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•Electroless Ag, Ni and Cr layers were successfully obtained on Cu particles.•Electroless plating layers were detected at the grain boundaries of Cu-based materials.•Electrical ...contact performances were improved over conventional electrical contacts.•Thanks to electroless Ni, wear performance was increased 3 times compared to Cu.•FGM design with Ni showed 10 times higher arc erosion performance compared to Cu.
In this study, hot pressing was used to fabricate the novel copper based functionally graded electrical contact materials synthesized by silver, nickel and chrome plated copper core particles. For the fabrication of functionally graded materials (FGMs) by hot-pressing; pure copper, two and three layered metallic powders were used in the lower, middle and upper layer, respectively. The wear and arc-erosion performances of the developed materials increased from 3 to 10 times as compared to that of pure copper. Wear tests showed that the abrasive wear mechanism was dominant for the FGMs including electroless nickel and chromium coating layer. The highest specific wear rate (SWR) value was found in Cuf-Ag′ (4.9 × 10−4 mm3/Nm) materials under the load of 20 N while the lowest SWR value belongs to Cuf-Ag-Ni′ (2.3 × 10−4 mm3/Nm) materials under the load of 10 N. While severely melted and deformed regions are dominant on arc erosion surfaces of pure copper and copper-silver containing contacts, flatter and relatively less melted regions were detected on the surfaces of FGMs containing nickel and chromium. The arc-erosion loss values (cm3 × 10−4) measured for FGM1 sample were 0.75 and 0.70, 0.99 and 0.88, 1.21 and 1.04 at 3000 cycles under the current of 5 A, 10 A and 15 A in fixed and moving contacts, respectively.
•Zn2SnO4, as a SnO2-based ternary oxide, can improve the arc resistance of Cu contact materials in comparison with SnO2.•Zn2SnO4 particles distribute uniformly on the eroded surface and enhance the ...electrical contact property.•The enhanced arc-resistance of Zn2SnO4/Cu contacts highly relies on the polar-covalent Cu-O bonds at the interfaces.•DFT calculations could be extended to the rational design of ternary oxides/Cu composites with high arc resistance.
Interface wettability is a vital role in directly impacting the electrical contact characteristics of oxides/Cu-based composites under arc erosion. Exploring its influence mechanism, especially at atomic/electronic scales, is significant but challenging for the rational design of oxides/Cu contacts. Here, we designed Zn2SnO4/Cu electrical contacts aiming to solve the poor wettability of SnO2/Cu composites. It was found that Zn2SnO4 could remarkably improve the arc resistance of Cu-based electrical contacts, which was benefited by the excellent interface wettability of Zn2SnO4/Cu. The characterization of eroded surface indicated that Zn2SnO4 particles distributed uniformly on the contact surface, leading to stable electrical contact characteristic. Nevertheless, SnO2 considerably deteriorated the arc resistance of SnO2/Cu composite by agglomerating on the surface. The effect mechanism of wettability on arc resistance was investigated through density function theory (DFT) study. It revealed that strong polar covalent bonds across the Zn2SnO4/Cu interface contributed to improving the interfacial adhesion strength/wettability and thus significantly enhanced the arc resistance. For binary SnO2/Cu interface, ionic bonds resulted in weak interface adhesion, giving rise to deterioration of electrical contact characteristic. This work discloses the bonding mechanism of oxide/Cu interfaces and paves an avenue for the rational design of ternary oxide/Cu-based electrical contact materials.
Motivated by the high expectation for efficient electrostatic modulation of charge transport at very low voltages, atomically thin 2D materials with a range of bandgaps are investigated extensively ...for use in future semiconductor devices. However, researchers face formidable challenges in 2D device processing mainly originated from the out‐of‐plane van der Waals (vdW) structure of ultrathin 2D materials. As major challenges, untunable Schottky barrier height and the corresponding strong Fermi level pinning (FLP) at metal interfaces are observed unexpectedly with 2D vdW materials, giving rise to unmodulated semiconductor polarity, high contact resistance, and lowered device mobility. Here, FLP observed from recently developed 2D semiconductor devices is addressed differently from those observed from conventional semiconductor devices. It is understood that the observed FLP is attributed to inefficient doping into 2D materials, vdW gap present at the metal interface, and hybridized compounds formed under contacting metals. To provide readers with practical guidelines for the design of 2D devices, the impact of FLP occurring in 2D semiconductor devices is further reviewed by exploring various origins responsible for the FLP, effects of FLP on 2D device performances, and methods for improving metallic contact to 2D materials.
New and in‐depth insight into the fundamental mechanism of Fermi level pinning in 2D semiconductor devices is presented in this review. The related device characteristics and contact strategies utilizing both the Fermi level pinning and depinning are introduced.
In this work, the wear and melt erosion behavior of tin-plated copper alloy contacts are investigated under fretting at current loads ranging from 0.1 to 12.5 A. Three typical variations in the ...average values of contact resistance and contact temperature with fretting cycles are recorded and interpreted explicitly. The material melt erosion in the contact interface is observed clearly at currents higher than 5 A due to substantial Joule heat. The increment of contact temperature together with the distortion of transient friction force are considered as the degradation characteristics in the fretting. The produced scars and oxides between the contact interface eventually lead to the electric circuit disconnection. The distinct physical mechanism of contact interface fretting wear and melt erosion at high current loads is presented.
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•BP/graphene forms a n-type, whereas BAs/graphene forms a p-type Schottky contact with a Schottky barrier height (SBH) of 0.4 eV and 0.16 eV respectively.•The contacts are tunable ...effectively via application of normal electric field within ±0.15 V/Å, which is very much small as compared to the previously reported graphene based heterostructures.•For an applied electric field within ±0.3 V/Å, electron/hole doping in graphene is inducible where the doping concentration is tunable by up to 1012 cm−2.•The vdWHs are found to be more stable and robust against mechanical deformation than the individual monolayers.
Electrical contacts arising at the van der Waals interface between boron pnictide (h-BP, h-BAs) and graphene monolayers have been systematically investigated using density functional theory. The electronic band structure of the individual monolayers is well preserved in the heterostructures constituted from them, indicating a weak van der Waals (vdW) interaction between them. BP monolayer is found to form n-type Schottky contact with a Schottky barrier height (SBH) of 0.4 eV in BP/graphene van der Waals heterostructure (vdWH), whereas a small p-type SBH of 0.16 eV occurs at BAs/graphene vdWH. The SBHs obtained for BX/graphene are lower than that of other transition metal dichalcogenide based graphene vdWH and electrical properties are found to be significantly tunable/transformable via small applied electric field of ±0.15 V/Å. These insightful results will motivate experimentalists and technologists to design high performance graphene-based hybrid field-effect transistors (FET). Also, the vdWHs are found to show significant robustness, structural integrity and flexibility. The bending modulus of BP (As)/graphene is found to be lower than that in graphene/MoS2. The graphene/h-BN vdWH has been experimentally studied, while the thin films of h-BP have been recently synthesized; thereby substantiating the experimental feasibility in building up the heterostructures proposed in this work.
Effects of silver content (5–35 wt %), sintering temperature (150–850 °C), sintering time (30–180 min), and compaction pressure (200, 300, and 400 MPa) were studied on characteristics of prepared ...contacts. XRD (X-Ray Diffraction), OM (Optical Microscope), SEM (Scanning Electron Microscope), and electrical resistance analyses were used to study the properties of the contacts. The Results showed that increasing the percentage of silver in the contacts as well as increasing the time and temperature of the sintering process increase the oxidation of copper. It was found that galvanic corrosion and the Kirkendall effect between Cu and Ag (especially in high silver content) resulted in the formation of microvoids around the copper particles facilitating the copper oxidation. Apparent bulk density remained almost constant as the sintering temperature increased from 150 to 700 °C, while it dropped sharply in a sintering temperature of 750 and 800 °C. It was determined that increasing the sintering time from 30 to 60 min increases the apparent bulk density, while increasing the sintering time to more than 60 min reduces it. Moreover, increasing the amount of compaction pressure in 200–400 MPa did not affect the apparent bulk density. The electrical resistance is almost independent of sintering temperature in 25 °C–700 °C. Further change in sintering temperature from 700 to 750 °C raised the electrical resistance from 0.2 Ω to 15 kΩ. A Study of the electrical resistance of the samples indicated that increasing the Ag content up to 25 wt% reduces the electrical resistance. The electrical resistance of the sample containing 35 wt% Ag was 14 kΩ that which was higher than that of the sample containing 25 wt% Ag (0.11 Ω).
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•Effects of silver content, sintering time and temperature, and compaction pressure were studied.•Increasing the silver content and the sintering time and temperature enhanced the Cu oxidation.•Galvanic corrosion and the Kirkendall effect promotes the Cu oxidation process.•Resistance is almost independent of sintering temperature in 25 °C–700 °C.•Resistance of the contact-35% Ag (14 kΩ) was higher than that of contact-25% Ag (0.11 Ω).
The majority of industrial, automobile processes, electrical appliances emit waste heat in the low-temperature range (<573 K), hence efficient thermoelectric materials operating in this range are ...highly needed. Bismuth telluride (Bi2Te3) based alloys are conventional thermoelectric material for the low-temperature application. The pure Bi2Te3 sample synthesized in this work exhibits n-type conduction. We demonstrate that by small doping of Pb at Bi site a transition in electrical transport form n- to p-type is observed. The figure-of-merit (ZT) of n-type Bi2Te3 is ~0.47 and optimized Bi1.95Pb0.05Te3 exhibit p-type conduction with enhanced ZT of ~0.63 at 386 K. The conversion efficiency of Bi1.95Pb0.05Te3 based single thermoelement with hot pressed Ni/Ag electrical contacts was found to be ~4.9% for a temperature difference (ΔT) of 200 K. The efficiency was further enhanced to ~12% (at ΔT ~ 494 K) in the segmented thermoelement consisting of Bi1.95Pb0.05Te3 and (AgSbTe2)0.15(GeTe) 0.85 (i.e. TAGS-85).
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•Bi2Te3 exhibits n- to p-type transition by substituting Bi with small amount of Pb.•p-Type Bi1.95Pb0.05Te3 exhibit improved ZT ~ 0.63 w.r.t. n-type Bi2Te3 (ZT ~ 0.47).•Bi1.95Pb0.05Te3 with Ni/Ag contacts exhibited η of ~4.9% (at ΔT ~ 200 K).•Segmented Bi1.95Pb0.05Te3/TAGS-85 design exhibited η of ~12% (ΔT ~494 K).
Dependences of arc duration D and contact gap at arc extinction d on contact opening speed v are studied for break arcs generated in a 48VDC resistive circuit at constant contact opening speeds. The ...opening speed v is varied over a wide range from 0.05 to 0.5m/s. Circuit current while electrical contacts are closed I0 is varied to 10A, 20A, 50A, 100A, 200A, and 300A. The following results were obtained. For each current I0, the arc duration D decreased with increasing contact opening speed v. However, the D at I0=300A was shorter than that at I0=200A. On the other hand, the contact gap at arc extinction d tended to increase with increasing the I0. However, the d at I0=300A was shorter than that at I0=200A. The d was almost constant with increasing the v for each current I0 when the I0 was lower than 200A. However, the d became shorter when the v was slower at I0=200A and 300A. At the v=0.05m/s, for example, the d at I0=300A was shorter than that at I0=100A. To explain the cause of the results of the d, in addition, arc length just before extinction L were analyzed. The L tended to increase with increasing current I0. The L was almost constant with increasing the v when the I0 was lower than 200A. However, when I0=200A and 300A, the L tended to become longer when the v was slower. The characteristics of the d will be discussed using the analyzed results of the L and motion of break arcs. At higher currents at I0=200A and 300A, the shorter d at the slowest v was caused by wide motion of the arc spots on contact surfaces and larger deformation of break arcs.
Aiming at the fast protection requirements of electrical ships LVDC distribution system, this paper studies a topology of unidirectional vacuum hybrid circuit breaker. The hybrid circuit breaker is ...an improved current injection LVDC breaker based on precharged capacitor, which improves the dielectric recovery capability of vacuum interrupter after artificial current zero by using a freewheel diode. A synthetic test platform is built to study the dielectric strength recovery characteristics of a 45 mm diameter CuCr50 butt contact vacuum interrupter (driven by Thomson coil actuator, average opening speed of about 3 m/s)under high current(about 20 kA) and small gap(about 1 mm). The experimental results indicate that the dielectric strength of the contact can recover at a very fast speed within the arc time of 100 µs; when the arc time is increased to 320 µs, the dielectric strength of the contact cannot recover for a long time. Therefore, the design principle of the circuit breaker is obtained: within the arc time of 100 µs, by increasing the arc time can increase the contact distance, so the transient interruption voltage tolerance margin of the circuit breaker can be improved. Based on the results of the test, this paper also proposes a calculation method of forced commutation circuit parameters, which is verified by the simulation. The research results show that the DC circuit breaker can realise the rapid breaking of 20 kA fault current within 2 ms, and has a good application prospect in the LVDC distribution system.
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