Negative Differential Conductance Effect Research Articles

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.

Exceptional Field Effect and Negative Differential Conductance in Spiro-Conjugated Single-Molecule Junctions.

The advancement of molecular electronics endeavors to build miniaturized electronic devices using molecules as the key building blocks by harnessing their internal structures and electronic orbitals. To date, linear planar conjugated or cross-conjugated molecules have been extensively employed in the fabrication of single-molecule devices, benefiting from their good conductivity and compatibility with electrode architectures. However, the development of multifunctional single-molecule devices, particularly those with unique charge transport properties, necessitates a more rigorous selection of molecular materials. Among different assortments of molecules suited for the construction of molecular circuits, Spiro-conjugated structures, specifically spirobifluorene derivatives, stand out as promising candidates due to their distinctive electronic properties. In this work, we focus on the charge transport characteristics of Spiro-conjugated molecules sandwiched between graphene nanogaps. Experiments reveal significant Coulomb blockade and distinct negative differential conductance effects. Beyond two-terminal device measurements, solid-state gate electrodes are utilized to create single-molecule transistors, successfully modulating the molecular energy levels to achieve an on/off ratio exceeding 1000. This endeavor not only offers valuable insights into the design and fabrication of future practical molecular devices, blessed with enhanced performance and functionality, but also presents a new paradigm for the investigation of fundamental physical phenomena.

Transport properties of Mn-doped/adsorbed zigzag boron nitride nanoribbon based nanodevices

We are conducting research into the spin transport characteristics of models that are built from zigzag Boron Nitride Nanoribbons (ZBNNRs) that have been doped and adsorbed with Mn. These investigations are made possible by using the non-equilibrium Green’s function (NEGF) formalism in conjunction with Density Functional Theory (DFT). We have scrutinized the electronic structures of six different models, and have chosen two for a deeper exploration of its’ transport characteristics. Our computational findings highlight an unusual occurrence where a Mn atom substitutes a B atom in ZBNNRs, resulting in ZB(Mn)NNRs that exhibit significant Giant Magnetoresistance (GMR) and Rectification ratio (RR) - peaking at 106 and 105 respectively, along with the presence of negative differential conductance (NDC) effects. The detected GMR, NDC, and rectification characteristics in ZB(Mn)NNRs offer an optimistic outlook for the conceptualization of future nanodevices.

Mechanism of avalanche charge domain transport for nonlinear mode of GaAs photoconductive semiconductor switches

Photoconductive semiconductor switch is of significance in the fields of ultafast electronics, high-repetition rate and high-power pulse power system, and THz radiation. The mechanism of the nonlinear mode of the switch is an important area of study. In this work, stable nonlinear wave forms are obtained by a semi-insulating GaAs photoconductive semiconductor switch triggered by a 5-ns laser pulse with pulsed energy of 1 mJ at a wavelength of 1064 nm under a bias of 2750 V. Based on two-photon absorption model, the photogenerated carrier concentration is calculated. The theory analysis and calculation result show that the photogenerated carrier can compensate for the lack of intrinsic carrier, and lead to the nucleation of photo-activated charge domain. According to transferred-electron effect principium, the electric field inside and outside the domain are calculated, indicating that the electric field within the domain can reach the electric field which is much larger than intrinsic breakdown electric field of GaAs material, and results in strong impact avalanche ionization in the bulk of the GaAs switch. According to the avalanche space charge domain, the typical experimental phenomena of nonlinear mode for GaAs switch are analyzed and calculated, the analysis and calculations are in excellent agreement with the experimental results. Based on drift-diffusion model and negative differential conductivity effect, the transient electric field in the bulk of the switch is simulated numerically under the optical triggering condition. The simulation results show that there are moving multiple charge domains with a peak electric filed as high as the intrinsic breakdown electric field of GaAs within the switch. This work provides the experimental evidence and theoretical support for studying the generation mechanism of the nonlinear photoconductive semiconductor switch and the improvement of the photo-activated charge domain theory.

Multiconfiguration b-AsP-based doping systems with enriched elements (C and O): novel materials for spintronic devices

Black arsenical phosphorus (b-AsP), a derivative of black phosphorus, is a bimetallic alloy compound with the advantage of high carrier mobility, high stability, and tailorable configuration. However, lack of an effective tool to facilitate the application of AsP as a magnetic device. Herein, band gap modulation and the introduction of magnetism can be achieved by doping non-metallic atoms in three different AsP configurations. And the doping of the same atom will cause variation in the electronic structure depending on the configuration. Surprisingly, doping with both enriched elements C and O transforms AsP into a magnetic material. Furthermore, the source of the magnetic moment is explained by solving the wave function of the doped AsP, which is caused by the orbital coupling of the C and O atoms to AsP. To excavate the potentials of this magnetic AsP system for magnetic devices, field-effect transistors based on two doped armchair AsP3 nanoribbons are simulated. The devices show considerable negative differential conductivity effect and good spin filtering efficiency. These findings suggest that AsP doping with enriched elements C and O could be an excellent candidate for future spintronics applications.

Negative differential thermal conductance between Weyl semimetals nanoparticles through vacuum

In this work, the near-field radiative heat transfer (NFRHT) between two Weyl semimetal (WSM) nanoparticles (NPs) is investigated. The numerical results show that negative differential thermal conductance (NDTC) effect can be obtained in this system, i.e., when the temperature of the emitter is fixed, the heat flux does not decrease monotonically with the increase of the temperature of the receiver. Specifically, when the temperature of the emitter is 300 K, the heat flux is identical when the temperature of the receiver is 50 K or 280 K. The NDTC effect is attributed to the fact that the permittivity of the WSMs changes with the temperature. The coupling effects of polarizability of two WSM NPs have been further identified at different temperature to reveal the physical mechanism of the NDTC effect. In addition, the NFRHT between two WSM NPs can be greatly enhanced by exciting the localized plasmon and circular modes. This work indicates that the WSMs maybe promising candidate materials for manipulating NFRHT.

Interfacial electrical properties and transport properties of monolayer black AsP alloy in contact with metal

With strong structural stability, ultra-high carrier mobility and controllable direct band gap of semiconductors, the new two-dimensional (2D) monolayer black arsenic-phosphorus (ML b-AsP) alloy has recently attracted much attention in nanoelectronic devices. Through first-principles electronic structure calculations and quantum transport simulations, the interfacial electrical properties of the ML b-AsP/metal (Ag, Al, Au, Fe, Pd, Pt) contacts and transport properties of the integral field effect transistor (FET) configurations constructed with ML b-AsP alloy are investigated first and systematically. The results of electronic structure calculations show that the ML b-AsP alloy is strongly adsorbed to metal substrates and has undergone metallization, which leads to a weak Schottky contact at all the AsP/metal interfaces. Whereas quantum transport simulations show that, with the exception of Pt electrode FET configuration, there are small lateral transport barriers at the electrode/channel interfaces for the other five configurations. The calculations show that the FET configuration with Pt electrode provides better electrical transport performance. In addition, except for the Pd electrode configuration, other configurations exhibit an excellent negative differential conductance (NDC) effect, and some configurations exhibit significant rectifying behavior. These theoretical findings provide guidance, inspiration and insight for the design of future electronic devices based on the ML b-AsP alloy.

Nonequilibrium thermal transport and photon squeezing in a quadratic qubit-resonator system

We investigate steady-state thermal transport and photon statistics in a nonequilibrium hybrid quantum system, in which a qubit shows longitudinal and quadratic coupling with an optical resonator. Our calculations are conducted with the method of the quantum dressed master equation combined with full counting statistics. The effect of negative differential thermal conductance is unravelled at finite temperature bias, which stems from the suppression of cyclic heat transitions and large mismatch of two squeezed photon modes at weak and strong qubit-resonator hybridizations, respectively. The giant thermal rectification is also exhibited at large temperature bias. It is found that the asymmetric composition of the hybrid system by spin and boson roles and negative differential thermal conductance show the cooperative contribution. Noise power and skewness, as typical current fluctuations, exhibit global maximum with strong hybridization at small and large temperature bias limits, respectively. Moreover, the effect of photon quadrature squeezing is discovered in the strong hybridization and low-temperature regime, which shows asymmetric response to two bath temperatures. These results would provide some insight to thermal functional design and photon manipulation in qubit-resonator hybrid quantum systems.

Managing Quantum Heat Transfer in a Nonequilibrium Qubit-Phonon Hybrid System with Coherent Phonon StatesSupported by the National Natural Science Foundation of China (Grant No. 11704093), the Opening Project of Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, the National Natural Science Foundation of China (Grant Nos. 11935010 and 11775159), and the Natural Science Foundation of Shanghai (Grant Nos.

We investigate quantum heat transfer in a nonequilibrium qubit-phonon hybrid open system, dissipated by external bosonic thermal reservoirs. By applying coherent phonon states embedded in the dressed quantum master equation, we are capable of dealing with arbitrary qubit-phonon coupling strength. It is counterintuitively found that the effect of negative differential thermal conductance is absent at strong qubit-phonon hybridization, but becomes profound at weak qubit-phonon coupling regime. The underlying mechanism of decreasing heat flux by increasing the temperature bias relies on the unidirectional transitions from the up-spin displaced coherent phonon states to the down-spin counterparts, which seriously freezes the qubit and prevents the system from completing a thermodynamic cycle. Finally, the effects of perfect thermal rectification and giant heat amplification are unraveled, thanks to the effect of negative differential thermal conductance. These results of the nonequilibrium qubit-phonon open system would have potential implications in smart energy control and functional design of phononic hybrid quantum devices.

Three-terminal normal-superconductor junction as thermal transistor

We propose a thermal transistor based on a three-terminal normal-superconductor (NS) junction with superconductor terminal acting as the base. The emergence of heat amplification is due to the negative differential thermal conductance (NDTC) effect for the NS diode in which the normal side maintains a higher temperature. The temperature dependent superconducting energy gap is responsible for the NDTC. By controlling quantum dot levels and their coupling strengths to the terminals, a huge heat amplification factor can be achieved. The setup offers an alternative tuning scheme of heat amplification factor and may find use in cryogenic applications.

Negative differential conductance effect and electrical anisotropy of 2D ZrB2 monolayers

Two-dimensional (2D) metal-diboride ZrB2 monolayers was predicted theoretically as a stable new electronic material (Lopez-Bezanilla 2018 Phys. Rev. Mater. 2 011002). Here, we investigate its electronic transport properties along the zigzag (z-ZrB2) and armchair (a-ZrB2) directions, using the density functional theory and non-equilibrium Green’s function methods. Under low biases, the 2D ZrB2 shows a similar electrical transport along zigzag and armchair directions as electric current propagates mostly via the metallic Zr–Zr bonds. However, it shows an electrical anistropy under high biases, and its I–V curves along zigzag and armchair directions diverge as the bias voltage is higher than 1.4 V, as more directional B–B transmission channels are opened. Importantly, both z-ZrB2 and a-ZrB2 show a pronounced negative differential conductance (NDC) effect and hence they can be promising for the use in NDC-based nanodevices.

Nonlinear dynamics in a terahertz-driven double-layer graphene diode * * Project supported by the National Natural Science Foundation of China (No. 11604126), the National Natural Science Foundation of China (No. 61601205), the Basic Research Program of Jiangsu Province (Natural Science Foundation for Young Scholars) (No. BK20160541), and the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (No.

By using the time-dependent hydrodynamic equations, we carry out a theoretical study of nonlinear dynamics in an n+nn+ double-layer graphene diode driven by terahertz radia-tion. A cooperative nonlinear oscillatory mode shows up due to the negative differential conductance effect. We use different chaos-detecting methods, such as the Poincaré bifurcation diagram and the first return map, to examine the transitions between the periodic and chaotic states. The double-layer graphene diode shows typical nonlinear dynamical behavior with the DC bias, AC amplitudes and the AC frequency as the control parameters.

Transmission spectrum and IV characteristics of dual-gate Z-shaped graphene nanoribbon FET

In this work, a dual-gate Z-shaped graphene nanoribbon field-effect transistor (DG-ZGNRFET) is presented. The transmission spectrum, current–voltage (IV) and differential conductance (dI/dV) characteristics have been calculated for different biasing configurations of gate voltages. The calculated transmission spectrum predicts the semiconducting nature of the channel as the transmission coefficient is zero around the Fermi level for all biasing configurations of the gate voltages. In this study, when both gates are biased with −1 V, a low threshold voltage, a high I on/I off ratio compared with those of other biasing configurations and a negative differential conductance (NDC) are observed. On the other hand, when either one or both gates are biased with +1 V, a large threshold voltage, a low value of the I on/I off ratio and negligible NDC effects are observed, which are technologically not very favourable conditions in which to operate the DG-ZGNRFET.

Si and Ge based metallic core/shell nanowires for nano-electronic device applications

One dimensional heterostructure nanowires (NWs) have attracted a large attention due to the possibility of easily tuning their energy gap, a useful property for application to next generation electronic devices. In this work, we propose new core/shell NW systems where Ge and Si shells are built around very thin As and Sb cores. The modification in the electronic properties arises due to the induced compressive strain experienced by the metal core region which is attributed to the lattice-mismatch with the shell region. As/Ge and As/Si nanowires undergo a semiconducting-to-metal transition on increasing the diameter of the shell. The current-voltage (I-V) characteristics of the nanowires show a negative differential conductance (NDC) effect for small diameters that could lead to their application in atomic scale device(s) for fast switching. In addition, an ohmic behavior and upto 300% increment of the current value is achieved on just doubling the shell region. The resistivity of nanowires decreases with the increase in diameter. These characteristics make these NWs suitable candidates for application as electron connectors in nanoelectronic devices.

Numerical Investigation of Short-Channel Effects in Negative Capacitance MFIS and MFMIS Transistors: Subthreshold Behavior

In this paper, we analyze the impact of length scaling on the ON-state operation of the two classes of double-gate negative capacitance transistors: metal–ferroelectric–metal–insulator–semiconductor (MFMIS) and metal–ferroelectric–insulator–semiconductor (MFIS). We show that for long-channel structures, MFMIS configuration shows a higher ON current than the MFIS due to a lower drain saturation voltage of the latter. For short-channel cases, we compare these negative capacitance field effect transistors (NCFETs) under two scenarios: equal flat band voltages (iso- ${V}_{\textsf {FB}}$ ) and equal OFF currents (iso- ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ ). In iso- ${V}_{\textsf {FB}}$ condition, a higher negative differential conductance (NDC) effect in the MFMIS suppresses its ON current below that of the MFIS. However, the MFMIS provides a higher ON current than the MFIS for all the channel lengths under iso- ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ condition. We further investigate the influence of quantum mechanical effects and velocity saturation of carriers on the electrical characteristics of short-channel NCFETs. We also explore the impact of inner and outer spacer fringings in NCFETs. We find that the ferroelectric voltage gain in NCFETs with spacers increases with the channel length scaling, which provides a further improvement in the ON current contrary to those without spacers. Moreover, increase in the spacer permittivity also boosts both the ON current and the NDC.

Theoretical Model for Negative Differential Conductance in 2D Semiconductor Monolayers

A simple theoretical model of electron heating in a system with two valleys is applied for the first time to describe 2D semiconductor monolayers of the MoS2 and WS2 types. The model is demonstrated to describe sufficiently well the available experimental data on the negative differential conductance effect in a WS2 monolayer. It confirms a possibility to fabricate Gunn diodes of a new generation based on the structures concerned. Such diodes are capable of generating frequencies of an order of 10 GHz and higher, which makes them attractive for many practical applications.

THz Emission from SiC Natural Superlattice Diodes Induced by Strong Electrical Field

Recently the intense terahertz electroluminescence from monopolar n++–n– –n+ structures of 6H- and 8H-SiC of natural superlattices at helium temperatures due to Bloch oscillations was discovered. In the present work we present the THz emission spectra of bipolar n++–π–n+ structures (π is a high-resistance layer of p-type conductivity) of natural superlattices 4H-, 8H- and 15R-SiC at 7 K. The bipolar n++–π–n+ structures of 4H- and 8H-SiC were analogous to those of structures for which the negative differential conductivity effect was observed earlier for three polytypes (4H, 6H and 8H) at T=300 K. We demonstrate resemblance and differences of the spontaneous THz emission spectra for the monopolar and bipolar 4H-, 6H- 8H- and 15R-SiC natural superlattices caused by Bloch oscillations of electrons in the SiC natural superlattice.

Negative Differential Conductance in Polyporphyrin Oligomers with Nonlinear Backbones.

We study negative differential conductance (NDC) effects in polyporphyrin oligomers with nonlinear backbones. Using a low-temperature scanning tunneling microscope, we selectively controlled the charge transport path in single oligomer wires. We observed robust NDC when charge passed through a T-shape junction, bistable NDC when charge passed through a 90° kink and no NDC when charge passed through a 120° kink. Aided by density functional theory with nonequilibrium Green's functions simulations, we attributed this backbone-dependent NDC to bias-modulated hybridization of the electrode states with the resonant transport molecular orbital. We argue this mechanism is generic in molecular systems, which opens a new route of designing molecular NDC devices.

Electron transport in mercury vapor: cross sections, pressure and temperature dependence of transport coefficients and NDC effects

In this work we propose a complete and consistent set of cross sections for electron scattering in mercury vapor. The set is validated through a series of comparisons between swarm data calculated using a multi term theory for solving the Boltzmann equation and Monte Carlo simulations, and the available experimental data. Other sets of cross sections for electron scattering in mercury vapor were also used as input in our numerical codes with the aim of testing their completeness, consistency and accuracy. The calculated swarm parameters are compared with measurements in order to assess the quality of the cross sections in providing data for plasma modeling. In particular, we discuss the dependence of transport coefficients on the pressure and temperature of mercury vapor, and the occurrence of negative differential conductivity (NDC) in the limit of lower values of E∕N. We have shown that the phenomenon of NDC is induced by the presence of mercury dimers and that can be controlled by varying either pressure or temperature of mercury vapor. The effective inelastic cross section for mercury dimers is estimated for a range of pressures and temperatures. It is shown that the measured and calculated drift velocities agree very well only if the effective inelastic cross section for mercury dimers and thermal motion of mercury atoms are carefully considered and implemented in numerical calculations.

Terahertz Luminescence and Electrical Characteristics of SiC Structures with Natural Superlattice in Strong Electric Fields

Recently, the intense terahertz electroluminescence from monopolar n++–n−–n+ structures of 8H-SiC natural superlattice at helium temperatures due to Bloch oscillations was found out. In the present work, we compare the THz emission and electrical characteristics of monopolar n++–n−–n+ and bipolar n++–π–n+ 8H-SiC structures at 7 K. The bipolar n++–π–n+ 8H-SiC structures were analogous to those on which the negative differential conductivity effect was observed earlier for three polytypes (4H, 6H, and 8H) at T = 300 K. The obtained results allow one to draw a conclusion about common nature of the negative differential conductivity and THz emission effects in the natural superlattice of SiC caused by Bloch oscillations. These results give the proof of fundamental importance supporting the objectivity of postulates of the F. Bloch – C. Zener – G. N. Wannier theory