Asymmetric Contacts Research Articles

Highly Concentrated Electrolyte Superlubricants Enhanced by Interfacial Water Competition Around Chemically Active MgO Additives.

The low concentration of water-based lubricants and the high chemical inertness of the additives involved are often regarded as basic norms in the design of liquid lubricants. Herein, a novel liquid superlubricant of an aqueous solution containing a relatively high concentration of salt, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), is reported for the first time, and the superlubricity stability and load-bearing capacity of the optimized system (MgO0.10/LiTFSI10) are effectively strengthened by the addition of only trace (0.10 wt %) water-chemically active MgO additives. It demonstrates higher applicable loads, lower COF (∼0.004), and stability relative to the base solution. Only a trace amount of MgO additive is needed for the superlubricity, which makes up for the cost and environmental deficiencies of LiTFSI10. The weak interaction region between free water and the outer-layer water of Li+ hydration shells becomes a possible ultralow shear resistance sliding interface; the Mg(OH)2 layer, generated by the reaction of MgO with water, further creates additional weakly interacting interfaces, leading to the formation of an asymmetric contact between the clusters/particles within the hydrodynamic film by moderating the competition between interfacial water and free water, thus achieving high load-bearing macroscopic superlubricity. This study deepens the contribution of electrolyte concentration to ionic hydration and superlubricity due to the low shear slip layer formed by interfacial water competition with water-activated solid additives, providing new insights into the next generation of high load-bearing water-based liquid superlubricity systems.

Tailoring Contacts for High-Performance 1D Ta2Pt3S8 Field-Effect Transistors.

Materials with van der Waals (vdW) unit structures rely on weak interunit vdW forces, facilitating physical separation and advancing nanomaterial research with remarkable electrical properties. Recently, there has been growing interest in one-dimensional (1D) vdW materials, celebrated for their advantageous properties, characterized by reduced dimensionality and the absence of dangling bonds. In this context, we synthesize Ta2Pt3S8, a 1D vdW material, and assess its suitability for field-effect transistor (FET) applications. Spectroscopic analysis and electrical characterization confirmed that the band gap and work function of Ta2Pt3S8 are 1.18 and 4.77 eV, respectively. Leveraging various electrode materials, we fabricated n-type FETs based on Ta2Pt3S8 and identified Cr as the optimal electrode, exhibiting a high mobility of 57 cm2 V-1 s-1. In addition, we analyzed the electron transport mechanism in n-type FETs by investigating Schottky barrier height, Schottky barrier tunneling width, and contact resistance. Furthermore, we successfully fabricated p-type operating Ta2Pt3S8 FETs using a molybdenum trioxide (MoO3) layer as a high work function contact electrode. Finally, we achieved Ta2Pt3S8 nanowire rectifying diodes by creating a p-n junction with asymmetric contact electrodes of Cr and MoO3, demonstrating an ideality factor of 1.06. These findings highlight the electronic properties of Ta2Pt3S8, positioning it as a promising 1D vdW material for future nanoelectronics and functional vdW-based device applications.

Asymmetric Rolling Contact Joint for Enhanced Payload Capabilities

Asymmetric Rolling Contact Joint for Enhanced Payload Capabilities

Polarity switch of PMMA powder transported through a PMMA duct

During pneumatic conveying, powder electrifies rapidly due to the high flow velocities. In our experiments, the particles even charge if the conveying duct is made of the same material, which might be caused by triboelectrification between two asymmetric contact surfaces. Surprisingly, we found the airflow rate to determine the polarity of the overall powder charge. This study investigates the charging of microscale PMMA particles in turbulent flows passing through a square PMMA duct. The particles are spherical and monodisperse. A Faraday at the duct outlet measured the total charge of the particles. At low flow velocities, the particles charged negatively after passing through the duct. However, the powder’s overall charge switched to a positive polarity when increasing the flow velocity.

The Impact of Asymmetric Contact Resistance on the Operating Parameters of Thermoelectric Systems

This paper presents a simulation model for a system equipped with thermoelectric elements, considering the impact of independent thermal contact resistances on each side of the module. An analytical model was constructed, taking into account the asymmetry of thermal resistances between the generator/cooler and the respective heat source/heat sink. A comparative analysis of thermoelectric device operating indicators such as conducted heat, efficiency, and the electricity/cooling power produced was performed. The selection of electrical current in the circuit was analysed based on the maximization of power or efficiency. This paper discusses deviations from ideal conditions, specifically the absence of thermal resistance between the heat source/sink and the thermoelectric junction. The model accurately simulates the operating conditions of the thermoelectric system with a low computational cost. The results indicate that the total thermal resistance, rather than its location, predominantly affects the operation of the thermoelectric generator. However, in cooling operations, the influence of thermal resistance significantly depends on the cooling power demand and temperature.

Asymmetric contact-induced selective doping of CVD-grown bilayer WS2 and its application in high-performance photodetection with an ultralow dark current.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are excellent candidates for high-performance optoelectronics due to their high carrier mobility, air stability and strong optical absorption. However, photodetectors made with monolayer TMDs often exhibit a high dark current, and thus, there is a scope for further improvement. Herein, we developed a 2D bilayer tungsten disulfide (WS2) based photodetector (PD) with asymmetric contacts that exhibits an exceptionally low dark current and high specific detectivity. High-quality and large-area monolayer and bilayer WS2 flakes were synthesized using a thermal chemical vapor deposition system. Compared to conventional symmetric contact electrodes, utilizing metal electrodes with higher and lower work functions relative to bilayer WS2 aids in achieving asymmetric lateral doping in the WS2 flakes. This doping asymmetry was confirmed through the photoluminescence spectral profile and Raman mapping analysis. With the asymmetric contacts on bilayer WS2, we find evidence of selective doping of electrons and holes near the Ti and Au contacts, respectively, while the WS2 region away from the contacts remains intrinsic. When compared with the symmetric contact case, the dark current in the WS2 PD with asymmetric (Au, Ti) contact decreases by an order of magnitude under reverse bias with a concomitant increase in the photocurrent, resulting in an improved on/off ratio of ∼105 and overall improved device performance under identical illumination conditions. We explained this improved performance based on the energy band alignment showing a unidirectional charge flow under light illumination. Our results indicate that the planar device structure and compatibility with current nanofabrication technologies can facilitate its integration into advanced chips for futuristic low-power optoelectronic and nanophotonic applications.

Self-formed asymmetric Schottky contacts between graphene and WSiGeN4.

In this paper, the electronic properties and transport characteristics of WSiGeN4/graphene heterostructures were explored by combining the quantum transport method with first-principle calculations. The band structures indicate that the heterostructures can form either p-type or n-type Schottky contacts, depending on the stacking mode. Due to the self-formed asymmetric Schottky contacts, we design an asymmetric van der Waals (vdW) metal-semiconductor-metal (MSM) structure, which exhibits a pronounced asymmetric current-voltage (I-V) curve. The corresponding physical mechanisms are attributed to carrier transport mechanisms, which are primarily governed by thermionic excitation at positive bias voltages and tunneling effects at negative bias voltages. Our study offers a viable strategy for integrating asymmetric Schottky barriers into MSM configurations, laying the groundwork for a wider range of applications in a range of Janus two-dimensional semiconductors.

Sm, Pt asymmetric n- and p-type contacts in WSe2 phototransistor for high-performance broadband photodetection

The development of high-performance broadband photodetectors working at room temperature is still attractive. The Schottky barrier phototransistor based on asymmetric junction seems to be endowed with such potential—as photodetectors with low device power consumption and high photoresponse; however, it is rarely studied. Herein, a Sm–WSe2–Pt phototransistor with asymmetric metal contacts is constructed, and it is systematically investigated for their electronic and photoelectronic tunability via gate voltage, wavelength, and illumination power density. It was found that the tunable photogating process dominates the photoresponse mechanism, which allows for an excellent broadband photodetection from 300 to 1000 nm wavelength. In addition, the responsivity (R) and specific detectivity (D*) at 450 nm can reach 1723 A/W and 2.3 × 1013 Jones, respectively, while that of infrared illumination of 900 nm can reach 4.7 A/W and 3.1 × 1010 Jones, respectively. In addition, the device exhibits obvious photoresponse at zero bias, the R and D* can reach up to 27 mA/W and 8.5 × 1010 Jones, which realizes self-driven photodetection. This work provides an optimal option for realizing high-integrated, high-performance, low-power-consuming, and room-temperature-working broadband photodetectors.

Asymmetric seismic pounding between multistorey reinforced concrete structures in a city block

Usually within city blocks land ownerships are not equal and exhibit various geometries. Therefore, it is most probable adjacent structures to be partly and in an asymmetric way in contact. Consequently, buildings asymmetrically restrained in lateral displacements during earthquake excitations carry out torsional oscillations. The interaction of an 8-storey reinforced concrete frame building designed according to Eurocodes with an adjoining structure for various parameters is thoroughly investigated. The 8-storey frame is considered with pilotis configuration and fully infilled whereas the other structure is studied for the cases of 6-stories, 3-stories and single storey. Further the two interacting structures form an L-shape plan and are studied for three cases of asymmetric contact, whereas two natural seismic excitations each one applied in two directions (positive – negative). Thereupon, for the thorough study of the problem more than 100 pounding pairs for structures having equal storey levels (floor-to-floor pounding) and 100 pairs for structures having unequal storey levels (floor-to-column or interstorey pounding) have been investigated. The whole study highlights crucial aspects of the issue such as the unfavourable role of pilotis configuration, the significant torsional vibrations induced and the almost inevitable shear failure of columns that suffer an impact by an adjacent building within their deformable height.

Anillin-related Mid1 as an adaptive and multimodal contractile ring anchoring protein: A simulation study

Cytokinesis of animal and fungi cells depends crucially on the anillin scaffold proteins. Fission yeast anillin-related Mid1 anchors cytokinetic ring precursor nodes to the membrane. However, it is unclear if both of its Pleckstrin Homology (PH) and C2 C-terminal domains bind to the membrane as monomers or dimers, and if one domain plays a dominant role. We studied Mid1 membrane binding with all-atom molecular dynamics near a membrane with yeast-like lipid composition. In simulations with the full C terminal region started away from the membrane, Mid1 binds through the disordered L3 loop of C2 in a vertical orientation, with the PH away from the membrane. However, a configuration with both C2 and PH initially bound to the membrane remains associated with the membrane. Simulations of C2-PH dimers show extensive asymmetric membrane contacts. These multiple modes of binding may reflect Mid1's multiple interactions with membranes, node proteins, and ability to sustain mechanical forces.

Nonlinear analysis and vibro-impact characteristics of a shaft-bearing assembly

This study investigates the nonlinear frequency response of a shaft-bearing assembly with vibro-impacts occurring at the bearing clearances. The formation of nonlinear behavior as system parameters change is examined, along with the effects of asymmetries in the nominal, inherently symmetric system. The primary effect of increasing the forcing magnitude or decreasing the contact gap sizes is the formation of grazing-induced chaotic solution branches occurring over a wide frequency range near each system resonance. The system's nominal setup has very hard contact stiffness and shows no evidence of isolas or superharmonic resonances over the frequency ranges of interest. Moderate contact stiffnesses cause symmetry breaking and introduce superharmonic resonance branches of primary resonances. Even if some primary resonances are not present due to the system's inherent symmetry, their superharmonic resonances still manifest. Branches of quasiperiodic isolas (isolated resonance branches) are also discovered, along with a cloud of isolas near a high-frequency resonance. Parameter asymmetries are found to produce a few significant changes in behavior: asymmetric linear stiffness, contact stiffness, and gap size could affect the behavior of primary resonant frequencies and isolas.

Interfacial electronic states and self-formed asymmetric Schottky contacts in polar α-In2Se3/Au contacts

In recent years, the two-dimensional (2D) semiconductor α-In2Se3 has great potential for applications in the fields of electronics and optoelectronics due to its spontaneous iron electrolysis properties. Through ab initio electronic structure calculations and quantum transport simulations, the interface properties and transport properties of α-In2Se3/Au contacts with different polarization directions are studied, and a two-dimensional α-In2Se3 asymmetric metal contact design is proposed. When α-In2Se3 is polarized upward, it forms an n-type Schottky contact with Au. While when α-In2Se3 is polarized downward, it forms a p-type Schottky contact with Au. More importantly, significant rectification effect is found in the asymmetric Au/α-In2Se3/Au field-effect transistor. The carrier transports under positive and negative bias voltages are found to be dominated by thermionic excitation and tunneling, respectively. These findings provide guidance for the further design of 2D α-In2Se3-based transistors.

Enhancement of terahertz response in a microstructure-integrated-type-II Dirac semimetal

Terahertz detection technology has been confronted with formidable impediments, notably the paucity of sensitivity and operating temperature for photodetectors based on traditional bulk materials. In an attempt to surmount the difficulties, we propose an innovative terahertz detector based on a PtSe2 (type-II Dirac semimetallic material) integrated asymmetric antenna structure that can enhance the terahertz photoresponse by capitalizing on meticulous fabrication procedures. Experimental outcomes demonstrate the remarkable characteristics of the photodetector in the terahertz band, encompassing fast response time (7 µs), large responsivity (3.267 A/W), and low noise equivalent power (3.96 pW/Hz0.5). These accomplishments can be ascribed to the incorporation of the asymmetric metal contact of the four-leaf clover antenna structure and the excellent thermoelectric characteristics of PtSe2. This pioneering investigation consequently unveils a novel methodology for the creation of proficient PtSe2-based terahertz detectors and serves as a catalyst for the promotion of applications and further research within the terahertz sphere.

Asymmetrically Contacted Tellurium Short‐Wave Infrared Photodetector with Low Dark Current and High Sensitivity at Room Temperature

AbstractLarge dark current at room temperature has long been the major bottleneck that impedes the development of high‐performance infrared photodetectors toward miniaturization and integration. Although infrared photodetectors based on layered 2D narrow bandgap semiconductors have shown admirable advantages compared with those based on conventional compounds, which typically suffer from the expensive cryogenic operation, it is still urgent to develop a simple but effective strategy to further reduce the dark current. Herein, a tellurium (Te)‐based infrared photodetector is reported with specifically designed asymmetric electrical contact area. The deliberately introduced asymmetric electrical contact raises the electric field intensity difference in the Te channel near the drain and the source electrodes, resulting in the spontaneous asymmetric carrier diffusion under global infrared light illumination under zero bias. Specifically, the Te‐based photodetector presents promising detector performance at room temperature including a low dark current of ≈1 nA, an ultrahigh photocurrent/dark current ratio of 1.57 × 104, a high specific detectivity (D*) of 3.24 × 109 Jones, and a relatively fast response speed of ≈720 µs at zero bias. The results prove that the simple design of asymmetric electrical contact areas can provide a promising solution to high‐performance 2D semiconductor‐based infrared photodetectors working at room temperature.

Asymmetric Schottky contacts induced via localized ultrafast laser irradiation for ultrasensitive, self-powered, 2D photodetectors

Self-powered photodetectors hold great promise for addressing power-related challenges in the “Internet of Things (IoT)” era. However, the self-powered performances of a metal-semiconductor-metal (MSM) structure photodetector are inherently limited due to the presence of the symmetric Schottky contacts, leading to canceling photocurrents in opposite directions, while constructing an asymmetric MSM structure demands complicated design or sustained external fields. Herein, we propose a novel contact engineering strategy based on localized femtosecond (fs) laser irradiation, achieving an asymmetric band structure in an MSM-structure photodetector with pristine symmetric Schottky contacts. As a result, a MoS2 photodetector that exhibits exceptional photoresponse and self-powered performances is successfully fabricated. The device type transitions from a photoconductor to a photodiode, exhibiting a significant improvement in the rectification ratio from 1 to > 104. A comprehensive study on fs laser-based contact engineering is conducted by investigating atom diffusion, element variation, and Schottky barrier height variation. Notably, the photodetector demonstrates an exceptional zero-bias responsivity of 1.72 A/W, with a short circuit current of 37.2 nA and maximum output electric power of 1.67 nW. Our work provides a new strategy for modifying the energy band structure and facilitates the fabrication of high-performance self-powered photodetectors.

Self‐Powered Perovskite Photodetector Arrays with Asymmetric Contacts for Imaging Applications

AbstractDesigning photodetectors (PDs) with fast response and low power consumption is important for the realization of photoelectric conversion in photoelectric integrated systems. The emerging metal halide perovskite is proven to be a promising material for PD array devices due to its excellent photoelectric performance and large‐area production. However, the array integration of self‐powered perovskite PDs still faces challenges due to the incompatibility between perovskite and micro‐nano processing, hindering practical applications. Here, a perovskite‐compatible device fabrication process is reported for the construction of a perovskite PD array (10 × 10 pixels) with asymmetric contacts, enabling self‐powered photodetection and high‐performance imaging applications. Au and ITO/ZnO electrodes are deposited on the substrate in sequence as the asymmetric contacts. Patterned CH3NH3PbI3 films with uniform and pinhole‐free morphology are then synthesized by a photolithography‐assisted vapor–solution fabrication method as the photosensitive material. The introduction of asymmetric electrodes enables the easy collection of holes at the Au electrode side and electrons at the ITO/ZnO electrode side with light irradiation, resulting in self‐powered photodetection performance. Moreover, the PD array exhibits a uniform distribution of light response and is successfully demonstrated for light imaging. This work opens up a new avenue to develop large‐scale high‐performance perovskite optoelectronic devices with low power consumption.

Nanoscale Channel Gate‐Tunable Diodes Obtained by Asymmetric Contact and Adhesion Lithography on Fluoropolymers (Small 35/2023)

Nanoscale Channel Gate‐Tunable Diodes Obtained by Asymmetric Contact and Adhesion Lithography on Fluoropolymers (Small 35/2023)

Tendon-Driven Crawling Robot with Programmable Anisotropic Friction by Adjusting Out-of-Plane Curvature

Origami crawling robots, inspired by the principles of origami folding, have emerged as a promising approach for developing lightweight and flexible robots capable of navigating tight spaces. These robots utilize anisotropic friction, where the frictional forces between surfaces vary depending on the direction of motion, enabling controlled movement by changing the robot’s body orientation. While various actuation methods have been explored, such as pneumatic and magnetic systems, they suffer from limitations such as bulkiness or restricted workspace. In this paper, we propose a tendon-driven crawling robot that achieves anisotropic friction by controlling its out-of-plane curvature. By manipulating the robot’s shape and out-of-plane curvature, we can modulate the friction forces and enable efficient crawling motion. To maximize anisotropic friction, we design an asymmetric contact film composed of elastomer and polyester. We analyze the relationship between out-of-plane curvature and frictional force through experiments on flat and sloped surfaces, considering different leg angles and slope angles of the contact film. The results demonstrate the gait loss ratio of 1.96% for the optimized design, highlighting the robot’s ability to crawl efficiently with quick response times and a low-profile system. This research contributes to the advancement of origami-based crawling robots and their potential applications in confined and unstructured environments.

Stiffness Analysis of High Contact Ratio Spur Gear with Asymmetric Teeth

The demands of high carrying capacity and low vibration of gear transmission systems in aviation, aerospace, and other areas are addressed by high contact ratio gears with asymmetric teeth, which have a wide range of potential applications. The Weber energy technique is utilized to determine the stiffness of high contact ratio spur gears with asymmetric teeth, and the effect law of the stiffness parameters is researched, due to the paucity of study on these gears. The influence of the drive side addendum factor, modulus, and pressure angle on the stiffness of asymmetric high contact ratio spur gears is investigated. The deformation of the gear will be exacerbated by an increase in the addendum factor, and the comprehensive stiffness of the gear will grow as more gear pairs participate in the meshing. The rigidity of gears may be greatly increased without ignoring modulus if the driving side pressure angle is properly increased.

Research on the Filling Process of Ultraviolet Nanoimprint Lithography with High-Resolution Stamps

With the rapid development of the semiconductor industry, the feature size of integrated circuits (ICs) is continuously getting smaller and smaller. Although traditional optical lithography and extreme ultraviolet (EUV) lithography can fabricate products with 5-nm feature size, the production cost is quite high. As a candidate of next-generation lithography, ultraviolet nanoimprint lithography (UV-NIL) can also achieve high-resolution imprints at a lower cost. Based on contact mechanics, the filling mechanism and imprint quality of UV-NIL were examined using high-resolution stamps with different feature sizes of 3 nm, 4 nm, and 5 nm. It was found that UV-NIL could successfully replicate patterns with feature sizes down to 3 nm; however, the imprinting process was more complicated. Among the selected nine stamps, the replications of 4-nm and 5-nm feature sizes had a relatively uniform residual layer and a symmetric contact pressure, whereas the replications of 3-nm feature size had an asymmetric contact pressure, resulting in an asymmetric residual layer. In order to obtain a more uniform residual layer with higher-quality imprinting, the pressure applied to the left and right sides of a stamp should be appropriately changed. The pattern density of a stamp had a certain influence on the contact pressure. As the pattern density increased, the contact pressure tended to be uniform; however, when the pattern density exceeded 0.5, the situation became worse. This research can provide guidance for promoting the development of UV-NIL in the direction of high-resolution pattern replication.