2S) detection technology at low temperatures provides critical support for the application of one-time alert systems under extreme conditions, ensuring reliable monitoring of H2S in low-temperature environments and enhancing safety and practicability. In this study, we developed a novel low-temperature H2S sensor based on Cu/Cu2O nanoarrays, prepared through a combination of 2D electrodeposition in situ assembly and the hydrothermal method. The heterointerface between Cu nanowires and Cu2O nanocubes presents a high barrier, which can be modulated to zero through the formation of continuous CuxS conductive channels via the vulcanization reaction, thereby achieving excellent sensitivity and selectivity towards H2S at low temperatures. At freezing temperatures and low H2S concentrations (≤20 ppm), the sensors show ideal recovery and reasonable sensitivity (R=150 to 10 ppm H2S at 0 °C). However, the response significantly increases (R=5624 at 10 ppm H2S at 50 °C) and recovery is lost under reversed conditions. First-principles calculations have confirmed that the enhanced H2S adsorption at the heterointerface is the primary reason for the robust response observed at 0 °C. Experimental results demonstrate that the Cu/Cu2O nanoarrays were capable of rapid detection of H2S at low temperatures through modulation of heterointerface barriers.

Cellulose nanofiber-induced metal–organic framework “armor” for the fabrication of carbon fibre composites with enhanced mechanical properties and electrical conductivity

Metal-organic frameworks (MOFs) possess significant potential in enhancing the interfacial performance of composites owing to their exceptional skeletal structures and substantial specific surface area. Herein, we prepared typical conductive MOFs (Ni-HHTP, HHTP = 2, 3, 6, 7, 10, 11-hexahydroxybenzene) at the interface by in situ synthesis using cellulose nanofibers (CNFs) assembled on the surface of carbon fibres (CFs) as precursors. CNFs can not only act as a smart cushion to promote stress release but also provide abundant oxygen-containing functional groups, such as hydroxyl and carboxyl groups, which can facilitate the growth of MOF on the surface of CFs. Furthermore, MOFs with porous structure and large specific surface area increase the interphase region for interfacial load transmission. The CF composites prepared using this strategy exhibited improvements in interlaminar shear strength (ILSS), interfacial shear strength (IFSS), flexural strength and flexural modulus by 57.9 %, 54.9 %, 35.1 % and 46.7 %, respectively. Additionally, the electrical conductivities of the composites in both thickness and in-plane directions were 1.04 × 10−4 S/cm and 7.3770 S/cm, respectively, which was attributed to the MOFs on the surface of the fibres facilitating the formation of good conductive channels between the fibres and resin. This study proposes an advanced interfacial modification approach to prepare CF composites with excellent mechanical and electrical conductivity properties.

Electrical properties of epoxy/graphite flakes microcomposite at the percolation threshold concentration

The electrical properties and activation energy of epoxy/graphite flakes (GFs) micro-composite with different content of GFs (0.0625–1 wt%) were studied for electrical properties using Novocontrol Alpha Analyser (10−2 Hz—107 Hz). GFs sizes ranged from (100 nm to 10 μm). The analysis was performed by scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), visible spectrum reflectance spectra (VIS) spectra, and Fourier Transform Infrared spectra (FTIR) spectroscopy. Increasing GFs content caused multiple changes in electrical characteristics. At 0.0625 wt%, all electrical properties noticeably increased. But at 0.125 to 0.25 wt%, immobilized nanolayers were formed leading to decreased permittivity, dielectric loss (tan(δ)), quality factor (Q-factor), capacitance, conductivity, and figure of merit (F-factor). At 0.25 wt%, the epoxy microcomposite had lower permittivity, tan(δ), conductivity, and capacitance compared with unfilled epoxy. With 0.5 wt% of GFs, signified the percolation threshold, initiating a rise in permittivity, conductivity, capacitance, and tan(δ), accompanied by the closer proximity of grain boundaries, facilitating the formation of conductive channels. At a concentration of 1 wt% of GFs, the establishment of continuous interfacial conductive pathways resulted in a remarkable augmentation of all dielectric properties. The Cole-Cole analysis has been employed to investigate variations in epoxy/GFs microcomposites based on concentration levels.

MoS2 Quantum Dot-Optimized Conductive Channels for a Conjugated Polymer-Based Synaptic Memristor.

Donor-acceptor-type conjugated polymers are widely used in memristors due to their unique push-pull electron structures and charge transfer mechanisms. However, the inherently inhomogeneous microstructure of polymer films and their low crystallinity produce randomness that destabilizes formed conductive channels, giving polymer-based memristors unstable switching behavior. In this contribution, we prepared a synaptic device based on PM6-MoS2 QD (molybdenum disulfide quantum dot) nanocomposites. In the composites, MoS2 QDs provided the active centers for forming conductive channels via electron trapping and detrapping. They also controlled the directional formation of conductive channels between PM6 and MoS2 QDs, reducing randomness and giving devices a narrow switching voltage range and cycling longevity. The device exhibited continuous multistage conductance states under a direct current voltage sweep and simulated a variety of synaptic functions, including long-term potentiation, long-term depression, short-term potentiation, short-term depression, paired-pulse facilitation, spiking-rate-dependent plasticity, and "learning experience" behavior. The memristor could also perform arithmetic, including "counting" and "subtraction" operations. This work provides a new approach to improving the performance of memristors for neuromorphic computing.

FeF3/(Acetylene Black and Multi-Walled Carbon Nanotube) Composite for Cathode Active Material of Thermal Battery through Formation of Conductive Network Channels.

Considerable research is being conducted on the use of FeF3 as a cathode replacement for FeS2 in thermal batteries. However, FeF3 alone is inefficient as a cathode active material because of its low electrical conductivity due to its wide bandgap (5.96 eV). Herein, acetylene black and multi-walled carbon nanotubes (MWCNTs) were combined with FeF3, and the ratio was optimized. When acetylene black and MWCNTs were added separately to FeF3, the electrical conductivity increased, but the mechanical strength decreased. When acetylene black and MWCNTs were both added to FeF3, the FeF3/M1AB4 sample (with 1 wt.% MWCNTs and 4% AB) afforded a discharge capacity of approximately 74% of the theoretical capacity (712 mAh/g) of FeF3. Considering the electrical conductivity and mechanical strength, this composition was confirmed to be the most suitable.

Estimation of the activation energy in the Ag/SnSe/Ge2Se3/W self-directed channel memristor

In this study, we conducted an investigation into the Ag/SnSe/Ge2Se3/W ionic memristor, focusing on the determination of activation energies associated with its two primary operational processes: the formation of conductive filaments and memristor degradation. To ascertain the electrical conductivity of the memristor in both its basic electronic states, a low resistance state and a high resistance state, we constructed current-voltage characteristics. The estimation of activation energy values was carried out employing the Arrhenius law and the provisions of irreversible thermodynamics, with specific reference to Onsager's second postulate. This fundamental concept posits that the growth rate of irreversible component of entropy can be expressed as the summation of products involving fluxes and thermodynamic forces when a system tends towards its equilibrium state. In the context of this study, the equilibrium state of the memristor is defined as the condition at which the memristor can no longer function as a resistive memory cell. Our experimentation involved the application of a flux of Ag+ ions (electromigration). The calculated activation energy values were found to be 0.24 eV for the initial process and 1.16 eV for the latter. These divergent activation energy values indicate the differentiation between the agglomerative mechanism that governs the formation of conductive channels, prevalent in the Ag/SnSe/Ge2Se3/W memristor, and the "conventional" substance transfer mechanism based on a group of point defects that manifests itself during the memristor's degradation.

High-Performance n-Type Organic Thermoelectrics Enabled by Synergistically Achieving High Electron Mobility and Doping Efficiency.

n-Doped polymers with high electrical conductivity (σ) are still very scarce in organic thermoelectrics (OTEs), which limits the development of efficient organic thermoelectric generators. A series of fused bithiophene imide dimer-based polymers, PO8, PO12, and PO16, incorporating distinct oligo(ethylene glycol) side-chain to optimize σ is reported here. Three polymers show a monotonic electron mobility decrease as side-chain size increasing due to the gradually lowered film crystallinity and change of backbone orientation. Interestingly, polymer PO12 with a moderate side-chain size delivers a champion σ up to 92.0 S cm-1 and a power factor (PF) as high as 94.3 µW m-1 K-2 in the series when applied in OTE devices. The PF value is among the highest ones for the solution-processing n-doped polymers. In-depth morphology studies unravel that the moderate crystallinity and the formation of 3D conduction channel derived from bimodal orientation synergistically contribute to high doping efficiency and large charge carrier mobility, thus resulting in high performance for the PO12-based OTEs. The results demonstrate the great power of simple tuning of side chain in developing n-type polymers with substantial σ for improving organic thermoelectric performance.

RF loss reduction by a carbon-regulated Si substrate engineering in GaN-based HEMT buffer stacks

A carbon-regulated Si substrate engineering has been adopted to reduce the RF loss of GaN-based HEMT buffer stacks. By implanting the substrate with high-dose carbon, undersaturation of Si self-interstitials is formed, and the self-interstitial-assisted aluminum diffusion into the Si substrate during the growth can be significantly suppressed. Consequently, the formation of parasitic conductive channel is suppressed, and the RF loss of the buffer stacks can be reduced. By combining the substrate engineering with low-temperature growth, the RF loss of the buffer stacks is reduced to as low as 0.13 dB/mm at 10 GHz. In addition, the crystal quality of the buffer stacks grown on the regulated substrates does not degrade. This work shows a great potential for fabrication of high-quality and low-loss GaN-on-Si RF devices.

Electron Beam Induced Current Study of Photocurrent Gain in κ-Ga2O3 Schottky Diodes

The κ-Ga2O3 polytype is attracting attention because of its high spontaneous electric polarization, which exceeds that of III-Nitrides. However, little is known of its transport and photoconductive properties. The electron beam induced current gain effect in Schottky barriers prepared on thick films of κ-Ga2O3 has been studied. It is shown that the gain originates in the depletion region of the Schottky barrier. It is demonstrated that the induced current gain takes place only in some local regions, several which increases with applied bias. Such unusual behavior can be explained by an inhomogeneous distribution of hole traps or by a formation of conductive channels under applied bias.

Fast Neutron Irradiation on GaN-Based Light-Emitting Diodes From Near-Ultraviolet to Green Spectral Ranges

Neutron irradiation effects were compared for GaN-based multi-quantum well (MQW) light emitting diodes (LEDs) with emission wavelength in the near-ultraviolet (NUV), blue and green spectral regions. Optical output power, current-voltage and peak wavelength were analyzed in detail before and after irradiation. Three colors of LEDs showed an increase and then a decrease in optical output power with the increase of neutron fluence ranging from 1.0×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> to 1.0×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . The enhanced light emission performance is attributed to the increase of carrier injection for neutron irradiated MQWs. In addition, the formation of tunneling conductivity channels in the p-doped AlGaN electron block layer (EBL) induced by neutrons is considered as the main factor that dominates the performance degradation. Among the three colors of LEDs, the order of severity for the optical and electrical properties influenced by this medium-fluence neutron irradiation is green, blue, and NUV LEDs, in turn becoming more serious. The NUV LEDs rely heavily on the EBL due to their poor carrier confinement in relatively shallow GaN/AlGaN MQWs, so an increase of carrier injection or leakage induced by neutrons has significant influence on device performance. As the green LEDs have deep quantum wells, the strong confinement of carriers leads to their being least sensitive to neutron irradiation. So we believe that design of LEDs with deep quantum wells to enhance the carrier confinement ability will be helpful to improve their radiation tolerance. The findings not only enrich the understanding of the influence mechanism of neutron irradiated GaN-based UV/visible LEDs, but are also helpful to radiation hardened design.

Investigating the growth of carbon traces in cardboard in oil-paper insulation

A large amount of contaminants are collected on the cardboard surface of the valve-side bushing outlet of a converter transformer that has been operating for a long period, and can cause the performance of the oil–paper insulation to degrade. The analysis of their energy spectrum has shown that these contaminants contain free carbon. To investigate causes of the formation of these carbon traces, the authors of this study analyze their law of growth on the surface of the insulating paper in the presence of pure insulating oil and insulating oil containing carbon particles. We examined the influence of carbon tracks of different lengths on the breakdown voltage along the surface of the oil–paper insulation. The results showed that carbonization on the surface of the insulating paper generated carbon traces in pure insulating oil and eventually led to the formation of conductive channels. Moreover, carbon traces were generated by carbon particles deposited on the surface of the insulating paper in insulating oil containing carbon particles. The carbon traces grew from the high-voltage electrode to the ground electrode along the direction of the electric field in both types of oils. The formation of the conductive channel through the poles of the paper in insulating oil containing carbon particles required a lower voltage and a shorter discharge time than that in pure insulating oil. As the concentration of the carbon particles increased, the rate of growth of carbon traces on the surface of the insulating paper increased such that the oil–paper insulation failed earlier than otherwise. Long carbon traces were formed on the surface of the insulating paper in case of a high concentration of carbon particles under the DC pre-pressure mode, and this led to a reduction in the breakdown voltage along the surface of the oil–paper insulation.

A self-healing polyvinyl alcohol-based composite with high thermal conductivity and excellent mechanical properties

Conventional thermally conductive polymeric composites are prone to mechanical failures when deployed in dynamic environments, which results in loss of functionality and reduced service life. Herein, self-healing thermally conductive composites are fabricated by dispersing polydopamine (PDA) modified boron nitride (BN) and borate ions into polyvinyl alcohol (PVA) matrix. Due to the decreased thermal interface resistance and formation of thermal conduction channels, the 13 vol% BN-PDA/PVA composite endows an enhancement of 562% in thermal conductivity (1.007 W/mK) comparing with pure PVA (0.152 W/mK). In addition, the hydrogen bonds between BN-PDA and PVA chains and the borate bonds in dynamic borax/PVA networks impart a high self-healing efficiency of more than 80% and excellent mechanical properties in BN-PDA/PVA composites. This study provides a straightforward method for the preparation of thermal interface materials with fast recovery and long service life for next generation electronic packaging applications.

Constructing “sesame‐biscuit” structured hybrids with SiC and Ag particles for enhancing thermal conductivity and dielectric constant of elastomer composites

AbstractWith the development of multifunctional and miniaturized integrated circuits, polymeric materials with large dielectric constant and high thermal conductivity have major significance in modern electronic industry. In this work, “sesame‐biscuit” structured thermally conductive hybrids were prepared by polydopamine (PDA) modification and in‐situ electroless silver (Ag) plating on the surface of silicon carbide (SiC), referred as SiC‐P‐Ag. Then, the SiC‐P‐Ag was incorporated into epoxidized natural rubber (ENR) matrix to yield polymeric composites (ENR/SiC‐P‐Ag) with excellent thermal and dielectric properties. It was found that PDA improved the interfacial compatibility and reduced the interface thermal resistance between SiC and ENR matrix. In addition, the formation of heat conduction channels and conductive Ag nanoparticles caused an increase in thermal conductivity of the 50 vol% ENR/SiC‐P‐Ag composite to 0.5655 W/(mK), which was 540% that of the pure ENR (0.1048 W/(mK)). Meanwhile, the 50 vol% ENR/SiC‐P‐Ag composite showed a low AC conductivity of 2.98 × 10−11 S/cm and a high dielectric constant of 35 at 10 Hz. It is noteworthy that this simple and efficient route for preparing ENR/SiC‐P‐Ag composites can also be applied in other fillers for simultaneously enhancing dielectric constant and thermal conductivity of polymeric composites.

Synergetic Enhancement of Seebeck Coefficients and Electrical Conductivity in Flexible Liquid Crystal Composites

The development of thermoelectric (TE) devices, which convert thermal gradient into energy, was motivated by the immense amount of heat wasted from solar radiation and industrial heat dissipation. Polymer-based organic thermoelectric (OTE) materials have garnered much interest owing to their distinctive advantages, including low thermal conductivity, minimal toxicities, low cost, and superior mechanical elasticity. However, the TE performance of these organic materials is mainly limited due to their low Seebeck coefficient and poor electrical conductivity. In this work, we simultaneously improve the Seebeck coefficients and electrical conductivity of polyvinylidene fluoride (PVDF) polymer and single-wall carbon nanotube (SWCNT)-based composites by incorporating a liquid crystal (LC). This is attributed to the thermodiffusion of ions and the formation of stable and efficient conductive channels with LC incorporation. The concentration of LC is suitably tuned, which results in an increment of ∼42% Seebeck coefficient and ∼72% electrical conductivity compared to the reference PVDF/SWCNT composite. The tensile strain curve shows that the durability of the composite samples has increased by incorporating the LC. Also, a flexible thermoelectric generator (TEG) device consisting of eight composite legs is constructed, which shows an open circuit voltage and output power of 35.7 mV and 46.1 nW, respectively, at a temperature difference of 60 K. The findings show that LC-based SWCNT/PVDF composites exhibit superior TE potential and provide a new route for fabricating flexible TE devices.

EBIC Imaging of Conductive Paths Formed in Graphene Oxide as a Result of Resistive Switching

The electron-beam-induced current (EBIC) method is utilized in this work to visualize conductive channels formed in graphene oxide as a result of resistive switching. Using metal–insulator–semiconductor (MIS) structures, an increase in the electron beam induced current by a few orders of magnitude as compared with the EBIC signal in metal–insulator–metal (MIM) structures is achieved. The mechanism of the EBIC image formation related to the conductive channels is explained by the separation and collection of the e-beam generated excess carriers by rectifying barrier nanocontacts formed at the graphene oxide/Si interface during resistive switching. It is shown that the collection efficiency of the formed nanocontacts decreases with the beam energy, in agreement with the theoretical predictions for the Schottky-like nanocontacts. An important advantage of the EBIC method is demonstrated in its ability to monitor the generation and elimination of high density conductive channels even when the current–voltage measurements cannot detect and separate these processes. EBIC study of the dynamics of the conductive channel formation can help better understand the underlying physical mechanisms of their generation.

Design of all-phase-change-memory spiking neural network enabled by Ge-Ga-Sb compound

The implementation of artificial spiking neural network (SNN) usually takes advantage of multiple heterogeneous circuits to mimic either neurons which generate spiking pulses, or synapses which store the weights of event correlations. Here, we design a homogeneous device using Ge-Ga-Sb (GGS) as a phase-change-memory (PCM) material which can do both jobs. The GGS compound shows high stability when used in data storage, such as high working temperature (281°C) and high 10-years data retention temperature (230°C), as well as low resistance drift. Interestingly, when the as-fabricated GGS device is set by iterative narrow-width electric pulses, it first experiences an abrupt resistance drop by two orders of magnitude, followed by a continuous resistance decrease. This unique abrupt-to-progressive transition can be used to mimic both neuronal and synaptic functions, mechanistically enabled by the formation of conductive channels and the continuous growth with the phase separation of crystalline areas. To this end, we propose an all-PCM SNN, which is emulated to have high accuracy (90%) in the standard pattern recognition.

Development of a comprehensive methodology for the design and fabrication of carbon fiber integrated cement composite toward health monitoring of structural components

The research aims to develop self-sensing cement composites (SSC) with various micro carbon fiber (CF) concentrations (0.05 %, 0.1 %, 0.15 %, 0.2 %, and 0.25 %) for application in structural health monitoring (SHM). This research evaluates the strength, conductivity, piezoresistivity, and stress-sensitive properties of developed SSC. As an innovative approach, in addition to the development of SSC, they are also embedded in macroscopic structural components to predict their deformation under external loads. The results indicate that the compressive strength is enhanced by 5.2 % due to the ability of CF to bridge cracks. The electrical resistivity of cement composite decreases by 75 % due to the increased contact conduction caused by the formation of continuous conductive CF channels. The performance-index approach optimizes the concentration of CF as 0.25 % with regard to electro-mechanical behavior. The resistivity variation of the optimized SSC embedded in the beam indicates a significant correlation (=98 %) with beam deformation. The embedded SSC identified the deformation of the column under external load with 95% accuracy. Thus, the CF shows the significant capability to develop SSC with good electro-mechanical properties that are capable of detecting the deformations of beams and columns.

Features of the Formation of Conductive Channels in Memristors Based on Solid Electrolytes

Experimental data on measurement of the resistance and electrical conductivity in the low-resistance mode of operation of a germanium-selenide-based memristor with a self-forming conductive channel in the form of a silver filament are obtained in the range of operating frequencies and temperatures. In the frequency experiment, the influence of the switching frequency is tested at room temperature in the range of 1–10 000 Hz. The main result of the experiment is the identification of a linear relationship between the electrical conductivity and the memristor operating cycle time in semilogarithmic coordinates, which made it possible to introduce a temperature-dependent kinetic constant. This experimental fact made it possible to establish the main parameter affecting the shape of the current–voltage characteristics, namely the thickness of the conductive channel.

Immobilizing imidazolium ionic liquid in flexible proton exchange membranes to modify microstructure fracture

The imidazolium ionic liquid of (Kevlar/bmimCl/SEBS)5 membrane was immobilized in flexible proton exchange membranes (PEMs) with the spin coating technology. In the prepared (Kevlar/bmimCl/SEBS)5 membrane, the imidazolium ionic liquid of 1-butyl-3-methylimidazolium chloride (bmimCl) functioned as glue to modify the microstructure fracture from the stretching operation through occupying the cracks. The proton conduction resistance was reduced with the well-ordered distribution of components in the multilayered microstructure. Although the doped phosphoric acid (PA) molecules charged the proton conductivity, the imidazolium cations of bmim+ could participate in the proton conduction through the formation of continuous proton conduction channels. In this research, the folding and stretching operations exerted the negligible effect on microstructure and property of the prepared PEMs. Besides the modification of bmimCl, the deformation of polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SBES) molecular chains and Kevlar nanofibers in the stretching operation contributed to maintain the stable microstructure. The stretching and folding operations led to slight variation on the membrane property. Specifically, the proton conductivities were respectively 3.21 × 10−2 S/cm and 4.16 × 10−2 S/cm at 160 °C, which were even superior to 2.77 × 10−2 S/cm of the pristine membranes. Furthermore, the tensile stress values of the folding and stretching membranes can reach (18.9 ± 1.19) MPa and (32.6 ± 2.63) MPa.