Photoresist Research Articles

Room-temperature negative differential resistance in gate-tunable Weyl semimetal transistors

Negative differential resistance (NDR) has garnered substantial interest in propelling the progression of next-generation electronic devices. Weyl semimetals (WSMs) are a potential candidate for NDR devices; however, the NDR effect in WSMs has not been investigated. Here, we propose the gate-tunable transistor to theoretically develop the NDReffect in WSMs for the first time. The maximum peak-to-valley current ratio (PVR) of over 2 with a high current density peak at the NDR regime is observed with the help of the control gate and periodicity. Notably, it is demonstrated that the NDR effect can present stability for varying temperatures, even at room temperature, making the proposed device to be applied into practice. Finally, theNDR performances of the proposed devices are better than those of the present literature. Our findings highlight the potential of the NDR devices utilizing WSMs.

Sensing-performance improvement of 2D MoSH based gas sensors for detecting NO, NO2, and NH3 gas molecules

Nitrogen group oxide is one of the major pollutants in the air, and its accurate and rapid detection is essential for environmental protection and human health. Therefore, it is of great significance to develop high-performance new line sensor for Nitrogen group oxide. Here, we investigate the potential of monolayer 2D MoSH materials as candidates for NO gas sensing using a combination of density functional theory and non-equilibrium functions to construct nanodevices based on MoSH monolayer, and theoretically study the adsorption behavior of MoSH monolayer to NO, NO2, and NH3 gas molecules. The results indicate that MoSH monolayer exhibit metallicity, and nanodevices based on 2D MoSH monolayer exhibit anisotropic transport properties and significant negative differential resistance effects(NDR). More interestingly, gas sensors based on MoSH monolayers exhibit typical chemical adsorption of NO, NO2, and NH3 gas molecules, and the anisotropic transport properties still maintain, but significant differences of sensitivity appear for these three gas molecules. Specifically, the MoSH based gas sensor has the highest sensitivity to NO, reaching 93.1% and 76.3% along the armchair and zigzag directions, respectively. These results show that 2D MoSH monolayer is an excellent gas-sensing material with excellent application prospects for NO gas detection.

Research on Directional Elements of Two-Terminal Weak-Feed AC Systems with a Negative Sequence Control Strategy

It has become a typical scenario in power systems that renewable energy power supply is connected to an AC system through flexible DC transmission. However, since both sides of the AC line are power electronic converters, the negative sequence suppression strategy will be put into the converters at both ends during the asymmetric fault, which causes fundamental changes in the fault characteristics of the system, which is reflected in the two-terminal weak-feed characteristics, leading to the decline of traditional protection performance and affecting the safe operation of the system. Therefore, this paper presents a directional element of a double-ended weakly fed AC system with a negative sequence control strategy. Firstly, the characteristics of the negative sequence impedance under the negative sequence suppression strategy are analyzed when the AC line has asymmetric faults. Secondly, the difference in negative sequence impedance amplitude is analyzed. Finally, the direction element is constructed by the method of de-wave trend analysis The proposed scheme can realize the rapid identification of fault directions at both ends. The simulation results show that the proposed scheme is suitable for a two-terminal weak-feed AC system and can operate reliably under 300 Ω transition resistance and 20 dB noise interference.

Silence is Also a Voice, Right? Reflections on Silence as Resistant Teacher Voice in the Context of Curriculum Change in South Africa

This article reports on findings from a qualitative case study that explored teacher voice in the context of educational change in implementing the Curriculum and Assessment Policy reform in South Africa. The study uses the meta-theoretical paradigm of social constructivism and the conceptual framework of “resistance as good sense” to explore how silence as a form of resistance can be viewed as a strategy for learner advocacy. Data were collected using semi-structured interviews and classroom observations captured over a school year. The findings revealed that teacher knowledge jars in educational environments where compliance is the custom and teachers’ decisions in consideration of contextual congruence are viewed as resistance to the fidelity of the reform. Some teachers see passive resistance as the only alternative to empowerment in these environments. Thus, the scope of teacher voice lies in subservience to the policy where curriculum enforcers ignore teacher intuition which could influence the success of reform and contribute to the goals of learning. The study concludes that teacher silence as a form of resistance can be viewed as “good sense” and should not always be seen as emblematic of negative resistance.

INFRARED FOURIER SPECTROSCOPY OF DIFFUSE REFLECTION OF THE AZ nLOF SERIES NEGATIVE PHOTORESISTS FILMS ON MONOCRYSTALLINE SILICON

Films of the AZ nLOF 2020, AZ nLOF 2070 and AZ nLOF 5510 negative photoresists (PR) with a thickness of 0,95 – 6,1 μm, deposited on the surface of silicon wafers by the centrifugation method, were studied by the method of IR-Fourier diffuse reflection spectroscopy. In the diffuse reflectance spectra of PR/silicon structures, absorption bands were observed against the background of interference fringes. It allows the technique to be used to measure film thickness or its refractive index. The most intense bands in the AZ nLOF series PR spectra are the bands of stretching vibrations of the aromatic ring, pulsation vibrations of the carbon skeleton of the aromatic ring, a wide structured band with several maxima in the range of 1050 – 1270 cm–1 and a band associated with the CH2 bridge. The structure of the absorption spectrum of photoresists of the AZ nLOF series is similar to the structure of the spectrum of phenol-formaldehyde photoresist FP9120. It was shown that the vibration band of CH3 groups at 2945 cm-1 is due to the solvent.

Параметричні автогенераторні перетворювачі для вимірювання товщини матеріалів на основі конденсаторних чутливих елементів

The article examines the main characteristics of parametric autogenerator thickness measurement transducers with a frequency output signal. The design of the proposed autogenerator transducers is based on transistor structures with negative differential resistance. Capacitors with round and rectangular covers are used as parametric transducers for measuring the thickness of materials, which are passive elements of autogenerator transducers, which greatly simplifies the design of devices for measuring the thickness of materials. Mathematical models of autogenerator transducers were developed based on the principle of converting the energy of a constant electric field into the energy of an alternating electric field, which made it possible to obtain the conversion and sensitivity functions of autogenerator transducers without using a rather complicated method of obtaining Kirchhoff equations from nonlinear equivalent circuits of parametric transducers. It is shown that the main contribution to the change in the conversion functions and the sensitivity equation is made by the change in the thickness of the measured material, which causes a change in the equivalent capacitance and negative differential resistance in the oscillating system of autogenerators, which changes the output frequency of the autogenerator transducers. The sensitivity of thickness measurement transducers varies from 5.31 kHz/μm to 7.5 kHz/μm in the thickness range from 0 to 500 μm. Autogenerator transducers for thickness measurement with frequency output do not require analog-digital transducers and amplifiers for further processing of informative signals, which significantly reduces the cost of information-measuring equipment, and when working at ultra-high frequencies, it is possible to transmit information over considerable distances.

Brayton–Moser passivity based controller for constant power load with interleaved boost converter

A DC microgrid with renewable energy sources can achieve reduced current ripple, higher efficiency, faster dynamics, high voltage gain, and less operational stress by interfacing with an interleaved boost converter (IBC). The stability of an IBC linked to a DC microgrid supplying a constant power load (CPL) can be imperceptibly guaranteed by a conventional controller. A tightly regulated CPL with nonlinear and negative incremental impedance characteristics will lead to stability issues. Uncertainties such as load and line variations will further affect the stability of the system. A nonlinear passivity-based control algorithm requires more attention than a traditional controller to achieve the stability of power converters. This article explains the Brayton–Moser (BM) passivity-based controller (PBC) for a 2-level interleaved boost converter (IBC) interfaced DC microgrid with CPL. The suggested controller can achieve high signal stability by injecting a series-connected virtual impedance. The stability of the proposed controller has been assessed using the Lyapunov stability approach. A BM passivity-based controller for a 2-level IBC with CPL has been derived and investigated under various operating modes using MATLAB and Simulink. It was also observed that the proposed system achieves at least 2%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2\\%$$\\end{document} improvement in efficiency and 50%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$50\\%$$\\end{document} reduction in current ripple. To evaluate the performance of BM Passivity-based controller, a comparative analysis was performed between the suggested controller and the traditional PI controller, which is also included in this paper.

Nanometer-Scale 1D Negative Differential Resistance Channels in Van Der Waals Layers.

Negative differential resistance (NDR) is the key feature of resonant tunneling diodes exploited for high-frequency and low-power devices and recent studies have focused on NDR in van der Waals heterostructures and nanoscale materials. Here, strong NDR confined along a 1-nm-wide 1D channel within a van der Waals layer 1T-TaS2 is reported. Using scanning tunneling microscopy, a double 1D NDR channel formed along the sides of a charge-density-wave domain wall of 1T-TaS2 is found. The density functional theory calculation elucidates that the strong local band-bending at the domain wall and the interlayer orbital overlap cooperate to bring about 1D NDR channels. Furthermore, the NDR is well controlled by changing the tunneling junction distance. This result would be important for nanoscale device applications based on strong nonlinear resistance within van der Waals material architectures.

3R-CuCrO2 delafosite: crystal growth, crystal structure, dielectric and DC conductivity properties

Single-crystal samples of the 3R-CuCrO2 phase (R3m, a = 2.9613(2) Å, c = 17.098(2) Å) with a delafossite structure were grown by the flux method. Structural parameters were refined by X-ray structural analysis. The elemental composition of the grown crystals was confirmed by Auger electron spectroscopy. A threshold electric field switching effect from a high-resistance to a low-resistance state was discovered. The effect is characterized by a jump in electrical resistance (up to 5 orders of magnitude at E = 4.7 kV/cm, T = 120 K) and S-shaped current–voltage characteristics with a region of negative differential resistance. The temperature dependences of dielectric permittivity and dielectric loss tangent exhibit a Debye-type relaxation process with an activation energy of 0.51(3) eV. The observed features of dc conductivity, current–voltage characteristics, and dielectric properties interpreted on the basis of the existence of charge carriers in a small polaron state and the destruction of this state by the electric field.

Tuning properties of binary functionalization of Sc2C MXenes for supercapacitor electrodes

Surface functionalization of two-dimensional (2D) materials like Sc2C MXenes offers a promising avenue for tailoring their properties for various applications. At the same time, significant research has focused on pure terminations involving oxygen (-O), fluorine (-F), or hydroxyl (-OH) groups. Binary surface functionalization still needs to be explored. Our work addresses this gap by investigating binary functionalized Sc2C monolayers, specifically Sc2CFN and Sc2COS. Using first-principles calculations, we explore the structural, electronic, and quantum capacitance (CQ) properties of pristine Sc2C and functionalized Sc2CFN and Sc2COS. The CQ measurements reveal distinctive electronic behaviour, with Sc2CFN and Sc2COS exhibiting indirect bandgaps of 0.90 and 1.48 eV, respectively. Introducing functional groups induces a metal-to-semiconductor transition, enhancing charge storage at the cathode and increasing the CQ to 371.64 and 341.23 μF/cm2 for Sc2CFN and Sc2COS, respectively. As far as energy applications are concerned, we also calculate the Shockley-Queisser (SQ) efficiency, which is a widely accepted quantity to get an estimate of the photovoltaic efficiency of 28.77 % for Sc2CFN and 32.97 % for Sc2COS materials. Additionally, we analyze the current-voltage (IV) characteristics, uncovering negative differential conductance (NDC) effects in Sc2COS, indicative of its potential for fast molecular switching applications. Our study provides valuable insights into the properties of binary functionalized Sc2C MXenes, paving the way for their utilization in energy storage and nanoelectronic devices.

Two-Level Electronic Switching in Individual Manganese-Phthalocyanine Molecules with Jahn-Teller Distortion.

Understanding single molecular switches is a crucial step in designing and optimizing molecular electronic devices with highly nonlinear functionalities, e.g., gate voltage-dependent current switching. An atomically thin insulating template, in combination with scanning probe techniques, is an ideal platform to study such switches on the single-molecule level. In this study, we investigate manganese-phthalocyanine (MnPc) molecules on monolayer-thin epitaxial hexagonal boron nitride (h-BN) on Rh(111) by scanning tunneling microscopy (STM), spectroscopy (STS), and theoretical calculations. Several interesting phenomena are found: (1) high-resolution STM imaging of the molecular orbitals reveals symmetry breaking from D4h to D2h, observed in one type of MnPc. By comparison with simulations, this phenomenon can be attributed to the Jahn-Teller effect due to the negative charging of the molecule. (2) Ambipolar transitions at the molecule occur at fixed sample biases of about ±0.4 V, which manifest as negative differential conductance signatures in dI/dV spectroscopy. (3) The stochastic two-level switching, resulting in telegraphic noise in the tunneling current, manifests as a one-electron activated process. We present a two-level switching model to accurately describe a bias-dependent current-driven transition between the levels and reveal a first-order transition. The understanding and tailoring of molecular switches on the ultrathin insulating layer will be very helpful for future organic electronics design and application.

Analyzing negative differential resistance and capacitive effects in SiOx-based resistive switching devices for security applications

In this work, we analyze the negative differential resistance and capacitive effects in SiOx-based resistive switching devices. The cause of the negative differential effect has been investigated through the study of the switching mechanism in the devices. It has been observed that there is a combination of trap-controlled space charge limited conduction and trap-assisted Poole-Frenkel effect in the devices. Trapping and de-trapping of injected electrons in the defects within the silica structure causes the negative differential resistance effect. This characteristic feature can be employed to design chaotic circuits for security applications. In addition, the high electric field developed in the device compared to the applied field during the change of bias voltage from ±5V–0V, results in a capacitor discharge-like effect. This work will be a step forward in achieving the global Sustainable Development Goal of Peace, Justice, and Strong Institutions (SDG 16).

Nanoimprinting and backside ultraviolet lithography for fabricating metal nanostructures with higher aspect ratio

This paper introduces an innovative approach to increasing the aspect ratio of metal nanostructures fabricated using nanoimprint lithography (NIL). Although conventional NIL and metal lift-off processes can fabricate metal nanostructures, the achievable aspect ratio is often limited by the inherent constraints of NIL. In this study, we demonstrate that for an ultraviolet (UV) transparent substrate, metal nanostructures patterned via NIL can serve as a photomask. A negative-tone photoresist (PR) layer was then deposited on top of the patterned metal nanostructures. By illuminating the substrate from the backside with UV light and subsequently developing the PR, PR structures complementary and self-aligned to the metal layer were obtained. This enabled a second round of metal deposition and lift-off, thereby increasing the height of the metal structures and enhancing the aspect ratio. Experimentally, we demonstrated that this method can improve the aspect ratio from less than 1.0 to as high as 2.1. This paper also addresses the further developments and potential applications of this technique.

AQUILA OPTIMIZED NONLINEAR CONTROL FOR DC-DC BOOST CONVERTER WITH CONSTANT POWER LOAD

Constant power loads (CPL) can be operated by tight-controlled power electronic converters, which have negative impedance and absorb continuous power. Constant power load creates instability in an open-loop system because of its negative incremental impedance. To tackle this problem, a discrete sliding-mode (AQO-DSM) nonlinear control technique has been proposed for a DC-DC boost converter fed CPL based on Aquila optimization. In this paper, the proposed AQO-DSM controllers provide the system stability during a steady state and maintain output voltage regardless of input voltage or CPL variations. In this case, the DSM controller of a DC-DC boost converter's characteristics are adjusted using the Aquila optimization method (AQO). The Lyapunov stability concept is utilized to assess the system's overall stability. Under various system operating conditions, an experimental study and simulation are carried out to validate the proposed controller. The existing methods, such as sliding mode controller (SMC), fuzzy-based SMC (F-SMC), and super twisting algorithm (STA)-based SMC strategies, are compared with a proposed plan to demonstrate the superiority of the proposed AQO-DSMC. Simulated and experimental results have shown that the AQO-DSMC achieves the fastest convergence, the smallest steady-state, settling time under loaded conditions, and consistent chatter reduction compared with all contrasted control methods.

III–V heterostructure tunnel field-effect transistor operation at different temperature regimes

Tunnel field-effect transistors (TFETs) are a potential alternative to MOSFETs for low-temperature electronics. We provide an in-depth experimental characterization of TFETs analyzing the fundamental physical behavior at different temperature regimes. TFET characteristics from 13 to 300 K both in forward and reverse bias are discussed by employing a variation in InAs/InGaAsSb/GaSb heterojunction vertical nanowire devices. Evaluation of the TFET Negative Differential Resistance (NDR) characteristics at different temperatures is established as a technique to probe the dopant incorporation. It is observed that the temperature dependence of the Fermi degeneracy and Fermi-Dirac distribution largely influences the transistor performance at each operating temperature. Our investigation reveals that the TFETs demonstrate lower subthreshold swing than the physical limit of MOSFETs above 125 K. For low-temperature applications, the devices can be operated down to a low operating bias of 0.1 V, while for high temperature, a larger bias of 0.3 V is preferred.

Features of current flow in the n-CoFe2O4/n-CdTe heterojunction

n-CoFe2O4/n-CdTe heterojunctions with a current rectification ratio of 3·105 at voltages |V| = 1.5 V were made by spray pyrolysis of aqueous solutions of cobalt and iron salts on n-CdTe substrates. Based on the analysis of the temperature dependence of I-V-characteristics in the forward voltage range, a change in the mechanisms of current flow in n-CoFe2O4/n-CdTe heterojunctions was established from overbarrier at voltages of 3kT/q < V < 0.3 V to tunneling at voltages of 0.4 V < V < 1 V. The role of surface states in the formation of the energy profile of the heterojunction and the participation of energy levels in the band gap of n-CdTe in the formation of the tunnel current have been clarified. The reasons for the occurrence of negative differential resistance at the forward biases of the structure have been clarified. The current at reverse biases in the range −3 V < V < -3kT/q was analyzed. According to the analysis of the C-V-characteristics, an inversion layer was found in the heterojunction and its behavior from voltage was explained.

Structural, electronic, and magnetic properties of binary zigzag antimonene-phosphorene nanoribbons and their mole fractions with different edge passivation: A DFT investigation

The study focuses on binary antimonene-phosphorene, a two-dimensional semiconductor material known for its high carrier mobility, suitable band gap, and strong environmental stability, making it appealing for electronics and spintronics applications. In this study, using density functional theory, we investigated the structural stability and electronic-magnetic properties of zigzag SbP nanoribbons, as well as single Sb and single P nanoribbons. Various edge passivation (H, F, Cl, O, S) are considered, along with different phosphorus mole fractions. The findings show that SbP structures with 25 % phosphorus mole fractions, as well as those passivated with various atoms, demonstrate strong conformational stability. SbP nanoribbons passivated with H, F, and Cl exhibit non-magnetic semiconductor behavior, while those passivated with O and S display magnetic metallic properties. Maximal magnetization is observed in SbP nanoribbons passivated with single S atoms, particularly magnetizing both Sb and P atoms at the edges. Additionally, SbP nanoribbons passivated with dual O atoms show negative differential resistivity and a complete spin filtering effect (100 %). The study also investigates the variation in magnetization across structures with different phosphorus mole fractions. Overall, the study demonstrates that adjusting phosphorus mole fractions and edge passivation can significantly modify the electronic and magnetic properties of SbP nanoribbons, making them suitable for spintronic nanodevices.

Theoretical investigation of the resistance effect of embedded isolation piles on tunneling-induced lateral ground movements

This paper presents an isolation pile–soil lateral interaction model that considers not only the relative linear sliding at the pile-soil interface but also the pile group–soil interaction. The model allows for the calculation of the pile–soil interaction force using the elastic continuum method combined with the displacement compatibility relationship at the pile–soil interface, thus enabling the total lateral ground displacement to be obtained. The proposed method is validated by comparisons with the elastic foundation method (EFM) and the boundary element method (BEM). The advantages of the proposed method in calculating the lateral ground deformation resisted by isolation piles are demonstrated. The mechanical mechanism of the isolation pile’s lateral resistance effect on ground deformation can be summarized as follows: the combination of positive and negative resistance effects drives the lateral ground displacements along the depth direction from the original inhomogeneity caused by the tunnel excavation to a relatively homogeneous state. The soil parameters including Poisson’s ratio, internal friction angle and ground volume loss; the isolation pile parameters including the distance of the tunnel axis from the pile axis, the pile length, the buried depth of the pile top and the relative pile bending stiffness; and isolation pile–soil interface parameters including relative pile shaft–soil stiffness and relative pile tip–soil stiffness all exert a significant influence on the lateral resistance effect of the isolation pile. In light of that the resistance effects at different depths below the surface are not uniform, it is of the utmost importance to assess the resistance performance of the isolation pile in accordance with the location and lateral deformation requirements of the protected structure in actual engineering.

Large magnetoresistance and spin negative differential resistance in photoisomers-based molecular spin valves

By using non-equilibrium Green's functions in combination with density functional theory, the spin transport properties of photoisomers-based molecular spin valves constructed by salicylidene methylamine connected with two cobalt- dibenzotetraaza[14]annulene (Co-DBTAA) complex molecules via acetylene linkers are explored. A large magnetoresistance (MR) effect with a MR ratio larger than 104 can be observed in the molecular spin valves whether salicylidene methylamine is in the cis-enol form or the trans-keto form. Moreover, spin negative differential resistance (NDR) effects are also observed in the photoisomers-based molecular spin valves. The spin transport mechanisms are explored for MR and spin NDR effects observed in the molecular spin valves.

In silico analysis of ventricular action potential with a current-voltage-time representation: Thresholds, membrane resistance, repolarization reserve.

The waveform of ventricular action potential (AP) is a key determinant of the cardiac cycle, a marker of beating pathophysiology, and a target for anti-arrhythmic drug design. The information contained in the waveform, though, is limited to the actual dynamics of the AP under consideration. By measuring quasi-instantaneous current-voltage relationships during repolarization, I propose a three-dimensional representation of the ventricular AP which includes potential dynamic responses that the beat can show when electrically perturbed. This representation is described in the case of a numerically reconstructed ventricular AP, but it can be, at least partially, derived in real cardiomyocytes. Simulation allows to disclose the potentialities and the limitations of the approach, that can be extended to any non-cardiac AP. By reporting, at any AP time, the ion current available within the physiological membrane potential range at that time, the representation makes all together available: (1) refractory period, (2) thresholds for eliciting full or calcium-driven APs, (3) threshold for all-or-none repolarization, (4) membrane resistance during repolarization, (5) the safety of membrane repolarization. It provides further evidence of a negative membrane resistance during the late phase of ventricular AP and a quantitative estimate of repolarization reserve (RR), key determinants of repolarization dynamics.