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High-performance flexible strain and pressure sensors are important components of the systems for human motion detection, human-machine interaction, soft robotics, electronic skin, etc., which are envisioned as the key technologies for applications in future human healthcare monitoring and artificial intelligence. In recent years, highly flexible and wearable strain/pressure sensors have been developed based on various materials/structures and transduction mechanisms. Piezoresistive three-dimensional (3D) monolithic conductive sponge, the resistance of which changes upon external pressure or stimuli, has emerged as a forefront material for flexible and wearable pressure sensor due to its excellent sensor performance, facile fabrication, and simple circuit integration. This review focuses on the rapid development of the piezoresistive pressure sensors based on 3D conductive sponges. Various piezoresistive conductive sponges are categorized into four different types and their material and structural characteristics are summarized. Methods for preparation of the 3D conductive sponges are reviewed, followed by examples of device performance and selected applications. The review concludes with a critical reflection of the current status and challenges. Prospects of the 3D conductive sponge for flexible and wearable pressure sensor are discussed.

The self‐potential (SP) method is expected to play an important role in the exploration of seafloor massive sulfide (SMS) resources. Since the redox potential changes with depth below the seafloor, SMS deposits are the source of an electrical (source) current density, generating in turn a recordable electrical field. This electrical field can be remotely measured at and above the seafloor. By integrating this electrical field, we obtained a so‐called SP profile or map. The electrical conductivity distribution of SMS deposits is an important ingredient in the inversion of these SP data in order to distinguish between causative primary sources (i.e., associated with the SMS deposits themselves) and secondary current sources associated with conductivity contrasts below the seafloor. Such ingredient is therefore necessary to properly localize SMS deposits and eliminating ghosts associated with high conductivity contrasts. The conductivity structure of the seafloor is however unknown in most SP surveys. This study presents the first joint interpretation of transient electromagnetic and SP surveys. The field data were acquired at the Trans‐Atlantic Geotraverse (TAG) hydrothermal mound. The conductivity structure of TAG mound was obtained by inverting transient electromagnetic data. This electrical conductivity distribution is then used to invert the SP data. The obtained (primary) source current distribution delineates the geometry of the SMS deposits. The deposits are located in the center of the mound as well as at its edges, in a way that is consistent with water column data. Combining the two geophysical methods improves our ability to better decipher the fine geometry of SMS deposits below the seafloor. Plain Language Summary: Seafloor massive sulfide (SMS) deposits contain abundant amounts of Cu, Zn, Au, and Ag, which are of growing economic interest for our civilization. In recent years, the exploration of SMS deposits has entered into a new era with the goal of better assess and characterize these resources. In this perspective, geophysical methods are in high demand to localize SMS deposits and obtain their three‐dimensional geometry. The self‐potential (SP) method provides an efficient non‐intrusive and cost‐effective approach to image SMS deposits. Previous surveys have documented the existence of recordable negative SP anomalies above the seafloor in association with SMS deposits. SP tomography can be used to assess the 3D geometry of SMS deposits. That said, the conductivity pattern below the seafloor is unknown in previous SP surveys while it is an important ingredient in the inversion of the SP data. Active source measurements like the transient electromagnetic (TEM) method can be used to obtain the electrical conductivity distribution below the seafloor. So, we propose to combine SP and TEM data to improve our ability to image SMS deposits. We apply the new methodology to a famous submarine hydrothermal field located in the Atlantic mid‐oceanic ridge Trans‐Atlantic Geotraverse and investigated in the past by various scientific teams. Our study demonstrates that the combination of the two methods has the ability to better image SMS deposits by eliminating source current ghosts associated with conductivity contrasts. Key Points: A joint self‐potential (SP) and transient electromagnetic survey has been performed at Trans‐Atlantic Geotraverse (TAG) hydrothermal field (Mid‐Atlantic Ridge)The transient electromagnetic method provides the electrical conductivity needed for SP tomographyThe inversion of the SP data reveals the distribution of the massive sulfide deposits at TAG [ABSTRACT FROM AUTHOR]

This paper investigated the effect of carbon nanotube (CNT) agglomeration on the electrical conductivity of CNT-polymer composites by experimental characterization and theoretical modeling. The present experimental results show that the acid treatment of CNTs has significantly alleviated the CNT agglomeration in CNT-polymer composites and improved the electrical conductivity of the composites compared with CNT-polymer composites made from the same pristine CNTs. The improvement by the acid treatment is further studied by a multiscale CNT percolation network model that considers the CNT agglomeration based on experimental observation. Numerical results are in good agreement with the experimental data. The smaller the size of CNT agglomerates is in the experiments, the closer the measured electrical conductivity of CNT-polymer composites is to its theoretical limit. The current study verifies that (i) the CNT agglomeration is the main cause that leads to a lower electrical conductivity of CNT-polymer composites than their theoretical limit, and (ii) the current multiscale percolation network model can quantitatively predict the electrical conductivity of CNT-polymer composites with CNT agglomeration. The comprehensiveness of the developed modeling approach enables an evaluation of results in conjunction with experimental data in future works. VC [ABSTRACT FROM AUTHOR]

Deep‐sea polymetallic sulfides associated with hydrothermal systems are considered a potential viable resource for base and precious metals. The Southwest Indian Ridge (SWIR, Indian Ocean) hosts active and inactive hydrothermal systems. Inactive hydrothermal fields are more abundant than active fields but are difficult to remotely characterize. We report a deep‐sea self‐potential investigation to locate inactive ore deposits at the Yuhuang hydrothermal field on the ultraslow‐spreading SWIR. A horizontal array of six nonpolarizing AgCl electrodes are attached to a deep‐towed transient electromagnetic system to record the electrical field at a height of 40 m above the seafloor. The observed electrical field strength near a previously recognized sulfide deposits (verified by drilling) reaches an amplitude of 0.5 mV/m. Negative self‐potential anomalies (~ −27 mV) were observed by integrating the measured electrical field. The high electrical conductivities (up to 12 S/m) of sulfide samples measured in the laboratory and the oxidized sulfides recovered from the surface of the deposit suggest that the self‐potential anomalies are due to sulfide mineralization and corrosion of the polymetallic sulfides. Inversion of the self‐potential data reveals a localized body with a thickness of ~65 m, which is interpreted as the Yuhuang ore deposit. Our field data demonstrate that the self‐potential method is a useful exploration method to identify and image seafloor massive sulfide deposits hosted in inactive hydrothermal fields at mid‐ocean ridges. Key Points: Seafloor sulfide deposits exhibit negative self‐potential anomaliesThe self‐potential mechanism results from redox processesExtend of sulfide body at depth is characterized using self‐potential tomography [ABSTRACT FROM AUTHOR]

This paper examines the effect of carbon nanotube (CNT) geometry upon the electrical properties of the corresponding functionalized nanocomposites. Specifically, Monte Carlo (MC) simulations are conducted to evaluate the effect of CNT length non-uniformity and waviness upon tunneling. Three aspects of the work are considered. The first is concerned with the application of periodic boundary condition that ensures periodic connectivity of the percolating paths via the use of an improved connective percolating network recognition scheme. The second is concerned with the determination of the electrical conductivity of the percolated system rather than the critical percolation threshold for varied CNT geometries using Weibull distribution to statistically account for the geometry variations. The third is concerned with the validation of our MC simulations. Our results reveal that (i) the CNT geometry, as determined by CNT length variability and waviness, plays a more dominant role in percolation threshold rather than tunneling barrier height and (ii) higher CNT loading beyond a critical percolation significantly influences the role of tunneling barrier height upon the electrical conductivity. [ABSTRACT FROM AUTHOR]

An explicit, analytical theory for the percolation threshold, percolation saturation, and effective conductivity of a two-component system involving randomly oriented ellipsoidal inclusions is proposed. The ellipsoids may take the shape of a needle, prolate or oblate spheroid, sphere, or disk. This theory is based upon consideration of Ponte Castaneda--Willis [P. Ponte Castaneda and J. R. Willis, J. Mech. Phys. Solids 43, 1919 (1995)] microstructure in conjunction with Hashin--Shtrikman [Z. Hashin and S. Shtrikman, J. Appl. Phys. 33, 3125 (1962)] upper bound. Two critical volume concentrations, c* and c**, that represent the respective percolation threshold at which the conductive network begins to develop, and the percolation saturation, are identified. During this very short range of concentration, the electrical conductivity of the composite is found to exhibit a very sharp increase, while over the entire range, the calcutilated conductivity exhibits the widely reported sigmoidal shape. Comparison with measurement on a multi-walled carbon nanotube/alumina composite indicates that the theory could capture the major features of the experimentally observed trends sufficiently well. [ABSTRACT FROM AUTHOR]

Ultrafine-grained Al-Mg-Si alloys with four different Mg/Si ratios (=0.75, 1.10, 1.48, and 1.94) were prepared by using extrusion and cold-drawing. The microstructural evolution during aging treatment was examined by using transmission electron microscopy. Hardness and electrical conductivity of the alloys were, respectively, measured before and after aging treatment. Experimental results showed that $$ \beta^{\prime\prime} $$ precipitates were dispersed within the grain interior in all the four aged alloys. Although the precipitate size was insensitive to the Mg/Si ratio, the precipitate number density as well as the inter-precipitate spacing was greatly dependent on the Mg/Si ratio. The optimized Mg/Si ratio within present work was 1.48, which led to the densest precipitation, and resulted in the highest hardness and simultaneously greatest conductivity. These findings are rationalized by considering the precipitation behaviors in the ultrafine-grained length scale and their effect on the hardness-conductivity relationship. A strengthening model was proposed for the ultrafine-grained Al-Mg-Si alloys, which accounted for the multiple contributions from grain size, dislocations, solid solution atoms, and precipitates to the hardness. The calculations were in good agreement with the experimental results. Similarly, the effect of multiple microstructural features on the electrical conductivity was also quantitatively described by adopting a model. The contribution of precipitation to both the hardness and conductivity is well demonstrated for the ultrafine-grained Al-Mg-Si alloys, which will be helpful for material design of advanced ultrafine-grained Al alloys with enhanced performance. [ABSTRACT FROM AUTHOR]

The Na doping effects on the high temperature thermoelectric properties of ( = 0, 0.05, 0.10, 0.15, 0.20 and 0.30) ceramics were investigated from 343 K to 973 K. When , the electrical resistivity of decreases with increasing Na doping amount due to the hole-doping effect, which exhibits metallic electrical conductivity behavior. While, at the temperature range of 480-830 K, the samples with exhibit semiconductor electrical conductivity behavior instead. The Seebeck coefficients are improved by Na doping at lower temperature, but they decrease slightly at higher temperature except for . Roughly, the thermal conductivity is depressed by the doping defects. As an overall result, the dimensionless figure of merit of reaches the maximum value of 0.3 K at 973 K, which is nearly twice the value of the undoped sample . [ABSTRACT FROM AUTHOR]

Fully relativistic first-principles calculations based on density functional theory are performed to study the spin-orbit-induced spin splitting in monolayer systems of the transition-metal dichalcogenides MoS2, MoSe2, WS2, and WSe2. All these systems are identified as direct-band-gap semiconductors. Giant spin splittings of 148-456 meV result from missing inversion symmetry. Full out-of-plane spin polarization is due to the two-dimensional nature of the electron motion and the potential gradient asymmetry. By suppression of the Dyakonov-Perel spin relaxation, spin lifetimes are expected to be very long. Because of the giant spin splittings, the studied materials have great potential in spintronics applications. [ABSTRACT FROM AUTHOR]

In this work the oxygen reduction reaction on Bi0.5Sr0.5FeO3-8 (BSF) and La0.5Sr0.5FeO3-8 (LSF) as cathodes for intermediate temperature solid oxide fuel cells (600-750°C) is compared in detail. Partial substitution of Sr in SrFeO3-δ with 50 mole % of Bi or La results in the distinct structural features which strongly impact its electrochemical characteristics due to the presence of a lone electron pair in Bi3+, which is not available in La3+ Cubic Structure for BSF favours higher ionic conductivity and enhanced formation of oxygen vacancies relative to rhombohedral structure for LSF. Large oxygen nonstoichiometry for BSF, nevertheless, leads to the dominance of Fe3+ and subsequent low electronic conductivity relative to LSF. It was found that upon cathodic polarization, the oxygen vacancies are created on LSF which helps reducing its interfacial resistance afterward, which is not the case for BSF. Overall, BSF demonstrates good electrochemical performance which can be further optimized by enhancing its electronic conductivity. [ABSTRACT FROM AUTHOR]

A theoretical investigation for the conductivity of single walled nanotube films is carried out with an effective medium model in the Terahertz region. The results are compared with the recent experiment and a decrease of the real conductivity with increasing frequency is predicted. Meanwhile, the off-diagonal components of the dielectric function of single-walled carbon nanotube films based on the magnetooptical effects are also shown. © 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of carbon nanotube (CNT) deformation on the electrical conductivity of CNT polymer composites at crossed nanotube junctions using a revised 3-dimensional CNT percolating network model. Two aspects of the work are considered. The first is concerned with the effect of CNT deformation on its intrinsic and contact resistances at CNT-CNT junctions. An analytical model based on electron ballistic tunneling theory and Landauer-Büttiker formula is proposed to describe the variation of CNT-CNT contact resistance at the CNT-CNT junction in terms of local deformation of CNT walls and CNT-CNT distance. In addition, a model exclusively based on experimental data to describe the change of CNT intrinsic resistance in terms of its cross-section deformation is adopted. The second is concerned with the relationship among the CNT-CNT distance, the angle between two adjacent CNTs, and the dimensions of local deformation of CNT walls and its impact on the corresponding intrinsic and contact resistance of CNTs near and at a CNT-CNT junction. Finally, Monte Carlo simulations are conducted to evaluate these effects on the electrical conductivity of nanocomposites for different CNT weight fractions. Our results reveal that the local deformation of CNT walls plays a significant role in the evaluation of electrical conductivity of CNT polymer composites. The intrinsic resistance in the deformed part of CNTs near a CNT-CNT junction increases much faster than the decrease of CNT-CNT contact resistance at the same junction when two CNTs are getting closer, resulting in a net increase of resistance at the junction. Numerical results show that the current model agrees with existing experimental data better than existing models without considering the effect of CNT deformation, which tends to overestimate the electrical conductivity of CNT polymer composites containing homogeneously dispersed percolating CNT network. [ABSTRACT FROM AUTHOR]

ZnO epitaxial films grown by pulsed laser deposition in an ambient of H2 or D2 exhibit qualitatively different electronic properties compared to films grown in vacuum or O2 or bulk single crystals annealed in H2. These include temperature-independent resistivities of ∼0.1 Ω cm, carrier (electron) concentrations in the 1018 cm-3 range, mobilities of 20–40 cm2/V s, and negligible (a few meV) activation energies for conduction. These transport properties are consistent with H (D) forming an ultrashallow donor or conduction band states not achievable by postgrowth annealing in H2. [ABSTRACT FROM AUTHOR]

Control of carrier transport in organic semiconductors by aluminum doping is realized in organic light-emitting devices (OLEDs) for which electroluminescence can sensitively reflect the status of carrier transport. It is found that an Al-doped layer with proper thickness (∼1–10 nm) may block hole transport completely and enhance electron transport to some extent regardless of its location in the organic carrier transport layers. Improvement in the efficiency of OLEDs with an aluminum cathode is achieved upon the introduction of a very thin (∼3 nm) Al-doped region near the light-emitting area. The current efficiency obtained with such Al-doped devices is about 30% higher than that with undoped devices. [ABSTRACT FROM AUTHOR]

In this paper, we examined the effect of electron tunneling upon the electrical conductivity of carbon nanotube (CNT) polymer nanocomposites. A CNT percolating network model was developed to account for the random distribution of the CNT network using Monte Carlo simulations, where the tunneling resistance between CNTs was established based on the electron transport theory. Our work shows several novel features that result from this tunneling resistance: (i) direct contact resistance is the result of one-dimensional electron ballistic tunneling between two adjacent CNTs, (ii) the nanoscale CNT-CNT contact resistance should be represented by the Landauer-Büttiker (L-B) formula, which accounts for both tunneling and direct contact resistances, and (iii) the difference in contact resistance between single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs) can be modeled by the channel number in the L-B model. The model predictions reveal that the contact resistance due to electron tunneling effects in nanocomposites with dispersed SWCNTs plays a more dominant role than those with MWCNTs. These results compare favorably with existing experimental data and demonstrate that the proposed model can properly estimate the electrical conductivity of nanocomposites containing homogeneously dispersed percolating CNT network. [ABSTRACT FROM AUTHOR]