Negative Differential Resistance Effect Research Articles

The negative differential resistance of nitrogen implanted TiO2

The microstructure and negative differential resistance (NDR) effect of nitrogen implanted rutile TiO2 were investigated by measuring the XPS, Raman spectra and current voltage curves. It was found that the light illumination has large influence on the NDR effect. Under the illumination of 60 mW laser light, a large NDR with a small electric field (1250 V/cm) is obtained. This electric field is about three orders smaller than that reported in literature (1×106 V/cm). The electric field induced tunneling is the possible mechanism of electric transport at higher field region. The NDR is thought to be related to the light and nitrogen dopant induced reaction including the destroying of water, the scavenging of electron, and the surface oxidation transform of non-stoichiometric TiO2−x to stoichiometric insulating state. The results of this paper are not only useful in understanding the mechanism of NDR, but also useful in providing an effective method in manipulation NDR.

Intrinsic single-layer multiferroics in transition-metal-decorated chromium trihalides

Two-dimensional materials possessing intrinsic multiferroic properties have long been sought to harness the magnetoelectric coupling in nanoelectronic devices. Here, we report the achievement of robust type I multiferroic order in single-layer chromium trihalides by decorating transition metal atoms. The out-of-plane ferroelectric polarization exhibits strong atomic selectivity, where 12 of 84 single-layer transition metal-based multiferroic materials possess out-of-plane ferroelectric or antiferroelectric polarization. Group theory reveals that this phenomenon is strongly dependent on p–d coupling and crystal field splitting. Cu decoration enhances the intrinsic ferromagnetism of trihalides and increases the ferromagnetic transition temperature. Moreover, both ferroelectric and antiferroelectric phases are obtained, providing opportunities for electrical control of magnetism and energy storage and conversion applications. Furthermore, the transport properties of Cu(CrBr3)2 devices are calculated based on the non-equilibrium Green’s function, and the results demonstrate outstanding spin-filtering properties and a low-bias negative differential resistance (NDR) effect for low power consumption.

Unveiling Negative Differential Resistance and Superionic Conductivity: Water Anchored on Layered Materials.

Unravelling the perplexing nature of negative differential resistance (NDR) in 2D transition metal dichalcogenide (2D TMD) devices, especially regarding intrinsic properties, is hindered by experiments conducted in ambient environments. A thorough investigation is essential for unveiling the actual mechanism. In this study, we provide compelling evidence of the NDR effect with a remarkably high peak-to-valley current ratio and proton-diffused superionic conductivity in quantum-confined water molecules anchored to a thin film of 2D TMDs. Our investigation underscores the crucial role of ambient moisture for this robust NDR effect independent of underlying materials used. The bonding of water molecules to the existing sulfur defect sites on 2D TMD nanoflakes facilitates the formation of bridges between two planar metal electrodes, thus enabling superionic in-plane protonic conduction. During electrolysis of chemisorbed water, protons are liberated at the anode and migrate toward the cathode during bias voltage sweeping. Nevertheless, proton diffusion encounters increasing impedance beyond a certain applied bias, thereby restricting current flow even with higher biasing voltages, which is attributed to the interfacial Schottky energy barrier influenced by the Fermi level pinning effect. Our DFT simulations corroborate this mechanism, revealing minimal intermolecular interaction of H+ ions compared to OH- ions at distinct atomic sites on 2D TMD nanoflakes.

Negative Differential Resistance in Single‐Molecule Junctions Based on Heteroepitaxial Spherical Au/Pt Nanogap Electrodes

AbstractSingle‐molecule junctions exploit the internal structure of molecular orbitals to construct a new class of functional quantum devices. The demonstration of negative differential resistance (NDR) in single‐molecule junctions is direct evidence of quantum mechanical tunneling through a molecular orbital. Here, a pronounced NDR effect is reported with a peak‐to‐valley ratio of 30.1 on a single‐molecule junction of π‐conjugated quinoidal‐fused oligosilole derivatives, Si2 × 2, embedded between the unique electroless gold‐plated heteroepitaxial spherical Au/Pt nanogap electrodes. This NDR feature persists in a consecutive endurance test of 180 current traces. the thermally stable NDR effects in the Si2 × 2 single‐molecule junctions between 9 and 300 K are demonstrated. The density functional theory calculations under electric fields indicate that the NDR effect can be ascribed to the bias‐dependent resonant tunneling transport via the polarized HOMO, which has asymmetrically changed electrode coupling with increased bias voltages. The results confirm a promising electrical platform for constructing functional quantum devices at the single‐molecule level.

The Negative Differential Resistance Effect of Substitutional Doped Monolayer GeS and Its Application in Gas Sensor

The Negative Differential Resistance Effect of Substitutional Doped Monolayer GeS and Its Application in Gas Sensor

Biaxila strain modulated high anisotropic gas-sensing performance of C5N-based two-dimensional devices: A first-principles study

Two-dimensional carbon nitride materials have been widely used in many applications such as device fabrication, gas adsorption and separation due to their abundant element resources, high physicochemical stability and excellent electronic properties. In this paper, density functional theory and non-equilibrium Green's function method are used to study the electronic structure, transport characteristics and gas sensitivity of C5N-based structures. The results show that the electron transport exhibits obvious anisotropy, in which the electron transport in the armchair direction is more conductive than that in the zigzag direction. It is worth noting that the negative differential resistance effect exists in both directions. Furthermore, the transport and sensing characteristics of inorganic molecules (NO, CO, NO2, SO2, and NH3) adsorbed on the C5N monolayer are studied. The results show that CO, SO2 and NH3 exist on the surface of C5N in the form of physical adsorption, while NO and NO2 adhere to the surface of C5N in the form of chemical adsorption. The designed C5N gas sensor exhibits high sensitivity to NO and NO2 molecules, reaching 81 % sensitivity to NO2 at a 0.1 V bias voltage. Finally, the effect of strain on the adsorption properties of gas sensing devices is studied. Studies have shown that the application of -4 % strain in the armchair direction significantly increases the current of NO and NO2, significantly improving the performance of the gas sensor. Whether strain is applied to the device or gas adsorption, C5N materials always maintain significant anisotropy. This study shows that C5N is a highly anisotropic and sensitive two-dimensional material, which has broad application potential in the field of electronic properties and gas sensing.

Analysis and Mitigation of Negative Differential Resistance Effects with Hetero-gate Dielectric Layer in Negative-capacitance Field-effect Transistors

Analysis and Mitigation of Negative Differential Resistance Effects with Hetero-gate Dielectric Layer in Negative-capacitance Field-effect Transistors

Nonvolatile behavior of resistive switching memory in Ag/WOx/TiOy/ITO device based on WOx/TiOy heterojunction

Two-terminal structure memristors are the most promising electronic devices that could play a significant role in artificial intelligence applications of the next generation and the post-Moore era. In this work, we fabricated the memristive device by depositing a heterojunction WOx/TiOy functional layer onto an indium tin oxide substrate using magnetron sputtering. The Ag/WOx/TiOy/ITO device exhibits improved memory behavior of bipolar resistive switching (RS) nonvolatile compared to TiOy-based single-layer memristors, enabling it to meet high-density information storage requirements. Moreover, our device exhibited the coexistence of the negative differential resistance effect and the behavior of the RS memory. Through a comprehensive analysis of conductivity on the curve of current–voltage (I–V), a physical model based on the mechanism of space charge-limited current, ohmic conduction, and Schottky emission was suggested to explain the behavior device RS memory. This study's findings demonstrate that including a heterojunction bilayer WOx/TiOy as a functional layer can significantly improve the performance of memristive devices. This advancement expands the potential application of ferroelectric metallic oxide heterojunctions within the field of memristors.

Unveiling the mechanism behind the negative capacitance effect in Hf0.5Zr0.5O2-Based ferroelectric gate stacks and introducing a Circuit-Compatible hybrid compact model for Leakage-Aware NCFETs

This paper addresses the lack of understanding of the origin of negative capacitance (NC) effect in the hafnium zirconium oxide (HZO) ferroelectric (FE) gate stack and proposes a new circuit-compatible hybrid compact model for NC field-effect transistors (NCFETs). The model supports Landau and Preisach FE models, encompassing multiple FE domains, FE leakage, and FE damping. The proposed model is experimentally validated, and the intrinsic switching speed of HZO is predicted. It is revealed that the NC effect in HZO stems from a mismatch in free charge and polarization switching rates. Performance evaluation of the model reveals that HZO-NCFET achieves ∼1.18x and ∼9.17x higher amplification at low and high frequencies compared to its PZT-NCFET counterpart. Our study demonstrates the superior ON-current (2.74 mA/µm) of the Engineered Leaky-HZO NCFET, surpassing FinFET and Germanium-source L-shaped TFET by ∼7.89x and ∼4.81x, respectively. This study briefly examines the direct causes of the negative drain-induced barrier lowering effect and negative differential resistance effect in Landau NCFETs. Furthermore, we emphasize the crucial role of FE thickness in determining the magnitude of the NC effect, offering valuable insights for the design and optimization of NC-based devices and circuits. Analysis of the Miller effect in NCFET-based inverters demonstrates significant improvements owing to high ON-current and voltage amplification, making them suitable for high-speed NCFET-based circuitry. Landau and Preisach NCFET-based inverters exhibit (50.70%, 51.34%) lower overshoots and (28.45%, 28.61%) reduced propagation delay compared to the NC nanowire FET-based inverter. Moreover, NCFET-based 2:1 fork circuits significantly reduce (46.69%, 51.37%) critical clock skew compared to CMOS FET-based circuits, showcasing the potential of NCFET technology in addressing timing violations in random logic paths. Furthermore, the Landau and Preisach NCFET-based ring oscillators (ROs) achieve (39.97%, 49.38%) and (52.65%, 62.92%) higher oscillation frequencies (fOSC) compared to state-of-the-art graphene FET-RO and CMOS-RO, respectively. The 15-stage Leaky-HZO and Engineered Leaky-HZO NCFET-ROs outperform the double gate-FET-RO by ∼2.19x and ∼16.69x in terms of fOSC, highlighting their superior performance in frequency-domain metrics. These findings demonstrate the potential of NCFET-based digital and mixed-signal circuits for high-performance integrated circuit designs.

Al2O3/SnC heterostructure: Physical properties, regulation effect and device design

Two van der Waals (vdW) heterostructures between Al2O3 and SnC monolayers are constructed by the Generalised Lattice Matching (GLM) method. We calculate the elastic constants of monolayers and heterostructure and find that the heterostructures show larger Young’s modulus (220−234) N/m compared with Al2O3 (SnC), the reasonable Poisson’s ratio is about 0.3 and gravity-induced bending is the order of 104, which is comparable to graphene. The electronic properties, optical absorption coefficient and transmission properties of the heterostructure also have been investigated. Some important discoveries can be obtained: The Al2O3/SnC heterostructure shows an indirect bandgap (Eg) semiconductor with 1.70 eV and type II band arrangement when the ferroelectric polarization of Al2O3 points to SnC. While the polarization direction of Al2O3 is opposite, the Eg is zero. The physical properties are manipulated by some conditions (strain and electric field), leading to transitioning between Type II and I semiconductors, semiconductors and metal can be experienced. Moreover, the heterostructures prefer the higher light adsorption coefficient (105 cm−1) compared to monolayers. The transport properties of the Al2O3/SnC linked by two silicene electrodes show an excellent tunnel electroresistance (TER) effect with 108, moreover, the negative differential resistance (NDR) effect and switching effect also can be observed.

Edge modified zigzag GeS nanoribbon devices with tunable electronic properties and significant negative differential resistance effect: A first principle study

Using density functional theory (DFT) in combination with non-equilibrium Green's function (NEGF), we study the effects of edge modification on the structural, electronic, and transport properties of zigzag germanium sulphide nanoribbons (ZGeSNRs). Two different types of modification by H, F, and Cl atoms are considered, i.e., the unilateral edge modification (Ge or S edge) and the bilateral edge modification. The addition of modification atoms eliminates the dangling bonds at the edges and enhances the stability in general though the edge structure may be significantly modulated. The unilateral edge modifications do not change the metallic characteristics of ZGeSNRs but the bilateral edge modifications make them semiconductor. In addition, structures with one half-filled energy band separated from other bands can be realized to obtain strong negative differential resistance effects. A maximal peak-to-valley current ratio of 1.01×105 in the bias range 0.49–1.07 V is predicted in a H modified ZGeSNR, which should be promising for applications in low power and high performance nanoelectronic devices.

Strain-Modulated Electronic Transport Properties in Two-Dimensional Green Phosphorene with Different Edge Morphologies

Based on two-dimensional green phosphorene, we designed two molecular electronic devices with zigzag (Type 1) and whisker-like (Type 2) configurations. By combining density functional theory (DFT) and non-equilibrium Green’s function (NEGF), we investigated the electronic properties of Types 1 and 2. Type 1 exhibits an interesting negative differential resistance (NDR), while the current characteristics of Type 2 show linear growth in the current–voltage curve. We studied the electronic transport properties of Type 1 under uniaxial strain modulation and find that strained devices also exhibit a NDR effect, and the peak-to-valley ratio of device could be controlled by varying the strain intensity. These results show that the transport properties of green phosphorene with different edge configuration are different, and the zigzag edge have adjustable negative differential resistance properties.

The electron transport properties and thermoelectric performance in graphene–boron–nitride-nanoribbon-based heterojunctions

The electron transport properties and thermoelectric performance in graphene–boron–nitride-nanoribbon-based heterojunctions (GNR-BNN heterojunctions) have been studied by first-principles calculation. It is found that the electronic transport properties and thermoelectric performance properties are highly sensitive to the geometry details of the GNR-BNN heterojunction. Notably, our calculations reveal that the GNR-BNN heterojunctions not only can present obvious negative differential resistance effects, but also can present high thermoelectric figure of merit ZT: the figure-of-merit ZT will be over 1 at room temperature T = 300 K. Moreover, the thermoelectric performance is significantly enhanced by the combination of defects and alternating boron-nitride structures. Therefore, the GNR-BNN heterojunctions will provide the possibilities for designing and fabrication of multifunctional molecular device design.

Analytical expression of negative differential thermal resistance in a macroscopic heterojunction

Heat flux (J) generally increases with temperature difference in a material. A differential coefficient of J against temperature (T) is called differential thermal conductance (k), and an inverse of k is differential thermal resistance (r). Although k and r are generally positive, they can be negative in a macroscopic heterojunction with positive T-dependent interfacial thermal resistance (ITR). The negative differential thermal resistance (NDTR) effect is an important effect that can realize thermal transistor, thermal memory, and thermal logic gate. In this paper, we examine analytical expressions of J, k, r, and other related quantities as a function of parameters related to thermal conductivity (κ) and ITR in a macroscopic heterojunction to precisely describe the NDTR effect.

Electronic, optical, and transport properties of boron arsenide monolayers tailored with hydrogenation and halogenation

In this study, density functional theory was used to demonstrate the effectiveness of a strategy involving chemical functionalization, specifically hydrogenation and halogenation, to tailor the electronic, optical, and transport properties of boron arsenide (BAs) monolayer. Compared to the half-functionalized BAs monolayers, the fully functionalized BAs monolayers (X–BAs–X, X = H, F, Cl, Br, and I) showed excellent stability. Moreover, functionalization not only disrupted the planar structure of BAs monolayer but also broke its mirror symmetry, enabling effective modulation of its bandgap and work function within the ranges of 0.29 eV–4.25 eV and 3.96 eV–6.98 eV, respectively. In addition, functionalization significantly enhanced optical absorption in the infrared and ultraviolet regions and induced the notable negative differential resistance effect in transmission devices. Thus, functionalization offers a versatile means for modulating the electronic, optical, and transport properties of BAs monolayers, thereby expanding their potential applications in optoelectronic and microelectronic devices.

Resistive Memory-Switching Behavior in Solution-Processed Trans, trans-1,4-bis-(2-(2-naphthyl)-2-(butoxycarbonyl)-vinyl) Benzene-PVA-Composite-Based Aryl Acrylate on ITO-Coated PET.

Resistive switching memories are among the emerging next-generation technologies that are possible candidates for in-memory and neuromorphic computing. In this report, resistive memory-switching behavior in solution-processed trans, trans-1,4-bis-(2-(2-naphthyl)-2-(butoxycarbonyl)-vinyl) benzene-PVA-composite-based aryl acrylate on an ITO-coated PET device was studied. A sandwich configuration was selected, with silver (Ag) serving as a top contact and trans, trans-1,4-bis-(2-(2-naphthyl)-2-(butoxycarbonyl)-vinyl) benzene-PVA-composite-based aryl acrylate and ITO-PET serving as a bottom contact. The current-voltage (I-V) characteristics showed hysteresis behavior and non-zero crossing owing to voltages sweeping from positive to negative and vice versa. The results showed non-zero crossing in the devices' current-voltage (I-V) characteristics due to the nanobattery effect or resistance, capacitive, and inductive effects. The device also displayed a negative differential resistance (NDR) effect. Non-volatile storage was feasible with non-zero crossing due to the exhibition of resistive switching behavior. The sweeping range was -10 V to +10 V. These devices had two distinct states: 'ON' and 'OFF'. The ON/OFF ratios of the devices were 14 and 100 under stable operating conditions. The open-circuit voltages (Voc) and short-circuit currents (Isc) corresponding to memristor operation were explained. The DC endurance was stable. Ohmic conduction and direct tunneling mechanisms with traps explained the charge transport model governing the resistive switching behavior. This work gives insight into data storage in terms of a new conception of electronic devices based on facile and low-temperature processed material composites for emerging computational devices.

Evolution between RS and NRS behaviors in BiFeO3@egg albumen nanocomposite based memristor

The coupling of resistance switching (RS) behavior and N-type negative differential resistance (NDR) effect provides a promising physical basis for the preparation of low-power and multifunctional electronic devices. N-type NDR effect can be expressed by the relationship between peak voltage (VP), valley voltage (VV) and the homologous current (IP, IV). In this work, a memristive device with Ag/BFO@EA/FTO structure was prepared by inserting BiFeO3 (BFO) nanoparticles into egg albumen (EA) as the functional layer, and observed the evolution between RS and NDR coupled RS (NRS) behaviors with the regulation of applied voltage window. Besides, it can be observed a wide current gap of 18.6 mA between IP and IV in the narrow voltage gap (about 0.4 V) between VP and VV, indicating that the device has low power consumption and fast reading/writing speed when it is applied to information processing. Finally, based on the obtained data, it was deeply analyzed the mechanism of NRS effect in the Ag/BFO@EA/FTO memristive device. Therefore, this work provides a new perspective for realizing multi-level storage and multifunctional advanced applications in the memristive device.

Enhancing Spin-Transport Characteristics, Spin-Filtering Efficiency, and Negative Differential Resistance in Exchange-Coupled Dinuclear Co(II) Complexes for Molecular Spintronics Applications.

Single-molecule spintronics, where electron transport occurs via a paramagnetic molecule, has gained wide attention due to its potential applications in the area of memory devices to switches. While numerous organic and some inorganic complexes have been employed over the years, there are only a few attempts to employ exchange coupled dinuclear complexes at the interface, and the advantage of fabricating such a molecular spintronics device in the observation of switchable Kondo resonance was demonstrated recently in the dinuclear [Co2(L)(hfac)4] (1) complex (Wagner et al., Nat. Nanotechnol. 2013, 8, 575-579). In this work, employing an array of theoretical tools such as density functional theory (DFT), the ab initio CASSCF/NEVPT2 method, and DFT combined with nonequilibrium Green Function (NEGF) formalism, we studied in detail the role of magnetic coupling, ligand field, and magnetic anisotropy in the transport characteristics of complex 1. Particularly, our calculations not only reproduce the current-voltage (I-V) characteristics observed in experiments but also unequivocally establish that these arise from an exchange-coupled singlet state that arises due to antiferromagnetic coupling between two high-spin Co(II) centers. Further, the estimated spin Hamiltonian parameters such as J, g values, and D and E/D values are only marginally altered for the molecule at the interface. Further, the exchange-coupled state was found to have very similar transport responses, despite possessing significantly different geometries. Our transport calculations unveil a new feature of the negative differential resistance (NDR) effect on 1 at the bias voltage of 0.9 V, which agrees with the experimental I-V characteristics reported. The spin-filtering efficiency (SFE) computed for the spin-coupled states was found to be only marginal (∼25%); however, if the ligand field is fine-tuned to obtain a low-spin Co(II) center, a substantial SFE of 44% was noted. This spin-coupled state also yields a very strong NDR with a peak-to-valley ratio (PVR) of ∼56 - a record number that has not been witnessed so far in this class of compounds. Additionally, we have established further magnetostructural-transport correlations, providing valuable insights into how microscopic spin Hamiltonian parameters can be associated with SFE. Several design clues to improve the spin-transport characteristics, SFE and NDR in this class of molecule, are offered.

Effect of vacancy defects on anisotropic electronic transport behaviors of CoN4C2 based 2D devices: a first-principles study

The strong anisotropic electronic transport properties of the single-atom-thick material CoN4C2 monolayer hold immense importance for the advancement of the electronics industry. Using density functional theory combined with non-equilibrium Green’s function systematically studied the electronic structural properties and anisotropic electronic transport properties of the CoN4C2 monolayer. The results show that Co, N, and C single-atom vacancy defects do not change the electronic properties of the CoN4C2 monolayer, which remains metallic. The pristine device and the devices composed of Co, N single-atom vacancy defects exhibit stronger electronic transport along the armchair direction than the zigzag direction, which exhibit strong anisotropy, and a negative differential resistance (NDR) effect can be observed. In contrast to the results mentioned above, the device with C single-atom vacancy defects only exhibits the NDR effect. Among them, the device with the N single-atom vacancy defect regime exhibits the strongest anisotropy, with an I Z/I A of up to 7.95. Moreover, based on the strongest anisotropy exhibited by N single-atom vacancy defects, we further studied the influence of different sites of the N-atom vacancy on the electronic transport properties of the devices. The results indicate that N-1, N-2, N-3, N-12, N-23, N-123, N-1234, and N-12345 model devices did not change the high anisotropy and NDR effect of the device, and among them the N-1234 exhibits the strongest anisotropy, the I Z/I A reaches 6.12. A significant NDR effect is also observed for the electronic transport along the armchair direction in these devices. However, the current gradually decreases as an increase of the number of N defects. These findings showcase the considerable potential for integration of the CoN4C2 monolayer in switching devices and NDR-based multifunctional nanodevices.

Size- and Voltage-Dependent Electron Transport of C2N-Rings-Based Molecular Chains.

C2N-ring-based molecular chains were designed at the molecular level and theoretically demonstrated to show distinctive and valuable electron transport properties that were superior to the parent carbonaceous system and other similar nanoribbon-based molecular chains. This new -type molecular chain presented an exponential attenuation of the conductance and electron transmission with the length. Essentially, the molecular chain retained the electron-resonant tunneling within 7 nm and the dominant transport orbital was the LUMO. Shorter molecular chains with stronger conductance anomalously possessed a larger tunnel barrier energy, attributing to the compensation of a much smaller HOMO-LUMO gap, and these two internal factors codetermined the transport capacity. Some influencing factors were also studied. In contrast to the common O impurity with a tiny effect on electron transmission of the C2N rings chain, the common H impurity clearly improved it. When the temperature was less than 400 K, the electron transmission varied with temperature within a narrow range, and the structural disorder deriving from proper heating did not greatly modify the transmission possibility and the exponentially decreasing tendency with the length. In a non-equilibrium condition, the current increased overall with the bias but the growth rate varied with size. A valuable negative differential resistance (NDR) effect appeared in longer molecular chains with an even number of big carbon-nitrogen rings and strengthened with size. The emergence of such an effect originated from the reduction in transmission peaks. The conductance of longer molecular chains was enhanced with the voltage but the two shortest ones presented completely different trends. Applying the bias was demonstrated to be an effective way for C2N-ring-based molecular chains to slow down the conductance decay constant and affect the transport regime. C2N-ring-based molecular chains show a perfect application in tunneling diodes and controllable molecular devices.