Negative Differential Resistance Peak Research Articles

Redox Polymer-Regulated Hysteresis in Ion Current Rectification through AAO Membranes and Single Nanopipettes

Nanopore technology has promising potential in fields such as high-density energy conversion, stochastic chemical sensing, logic operation and neuromorphic computing, separation and fundamental nanoelectrochemistry due to its rich ion transport features and easy fabrication. Understanding the ion transport dynamics at the solid-liquid interface is essential for further technological advancements. Ion current rectification (ICR) and its time-dependent hysteresis have been found to arise from the asymmetric nanointerfaces (geometry, together with surface charges in polarity and density). While various nanostructures can be fabricated and surface charges can be modified, active controls in ICR and hysteresis during transport applications are lacking. Here, we report actively controlled transport hysteresis in ion current rectification though PEDOT-modified single nanopipettes and anodic aluminum oxide (AAO) membranes. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) provides high conductivity and chemical stability, low operating voltages, and enhanced performances in hydrophilicity, processability, and flexibility. The PEDOT:PSS aqueous dispersion is crosslinked inside a nanopipette or assembled onto one side of the AAO surface. Oxidation and reduction reversibly switch the PEDOT between the positive and neutral form, and thus modulate the space charge in nanopores or across the AAO membranes, correspondingly, the ion transport behaviors. The amplitude and polarity of ICR and the scale of hysteresis through a nanopore or AAO membrane have been altered by oxidizing/reducing the PEDOT substrate by adjusting the external electrical field. In contrast, the surface charge varying on pH, ionic strength, and electrolyte type is commonly adopted in ion transport studies but cannot be externally regulated in real-time. Interestingly, negative differential resistance (NDR) is also found in the PEDOT-modified nanopores in simple KCl systems without external pressure differential or concentration gradients. The NDR peak position and magnitude can be easily adjusted by controlling the redox states of the PEDOT fillings. Figure 1

Negative Differential Resistance and Long-Lived Changes in the Electrical Conductivity of Carbon Composites Induced by Electrothermal Effects

In this study, the negative differential resistance (NDR) phenomenon in two-terminal devices composed of pyrogallol-formaldehyde/ZrO2 composite materials is investigated. It is demonstrated that the NDR is caused by electrothermal effects, which can be observed through the dependence of the NDR on both voltage and temperature. Additionally, it is showed that the NDR peak current and peak/valley voltages can be effectively modulated using electrical pulses that produce mild Joule heating. This modulation arises from the formation of a conductive metastable state, which decays to equilibrium according to power law kinetics. It is suggested that this metastable state is generated through a reversible structural rearrangement induced by heat. The ability to electronically tune the NDR characteristics of carbon composites may have potential applications in electronically controlled oscillators and neuromorphic circuits.

All-Carbon Negative Differential Resistance Nanodevice Using a Single Flake of Nanoporous Graphene

A temperature-induced degenerate p-type graphene nanopore/reduced graphene oxide (GNP/rGO) heterojunction-based nanodevice was prepared and studied for the first time, showing a robust negative differential resistance (NDR) feature. In this regard, cellulose-based perforated graphene foams (PGFs), containing numerous nanopores (with an average size of ∼2 nm surrounded by nearly six-layer rGO walls) were synthesized using bagasse as a green starting material. The PGFs with an essential p-type semiconducting property showed a band gap energy of ∼1.8 eV. The observed two-terminal NDR peak could present stable and reversible features at high temperatures of 586–592 K. It was demonstrated that the O2 gas of the ambient would be involved in a crucial activity in water-based degeneration of the initial p-type regions around the GNPs and, consequently, the appearance of an intensive quantum tunneling NDR peak. An electron-band structure-based mechanism is proposed to describe the lateral quantum tunneling current within the degenerate p-type GNP and rGO heterojunction that is induced by the energized water molecules (EWMs). These results can shed light on more investigations regarding lateral quantum tunneling-based NDR features in upcoming and highly desired two-dimensional electronic nanodevices.

Modulation of Negative Differential Resistance in Black Phosphorus Transistors.

Negative differential resistance (NDR), which describes the current decrease as the applied bias increases, holds great potential for varieties of electronic applications including radio-frequency oscillators, multipliers, and multivalue logics. Here, the modulation of a unique NDR effect in ambipolar black phosphorus (BP) transistors is reported, which is activated by specific electrical field dependence of lateral carrier distribution and is distinct from conventional NDR devices that rely on quantum tunneling. The NDR device exhibits a high peak current density (34 µA µm-1 ) and a high operating temperature. More importantly, due to the strong coupling between the channel and the gate electrode, both the NDR peak current and peak/valley voltages can be effectively modulated by the electrostatic gate. Furthermore, it is demonstrated that light can serve as an additional terminal for NDR modulation. The findings could provide an important insight into the transport behavior of BP transistors and contribute to the design of ambipolar-semiconductor-based electrical circuits.

DNA-Immobilized CoFe2O4 Magnetic Nanoparticles: A Nature-Friendly Material Manifesting Negative Differential Resistance and Hysteresis Effects

Negative differential resistance (NDR) and hysteresis effects have been successfully achieved by synthesizing DNA-immobilized CoFe2O4 magnetic nanoparticles using wet chemical co-precipitation method. These multiple effects in a single compound particle can open the door for several next generation applications from high frequency communication device development to memory storage device. Here, for both positive and negative bias condition during electrical characterization, reproducible NDR peaks have been found. For the sample with maximum DNA conjugation with CoFe2O4 magnetic nanoparticles consistent hysteresis effects have also been found. Both of these features i.e., NDR and hysteresis can be attributed to conformational changes in crystal structure due to addition of DNA and polaron transform phenomena at the molecular level, respectively. By achieving these two features in one material, multifunctional devices can be developed for molecular electronic applications.

Resonant Tunneling and Negative Differential Resistance in Black Phosphorus Vertical Heterostructures

AbstractResonant tunneling diodes with negative differential resistance (NDR) have attracted significant attention due to their unique quantum resonant tunneling phenomena and potential applications in terahertz emission/detection and high‐density logic/memory. In this paper, resonant tunneling devices, where the carriers tunnel through a hexagonal boron nitride (hBN) barrier sandwiched by two black phosphorus (BP) layers, are explored. The resonance occurs when the energy bands of the two black phosphorus layers are aligned. The conductive atomic force microscopy (CAFM) measurements reveal prominent NDR peaks with large peak‐to‐valley ratios at room temperature. It is found that the positions of the NDR peaks are very sensitive to the amplitude and the shape of the voltage waveform used in CAFM, which can be explained by the charge trapping effect. Furthermore, resonant tunneling transistors are demonstrated based on BP/hBN/BP stacks in which the locations of the NDR peaks are tunable by the electrostatic gating. As compared to the traditional tunneling diodes based on bulk materials, the tunneling devices based on thin boron nitride tunneling barrier and high mobility black phosphorus offer ultra‐high‐speed response. This feature, together with the NDR characteristics, provides the potential for applications in THz oscillators and multi‐value logic devices.

Temperature- and pulse-dependent negative differential resistances in ZnO/Nb:SrTiO3 heterojunctions

Temperature- and pulse amplitude/width dependent current-voltage characteristics were performed to study the variance of negative differential resistance (NDR) features accompanying bipolar resistive switching. Interestingly, the absolute value of the NDR peak intensity is enhanced at first and then weakened, while the NDR peak position gradually shifts toward the lower absolute bias value with an increase in temperature from 140 to 300 K, and shifts toward the larger absolute bias value with an increase in temperature from 300 to 400 K. Furthermore, the NDR peak is absent after applying a small and narrow positive pulse, while it gradually increases with increasing the applied pulse amplitude or width. These temperature- and pulse-dependent NDR behaviors can be fully understood based on a model of generation and drift of ionized oxygen vacancies coupled with trapping/detrapping electrons. The clarification of the mechanism will pave the way for practical applications.

Controllable negative differential resistance on charge transport through strained and tilted DNA molecules

A double-stranded DNA molecule subject to a perpendicular gating electric field and a small mechanical strain exhibits a negative differential resistance (NDR) in its current–voltage (I–V) characteristics. Using an advanced two-dimensional tight-binding model including hopping integrals for the next nearest-neighbors, we implement perturbative strain- and tilted angle-dependent DNA helix conformation in conjunction with the theories of Slater–Koster and linear elasticity. The degree of NDR can be tuned by adjusting the tilt angle and mechanical strain of the DNA. This effect arises because of a surface charge distribution near the contacts due to the normal component of the electric field and structural change of the DNA molecule due to the strain. It is shown that enhancement of NDR peak current and a large peak-to-valley ratio of NDR are achieved by an increase of the tilt angle and stretching strain. Finally, a series of step-like current jumps without NDR features are exhibited in the weak DNA-lead coupling regime. This disappearance of NDR stems from the fact that reduced conduction through metal electrodes with a sufficiently small tunneling rate compensates the current drop.

Perovskite Resonant Tunneling FET with Sequential Negative Differential Resistance Peaks

A vertical resonant tunneling (RT) field effect transistor (VRTFET), fabricated using perovskite (CH3NH3PbI3), has been analyzed for sequential sharp negative differential resistance (NDR) peaks useful in multiple-valued logic devices. NDR peaks are attributed to the sub-bands formation within the parabolic shaped band gap, present at the channel and drain/source interface due to Schottky barriers. Ambipolar CH3NH3PbI3 imparts both p and n mode characteristics with RT NDR peaks. An unprecedentedly high (100 to 1000 V–1) curvature coefficient (ϒ) has been found with two NDR peaks at a short interval, whose positions shift left, with gate bias. Due to the ionic nature of CH3NH3PbI3, hysteresis has also been observed in the transfer characteristics. This structure can overcome the limit of 60 mV/decade as well as a curvature limit of 40 V–1, important parameters for analog and digital applications. So, these devices promise cheaper and easy fabrication at commercial scale operation at ultralow voltage and lo...

InAs/GaSb superlattice resonant tunneling diode photodetector with InAs/AlSb double barrier structure

We report on a resonant tunneling diode (RTD) photodetector using type-II InAs/GaSb superlattices with an InAs/AlSb double barrier structure. At 80 K, the maximum response of the detector is at about 4.0 μm and the 50% cutoff wavelength is 4.8 μm. The resonant tunneling mechanism is confirmed by observing the negative differential resistance (NDR) phenomenon. The detector is also tested under illumination by a laser with a wavelength of 3.3 μm. A significant photocurrent and NDR peak shift are observed when changing the laser illumination power. The internal multiplication factor, which means how many excess electrons can be triggered by one absorbed photon, is estimated to be 1.01 × 105 at 4.9 V and is 1.90 × 103 at 1.4 V.

Effects of Molecular Combination and Side Groups for Thiophene-Benzene-Based Nanodevices

The electron transport properties of thiophene-benzene-based molecules attached to zigzag graphene nanoribbon (ZGNR) electrodes are investigated using density functional theory and the nonequilibrium Green function. The results show that 3,6-(dithiophen-2-yl)benzene has better performance compared to 2,5-diphenylthiophene. Interestingly, both the devices exhibit two negative differential resistance (NDR) peaks while a thiophene or a benzene molecule tethered to ZGNR electrodes shows one NDR peak. Although the side groups −OH, −NO2, and −NH2 controllably repress the transmission and current of 3,6-(dithiophen-2-yl)benzene, the current rectification performance is found because of its asymmetry of molecule structure. Unexpectedly, 2,5-diphenylthiophene system added by a thiophene shows semiconductor behavior under a certain bias region. These results contribute to a deep understanding of the electron transport properties of molecular combination and are valuable for designing molecular devices with excellen...

The negative differential resistance mechanism of a molecular device based on double‐cage fluorinated fullerene C20F18(NH)2C20F18: A theoretical study

AbstractThe electronic transport properties of the molecular device based on double‐cage fluorinated fullerene C20F18(NH)2C20F18 were studied theoretically. The results show that the device exhibits two negative differential resistance (NDR) peaks in its I‐V curve. The NDR peak under low bias voltage originates from the bias‐induced alignment of the molecular orbitals, and the conduction channel being suppressed at a certain bias voltage is the main reason for the NDR peak under a relatively high bias voltage.

Negative Differential Resistance Behavior of the Iron Storage Protein Ferritin.

Realization of useful nanometer length scale devices in which metalloproteins are junction-confined in a distinct molecular arrangement for generating practical electronic signals (e.g., in bioelectronic switch configuration) is elusive till date. This is mostly due to difficulties in observing an electronically appropriate signal (i.e., reproducible and controllable), when studied under junction-assembled condition. A useful "ON"-"OFF" behavior, based on the negative differential resistance (NDR) peak characteristics in the current-voltage response curves, acquired using metal-insulator-metal (MIM) configuration, has been observed only in the case of a few proteins, namely, azurin, cytochrome c, bacteriorhodopsin, so far. The case of NDR in ferritin, an iron storage protein having a semiconducting iron core consisting of few thousands of iron atoms connected in an oxide network, has not been studied in the MIM configuration where single (or a few) molecule(s) are junction-trapped, for example, as in the case of local probe configuration of scanning probe microscopy. The present study by scanning tunneling microscopy (STM), using the naturally occurring iron-containing ferritin (human liver), as well as different iron-loaded ferritins, provides clear indication of the capability of ferritins to be NDR capable, at varying sweep conditions. As ferritin can be tailor-made in a structurally conserved manner, metal core-reconstituted ferritins, that is, Mn(III)-ferritin, Cu(II)-ferritin, and Ag-ferritin, were prepared. A correlation between the NDR peak signatures, as observed in the respective current-voltage response curves of these reconstituted ferritins, and the nature of the metal core is demonstrated. In support of our earlier proposition, here, we affirm that the ferritin protein behaves as a conductor-insulator (metal core-polypeptide shell) composite, where the overall electronic structure of the material can alter as a function of the nature of the conducting filler placed inside the insulated matrix.

Modulation of Response Patterns by Loading-Rate-Dependent Interface Polarization and Doping

In this study, we established the energy alignment of the Ca(CF3SO3)2-doped poly(ethylene oxide)/poly(3-hexylthiophene-2,5-diyl), i.e., CaTf2-PEO/P3HT, heterojunction. The concentration polarization of ions could dynamically adjust the energy level of the PEO complex, similar to light-emitting electrochemical cells (LECs). When bias is loaded in the orientation from CaTf2-PEO-PEO to P3HT, the charge diffusions appears and the internal electric field (Ein) is generated. Simultaneously, the accumulation of the ions also induces the interface stress which could be released partially after some ions are doped into the P3HT layer. The interface polarization and doping are found to be modulated by the external field under various loading rates. These two effects interact together thereby determining the size of Ein and resulting in the negative differential resistance (NDR) phenomenon. The NDR peak increases with the sweeping times under conditions of slow loading rates, while it decreases under conditions of e...

Quantum Transport Simulation of Nanowire Resonant Tunneling Diodes Based on a Wigner Function Model With Spatially Dependent Effective Masses

We present a self-consistent and three-dimensional quantum simulation for nanowire resonant tunneling diodes (RTDs) based on the Wigner transport equation with spatially dependent effective masses (SDEM), which is discretized by a third-order upwind difference scheme for high-accuracy calculation. Our calculation shows that the current density/voltage ( $J\text{--}V$ ) characteristics of nanowire RTDs with a radius ( $R$ ) $ 5 nm largely deviate from those of the one-dimensional RTDs. As $R$ decreases below 5 nm, the peak-to-valley ratio (PVR) of the low- $V$ negative differential resistance (NDR) decreases rapidly, and the high- $V$ NDR peak shifts sensitively to lower $V$ and becomes sharper. In this study, these results are shown to be closely related to the SDEM. According to our analysis, the SDEM along the transport direction contributes to the formation of an ‘effective double barrier’ in the energy subbands that is higher than the double barrier expected by the band offset, and the SDEM along the confinement direction reduces the height of the effective double barrier. The performance of nanowire RTDs with $R 5 nm was proven to be highly dependent on $R$ because of the SDEM along the confinement direction.

Negative differential resistance in partially fluorinated graphene films

Partially fluorinated graphene films were created by chemical functionalization of graphene layers in an aqueous solution of hydrofluoric acid. The formation of graphene islands or graphene quantum dots (GQDs) and a fluorinated graphene network is demonstrated in such films. Negative differential resistance (NDR) resulting from the formation of the potential barrier system in the films was observed for different fluorination degrees of suspension. The origin of the NDR varies with an increase in the fluorination degree of the suspension. Numerical calculations were performed to elucidate the tunneling between adjacent energy levels and creation of NDR. It was found that in the case of films with smaller flake and smaller GQD sizes, multi-peak NDR appears in the I–V curve. We predict that the NDR peak position shifts towards lower voltage with a decrease in the GQD size. Surprisingly, we observed a negative step-like valley for positive biases in the I-V curve of samples. Our findings with detailed analysis shed light on understanding the mechanisms of the NDR phenomenon in a partially fluorinated graphene system.

Effect of doping on the transport properties of single-walled carbon nanotube two probe systems

This paper reports the doping induced negative differential resistance (NDR) in chromium substituted zig-zag (4, 0) single walled carbon nanotube (SWCNT) devices and the effect of the doping level on this property by using non-equilibrium Green's function theory formalism in combination with semi-empirical extended Huckel theory (EHT) calculations of the Atomistic Tool Kit software in device mode. The results show that the tunneling current, number of NDR peaks and the conductance increases with an increase in the level of doping. The high peak to valley current ratio (PVR) of the three proposed models are presented in the form of tables for comparative studies. The highest peak to valley current ratio of 5.70 is found in the two atom chromium doped SWCNT geometry. It is believed that the explored chromium doped CNT devices in this study will find number of applications in the future, particularly for fast switching and high speed signal processing.

Carbon-doping-induced negative differential resistance in armchair phosphorene nanoribbons**Project supported by the National Natural Science Foundation of China (No. 11274096), the University Science and Technology Innovation Team Support Project of Henan Province (No. 13IRTSTHN016), the University key Science Research Project of Henan Province (No.16A140043). The calculation about this work was supported by the High Performance Computing Center of Henan Normal University.

By using a combined method of density functional theory and non-equilibrium Green’s function formalism, we investigate the electronic transport properties of carbon-doped armchair phosphorene nanoribbons (APNRs). The results show that C atom doping can strongly affect the electronic transport properties of the APNR and change it from semiconductor to metal. Meanwhile, obvious negative differential resistance (NDR) behaviors are obtained by tuning the doping position and concentration. In particular, with reducing doping concentration, NDR peak position can enter into mV bias range. These results provide a theoretical support to design the related nanodevice by tuning the doping position and concentration in the APNRs.

Organic quantum wells with multiple negative differential resistance peaks and its photoswitch effect

Organic optoelectronic devices have experienced great progress in recent decades. However, quantum well has long been a challenge for organic semiconductors due to the weak intermolecular interactions, the difficulty of realizing high quality alternate crystalline films. Here, we construct a type II organic crystalline quantum well, in which both electron quantum well and hole quantum well show symmetrical and multiple negative differential resistance peaks, respectively. The blueshifts of absorption spectra and the peak voltage decreasing under illumination conditions are observed. Due to high absorption coefficient of organic semiconductors, photoswitch effect by taking advantage of negative differential resistance of organic quantum well, which owns very thin device structure is demonstrated. Our results prove the promising applications of organic quantum wells, which broaden the types of organic optoelectronic devices.

Enhanced oscillatory rectification and negative differential resistance in pentamantane diamondoid-cumulene systems.

We propose a new functionality for diamondoids in nanoelectronics. Based on the nonequilibrium Green's function formalism and density functional theory, we reveal that when attached to gold electrodes, the pentamantane-cumulene molecular junction exhibits large and oscillatory rectification and negative differential resistance (NDR) - depending on the number of carbon atoms in cumulene (Cn). When n is odd rectification is greatly enhanced where the rectification ratio can reach ∼180 and a large negative differential resistance peak current of ∼3 μA. This oscillatory behavior is well rationalised in terms of the occupancy of the carbon 2p states in Cn. Interestingly, different layers of C atoms in the pentamantane molecule have different contributions to transmission. The first and third layers of C atoms in pentamantane have a slight contribution to rectification, and the fifth and sixth layers have a stronger contribution to both rectification and NDR. Thus, our results suggest potential avenues for controlling their functions by chemically manipulating various parts of the diamondoid molecule, thus extending the applications of diamondoids in nanoscale integrated circuits.