Stacking two-dimensional van der Waals (vdW) materials rotated with respect to each other show versatility for studying exotic quantum phenomena. In particular, anisotropic layered materials have ...great potential for such twistronics applications, providing high tunability. In this work, we report anisotropic superconducting order parameters in twisted Bi2Sr2CaCu2O8+x (Bi-2212) vdW junctions with an atomically clean vdW interface, achieved using the microcleave-and-stack technique. The vdW junctions with twist angles of 0° and 90° showed the maximum Josephson coupling, comparable to that of intrinsic Josephson junctions. As the twist angle approaches 45°, Josephson coupling is suppressed, and eventually disappears at 45°. The observed twist angle dependence of the Josephson coupling can be explained quantitatively by theoretical calculation with the d-wave superconducting order parameter of Bi-2212 and finite tunneling incoherence of the junction. Our results revealed the anisotropic nature of Bi-2212 and provided a novel fabrication technique for vdW-based twistronics platforms compatible with air-sensitive vdW materials.
Gear whine noise has become one of the primary challenges facing noise, vibration, and harshness engineers; this is because the electrification of the powertrain has largely eliminated engine masking ...noise while increasing the working speed of the E-powertrain. In this study, a hybrid metal-composite gear was proposed to reduce gear whine noise, and its performance was evaluated by means of dynamic transmission error (DTE). The test results showed that the hybrid metal-composite gear produced an effectively lower DTE than that of alternatives, particularly when approaching resonance speeds. In addition, a reduction in resonance DTE was verified by acquiring and comparing the frequency response functions of a steel gear and a hybrid metal-composite gear. As DTE is the primary excitation source contributing to whine noise, the hybrid metal-composite gear is expected to be a significant candidate for the reduction in powertrain whine noise.
We present a quantum switch based on analogous Dirac fermion optics (DFO), in which the angle dependence of Klein tunneling is explicitly utilized to build tunable collimators and reflectors for the ...quantum wave function of Dirac fermions. We employ a dual-source design with a single flat reflector, which minimizes diffusive edge scattering and suppresses the background incoherent transmission. Our gate-tunable collimator–reflector device design enables the quantitative measurement of the net DFO contribution in the switching device operation. We obtain a full set of transmission coefficients between multiple leads of the device, separating the classical contribution from the coherent transport contribution. The DFO behavior demonstrated in this work requires no explicit energy gap. We demonstrate its robustness against thermal fluctuations up to 230 K and large bias current density up to 10² A/m, over a wide range of carrier densities. The characterizable and tunable optical components (collimator–reflector) coupled with the conjugated source electrodes developed in this work provide essential building blocks toward more advanced DFO circuits such as quantum interferometers. The capability of building optical circuit analogies at a microscopic scale with highly tunable electron wavelength paves a path toward highly integrated and electrically tunable electron-optical components and circuits.
•TVMS and TE are the main internal sources of vibration and noise in gear systems.•Improved analytical model (IAM) is developed to predict TVMS, LSTE, and PPTE.•IAM was more accurate and effective ...than TAM in calculating tooth stiffness.•IAM and FEA results were compared and IAM was successfully validated.
Time-varying mesh stiffness (TVMS) and loaded static transmission error (LSTE) are considered the main sources of vibration in a gear system. TVMS and LSTE of a helical gear pair have been calculated by using an instantaneous pressure angle. However, this method could not consider the root profile accurately. In this study, an analytical model is proposed to calculate TVMS and LSTE of a helical gear pair. To consider the trochoidal root profile, the profile model is also developed by a virtual rack reflecting the cutter information. The finite element (FE) model of a helical gear is used to validate the proposed analytical model. The LSTE results are highly similar to FE analysis results and relative errors in peak-to-peak values of LSTE are also small. The proposed model is found to be more effective than traditional models in calculating the TVMS and LSTE of both helical gear pairs and spur gears. The changes in the radii of the base circle and root circle according to the helix angle are also investigated.
A two-dimensional (2D) atomic crystalline transition metal dichalcogenides has shown immense features, aiming for future nanoelectronic devices comparable to conventional silicon (Si). 2D molybdenum ...ditelluride (MoTe2) has a small bandgap, appears close to that of Si, and is more favorable than other typical 2D semiconductors. In this study, we demonstrate laser-induced p-type doping in a selective region of n-type semiconducting MoTe2 field effect transistors (FET) with an advance in using the hexagonal boron nitride as passivation layer from protecting the structure phase change from laser doping. A single nanoflake MoTe2-based FET, exhibiting initial n-type and converting to p-type in clear four-step doping, changing charge transport behavior in a selective surface region by laser doping. The device shows high electron mobility of about 23.4 cm2V−1s−1 in an intrinsic n-type channel and hole mobility of about 0.61 cm2V−1s−1 with a high on/off ratio. The device was measured in the range of temperature 77–300 K to observe the consistency of the MoTe2-based FET in intrinsic and laser-dopped region. In addition, we measured the device as a complementary metal–oxide–semiconductor (CMOS) inverter by switching the charge-carrier polarity of the MoTe2 FET. This fabrication process of selective laser doping can potentially be used for larger-scale MoTe2 CMOS circuit applications.
All‐Van der Waals (vdW)‐material‐based heterostructures with atomically sharp interfaces offer a versatile platform for high‐performing spintronic functionalities at room temperature. One of the key ...components is vdW topological insulators (TIs), which can produce a strong spin‐orbit‐torque (SOT) through the spin‐momentum locking of their topological surface state (TSS). However, the relatively low conductance of the TSS introduces a current leakage problem through the bulk states of the TI or the adjacent ferromagnetic metal layers, reducing the interfacial charge‐to‐spin conversion efficiency (qICS). Here, a vdW heterostructure is used consisting of atomically‐thin layers of a bulk‐insulating TI Sn‐doped Bi1.1Sb0.9Te2S1 and a room‐temperature ferromagnet Fe3GaTe2, to enhance the relative current ratio on the TSS up to ≈20%. The resulting qICS reaches ≈1.65 nm−1 and the critical current density Jc ≈0.9 × 106 Acm−2 at 300 K, surpassing the performance of TI‐based and heavy‐metal‐based SOT devices. These findings demonstrate that an all‐vdW heterostructure with thickness optimization offers a promising platform for efficient current‐controlled magnetization switching at room temperature.
Current‐driven magnetization switching via spin‐orbit torque is achieved at room temperature in a van der Waals heterostructure of a bulk‐insulating topological insulator Sn‐doped Bi1.1Sb0.9Te2S1 and a room temperature ferromagnet, Fe3GaTe2. By controlling the thickness of the constituent layers and maximizing the relative current ratio on the topological surface states, the highly efficient spin‐orbit‐torque operation is realized, surpassing the performance of most previous devices.
Transition metal dichalcogenides (TMDs) are of great interest owing to their unique properties. However, TMD materials face two major challenges that limit their practical applications: contact ...resistance and surface contamination. Herein, a strategy to overcome these problems by inserting a monolayer of hexagonal boron nitride (h-BN) at the chromium (Cr) and tungsten disulfide (WS
) interface is introduced. Electrical behaviors of direct metal-semiconductor (MS) and metal-insulator-semiconductor (MIS) contacts with mono- and bilayer h-BN in a four-layer WS
field-effect transistor (FET) are evaluated under vacuum from 77 to 300 K. The performance of the MIS contacts differs based on the metal work function when using Cr and indium (In). The contact resistance is significantly reduced by approximately ten times with MIS contacts compared with that for MS contacts. An electron mobility up to ≈115 cm
V
s
at 300 K is achieved with the insertion of monolayer h-BN, which is approximately ten times higher than that with MS contacts. The mobility and contact resistance enhancement are attributed to Schottky barrier reduction when h-BN is introduced between Cr and WS
. The dependence of the tunneling mechanisms on the h-BN thickness is investigated by extracting the tunneling barrier parameters.
Stacking of graphene with hexagonal boron nitride (h-BN) can dramatically modify its bands from their usual linear form, opening a series of narrow minigaps that are separated by wider minibands. ...While the resulting spectrum offers strong potential for use in functional (opto)electronic devices, a proper understanding of the dynamics of hot carriers in these bands is a prerequisite for such applications. In this work, we therefore apply a strategy of rapid electrical pulsing to drive carriers in graphene/h-BN heterostructures deep into the dissipative limit of strong electron-phonon coupling. By using electrical gating to move the chemical potential through the "Moiré bands", we demonstrate a cyclical evolution between metallic and semiconducting states. This behavior is captured in a self-consistent model of non-equilibrium transport that considers the competition of electrically driven inter-band tunneling and hot-carrier scattering by strongly non-equilibrium phonons. Overall, our results demonstrate how a treatment of the dynamics of both hot carriers and hot phonons is essential to understanding the properties of functional graphene superlattices.
Unintentionally formed nanocrystalline graphene (nc‐G) can act as a useful seed for the large‐area synthesis of a hexagonal boron nitride (h‐BN) thin film with an atomically flat surface that is ...comparable to that of exfoliated single‐crystal h‐BN. A wafer‐scale dielectric h‐BN thin film was successfully synthesized on a bare sapphire substrate by assistance of nc‐G, which prevented structural deformations in a chemical vapor deposition process. The growth mechanism of this nc‐G‐tailored h‐BN thin film was systematically analyzed. This approach provides a novel method for preparing high‐quality two‐dimensional materials on a large surface.
A hexagonal boron nitride (h‐BN) thin film with an atomically flat surface was obtained using unintentionally formed nanocrystalline graphene (nc‐G). A wafer‐scale dielectric h‐BN thin film was synthesized on a bare sapphire substrate with the assistance of nc‐G, which prevented structural deformations during chemical vapor deposition. The sp3‐hybridized edges of nc‐G play a key role during these processes.
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