High Electrical Resistivity Research Articles

Favorable Contact with Low Interfacial Resistance for n-Type TiCoSb-Based Thermoelectric Devices.

In the past decade, significant efforts have been made to develop efficient half-Heusler (HH) based thermoelectric (TE) materials. However, their practical applications remain limited due to various challenges occurring during the fabrication of TE devices, particularly the development of stable contacts with low interfacial resistance. In this study, we have made an effort to explore a stable contact material with low interfacial resistance for an n-type TiCoSb-based TE material, specifically Ti0.85Nb0.15CoSb0.96Bi0.04 as a proof of concept, using a straightforward facile synthesis route of spark plasma sintering. We tested many metals with compatible coefficients of thermal expansion to TiCoSb, like Fe and Co. Still, we failed to form proper atomic bonds with the TE material. In contrast, Ti metal bonded correctly but showed very high electrical contact resistance (∼300 mΩ at one side), reducing performance due to Ti diffusion and a high potential barrier at the interface. This issue was addressed by highly doped semiconductor (HDS) contact Ti0.7Nb0.3CoSb, which matched the TE material in terms of atomic bonding, crystal structure, and stability. The leg with the HDS contact demonstrated superior electronic transport performance and low interface resistance (∼15 mΩ at one side), achieving a maximum output power of 30.7 mW at ΔT = 451 K due to the sharp interface with a low barrier height. These findings suggest that using HDS material as a contact with the same HH TE material would be an effective way to develop a TE device with low interface resistance and high thermal stability.

The effect of Aluminum (Al) ratio on the synthesis of the laminated Mn2AlB2 MAB Phase

MAB phases have recently garnered significant interest due to their excellent properties, such as high thermal and electrical conductivity, oxidation resistance, and exceptional corrosion resistance. Although the Mn2AlB2 phase has been synthesized using multiple methods recently, it requires long experimental durations (up to 7 days), high costs, and extensive experimental efforts to achieve high purity. In our study, the Mn2AlB2 MAB phase was synthesized using Al, B, and Mn as precursor materials. Specifically, we investigated the effect of Al ratios (Al:1.3, Al:3, and Al:10) on the formation of the Mn2AlB2 MAB phase. The precursor powders were mixed homogeneously in stoichiometric ratios using ball milling and cold-pressed in a 1-inch die set to form green pellets, which were then sintered in a high-temperature vacuum furnace at 1200°C. The resulting Mn2AlB2 MAB phase were characterized in terms of crystal structure, impurity, and microstructure using XRD, FESEM, and EDS.

Next Generation of 3D‐Printed Electronics: Electroplating Inside Channels to Embed 3D Copper Features within Polymeric Structures Fabricated Through Material Extrusion

AbstractMaterial Extrusion (MEX) 3D printing has been largely employed to process electrically conductive polymers to fabricate electronic components, which still suffer from bad performance due to high electrical resistance. The electroplating process is proven to drastically reduce the resistance by depositing a thin layer of copper on top of the electrically conductive polymer; however, this method comes with a price to pay: only external features can be plated with copper. The present research paper presents an innovative solution to overcome this issue by performing electroplating inside 3D‐printed parts to plate internal layers (inaccessible for electroplating purposes with traditional approaches) with copper. Electroplating inside closed channels is performed: a remarkable reduction in electrical resistance of 5 orders of magnitude (from 2300 up to 0.08 Ω) is achieved in internal tracks. The proposed approach has also been implemented “on board” a commercial MEX machine to fabricate an assembly‐free smart structure with a copper sensor completely embedded within dielectric material (improved performance compared to traditional counterpart). Furthermore, the proposed approach is proven to fully plate with copper not only planar tracks but also embedded 3D features such as coils. The present research unlocks the fabrication of assembly‐free functional devices with embedded copper elements by only extruding polymers through MEX Additive Manufacturing.

Structural, Optical, Magnetic and Electrical Properties of Zinc Oxide Doped with Iron: A Review

This study reviewed the structural, optical, magnetic and electrical properties of zinc oxide (ZnO) nano-particles doped with iron relative to zinc oxide. ZnO is an excellent nanomaterial in semiconductor industries because of its properties such as low cost, high stability and high absorbance. However, its application has been limited because of some undesirable characteristics. Hence, doping with iron has proven essential in overcoming these limitations. The X-ray diffraction studies show that the structure is hexagonal with wurtzite structure, ZnO films prefer to grow in the (002) direction. This is because each apex is parallel to the c-axis in the wurtzite structure. This review reported that optical band gap ZnO nano-particles doped with iron was found to be in the range to (3.26 - 3.35) eV. The electrical properties of these films indicated low resistivity and consequently high electrical conductivity at high dopant iron concentration. Consequently, higher electrical resistivity was observed with lower conductivity at lower iron dopant concentration. Higher iron-doped ZnO (x=0.10 and 0.20) samples exhibited obvious ferromagnetic behaviors suggesting that saturation magnetization of Zn1-xFexO nano-particles increases with the increasing of Fe doping concentration compared with pure ZnO. Hence the SEM of iron-doped zinc oxide nano-particles consists of ellipsoidal shape particles, which are well dispersed with smooth surface and uniform size.

Optical and electrical properties of proton-implanted p-GaSb for electrical isolation

Abstract The effect of proton implantation as isolation implant and subsequent annealing on the optical absorption and electrical resistivity of low-bandgap p-GaSb is reported. The measured transmittance spectra indicates that implantation creates a distribution of energy levels extending into the bandgap. Electrical measurements show that the average sheet resistance of the implanted layer increases only by an order of magnitude from its pre-implantation value at a proton dose of ∼1013 cm−2 followed by 200 °C annealing. It is also shown that annealing reduces the implantation-induced optical absorption while still retaining a high electrical resistivity.

The Effects of Turbulent Electrical Resistivity on the Response of the Solar Atmosphere to Flare Energy Input. I. Results of Radiative Hydrodynamic Simulations

A number of works have considered the role of turbulence in energy release and transport in solar flares, and in particular, on the transport of energy by thermal conduction. Here, we point out that for physical consistency, the effects of turbulence on the electrical conductivity, and hence on the ohmic heating by the return current that neutralizes the current in injected electron beams, must also be considered. Using radiative hydrodynamic simulations, in conjunction with thermal and electrical conductivities modified from their collisional values by turbulent processes, we model the heating rate along a flare loop. We derive the resulting temperature, pressure, velocity, and density profiles, and use them to calculate quantities such as the differential emission measure (DEM) and the emitted X-ray spectrum. For high levels of turbulence, the combination of high electrical resistivity and low thermal conductivity acts to create and sustain a region of very large temperature near the loop apex, creating a large overpressure that acts to suppress the upward evaporation of chromospheric material. Further, the associated large temperature gradients result in a reduction of the DEM at temperatures from 105 K to 107 K. The hard X-ray spectrum at high energies is reduced due to a lower electron flux reaching the chromosphere, but at low energies, it is enhanced due to thermal emission from the very hot coronal plasma. We assess the extent to which these results can be used to constrain the nature and role of turbulent motions in the flare volume.

Simultaneously Achieved High Piezoelectricity and High Resistivity in Na0.5Bi4.5Ti4O15-Based Ceramics with High Curie Temperature.

Good piezoelectricity and high resistivity are prerequisites for high-temperature acceleration sensors to function correctly in high-temperature environments. Bismuth layered structure ferroelectrics (BLSFs) are promising candidates for piezoelectric ceramics with excellent piezoelectric performance at high temperatures, high electrical resistivity, and high Curie temperatures (Tc). In this study, (LiMn)5+ is substituted for Bi at the A-site, and Ce-doping is performed to replace Ti ions in Na0.5Bi4.5Ti4O15, which achieves the desired combination of high piezoelectric coefficients and high resistivity. Herein, we prepared Na0.5Bi3(LiMn)0.9Ti4-xCexO15 high-temperature piezoelectric ceramics, achieving a high piezoelectric coefficient d33 of 32.0 pC/N and a high resistivity ρ of 1.2 × 108 Ω·cm (at 500 °C), and a high Curie temperature of 648 °C. It is important that the d33 variation remains within 8% over a wide temperature range from 25 °C to 600 °C, demonstrating excellent thermal stability. Structural characterization and microstructure analysis showed that the excellent piezoelectric coefficient and high resistivity of cerium-doped Na0.5Bi4.5Ti4O15-based ceramics are attributable to the synergistic effects of structural characteristics, defect concentration, refined grain size and domain morphology. This study demonstrates that the superior properties of Na0.5Bi3(LiMn)0.9Ti4-xCexO15 ceramics are crucial for the stable operation of high-temperature accelerometer sensors and for the development of high-temperature devices.

Novel Front Contacts for Hydrophobic Gas Diffusion Layers Enable High Energy Efficiency and Durability for Electrochemical CO2 Reduction to C2+ Products.

Electrochemical CO2 reduction (eCO2R) is an attractive route to mitigate the rise in the global CO2 concentration while producing value-added chemicals. Ethylene (C2H4) is one such product of eCO2R which is an essential industrial precursor with a prominent global market of $230 billion. The large-scale implementation of C2H4-selective CO2 electrolyzers is still challenge due to the low energy efficiencies causes by high ohmic resistances when either employing a hydrophobic gas diffusion layer such as expanded polytetrafluoroethylene (ePTFE), or employing a near neutral catholyte in a single-gap electrolyzer. In this work, we have developed a novel front contact for a CO2 electrolyzer in a zero-gap architecture for electrically insulating gas diffusion layers. This front contact layer allows for incorporating an ePTFE gas diffusion layer while achieving similar full cell voltages as carbon-based gas diffusion electrodes; this configuration also has the added benefits of increased cell stability and selectivity for ethylene. By tailoring the catalyst layer, gas diffusion medium, and operating conditions for a zero-gap ePTFE gas diffusion layer, we were able to achieve a full cell voltage of 2.5 V, with faradaic efficiencies of 48% for ethylene and over 90% faradaic efficiency for reduced carbon species at 200 mA cm-2 and 25 cm2 geometric area cell. This work points towards strategies for developing a scalable, stable, and high energy efficiency eCO2R for C2+ products.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Investigating the Factors Influencing the Activity of Iridium-Based Perovskite Oxide Electrocatalyst for Acidic Water Oxidation By Operando XAS

To mitigate global warming, the integration of renewable energy sources into energy conversion/generation systems is fundamental. Currently the dominant alkaline water electrolysis (AWE) technology suffers from challenges including the crossover of product gases, high ohmic resistance, limited current density and low operating pressure, mainly because of utilization of a diaphragm and a liquid electrolyte in the AWE device. Using a polymer-based proton exchange membrane (PEM) for efficient proton transfers, PEM water electrolysis (PEM–WE) technology can effectively tackle the above challenges with markedly enhanced performance, and is thus attracting broad research interest,1 but relies on scarce iridium oxide at the anode. In the quest for efficient oxygen evolution reaction (OER) electrocatalysts, iridium-based perovskite oxides have attracted attention due to their unique AxIryO3 structures and cost-effectiveness, with the diversity of these structures determining their catalytic activity.2 The geometric arrangement of [IrO6] octahedra and their interaction with A-site cations influence their OER performance, particularly those with distorted [IrO6] octahedra showing higher activity due to the proximity of π- and π* orbital structures to the Fermi level.3 Furthermore, these materials undergo surface reconstruction and metal ion dissolution under electrochemical conditions, indicating a close connection between structural evolution and catalytic activity.4 This dynamic evolution process reflects changes on the catalyst surface under various external conditions, emphasizing the importance of utilizing in-situ or operando analytical techniques to track active structures for understanding catalytic mechanisms and guiding the design of new catalysts.In this research, four iridium-based perovskite oxides with distinct crystal structures (9R-BaIrO3, 6H-SrIrO3, 3C-SrIrO3, and BCC-SrIrO3) were synthesized through the solution calcination method, aimed to act as catalysts for the OER in PEM–WE. The material characteristics and electrocatalytic performances of the surface IrOx layers post-acid treatment was rigorously analyzed utilizing ex-situ X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and electrochemical measurement. Among these catalysts, 9R-BaIrO3 demonstrated superior OER activity and durability, attributed to its exclusive face-shared [IrO6] octahedral trimer structure alongside extensive surface hydroxylation. The operando Ir L3-edge XAS and high-energy-resolution fluorescence-detected XAS (HERFD-XAS) measurement revealed changes in the oxidation state of the Ir (3+ to 4+σ) with increasing potentials, highlighting a lower Ir-O coordination environment and longer bond length as crucial factors for enhanced OER activity. Moreover, operando O K-edge XAS analysis provided in Figure 1 provides further insight into the selective oxygen binding sites during the OER, which are influenced by the degree of distortion in the [IrO6] octahedra. Specifically, oxygen species showed a preference for binding to the μ1 sites in catalysts with less symmetrical monoclinic structures, whereas, in more symmetrical tetragonal/cubic structured catalysts, oxygen species predominantly bonded to μ2 sites. Moreover, in perovskite-structured catalysts, activation at the μ3 sites leads to lattice oxygen involvement, resulting in a disordered surface structure. This disorder surpasses that observed in conventional amorphous IrOx catalysts, thereby enhancing the catalyst's efficiency in OER by promoting more dynamic and effective surface interactions. By deepening our comprehension of the operational dynamics of iridium-based perovskite oxides in OER, this research not only enriches the fundamental knowledge base but also forges a path toward the creation of more efficient and stable catalysts. Acknowledgment This work is based on results obtained from a project (JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

(Invited) Organic Coatings for Corrosion Protection: Highlighting the Polymer Molecular Mobility Contribution to the EIS Response

Organic coatings are the single most widely applied method for corrosion protection of metallic materials. The coatings have generally low permeability to water and oxygen [1,2] and high electrical resistivity (specifically ionic resistance) to impede electrochemical reactions [3,4]. Protective performance of organic coatings are commonly assessed by electrochemical impedance spectroscopy (EIS) [5]. Monitoring of impedance diagrams over immersion time in an electrolytic solution generally allows corrosion appearance in the impedance spectra to be detected, hence predicting the coating’s lifetime. Moreover, most failure modes leading to corrosion damage at the macroscopic scale do not occur without water uptake first taking place [6,7]. EIS can be used to monitor the water uptake [8-11] but rarely at elevated temperatures [12].In the field of polymer physics, molecular mobility is of prime importance as it governs the physical behavior of these macromolecular material. Broadband dielectric spectroscopy (BDS) is a widespread technique in the polymer physics community as it yields the dipole relaxation modes associated with molecular mobility in polymers [13].EIS studies of organic coatings hardly ever approach the barrier properties from a molecular mobility point of view. In recent papers [14-18], our group has studied industrial organic coatings with the objective of identifying the contribution of the molecular mobility on their electrochemical impedance responses. The coatings were first analyzed in the dry state by means of BDS, and then in the wet state by EIS. By performing EIS measurements at various constant temperatures and by applying the dielectric permittivity formalism to the impedance data, the signature of the molecular mobility (α-mode, dielectric manifestation of the glass transition) was shown in their impedance response.Through our recent studies, the presentation will highlight that temperature-controlled EIS (including ambient temperature) brings insights in the molecular mobility of protective organic coatings. Over long immersion times, such studies identified the influence of plasticization (linked to water uptake) or ageing of the polymer matrix (leaching of plasticizers, for example), which has a direct impact on the coatings performance against corrosion. The dielectric manifestation of the glass transition was evidenced from EIS measurements through the use of the dielectric permittivity formalism.

VOC Detection Using p-Type Sm(Fe,Co)O3 Perovskite Oxides

In recent years, there has been concern about the resurgence of sick house syndrome caused by volatile organic compounds (VOCs) emitted from building materials, and there is an urgent need to develop sensors that can continuously detect VOCs with high sensitivity. Our research group is conducting research on VOC detection characteristics using SmFeO3. SmFeO3 is a p-type semiconductor with a perovskite crystal structure and has high oxidation activity against VOCs. However, SmFeO3 has high electrical resistance in air, and sensors using SmFeO3 require heating to a measurable resistance range (approximately 300°C or higher), and also require a measurement system with high input impedance. For this reason, a high cost for apparatus and high power consumption are issues for practical application. Therefore, in this study, we focused on SmFe1-xCoxO3 as the sensing electrode material to operate sensors at reduced temperature. Since SmFeO3 is a p-type semiconductor, Co substitution or hole doping is expected to increase electrical conductivity, and a good redox property of cobalt ion may enhance catalytic activity of VOC decomposition. Regarding the oxidation activity of SmFe1-xCoxO3 powder, the oxidation activity against toluene increased with increasing Co content. T50 = 210oC (x=0), 205 oC (x=0.1), 155 oC (x=0.3), 165 oC (x=0.5). The oxidation activity for ethanol also increased with the amount of substitution, T50 =130oC (x=0), 110 oC (x=0.1), 85 oC (x=0.3), 75 oC (x=0.5). The temperature at which the maximum response value of each sensor was shown is 300℃ (x=0), 250℃ (x=0.1), 250℃(x=0.3), and 200oC (x=0.5). It was found that the Co substitution effectively reduce operating temperature. The response value (RVOC/Rair) in ethanol was results in S=4.6 (x=0 at 300oC), S=6.4 (x=0.1 at 250oC) and the sensor with x=0.1 increased sensor response at reduced temperature. The increase in the response value is thought to be because the sensor with x=0.1 has a higher oxidation activity at 250 oC than that with x=0 at 300 oC, The response of the sensors followed the power law, S=aPVOC n. Here, a and n are constants, and PVOC is the partial pressure of the gas. The constants a and n were determined from the equation log(S)=log(a)+nlog(PVOC), and the response value to 0.1 ppm ethanol was predicted as S=1.11 (x=0), 1.88 (x=0.1), 1.88 (x=0.3), and 1.94 (x=0.5), and it was expected that the response values at 0.1 ppm would increase due to cobalt substitution. Sensor properties mainly depend on material properties and sensor structure (sensing membrane structure). Therefore, it is suggested that higher sensitivity can be achieved by optimizing the sensor structure in the future, and it is considered that the use of cobalt substitutes as a sensor material is useful from the viewpoint of sensitivity.

Influence of Ag-18Cu-10Zn Filler Material on Microstructure and Properties of Laser-Welded Al/Cu Dissimilar Butt Joints.

Dissimilar welding between aluminum and copper poses significant challenges, primarily due to differences in their thermal and mechanical properties, resulting in brittle intermetallic compounds, limited joint strength, and high electrical resistivity. This study aims to overcome these issues by employing Ag-18Cu-10Zn filler material and optimizing laser power with a focus on improving joint strength and electrical conductivity. The results indicate that the incorporation of silver and zinc enhances the phase composition and microstructure of the weld. By forming solid solution phases such as Ag2Al and Cu5Zn8, the brittle Al2Cu phase commonly found in traditional Al/Cu welding is replaced. This not only promotes the heterogeneous nucleation of fine silver-rich grains but also restricts the excessive growth of silver-poor grains, resulting in a uniform distribution of fine grains throughout the weld. These modifications contribute to both fine-grain strengthening and dispersion strengthening. At an optimal laser power of 750 W, joint strength reaches 109 MPa, while joint resistivity decreases to 3.19 μΩ·cm, 12.6% lower than that of the aluminum alloy base material. This study proposes a process for achieving highly conductive, reliable Al/Cu dissimilar metal joints, potentially impacting the aluminum-copper connections in battery modules for new energy vehicles.

(Digital Presentation) Nanoscale Sculpturing of Al and Al Alloys for Heterogeneous Al-Cu Joints

Heterogeneous Al-Cu joints are nowadays generated in a huge variety of different techniques depending on the intended application, such as corrosion protection of Al components, electric connections with improved interfaces, or even lightweight current collectors for batteries. Four major techniques are commonly used that can be further subdivided into cladding (including roll cladding, thermo-compression bonding, friction welding etc.), vapor deposition (including PVD, CVD etc.), thermal spraying and chemical plating (including electroless and electrochemical plating). Each of the methods offers certain advantages and disadvantages for the formation of Al-Cu joints. Typically observed disadvantages are the formation of intermetallic Al-Cu compounds (IMC), higher electric resistivity, a rather low mechanical strength under static or cyclic mechanical load conditions.The present work follows the electrochemical route to form Al-Cu joints utilizing nanoscale sculpturing of the Al substrate [1] as a starting point to overcome these above described typically observed disadvantages of Al-Cu joints. The resulting nanoscale sculptured Al-Cu joint is intensively characterized with respect to its structural (see Fig. 1), chemical and mechanical properties. It was found that such Al-Cu joints offer a high mechanical load bearing capability because of the interlocking zone between Al and Cu offering a gradual change, so that an optimum stress transfer can occur without the risk of a stress pile-up at the interface between both metals.Furthermore, no intermetallic Al-Cu phases grow at the interface between Al and Cu during deposition which could mechanically weaken the joint due to embrittlement, especially under cyclic loading conditions. Another advantage is the absence of Al-Cu intermetallics in the joint, being of great importance if high current or high voltage applications are intended.Fig 1: Nanoscale sculptured Al surface with cubic interlocking surface structures in cross-section (left) and cross-sectional view on Al-Cu joint after electrochemical Cu deposition on nanoscale sculptured Al surface (right).[1] M. Baytekin-Gerngross, M.D. Gerngross, J. Carstensen, and R. Adelung, Nanoscale Horizon 1(6), 467 (2016). Figure 1

Electrical Properties of Micro-Nano Hierarchically Controlled Tin Dioxide Gas Sensors

Metal oxide semiconductor gas sensors, particularly those utilizing tin dioxide, are indispensable across various sectors, including medical diagnostics. The medical industry demands high sensitivity and selectivity to detect low gas concentrations. In our previous proposal, we integrated pulse-driven techniques with a micro gas sensor to achieve this goal. Additionally, nanostructure control, involving nanoparticles, nanoclusters, and nano/mesopores, is crucial for attaining these properties. Typically, this type of gas sensor exhibits high resistance at elevated temperatures. However, maintaining low electrical resistance at temperatures between 200°C to 400°C poses a challenge due to the associated low cost of electronic circuits. At lower temperatures, sensor resistance in the air often surpasses measurement limits. In the microsensors' sensing film, it is believed that as the sizes of secondary and tertiary particles draw closer to the electrode gap due to particle agglomeration, the contact area of these larger particles with the electrodes decreases, resulting in higher electrical resistance. Although metal oxide semiconductor gas sensors have primarily focused on the nano effect of particles, the combined nano and micro effects arising from micro-size agglomeration have not been extensively explored. Therefore, our research aims to investigate the micro-size effect of tin dioxide on micro gas sensors and evaluate its impact on electrical properties such as electrical resistance and sensor response.To synthesize tin dioxide, we utilized the reverse homogeneous precipitation method using SnCl4 and NH4HCO3, followed by the elimination of Cl ions through centrifugation. The resulting sol was dried, ground, and calcined in wet-O2 at 600°C for 3 hours. The obtained powder was mixed with water and separated into fine and coarse agglomeration using sedimentation and centrifugation method. Material characterization included X-ray diffraction (XRD) for analyzing crystallite structure, scanning electron microscopy (SEM) for observing microstructure, Brunauer-Emmett-Teller and Barrett-Joyner-Halenda (BET-BJH) analysis to assess pore structure from nitrogen adsorption-desorption isotherm, and particle size distribution (PSD) analysis. Micro gas sensor devices were fabricated for sensor measurements, with a focus on assessing the electrical resistance of SnO2 micro gas sensors in air and their response to various gases.XRD analysis revealed a rutile structure pattern in all tin dioxide samples, with no distinct average crystallite sizes (around 18 nm). SEM results showed fine SnO2 agglomerates predominantly less than 1 μm, while coarse SnO2 agglomerates were less than 5 μm, consistent with PSD analysis showing narrower distributions for fine and coarse SnO2, with mean particle sizes of 0.2 μm and 2 μm, respectively. BET results indicated that fine SnO2 had a specific surface area of 22 m2g-1, while coarse SnO2 had 19 m2g-1. BJH results showed that fine SnO2 had a specific pore volume of 0.17 cm3g-1, whereas coarse SnO2 had 0.09 cm3g-1. These pore properties suggest that fine SnO2 has a larger specific surface area and pore volume than coarse SnO2. Measurements of electrical resistance in air were conducted across temperatures ranging from 350°C to 200°C. Sensors containing fine SnO2 particles exhibited lower resistance compared to conventional tin dioxide sensors, indicating a potential influence of finer agglomerates on electrical properties. The sensor's response to various gases will be shown during the presentation.

Improving Patterning Resolution Via Solid-State Anodic Dissolution at the Polymer Electrolyte Membrane/Cu Interface Under Optimal Electrolytic Conditions

Copper (Cu) is used for metal interconnects in integrated circuits and other applications because of its high electrical conductivity and resistance to electromigration. In addition, patterned Cu has been applied as a metasurface for flexible design of refractive indices, reflectance, and transmittance,[1] and as a graphene growth catalyst for graphene transistors,[2] which provide high carrier mobility. Other applications include current collectors to improve the performance of lithium-ion batteries[3] and transparent conductive electrodes used in optoelectronic devices such as solar cells and displays.[4] Micro and nanoscale patterning of Cu surface is conventionally complex and has a high environmental impact. Photolithography and nanoimprinting are widely employed in the fabrication of semiconductor devices because of their high pattern resolution and are used for nanopatterning of Cu surfaces. However, these patterning techniques, which require resists and harsh chemicals, are complex processing processes and increase processing costs. There are also direct patterning techniques based on electrochemical approaches, such as electrochemical micromachining, however, these techniques have low resolution and a high environmental impact due to the treatment of electrolytic solutions. We previously demonstrated Cu direct patterning without using a liquid electrolyte by utilizing solid-state anodic dissolution at the polymer electrolyte membrane (PEM)/Cu interface.[5] In this approach, a PEM stamp with a patterned surface attached to Cu (anode) and electrochemical treatment in anode/PEM stamp/cathode sandwich electrochemical system enables the pattern of the PEM stamp to be transferred to the Cu surface. Although this method has been demonstrated to form patterns with a resolution of 500 nm, higher-resolution nanoscale pattern formation has not been achieved. Therefore, this study analyzed the reaction at the PEM/Cu (anode) interface using electrochemical measurements and attempted to form high-resolution Cu patterns by optimizing the electrolytic conditions. Cyclic voltammetry (CV) was performed on a potentiostat using a two-electrode electrochemical system consisting of Cu (anode)/PEM stamp/Pt(cathode) with Cu as the anode (working electrode) and Pt as the cathode (which serves both the counter and the reference electrode). The voltage range was set to -1 to +1 V to avoid the influence of oxygen and hydrogen generation, and the scanning speed was 5 mV/s. PEM stamps were prepared via hot embossing and immersed in deionized water before use, and the experiments were conducted at room temperature and pressure. The CV curve exhibited peaks at a voltage of around 500 mV (Fig. 1(a)). The standard electrode potentials for the Cu ionization reaction are 337 and 520 mV for Cu2+ and Cu+, respectively, and can be attributed to peaks at around 500 mV. This result indicates that at voltage after 500 mV, Cu+ reactions occur in addition to Cu2+. The CV curves also exhibited peaks in the negative bias region, suggesting that the Cu ions in PEM were reduced at the PEM/Cu interface. Although previous studies have discussed the problem of degradation of PEM etching performance due to the deposition of Cu ions inside the PEM by repeated use, this negative bias reduction was demonstrated to restore the PEM etching performance to its pre-use state. To demonstrate nanoscale patterning, PEM stamps with 100 nm scale Line & Space (L&S) patterns were used to fabricate patterns on a 200 nm Cu thin film deposited on a silicon (Si) substrate by electrolysis at a constant voltage of 1 V and 500 mV for 1 min, respectively. The scanning electron microscopy (SEM) image shown in Fig. 1(b-1), the pattern width was non-uniform under the 1 V electrolysis condition, suggesting excessive etching. In contrast, under the 500 mV electrolysis condition, the pattern was uniform, and a 100 nm scale L&S pattern was fabricated with high resolution (Fig. 1(b-2)). Therefore, the electrolysis time was changed from 1 min to 10 s under the 1 V electrolysis condition, resulting in the formation of a high-resolution pattern as well as 500 mV electrolysis condition. These results suggest that the amount of charge is an important factor in the application of our technology to nanopatterning. Thus, by adjusting the electrolysis conditions, such as 10 s of 1 V electrolysis, ultrafast patterning can be achieved, resulting in improved processing efficiency.

Theory Guided Discovery of Superior Ru-Based Electrocatalyst for Durable Acidic Oxygen Evolution Reaction

Water electrolysis (WE) using hydrogen evolution reaction is widely recognized as a promising method for clean and sustainable hydrogen production. The currently dominant alkaline-based water electrolysis encounters several challenges including high ohmic resistance, limited current density, low efficiency, and poor long-term stability. Proton exchange membrane (PEM) electrolysis can tackle these challenges by providing efficient proton transfer. However, sluggish oxygen evolution reaction (OER) in acid has been a major long-existing obstacle in PEM systems and, therefore, has attracted great research interest.Due to its high activity and durability, IrO2 is currently considered the only practical OER electrocatalyst in PEM devices. However, Ir’s high cost and low global reserve limit its large-scale applications. Hence, less-expensive catalysts for acidic OER are in great demand. RuO2 has been recognized as an attractive alternative to IrO2 because Ru is ~100x abundant and costs ~10x less. Although RuO2 presents higher activity than IrO2, it deteriorates severely in a few hours due to its dissolution under oxidizing conditions. Its long-term stability remains a big challenge.To overcome the challenge of improving the stability of Ru-based oxides, in this work we provide a rigid theoretical framework of RuO2 dissolution under the influence of other metal species. We show that the stability of Ru-based oxides could be controlled by varying the properties of incorporated metal oxides as well as the synergy to form a complex oxide. Surveying the Materials Project database led to the rationalization of a series of metal elements that could positively improve the stability of RuO2. Guided by our theoretical approach, we conducted high-throughput screening and experimental evaluation of Ru-based oxides for acid OER.Our study discovered a novel Ru-based oxide with superior performance in acid OER application. A new wet-impregnation method was developed to synthesize the desired phase. The as-obtained product were uniform nanoparticles with diameters less than 5 nm in a single rutile structure. The new catalyst showed significantly better performance than pristine RuO2. In the rotating-disk-electrode experiment, our catalyst delivered a current density of 10 mA·cm-2 at an overpotential of less than 170 mV in 0.1 M HClO4. The catalyst exhibited a low degradation rate smaller than 25 μVh-1 for over 200 hours of operation at 10 mA·cm-2. Our results show great promise of Ru-based oxides as Ir-free electrocatalysts for acidic OER in PEM water electrolysis.

Reactive Force-Field Molecular Dynamics Study for Analysis of Silicon Nanocrystal Formation Process in Silicon Oxide Film

Recently, Tunnel Oxide Passivated Contact (TOPCon) solar cells using ultra-thin silicon oxide (SiO x ) films as passivation films have attracted attention due to the high conversion efficiency of 25.7% [1]. Generally, thick SiO x films exhibit excellent passivation performance and lead to long-term reliability of the solar cells[2]. However, in TOPCon solar cells, the thickness of the passivation film is limited to 1~2 nm due to the high electrical resistance of the SiO x film. Therefore, a new SiO x film (named NATURE contact) with improved conductivity through silicon nanocrystals (Si NCs) have been developed by Tsubata et al. [3]. The left figure shows the structure of NATURE contact. It consists of three SiO x layers with different oxygen concentrations. The Si NCs formed in the thin Si-rich layer in the center functions as a carrier transport pathway. The passivation film with the NATURE contact has shown a good passivation performance and conductivity even for relatively thick SiO x films. Since the effects of multidimensional process parameters during NATURE contact formation have been neither elucidated nor optimized, there is significant room for performance improvement in NATURE contact. Therefore, it is of crucial importance to understand the atomic level growth process of Si NCs during formation of NATURE contact and its impact of the oxygen concentration and temperature.We employed Reactive force-field molecular dynamics (ReaxFF MD) method, which reproduces chemical reactions using a bond order-dependent concept. The method has been used in studies such as Si deposition simulations [4]. The periodic boundary conditions were applied to the simulation box for all directions in the size of 65 Å × 40 Å × 45 Å. Crystalline silicon was placed throughout the simulation box and the atoms of the simulated Si NC section were fixed in the center of the box. Crystals other than the fixed portion are then made amorphous using the Melt-Quench method. Finally, the fixation was released to allow the entire box to react. Crystallinity was evaluated by the average radius calculated from the number of atoms constituting the crystal. It is noted that the average radius is evaluated up to 25 Å due to the size of the simulation box. Annealing was performed in the following three processes: pre-moistening, amorphization, and crystal growth. We varied the temperature of crystal growth at 1500 - 2500 K and the oxygen concentration at 0 - 5 %. We investigated the effects of temperature and oxygen concentration on the growth of Si NCs in a-SiO x .The right figure shows the transition of the mean radius of the Si NCs at different temperatures. As a result, when the temperature was varied, a peak in the size of crystal growth was observed at 2250 K, and the crystals disappeared at 2500 K. The trend of maximum crystal growth at a certain temperature and the qualitative agreement were experimentally confirmed [5]. This result suggests that the change in the size of Si NCs occurred because the kinetic energy of Si atoms is larger than the energy barrier required from a-Si to c-Si. The initially placed Si NC of 269 atoms was appropriately shaped or grown. This is consistent with the nucleation theory[6]. When the oxygen concentration was increased, no crystal growth was observed. Experiments have shown that increasing oxygen concentration tends to suppress crystallization [3]. This result suggests that the change in the size of Si NCs was caused by the interdiffusion of silicon and oxygen.

Study of structural, elastic, optical, dielectric, and magnetic properties of sol-gel synthesized Li0.2Co0.3Zn0.3Fe2.2O4 ferrite for optoelectronic and electrical applications

This work presents a detailed investigation of the structural, elastic, optical, dielectric, and magnetic properties of Li0.2Co0.3Zn0.3Fe2.2O4 ferrite synthesized through the sol-gel process. The experimental structural parameters closely match the theoretical values, confirming the proposed cation distribution of the prepared sample. The FTIR spectrum and ultrasonic pulse transmission method analysis showed that the sample has brittle mechanical properties. According to UV-Vis optical absorbance analyses and based on Tauc's law, the sample exhibits a direct optical transition, with the band gap energy (Eg) determined to be 2.51 eV. The study of electrical conductivity showed that the sample exhibited a reduced activation energy (Ea= 0.154 eV) and remarkable electrical resistivity at room temperature (ρdc ∼ 104 Ω.m), indicating the material's potential for microwave device applications. The conduction process of the sample aligns with the NSPT model. Additionally, the temperature coefficient of resistance (TCR) suggests that the sample is a promising candidate for infrared radiation detection. A low coercive field was also derived from the hysteresis loop, confirming the soft nature of the sample operating within a microwave frequency range of 8–9 GHz. Our results show that the Li0.2Co0.3Zn0.3Fe2.2O4 compound offers advantages over the undoped Li0.5Fe2.5O4 compound, including a lower band gap, reduced activation energy, and higher electrical resistivity. This suggests that substituting Co and Zn into Li0.5Fe2.5O4 ferrites improves their performance in electrical and optoelectronic applications.

High‐performance and flexible thermoelectric generator based on a robust carbon nanotube/BiSbTe foam

AbstractOrganic thermoelectric generators (TEGs) are flexible and lightweight, but they often have high electrical resistance, poor output power, and low mechanical durability, because of which their thermoelectric performance is poor. We used a facile and rapid solvent evaporation process to prepare a robust carbon nanotube/Bi0.45Sb1.55Te3 (CNT/BST) foam with a high thermoelectric figure of merit (zT). The BST sub‐micronparticles effectively create an electrically conductive network within the three‐dimensional porous CNT foam to greatly improve the electrical conductivity and the Seebeck coefficient and reinforce the mechanical strength of the composite against applied stresses. The CNT/BST foam had a zT value of 7.8 × 10−3 at 300 K, which was 5.7 times higher than that of pristine CNT foam. We used the CNT/BST foam to fabricate a flexible TEG with an internal resistance of 12.3 Ω and an output power of 15.7 µW at a temperature difference of 21.8 K. The flexible TEG showed excellent stability and durability even after 10,000 bending cycles. Finally, we demonstrate the shapeability of the CNT/BST foam by fabricating a concave TEG with conformal contact on the surface of a cylindrical glass tube, which suggests its practical applicability as a thermal sensor.

Regulation of Interface Compatibility and Performance in Soft Magnetic Composites with Inorganic Insulation Layers by FePO4 Intermediate Transition Layer.

In the fabrication of soft magnetic composites, the lattice mismatch between the inorganic insulation layer and the iron matrix often leads to the formation of cracks during the molding process, which significantly impairs the operational performance of the materials. Consequently, it is imperative to develop novel strategies for inorganic insulation coatings that offer high electrical resistivity and thermal stability and are less susceptible to cracking during formation. This paper presents a new structure for soft magnetic composites that incorporates FePO4 as an intermediate transition layer between the iron-based soft magnetic particles and the inorganic ceramic insulation layer. This configuration is designed to provide insulation coatings with superior voltage and thermal resistance, as well as high electrical resistivity. The research details the processes forming the FePO4 intermediate transition layer and the SiO2 insulation layer on the iron powder surface, along with their interaction mechanisms. An analysis comparing the scenarios with and without the FePO4 intermediate transition layer shows its beneficial impact on the magnetic properties and mechanical strength of the soft magnetic composites. Further investigations reveal that at a phosphoric acid concentration of 1 wt.%, the FePO4 layer significantly enhances the interface compatibility between the Fe powder matrix and the SiO2 insulation layer. Under these conditions, the Fe@ FePO4/SiO2 soft magnetic composites demonstrate outstanding overall performance: the saturation magnetization stands at 215.60 emu/g, effective permeability at 83.2, resistivity at 57.42 Ω·m, power loss at 375.0 kW/m3 under 30 mT/100 kHz, and radial compressive strength at 15.95 Kgf. These findings offer novel insights and practical approaches for advancing inorganic insulation coating strategies and provide vital scientific support for further enhancing the magnetic and mechanical properties of soft magnetic composites.