Two-dimensional Device Research Articles

Morphological Differences of Knee Extensor Muscles Between Women With and Without Lateral Patellar Compression Syndrome

Background and Aims: The morphology of knee joint extensor muscles including vastus medialis (VM) and vastus lateralis (VL), is one of the important and effective factors in lateral patellar compression syndrome (LPCS). This study aims to examine the morphological differences of these knee extensor muscles between women with and without LPCS. Methods: In this causal-comparative study, 15 women with LPCS aged 18-30 years and 15 women without LPCS as controls participated who were selected by a convenience sampling methhod. For muscle imaging, the anteromedial (VM) and anterolateral (VL) thigh distal ends were scanned by using a two-dimensional digital ultrasound device (SonoSite Co., USA). The muscles’ cross-sectional area at the patellar base was measured in square centimeters and the muscle-fiber pennation angles of these muscles was measured in degree. Independent t-test was used to compare the variables between the two groups. The significance level was set at 0.05. Results: The cross-sectional area of VM in the control group was significantly higher than in the LPCS group (P=0.001), while the cross sectional area of VL was not significantly different between the two groups (P>0.05). The muscle-fiber pennation angle of VM in the LPCS group was significantly lower than in the control group (P=0.016), while the muscle-fiber pennation angles of VL in the LPCS group was significantly higher than in the control group (P=0.021). Conclusion: The morphology of VM and VL in women with LPCS symptoms shows a significant muscle imbalance that can change the patella position from normal to a more lateral position and increase the contact between the lateral facet of the patella and the lateral femoral condyle, resulting in increased pressure on this area and eventually knee pain.Muscle morphology, Cross-sectional area, Muscle-fiber pennation angle, Lateral patellar compression syndrome, Knee extensors

Reconfigurable logic-in-memory architectures based on a two-dimensional van der Waals heterostructure device

Reconfigurable logic-in-memory architectures based on a two-dimensional van der Waals heterostructure device

Robust 2D MoS2 Artificial Synapse Device Based on a Lithium Silicate Solid Electrolyte for High-Precision Analogue Neuromorphic Computing.

High-precision artificial synaptic devices compatible with existing CMOS technology are essential for realizing robust neuromorphic hardware systems with reliable parallel analogue computation beyond the von Neumann serial digital computing architecture. However, critical issues related to reliability and variability, such as nonlinearity and asymmetric weight updates, have been great challenges in the implementation of artificial synaptic devices in practical neuromorphic hardware systems. Herein, a robust three-terminal two-dimensional (2D) MoS2 artificial synaptic device combined with a lithium silicate (LSO) solid-state electrolyte thin film is proposed. The rationally designed synaptic device exhibits excellent linearity and symmetry upon electrical potentiation and depression, benefiting from the reversible intercalation of Li ions into the MoS2 channel. In particular, extremely low cycle-to-cycle variations (3.01%) during long-term potentiation and depression processes over 500 pulses are achieved, causing statistical analogue discrete states. Thus, a high classification accuracy of 96.77% (close to the software baseline of 98%) is demonstrated in the Modified National Institute of Standards and Technology (MNIST) simulations. These results provide a future perspective for robust synaptic device architecture of lithium solid-state electrolytes stacked with 2D van der Waals layered channels for high-precision analogue neuromorphic computing systems.

Operation Mechanisms of Flexible RF Silicon Thin Film Transistor under Bending Conditions

We fabricate a flexible silicon thin-film transistor (TFT) on a plastic substrate as a key component and representative example to analyze the major influencing factors of flexible devices under bending conditions. Experimental and two-dimensional device modeling results reveal that bending radius and device dimensions have a significant influence on the radio-frequency (RF) performance of the flexible silicon nanomembrane (SiNM) TFT under bending conditions. Carrier mobility and electric field extracted from the model, together with theoretical analysis, were employed to study the performance dependence and the operation mechanisms of the bended TFTs. The carrier mobility and electric field are increased monotonically with larger bending strains, which lead to better RF performance. They also showed a consistent change trend with different device parameters (e.g., gate length, oxide thickness). Flexible SiNM TFTs with a smaller gate length and a larger gate dielectric thickness are shown to have better RF performance robustness with bending strains. The analysis provides a guideline for the study of flexible electronics under bending conditions.

Investigation on holding voltage of asymmetric DDSCR with floating heavy doping in 0.18 μm CMOS process

In the ESD protection design work, the most effective way to improve the holding voltage of bidirectional silicon-controlled rectifier or SCR device is to increase the distance between the cathode and anode of it. However, for DDSCR devices with multi-finger layouts, increasing this distance will result in a decrease in failure current and require a larger layout area. In this work, five types of asymmetric dual direction silicon-controlled rectifier devices with different floating heavy doping combinations are designed based on the traditional ADDSCR structure. Meanwhile, the dimensions, number of fingers, metal layout and number of CONT holes of the five ADDSCR structures are strictly kept the same, aiming at studying the influence of different floating heavy doping combinations on the performance of SCR devices and find the optimal floating heavy doping combination. Their ESD performances are predicted and verified through the two-dimensional device simulations and transmission line pulse (TLP) test results. All the five types of ADDSCR structures are designed to improve the holding voltage. From the results, the forward and reverse holding voltage of ADDSCR_PP, which is inserted floating P+ in NW and PW, are increased to 20.4 V and 17.6 V respectively, compared with the traditional devices without floating heavy doping at 14.2 V and 8.7 V. At the same time, the physical mechanism for the effect of floating heavy doping insert into NW and PW separately were investigated. Finally, the one that best meets the ESD window of automotive application is found.

Variable range hopping conductivity in molecular beam epitaxial InSb

A variable range hopping (VRH) transport mechanism can be induced in molecular beam epitaxial, n-type doped InSb wafers with focussed Ga+ ion beam damage. This technique allows areas of wafer to be selectively damaged and then subsequently processed into gated metal–insulator–semiconductor (MIS) devices where a disordered, two-dimensional (2D) device can be established. At high levels of damage (dose >1016 Ga+ ions cm−2) amorphous crystalline behavior results with activated conductivity characteristic of a three-dimensional system with VRH below 150 K. At lower doses (1014–1016 Ga+ ions cm−2) a thermally activated conductivity is induced at ∼0.9 K, characteristic of Mott phonon-assisted VRH. At 1 K the devices either conduct with conductivity >∼(e 2/h) where e is the fundamental charge and h is Planck’s constant, or are thermally activated depending on the dose level. The lightly damaged devices show weak antilocalization signals with conductivity characteristic of a 2D electronic system. As the Ga+ dose increases, the measured phase coherence length reduces from ∼500 nm to ∼100 nm. This provides a region of VRH transport where phase-coherent transport processes can be studied in the hopping regime with the dimensionality controlled by a gate voltage in an MIS-device.

Vanadium-Doped Porous Cobalt Oxide for Its Superior Peroxidase-like Activity in Simultaneous Total Cholesterol and Glucose Determination in Whole Blood Based on a Simple Two-Dimensional Paper-Based Analytical Device.

Vanadium-doped porous Co3O4 (V-porous Co3O4) was synthesized via a simple soft-templating method and used as a superior peroxidase mimic for the simultaneous colorimetric determination of glucose and total cholesterol (TC) in whole blood samples on a two-dimensional microfluidic paper-based analytical device (2D-μPAD). The large surface area and the presence of two metals in V-porous Co3O4 contributed to its excellent catalytic activity toward 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and 3,3',5,5'- tetramethylbenzidine (TMB) with Michaelis-Menten constants (KM) of 0.1301 and 0.0141 mM, respectively. The 2D-μPAD was fabricated using simple wax screen-printing and cutting techniques. The colorimetric reactions of both glucose and TC on 2D-μPAD were simultaneously performed by adding a single drop of a whole blood sample on the sample zone made of the LF1 membrane. After the enzymatic reactions, the generated hydrogen peroxide (H2O2) was oxidized by V-porous Co3O4 to produce hydroxy radicals (•OH), inducing ABTS and TMB to generate colored products. The generated H2O2 was proportional to the intensities of the green and blue products of the glucose and TC systems, respectively. The developed 2D-μPAD required a short analysis time (∼5 min) with small volumes of samples (15 μL of whole blood) whereby no sample preparation was needed. Owing to several advantages including simplicity, low cost, long-term stability, and simultaneous readout, the novel V-porous Co3O4 coupled with 2D-μPAD proved to be promising for practical uses as a pioneering portable device for the determination of glucose, TC, and other important biomarkers without the need of technical supports.

Multifunctional on-chip directional coupler for spectral and polarimetric routing of Bloch surface wave.

Integration of multiple diversified functionalities into an ultracompact platform is crucial for the development of on-chip photonic devices. Recently, a promising all-dielectric two-dimensional platform based on Bloch surface waves (BSWs) sustained by dielectric multilayer has been proposed to enable various functionalities and provide novel approach to photonic devices. Here, we design and fabricate a multifunctional directional coupler to achieve both spectral and polarimetric routing by employing asymmetric nanoslits in a dielectric multilayer platform. Due to the dispersion property of BSWs, the directional coupling behavior is sensitive to wavelength and polarization. We demonstrate numerically and experimentally the wavelength selective directional coupling of TE BSW mode with an intensity ratio of the BSW excitation in opposite directions reaching 10 dB. Polarization selective directional coupling is also achieved at specific operating wavelength due to different response to a nanoantenna for TE and TM BSWs. The proposed two-dimensional photonic device opens new pathway for a wide range of practical applications such as molecular sensing, imaging with different polarization, and spectral requirements.

Real-time numerical system convertor via two-dimensional WS2-based memristive device

The intriguing properties of two-dimensional (2D) transition metal dichalcogenides (TMDCs) enable the exploration of new electronic device architectures, particularly the emerging memristive devices for in-memory computing applications. Implementation of arithmetic logic operations taking advantage of the non-linear characteristics of memristor can significantly improve the energy efficiency and simplify the complexity of peripheral circuits. Herein, we demonstrate an arithmetic logic unit function using a lateral volatile memristor based on layered 2D tungsten disulfide (WS2) materials and some combinational logic circuits. Removable oxygen ions were introduced into WS2 materials through oxygen plasma treatment process. The resistive switching of the memristive device caused by the thermophoresis-assisted oxygen ions migration has also been revealed. Based on the characteristics of excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), and spike rate dependent plasticity (SRDP), a real-time numerical system convertor was successfully accomplished, which is a significant computing function of arithmetic logic unit. This work paves a new way for developing 2D memristive devices for future arithmetic logic applications.

Designing high-efficiency metal and semimetal contacts to two-dimensional semiconductor γ-GeSe

Forming a low-resistance semiconductor–metal contact is a critical step to achieve a high-performance two-dimensional (2D) semiconductor nanoelectronic device. Motivated by the recent discovery of monolayer γ-GeSe with exceptional high electrical conductivity reaching 105 S/m, we computationally investigate the interface contact properties of γ-GeSe with four representative classes of metallic systems, including 2D semimetal (graphene), 2D metal (NbS2), 3D semimetal (Bi), and 3D metal (Au) using first-principle density functional theory simulations. We found that these metals exhibit rich contact formation physics with 2D γ-GeSe, yielding contacts of heterostructures with weak and moderate couplings. Importantly, γ-GeSe/NbS2 is an Ohmic contact while γ-GeSe/Bi is an n-type Schottky contact with an ultralow barrier height of 0.07 eV. For γ-GeSe/graphene contact, the electronic properties can be adjusted via the interlayer distance or via an external electric field. Finally, we show that the contact properties can also be further controlled using layer-number engineering of γ-GeSe. Our findings provide a useful guideline for designing high-performance 2D nanoelectronics based on 2D γ-GeSe.

Deep reinforcement learning with a critic-value-based branch tree for the inverse design of two-dimensional optical devices

In optical engineering, designing a device or a system with the desired property is an important but challenging task. It is relatively straightforward to compute the physical properties of a given design; however, there is no general method for the reverse, i.e., designing with desired properties. To address this problem with a computational method, this paper proposes a deep reinforcement learning-based inverse design framework consisting of two methods: Inverse DEsign Agent (IDEA) and Critic-Value-based Branch Tree (CVBT) algorithm. IDEA is a deep reinforcement learning model based on the Advantage Actor–Critic (A2C) method using a deep learning simulator as a replacement for a real environment, significantly reducing training time compared to conventional methods. The CVBT algorithm suggests several design candidates using the critic values of IDEA, while conventional methods propose only one candidate. In this study, the proposed framework was applied to a two-dimensional optical device design problem. Experimental results with untrained target properties demonstrated that the proposed model, IDEA-CVBT, achieved state-of-the-art performance in terms of accuracy and stability. For instance, in a scenario with a binary type design, IDEA-CVBT exhibited an accuracy of 91.5%, while conventional deep reinforcement models showed 36.1% and 7.4% accuracies. Extensive analyses verified that IDEA-CVBT can be employed as an assistance system for engineers since IDEA-CVBT suggests several appropriate candidates that satisfy target properties.

Two-Dimensional Position Tracking Using Gradient Magnetic Fields

In this work, a two-dimensional (2D) position-detection device using a single axis magnetic sensor combined with orthogonal gradient coils was designed and fabricated. The sensors used were an induction coil and a GMR spin-valve sensor GF807 from Sensitec Inc. The field profiles generated by the two orthogonal gradient coils were analyzed numerically to achieve the maximum linear range, which corresponded to the detection area of the tracking system. The two coils were driven by 1-kHz sine wave currents with a 90° phase difference to generate the fields with uniform gradients along the x- and y-axis in the plane of the tracking stage. The gradient fields were detected by a single-axis sensor incorporated with a digital dual-phase lock-in detector to retrieve the position information. A linearity correction algorithm was used to improve the location accuracy and to extend the linear range for position sensing. The mean positioning error was found to be 0.417 mm, corresponding to the relative error of 0.21% in the working range of 200 mm × 200 mm, indicating that the proposed tracking system is promising for applications requiring accurate control of the two-dimensional position.

Oxidation of tantalum disulfide (TaS2) films for gate dielectric and process design of two-dimensional field-effect device

Ta-based high-κ dielectrics can be synthesized via the oxidation of TaS2 films. In this study, we investigated the wet and dry oxidation of TaS2 films via thermal annealing and plasma irradiation, respectively. The specific vibration observed via Raman spectroscopy, the bonding states observed via x-ray photoelectron spectroscopy, and capacitance measurements confirmed the oxidation of TaS2 films with a dielectric constant of ∼14.9. Moreover, the electrical transport of the TaS2 films along the in-plane direction indicated a change in conductivity before and after the oxidation. The thickness of the oxidized film was estimated. Accordingly, the layer-by-layer oxidation was limited to approximately 50 nm via plasma irradiation, whereas the TaS2 films within 150 nm were fully oxidized via thermal annealing in ambient air. Therefore, a Ta-oxide/TaS2 structure was fabricated as a stack material of insulator and metal when the thickness of the pristine film was greater than 50 nm. In addition, Ta-oxide films were integrated into bottom-gated two-dimensional (2D) field-effect transistors (FETs) using the dry transfer method. 2D FETs with multilayer MoTe2 and MoS2 films as p-type and n-type channels, respectively, were successfully fabricated. In particular, the Ta-oxide film synthesized via dry oxidation was used as a gate dielectric, and the device process could be simplified because the Ta-oxide/TaS2 heterostructure can function as a stack material for gate insulators and gate electrodes. An anti-ambipolar transistor consisting of an MoTe2/MoS2 heterojunction was also fabricated. For the transfer characteristics, a relatively sharp on-state bias range below 10 V and sufficiently high peak-to-valley ratio of 106 at V DS = 3 V were obtained using the high-κ gate dielectric of Ta-oxide despite the presence of the multilayer channels (∼20 nm).

Effects of airflow rate distribution and nitrobenzene removal in an aquifer with a low-permeability lens during surfactant-enhanced air sparging

The application of surfactant-enhanced air sparging (SEAS) in heterogeneous aquifers has received increasing attention. In this study, a two-dimensional laboratory visualization device was used to study the migration and distribution mechanism of airflow and the nitrobenzene removal effect in an aquifer with a low-permeability lens during AS and SEAS. Experimental results showed that the surfactant significantly reduced the blocking effect of the geological interface on airflow, and the ΔPe (the air entry pressure difference between the background media and the lens) value of the geological interface decreased from 1.1 kPa to 0.3 kPa when the surfactant concentration was 800 mg/L. When the surfactant injection location was at the center of the lens and the injection volume was 1 PV (pore volume of the lens), part of the airflow entered the lens through its below interface, which clearly improved the nitrobenzene removal inside and above the lens compared with AS remediation. However, when SEAS remediation was 24 h, the surfactant redistribution caused by air sparging resulted in the airflow entering the lens to bypass the lens again, which changed the spatial distribution of airflow rate and was not conducive to the continuous removal of nitrobenzene inside the lens.

Development of a Two-Dimensional Ultrasonic Device for Vibration-Assisted Milling

Two-dimensional vibration-assisted machining (VAM) is a technique used to improve the cutting performance of machining processes by reducing the cutting forces and the temperature, extending the tool life, and improving the surface quality. Among the developed 2D vibratory devices for VAM, some limitations affect the process stability. This paper aims to present a 2D vibratory device to be applied during the milling process with a setup structure overcoming the limitations of the other developed devices. The device operates at high vibration frequency, prevents the coupling effect problem, provides precise vibration motion, and is easily manufactured, assembled, installed, and maintained. Finite element analysis (FEA) was applied to verify and modify the proposed design. The components of the final design were manufactured, and the generated vibration in each direction was evaluated. A detailed control system was presented to maintain the stability for the applied vibration. Finally, slot-milling experiments were conducted to validate and test the device’s performance. The cutting experiments results showed some benefits of applying the ultrasonic vibration and validated that the 2D vibratory device is functioning properly.

Design of high voltage electrostatic protection device for CAN bus

The Dual-Direction Silicon Controlled Rectifier (DDSCR) device has dual-direction electrostatic protection function and strong current discharging ability, which is widely used in ESD on-chip protection. In this paper, a high performance symmetric high voltage Dual-Direction Silicon Controlled Rectifier with floating P+ (HVDDSCR_FP+) is designed for CAN bus under 0.18 μm BCD process. In order to predict and verify the ESD performance of the device, TCAD two-dimensional device simulation and Transmission Line Pulse (TLP) test system were used. The experimental results show that the HVDDSCR_FP + structure has not only symmetrical positive and reverse I-V curves, but also the characteristics of high holding voltage and high failure current. Compared with the traditional HVDDSCR, HVDDSCR_FP+, at 25V forward and reverse trigger voltages (Vt), has increased its holding voltage (Vh) from 12V to 20V, failure current (It2) from 5A to 35A. In the actual tape-out process, it is found that the width of the N-well has a great influence on the performance of the device. After analyzing the reason and improving it, the leakage current of the device is reduced from μA level to nA level.

Hysteretic temperature dependence of resistance controlled by gate voltage in LaAlO3/SrTiO3 heterointerface electron system

For two-dimensional electron gas device applications, it is important to understand how electrical-transport properties are controlled by gate voltage. Here, we report gate voltage-controllable hysteresis in the resistance–temperature characteristics of two-dimensional electron gas at LaAlO3/SrTiO3 heterointerface. Electron channels made of the LaAlO3/SrTiO3 heterointerface showed hysteretic resistance–temperature behavior: the measured resistance was significantly higher during upward temperature sweeps in thermal cycling tests. Such hysteretic behavior was observed only after application of positive back-gate voltages below 50 K in the thermal cycle, and the magnitude of hysteresis increased with the applied back-gate voltage. To explain this gate-controlled resistance hysteresis, we propose a mechanism based on electron trapping at impurity sites, in conjunction with the strong temperature-dependent dielectric constant of the SrTiO3 substrate. Our model explains well the observed gate-controlled hysteresis of the resistance–temperature characteristics, and the mechanism should be also applicable to other SrTiO3-based oxide systems, paving the way to applications of oxide heterostructures to electronic devices.

Analytical Modeling of MgZnO/ZnO MOSHEMT Based Biosensor for Biomolecule Detection

In recent development, the High Electron Mobility Transistor (HEMT) technology was used for biosensor applications. In this contribution, an analytical model of MgZnO/ZnO MOSHEMT (Metal Oxide Semiconductor HEMT) was reported. For the first time, a nanogap cavity-based biosensor aimed at detecting various biomolecules, such as uricase, streptavidin, ChOx, and proteins, was designed. The developed analytical model was used to calculate the two-dimensional electron gas (2DEG) density, device capacitance, drain current (ID), output conductance (gd), and transconductance (gm) by using the dielectric modulation approach. MOSHEMTs used dielectric modulation, with the nanogap cavity considered under the gate region. The effective capacitance in the cavity region was obtained by using dielectric modulation. Hence, the nanogap cavity acts as a sensing area for the immobilisation of target biomolecules. The sensitivity of the device was analysed by observing the strong changes in drain current with the addition of different biomolecules in the nanogap cavity region. The proposed MgZnO/ZnO MOSHEMT biosensor exhibits a quick response to biomolecule changes since its drain-on-sensitivity (SIon) is comparatively higher than that of other semiconductor-based biosensors. The obtained analytical model results were verified by a comparison with other works available in the literature, and they showed good agreement with our results.

Half-metallic of non-metal-adsorbed AsP and multifunctional two-dimensional spintronic device of impure AsP from first-principles calculations

Black arsenic phosphorus (b-AsP) monolayer is a new two-dimensional (2D) nano material with medium band gap and ultra-high carrier mobility , which will have broad application prospects in 2D electronic devices. Here the electron and magnetic of non-metallic light atoms adsorbed AsP are studied by density functional theory (DFT). The hollow sites of B and N adsorbed AsP are half-metallic make them a promising spin material. According to the calculation of the hollow site devices of AsP adsorbed by B and N exhibit almost perfect spin filtering effect. In addition, the I–V curve of the device for B-adsorbed AsP shows a significant negative differential resistance effect. The magnetoresistance of N-adsorbed AsP device is as high as 10 3 %. These results indicate that B-adsorbed and N-adsorbed AsP systems have potential applications in spintronics . • Pure arsenic phosphorus can be changed from non-magnetic semiconductor to half-metal by doping B and N at specific sites. • The spin filtration effect of 100% and tunnel maganetoresistance of around 10 3 % can be obtained in B and N adsorbed arsenic phosphorus devices. • The negative differential resistance effect is found in B adsorbed arsenic phosphorus devices.

Highly accurate, reliable, and non-contaminating two-dimensional material transfer system

The exotic properties of two-dimensional materials and heterostructures, built by forming heterogeneous multi-layered stacks, have been widely explored across several subject matters following the goal to invent, design, and improve applications enabled by these materials. Successfully harvesting these unique properties effectively and increasing the yield of manufacturing two-dimensional material-based devices for achieving reliable and repeatable results is the current challenge. The scientific community has introduced various experimental transfer systems explained in detail for exfoliation of these materials; however, the field lacks statistical analysis and the capability of producing a transfer technique enabling (i) high transfer precision and yield, (ii) cross-contamination free transfer, (iii) multi-substrate transfer, and (iv) rapid prototyping without wet chemistry. Here, we introduce a novel two-dimensional material deterministic transfer system and experimentally show its high accuracy, reliability, repeatability, and non-contaminating transfer features by demonstrating fabrication of two-dimensional material-based optoelectronic devices featuring novel device physics and unique functionality. The system paves the way toward accelerated two-dimensional material-based device manufacturing and characterization. Such rapid and material analyzing prototype capability can accelerate not only layered materials science in discovery but also engineering innovations.