Transport Measurements Research Articles

Strain free thin film growth of vanadium dioxide deposited on 2D atomic layered material of hexagonal boron nitride investigated by their thickness dependence of insulator-metal transition behavior

Abstract We report preparation of Vanadium dioxide (VO2) ultrathin films on hexagonal boron nitride (hBN), which is a typical two-dimensional material, to show clear Metal -Insulator transition owing to weak van der Waals interaction at their surface. It is confirmed that VO2 films on hBN with the thickness ranging from 10 to 40 nm exhibit bulk like Metal -Insulator transition without degradation by using the Raman scattering spectroscopy and electric transport measurements. These results are demonstrating the importance of 2D material nature of hBN for producing the strain-free oxide thin films.

Defects vibrations engineering for enhancing interfacial thermal transport in polymer composites.

To push upper boundaries of thermal conductivity in polymer composites, understanding of thermal transport mechanisms is crucial. Despite extensive simulations, systematic experimental investigation on thermal transport in polymer composites is limited. To better understand thermal transport processes, we design polymer composites with perfect fillers (graphite) and defective fillers (graphite oxide), using polyvinyl alcohol (PVA) as a matrix model. Measured thermal conductivities of ~1.38 ± 0.22 W m-1 K-1 in PVA/defective filler composites is higher than those of ~0.86 ± 0.21 W m-1 K-1 in PVA/perfect filler composites, while measured thermal conductivities in defective fillers are lower than those of perfect fillers. We identify how thermal transport occurs across heterogeneous interfaces. Thermal transport measurements, neutron scattering, quantum mechanical modeling, and molecular dynamics simulations reveal that vibrational coupling between PVA and defective fillers at PVA/filler interfaces enhances thermal conductivity, suggesting that defects in polymer composites improve thermal transport by promoting this vibrational coupling.

The evolution and development of railway passenger transportation clearing method in China

PurposeAs an important part of the management of railway passenger transport, the rationality and effectiveness of the clearing method of railway passenger transport are directly related to the operating efficiency and service quality of railway passenger transport enterprises. This paper aims to comprehensively and deeply discuss the evolution and development process of China’s railway passenger transport clearing method, analyze its characteristics and influences in each stage, identify the main factors affecting its evolution and development and then put forward thoughts on improving the future development of the clearing method.Design/methodology/approachThrough a detailed review of the railway passenger transport clearing methods from the planned economy period to the reform and opening up period and into the new century, the basis, mode, subject and object of clearing in different development stages are systematically compared.FindingsIt comprehensively reveals the evolution of the clearing method, sorted out the characteristics and changes of the clearing method at each stage and the adaptability to the development of railway passenger transport at that time. The characteristics of the development of clearing measures for railway passenger transport in different stages and their far-reaching influence on railway passenger transport business are deeply analyzed.Originality/valueThis paper summarized the factors influencing the development of China’s railway passenger transportation clearing approach evolution, including the simplified rules of clearing, enhanced the market adaptability, establishing and perfecting the incentive mechanism, strengthening the construction of informatization, etc. This paper puts forward the ways to improve the railway passenger transportation clearing future development thinking.

Combined Effect of Temperature and Different Light Regimes on the Photosynthetic Activity and Lipid Accumulation in the Diatom Phaeodactylum tricornutum

The aim of this study was to investigate the combined effects of temperature and light on the photosynthetic parameters and lipid accumulation in the diatom Phaeodactylum tricornutum, a model organism widely used for studies on diatom physiology, ecology, and biotechnology. Our results highlight the importance of the interaction between temperature and light intensity in influencing growth rates, pigments and active photosystems content, photosynthetic efficiency, lipid production and fatty acid composition in P. tricornutum. Measurements of the maximum electron transport rate (rETRmax) and rETR at maximum PAR (830 µmol m−2 s−1) confirmed that P. tricornutum exhibits significantly higher light sensitivity as growth temperature increases under light/dark cycles at two light intensities (25–60 µmol m−2 s−1). However, this trend was reversed under continuous light (25 µmol m−2 s−1). Moreover, higher rETRmax values (up to double) were observed at higher irradiance, either in intensity or under continuous light regimes, at the two temperatures tested. On the other hand, increasing light intensity amplified the observed effect of temperature on photosystem I (PSI) activity under light/dark regimes, but not under continuous light conditions. This resulted in a greater deficiency in PSI activity, likely due to limitations in electron supply to this photosystem. Furthermore, increasing the culture temperature from 20 °C to 25 °C triggered an increase in the number and size of cytoplasmic lipid droplets under conditions of increased light intensity, with an even more pronounced effect under continuous illumination. Notably, the combination of 25 °C and continuous illumination resulted in a more than twofold increase in triacylglyceride (TAG) content, reaching approximately 17 mg L−1. This condition also caused a substantial rise (up to ≈90%) in the proportions of palmitoleic and palmitic acids in the TAG fatty acid profile.

Flow cytometric measurement of CFTR-mediated chloride transport in human neutrophils.

Immune cells express a variety of ion channels and transporters in the plasma membrane and intracellular organelles, responsible of the transference of charged ions across hydrophobic lipid membrane barriers. The correct regulation of ion transport ensures proper immune cell function, activation, proliferation, and cell death. Cystic fibrosis (CF) is a genetic disease in which the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) chloride channel gene is defective, consequently, the CFTR protein is dysfunctional, and the chloride efflux in CF cells is markedly impaired. Cystic fibrosis is characterized by chronic inflammation in the airways, mainly triggered by neutrophilic infiltration and recurring bacterial infections, causing the decline of lung function and eventually respiratory failure. Novel modulator-based therapies have improved lung function in people with Cystic Fibrosis (pwCF) by increasing expression and function of CFTR in the plasma membrane of lung cells, however, the effects of these drugs in the lung recruited inflammatory cells, specifically neutrophils, remains unknown. Given the complex biology of neutrophils and their short lifespan, we aimed to develop a fluorometric method to evaluate CFTR-mediated chloride transport in human neutrophils by using flow cytometry and the intracellular chloride-binding MQAE dye. Our results show that CFTR-mediated chloride transport in human neutrophils or human neutrophil-like cell lines can be consistently evaluated in vitro by this methodology. Additionally, this assay measured increased chloride efflux in neutrophils collected from pwCF under modulator therapy, as compared to healthy donors, indicating this method can evaluate restoration of CFTR-mediated chloride transport in CF neutrophils.

Extended quantum anomalous Hall states in graphene/hBN moiré superlattices.

Electrons in topological flat bands can form new topological states driven by correlation effects. The pentalayer rhombohedral graphene/hexagonal boron nitride (hBN) moiré superlattice was shown to host fractional quantum anomalous Hall effect (FQAHE) at approximately 400 mK (ref. 1), triggering discussions around the underlying mechanism and role of moiré effects2-6. In particular, new electron crystal states with non-trivial topology have been proposed3,4,7-15. Here we report electrical transport measurements in rhombohedral pentalayer and tetralayer graphene/hBN moiré superlattices at electronic temperatures down to below 40 mK. We observed two more fractional quantum anomalous Hall (FQAH) states and smaller Rxx values in pentalayer devices than those previously reported. In the new tetralayer device, we observed FQAHE at moiré filling factors v = 3/5 and 2/3. With a small current at the base temperature, we observed a new extended quantum anomalous Hall (EQAH) state and magnetic hysteresis, where Rxy = h/e2 and vanishing Rxx spans a wide range of v from 0.5 to 1.3. At increased temperature or current, EQAH states disappear and partially transition into the FQAH liquid16-18. Furthermore, we observed displacement field-induced quantum phase transitions from the EQAH states to the Fermi liquid, FQAH liquid and the likely composite Fermi liquid. Our observations established a new topological phase of electrons with quantized Hall resistance at zero magnetic field and enriched the emergent quantum phenomena in materials with topological flat bands.

The First Molecular Ferroelectric Mott Insulator.

With the discovery of colossal magnetoresistance materials and high-temperature superconductors, Mott insulators can potentially undergo a transition from insulating state to metallic state. Here, in molecular ferroelectrics system, a Mott insulator of (C7H14N)3V12O30 has been first synthesized, which is a 2D organic-inorganic ferroelectric with composition of layered vanadium oxide and quinuclidine ring. Interestingly, accompanied by the ferroelectric phase transition, (C7H14N)3V12O30 changes sharply in conductivity. The occurrence of a Mott transition has been proven by electric transport measurements and theoretical calculations. This research has significantly expanded the applicative horizons of ferroelectric materials, and offering an ideal platform for the investigation of strongly correlated electron systems.

Single-layer MoSeN – a synthetic Janus two-dimensional transition-metal compound grown by plasma-assisted molecular beam epitaxy

Abstract Two-dimensional (2D) nanomaterials hold immense application potentials such as in high-performance nano-electronics, and asymmetric 2D structures with inherent electric dipoles will extend the application promises. Yet synthesizing asymmetric 2D structures remains challenging. Herein, we report the first synthesis of single-layer (SL) hexagonal (H-) phase polar Janus MoSeN via nitrogen-plasma-assisted molecular beam epitaxy. This is a significant achievement given the incommensurate valence between Mo, Se, and N, and the inherent strain from the Janus architecture. Using an array of compositional and structural characterization methods, we establish the atomic configurations of the synthesized MoSeN SL, confirming that they are 2D Janus transition-metal chalcogen-nitrides rather than alloys. By employing density functional theory calculations and transport measurements, we explore the structural feasibility and offer insights into its electronic properties, demonstrating its metallic behavior with ohmic contact characteristics. Piezoresponse force microscopy measurements reveal vertical piezoelectricity and ferroelectric potentials from the Janus MoSeN SL. Therefore, it exhibits great potential for applications in, e.g. piezoelectric and ferroelectric devices, sensing technologies, and optoelectronic devices. This work not only addresses existing challenges in 2D nanomaterial research but also opens new avenues for the development of advanced functional materials.

Development of a Nb‐Based Semiconductor‐Superconductor Hybrid 2DEG Platform

AbstractSemiconductor‐superconductor hybrid materials are used as a platform to realize Andreev bound states, which hold great promise for quantum applications. These states require transparent interfaces between the semiconductor and superconductor, which are typically realized by in‐situ deposition of an Al superconducting layer. Here a hybrid material is presented, based on an InAs 2D electron gas (2DEG) combined with in‐situ deposited Nb and NbTi superconductors, which offer a larger operating range in temperature and magnetic field due to their larger superconducting gap. The inherent difficulty associated with the formation of an amorphous interface between III‐V semiconductors and Nb‐based superconductors is addressed by introducing a 7 nm Al interlayer. The Al interlayer provides an epitaxial connection between an in‐situ magnetron sputtered Nb or NbTi thin film and a shallow InAs 2DEG. This metal‐to‐metal epitaxy is achieved by optimization of the material stack and results in an induced superconducting gap of approximately 1 meV, determined from transport measurements of superconductor‐semiconductor Josephson junctions. This induced gap is approximately five times larger than the values reported for Al‐based hybrid materials and indicates the formation of highly‐transparent interfaces that are required in high‐quality hybrid material platforms.

Molecular H2 as the Reducing Agent in Low-Temperature Oxide Reduction Using Calcium Hydride.

Low-temperature synthesis is crucial for advancing sustainable manufacturing and accessing novel metastable phases. Metal hydrides have shown great potential in facilitating the reduction of oxides at low temperatures, yet the underlying mechanism─whether driven by H-, H2, or atomic H─remains unclear. In this study, we employ in situ electrical transport measurements and first-principles calculations to investigate the CaH2-driven reduction kinetics in epitaxial α-Fe2O3 thin films. Intriguingly, samples in direct contact with or separated from CaH2 powders exhibit similar apparent activation energies for H2 reduction, although direct contact significantly increases the reduction rate. These findings indicate that molecular H2 is the dominant reducing species in the low-temperature reduction of oxides using CaH2, with a key aspect of the hydrides' superior reducing power attributed to their ability to eliminate residual moisture. This work underscores the critical role of moisture control in enabling effective low-temperature oxide reduction for advanced material synthesis.

Ferromagnetism and structural phase transition in monoclinic FeGe film

Binary compound FeGe hosts multiple structures, from cubic and hexagonal to monoclinic. Compared to the well-known skyrmion lattice in the cubic phase and the antiferromagnetic charge–density wave in the hexagonal phase, the monoclinic FeGe is less explored. Here, we synthesized the monoclinic FeGe films on Al2O3 (001) and studied their structural, magnetic, and transport properties. X-ray diffraction and transmission electron microscopy characterizations indicate that the FeGe films are epitaxial to the substrate. Unlike the antiferromagnetic bulk, the monoclinic FeGe films are ferromagnetic with Curie temperature as high as ∼800 K, contributing to the anomalous Hall effect in the transport measurements. Similar to the hexagonal FeGe, we captured a structural phase transition in the monoclinic FeGe films at ∼100 K in real and reciprocal spaces by transmission electron microscope. Our work enriches the phase diagram of the FeGe family and suggests that FeGe offers an ideal platform for studying multiphase transitions and related device applications.

Hydrated cable bacteria exhibit protonic conductivity over long distances

This study presents the direct measurement of proton transport along filamentous Desulfobulbaceae, or cable bacteria. Cable bacteria are filamentous multicellular microorganisms that have garnered much interest due to their ability to serve as electrical conduits, transferring electrons over several millimeters. Our results indicate that cable bacteria can also function as protonic conduits because they contain proton wires that transport protons at distances >100 µm. We find that protonic conductivity (σP) along cable bacteria varies between samples and is measured as high as 114 ± 28 µS cm-1 at 25 °C and 70% relative humidity (RH). For cable bacteria, the protonic conductance (GP) and σP are dependent upon the RH, increasing by as much as 26-fold between 60% and 80% RH. This observation implies that proton transport occurs via the Grotthuss mechanism along water associated with cable bacteria, forming proton wires. In order to determine σP and GP along cable bacteria, we implemented a protocol using a modified transfer-printing technique to deposit either palladium interdigitated protodes (IDP), palladium transfer length method (TLM) protodes, or gold interdigitated electrodes (IDE) on top of cable bacteria. Due to the relatively mild nature of the transfer-printing technique, this method should be applicable to a broad array of biological samples and curved materials. The observation of protonic conductivity in cable bacteria presents possibilities for investigating the importance of long-distance proton transport in microbial ecosystems and to potentially build biotic or biomimetic scaffolds to interface with materials via proton-mediated gateways or channels.

Tunable in-plane conductance anisotropy in 2D semiconductive AgCrP2S6 by ion-electron co-modulations.

In-plane anisotropic two-dimensional (2D) semiconductors have gained much interest due to their anisotropic properties, which opens avenues in designing functional electronics. Currently reported in-plane anisotropic semiconductors mainly rely on crystal lattice anisotropy. Herein, AgCrP2S6 (ACPS) is introduced as a promising member to the anisotropic 2D semiconductors, in which, both crystal structure and ion-electron co-modulations are used to achieve tunable in-plane conductance anisotropy. Scanning tunneling electron microscopy and polarized Raman spectroscopy show the structural anisotropy of ACPS. Electrical transport measurements show that its tunable in-plane conductance anisotropy is related to the ion-electron co-modulations, where Ag ion migration is anisotropic along a axis and b axis. Electrical transport measurements show the semiconducting properties of ACPS, as also supported by photoluminescence results. Moreover, the transfer curves of ACPS showcase large Vg-related hysteresis, which is directionally controlled by anisotropic Ag ion migration. This work offers a possibility of using anisotropic charge transport in functional electronics by ion-electron co-modulations.

Stabilizing Schottky-to-Ohmic Switching in HfO2-Based Ferroelectric Films via Electrode Design.

The discovery of ferroelectric phases in HfO2-based films has reignited interest in ferroelectrics and their application in resistive switching (RS) devices. This study investigates the pivotal role of electrodes in facilitating the Schottky-to-Ohmic transition (SOT) observed in devices consisting of ultrathin epitaxial ferroelectric Hf0.93Y0.07O2 (YHO) films deposited on La0.67Sr0.33MnO3-buffered Nb-doped SrTiO3 (NbSTO|LSMO) with Ti|Au top electrodes. These findings indicate combined filamentary RS and ferroelectric switching occurs in devices with designed electrodes, having an ON/OFF ratio of over 100 during about 105 cycles. Transport measurements of modified device stacks show no change in SOT when the ferroelectric YHO layer is replaced with an equivalent hafnia-based layer, Hf0.5Zr0.5O2 (HZO). However, incomplete SOT is observed for variations in the top electrode thickness or material, as well as LSMO electrode thickness. This underscores the importance of employing oxygen-reactive electrodes and a bottom electrode with reduced conductivity to stabilize SOT. These findings provide valuable insights for enhancing the performance of ferroelectric RS devices through integration with filamentary RSmechanism.

Advanced Method for the In Vivo Measurements of Lysophospholipid Translocation Across the Inner (Cytoplasmic) Membrane of Escherichia coli.

Phospholipid translocation occurs ubiquitously in biological membranes and primarily is protein catalyzed. Lipid flippases mediate the net translocation of specific phospholipids from one leaflet of a membrane to the other. In the inner (cytoplasmic) membrane (IM) of Gram-negative bacteria, lysophospholipid translocase (LplT) and cytosolic bifunctional acyl-acyl carrier protein (ACP) synthetase/2-acylglycerolphosphoethanolamine acyltransferase (Aas) form a glycerophospholipid regeneration system, which is capable of facilitating rapid retrograde translocation of lyso forms of phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and cardiolipin (CL) but not exogenous (host-derived) phosphatidylcholine (PC) across the IM of Gram-negative diderm (two-membraned) bacteria in consequential order lyso-PE=lyso-PG >>lysophosphatidic acid (lyso-PA) >>lyso-PC. Although several flippases that bind and move non-glycerophosphatidyl lipids across the IM are characterized in Gram-negative bacteria, LplT appears to be the first example of a bacterial protein capable of facilitating the rapid translocation of monoacylated glycerophospholipids. On the cytoplasmic surface, Aas restores the lysophospholipids to their diacyl forms with comparable efficiency but excludes any exogenous monoacylated lipid species. This coupled remodeling enzyme tandem provides an effective means to examine substrate specificity of lipid regeneration and lysophospholipid transport per se across the membrane. The current chapter describes two distinct but complementary methods for the measurement of lysophospholipid transport across membranes using Escherichia coli spheroplasts.

Measurement of Lipid Transport in Mitochondria by the MTL Complex.

Membrane biogenesis requires an extensive traffic of lipids between different cell compartments. Two main pathways, the vesicular and non-vesicular pathways, are involved in such a process. Whereas the mechanisms involved in vesicular trafficking are well understood, less is known about non-vesicular lipid trafficking, particularly in plants. This pathway involves the direct exchange of lipids at membrane contact sites (MCSs) between organelles. In plants, extensive traffic of the chloroplast-synthesized digalactosyldiacylglycerol (DGDG) to mitochondria is specifically promoted during phosphate starvation. This lipid exchange likely occurs by non-vesicular trafficking pathways at MCSs between mitochondria and plastids. By a biochemical approach, a mitochondrial lipoproteic super-complex called MTL (mitochondrial transmembrane lipoprotein complex) involved in mitochondrial lipid trafficking has been identified in Arabidopsis thaliana. This protocol describes the method used to separate the MTL complex and to study the implication of a component of this complex (AtMic60) in mitochondrial lipid transport.

Electronic confinement induced quantum dot behavior in magic-angle twisted bilayer graphene.

Magic-angle twisted bilayer graphene (TBLG) has emerged as a versatile platform to explore correlated electron phases driven primarily by low-energy flat bands in moiré superlattices. While techniques for controlling the twist angle between graphene layers have spurred rapid experimental progress, understanding the effects of doping inhomogeneity on electronic transport in correlated electron systems remains challenging. In this work, we investigate the interplay of confinement and doping inhomogeneity on the electrical transport properties of TBLG by leveraging device dimensions and twist angles. We show that reducing device dimensions can magnify disorder potentials caused by doping inhomogeneity, resulting in pronounced carrier confinement. This phenomenon is evident in charge transport measurements, where the Coulomb blockade effect is observed. Temperature-dependent measurements reveal a large variation in the activation gap across the device. These findings highlight the critical role of doping inhomogeneity in TBLG and its significant impact on the transport properties of the system.

Pressure-tunable superconductivity on cage-like compound Y5Rh6Sn18

In this work, we report the pressure-dependent evolution of superconductivity in cage-like compound Y5Rh6Sn18 by combining electrical transport measurements, synchrotron x-ray diffraction (XRD) and theoretical computation. The application of external pressure leads to the enhancement of metallic nature in Y5Rh6Sn18. There is a noted pressure-tunable superconducting temperature (Tc), which climbs to 3.70K at 7.4GPa, and then reverses to 2.37K at the higher pressure of 30.6GPa. High-pressure XRD analysis confirm the robustness of Y5Rh6Sn18, which exhibits stability without transitioning into other structural phases up to approximately 30GPa. The ab initio calculations show a significant contribution of Sn s and p electrons as well as Rh and Y d electrons to the total density of states (DOS) near the Fermi level, which supports the multi-band superconductivity of this compound. The enhancement of Tc in Y5Rh6Sn18 could be explained by the strengthening of Sn-Sn bonds and the redistribution of Sn atoms in partial density of states (PDOS).

Percolative phase transition in few-layered MoSe2 field-effect transistors using Co and Cr contacts.

The metal-to-insulator phase transition (MIT) in two-dimensional (2D) materials under the influence of a gating electric field has revealed interesting electronic behavior and the need for a deeper fundamental understanding of electron transport processes, while attracting much interest in the development of next-generation electronic and optoelectronic devices. Although the mechanism of the MIT in 2D semiconductors is a topic under debate in condensed matter physics, our work demonstrates the tunable percolative phase transition in few-layered MoSe2 field-effect transistors (FETs) using different metallic contact materials. Here, we attempted to understand the MIT through temperature-dependent electronic transport measurements by tuning the carrier density in a MoSe2 channel under the influence of an applied gate voltage. In particular, we have examined this phenomenon using the conventional chromium (Cr) and ferromagnetic cobalt (Co) as two metal contacts. For both Cr and Co, our devices demonstrated n-type behavior with a room-temperature field-effect mobility of 16 cm2 V-1 s-1 for the device with Cr-contacts and 92 cm2 V-1 s-1 for the device with Co-contacts, respectively. With low temperature measurements at 50 K, the mobilities increased significantly to 65 cm2 V-1 s-1 for the device with Cr and 394 cm2 V-1 s-1 for the device with Co-contacts. By fitting our experimental data to the percolative phase transition theory, the temperature-dependent conductivity data show a transition from an insulating-to-metallic behavior at a bias of ∼28 V for Cr-contacts and ∼20 V for Co-contacts. This cross-over of the conductivity can be attributed to an increase in carrier density as a function of the gate bias in temperature-dependent transfer characteristics. By extracting the critical exponents, we find that the transport behavior in the device with Co-contacts aligns closely with the 2D percolation theory. In contrast, the devices with Cr-contacts deviate significantly from the 2D limit at low temperatures.

Desertion of anomalous magnetic transition and emergence of metallic state in Cu doped Eu2Ru2O7 pyrochlore.

In this paper, we present a detailed investigation of the structural, magnetic, and electrical transport properties of Eu2-xCuxRu2O7 (x = 0, 0.2, 0.4) pyrochlores. X-ray diffraction measurements confirm the single-phase nature of all samples and also manifest the reduction of lattice parameters with the increase in copper doping concentration. The experimental results of the magnetic measurements indicate that an anomalous magnetic transition around 23K arises due to the contribution of non-magnetic Eu3+ ions. The strength of this unnatural magnetic transition reduces with decreasing Eu concentration [i.e., with increasing copper doping (x)] and finally disappears for x = 0.4. Moreover, electrical transport measurements reveal a considerable decrease in resistivity for Cu doped samples compared to undoped samples, which indicates the increase in charge carrier concentration with increasing Cu content.