Formation Of Conducting Channels Research Articles

Simultaneous enhancement of electrical conductivity and seebeck coefficient in organic thermoelectric SWNT/PEDOT:PSS nanocomposites

High electrical conductivity and high Seebeck coefficient are the two important prerequisites for achieving high power factor in organic thermoelectric (TE) materials. However, these two properties are quite often in conflict. In this work, we demonstrate that incorporating CNT in a conducting polymer PEDOT:PSS could facilitate the formation of stable and effective conductive channels, which provides an effective approach to optimize the TE parameters with simultaneously enhanced electrical conductivity and Seebeck coefficient against the initial organic TE materials. With further tailoring charge concentration of the SWNT/PEDOT:PSS composite by base treatment, the TE performance could be improved. Nanocomposite of 60 wt% SWNT and PEDOT:PSS exhibits high TE power factor of ∼526 μW m−1 K−2 with Seebeck coefficient of 55.6 μV K−1 and electrical conductivity of 1701 S cm−1, which is by far one of the highest power factors among the reported organic TE nanocomposites. Considering thermal conductivity around 0.4–0.6 W/m K, the highest estimated ZT value of our TE nanocomposite can approach 0.39, demonstrating the feasibility of this strategy to enhance TE performance of organic composite materials.

Using ANN and SVM for the Detection of Acoustic Emission Signals Accompanying Epoxy Resin Electrical Treeing

Electrical treeing is one of the effects of partial discharges in the solid insulation of high-voltage electrical insulating systems. The process involves the formation of conductive channels inside the dielectric. Acoustic emission (AE) is a method of partial discharge detection and measurement, which belongs to the group of non-destructive methods. If electrical treeing is detected, the measurement, recording, and analysis of signals, which accompany the phenomenon, become difficult due to the low signal-to-noise ratio and possible multiple signal reflections from the boundaries of the object. That is why only selected signal parameters are used for the detection and analysis of the phenomenon. A detailed analysis of various acoustic emission signals is a complex and time-consuming process. It has inspired the search for new methods of identifying the symptoms related to partial discharge in the recorded signal. Bearing in mind that a similar signal is searched, denoting a signal with similar characteristics, the use of artificial neural networks seems pertinent. The paper presents an effort to automate the process of insulation material condition identification based on neural classifiers. An attempt was made to develop a neural classifier that enables the detection of the symptoms in the recorded acoustic emission signals, which are evidence of treeing. The performed studies assessed the efficiency with which different artificial neural networks (ANN) are able to detect treeing-related signals and the appropriate selection of such input parameters as statistical indicators or analysis windows. The feedforward network revealed the highest classification efficiency among all analyzed networks. Moreover, the use of primary component analysis helps to reduce the teaching data to one variable at a classification efficiency of up to 1%.

Investigating the Effectiveness of Emulsified Acid on Sandstone Formation under High Temperature Conditions

Acid stimulation supports the oil and gas industry as a versatile mean in enhanced oil recovery to fulfil the world energy demand. Although hydrochloric acid can significantly improve the reservoir permeability, its rapid reaction rate at high temperature has created a barrier for acid penetration. Subsequently, emulsified acid has slowly gain its popularity due to its retardation effect which allows deeper penetration of acid into the formation and achieves minimal corrosion issues. Nonetheless, emulsified acid has rarely applied on sandstone formation. Since a large portion of reservoirs are made up of sandstone, the effects of emulsified acid on sandstone under high temperature conditions should be studied to unlock the effective usage of emulsified acid in restoring the hydrocarbon recovery from the potential sandstone reservoirs. Besides, it is also crucial to explore cheaper and greener substitute to formulate innovative emulsified acid in minimizing the high acidizing budget along with environmental concerns. In this project, 10 different emulsified acid combinations are prepared using hydrofluoric acid, hydrochloric acid, phosphoric acid, formic acid, acetic acid, cationic surfactant, diesel and waste oil. The pre-flush treatment (5 % CH3COOH: 10 % HCl) is followed by the main flush (emulsified acids) saturation for 3 days. The thermal stability of emulsified acids and their effect on the Berea sandstone properties are evaluated. Major outcome is that the emulsified acids have the capability to remain stable at 275 °F up to 6 hours with uniform and fine droplet size. It is also proven that most of the emulsified acids can improve the porosity and permeability of Berea sandstone core samples except for HF: H3PO4. Regardless of the types of oil used for emulsified acid formulation, HF: HCl acid combination shows the best performance enhancement for both diesel-based and waste oil-based emulsified acids. In sandstone acidizing, emulsified acid dissolves the minerals and create acid transport pathway with close connectivity between pore spaces, causing the formation of large and conductive channels within the rock. Hence, these positive results clearly reflect on the feasibility of emulsified acid application in sandstone matrix acidizing and the effectiveness of waste oil as a replacement fluid for diesel.

On the role of isotopic composition in crystal structure, thermal and charge-transport characteristics of dodecaborides LuNB12 with the Jahn-Teller instability

Crystal structures, thermal and charge-transport (resistivity and Seebeck coefficient) characteristics of dodecaborides LuNB12 are studied to determine the role of boron isotopic composition N = 10, 11, natural. Small distortions of the fcc lattice are observed and attributed to cooperative Jahn-Teller effect in the boron sublattice. The Einstein and Debye temperatures, respectively for Lu and B atoms, are determined based on equivalent atomic displacement parameters (ADPs) refined as a part of structure model. Additionally, ADP values are separated into temperature dependent and independent components, arising from (i) thermal and (ii) zero temperature vibrations, together with (iii) static shifts of few atoms from lattice sites. Atomic disordering is most expressed in LunatB12 as follows from its ADP values and the Schottky anomalies in heat capacity. The largest static ADP components of LunatB12 are surprisingly combined with the lower resistivity and thermopower as compared to isotopically pure crystals. One may suppose the static shifts (defects) are centers of pinning facilitating formation of additional conductive channels (dynamic charge stripes), which reveal themselves on difference Fourier maps of electron density.

The effects of conductive nano fillers alignment on the dielectric properties of copolymer matrix

This research focuses on the improvement of the dielectric and energy harvesting properties of piezoelectric P(VDF-TrFE) copolymer matrix by the alignment of conductive reduced graphene oxide nano fillers. The dispersion and the morphology of the conductive nano fillers on the co-polymer matrix were characterized by scanning electron microscopy which showed a configurational phase transition due to highly conductive nano channel formation, steric hindrance, excluded volume interaction van-der-walls forces between adjacent reduced graphene oxide sheets. Five different piezoelectric nanocomposites were prepared by varying the reduced graphene oxide contents in P(VDF-TrFE) matrix to realize its optimum concentration in the matrix. From our analysis, we observed that, an optimized morphological structure plays a vital role in the formation of polar electroactive β phase on the co-polymer matrix through the good dispersion, filler alignment and interfacial interaction of reduced graphene oxide nano fillers. The as prepared nanocomposite film showed an enhanced crystallinity (50 ∼ 52%), dielectric constant (72 at 1 kHz), piezoelectric charge constant (−23 pC/N) with an output power of 3.2 µW at 1.8 MΩ load for 2 N mechanical force. All the outputs were observed without applying poling process. We expect that our synthesized self-poled nanocomposite can be a useful candidate for energy harvesting applications.

The Discharge Mechanism Leading to the Tracking Progress in Polyvinyl-Chloride-Sheathed Flat Cord

This paper suggests the mechanism of the discharge phenomenon that leads to tracking progress. For this purpose, a polyvinyl-chloride-sheathed flat cord (PVCSFC), which is widely used as a distribution cord, was employed and an artificial crack was intentionally made on the surface. Tracking was progressed using electrolyte droplets. The mechanism of the discharge phenomenon was suggested from the measurement and analysis of the current waveform. As carbonization progressed during the tracking progress, the frequency of scintillation discharge also significantly increased. The mechanism for scintillation discharge during the tracking progress was based on the change in the electric field of the dry band, initial electron, electron avalanche, photoionization, secondary electron generation (electron detachment, photoemission, and secondary electron emission avalanche), space charge due to positive ions, and formation of conductive channels. This discharge mechanism could explain the physical phenomenon and change in the current waveform that occurs during the tracking progress.

First principles study of effect of vaiable component Al on HfO<sub>2</sub> resistance

<sec>In order to improve the resistance properties of HfO<sub>2</sub> and increase the consistency and uniformity of conductive filaments formed by oxygen vacancies (VO), the first-principles calculation method based on density functional theory is used to study the micro-properties of Al-doped HfO<sub>2</sub> resistive materials. The results show that the interval Al (Int-Al) is more suitable for being incorporated into HfO<sub>2</sub>, and the closer to the relative position of VO the Int-Al, the faster the convergence rate of the resistive material tends to be stable, and the smaller the formation energy. The effects of different Int-Al concentrations on the formation of HfO<sub>2</sub> supercells with VO defects show that when the concentration of doped Int-Al is 4.04%, the fractional charge state density map can form relatively good charge channels. The maximum and critical equipotential surface values are highest, which is conducive to improving the consistency and uniformity of the formation of conductive filaments in HfO<sub>2</sub> resistive materials. The calculation of energy formation shows that the change is slow when the concentration of Int-Al is lower than 4.04%. When the concentration of Int-Al is higher than 4.04%, the abnormal increase occurs, which indicates that the defect system becomes more and more difficult to form with the increase of the concentration of Int-Al. </sec><sec>The introduction of the impurity and the VO defect destroy the original complete crystal structure, which causes the position of the atoms around the impurity to shift, and the valence electron orbit and the energy level of the crystal are changed, and the distribution of the internal charges of the HfO<sub>2</sub> defect system is affected. In order to study the effect of the change of the lattice structure on the formation of the VO conductive filament, the VASP software package is used to calculate the relative ratio of the atoms in the lattice structure of the HfO<sub>2</sub> defect system as the reference and the relative ratio of the HfO<sub>2</sub> defect system after the optimizing the lattice structure. Further study of the change of lattice structure, when the concentration of doped Int-Al is 4.04%, shows that the defect formation energy decreases significantly, which is conducive to the formation of perfect conductive channel. The conductive channel has a certain reference significance for improving the performance of HfO<sub>2</sub> based resistive variable memory materials.</sec>

Nanoscale Ring-Shaped Conduction Channels with Memristive Behavior in BiFeO₃ Nanodots.

Nanoscale ring-shaped conduction channels with memristive behavior have been observed in the BiFeO3 (BFO) nanodots prepared by the ion beam etching. At the hillside of each individual nanodot, a ring-shaped conduction channel is formed. Furthermore, the conduction channels exhibit memristive behavior, i.e., their resistances can be continuously tuned by the applied voltages. More specifically, a positive (negative) applied voltage reduces (increases) the resistance, and the resistance continuously varies as the repetition number of voltage scan increases. It is proposed that the surface defects distributed at the hillsides of nanodots may lower the Schottky barriers at the Pt tip/BFO interfaces, thus leading to the formation of ring-shaped conduction channels. The surface defects are formed due to the etching and they may be temporarily stabilized by the topological domain structures of BFO nanodots. In addition, the electron trapping/detrapping at the surface defects may be responsible for the memristive behavior, which is supported by the surface potential measurements. These nanoscale ring-shaped conduction channels with memristive behavior may have potential applications in high-density, low-power memory devices.

Composition-dependent conductivity of InxGa1-xAs nanowires

Using the methods of scanning probe microscopy, I-V characteristics of individual InxGa1-xAs nanowires with different In content (x) were measured. A sharp decrease in the conductivity was observed at x=0.7. It is shown that type of contact between nanowire and probe changes from ohmic at x=1 to Schottky at x=0.85. These changes were explained by the formation of surface conductive channel, induced by surface Fermi level pinning in conduction band for x>0.85.

Oxygen vacancy drift controlled three-terminal ReRAM with a reduction in operating gate bias and gate leakage current

Three-terminal structures have an advantage over two-terminal structures in logic applications and neuromorphic circuits, However, three-terminal operation based on Valence Change RAM still requires a larger gate bias to form/dissolve a conductive path between the source and the drain, especially for turning off. Here, reduction in gate bias and gate leakage current in nonvolatile operation of oxygen vacancy drift-controlled three-terminal ReRAM is demonstrated by W/Ti (gate)/TaOx (resistance switching layer)/Pt (source), Pt (drain) structure. Introduction of a Ti thin layer between W and TaOx layers prevents a conductive channel formation between gate and source/drain electrodes. Consequently, as-fabricated high resistance between gate and source/drain is kept, resulting in smaller gate leakage current. We also achieved interface engineering on a sidewall structure of Pt (source)/SiO2 (insulator)/Pt (drain) multi-layer, reducing in an operating bias from 10 V to 4 V or less.

Electrical conductance of near-infrared femtosecond air filaments in the multi-filament regime.

Electrical conductive properties of femtosecond laser filaments are of significant interest for applications such as remote arc suppression and discharge guiding. We transmitted electrical current through a DC-biased air plasma channel formed in the wake of an energetic femtosecond laser pulse and observed an increased rate of change of the charge transmitted through the ionized channel with laser energy when crossing from the single- to multi-filament regimes. This behavior is attributed to the confluent effects of greater electron density and an increased cross-sectional area of the multi-filament plasma structures. As the laser energy is increased, the formation of additional conductive channels in the multi-filamentation regime becomes a significant contributor to the rapid increase of conductivity. These observations suggest a potential path to attractive applications such as efficient energy transfer in air mediated by femtosecond laser-produced filaments.

Effect of oxygen content on the electrical properties of sputter deposited vanadium oxide thin-films

In this article, different oxidation states of vanadium in vanadium oxide (VO) thin-films, deposited on Si(100) at room temperature by reactive rf-sputtering of a pure metallic vanadium target at different Ar/O2 ratios, have been identified. A qualitative assessment of the XPS spectra reveals that vanadium exists in the V5+ and V4+ oxidation states in the oxide thin-films. The highest content of V5+ oxidation state is present in the oxide film deposited at highest O2 ratio (Ar:O2 = 1:4). Vanadium oxide deposited at highest O2 ratio shows insulator-to-metal (IM) transition whereas the devices, deposited at other oxygen ratios do not show any appreciable change. This transition has been ascribed to a voltage-induced joule heating effect which in turn results in formation of metallic conduction channel across the device. Thus, the ratios of Ar and O2 in the reactive plasma play a critical role in determining the IM transition properties of vanadium oxide thin-films.

Phototransistors with Negative or Ambipolar Photoresponse Based on As‐Grown Heterostructures of Single‐Walled Carbon Nanotube and MoS2

AbstractA facile synthesis method for the heterostructures of single‐walled carbon nanotubes (SWCNTs) and few‐layer MoS2 is reported. The heterostructures are realized by in situ chemical vapor deposition of MoS2 on individual SWCNTs. Field effect transistors based on the heterostructures display different transfer characteristics depending on the formation of MoS2 conduction channels along SWCNTs. Under light illumination, negative photoresponse originating from charge transfer from MoS2 to SWCNT is observed while positive photoresponse is observed in MoS2 conduction channels, leading to ambipolar photoresponse in devices with both SWCNT and MoS2 channels. The heterostructure phototransistor, for negative photoresponse, exhibits high responsivity (100–1000 AW−1) at low bias voltages (0.1 V) in the visible spectrum (500–700 nm) by combining high mobility conduction channel (SWCNT) with efficient light absorber (MoS2).

Implementation of Trench-based Power LDMOS and Low Voltage MOSFET on InGaAs

ABSTRACTIn this paper, we propose a design concept of integration of trench-based power and low voltage small signal metal-oxide-semiconductor field-effect transistors (MOSFETs) on high mobility InGaAs material. A high power dual-trench-gate (DTG) MOSFET and a low voltage MOSFET are implemented side by side in same InGaAs epitaxial layer using junction isolation technique. The high voltage DTG-MOSFET has two gates which are placed in oxide-filled trenches in the drift region. This structure provides a better trade-off between specific on-resistance (Ron−sp) and breakdown voltage (Vbr) due to the formation of dual conduction channels and enhancement in reduced-surface-field (RESURF) effect caused by folding of the drift region in the vertical direction. Further, simultaneous conduction of channels increases the drain current (ID) and transconductance (gm) leading to better cut-off frequency (ft) and maximum oscillation frequency (fmax). On the other hand, the gate of low voltage MOSFET is placed in an oxide trench to make two n-channels in the p-base. The parallel conduction of two channels gives substantial improvement in ID, peak gm, ft and fmax with good control over the short channel effects. Two-dimensional simulations are carried out to evaluate the performance of both high voltage and low voltage MOSFETs.

TCNQ molecular semiconductor of the Cu(II)TAAB macrocycle: Optical and electrical properties

The present study reports the doping of a semiconducting molecular material through the formation of hydrogen bonds between the macrocycle Cu(II)(TAAB) and the electronic acceptor TCNQ. According to density functional theory (DFT) calculations and electron paramagnetic resonance (EPR) analysis, the doped compound has the shape of a distorted square pyramid, with four nitrogen atoms in the equatorial position and the apical oxygen atom from the water ligands. These water molecules can generate strong hydrogen bonds with TCNQ and the TAAB metallic complex. Thin films of copper molecular material were obtained through high vacuum evaporation and were structurally characterized by IR spectroscopy, EPR and scanning electron microscopy (SEM). Additionally, the absorption coefficient (α) and photon energy (hν) were calculated from UV–vis spectroscopy and used to determine the optical activation energy in each film, from which its semiconducting behavior was established. An important aspect to consider is that the presence of hydrogen bonds is essential to establish the semiconducting nature of these species; this chemical behavior, as well as the resulting electronic mobility, have been studied by DFT theoretical calculations, which reinforce the experimental conclusion of a relationship between Cu(II)TAAB and TCNQ moieties generated by a weak bond. Finally, I–V characteristics have been obtained from a glass/ITO/doped molecular semiconductor/Ag device using Ag and ITO electrodes. Results for the copper-based device show that, at low voltages, the conduction process is of an ohmic nature while, at higher voltages, space-charge-limited current (SCLC) is found. It is highly probable that the doping effect in TCNQ favors electronic transport due to the formation of conduction channels caused by dopant-favored anisotropy.

Measuring the Changes in Copper Nanopowder Conductivity during Heating as a Method for Diagnosing its Thermal Stability

This work researches the impact of the temperature of compacted copper nanopowder on the amperage of the current flowing through the nanopowder sample. It was determined that upon reaching its oxidation temperature (~ 1900C), the copper nanopowder started conducting electricity, and at 280-320°C electric breakdown of sample was occurring. This is caused to irreversible processes taking place in nanomaterials during heating, such as sintering and mass-transfer, those processes leading to the formation of conductivity channels. This speaks in favor of an evident dependency between copper nanopowder conductivity and the chemical transformations taking place in it; this allows for recommending this research method for instant diagnostics of copper nanopowders.

Microphase separation and the formation of ion conductivity channels in poly(ionic liquid)s: A coarse-grained molecular dynamics study.

We study generic properties of poly(ionic liquid)s (PILs) via coarse-grained molecular dynamics simulations in bulk solution and under confinement. The influence of different side chain lengths on the spatial properties of the PIL systems and on the ionic transport mechanism is investigated in detail. Our results reveal the formation of apolar and polar nanodomains with increasing side chain length in good agreement with previous results for molecular ionic liquids. The ion transport numbers are unaffected by the occurrence of these domains, and the corresponding values highlight the potential role of PILs as single-ion conductors in electrochemical devices. In contrast to bulk behavior, a pronounced formation of ion conductivity channels in confined systems is initiated in close vicinity to the boundaries. We observe higher ion conductivities in these channels for increasing PIL side chain lengths in comparison with bulk values and provide an explanation for this effect. The appearance of these domains points to an improved application of PILs in modern polymer electrolyte batteries.

Optical absorption and electrical properties of MPc (M =Fe, Cu, Zn)-TCNQ interfaces for optoelectronic applications

This research is related to the growth and characterization of doped molecular semiconductor metallophthalocyanine-tetracyanoquinodimethane (MPc-TCNQ) films, with M = Fe, Zn, Cu. FT-IR and Raman spectroscopies were employed to study the chemical interactions taking place in the MPc-TCNQ films. XRD was carried out to determine the crystalline structure present in the samples, due to the facility of the MPcs to be in alpha and/or beta phases. The thin films were analized by SEM and UV–vis spectroscopy in order to study their morphological and optical properties. The absorption spectra recorded in the UV–Vis region for the deposited samples showed two bands, namely the Q and Soret bands. The absorption coefficient (α) and photon energy (hν) were calculated from the UV–vis spectra, to in turn determine the optic activation energy in each film and its semiconductor behavior. The values obtained for direct transitions due to the crystallinity of the films were: 1.2, 1.4 and 2 eV for FePc-TCNQ (MMFe), ZnPc-TCNQ (MMZn) and CuPc-TCNQ (MMCu), respectively. Additionally, I-V characteristics have been obtained from fabricated glass/ITO/MM/Ag devices using ohmic contacts both after annealing. The electrical properties of the devices, e.g. carrier mobility and concentration of thermally generated holes, were extracted from the J-V characteristics. The results show that the conduction process is ohmic for the MMZn and MMCu devices, at low voltages, while at high voltages, a space-charge-limited conduction (SCLC) is present. The effect of temperature on conductivity was also measured in these samples and the lower thermal activation energy calculated was 0.37 eV for MMZn. Moreover, it was found that the temperature-dependent electric current is always higher for the MMZn device and suggests a semiconductor-like behavior with an important conductivity of the order of 103 S cm−1. Anyhow, in terms not only of electric properties, but also of optic behavior, the results suggest that all three devices manufactured, MMFe, MMCu and MMZn, are of potential use in optoelectronics. The doping effect of TCNQ favors the electronic transport, most likely due to the formation of conduction channels caused by the anisotropy induced by the dopant.

Fluid modeling of radical species generation mechanism in dense methane-air mixture streamer discharge

Atmospheric dielectric barrier discharge (DBD) was found to be promising in the context of plasma chemistry, plasma medicine, and plasma-assisted combustion. In this paper, we present a detailed fluid modeling study of abundant radical species produced by a positive streamer in atmospheric dense methane-air DBD. A two-dimensional axisymmetric fluid model is constructed, in which 82 plasma chemical reactions and 30 different species are considered. Spatial and temporal density distributions of dominant radicals and ions are presented. We lay our emphasis on the effect of varying relative permittivity (εr = 2, 4.5, and 9) on the streamer dynamics in the plasma column, such as electric field behavior, production, and destruction pathways of dominant radical species. We find that higher relative permittivity promotes propagation of electric field and formation of conduction channel in the plasma column. The streamer discharge is sustained by the direct electron-impact ionization of methane molecule. Furthermore, the electron-impact dissociation of methane (e + CH4 = >e + H+CH3) is found to be the dominant reaction pathway to produce CH3 and H radicals. Similarly, the electron-impact dissociations of oxygen (e + O2 = >e + O+O(1D), e + O2 = >e + O+O) are the major routes for O production.

Elastic Modulus and Thermal Conductivity of Thiolene/TiO2 Nanocomposites.

Metal oxide based polymer nanocomposites find diverse applications as functional materials, and in particular thiol-ene/TiO2 nanocomposites are promising candidates for dental restorative materials. The important mechanical and thermal properties of the nanocomposites, however, are still not well understood. In this study, the elastic modulus and thermal conductivity of thiol-ene/TiO2 nanocomposite thin films with varying weight fractions of TiO2 nanoparticles are investigated by using Brillouin light scattering spectroscopy and 3ω measurements, respectively. As the TiO2 weight fraction increases from 0 to 90%, the effective elastic longitudinal modulus of the films increases from 6.2 to 37.5 GPa, and the effective thermal conductivity from 0.04 to 0.76 W/m K. The former increase could be attributed to the covalent cross-linking of the nanocomposite constituents. The latter one could be ascribed to the addition of high thermal conductivity TiO2 nanoparticles and the formation of possible conductive channels at high TiO2 weight fractions. The linear dependence of the thermal conductivity on the sound velocity, reported for amorphous polymers, is not observed in the present nanocomposite system.