Contact Edge Research Articles

Scalable Fabrication of Edge Contacts to 2D Materials: Implications for Quantum Resistance Metrology and 2D Electronics

We report a reliable and scalable fabrication method for producing electrical contacts to two-dimensional (2D) materials based on the tri-layer resist system. We demonstrate the applicability of this method in devices fabricated on epitaxial graphene on silicon carbide (epigraphene) used as a scalable 2D material platform. For epigraphene, data on nearly 70 contacts result in median values of the one-dimensional (1D) specific contact resistances ρc ∼ 67 Ω·μm and follow the Landauer quantum limit ρc ∼ n–1/2, consistently reaching values ρc < 50 Ω·μm at high carrier densityn. As a proof of concept, we apply the same fabrication method to the transition metal dichalcogenide (TMDC) molybdenum disulfide (MoS2). Our edge contacts enable MoS2 field-effect transistor (FET) behavior with an ON/OFF ratio of >106 at room temperature (>109 at cryogenic temperatures). The fabrication route demonstrated here allows for contact metallization using thermal evaporation and also by sputtering, giving an additional flexibility when designing electrical interfaces, which is key in practical devices and when exploring the electrical properties of emerging materials.

Simulation research on fretting wear of train axles with interference fit based on press-fitted specimen

Based on dimensional analysis and similarity theorem, this paper deduces the scaling relationship considering the fretting fatigue problem of the wheel and axle, and verifies it through finite element simulation analysis. A finite element model of a 1/10 reduction ratio press-fit specimen was established to simulate the fretting characteristics of the interference fit of the train axle, and the ABAQUS finite element software combined with the Fortran wear subroutine Umeshmotion was used to apply the rotational bending load. Only considering the cumulative effect of fretting wear in the slip zone, the variation characteristics of the wear width and depth of the specimen shaft with the number of load cycles were studied. The simulation results show that the fretting wear area and wear depth increase with the increase of the number of load cycles, and the axial width of the wear area of the contact surface is about 0.2 mm; the existence of the overlap of the specimen hub can restrain the position of the contact edge of the specimen shaft fretting wear effect. This makes the maximum wear depth of the specimen shaft occur at 0.03 mm from the contact edge, while the maximum wear depth of the specimen hub contact area occurs at the contact edge.

Wear and deformation of metal-on-polyethylene hip bearings under edge loading conditions due to variations in component positioning

Despite the clinical success of hip joint replacement, the risk of revision, particularly in younger and more active patients, still remains a concern. To identify conditions of high wear, fatigue and potential failure modes, there is need to be able to replicate a range of in vivo conditions with pre-clinical testing methods in order to predict the range of clinical wear. In particular, edge loading of metal-on-polyethylene hip replacements has the potential to have impact on both surface wear and fatigue failure. The mode of edge loading explored in this study involves separation of the centres of the femoral head and acetabular cup during a portion of the gait cycle. Such edge loading can occur due to variations in translational and/or rotational positioning of the hip replacement. In this study, the influence of translational positioning along the medial-lateral axis (medial-lateral translational mismatch) combined with rotational positioning of the acetabular cup about the anterior-posterior axis (cup inclination angle) on the occurrence and severity of edge loading, and wear and plastic deformation, was investigated for size 36 mm metal-on-polyethylene total hip replacements on a ProSim EM13 electromechanical hip joint simulator. A two phase approach was used; a short term study where the mechanics of the hip bearing were assessed under a wide range of input conditions (45° and 65° cup inclination angle and 1, 2, 3, 4 mm medial-lateral translational mismatch); followed by wear simulation for a lower number of conditions.Larger medial-lateral translational mismatch conditions led to increased levels of dynamic separation between the femoral head and acetabular cup with the largest dynamic separation (2.4 ± 0.2 mm, mean ± 95% confidence limits) measured under 4 mm translational mismatch with the 65° cup inclination angle conditions. The load at the rim at 0.5 mm of separation was also highest at this condition, as was the mean wear rate (23.0 ± 2.4 mm3 / million cycles).Dynamic separation, load at the rim and wear was consistently greater with the steeper cup inclination angle of 65° compared to 45° for all translational mismatch conditions. Translational mismatch conditions of 3 mm and 4 mm resulted in dynamic separation displacements >0.5 mm. At a 45° cup inclination angle under standard concentric conditions (zero translational mismatch) minimal wear and plastic deformation occurred at the rim of the cup, however at a 65° cup inclination edge contact at the rim was identified.Variations in rotational (cup inclination angle) and translational (medial-lateral) positioning influenced the magnitude of dynamic separation, severity of edge loading, and wear of metal – on - moderately cross-linked polyethylene hip replacements, demonstrating the importance of surgical component positioning.

The transition from Elasto-Hydrodynamic to Mixed Regimes in Lubricated Friction of Soft Solid Surfaces.

Lubricated contacts in soft materials are common in various engineering and natural settings, such as tires, haptic applications, contact lenses, and the fabrication of soft electronic devices. Two major regimes are elasto-hydrodynamic lubrication (EHL), in which solid surfaces are fully separated by a fluid film, and mixed lubrication (ML), in which there is partial solid-to-solid contact. The transition between these regimes governs the minimum sliding friction achievable and is thus very important. Generally, the transition from EHL to ML regimes is believed to occur when the thickness of the lubricant layer is comparable with the amplitude of surface roughness. Here, it is reported that in lubricated sliding experiments on smooth, soft, poly(dimethylsiloxane) substrates, the transition can occur when the thickness of the liquid layer is much larger than the height of the asperities. Direct visualization of the "contact" region shows that the transition corresponds to the formation of wave-like surface wrinkles at the leading contact edge and associated instabilities at the trailing contact edge, which are believed to trigger the transition to the mixed regime. These results change the understanding of what governs the important EHL-ML transition in the lubricated sliding of soft solids.

WS2 Transistors with Sulfur Atoms Being Replaced at the Interface: First-Principles Quantum-Transport Study.

Reducing the contact resistance is one of the major challenges in developing transistors based on two-dimensional materials. In this study, we perform first-principles quantum-transport calculations by adopting a novel type of partially sulfur-replaced edge contact metal/WSX/WS2 in order to lower the Schottky barrier height and in turn reduce the contact resistance. Here, the sulfur replacements produce a segment of the metamaterial WSX (X = P, As, F, and Cl), using group V or halogen atoms to substitute sulfur atoms on one side of a WS2 monolayer. We further compare the effects of such sulfur replacements on the interface metallization and bonding. Such WSX-buffered contacts exhibit contact resistances as low as 142 and 173 Ω·μm for the p-type Pt/WSP/WS2 and n-type Ti/WSCl/WS2 edge contacts, respectively. Moreover, ab initio molecular dynamics is employed to observe a stable standalone WSX monolayer at room temperature.

Mechanical–Thermal–Electrical Coupling Modeling and Temperature Rise Characteristic of a Parallel Groove Clamp With Improved Representation of Contact Interactions

The electrical contact resistance and thermal contact resistance caused by the actual rough surfaces of parallel groove clamps exist during contact interactions, which affects the heat generation rate and thermal conductivity, and then the accuracy of multi-field coupling numerical simulation. Thus, first, a mechanical-thermal-electrical coupling model of the parallel groove clamp is created based on the improved representation of contact interactions. Then, a progressive sequential coupling method is proposed to improve the calculation accuracy and efficiency of the multi-field coupling. Meanwhile, the validity of the coupling model is verified by electrical resistance and temperature measurement experiments. Finally, the temperature rise characteristic of the parallel groove clamp is analyzed under normal and large current impact conditions. The results show that the experimental and numerical electrical resistance and temperature show a good agreement. The electrical resistance of parallel groove clamps stabilizes when the preload force is greater than the critical value, 5000 N. The highest temperature of parallel groove clamps is always located at the contact edge between the upper clamp block and branch line, and the influence of current intensity on temperature rise is significant under normal condition, while the effect of preload force is less. The large current impact mainly affects the transient temperature rise. However, the effect of the large current impact on steady-state temperature is negligible.

Study on nonlinear dynamic characteristics of power six-branch herringbone gear transmission system with 3D modification

The power six-branch herringbone gear transmission system has the advantages of large power transmission and transmission ratio. Because of its multi-way transmission and over-constraint structure, to prevent loaded tooth interference, there are large backlashes between teeth. The system shows complex nonlinear dynamic characteristics under the influence of backlashes, which seriously affects meshing performance. The modification technology can effectively improve gear meshing performance. Hence, on the basis of optimizing meshing performance of the active pair of the six-branch herringbone gear transmission system, this article will combine 3D modification with system nonlinear vibration characteristics and propose an analysis method of the system nonlinear vibration characteristics under 3D modification to reduce vibration and noise. First, the 3D modified tooth surface equation is determined by forming grinding, the loaded transmission error (LTE) of the system's active pair is obtained by tooth contact analysis (TCA) and loaded tooth contact analysis (LTCA) technology, and the optimal modification parameters are obtained by Ant Lion Optimizer (ALO) with the minimum error amplitude as optimization objective. Then, the time-varying meshing stiffness of system under the optimal modification is calculated, and the pure torsional nonlinear dynamic model with backlashes, meshing stiffness, and static transmission error (STE) is established. Finally, the global vibration characteristics in parameter field are studied through time domain and bifurcation diagram of system. Results show that the 3D modification can eliminate edge contact of tooth and improve tooth contact performance. With the increase of input power, the root mean square (RMS) values of acceleration increase and the RMS values and jump decrease after 3D modification. With the increase of input speed, the RMS curves appear multiple resonance peaks and jumps at low input speed. After 3D modification, the RMS, jump, and resonance peak values decrease. Compared with level І, the backlashes and STEs of level II and phase difference ϛsII have great influence on system dynamic characteristics and easily make system in chaotic motion, while the 3D modification reduces their influence and makes system motion periodic.

Parametric model for a cutting edge contour of the geokhod cutting body blade

a parametric model for a cutting body blade cutting edge contour of geokhod, which is a new class of mining equipment. The research relevance is due to the need to create a unified methodology for forming the cutting body cutting edge for geokhods of various sizes, since the cutting edge design parameters are heavily dependent on geokhod geometry and force parameters. The research objective is to obtain parametric equations for determining the geometric coordinates of the points of the geokhod cutting body blade cutting edge in Cartesian coordinates. Methods of research. The paper describes the principles of parameterization of the complex geometry of geokhod cutting body blade cutting edge. Research methods include the study of blade edge geometry, as well as its design parameters dependence on geokhod’s force and design parameters. To achieve that, analytical dependencies were selected from the method of calculating the cutting body force parameters, and then parametric functions affecting the cutting body cutting edge geometry were selected. Results. As a result, a geometric model of the cutting body cutting edge in a parametric form was obtained. To demonstrate the formation of the blade cutting edge contact with rock based on the obtained parametric-time dependencies, a computer program was developed with the calculated values probability construction. The dependence between the cutting edge geometry and the geokhod design parameters dictated the modeling of the cutting edge shape for geokhods of different diameters. Conclusions. The obtained parametric expressions for calculating the coordinates of geokhod cutting body contact make it possible to build contact lines of the blade and the rock mass according to the input data. Is has also been proved that geokhod cutting edge shape depends on the geokhod diameter, and its geometric parameters will be individual for each type of geokhod

Derivation and exploration of permeability function for contact of wedge-shaped edge of metal seal with flange

Derivation and exploration of permeability function for contact of wedge-shaped edge of metal seal with flange

Molecular dynamics simulation of illite: From particle associations to hydration properties

Water-in-clay nanopores are one of the hallmarks of the terrestrial weathering and sedimentary environment. However, much of their properties were still poorly understood. In the present work, illite particles were defined as face-face, edge-edge, edge-face, or edge-vertical edge aggregate structures while aggregates were modeled using overlapping-surface and edge-sloping edge contact configurations for randomly placed building blocks. With the increase of moisture content, the proportion of edge-sloping configuration decreased, while surface overlap configuration and enthalpy were the opposite. The pore width increased with the moisture content, with water molecules being primarily distributed within 1 nm of the clay mineral surface. Overall, the molecular dynamics (MD) simulations provided realistic predictions of the nature of hydrated illite nanoparticle combinations that can provide essential insights into the macroscopic structure.

Role of impact ionization and self-consistent tunnel injection in Schottky-barrier diodes operating under strong reverse-bias conditions

This work shows that for a correct analysis of Schottky barrier diodes operating under strong reverse-bias conditions, it is necessary to account for the self-consistency between the shape of the energy barrier and carrier concentration in the depletion region since the full-depletion approximation fails to estimate the current. This happens for very high applied voltages, at which impact ionization by electrons and holes must also be considered. Two example GaN diodes with different doping concentrations and barrier heights are analyzed. The results are relevant to regions of the diodes where a very high tunnel injection takes place, like the contact edge or surface inhomogeneities.

Mechanism of polishing lutetium oxide single crystals with polyhedral diamond abrasive grains based on molecular dynamics simulation

Lutetium oxide single crystal is an excellent laser crystal material with the advantages of low phonon energy, high thermal conductivity, and high laser-induced damage threshold. Polishing is an important method to achieve ultrasmooth, damage-free surfaces of lutetium oxide wafers. The diamond abrasive grains used in mechanical polishing are mainly in the form of blocks, flakes, and balls. In this study, the molecular dynamics simulation method is used to simulate the process of polishing a lutetium oxide single crystal with different shapes of polyhedral diamond abrasive grains, and the polishing force, subsurface damage, and material removal are analyzed. Results show that the compressive stress and thickness of the machined amorphous layer in the subsurface are minimum at the vertex contact position and maximum at the face contact position. The values at the sphere and edge contact positions are somewhere in between. In terms of material removal, polyhedral and spherical abrasive grains have a plowing effect on the material removal process. However, the vertices and edges of polyhedral abrasive grains can be more easily cut into the workpiece than spherical abrasive grains, so polyhedral abrasive grains are conducive to the removal of materials in specific cases.

Process optimization of contact hole patterns via a simulated annealing algorithm in extreme ultraviolet lithography.

The critical dimension (CD), roughness, and sensitivity are extremely significant indicators for evaluating the imaging performance of photoresists in extreme ultraviolet lithography. As the CD gradually shrinks, tighter indicator control is required for high fidelity imaging. However, current research primarily focuses on the optimization of one indicator of one-dimensional line patterns, and little attention has been paid to two-dimensional patterns. Here, we report an image quality optimization method of two-dimensional contact holes. This method takes horizontal and vertical contact widths, contact edge roughness, and sensitivity as evaluation indicators, and uses machine learning to establish the corresponding relationship between process parameters and each indicator. Then, the simulated annealing algorithm is applied to search for the optimal process parameters, and finally, a set of process parameters with optimum image quality is obtained. Rigorous imaging results of lithography demonstrate that this method has very high optimization accuracy and can improve the overall performance of the device, dramatically accelerating the development of the lithography process.

Slip at the edge of complete contacts

We describe an asymptotic method for calculating the size of a zone of partial slip at the edge of a complete contact of arbitrary edge angle and coefficient of friction. Above a critical coefficient of friction the contact remains stuck, and this critical value is explored. A distributed dislocation method is used and the use of different types of numerical quadrature is explored. The size of the slip zone, and its dependence on the contact edge angle and coefficient of friction, are explored.

Contact optimisation strategy for wafer-scale field-effect transistors based on two-dimensional semiconductors

• Wafer-scale multilayered MoS2 films were fabricated by vacuum transferring technique. • A novel electrical contact architecture was proposed to improve the contact capability between 3D metal and 2D semiconductors. • A novel edge-treatment method for the MoS2 side was developed by employing a mature magnetron sputtering system. • Approximately 16 times lower contact resistivity (22.8 kΩ μm) and 3 times lower Schottky barrier height (34.6 meV) than that of the conventional top contacted devices were achieved. • Simplified resistor network model and energy-band diagrams were elaborately illustrated to discuss the mechanisms. Two-dimensional (2D) semiconductors can be utilized to continually miniaturize nanoscale electronic devices. However, achieving a practical solution for satisfying electrical contact with 2D semiconductors remains challenging. In this study, we developed a novel contact structure with transferred multilayer (t-ML) MoS 2 by integrating both edge and top contact. After in-situ plasma treatment for the edge of the MoS 2 channel and successive metal deposition, we achieved 16 times lower contact resistivity (22.8 kΩ µm) than that of the top contacted devices. The thickness-dependent electrical measurement indicates that edge contact is highly effective with thick MoS 2 due to the alleviated current-crowding effect resulting from the small contact area. The temperature-dependent transport measurement further confirms the effective minimization of the influence from the Schottky barrier and tunnelling barrier. Finally, the simplified resistor network model and energy-band diagram were proposed to understand the carrier transport mechanism. Our work provides a practical strategy for achieving excellent electrical contact between bulk metals and 2D semiconductors, paving the way for future large-scale 2D electronic devices.

Neural Network-based Model Parameter Estimation for End Milling of Carbon Fiber Reinforced Polymer (CFRP) Composites

A predictive cutting force model is critical during the end milling of Carbon Fiber Reinforced Polymer (CFRP) composites to achieve optimum fiber delamination, tool wear, and surface accuracy. The mechanistic force model showed robust prediction abilities; however, cutting constant estimation is challenging due to the involvement of multiple variables resulting in higher-order mathematical formulations. This paper presents augmenting the Feed Forward Neural Network (FFNN) with a mechanistic force model to approximate independent relationships of the chip load and edge contact length with shearing and rubbing constants. The prediction abilities of the proposed approach are compared with the traditional Fourier fitting model and experimentally measured values over diverse cutting conditions. It has been demonstrated that the proposed approach can accurately estimate cutting forces during the end milling of CFRPs.

Transient Calculation Studies of Liquid–Solid Collision in Jet Descaling

Sichuan is gradually being transformed and is utilizing groundwater and thermal resources. However, this investigation found that the high mineralization rate of geothermal resources in the Sichuan Basin is common and efficient, and environmentally friendly descaling technology is the key to promoting the utilization of thermal resources in low-yield oil and gas wells. Due to the high efficiency, low cost, and lack of pollution of high-pressure jet descaling, it has attracted more and more attention recently, but the mechanism of jet descaling is still unclear. The key to jet descaling is the stress concentration in the scale caused by the impact of droplets from the jet. In this paper, the process of jet descaling is simplified as a 2D droplet–scale collision with a detailed theoretical analysis of the stress on the scale. A circular droplet was simulated to impact the surface of the scale. By using numerical methods for transient calculations, we couple the pressure of the droplets and the scale strain. We acquired transient equivalent stress fields inside scales and pressure distributions inside the water droplet. As a result of the impact, areas of high stress in the scale appeared. Due to the stress superposition, the highest stress is concentrated in two areas: the contact edge and the shaft. These results can identify the mechanism for high-pressure jet descaling and help improve the efficiency of high-pressure water-jet descaling.

Highly responsive SnSe/GaN heterostructure-based UVC-SWIR broadband photodetector

Broadband photodetection spans the ultraviolet-C (250 nm) to shortwave-infrared (1250 nm) range is essential and desirable for various applications such as optical communication, spectral switching, and memory storage. We have utilized ultraviolet-responsive gallium nitride (GaN) and Tin selenide (SnSe) as the infrared-activated material to fabricate a broadband heterojunction-based optical detector. Through SnSe/GaN heterostructure, the fabricated detector combines GaN's ultraviolet to visible, with SnSe's visible to shortwave-infrared detectability. The device also possesses great responsiveness and a low dark current due to edge contact geometry, which directly accesses the heterostructure interface for both materials. The fabricated device functions well from the ultraviolet-C to the shortwave-infrared region, exhibiting the highest responsivity of 128 AW-1 and the lowest noise equivalent power of 5.2 × 10−14 WHz−1/2, the quantum efficiency ∼5 × 104% with a response time ∼800 μs for ultraviolet illumination while the highest responsivity of 6.06 AW-1 and noise equivalent power of 1 × 10−12 WHz−1 for the device under infrared illumination. The research will open up new possibilities for optoelectronic applications utilizing heterostructure-based wideband detection.

The influence of substrate stiffness on interfacial stresses for adhesive microfibrils

Bioinspired microfibrillar surfaces adhere by exploiting the presence of intermolecular forces at the contact interface. Experimental work has shown that compliant mushroom shaped fibrils can facilitate optimal adhesion across a range of substrates. This work evaluates numerically how fibril contact tip shape and the degree of elastic mismatch at the fibril-substrate interface influence adhesion. In a finite element simulation of fibrils subject to a remote stress, the interfacial stress distributions that define the detachment behaviour are computed for a range of fibril cap diameters, thicknesses, and substrate stiffnesses. Depending on the substrate stiffness, there is a singular stress field present at the edge of contact for smaller mushroom cap and straight punch fibrils while the stress at the corner for larger mushroom fibrils tends to zero. This variation in fibril-substrate interfacial stress has implications for the most probable defect type to initiate detachment and the stability of this crack growth. For fibrils within this corner singularity regime, the adhesion strength of a patch of fibrils is determined using interfacial fracture mechanics. The simulations are compared with experimental data of pull-off strengths and the biomedical applications of adhesive microfibrillar patches are considered.

The study of contact properties in edge-contacted graphene–aluminum Josephson junctions

Transparent contact interfaces in superconductor–graphene hybrid systems are critical for realizing superconducting quantum applications. Here, we examine the effect of the edge contact fabrication process on the transparency of the superconducting aluminum–graphene junction. We show significant improvement in the transparency of our superconductor–graphene junctions by promoting the chemical component of the edge contact etch process. Our results compare favorably with state-of-the-art graphene Josephson junctions. The findings of our study contribute to advancing the fabrication knowledge of edge-contacted superconductor–graphene junctions.