Four-probe Measurements Research Articles

Effect of incorporating ultrafine palm oil fuel ash on the resistance to corrosion of steel bars embedded in high-strength green concrete

Abstract Durability degradation in reinforced concrete (RC) constructions is commonly attributed to the steel reinforcement corrosion caused by chloride. The utilization of supplemental cementitious resources, such as waste materials from industrial and agricultural sectors, typically improves the impermeability and strengthens concrete resistance to corrosion, sulfate, and acid attacks. Therefore, the prevention of steel reinforcement corrosion is greatly important in resolving challenges related to the durability and stability of RC structures, particularly when utilizing agriculture waste materials. This approach also serves as a solution for waste disposal. The aim of this study is to investigate the corrosion-resistant characteristics of high-strength concrete that contains ultrafine palm oil fuel ash (U-POFA) as a partial replacement for cement. Four high-strength green concrete (HSGC) mixes were investigated in this study with a partial replacement of ordinary Portland cement (OPC) by U-POFA at 0, 20, 40, and 60% by mass. The aim of this study is to analyze the workability, strength activity index (SAI), compressive strength, rapid chloride permeability, linear polarization resistance (LPR) by different measurement methods, and four-probe resistivity measurement by electrical resistivity measurement method of over a curing period of 7, 28, 60, and 90 days. The use of U-POFA in the different mixes results in improved workability, SAI, compression strength, and chloride penetration resistance compared with the zero-POFA mix. It is clear from the study results that adding U-POFA as a partial replacement for OPC improved the corrosion resistance of HSGC mixtures. Thus, the incorporation of U-POFA 60% succeeded in reducing the chloride ion penetration by 80% and the LPR by 93% at the test age of 90 days, compared to the reference mixture.

Structural, magnetic, and electrical properties of LaMnO3 doped with Na by microwave-assisted synthesis method

Abstract The electric and magnetic transport properties of La1-xNaxMnO3 (x = 0.15, 0.2, 0.25, 0.3) are studied using the X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and four-probe resistivity measurement method. The samples are synthesized by the method of microwave heating. The obtained samples show phase changes around x = 0.25. The magnetization measurement shows the curie temperature (Tc) increases as the level of doping increases and saturates around x = 0.25. The resistivity measurement dramatically decreases at a metal-insulator transition temperature close to Tc. These findings are discussed along with the structural features of different Na concentrations.

Long-distance electron transport in multicellular freshwater cable bacteria.

Filamentous multicellular cable bacteria perform centimeter-scale electron transport in a process that couples oxidation of an electron donor (sulfide) in deeper sediment to the reduction of an electron acceptor (oxygen or nitrate) near the surface. While this electric metabolism is prevalent in both marine and freshwater sediments, detailed electronic measurements of the conductivity previously focused on the marine cable bacteria (Candidatus Electrothrix), rather than freshwater cable bacteria, which form a separate genus (Candidatus Electronema) and contribute essential geochemical roles in freshwater sediments. Here, we characterize the electron transport characteristics of Ca. Electronema cable bacteria from Southern California freshwater sediments. Current-voltage measurements of intact cable filaments bridging interdigitated electrodes confirmed their persistent conductivity under a controlled atmosphere and the variable sensitivity of this conduction to air exposure. Electrostatic and conductive atomic force microscopies mapped out the characteristics of the cell envelope's nanofiber network, implicating it as the conductive pathway in a manner consistent with previous findings in marine cable bacteria. Four-probe measurements of microelectrodes addressing intact cables demonstrated nanoampere currents up to 200 μm lengths at modest driving voltages, allowing us to quantify the nanofiber conductivity at 0.1 S/cm for freshwater cable bacteria filaments under our measurement conditions. Such a high conductivity can support the remarkable sulfide-to-oxygen electrical currents mediated by cable bacteria in sediments. These measurements expand the knowledgebase of long-distance electron transport to the freshwater niche while shedding light on the underlying conductive network of cable bacteria.

Electrodeposition of ReMo alloys

The electrodeposition of superconducting ReMo alloys is investigated using highly concentrated electrolytes with acetate, citrate, and the two oxometallate anions, MoO42− and ReO4−. The effects of applied deposition current, the concentrations of acetate, citrate, and metal source in the electrolyte on the film composition, faraday efficiency as well as the partial current densities of Re and Mo are systematically studied. A hybrid complex species, such as (MoO42−)(ReO4−)(HCit3−)2 and its partially reduced form, is proposed to form and mediate the co-deposition reaction. The morphology and superconductivity of alloy films are characterized using microscopy and cryogenic four-probe measurements. The electrodeposited ReMo alloy films maintain the same amorphous grain structure and the same enhanced superconducting transition temperature as pure Re films.

Failure Analysis and Piezo-resistance Response of Intralaminar Glass/Carbon Hybrid Composites Under Blast Loading Conditions

Abstract In this study, damage mechanisms and the piezo-resistance response of glass/carbon intralaminar hybrid composites are examined under blast loading conditions. Two-ply orientations are considered, namely a repeating ((G45C45)R) and an alternating ((G45C45)A) +/− 45° glass/carbon layers, along with three boundary condition configurations: simply supported, partially fixed, and fully fixed are applied. A shock tube apparatus and the three-dimensional digital image correlation technique are utilized to investigate the interaction of shock waves with the composites and gather a comprehensive deformation field during the loading. A modified four-probe resistivity measurement method is implemented to comprehend the piezo-resistance response associated with damage evolution. The results underscore the substantial influence of boundary conditions on the blast mitigation capacity of the composites. Analysis following the experiments reveals that the damage to the specimens primarily involves the fracture of fibers accompanied by internal delamination. Thermal imaging of the tested composite specimens provides enhanced insight into the precise occurrences of internal fiber breakage and delamination. Composites of (G45C45)A type demonstrate an increased energy dissipation ranging from 18% to 33% compared to (G45C45)R composites, depending on the specific boundary conditions among the three types considered. Furthermore, the findings indicated a strong correlation between changes in piezo-resistance and the fracture of carbon fibers, coupled with the sustained deformation of the composites. Notably, (G45C45)A composites exhibited 100% ∼ 300% higher change in piezo-resistance compared to (G45C45)R composites, indicative of the superior damage-sensing capabilities of the former.

Characterisation of Sn-Cl co-doped β-Ga2O3 thin films deposited via spray pyrolysis and their application in UV detector devices

Ga2O3, an ultrawide bandgap semiconducting oxide, is currently emerging as a promising candidate for various applications, such as power devices, solar-blind UV detectors, high temperature oxygen sensors and biomedical imaging. One significant limitation hindering the application of Ga2O3 as a wide-bandgap semiconductor is its poor conductivity. In this work, we investigate whether doping with tin and chlorine can mitigate this condition. Sn-Cl co-doped β-Ga2O3 thin films are deposited on glass substrates using spray pyrolysis technique. The deposited films are subjected to comprehensive analysis, including structural, optical and morphological measurements using techniques like X-ray diffraction, UV-Vis-NIR spectroscopy, X-ray photoelectron spectroscopy and EDX studies. Electrical properties are assessed using the four-probe method and Hall measurements. The best conductivity of 8.86 Ω−1m−1 is observed when 8.68 at% of Sn and 3.37 at% of Cl were co-doped into Ga2O3 (S(3)) and its optical band gap is calculated to be 4.65 eV. This is about five orders of improvement in conductivity as compared to that of pure Ga2O3 thin film deposited by the same method. Furthermore, we have constructed a deep UV detector utilizing doped β-Ga2O3 thin films as the semiconducting absorbing layer. The detector demonstrated the highest responsivity of 2.54 × 10−4 A/W at 260 nm and the corresponding specific detectivity is 1.4 × 109 Jones. The current research validates the potential of Sn-Cl co-doped β-Ga2O3 thin film as an excellent choice for UV detector application.

Effect of internal moisture on the electric conductivity of cement composites with expanded graphite determined by impedance spectroscopy

The paper presents the results of a study of the effect of internal moisture on the electrical conductivity of cement composites with expanded graphite. Cement pastes with different content of expanded graphite were prepared for measurement. The electrical conductivity was determined by using impedance spectroscopy at different degrees of water saturation. The results of the impedance spectroscopy were presented in Nyquist plots. On the basis of the obtained Nyquist plots, electrical equivalent circuits were fitted for different water saturation. Capacitance and resistance were calculated from the fitted equivalent circuits. Additionally, DC four-probe resistance measurements were carried out. The results showed that internal moisture affects the electrical conductivity of composites not only for a low amount of expanded graphite but also for the content in the percolation zone. For composites with expanded graphite with percolation zone (4 and 5 wt%), the dominant conduction mechanism changed from electron to ionic with moisture content. This change is observed as a change in the nature of the Nyquist plot from a vertical line to a semicircle. Internal moisture does not affect the conductivity of cement composites with expanded graphite higher than the percolation threshold.

Full lifetime demonstration of a Micro-Cathode-Arc thruster evolution characteristics

Ground lifetime test is the most crucial experiment to assess the performance, reliability, and flight qualification of electric propulsion, and it can bring new insights for understanding the operation characteristics. This work demonstrates a full lifetime test of 140000 cycles on a Micro-Cathode-Arc Thruster (μCAT) with 160 μs charging time and 86 mJ charging energy. A four-probe resistivity measurement method is utilized to investigate variations in the conductive film thickness and resistivity throughout the thruster lifespan. Direct film parameters show that the lifetime of the μCAT can be divided into three stages. In the initial stage, the film thickness decreases by 1.2 μm and the resistivity increases significantly due to the high discharge intensity and intense film ablation; In the steady stage, the change of the film thickness is within 5%, and the resistivity of the film increases slowly from 0.050 Ω·mm to 0.223 Ω·mm. In the end stage, the resistivity exponentially increases from 0.223 Ω·mm to 1.176 Ω·mm, with the increase accounting for 81%, ultimately resulting in the failure of the thruster open circuit. Additionally, the evolution of discharge parameters, and the variation of plume parameters are measured throughout the lifetime. The discharge characteristics also show significant differences in the duration of voltage and current in these three stages. The results of plume shape and plasma parameters are also well consistent with the discharge parameters and film state. These results suggest that, for evaluating the steady stage lifetime of thrusters, the film thickness is the best indicator compared to the variations in resistivity and voltage-current characteristics. For the end stage, the plasma plume morphology, discharge duration, and plume parameters can conveniently and clearly characterize the thruster failures and irregularity.

High carrier mobility in organic cations intercalated multilayer MoS2

Two-dimensional semiconductors, such as MoS2, have demonstrated great potential applications in post-Moore electronic and optoelectronic devices, and organic cations intercalation has been widely utilized to modulate their physical properties. However, the correlation between the conductivity, carrier mobility, carrier density, and structure of organic cations intercalated MoS2 is still unclear. In this Letter, we systematically investigated the structural and electrical transport properties of pristine MoS2 and MoS2 intercalated with various organic cations such as tetradecyltrimethyl-ammonium, tetraheptyl-ammonium, and cetyltrimethyl-ammonium. Semimetal bismuth (Bi) was used as electrodes to make Ohmic contact with MoS2, and four-probe measurements were employed to obtain the intrinsic conductivity of MoS2. The intercalated organic cations greatly expand interlayer spacing and strongly dope MoS2 up to an electron concentration of 6.1 × 1013 cm−2 depending on the size and intercalation amount of organic cations. The severe electron doping constrains the out-of-plane A1g vibration mode and screens the Coulomb scattering, such that the intercalated MoS2 has enhanced Hall mobility of >50 cm2 V−1 s−1 at room temperature and even >1700 cm2 V−1 s−1 at 5 K. The intercalated MoS2 responds much faster than pristine MoS2 when functioning as a phototransistor. Our work provides insight for understanding the electrical transport properties of MoS2 and designing more efficient electronic and optoelectronic devices.

Study of the ZnO/MoS2 heterostructures-based gas sensor for humidity-independent response

In this study, several strategies including coating with a hydrophobic MoS2 layer, UV light illumination, raising temperature, alternating current (AC), and four-probe measurement have been systematically studied to overcome humidity dependence response behavior for the ZnO sensor. Catalyst-free CVD method was used to prepare pure ZnO nanorods and ZnO/MoS2 heterostructures, and the prototypes were then fabricated on the substrates with Pt interdigital (ID) electrodes, respectively. The gas sensing properties of two sensors were systematically investigated. The ZnO/MoS2 heterostructures-based sensor with four-probe measurement operating at 150 °C shows stable responses during a wide humidity variation range. Furthermore, the ZnO/MoS2 sensor obtains excellent sensing performance to NO2 with a high sensitivity of 12.6 %/ppm and high sensor responses at 150 °C and UV light illumination. Additionally, a low theoretical LoD of 6.5 ppb NO2 is achieved for ZnO/MoS2 heterostructures-based sensor.

Comparison between Four-Probe and Two-Probe Electrical Resistivity Measurement to Monitor the Curing and Piezoresistivity Behavior of Smart Cement Paste Modified with Waste Steel Slag and Green Nano-magnetite

Abstract This study aims to examine the compressive strength, electrical resistivity, and piezoresistivity characteristics of ordinary Portland cement (OPC) with a constant water-to-cement ratio (w/c) of 0.38. The optimal value of steel slag (SS) was determined to be 5 % based on the compressive strength of six different mixes of cement paste modified with various SS from 0 % to 30 % weight of cement. Additionally, the investigation will include modified cement samples containing 1 % green synthesized material and commercially available nano-magnetite (NM). Because iron is the primary component of SS and NM, the electrical resistivity, which is the primary criterion for structural health monitoring of cementitious material, can be increased by adding SS and NM. Hence, a comparative analysis was conducted to assess the resistivity of cement paste throughout the early curing period up to 28 days using an alternative current (AC) and embedding wires into the specimen, employing both the two-probe (2P) and four-probe (4P) methodologies. The findings suggest that the 4P method is a more precise approach for determining electrical resistivity than the 2P method, as the wire probe is not considered in the 4P method. Hence, it is imperative to compute the correlation between the 2P and 4P methodologies in order to attain a precise resistivity measurement. The suggested model indicates that the expected 4P resistivity can be measured with high precision, a high coefficient of determination (R2) of .97, and a low root mean square error (RMSE) of 7.33 Ω·m, based on the 2P result. The piezoresistivity results demonstrated that the cement paste modified with green synthesis nano-magnetite (GSNM) had a higher electrical resistivity (ER) change, 10.85 % greater than cement paste only, 57 % higher than cement modified with SS, and 34.2 % higher than cement paste modified with commercial nano-magnetite (CNM) after 28 days of curing. In addition, the compressive strength of cement paste modified with GSNM was higher than that of cement paste, cement paste modified with SS, and cement paste modified with CNM by 15.96 %, 21 %, and 1.7 %, respectively, after 28 days of curing. A Vipulanandan p–q model was used to forecast the electrical resistivity of cement paste versus time at start hydration during 28 days of curing and the change of electrical resistivity versus compressive strength at 3, 7, and 28 days. The Vipulananda p–q model anticipated both electrical resistivity and piezoresistivity behavior well.

Origin of the near-room temperature resistance transition in lutetium with H2/N2 gas mixture under high pressure.

The recent report of room-temperature superconductivity at near-ambient pressure in nitrogen-doped lutetium hydride (Lu-H-N) by Dasenbrock-Gammon etal. [Nature 615, 244-250 (2023)] has attracted tremendous attention due to its anticipated great impact on technology. However, the results could not be independently reproduced by other groups worldwide in follow-up studies, which elicited intense controversy. Here, we develop a reliable experimental protocol to minimize the extensively concerned extrinsic influences on the sample by starting the reaction from pure lutetium loaded with an H2/N2 gas mixture in a diamond anvil cell under different pressures and temperatures and simultaneously monitoring the entire chemical reaction process using in situ four-probe resistance measurements. Therefore, we could repeatedly reproduce the near-room temperature upsurge of electrical resistance at a relatively early stage of the chemical reaction. However, the mechanism is suggested to be a metal-to-semiconductor/insulator transition associated with the structural modulation in the non-stoichiometric Lu-H-N, rather than superconductivity.

Negative Differential Interlayer Resistance in WSe2 Multilayers via Conducting Channel Migration with Vertical Double-Side Contacts.

The inherent interlayer resistance in two-dimensional (2D) van der Waals (vdW) multilayers is expected to significantly influence the carrier density profile along the thickness, provoking spatial modification and separation of the conducting channel inside the multilayers, in conjunction with the thickness-dependent carrier mobility. However, the effect of the interlayer resistance on the variation in the carrier density profile and its direction along the thickness under different electrostatic bias conditions has been elusive. Here, we reveal the presence of a negative differential interlayer resistance (NDIR) in WSe2 multilayers by considering various contact electrode configurations: (i) bottom contact, (ii) top contact, and (iii) vertical double-side contact (VDC). The contact-structure-dependent shape modification of the transconductance clearly manifests the redistribution of carrier density and indicates the direction of the conducting channel migration along the thickness. Furthermore, the distinct characteristic of the electrically tunable NDIR in 2D WSe2 multilayers is revealed by the observed discrepancy between the top- and bottom-channel resistances determined by four-probe measurements with VDC. Our results provide an optimized device layout and further insights into the distinct carrier transport mechanism in 2D vdW multilayers.

Influence of A-Site Modifications on the Electrical and Crystallographic Properties of Ln0.2Sr0.7-XCaxTi0.95Fe0.05O3-δ (Ln=La, Nd) Based Fuel Electrode for Solid Oxide Cell

Perovskite oxides, in particular SrTiO3–based compounds have attracted particular attention over the past years due to their decent conductivity, good dimensional stability and high tolerance and resistance towards sulfur poisoning and carbon depositions [1, 2]. Optimal doping and stoichiometry levels on A- (La, Nd etc.) and B-sites (Fe, Ni etc.) of SrTiO3 based compounds allow to improve catalytic activity, electrical conductivity and chemical stability [2]. In addition, doping of A-site with calcium is predicted to enhance the electronic conductivity because it should decrease the unit cell volume bringing the conduction orbitals of titanium closer to each other [3].In this research influence of chemical composition of A-site on electrical and electrochemical performance of Ln0.2Sr0.7-xCaxTi0.95Fe0.05O3-δ (Ln=La, Nd) (x=0.35, 0.45) (LSCTF-x, NSCTF-x) hydrogen electrode has been investigated. The crystal structure and microstructure have been studied using X-ray diffraction and SEM to confirm the phase purity and visualize the microstructure of studied electrode layers. To understand the influence of MIEC material composition on electrical conductivities of LSCFT and NSCTF, the DC four-probe conductivity measurements of porous electrode layers has been performed. Conductivities have been measured at two different atmospheres: 1% H2 + 3% H2O + 96% Ar and 97% H2 + 3% H2O. It has been shown that the both LSCTF and NSCTF materials behave like semiconductor and the conductivity is significantly dependent on composition. The maximal total electrical conductivity of porous electrode layers were 5.5 S cm− 1 and 4.8 S cm− 1 at 850 °C characteristic for the La0.2Sr0.25Ca0.45Ti0.95Fe0.05O3-δ (LSCTF-45) and Nd0.2Sr0.35Ca0.35Ti0.95Fe0.05O3-δ (NSCTF-35) materials, respectively, in 97% H2 + 3% H2O atmosphere. Keywords: solid oxide fuel cell; perovskite; fuel electrode; MIEC; LST. [1] X. Li, H. Zhao, X. Zhou, N. Xu, Z. Xie, N. Chen, Electrical conductivity and structural stability of La-doped SrTiO3 with A-site deficiency as anode materials for solid oxide fuel cells, international journal of hydrogen energy 35 (2010) 7913-7918.[2] A. Gondolini, E. Mercadelli, G. Constantin, L. Dessemond, V. Yurkiv, R. Costa, A. Sanson, On the manufacturing of low temperature activated Sr0.9La0.1TiO3-δ-Ce1-xGdxO2-δ anodes for solid oxide fuel cell, Journal of the European Ceramic Society, 38 (2018) 153–161.[3] A.D. Aljaberi, J.T.S. Irvine, Ca-substituted, A-site deficient perovskite La0.2Sr0.7TiO3 as a potential anode material for SOFCs. J. Mater. Chem. A 2013, 1, 5868-5874.

Influence of A-Site Deficiency and B-Site Composition on the Electrical and Crystallographic Properties of (La0.25Sr0.25Ca0.45)yTi0.95Ni0.05-xMnxO3-δ Solid Oxide Fuel Cell Anode

(La,Sr)TiO3-δ has attracted specific attention over the past years due to its superior dimensional stability, high conductivity, and significant tolerance against sulfur poisoning and carbon depositions. To increase the catalytic activity and chemical stability, many different doping levels and stoichiometries for LaxSr1-xTiO3-δ (LST) have been investigated [1, 2]. Doping of B-site with Mn has been shown to promote electroreduction under SOFC conditions [3]. Furthermore, Mn is known to accept lower coordination numbers in perovskites, especially for Mn3+ (3d4), and so may enhance oxide-ion migration [4]. In addition, MnO is clearly stable under fuel conditions unlike Co or Ni oxides [4].In this research influence of A-site deficiency and B-site chemical composition on electrical performance of La0.25Sr0.25Ca0.45Ti0.95Ni0.05-xMnxO3-δ (x=0-0.05) (LSCTNM-x) hydrogen electrode has been studied. The crystal structure and microstructure have been studied using X-ray diffraction and SEM to confirm the phase purity and visualize the microstructure of studied electrode layers. To understand the influence of MIEC material composition on electrical conductivities of LSCTNM, the DC four-probe conductivity measurements of porous electrode layers has been performed. Conductivities have been measured at two different atmospheres: 1% H2 + 1.7% H2O + 97.3% Ar and 98.3% H2 + 1.7% H2O. It has been shown that all materials with LSCTNM compositions behave like semiconductor and the conductivity is significantly dependent on composition. The maximal total electrical conductivity of porous electrode layers was characteristic for the LSCTNM materials with 10% A-site deficiency, in 98.3% H2 + 1.7% H2O atmosphere. Keywords: solid oxide fuel cell; conductivity; perovskite; fuel electrode; MIEC.[1] X. Li, H. Zhao, X. Zhou, N. Xu, Z. Xie, N. Chen, Electrical conductivity and structural stability of La-doped SrTiO3 with A-site deficiency as anode materials for solid oxide fuel cells, international journal of hydrogen energy 35 (2010) 7913-7918.[2] A. Gondolini, E. Mercadelli, G. Constantin, L. Dessemond, V. Yurkiv, R. Costa, A. Sanson, On the manufacturing of low temperature activated Sr0.9La0.1TiO3-δ-Ce1-xGdxO2-δ anodes for solid oxide fuel cell, Journal of the European Ceramic Society, 38 (2018) 153–161.[3] P. Holtappels, J. Bradley, J.T.S. Irvine, A. Kaiser, M. Mogensen, Electrochemical characterization of ceramic SOFC anodes, J. Electrochem. Soc. A 148 (2001) 923–929.[4] S. Tao, J.T.S. Irvine, A redox-stable efficient anode for solid-oxide fuel cells, nature materials, 2 (2003) 320-323.

Properties of superconducting MgB2 spherical shells deposited on 2 mm and 1 mm diameter Si3N4 spheres

Superconducting spherical shells may not only provide an appealing platform for exploring superconductivity in three-dimensional (3D) geometries with curved surfaces, but also be practically applied in important fields, such as in gyroscopes and gravimeters. In inertial confinement fusion (ICF), the perturbation on the target capsule caused by traditional contact support methods is recognized as one of the major contributors to performance degradation in ICF implosions. It was proposed recently that coating the capsule with a thin superconducting MgB2 spherical shell to realize non-contact support by means of magnetic levitation at the required temperatures K might offer a promising solution to this longstanding problem. To simulate the coating of ICF capsules, we deposited MgB2 spherical shells onto polycrystalline Si3N4 spheres (diameter d = 2 mm and 1 mm) via a hybrid physical–chemical vapour deposition technique. For both diameters, the spherical shells, of about 1 µm in thickness and covering the whole spheres completely, were polycrystalline with thin plate-shaped MgB2 crystallites oriented randomly and closely connected. The spherical shells exhibited superconducting transition at a zero resistance temperature of 38.5–39.4 K in four-probe resistance measurements and ideal diamagnetism at low temperatures in magnetization measurements, suggesting the good crystallinity and homogeneity of the shells. The upper critical field , the irreversibility field and the lower critical field were characterized and showed similar magnitudes and temperature dependencies for the d = 2 mm and 1 mm shells, yielding of 7–8 T and of 7–12 mT at 20 K. The superconducting critical current density values, evaluated from the magnetization hysteresis loops, were A cm−2 and A cm−2 at 20 K under zero and 2 T applied field, respectively, for the d = 1 mm shell. The occurrence of small flux jumps was observed at low temperatures up to 12 K and in low fields below 0.3 T. The results demonstrate the feasibility of fabricating MgB2 spherical shells with properties applicable to potential areas employing magnetic levitation such as in ICF and that MgB2 spherical shells may be exploited as an experimental system to study superconductivity in 3D curvilinear geometry.

Hydrogenation Effect on Interlayer Coupling and Magneto-Transport Properties of Pd/Co/Mg/Fe Multilayers.

Hydrogenation-induced modification of magnetic properties has been widely studied. A Mg spacer layer with high hydrogen storage stability was clamped in a Pd/Co/Mg/Fe multilayer structure to enhance its hydrogen storage stability and explore the structure's magneto-transport properties. After 1 bar hydrogen exposure, the formation of a stable MgH2 phase was demonstrated in an ambient environment at room temperature through X-ray diffraction. Lower magnetic coupling and enhanced magnetoresistance, compared to those of the as-grown sample, were observed using the longitudinal magneto-optical Kerr effect and a four-probe measurement. In this study, the hydrogenation stability of ferromagnetic multilayers was improved, and the concept of a hydrogenation-based spintronic device was developed.

Ru thin films prepared by RF magnetron sputtering with Ru targets of different microstructures

Ruthenium (Ru) exhibits excellent electrical properties at the nanoscale, and it can be used to replace Al and Cu as interconnect metals for nodes of 20 nm and below in the next generation of integrated circuits. Ru interconnects mainly exist in the form of films, and Ru targets are used as the key raw materials to produce these films. Establishing whether there is an inheritance relationship in terms of microstructure and electrical properties between these targets and the resultant films will determine whether these are important factors for improving the electrical properties of Ru films and will provide directional guidance for the preparation of Ru targets. In this work, Ru targets were prepared by vacuum hot pressing with two different Ru powders with different morphologies and particle sizes. Ru films were then deposited on SiO2/Si(100) substrates by RF magnetron sputtering at substrate temperatures ranging from room temperature (RT, about 25 °C) to 400 °C. The microstructures and electrical properties of the Ru targets and Ru films were investigated by high-resolution field-emission scanning electron microscopy, x ray diffraction, atomic force microscopy, four-probe resistivity measurements, and digital conductivity tests. The results showed that Ru targets with a more uniform microstructure had lower resistivity; furthermore, Ru films deposited by Ru targets with a more uniform microstructure were preferentially crystallized, and they also had a faster average deposition rate, a smaller average grain size, and lower surface roughness. However, no correlation was found between the crystal orientations of the Ru films and Ru targets.

Probing superconducting granularity using nonlocal four-probe measurements

Probing superconducting granularity using nonlocal four-probe measurements

Metal-insulator crossover in monolayer MoS2

We report on transport measurements in monolayer MoS2 devices, close to the bottom of the conduction band edge. These devices were annealed in situ before electrical measurements. This allows us to obtain good ohmic contacts at low temperatures, and to measure precisely the conductivity and mobility via four-probe measurements. The measured effective mobility up to μ eff = 180 cm2 V−1 s−1 is among the largest obtained in CVD-grown MoS2 monolayer devices. These measurements show that electronic transport is of the insulating type for σ ≤ 1.4e 2/h and n ≤ 1.7 × 1012 cm−2, and a crossover to a metallic regime is observed above those values. In the insulating regime, thermally activated transport dominates at high temperature (T > 120 K). At lower temperatures, conductivity is driven by Efros–Schklovkii variable range hopping in all measured devices, with a universal and constant hopping prefactor, that is a clear indication that hopping is not phonon-mediated. At higher carrier density, and high temperature, the conductivity is well modeled by the Boltzmann equation for a non-interacting Fermi gas, taking into account both phonon and impurity scatterings. Finally, even if this apparent metal-insulator transition can be explained by phonon-related phenomena at high temperature, the possibility of a genuine 2D MIT cannot be ruled out, as we can observe a clear power-law diverging localization length close to the transition, and a one-parameter scaling can be realized.