Sheet Conductivity Research Articles

Quantifying the electrical behavior of carbon nanotube sheet enhanced with acid functionalization and polymer intercalation

The electrical properties of carbon nanotube (CNT) sheet manufactured using different production (standard and enhanced) and post-processing (none, acid treatment, polymer intercalation) methods were analyzed. These properties included the electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE). The acid treatment significantly improved the electrical conductivity of the CNT sheet, while polymer intercalation did not affect the electrical conductivity. The enhanced production reduced the electrical conductivity by more than 40% for all specimen sets. With the exception of the acid-treated standard specimen, the EMI SE was consistent throughout all specimen sets. The electrical conductivity and EMI SE were presented as functions of the thickness, areal density, and density. There was no correlation between these material properties and the electrical conductivity of the untreated or polymer-intercalated specimens. The production method seems to influence how these properties affect the acid-treated specimens. The EMI SE was directly correlated to the thickness and inversely correlated to the density. The EMI SE was directly correlated to the areal density for almost all specimen types. Scanning electron microscopy revealed an increase in catalyst impurities in the enhanced production specimens and an increase in CNT agglomeration in both the acid-treated and polymer-intercalated specimens.

Fabrication and electrochemical behavior of thin composite solid electrolyte for all-solid lithium batteries

Loading level, active material content of the cathode, and the thickness of composite solid electrolyte (CSE) sheets were optimized as 13 mg cm−2, 88 wt%, and 60 μm, respectively, for the development of all-solid lithium batteries (ASLBs) with high energy density. Thin CSE sheets were fabricated by adding PVDF binder with Al-LLZO powder and PEO-Li salt solution. PVDF had effects on the ionic conductivity, strength, and electrochemical stability of the CSE sheet. When the PVDF content was increased to 7 wt%, CSE sheet strength increased from 1.4 to 2.83 MPa, while the electrochemical stability has significantly improved at the range of oxidation and reduction potential. However, the ionic conductivity decreased from 3.7 × 10−4 to 1.73 × 10−4 S cm−1 at 70 °C. Moreover, the surface layer of the composite cathode was smoother than that of normal composition, and the interfacial resistance between the cathode compound layer and Al current collector has also decreased by adding PVDF. As a result of the test, the initial discharge capacity of the coin cell showed 207 mAh g−1 and 2.3 mAh cm−2 at 70 °C.

VO2·0.2H2O nanocuboids anchored onto graphene sheets as the cathode material for ultrahigh capacity aqueous zinc ion batteries

Aqueous Zinc-ion batteries (ZIBs), using zinc negative electrode and aqueous electrolyte, have attracted great attention in energy storage field due to the reliable safety and low-cost. A composite material comprised of VO2·0.2H2O nanocuboids anchored on graphene sheets (VOG) is synthesized through a facile and efficient microwave-assisted solvothermal strategy and is used as aqueous ZIBs cathode material. Owing to the synergistic effects between the high conductivity of graphene sheets and the desirable structural features of VO2·0.2H2O nanocuboids, the VOG electrode has excellent electronic and ionic transport ability, resulting in superior Zn ions storage performance. The Zn/VOG system delivers ultrahigh specific capacity of 423 mAh·g−1 at 0.25 A·g−1 and exhibits good cycling stability of up to 1,000 cycles at 8 A·g−1 with 87% capacity retention. Systematical structural and elemental characterizations confirm that the interlayer space of VO2·0.2H2O nanocuboids can adapt to the reversible Zn ions insertion/extraction. The as-prepared VOG composite is a promising cathode material with remarkable electrochemical performance for low-cost and safe aqueous rechargeable ZIBs.

Enhancement of the electrical conductivity of defective carbon nanotube sheets for organic hybrid thermoelectrics by deposition of Pd nanoparticles

Pd nanoparticles can cover the defects of carbon nanotubes by a chemical reduction, which results in an increased carrier transport, then a high thermoelectric figure-of-merit, ZT = 0.3, in the sheets of the defect-repaired carbon nanotubes.

Experimental study on the effect of graphene on the thermal conductivity of natural rubber latex

Graphene is a new type of carbon material with excellent performance. It not only has good electrical, mechanical and thermal properties, but also can be used as a filler of natural latex materials to optimize the thermal conductivity of natural latex materials. Therefore, graphene is widely used in aviation, automobile, machinery and other fields. In order to study the influence of the coordination ratio of graphene and rubber materials on the thermal conductivity, the natural rubber latex was first diluted and dissolved with volatile organic solvent toluene; then 0g, 0.5g, 1g, 1.5g, 2g, and graphene were respectively mixed into 20g natural rubber latex to prepare 6 thin samples (type I, type II, type III, type IV, type V, type VI). Finally, the thermal conductivity of 6 samples was measured by fla laser thermal conductivity instrument. The results showed that with the increase of graphene dosage, the thermal conductivity of natural rubber latex sheet increased significantly; when the ratio of graphene dosage to natural rubber latex was about 1:10, the rate of improving thermal conductivity of natural rubber latex decreased.

Materials Requirements of High-Speed and Low-Power Spin-Orbit-Torque Magnetic Random-Access Memory

As spin-orbit-torque magnetic random-access memory (SOT-MRAM) is gathering great interest as the next-generation low-power and high-speed on-chip cache memory applications, it is critical to analyze the magnetic tunnel junction (MTJ) properties needed to achieve sub-ns, and ~fJ write operation when integrated with CMOS access transistors. In this paper, a 2T-1MTJ cell-level modeling framework for in-plane type Y SOT-MRAM suggests that high spin Hall conductivity and moderate SOT material sheet resistance are preferred. We benchmark write energy and speed performances of type Y SOT cells based on various SOT materials experimentally reported in the literature, including heavy metals, topological insulators and semimetals. We then carry out detailed benchmarking of SOT material Pt, beta-W, and BixSe(1-x) with different thickness and resistivity. We further discuss how our 2T-1MTJ model can be expanded to analyze other variations of SOT-MRAM, including perpendicular (type Z) and type X SOT-MRAM, two-terminal SOT-MRAM, as well as spin-transfer-torque (STT) and voltage-controlled magnetic anisotropy (VCMA)-assisted SOT-MRAM. This work will provide essential guidelines for SOT-MRAM materials, devices, and circuits research in the future.

Enhancing the cycling stability of all-solid-state lithium-ion batteries assembled with Li1.3Al0.3Ti1.7(PO4)3 solid electrolytes prepared from precursor solutions with appropriate pH values

NASICON-type solid electrolyte powders Li1.3Al0.3Ti1.7(PO4)3 (LATP) are synthesized by spray-drying and assisted sintering processes. The effects of different pH values of the spray-dried precursor solution on the crystallinity, morphology, ionic conductivity, compaction density and cycling stability of the LATP solid electrolyte sheets are investigated. The LATP-6.0 solid electrolyte sheets present the most perfect microstructure with a compaction density of 2.968 g cm−1 and the highest ionic conductivity of 1.182 E−4 S cm−1 with an activation energy of 0.273 eV at room temperature when the pH value of the precursor solution is adjusted to 6.0. Additionally, the assembled LiCoO2/LATP-6.0/Li all-solid-state coin cell delivers commendable cycling stability with a high discharge specific capacity of 150.5 mAh g−1 at 0.1 C after five activation cycles and retains a specific capacity retention rate of 94.28% after 300 cycles with various current densities at room temperature. Moreover, the LATP-6.0 solid electrolyte sheets maintain an intact morphology and uniformly-distributed elements composition after cycling. Based on these excellent results, the use of the LATP-6.0 sheets as solid electrolytes in high-performance all-solid-state lithium-ion batteries is a promising strategy.

Investigation of Piezoelectricity and Resistivity of Surface Modified Barium Titanate Nanocomposites.

Polymer-ceramic nanocomposite piezoelectric and dielectric films are of interest because of their possible application to advanced embedded energy storage devices for printed wired electrical boards. The incompatibility of the two constituent materials; hydrophilic ceramic filler, and hydrophobic epoxy limit the filler concentration, and thus, their piezoelectric properties. This work aims to understand the role of surfactant concentration in establishing meaningful interfacial layers between the epoxy and ceramic filler particles by observing particle surface morphology, piezoelectric strain coefficients, and resistivity spectra. A comprehensive study of nanocomposites, comprising non-treated and surface treated barium titanate (BTO), embedded within an epoxy matrix, was performed. The surface treatments were performed with two types of coupling agents: Ethanol and 3-glycidyloxypropyltrimethoxysilan. The observations of particle agglomeration, piezoelectric strain coefficients, and resistivity were compared, where the most ideal properties were found for concentrations of 0.02 and 0.025. This work demonstrates that the interfacial core-shell processing layer concentration influences the macroscopic properties of nanocomposites, and the opportunities for tuning interfacial layers for desirable characteristics of specific applications.

Influence of Coulomb interaction effect on the electrical transport for few-layered PtSe2 films

The Coulomb effect is a particularly significant topic in quasi-two-dimensional systems. Here, we carried out comprehensive measurements of electrical transport properties of fewer-layer PtSe2 films with and without antidot arrays. For as-grown PtSe2 films, the sheet conductance σ□ varies linearly with the logarithm of temperature at low temperature, which can be well described by the Altshuler and Aronov electron-electron interaction (EEI) effect, and then the result was further quantitatively confirmed by the ratios of a relative change of the Hall coefficient ΔRH/RH to that of sheet resistance ΔR□/R□. While after milling of antidot arrays the PtSe2 film possesses inhomogeneous structure, it still presents metallic transport behavior. The overall σ□ and RH characteristics can be explained by the current EEI theories in granular metals. Our results not only reveal the fundamental physics of PtSe2 films, but also provide powerful experimental evidence for the presence of the Coulomb EEI effect in the family of transition metal dichalcogenides. This work presents the subtle change of charge transport properties by introducing antidot arrays, which may be of benefit in improving sensitivity and stability of nanoscale electronic devices.

Novel Bi2WO6 loaded N-biochar composites with enhanced photocatalytic degradation of rhodamine B and Cr(VI)

In this work we report the production of Bi2WO6 loaded N-biochar composites (BW/N-B) for the removal of rhodamine-B and the reduction of Cr(VI) in water. Biochar was treated with urea to produce a N-modified biochar (N-Biochar), with great conductivity and special 2D sheet platform structure. Materials with different ratios of biochar and urea were produced. These materials were used as platform for supporting Bi2WO6. The characteristics of the as-prepared composites were investigated in detail by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectra (FT-IR), UV–vis diffuse reflectance spectra (UV-DRS), Photoluminescence spectra (PL), Electrochemical Impedance Spectroscopy (EIS) and Mott-Schottky curves. After loading N-Biochar, the band gaps of the as-prepared composites were narrower than those of Bi2WO6, which could improve separation and migration of photogenerated electron-hole pairs of BW/B-N under visible-light excitation, enhancing photocatalytic activity. BW/N1-B (ratio of urea to biochar 2:1 and 1 g/L) exhibited excellent photocatalytic activity for the degradation of 10 mg/L Rhodamine B (RhB) (99.1 %, 45 min) and reduction of Cr(VI) (96.7 %, 30 min) under visible-light irradiation. The results will provide a novel theoretical foundation on the application of biochar for photocatalysis and environmental remediation.

Graphene-Amplified Photoelectric Response of CdS Nanoparticles for Cu2+ Sensor.

Graphene/CdS composites were synthesized through the direct deposition of CdS nanoparticles on graphene sheets. The high conductivity of graphene sheets and the intimate heterointerfacial connection between graphene sheets and CdS nanoparticles provided prominent advantages for enhancing light absorption and facilitating the transfer of photogenerated carriers from CdS nanoparticles, thus leading to an effectively separation of electron-hole pairs and consequently an improvement in photocurrent intensity. A highly sensitive and selective photoelectrochemical sensor for detecting copper ions (Cu2+) was developed based on the interaction between Cu2+ and CdS by forming CuxS-coated CdS nanoparticles, which serves as the recombination centers, impedes the transfer of electron from the conduction band of CdS to graphene sheets, and consequently leads to a decrease in photocurrent intensity. The sheets not only effectively transferred the photogenerated electrons deriving from CdS nanoparticles but also resulted in an enhancement in photocurrent intensity in the presence of various metal ions except Cu2+. The sheets amplified the photoelectric response of CdS semiconductor for Cu2+ sensing, in which the photocurrent intensity decreased dramatically.

Coat-and-print patterning of silver nanowires for flexible and transparent electronics

Silver nanowires (Ag NWs) possess excellent optoelectronic properties, which have led to many technology-focused applications of transparent and flexible electronics. Many of these applications require patterning of Ag NWs into desired shapes, for which mask-based and printing-based techniques have been developed and widely used. However, there are still several limitations associated to these techniques. These limitations, such as complicated patterning procedures, limited patterning area, and compromised optical transparency, hamper the efficient fabrication of high-performance Ag NW patterns. Here, we propose a coat-and-print approach for effectively patterning Ag NWs. We printed a polymer-based ink on the spin-coated Ag NW films. The ink acts as a protective layer to help remove excess Ag NWs from the substrate and then dissolves itself into an organic solvent. In this way, we can take advantage of both coating-based techniques (lead to Ag NWs with high transparency) and printing-based techniques (efficiently pattern diverse shapes). The resultant Ag NW patterns exhibit comparable conductivity (sheet resistance: 7.1 to 30 Ohm/sq) and transparency (transmittance: 84 to 95% at λ = 550 nm) to those made by conventional coating methods. In addition, the patterned Ag NWs exhibit robust mechanical stability and reliability, surviving extensive bending and peeling tests. Due to higher conductivity, efficient patterning ability and inherent transparency, this material system and application method is highly suitable for transparent and flexible electronics. As a proof of concept, this research demonstrates a wide-band antenna, operating in the mm-wave range that includes the 5G communication band. The proposed antenna exhibits a wide bandwidth of 26 GHz (from 17.9 GHz to 44 GHz), robust return loss under 1000 cyclic bending (bending radius of 3.5 mm), and decent transparency over the entire visible wavelength (86.8% transmittance at λ = 550 nm). This work’s promising results indicate that this method can be adapted for roll-to-roll manufacturing to efficiently produce patterned and optically transparent devices.

Constructing Mono-/Di-/Tri-Types of Active Sites in MoS2 Film toward Understanding Their Electrocatalytic Activity for the Hydrogen Evolution

The availability and catalytic activity of the cost-efficient electrocatalysts are the dominant factors for the hydrogen evolution reaction (HER) performance in the renewable hydrogen economy. Extensive efforts have been devoted to maximize the amount of various active sites in non-noble-metal electrocatalysts for HER. This work reported a physically sputtering strategy to construct porous and ordered 2H-MoS2 films with mono-/di-/tri-types of active sites via controlling the film thickness (from ∼15 to 3050 nm) in the energetic plasma. As the pure (2H-) MoS2 for HER electrocatalyst, the as-fabricated 3050 nm additive-free columnar film electrode shows a stable electrochemical activity for HER (an overpotential of 204 mV at a current density of −10 mA/cm2). Interestingly, the MoS2 film with controllable thickness can serve as an innovative platform to study the electrocatalytic activity of the customized different active sites (the exposed active edge of sheets (eE), stepped-termination surfaces (sS), and terrace on the basal planes (tB)) and the dependence of electrocatalytic efficiency of the vertically aligned MoS2 eE active sites on their distance to the current collector. The results first revealed that the tB active sites possessed almost the same electrocatalytic activity as that of the eE active sites but higher than the sS active sites. The electrocatalytic efficiency of the eE active sites decreased as their distances to the current collector were gradually increasing, due to the limited conductivity of the semiconductive 2H-MoS2 sheets. This work proposes and evaluates a facile strategy for replying to the question of how to investigate the electrocatalytic activities of various active sites in the electrocatalysts.

Polymer/magnesia nanofiber composite sheets with anisotropic high thermal conductivity

The performance of an electronic product depends on how efficiently it can dissipate the heat of its parts. As a result, intensive ongoing research seeks to improve the thermal conductivity of polymeric materials. In this study, we investigate magnesia nanofibers as thermal conductive filler in the resin and compared them to conventional spherical filler. Magnesia nanofiber mats were fabricated by electrospinning a solution of polyvinyl alcohol and magnesium ethoxide mixtures; they were then impregnated with resins to obtain a composite sheet. We assessed the thermal conductivity of the composite sheet. The resin sheet with aligned magnesia nanofibers content (49 vol%) had high thermal conductivity (12.9 W/mK) in the direction parallel to the aligned magnesia nanofibers. The conductivity increased in proportion to magnesia nanofiber content. In addition, the magnesia nanofiber composite sheet showed anisotropic thermal conductivity derived from the fiber direction and had electrical insulation (7.7 × 1012 Ω/□), and flexibility. These electrically insulating sheets with anisotropy in thermal conductivity would be useful in designing effective heat removal paths in electronic devices.

Investigation on Strength, Ductility and Electrical Conductivity of Cu-4Ag Alloy Prepared by Cryorolling and Subsequent Annealing Process

Cu-Ag alloy is widely used as conductive material for high-field pulsed magnets in electrical industry. The cryorolling technique is considered as the most applicable severe plastic deformation technique. Therefore, in this study, cryorolling and subsequent annealing process were used to prepare Cu-4Ag (in wt.%) alloy sheets. The strength, ductility and electrical conductivity of Cu-4Ag alloy sheets were investigated. Microstructure of Cu-4Ag alloy was also studied by OM, SEM, XRD and TEM. As a result, the cryorolling specimens after annealing at temperature of 300 °C display a good combination of tensile strength of 652.2 ± 6.0 MPa, moderate elongation of 12.5 ± 0.7% and electrical conductivity of 80.6 ± 0.2% IACS. This is due to the presence of dislocations, dislocation cells, nanograins and nanotwins in the non-recrystallized regions and fine nanoscaled silver precipitates. Besides, a good ductility is achieved in this condition due to its desirable ductile fracture characteristics.

Effect of dopant on the conductivity and stability of three different cotton fabrics impregnated with PEDOT:PSS

This study has investigated the electrical conductivity (sheet resistance) and morphological properties of dental cotton, textile cotton and gauze cotton after drop casting each type with mixtures of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as primary dopant and dimethylsulfoxide as secondary dopant to further enhance conductivity. These cottons were chosen because they are representative of the wide range of cottons available in the marketplace. Results show that the dental cotton with 96.82 wt% PEDOT:PSS had a minimum sheet resistance of 0.0615 Ω/□ by comparison with the gauze and textile cottons which showed sheet resistances of 0.5061 Ω/□ (64.79 wt% PEDOT:PSS) and 1.2159 Ω/□ (37.20 wt% PEDOT:PSS) respectively. Further, all sheet resistances were found to be stable over a period of approximately 1 month. The sheet resistances of the conductive cottons were also investigated as a function of temperature in the range from 30 to 100 °C.

Annealing induced a well-ordered single crystal \u03b4-MnO2 and its electrochemical performance in zinc-ion battery

Herein, the formation and electrochemical performance of a novel binder-free turbostratic stacked/ well-ordered stacked δ-MnO2-carbon fiber composite cathodes in deep eutectic solvent (DES) based zinc-ion battery (ZIB) is reported. Results of morphological, elemental, and structural analyses revealed directly grown and interconnected δ-MnO2 crumpled nanosheets on a carbon fiber substrate. Moreover, an improvement via a simple annealing strategy in the stacking, surface area and conductivity of the δ-MnO2 sheets was observed. Annealing induces the rearrangement of δ-MnO2 sheets resulting in the transformation from turbostratic stacking to a well-ordered stacking of {delta }-MnO2 sheets, as indicated by the selected area electron diffraction (SAED) hexagonal single crystal pattern. Besides, the formation of the well-ordered stacking of {delta }-MnO2 sheets exhibited improved electrochemical performance and cyclability, as cathode material for ZIB. The novel strategy described in this study is an essential step for the development of binder-free δ-MnO2-C fiber composite with a well-ordered stacking of δ-MnO2 sheets. This study also demonstrated comparable electrochemical performance between the turbostratic {delta }-MnO2 sheets and the well-ordered stacked δ-MnO2 sheets.

Anomalous electron inelastic scattering rate probed via superconducting fluctuation in epitaxial NbN thin films

We investigated transport properties in superconducting NbN thin films for various values of the normal state sheet conductance σN at temperatures above the superconducting transition temperature Tc. The magnetic field dependence of the magnetoconductance Δσ(T, H) data was primarily analyzed using the theoretical expression given by the sum of three contributions due to the Aslamazov–Larkin ΔσAL(T, H, D) and Maki–Thompson ΔσMT(T, H, D, τin) superconducting fluctuations terms, and the electron localization ΔσL(T, H, Dτin) term, where D is the diffusion constant and τin(T) is the electron inelastic scattering time. It was determined that (1) the Δσ(T, H) data are well explained by the theory for wide temperature and magnetic field ranges, regarding τin(T) and the temperature independent D as fitting parameters, and (2) the rate 1/τin(T) at temperatures near Tc shows anomalous decreases with a V-shape from the values based on the theory. This theory indicates a gradual temperature dependence with a U-shape, given by the sum of three dominant terms 1/τfluc(T), 1/τe−e(T) and 1/τe−ph(T), where these terms correspond to superconducting fluctuation, electron–electron scattering and electron–phonon scattering mechanisms. The discrepancy between experimental data and theory suggests the existence of an additional quantum contribution to the rate 1/τin(T), such as that due to the correction of the density of state.

Quantifying the effects of hyperthermal atomic oxygen and thermal fatigue environments on carbon nanotube sheets for space-based applications

The effects of atomic oxygen and thermal fatigue on two different types of carbon nanotube sheets were studied. One set was treated with nitric acid, while the other set was left untreated. Monotonic tensile tests were performed before and after exposure to determine the effects of either exposure type on the sheets’ mechanical properties. Electrical conductivity and electromagnetic interference measurements were recorded to determine the effects of AO-exposure and thermal cycling on the sheets’ electrical properties. Neither exposure type affected the sheets’ specific strengths. Both exposure types increased the sheets’ specific stiffnesses and decreased the sheets’ strains at failure. The electrical conductivity of both sheets decreased due to the different exposure types, while the EMI shielding effectiveness was unaffected. Scanning electron microscopy was used to observe any changes in the sheets’ surface morphologies, while energy-dispersive X-ray spectroscopy was used to determine the effects of AO on the sheets’ chemical makeup.

Tunable Array Antenna with CRLH Feeding Network Based on Graphene

This paper introduces a novel design of compact tunable monopole antenna array, employing composite right/left handed (CRLH) feeding network. The feeding network configuration is coplanar waveguide (CPW). A graphene sheet is placed beneath the CRLH cell to achieve the tunability behavior in the antenna design. The antenna array configuration achieves the tunability function with an accepted gain. The surface conductivity of the graphene sheet is tuned by changing the applied DC bias voltage. The DC voltage changes the chemical potential of the graphene sheet. The antenna array is tuned from 2.5–2.46, 2.43, and 2.42 GHz when the chemical potential of graphene is changed from 0.0, 0.15, and 0.2 eV, respectively. The array antenna has a reasonable gain of 5.34 dB without placing the graphene sheet. By placing the graphene and changing the chemical potential, the array gain values become 4.42, 3.82, and 3.74 dB at the specified chemical potential. The radiation properties of the array are studied at the desired resonant frequency. The proposed design can be fabricated by using the transparent transfer process. All the presented designs are verified using the electromagnetic solver CST Studio.