Electrical Contact Research Articles

Fabrication of Surfactant-Free Mixed-Metal Nanocatalyst-Carbon Fiber Paper Composites via Pulsed Laser Grafting.

We present a novel methodology for fabricating surfactant-free mixed-metal nanocatalyst-carbon fiber paper composites, demonstrating significant improvements in impedance, electrocatalytic activity, and long-term stability over laser synthesized drop cast analogues on carbon fiber paper or highly ordered pyrolytic graphite. Our innovative pulsed laser grafting technique is a versatile, one-step aqueous process that integrates nanoparticle generation with surface attachment on macroscopic solid supports, such as sheets, rather than being limited to powders, particulate supports, or organic solvents as in prior methods. It effectively addresses longstanding challenges with nanoparticle adhesion and electrical contact between nanoparticles and macroscopic electrodes, and it alleviates environmental concerns associated with organic solvents. Laser grafting eliminates laborious synthesis, separation, purification, and postsynthesis attachment steps, thus significantly reducing composite preparation time. We fabricated [NiFe]-(OH)2-hydrophilic carbon fiber paper composites using aqueous nickel-iron nitrate solution. Low-fluence 532 nm nanosecond laser pulses minimized surface damage and facilitated effective metal ion excitation for nanoparticle assembly. SEM, EDX and XPS data revealed surface [NiFe]-(OH)2 without carbon encapsulation and prominent Ni-C interactions. The pulsed laser grafted composites showed enhanced electrocatalytic performance for alkaline water oxidation and decreased material charge transfer resistance, compared to drop cast analogues, leading to improved electrical conductivity and mass activity. Additionally, they demonstrated exceptional long-term stability, overcoming common adhesion issues in conventional nanoparticle-support systems, marking a significant advancement in the manufacturing of multimetallic nanoparticle-support composites, with promising implications for electrochemistry and electrocatalysis technologies.

Enhanced Electrical Connectivity in High Energy Density Single-Crystal NCA Electrodes via Polycrystalline Blending Design.

Single-crystal (SC) Ni-rich cathodes offer superior cycle stability compared to polycrystalline (PC) cathodes but face challenges with lower rate capability, particularly in high-energy-density commercial electrodes with limited conductive additives. It remains unclear whether this limitation stems primarily from insufficient interparticle connectivity or sluggish lithium diffusion within individual SC particles. Moreover, quantitatively visualizing the utilization of electrodes based on electrical connectivity or lithium diffusion remains challenging. In this study, we employed electrochemical analysis, 46-point probe resistance measurements, and synchrotron-based transmission X-ray microscopy (TXM) to reveal that the poor rate capability of SC electrodes is primarily due to inferior interparticle connectivity. Incorporating PC particles significantly reduces electrical contact resistance, while larger particle sizes further enhance electrode connectivity. Based on these insights, blending a minor fraction of large PC particles effectively improves the rate capability of SC electrodes. TXM lithium imaging at high cycling rates reveals that improved electrical contact between SC and PC particles boosts electrical connectivity, ensuring effective particle utilization and enhanced performance across the electrode.

Tailoring electrical contact properties of Cu-5wt%W composites through HfC and TaC nanoparticle addition

Tailoring electrical contact properties of Cu-5wt%W composites through HfC and TaC nanoparticle addition

Effect of coating plasticity parameters on the fretting wear behavior of electrical contacts

Effect of coating plasticity parameters on the fretting wear behavior of electrical contacts

Improving arc erosion resistance of AgNi electrical contact material by a three-dimensional graphene network

Improving arc erosion resistance of AgNi electrical contact material by a three-dimensional graphene network

Fabrication of n+ contact on p-type high purity Ge by cathodic electrodeposition of Li and impedance analysis of n+/p diode at low temperatures

The fabrication of diodes by forming n-type electrical contact on germanium (Ge) and its AC impedance analysis is important for radiation detection in the form of pulses. In this work, lithium (Li) metal has been electro-deposited on p-type Ge single crystal from molten lithium nitrate at 260 °C. The depth of Li diffusion in Ge was successfully varied by changing the electroplating time as determined by sheet resistance (SR) measurement after successive lapping of the Ge surface. Li is found to diffuse up to 500 µm inside Ge by heat treatment of as-deposited Li/Ge at 350 °C for 1 h. A stable n-type electrical contact on Ge with SR ~ 1 Ω/□ and impurity concentration ~ 3.7 × 1015/cm3 is developed by Li incorporation in p-type Ge crystal showing net carrier concentration ~ 3.4 × 1010/cm3 and SR ~ 100 KΩ/□. Carrier concentration determined from the 1/C2 vs. V plot shows similar temperature dependence as found by Hall measurement. The fabricated n+/p junction exhibits excellent diode characteristics with a gradual increase in cutoff voltage at low temperatures. Under forward bias, junction capacitance mainly comprises diffusion capacitance (~ 10 µF), showing strong frequency dependence, and the impedance is partly resistive, resulting in a semi-circular Cole–Cole plot. Imaginary impedance spectra reveal that the relaxation time for the diffusion of majority carriers decreases at higher temperatures and increased forward voltages. The diode is purely capacitive under reverse bias, showing a line parallel to the y-axis in the Cole–Cole plot with frequency-independent (100 Hz–100 MHz) depletion capacitance of ~ 10 pF.

Effect of SnO2 particulate characteristics on mechanical properties of Ag/SnO2 electrical contact materials

Effect of SnO2 particulate characteristics on mechanical properties of Ag/SnO2 electrical contact materials

Research of Temperature Rise Effect and Wear Characteristics of the Armature-rail Interface under High-speed Sliding Electrical Contact Conditions

Research of Temperature Rise Effect and Wear Characteristics of the Armature-rail Interface under High-speed Sliding Electrical Contact Conditions

Quantum melting of generalized electron crystal in twisted bilayer MoSe2

Electrons can form an ordered solid crystal phase ascribed to the interplay between Coulomb repulsion and kinetic energy. Tuning these energy scales can drive a phase transition from electron solid to liquid, i.e., melting of Wigner crystal. Generalized Wigner crystals (GWCs) pinned to moiré superlattices have been reported by optical and scanning-probe-based methods. Using transport measurements to investigate GWCs is vital to a complete characterization, however, still poses a significant challenge due to difficulties in making reliable electrical contacts. Here, we report the electrical transport detection of GWCs at fractional fillings ν = 2/5, 1/2, 3/5, 2/3, 8/9, 10/9, and 4/3 in twisted bilayer MoSe2. We further observe that these GWCs undergo continuous quantum melting transitions to liquid phases by tuning doping density, magnetic and displacement fields, manifested by quantum critical scaling behaviors. Our findings establish twisted bilayer MoSe2 as a novel system to study strongly correlated states of matter and their quantum phase transitions.

2D Cd metal contacts via low-temperature van der Waals epitaxy towards high-performance 2D transistors

Two-dimensional (2D) semiconductors hold great promise for future electronics, yet the fabrication of clean ohmic electrical contacts remains a key challenge. Traditional lithography and metallization processes often introduce interfacial disorder, and recently developed electrode-transfer-based techniques are difficult to implement without contaminating the interfaces between 2D crystals and metals. Here, we demonstrate a low-temperature chemical vapor deposition (CVD)-based van der Waals (vdW) epitaxy method to grow 2D metal (Cd) electrodes, eliminating lithography, deposition, or transfer processes and enabling the damage-free integration of 2D semiconductors. This thermodynamic integration strategy significantly mitigates the interfacial disorder and metal-induced gap states (MIGS), leading to low contact resistance (RC) and near-zero barrier ohmic contacts. Cd-MoS2 field-effect transistors (FETs) exhibit RC down to 70–100 Ω·μm, on-state current densities up to 942 μA/μm, on/off ratios exceeding 108, and mobilities up to 160 cm2 V−1 s−1. These results position vdW epitaxially grown 2D metals as a promising contact technology for next-generation electronics beyond silicon.

Electrochemical Formation and Characterization of Functional Ag-Re Coatings.

Silver-white, matte, smooth, and durable deposits of silver-rhenium, with thicknesses ranging from 2.0 to 13.7 μm and containing 0.15 to 13.5 wt.% Re, were obtained with a current efficiency of 66-98% from a developed dicyanoargentate-perrhenate bath based on a borate-phosphate-carbonate silver-plating electrolyte. This study was focused on the influence of bath composition, the [Ag(I)]:[ReO4-] ratio, surfactant additives, applied current density, temperature, and stirring, on the alloys' composition, structure, morphology, microhardness, adhesion, and porosity. A voltammetric analysis was conducted, considering the influence of ethanolamines on electrode processes. In baths with triethanolamine (TEA), coatings similar to a silver matrix with rhenium doped in mass fractions are likely achievable. Monoethanolamine (MEA) is recommended due to its process-activating properties. All coatings were nanocrystalline (τ = 28.5-35 nm). For deposits containing less than 10 wt.% Re, characteristic silver XRD peaks were observed, while for other deposits, additional peaks attributed probably to Re(VII) and Re(VI) oxides. A linear relationship Hv - τ-1/2, typical for Hall-Petch plots, was obtained, confirming that grain boundaries play a crucial role in mechanical properties of coatings. The conditions for stable electrochemical synthesis of promising functional Ag-Re coatings of predetermined composition (0.7-1.5 wt.% Re) were proposed for practical use in power electronics and energy sectors for manufacturing electrical contacts operating across a wide temperature range. This was realized by deposition from an Ag-rich bath in the area of mixed electrochemical kinetics, at potential values corresponding to the region of half the limiting current: j = 2.5-6 mA cm-2, t = 19-33 °C.

High-Precision Surface Tension Measurements of Sodium, Potassium, and Their Alloys via Du Noüy Ring Tensiometry.

The development of post-lithium-ion batteries has sparked significant interest in alkali-metal anodes, particularly sodium (Na), potassium (K), and sodium-potassium (Na-K) alloys. Na-K alloys are promising for partially liquid anodes due to their unique low melting points. A critical factor influencing Na-K-based anode performance is wetting behavior, which governs electrical conductivity, mechanical contact, and long-term stability. At the heart of wetting lies surface tension, a fundamental property of solid-liquid-gas interactions. However, the surface tension of alkali metals and their alloys, particularly Na-K systems, remains poorly understood due to experimental and theoretical challenges. This study bridged these gaps by employing Du Noüy ring tensiometry for the first time in alkali-metal systems to measure the surface tension of Na, K, and Na-K alloys across temperatures from ambient to 180 °C. A key innovation in this work is the development of the push-in Du Noüy method, which provided significantly higher precision and reliability compared to the traditional pull-out technique, without requiring a correction factor. The measured surface tension decreased with increasing temperature for the studied Na-K alloys. For instance, for a eutectic Na-K mixture, the surface tension decreases from 121.7 mN m-1 to 112.2 mN m-1 when increasing the temperature from ambient to 180 °C. Additionally, this study presented the first use of Gibbs free energy minimization to model the surface tension of the Na-K system. The robust method significantly enhanced the predictive accuracy compared to the previous simplified model, reducing deviations from 25% to 2%. Our findings reveal that surface tension increases with sodium mole fraction in the bulk phase, yet the surface monolayer remains potassium-rich, indicating non-ideal surface behavior. This study deepens the understanding of alkali-metal wetting behavior, providing valuable insights for designing optimized interfaces in next-generation semi-solid alkali-metal batteries.

Edge-Surface-Inter Carbon Nanoarchitecture on Silicon.

The huge volume changes of silicon (Si) anodes during cycling lead to continuous solid electrolyte interphase thickening, mechanical failure, and loss of electrical contact, which have become key bottlenecks limiting their practical applications. This work presents a trimodal in situ growth strategy for constructing hierarchical carbon nanoarchitecture networks on Si substrates (Si@Gr@CNT). The designed "Edge-Surface-Inter" (E-S-I) architecture exhibits three synergistic features: an edge-protruding structure forming vertical conductive channels for rapid Li+ transport, a surface-entangled structure providing mechanical enhancement, and an interbridging structure constructing continuous three-dimensional electron transport networks. The Si@Gr@CNT electrode demonstrates a 63.2% improvement in half-cell rate performance compared with traditional Si@Gr. The E-S-I architecture contributes to suppressing excessive LiF formation through improved local current distribution, devoted to the stable and thinner solid electrolyte interphase layer. The three-dimensional conductive network possesses a significant stress regulation effect, which provides stress release space in the vertical direction and lateral stress buffering through surface flexible entanglement. For practical applications, the full cell assembled with the LiFePO4 cathode and the Si@Gr@CNT/graphite composite anode delivers high energy density and enhanced durability. This study establishes a strategy for hierarchical carbon nanoarchitectures and provides design insights into high-performance Si-based electrodes.

Arc erosion behaviour of Ag–La2Sn2O7/SnO2 electrical contact composites in SF6, N2, and CO2

ABSTRACT Ag-La2Sn2O7/SnO2 composites (with a mass ratio of 88:4:8) were prepared by powder metallurgy using Ag powder and La2Sn2O7/SnO2 composite powder (synthesised by chemical co-precipitation). The arc erosion behaviour under discharging atmospheres of SF6, N2, and CO2 at a constant voltage of 7 kV was investigated by analysing arc parameters, erosion morphology, and compositional variation. Results indicated that the arc duration and arc energy increased in the order of SF6, N2, and CO2, with the highest breakdown current observed in CO2. The erosion area in SF6 exhibited fewer bulges and splash particles owing to its shorter arc duration and lower energy. In contrast, the erosion in N2 and CO2 was more severe, with microcracks being observed particularly in CO₂. Raman and X-ray photoelectron spectroscopy (XPS) analyses revealed that the erosion area in SF6 was primarily composed of LaF3, while in N2 and CO2, partial decomposition of La2Sn2O7 formed La2O3 and SnO2. The addition of La2Sn2O7 positively influenced the arc erosion resistance by increasing the viscosity of the molten pool, hindering the flow and splashing of Ag liquid. Under high arc energy conditions, La2Sn2O7 underwent partial decomposition, effectively protecting the Ag matrix from further damage.

Normally Off AlGaN/GaN MIS-HEMTs with Self-Aligned p-GaN Gate and Non-Annealed Ohmic Contacts via Gate-First Fabrication.

This study introduces an enhancement-mode AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) featuring a self-aligned p-GaN gate structure, fabricated using a gate-first process. The key innovation of this work lies in simplifying the fabrication process by utilizing gate metallization for both electrical contact and etching mask functions, enabling precise self-alignment. A highly selective Cl2/N2/O2 inductively coupled plasma (ICP) etching process was optimized to etch the p-GaN layer in the access regions, with a selectivity ratio of 33:1 and minimal damage to the AlGaN barrier. Additionally, a novel, non-annealed ohmic contact formation technique was developed, leveraging ICP etching to create nitrogen vacancies that facilitate contact formation without requiring thermal annealing. This technique streamlines the process by combining ohmic contact formation and mesa isolation into a single lithographic step. Incorporating a SiNx gate dielectric layer led to a 4.5 V threshold voltage shift in the fabricated devices. The resulting devices exhibited improved electrical performance, including a wide gate voltage swing (>10 V), a high on/off current ratio (~107), and clear pinch-off characteristics. These results demonstrate the effectiveness of the proposed fabrication approach, offering significant improvements in process efficiency and manufacturability.

Selection of the best alternative of railway traction for passenger transportation using the analytic hierarchy process method distributive and ideal modes

The rail industry uses a variety of traction types for passenger transport, each with its own advantages and disadvantages. The renewal and development of a country’s rolling stock is aimed at selecting the optimal strategy and practical means to achieve the best result. A quantitative analysis of the different rail traction alternatives and the selection of the best alternative allows the optimal development strategy to be identified. The aim of this study is to present a methodology for assessing the quality criteria of traction rolling stock for rail passenger transport and to select the best traction alternative based on these criteria. This study has developed a framework of nine factors (criteria) that affect the quality (serviceability) of rolling stock. The significance of the criteria in terms of their normalised relative weights was calculated using rank correlation and Analytic Hierarchy Process (AHP) methods. The study used the judgements of 22 experts whose opinions were in agreement. The AHP method was used to compare four types of traction for each criterion: diesel (DT), electric contact (ET), battery electric (BT) and hydrogen (HT). The novelty of research – distributive and ideal modes of the AHP method were used to evaluate all types of traction for selection the best alternative among them according to the original formulae provided by the authors. The results show that the agreed opinions of the expert team, expressed as normalised relative weights, have the highest mean values for ET (0.3866 and 0.3808). The second highest ranking is for BT (0.2164 and 0.2239). DT (0.2160 and 0.2060) is not far behind. The lowest ranking is that of HT (0.1810 and 0.1893). It can therefore be concluded that ET is the best traction alternative for passenger transport. The results of the study may prove useful for decision makers in the field of rolling stock fleet development strategy and dynamics.

Evaluation of Ag-coated Cu paste as Ag-saving electrode paste for silicon heterojunction solar cells

Abstract This study evaluates an Ag-saving electrode paste of Ag-coated Cu particles mixed with conventional Ag powder (Ag-coated Cu paste) for silicon heterojunction (SHJ) solar cells. The results show that the Ag-coated Cu paste achieves electrical properties comparable to conventional Ag paste when the blending ratio of Ag powder is 37% or higher. The SHJ solar cells fabricated using the Ag-coated Cu paste exhibit comparable efficiencies to those of SHJ solar cells fabricated using conventional Ag paste while reducing the usage of Ag by approximately 60%. Furthermore, the Ag-coated Cu paste shows superior electrical contact properties with resource-saving Al-doped ZnO compared to conventional Ag paste. The hard x-ray photoelectron spectroscopy analysis reveals that this superiority is attributed to a reduction in contact resistance resulting from optimized band alignment. These results highlight the Ag-coated Cu paste potential as a cost-effective and sustainable solution for next-generation solar technologies.

Imaging the 4D Chemical Heterogeneity of Single V2O5 Particles During Charging/Discharging Processes.

Microparticle cathode materials are widely used in secondary batteries. However, obtaining dynamic chemical heterogeneities of these microparticles is challenging, hindering in-depth mechanistic investigation of the underlying processes. For example, although vanadium pentoxide shows promise as an electrode material for zinc ion batteries, its poor performance's root cause is elusive. Herein, a fluorescence/scattering dual-mode spinning disk confocal microscopy-based approach is developed to visualize the 4D chemical heterogeneity of single V2O5 particles during cycling. Dual-mode in situ imaging identifies valence state changes of vanadium ions with high spatiotemporal resolution. A unique difference is observed between the scattering intensities of a particle's bottom electric contact points and the rest parts during the discharging process. In contrast, fluorescence intensity variation suggests high consistency across the particles. Correlative Raman, UV-Vis spectroscopy, and electrochemical impedance spectroscopy analyses suggest the precipitation of V3+ species at the bottom interface of the V2O5 electrode, leading to increased electron transfer resistance and compromised overall performance. A coordination strategy between ethylene diamine tetraacetic acid and V3+ is proposed for inhibiting V3+ precipitation, and its effectiveness is further verified by imaging and electrochemical impedance spectroscopy analyses. Insights from the imaging approach presented herein will enable the rational design of high-performance batteries.

Temperature- and stress-dependent electrical responses of frozen soils

Abstract Characterisation of freezing conditions (i.e. temperature and unfrozen water content) and stress states (e.g. stress level and specific volume) is critical to evaluate the thermo-hydro-mechanical properties of frozen soils. This study aims to utilise frozen soils’ electrical responses to characterise mechanical properties and interpret the associated frost heave phenomenon and compression characteristics. Frozen soils were prepared by freezing sand and bentonite at various temperatures (i.e. −5, −10, −20 °C), in which the electrical conductivity and frost heave were monitored. A modified oedometer was thereafter utilised to conduct compression tests on frozen soils. Results showed that electrical responses were highly sensitive to soil temperature variations during freezing: electrical conductivity decreasing by 2–5 orders of magnitude in response to the temperature drop of 15–40 °C. Soil freezing characteristic curves were associated with freezing point depression phenomena, as reflected in correlations between electrical conductivity and unfrozen water content. Frozen soils exhibited sensitive electrical responses to stress changes along the loading path (e.g. electrical conductivity increased by 2–4 orders of magnitude due to stress increase from 1 to 2500 kPa); while no significant stress-dependent electrical responses were observed during unloading, likely due to the loss of electric contacts. Moreover, the preconsolidation pressure of the frozen bentonite increased by 10–60 times compared to the unfrozen bentonite because of the ice invasion mechanism. This study investigates thermomechanical couplings in frozen soils and highlights the potential applicability of electrical conductivity for monitoring thermal and stress states of frozen soils in cold regions.

Electromagnetic interference shielding in soft, lightweight, and flexible conducting polymer-based sponges

Abstract The development of high efficiency, low density, and mechanically flexible electromagnetic interference (EMI) shielding materials based on conducting polymers has gained significant momentum. In this work, we investigated the EMI shielding behavior of uniaxially compressible sponges based on the conducting polymer poly(3,4-ethylenedixoythiophene) polystyrene sulfonate doped with polystyrene sulfonate (PEDOT:PSS) in the X-band frequency range ( 8-12.4 GHz). Two types of PEDOT:PSS sponges, containing glycerol and (3-glycidyloxypropyl) trimethoxysilane or glycerol and polyethylene glycol, were prepared by freeze-drying method. Both types of sponges exhibited a rapid resistance decrease after an initial compressive strain of < 20%, which remained stable at higher strains. This behavior was likely due to the 3D complex porous structures of the sponges and linked to the creation of new electrical contacts due to pore collapse upon compressive strain. The enhanced electrical conductivity, together with the porous structure, resulted in EMI shielding as high as about 70 dB. The EMI shielding in these materials was primarily dominated by the reflection process. This work contributes to developing flexible and high-efficiency EMI shielding materials for future flexible electronic applications.