Interfacial Electrical Conductivity Research Articles

Mechanical and Electrical Conductivity Properties of Graphene/Cu Interfaces: A Theoretical Insight.

For graphene/copper (Gr/Cu) composites, achieving high-quality interfaces between Gr and Cu (strong interfacial bonding strength and excellent electron transport performance) is crucial for enabling their widespread applications in electronic devices. This study employs first-principles calculations and the nonequilibrium Green's function method to systematically investigate the mechanical and electrical conductivity properties of Cu(111)/Gr/Cu(111) interfaces with various stacking sequences and different forms of Gr. For these interface systems, the binding energy, separation work, charge transfer, and electrical conductivity across the interface were obtained. The results show that the top-fcc interface exhibits superior interfacial properties, characterized by relatively high binding energy (-3.00 eV/C atom) and separation work (≥0.78 J/m2), a small interfacial distance (2.85 Å), and enhanced electron transport capacity (2.12 G0/nm2). A bilayer form of Gr significantly reduces electronic conductance across the Gr/Cu interface by nearly 2.46 orders of magnitude. Furthermore, point defects in Gr, especially single-vacancy defects, disrupt the traditional trade-offs between mechanical and electrical performance, simultaneously enhancing mechanical performance by 7.50-124.36% and electrical performance by 33.02%. Additionally, stress mechanisms have been proposed to further enhance the interfacial electrical conductivity of Gr/Cu composites. The present study provides a theoretical basis for exploring the engineering applications of Gr/Cu composite materials.

Engineering the PEM Water Electrolysis Anode for Better Interfacial Electrical Conductivity

In pursuing cost-effective green hydrogen production via proton exchange membrane water electrolysis (PEMWE), the high expense of the iridium (Ir)-based oxygen evolution reaction (OER) catalysts poses a significant challenge. To overcome this issue, researchers have focused on developing active OER catalysts and catalyst layers (CLs) with minimum uses of Ir. However, they frequently encountered performance problems at the single-cell level that originate not only from the kinetic polarization but also from the ohmic polarization. In this aspect, we have focused on identifying the reasons for the poor performance of low IrOx-loaded anodes, with loadings as low as 0.10 mg cm-2. We pinpoint the cause of the poor performance of the low loaded anodes to an electron transport problem within the native oxide on the Ti porous transport layer (PTL). Our analysis, grounded in the metal-insulator band model, reveals that the primary factors contributing to electron conductivity loss in the Ti oxide are the upward band bending induced by the Schottky contact with high work function IrOx and by the pinch-off effect from the extensive ionomer contact. Based on the above understanding, we propose an anode CL composed of a one-dimensional iridium catalyst, fabricated by electrospinning and calcination processes. Our nanofiber-based CL effectively mitigates the electron transport problem of the native Ti oxide. This improvement stems from the low work function of the Ir nanofiber catalyst and the highly porous structure that reduces the ionomer contact with the Ti oxide. Furthermore, the highly porous nature of the nanofiber-based CL enhances two-phase mass transport, facilitating the high current operation. These findings underscore the critical role of the CL/PTL interface of the PEMWE anode and present the necessity of a well-structured CL to achieve efficient and cost-effective water electrolysis.

Preparation and properties of nitride multilayer coating modified stainless steel as bipolar plates for proton exchange membrane fuel cells

Nitride multilayer coating is prepared on 316L stainless steel (SS) by employing multi-arc ion planting to enhance the corrosion resistance, interfacial electrical conductivity, and hydrophobicity. The electrochemical results show that the coating can effectively inhibit the interface reactions. The icorr of the coated 316L SS was 0.04 μA cm−2, which was significantly lower than that of the substrate (54.7 μA cm−2). The protection efficiency (Pi) of the multilayer nitride coating was 99.93%. After 9 hours of PP, the current density of the coated 316L SS stabilized at 0.085 μA cm−2. The typical ICR value of the coated 316L SS slightly increased from 8.6 mΩ cm2 to 12.6 mΩ cm2. The XPS results demonstrated that the significantly increased ICRs (114.7–200.4 mΩ cm2) of the 316L SS substrate were mainly attributed to the increased proportion of Cr oxide, while the oxide content of the coating was still relatively small. The change in surface morphology and current transient events are further discussed.

Electrical Conductance at Directly Bonded Si/Si Interfaces in Dependence on Oxygen Concentration in Bonding Ambient

Direct semiconductor wafer bonding is a versatile fabrication scheme for high-performance optoelectronic devices. In the present study, the influence of oxygen concentration in the bonding ambient on the electrical conductance at directly bonded Si/Si interfaces is experimentally investigated in relation to interfacial oxidation. The interfacial electrical conductivity is observed higher for lower oxygen concentration at each bonding temperature in the range of 200 °C–400 °C. Ohmic contact characteristics are found attainable in the bonded interfaces by proper choice of bonding conditions. To support the electrical conductance trend, an X-ray photoelectron spectroscopy analysis confirms the extent of interfacial oxidation to be higher for lower oxygen concentration and higher bonding temperature. In addition, solar cell fabrication and operation with a current path through the bonded interface are demonstrated by using the bonding method in a low oxygen concentration ambient. The energy conversion efficiency of the bonded cell is observed comparable to that of an unbonded reference, to thus verify the suitability of the bonding scheme for device applications.

Novel Au nanoparticles-inlaid titanium paper for PEM water electrolysis with enhanced interfacial electrical conductivity

Novel Au nanoparticles-inlaid titanium paper for PEM water electrolysis with enhanced interfacial electrical conductivity

Potential polarization accelerated degradation of interfacial electrical conductivity for Au/TiN coated 316L SS bipolar plates used in polymer electrolyte membrane fuel cells

Influence of four types of potential polarization on the interfacial contact resistance (ICR) of Au/TiN coated 316 L SS bipolar plates used in polymer electrolyte membrane fuel cells is investigated. Au/TiN coating gives superior small ICRs under single potentiostatic or cyclic potentiodynamic polarization, demonstrating great potential for commercial application. However, cyclic combined polarization induces significant delamination of Au dots, and thus Au/TiN/SS exhibits a remarkable increase of ICR. Analysis of ICR and its dependence on Au dots suggest that 4–6% of Au surface coverage is the critical threshold value for Au/TiN coated metal bipolar plates to achieve the target of ICR.

Evaluation of vacuum heat-treated α-C films for surface protection of metal bipolar plates used in polymer electrolyte membrane fuel cells

Proton exchange membrane fuel cells (PEMFCs) assembled with metal bipolar plates (BPPs) is a promising power source for new energy vehicles. However, metal BPPs have serious corrosion issues and the surface electrical performance degrades in the harsh PEMFC environment. Amorphous carbon (α-C) films exhibit improved properties with both high corrosion resistance and electrical conductivity. Subsequent vacuum heat treatment of the as-coated α-C films can change their phase composition and film structure, modifying their performance. This study prepared α-C films with a titanium interlayer on a SS316L substrate by DC balance magnetron sputtering and then subjected them to vacuum heat treatment at different temperatures (400–700 °C). These treated α-C films are systemically analyzed in terms of surface and cross-sectional morphologies, sp bond hybridization, interfacial electrical conductivity, and corrosion resistance. The results indicate that the conversion of sp3 to sp2 and the compact density of α-C films are greatly enhanced with an increase in temperature, greatly improving the corrosion resistance and surface conductivity of the films. These promising results lead to a potential direction for the post-coating treatment of α-C films on metal BPPs in PEMFCs.

Tuning of organic heterojunction conductivity by the substituents’ electronic effects in phthalocyanines for ambipolar gas sensors

Exploiting organic heterojunction effects in electrical devices are an important strategy to improve the electrical conductivity, which can be utilized into improving the conductometric gas sensors performances. In this endeavor, the present article reports fabrication of organic heterostructures in a bilayer device configuration incorporating octa-substituted nickel phthalocyanines (NiPc) and radical lutetium bis-phthalocyanine (LuPc2) and investigates their sensing properties towards NH3 vapor. NiPc having hexyl sulfanyl, hexyl sulfonyl and p-carboxyphenoxy moieties are synthesized, which electronic effects are electron donating, accepting and moderate accepting, respectively, also validated by cyclic voltammetry. The electronic effects of substituents in NiPc modulate the interfacial electrical conductivity and the type of the organic heterojunction formed. The electron acceptor and donor groups favor the formation of accumulation and accumulation/depletion heterojunctions, which are also correlated to negative and positive response towards NH3, respectively. Among the studied heterojunction devices, the one based on hexyl sulfanyl groups, revealed the highest and the most stable response in 10−90 ppm of NH3 and under variable relative humidity (rh) (10–70 %). Interestingly, the bilayer device having p-carboxyphenoxy substituted NiPc, exhibited ambipolar behavior such that its p-type semiconducting nature is changed into n-type at higher rh values, also demonstrated by change in its negative response into positive towards NH3.

A first principles and experimental study on the influence of nitrogen doping on the performance of amorphous carbon films for proton exchange membrane fuel cells

Amorphous carbon (a-C) films exhibit promising application in the field of Proton Exchange Membrane Fuel Cells (PEMFCs) due to their unique properties and have been coated on the metallic bipolar plates (BPPs) of PEMFCs to improve the interfacial electrical conductivity and corrosion resistance of BPPs. However, a-C is still gradually oxidized in the harsh environments of PEMFCs and the performance of a-C needs to be further improved to achieve the lifetime target of PEMFCs. In this paper, nitrogen with different content is doped in a-C and the further understanding of corresponding mechanism on the structure and performance of a-C is revealed via first principles calculation and several experimental methods. The results indicate that doping nitrogen promotes the formation of stable CNx phase with better corrosion resistance and improves the compactness of the films. In addition, moderate content of nitrogen can improve the sp2 fraction of a-C. Furthermore, the film doped with about 10 at. % nitrogen exhibits excellent improvement of the electrical conductivity, corrosion resistance, durability and stability, especially the corrosion resistance under start-up/shut-down operating condition of PEMFCs. This study is beneficial to enhance the lifetime of a-C films and promote the commercialization of PEMFCs.

The frequency of pulsed DC sputtering power introducing the graphitization and the durability improvement of amorphous carbon films for metallic bipolar plates in proton exchange membrane fuel cells

Amorphous carbon (a-C) films have been coated on the metallic bipolar plates (BPPs) in Proton Exchange Membrane Fuel Cells (PEMFCs) to improve the corrosion resistance and the interfacial electrical conductivity of metallic BPPs. However, the durability of a-C in the harsh environments of PEMFCs is still confronted with enormous challenges. In this paper, a-C films are prepared on SS316L BPPs via pulsed DC sputtering power with different frequency and the further understanding of corresponding mechanism on the structure and the performance of a-C is revealed. The results indicate that the compactness of films is enhanced significantly by pulsed DC power. Moreover, the moderate frequency is beneficial to the formation of nanographite clusters, which are embedded into a-C and reduce the interfacial contact resistance (ICR). Furthermore, the analyses of corrosion performance of the films conclude that the embedded nanographite clusters form micro primary cell with a-C and protect a-C from corrosion. The ICR of the film prepared at 200 kHz after corrosion for 200 h at 0.84 Vvs.SHE is 2.44 mΩ⋅cm2, which exhibits ultra-low ICR and achieves excellent durability during the operating procedures of PEMFCs. This study is beneficial to enhance the lifetime of a-C and promote the commercialization of PEMFCs.

Superlattice stacking by hybridizing layered double hydroxide nanosheets with layers of reduced graphene oxide for electrochemical simultaneous determination of dopamine, uric acid and ascorbic acid.

A self-assembled periodic superlattice material was obtained by integrating positively charged semiconductive sheets of a Zn-NiAl layered double hydroxide (LDH) and negatively charged layers of reduced graphene oxide (rGO). The material was used to modify a glassy carbon electrode which then is shown to be a viable sensor for the diagnostic parameters dopamine (DA), uric acid (UA) and ascorbic acid (AA). The modified GCE displays excellent electrocatalytic activity towards these biomolecules. This is assumed to be due to the synergistic effects of (a) excellent interfacial electrical conductivity that is imparted by direct neighboring of conductive rGO to semiconductive channels of LDHs, (b) the superb intercalation feature of LDHs, and (c) the enlarged surface with an enormous number of active sites. The biosensor revealed outstanding electrochemical performances in terms of selectivity, sensitivity, and wide linear ranges. Typically operated at working potentials of -0.10, +0.13 and + 0.27V vs. saturated calomel electrode, the lower detection limits for AA, DA and UA are 13.5nM, 0.1nM, and 0.9nM, respectively, at a signal-to-noise ratio of 3. The sensor was applied to real-time tracking of dopamine efflux from live human nerve cells. Graphical abstract Schematic of the preparation of a superlattice self-assembled material by integrating positively charged semiconductive sheets of Zn-NiAl layered double hydroxide (LDH) with negatively charged reduced graphene oxide (rGO) layers. It was applied to simultaneous electrochemical detection of dopamine (DA), uric acid and ascorbic acid.

Nanoparticle-based biosensing using interfacial electrokinetic transduction

We present a novel label-free electrokinetic method for detecting biomolecular binding on nanoparticles suspended in the vicinity of a laminar microfluidic interface. The sensor is based on the deflection of the liquid interface in an external AC electric field. Biomolecular binding on particles is shown to increase the interfacial electrical conductivity of the suspending electrolyte, which is sensitively transduced as a change in electrokinetic interfacial deflection. Using this approach, we detect the binding of biotin on streptavidin-functionalized nanoparticles at concentrations as low as 500 aM and perform detection of human IgG at clinically relevant concentrations (1.25–12mg/mL) without labels. The interface response is only influenced by specific binding on nanoparticle binding sites and decreases when the particle concentration of reactive particles is reduced. Furthermore, we show that control experiments with both non-reactive particles and lack of a specific target analyte do not produce interfacial deflection. This work provides a promising method for quantifying bead-based binding kinetics for sensitive and specific biosensing in solution without labels.

Interfacial electrical conductivity controlled crystallization of amorphous LaAlO 3 under electron-beam irradiation

Interfacial electrical conductivity controlled crystallization of amorphous LaAlO 3 under electron-beam irradiation

Capacitance behavior of nanostructured ϵ-MnO2/C composite electrode using different carbons matrix

In this work nanostructured ϵ-MnO2/C composite electrode was synthesized via the reduction reaction of potassium permanganate. A wide range of carbons such as mesoporous carbon (MC), graphite (GC), super P carbon (super P) and Vulcan carbon (VC) were used in order to enhance the interfacial electrical conductivity and the electrochemical capacitance of the composite electrodes. Physical properties, structure and specific surface area of electrode materials were investigated by scanning electron microscopy (SEM), x-ray diffraction and nitrogen adsorption measurements. The capacitance behavior of MnO2/C materials was studied in aqueous and non-aqueous solution using cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy measurements. The composite electrode exhibits the highest capacitance at 30 wt% activated carbon. Among different carbons used, the maximum capacitance of MnO2/super P electrode is as high as 205 F g−1 at 50 mV s−1 and retains 98% after 300 cycles.

Surface properties of Ti(N,C,O) thin coating layers deposited by PA-MOCVD for bipolar plates used PEMFC

Ti(N,C,O) thin films were deposited by means of metal-organic chemical vapor deposition using a glow discharge with the aim of enhancing the corrosion resistance and electrical contact conductivity of austenitic stainless steel as a candidate materials for the bipolar plates used in polymer electrolyte membrane fuel cells. The corrosion properties were found to be dependent on the composition, i.e., the precursor source, and on the thickness of the thin films. Tetrakis(diethylamino) titanium used as a liquid metal organic source for the deposition of thin Ti(N,C,O) layers onto austenitic stainless steel provided a significant improvement of the corrosion resistance, which resulted in superior interfacial electrical conductivity after corrosion tests.

Fabrication of electrically pumped InAs/GaAs quantum dot lasers on Si substrates by Au‐mediated wafer bonding

AbstractAn electrically pumped 1.3 μm room‐temperature InAs/GaAs quantum dot laser on a Si substrate has been demonstrated with a threshold current density of 360 A/cm2. The double‐hetero laser structure was grown on a GaAs substrate by metal‐organic chemical vapor deposition and layer‐transferred onto a Si substrate by GaAs/Si wafer bonding mediated by a 380‐nm‐thick Au‐Ge‐Ni alloy layer. We have demonstrated that insertion of a metal thin film in a wafer‐bonded GaAs/Si interface enhances interfacial electrical conductivity and suppresses optical leakage from the laser cavity into the substrate and therefore is suitable for III‐V‐on‐Si hybrid laser applications. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanosized TiN–SBR hybrid coating of stainless steel as bipolar plates for polymer electrolyte membrane fuel cells

In attempt to improve interfacial electrical conductivity of stainless steel for bipolar plates of polymer electrolyte membrane fuel cells, TiN nanoparticles were electrophoretically deposited on the surface of stainless steel with elastic styrene butadiene rubber (SBR) particles. From transmission electron microscopic observation, it was found that the TiN nanoparticles ( ca. 50 nm) surrounded the spherical SBR particles ( ca. 300–600 nm), forming agglomerates. They were well adhered on the surface of the type 310S stainless steel. With help of elasticity of SBR, the agglomerates were well fitted into the interfacial gap between gas diffusion layer (GDL) and stainless steel bipolar plate, and the interfacial contact resistance (ICR), simultaneously, was successfully reduced. A single cell using the TiN nanoparticles-coated bipolar plates, consequently, showed comparable cell performance with the graphite employing cell at a current density of 0.5 A cm −2 (12.5 A). Inexpensive TiN nanoparticle-coated type 310S stainless steel bipolar plates would become a possible alternate for the expensive graphite bipolar plates as use in fuel cell applications.

Preparation of C-Ru-RuO<sub>2</sub> Nano-Composite Films by Plasma-Enhanced CVD and their Electrode Property

C-Ru-RuO2 nano-composite films were prepared by plasma-enhanced chemical vapor deposition and their microstructure and electrode properties were investigated. Ru-C nano-composite films consisted of Ru nano-particles of 3 nm in diameter and an amorphous C matrix. With increasing oxygen gas flow rate (FRO2), the volume fraction of C decreased from 0.91 to 0 and Ru nano-particle size increased from 2.5 to 4.5 nm. At high FRO2, the film consisted on the fibrous RuO2 and Ru-C nano-composite layer. Ru-C nano-composite containing 91 vol% C showed the highest interfacial electrical conductivity below 673 K, and Ru-C/RuO2 composite containing 0 – 5 vol% C showed the highest interfacial electrical conductivity at 873 K. Electro-motive-force (EMF) values of an oxygen concentration cell constructed from a YSZ electrolyte and Ru-C or Ru-C/RuO2 composite electrodes responded to the change of oxygen gas partial pressure at more than 473 K. The response time of the concentration cell with Ru-C nano-composite electrodes at 573 K was less than 10 s, and that with Ru-C/RuO2 composite electrodes was about 300 s.

Microstructures and Electrical Properties of Ru-C Nano-Composite Films by PECVD

Ruthenium-Carbon (Ru-C) nano-composite films were prepared by plasma-enhanced chemical vapor deposition (PECVD) and the effects of deposition conditions on the microstructure and electrical properies were investigated. The films consisted of agglomerated grains of 10 to 20 nm in diameter, in which Ru particles of 2.5 to 3.5 nm in diameter were dispersed in a C matrix. The C content of the films was about 90 vol%. The electrical properties of Ru-C nano-composite films as a catalytic electrode for an yttria-stabilized zirconia (YSZ) solid electrolyte were evaluated by AC impedance spectroscopy. The interfacial electrical conductivity at the Ru-C/YSZ interface was 0.2 x 10 -3 Sm -1 at 500 K and increased with increasing temperature. The activation energy of the interfacial electrical conductivity was about 70kJ/mol, implying an oxygen diffusion limited process at the interface.

Nanoscale Electrical Conductivity and Surface Spectroscopic Studies of Indium−Tin Oxide

Optically transparent indium−tin oxide (ITO) is a “universal” electrode for various optoelectronic devices such as organic light emitting diodes (OLEDs). It is known that the performance of OLEDs improves significantly by exposing the ITO surface to an oxygen plasma. This study employs conducting atomic force microscopy (C-AFM) for unique nanometer-scale mapping of the local current density of a vapor-deposited ITO film. The local conductance is shown to increase by orders of magnitude and becomes more uniform after oxygen plasma treatment for measurements of the identical 200-nm2 regions. Scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy measurements of separate regions of the same films suggest that the oxygen plasma removes a thin layer of insulating carbon-rich material from the surface. The extensive heterogeneity in interfacial electrical conductivity measured by C-AFM calls into question previous studies of STM-induced electroluminescence of polymer films on ITO as well as STM imaging of such films. The impact of this study on the future development of optoelectronic devices is discussed.