Additional Conduction Paths Research Articles

Phase formation and electrical properties of reactively sputtered Fe1−x O thin films

Wüstite, Fe1−x O, is a crucial phase for the transition to CO2-free steel manufacturing as well as promising for electrochemical applications such as water splitting and ammonia synthesis. To study the effect of interfaces in these applications, thin-film model systems with defined interfaces are ideal. Previous studies lack a description of the growth mechanism to obtain Fe1−x O thin films. Here, we investigate the phase formation of metastable Fe1−x O during reactive magnetron sputtering while systematically varying the O2/Ar flow ratio from 1.8% to 7.2% and the pressure–distance product between 3.5 and 7.2 Pa cm. If bulk diffusion is minimized, thin films containing 96 vol.% wüstite and 4 vol.% Fe as impurity phase were achieved. Therefore, the wüstite phase formation appears to be surface diffusion dominated. To reveal the influence of impurity phases in wüstite on the electrical resistivity, systematic electrical resistivity measurements while cooling in situ were performed for the first time. The electrical resistivity was lower than that of single crystals of the respective iron oxides. This is attributed to the formation of Fe-rich layers at the substrate-film interface, which serve as additional conduction paths.

Materials and Design Approaches for a Fully Bioresorbable, Electrically Conductive and Mechanically Compliant Cardiac Patch Technology.

Myocardial infarction (MI) is one of the leading causes of death and disability. Recently developed cardiac patches provide mechanical support and additional conductive paths to promote electrical signal propagation in the MI area to synchronize cardiac excitation and contraction. Cardiac patches based on conductive polymers offer attractive features; however, the modest levels of elasticity and high impedance interfaces limit their mechanical and electrical performance. These structures also operate as permanent implants, even in cases where their utility is limited to the healing period of tissue damaged by the MI. The work presented here introduces a highly conductive cardiac patch that combines bioresorbable metals and polymers together in a hybrid material structure configured in a thin serpentine geometry that yields elastic mechanical properties. Finite element analysis guides optimized choices of layouts in these systems. Regular and synchronous contraction of human induced pluripotent stem cell-derived cardiomyocytes on the cardiac patch and ex vivo studies offer insights into the essential properties and the bio-interface. These results provide additional options in the design of cardiac patches to treat MI and other cardiac disorders.

Nitrogen-Oxyanion-Doped HfO2 Resistive Random-Access Memory With Chemically Enhanced Forming

The high forming voltage of resistive random-access memory (RRAM) is one of the key bottlenecks for its integration in advanced silicon technology nodes. Here a nitrogen-oxyanion-doped (N-doped) hafnium oxide (HfO2) RRAM with overall improvement on forming voltage, on/off ratio and endurance is demonstrated. The critical electric field of N-doped RRAM for forming is 40% less than that of undoped RRAM. Therefore, a thicker resistive switching layer (RSL) can be used to obtain the same forming voltage, which benefits the on/off ratio and endurance performance. The N-doped RRAM achieves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times $ </tex-math></inline-formula> improvement in on/off ratio and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10\times $ </tex-math></inline-formula> improvement in endurance at the forming voltage of 2 V, a value applicable for integration with advanced silicon technology node. We propose the hypothesis that the nitrites ((NO2)−) in the RSL of N-doped devices promote forming through introducing extra chemical process as well as additional conductive paths. Physical characterization and first-principles calculations are further carried out to validate our hypothesis.

Electrochemical Impedance Spectroscropy Study on the Behavior of Reinforced Concrete Elements under Loading

Concrete is a material of porous nature that, when humidified, becomes an ionic conductor whose apparent conductivity depends on the ionic load (typically based on OH−, Ca2+, Na+, and K+) and the amount of available free water. Under conditions of partial pore-saturation, the amount of free water can be modulated by an external load, which leads to observable changes in electrical properties such as conductivity and capacitance. Moreover, metallic reinforcements, either as bars or fibers, represent an additional parallel conduction path but of an electronic nature in this case. The free water develops a double-layer capacitance structure at the metallic interfaces, with associated charge-transfer resistance, representing an additional contribution to the capacitive behavior that can be modulated with an external load. The dependence that the electrical and/or ionic conducting properties of concrete and reinforced concrete elements have on the available free water makes them suitable for transductors in various sensing and self-sensing applications discussed in the text.

Crystal Structures and Conduction Paths of Sc-Doped CaTiO3 Fast Oxide-Ion Conductors with Orthorhombic Symmetry

The crystal structures and electron density distributions (EDDs) of Ca-deficient Sc-doped CaTiO3 fast oxide-ion conductors, Ca0.97(Ti0.97Sc0.03)O3-δ (CTS3) and Ca0.96(Ti0.9Sc0.1)O3-δ (CTS10), were investigated in the temperature range of 298-1173 K in N2 to analyze the effect of composition on the perovskite structure and oxide-ion transport mechanism. CTS3 and CTS10 exhibited orthorhombic Pnma symmetry in temperature ranges of 298-1173 K and 973-1173 K, respectively, with CTS10 exhibiting lower symmetry and reduction in oxide-ion conductivity below 973 K. The EDDs of CTS3 and CTS10 at 1173 K indicated unique chemical bonds and conduction paths. CTS3 and CTS10 showed covalent bonds between (Ti,Sc) and O1 (or O2) sites. CTS3, with a lower oxide-ion conductivity than that of CTS10, exhibited pseudo-one-dimensional (1D) zig-zag curved conduction paths for oxide-ions along the a-axis, unlike previously reported curved migration paths along the b-axis in CaTiO3, and chemical bonds between Ca and O1 sites, indicating oxide-ion conduction suppression. In CTS10, additional conduction paths were observed along the a-axis, forming three-dimensional (3D) zig-zag curved conduction paths in the ac-plane and along the b-axis, with the weakening of the chemical bonds between the Ca and O1 sites. The oxide-ion conductivity and mobile oxide-ion concentration of CTS10 were 3.6 and 2.0 times those of CTS3, respectively, at 1173 K; the higher oxide-ion conductivity of CTS10 could be attributed to an increase in the mobile oxide-ion concentration and mobility with a 1D to 3D change in the conduction paths and a weakening of chemical bonds between the Ca and O1 sites.

Improving the Performance of Lithium‐Ion Batteries Using a Two‐Layer, Hard Carbon‐Containing Silicon Anode for Use in High‐Energy Electrodes

Lithium‐ion battery cells with high‐energy density and good fast charging properties are subject of current research. One approach to achieve high‐energy densities is the use of higher mass loadings. The challenges of these so called “thick” electrodes are transport limitations: lithium ions cannot reach all layers of the electrode, which results in a drop of performance. Possible concepts to overcome these limitations are the use of different active materials (silicon oxide, graphite, and hard carbon (HC)), and a two‐layer coating of the anode to create a defined pore network, which reduces the ionic resistance and ensure better fast charging capability even at higher mass loadings (8 mAh cm−2). It could be demonstrated that by using a two‐layered anode with HC in the upper layer, the electrical conductivity could be increased by a factor of 10 compared to the reference anode. Furthermore, the interporous HC leads to a capacity retention increase up to 20% with no loss of capacity at moderate C‐rates and a low electrode density. This can be explained by the low tortuosity that results in additional conductive paths for the ions through the coating, reduces the ionic resistance, and ultimately enables faster lithiation of the anode.

UV-A to UV-B electroluminescence of core-shell GaN/AlGaN wire heterostructures

Core-shell GaN/AlGaN multiple quantum wells (MQWs) embedded in a p–n junction are integrated on the upper part of GaN microwires grown by silane-assisted metal organic vapor phase epitaxy. Dispersed wires are then contacted by electron beam induced deposition for fabrication of single wire UV-LED devices. Rectifying diode-like behavior is first demonstrated for both GaN and GaN/AlGaN p-n junctions without a MQW active region. A weak leakage current in the GaN/AlGaN core-shell heterostructure is attributed to an additional conduction path along wire sidewalls. Electroluminescence at 340 nm in UV-A is demonstrated using a GaN (2.6 nm)/Al0.3Ga0.7N (3 nm) heterostructure embedded in a GaN/Al0.3Ga0.7N p–n junction. This value is even decreased to 310 nm by reducing the well thickness to 0.9 nm and increasing the Al-content of barriers (up to 60%) integrated in the GaN/Al0.3Ga0.7N p–n junction. This work demonstrates UV-B emission based on single wire core-shell UV-LEDs.

Fabrication and electrochemical behavior of flexible composite solid electrolyte for bipolar solid-state lithium batteries

To improve the performance of solid-state lithium batteries (SSLB), solid-state succinonitrile (SCN) is incorporated into a composite solid electrolyte (CSE) comprising Al-doped LLZO (Li6.4Al0.2La3Zr2O12), poly(ethylene oxide) (PEO), and lithium salts, thereby conferring flexibility to the CSE. SCN acts as a solid-state plasticizer that increased the ion conduction and interfacial control between the materials. The flexible CSE sheet exhibits a high ionic conductivity of 2.5 × 10−4 S cm−1 at 40 °C and a wide potential window of ∼5.2 V vs. Li/Li+. The solid SCN provides new synergistic properties such as an additional ion conduction path and suppresses PEO oxidation. When the CSE with 7 wt% SCN is utilized as the cathode layer and solid electrolyte layer in SSLBs, instead of the liquid electrolyte, a discharge capacity of approximately 130 mAh g−1 is realized at 45 °C and 0.1C, whilst a capacity retention rate of 90% and a coulombic efficiency of 99% are obtained over 100 cycles. A 3-stack bipolar cell is fabricated to evaluate the mechanical properties of the flexible CSE sheet, demonstrating stable cycle performance over 50 cycles without any short circuiting or leakage current.

High-Sensitivity Flexible Piezoresistive Pressure Sensor Using PDMS/MWNTS Nanocomposite Membrane Reinforced with Isopropanol for Pulse Detection

Flexible pressure sensors with high sensitivity and good linearity are in high demand to meet the long-term and accurate detection requirements for pulse detection. In this study, we propose a composite membrane pressure sensor using polydimethylsiloxane (PDMS) and multiwalled carbon nanotubes (MWNTS) reinforced with isopropanol prepared by solution blending and a self-made 3D-printed mold. The device doped with isopropanol had a higher sensitivity and linearity owning to the construction of additional conductive paths. The optimal conditions for realizing a high-performance pressure sensor are a multiwalled carbon nanotube mass ratio of 7% and a composite membrane thickness of 490 μm. The membrane achieves a high linear sensitivity of −57.07 kΩ∙kPa−1 and a linear fitting correlation coefficient of 98.78% in the 0.13~5.2 kPa pressure range corresponding to pulse detection. Clearly, this device has great potential for application in pulse detection.

Silicon-Controlled Rectifier Embedded Diode for 7 nm FinFET Process Electrostatic Discharge Protection.

A new silicon-controlled rectifier embedded diode (SCR-D) for 7 nm bulk FinFET process electrostatic discharge (ESD) protection applications is proposed. The transmission line pulse (TLP) results show that the proposed device has a low turn-on voltage of 1.77 V. Compared with conventional SCR and diode string, the proposed SCR-D has an additional conduction path constituting by two additional inherent diodes, which results in a 1.8-to-2.2-times current surge capability as compared with the simple diode string and conventional SCR with the same size. The results show that the proposed device meets the 7 nm FinFET process ESD design window and has already been applied in actual circuits.

Bamboo-inspired mechanically flexible and electrically conductive polydimethylsiloxane foam materials with designed hierarchical pore structures for ultra-sensitive and reliable piezoresistive pressure sensor

Flexible pressure-sensing materials with high sensitivity and good mechanical reliability are highly required to meet the long-time and accurate detecting requirement for wide-stress motions. Herein, we describe a bamboo-inspired design approach to fabricate mechanically flexible and electrically conductive carbon nanofiber/polydimethylsiloxane foam composites with unique and designed hierarchical pore structures. The optimized multi-level pore structures not only show outstanding mechanical flexibility and reliability, but also possess high sensitivity at a relatively wide stress range. Typically, the hierarchical pore structures (i.e. large-size pore structure of several hundreds of micrometers, hollow structure of several micrometers, micro-/nano-irregular pores on the hollow skeleton) are sensitive to tiny pressures to construct additional conductive paths and thus achieve high sensitivity of ~0.6 kPa −1 at 0–1 kPa. Further, such hierarchical structures easily form highly interconnected conductive network induced by the serious deformation of large pores and sinking of hollow-structure, thus providing the extremely sensitive sensing behavior for a relatively large pressure level as large as 20 kPa. Moreover, the optimized sensor presents good repeatability and excellent reliability after 10000 compressive cycles, which can satisfactorily meet the critical requirements of subtle vital signs, human motions monitoring and so on. Clearly, this work offers a route to design and development of the multifunctional advanced pressure-sensor for potential artificial intelligence application. Bamboo-inspired hierarchical pore structures of conductive CNF/PDMS foam composites were constructed to fabricate a flexible pressure sensor with excellent sensitivity and cyclic mechanical reliability. Such hierarchical pore structures show accurate detection of subtle physiological signs and human motions, together with sensitivity to temperature variation and volatile organic compound, showing promising applications in multifunctional wearable smart devices. • Bamboo-inspired hierarchical pore structures of conductive polymer composites were constructed. • The foam composites had excellent piezoresistivity with high sensitivity and good cyclic reliability. • The related electrical resistance response behaviors and mechanisms were discussed and analyzed. • The as-prepared sensors showed good response for detecting physiological signs and body motion.

Synthesis and broadband dielectric-infrared spectroscopy of La1-xSrxMnO3@BaTiO3 nanocomposite

The study deals with design, structural and magnetic characterization, electric and magnetoelectric transport and broad-band dielectric spectroscopy of the all-perovskite core-shell composite nanoceramics of 0–3 connectivity, in which ∼50 nm cores of ferromagnetic La0.65Sr0.35MnO3 (LSMO) metal are embedded in ferroelectric BaTiO3 (BTO) shells of mean 13 nm thickness. The BTO spacers lead to significant barriers for itinerant carriers, at low temperatures being transmitted by tunnelling, but additional conduction paths are temperature activated by hopping across them. The dielectric, terahertz and infrared spectroscopy data of LSMO@BTO are modelled by effective medium approaches, which enables to explain the broad dielectric and AC conductivity dispersion including the giant low-frequency permittivity values. Temperature dependant terahertz transmission spectroscopy clearly indicates the ferroelectric transition in the nano-BTO shells in the same temperature range as in the bulk BTO.

Enhancing through-plane electrical conductivity by introducing Au microdots onto TiN coated metal bipolar plates of PEMFCs

Developing a high electrically conductive and corrosion-resistant coating on metal bipolar plate is of prime importance for its application in polymer electrolyte membrane fuel cells. To achieve it and further improve its through-plane conductivity, we herein prepared a composite coating by introducing Au microdots onto TiN coated stainless steel (Au/TiN/SS). Au dots provide additional conduction paths and thus Au/TiN/SS exhibits a remarkably lower interfacial contact resistance than that of TiN/SS after 200 h of test, suggesting that incorporation of Au dots into TiN provides an effective approach to achieving dual merits of high conductivity and corrosion resistance.

Flexibility of Fluorinated Graphene-Based Materials.

The resistivity of different films and structures containing fluorinated graphene (FG) flakes and chemical vapor deposition (CVD)-grown graphene of various fluorination degrees under tensile and compressive strains due to bending deformations was studied. Graphene and multilayer graphene films grown by means of the chemical vapor deposition (CVD) method were transferred onto the flexible substrate by laminating and were subjected to fluorination. They demonstrated a weak fluorination degree (F/C lower 20%). Compressive strains led to a strong (one-two orders of magnitude) decrease in the resistivity in both cases, which was most likely connected with the formation of additional conductive paths through fluorinated graphene. Tensile strain up to 3% caused by the bending of both types of CVD-grown FG led to a constant value of the resistivity or to an irreversible increase in the resistivity under repeated strain cycles. FG films created from the suspension of the fluorinated graphene with a fluorination degree of 20–25%, after the exclusion of design details of the used structures, demonstrated a stable resistivity at least up to 2–3% of tensile and compressive strain. The scale of resistance changes ΔR/R0 was found to be in the range of 14–28% with a different sign at the 10% tensile strain (bending radius 1 mm). In the case of the structures with the FG thin film printed on polyvinyl alcohol, a stable bipolar resistive switching was observed up to 6.5% of the tensile strain (bending radius was 2 mm). A further increase in strain (6.5–8%) leads to a decrease in ON/OFF current ratio from 5 down to 2 orders of magnitude. The current ratio decrease is connected with an increase under the tensile strain in distances between conductive agents (graphene islands and traps at the interface with polyvinyl alcohol) and thickness of fluorinated barriers within the active layer. The excellent performance of the crossbar memristor structures under tensile strain shows that the FG films and structures created from suspension are especially promising for flexible electronics.

Correlations between structural, magnetic and electronic transport properties of nano-sized (Sr,La)-(Fe,Mo) double perovskites

We report a study on the influence of microstructure on the magnetic and electronic properties of nanoscale Sr2-xLaxFeMoO6 materials. The temperature dependence of the saturation magnetization of the samples in the low temperature range follows the spin wave theory which is described by a T3/2 law. The analysis of the temperature dependence of the conductivity of the sample with x = 0 shows distinct mechanisms of spin-dependent tunneling and spin-independent hoping channels. Up on La substitution, additional metallic-type conduction paths appear which reduces the resistivity of the samples and also changes its temperature dependence behavior. Spin polarization as a function of temperature was obtained via fitting the MR curves recorded at different temperatures using the spin-dependent elastic tunneling model with correction for the spin-independent conductance. At a temperature 5 K, the spin polarizations of the samples are found to be roughly proportional to the net magnetic moment. Moreover, their values are considerably higher than those derived from theoretical calculations for the double perovskite lattices with the same antisite disorder levels which reveals an inhomogeneous distribution of the antisite defects in the samples. The decay rate of the spin polarization with increasing temperature is faster for the samples with a larger amount of antisite defects.

Improved thermal conductivity and dielectric properties of flexible PMIA composites with modified micro- and nano-sized hexagonal boron nitride

A series of flexible poly(m-phenylene isophthalamide) (PMIA)-based composites with different sizes and mass fractions of hexagonal boron nitride (hBN) were successfully manufactured for the first time via the casting technique. The effects of modified hBN particles on microstructure, mechanical properties, dielectric properties and thermal conductivities of fabricated composites were investigated. The results indicate that modified hBN particles manifest good compatibility with the PMIA matrix. The Young’s modulus and Theat-resistance index of PMIA-based composites are increased with increasing the mass fraction of hBN particles. Due to additional thermal conductive paths and networks formed by nano-sized hBN particles, the K-m/n-hBN-30 composite displays the thermal conductivity of 0.94 W·m-1·K-1, higher than that of the K-m-hBN-30 composite (0.86 W·m-1·K-1), and more than 4 times higher than that of neat PMIA. Moreover, the obtained PMIA-based composites also show low dielectric constant and ideal dielectric loss. Owing to the excellent comprehensive performance, hBN/PMIA composites present potential applications in the broad field of electronic materials.

4H-SiC trench MOSFET with splitting double-stacked shielded region

A Silicon Carbide(SiC) MOSFET with double–stacked shielded region beneath the trench bottom(DSS-MOS) is presented and investigated through Sentaurus TCAD simulations. The proposed structure introduces additional electron conduction path beneath the trench without degradation of shielding effect for the gate oxide. As a result, the DSS-MOS exhibits a higher figure of merit related to the breakdown voltage and specific ON-resistance (VBR2/RON) compared with that of trench MOSFET with L-shaped gate(LSG-MOS). Furthermore, owing to the strong p + shielding effect, the feedback capacitance and the gate-to-drain charge of the DSS-MOS are significantly reduced, thus leading to improved switching performance. We believe that the proposed DSS-MOS could provide an effective solution to improve gate oxide reliability and reduce switching losses for SiC power device operating in high-frequency applications.

Multi-functional interface tailoring for enhancing thermal conductivity, flame retardancy and dynamic mechanical property of epoxy/Al2O3 composites

Interfacial tailoring is always the key to preparing high-performance polymer-based thermal conductive composites (PTCs). Herein, we reported a multi-functional interface tailoring approach to simultaneously improve the thermal conductivity, flame retardancy, thermal and mechanical properties of PTCs, by forming a core-shell structured graphene oxide coating Al2O3 hybrid (Al2O3@HGO). Simultaneously a flame retardant bridging agent was introduced to improve the coating amount and flame retardant efficiency of the hybrid. The morphology analysis revealed the significant reinforcement of interfacial interaction of Al2O3 in epoxy (EP) by HGO coating. As a result, such the interfacial tailoring induced both the significant decrease in interfacial thermal resistance and the formation of additional thermal conductive paths by the graphene coating layer, resulting in the significant improvement in thermal conductivity of EP/Al2O3@HGO composites. The flame retardant parameters, peak heat release rate, total heat release and total smoke production, showed a 49.3%, 40.9% and 71.2% reduction, respectively, comparing to neat EP, which was ascribed to the strong interface with GO coating layer and the flame retardant bridging agent catalyzed charring to form an intact and compact char protective layer with Al2O3. Moreover, the strong interfacial interaction also restricted the segment movement, increasing the storage modulus and Tg.

Simultaneously improving the mechanical strength and electromagnetic interference shielding of carbon/carbon composites by electrophoretic deposition of SiC nanowires

Electrophoretic deposition of SiC nanowires in C/C composites reinforces the matrix and creates additional conduction paths in the matrix.

Humidity‐Tolerant Single‐Stranded DNA‐Functionalized Graphene Probe for Medical Applications of Exhaled Breath Analysis

Highly sensitive and selective chemiresistive sensors based on graphene functionalized by metals and metal oxides have attracted considerable attention in the fields of environmental monitoring and medical assessment because of their ultrasensitive gas detecting performance and cost‐effective fabrication. However, their operation, in terms of detection limit and reliability, is limited in traditional applications because of ambient humidity. Here, the enhanced sensitivity and selectivity of single‐stranded DNA‐functionalized graphene (ssDNA‐FG) sensors to NH3 and H2S vapors at high humidity are demonstrated and their sensing mechanism is suggested. It is found that depositing a layer of ssDNA molecules leads to effective modulation of carrier density in graphene, as a negative‐potential gating agent and the formation of an additional ion conduction path for proton hopping in the layer of hydronium ions (H3O+) at high humidity (&gt;80%). Considering that selectively responsive chemical vapors are biomarkers associated with human diseases, the obtained results strongly suggest that ssDNA‐FG sensors can be the key to developing a high‐performance exhaled breath analyzer for diagnosing halitosis and kidney disorder.