Robust Negative Differential Resistance Research Articles

Tuning of the electronic structures and spin-dependent transport properties of phosphorene nanoribbons by vanadium substitutional doping

Based on vanadium-doped zigzag phosphorene nanoribbon (ZPNRs), we investigate the electronic structures and spin-dependent transport properties by the first-principles calculations in combination with the nonequilibrium Green's function approach. We find that the ZPNRs can be tuned from nonmagnetic metals to magnetic metals or half-metals by different doping positions, which are caused by the hybridization among different electron orbitals under the crystal field. Moreover, a robust negative differential resistance effect is observed in all studied devices, and a perfect spin-filter effect with almost 100% spin polarization can be found under low bias. We analyze the transport properties in detail from the viewpoint of the transmission spectrum and molecular energy levels. These results indicate that the vanadium-doped ZPNRs have potential applications as multi-functional spintronic devices. • Zigzag phosphorene nanoribbons can be tuned from nonmagnetic metals to magnetic metals or half-metals. • Robust negative differential resistance effect is observed. • Perfect spin-filter effect with almost 100% spin polarization can be found. • We analyze the transport properties in detail.

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.

TPDH-graphene: A new two dimensional metallic carbon with NDR behaviour of its one dimensional derivatives

Abstract A new two dimensional carbon allotrope TPDH-graphene (Tetra-Penta-Deca-Hexagonal-graphene) belonging to the tetragonal-pentagonal carbon ring family is proposed in this work using density-functional method. The allotrope satisfies all the conditions of structural stability. This allotrope has lower cohesive energy than many existing planar carbon allotropes. It can withstand temperature as high as 1000 K without loosing its structural integrity. However, its electronic structure reflects metallic character due to delocalised pz orbital near the Fermi level. Further, this mechanically stable elastically anisotropic structure shows directional variation of In-plane Young's modulus and Poisson's ratio. It is stronger than graphene in a particular direction. Moreover, The material can be identified by four characteristic peaks in the electron energy loss spectra within 10 eV energy. It has optical reflectance peaks in the visible range at ∼600 nm yellow colour. Interestingly, some nanoribbons of this material show semimetallic, semiconducting and metallic behaviour. Non-equilibrium Green's function method along with density-functional theory is employed to study the nanodevices made of these nanoribbons. Strong current regulation property and robust negative differential resistance effect with a peak-to-valley ratio 3.3 are observed in two nanodevices making TPDH-graphene an attractive material for use in nanoelectronics.

Tunable transport characteristics of armchair phosphorene nanoribbon-based three-terminal devices by the channel length and gate dielectrics

The effects on the transport characteristics of the channel length and gate dielectrics in a type of armchair phosphorene nanoribbon-based three-terminal device are investigated using the density functional theory. The simulation results show that not only the variation of gate voltage, but also the channel length and gate dielectrics can effective modulate the transport properties of the three-terminal devices. Meanwhile, the robust negative differential resistance behavior rises in the scale from 3 nm to 9 nm devices with SiO2, Al2O3, HfO2 gate dielectrics. The current peak-to-valley ratio ascends with the channel length due to the existence of short-channel effect, but descends with the gate dielectric constant because of the increased ability to suppress the current. This finding suggests a possible route to manipulate the current-voltage characteristics of a type of three-terminal device, which is expected to have great potential application in logic, high-frequency nanodevices.

Tailoring electronic and transport properties of edge-terminated armchair graphene by defect formation and N/B doping

First principle calculations based on Density Functional Theory and nonequilibrium Green's function methods were carried out on a p-n junction device made of armchair graphene nanoribbons (GNR), with B and N doping and with defects, to examine transport properties of these systems. Doping and defects were found to lower band gap compared to pristine GNR. N-doping leads to the smallest band gap and the highest current (17.18 μA at 0.9 V bias, −12.82 μA at −1 V bias). B-doping shows the least current. Extensive delocalisation in N-doped system suggests a strong coupling between p and n parts, making the system a high rectifying diode. Linear correspondence between transmission coefficient and projected density of states suggest robust negative differential resistance effect. Tuning of efficiency of such p-n junction by doping and defect suggests the design of suitable nanoelectronic devices in future.

Negative differential resistance in hybrid carbon-based structures

Here we study negative differential resistance effect in hybrid carbon nanostructures composed of graphene nanoribbons and carbon nanotubes. In the coupled structure, the finite flakes of nanotubes allow the formation of resonant states in the system tuning the conductance and generating Fano antiresonances. A single-band tight-binding approximation is adopted, and the density of states and conductance of the hybrid systems are calculated within the Green's function formalism and recursive numerical approaches. Armchair and zigzag edge geometries are chosen to investigate the topology effects on the electronic and transport properties for different configurations of the hybrid systems. For nanoribbons with armchair edges we derive a multiple-mode approach to analytically calculate the transmission function for the hybrid coupled system. Large and robust negative differential resistance effects are observed in the nanotube-nanoribbon zigzag hybrids that may be used in switching electronic transport responses.

Robust negative differential resistance and abnormal magnetoresistance effects in heteroatom-substituted zigzag γ-graphyne nanoribbon homojunctions

By using O atoms to substitute H atoms while B or N atoms to substitute edge C atoms to obtain chemically modified ZγGYNRs, then coupling two ZγGYNRs by the interface to build corresponding homojunctions, the transport properties of spintronic devices can be dramatically enhanced.

Tunable rectification and negative differential resistance induced by asymmetric doping in phosphorene nanoribbon

By using first-principles calculations based on density functional theory and non-equilibrium Green's function, we present the electronic transport properties of two kinds of devices based on armchair phosphorene nanoribbons, namely, A device, and B device. In A device, the phosphorus atoms in the center of armchair phosphorene nanoribbon have been replaced by impurity atoms of the S and Si, whereas in the B device, the impurity atoms are at the edge of ribbon. The results show that the current–voltage characteristics for both devices have striking nonlinear features and the rectifying behaviors strongly depend on the positions of impurity atoms. The highest rectification ratio is obtained about 125992 at 0.8 V bias for B device. Moreover, only for A device, robust negative differential resistance is observed with a high peak–valley ratio 27500 in the bias range [−0.2,−0.6] V. The mechanism of the rectification behavior is analyzed in terms of the evolution of energy levels of the related electrodes and transmission spectra as well as the projected self-consistent Hamiltonian eigenvalues with the applied bias voltage. The results indicate that the asymmetric doping of the impurity atoms can lead to a robust rectification which can be utilized to design phosphorene-base rectifier with good performance.

Negative differential resistance in heterojunction polymeric films

For the first time, Negative Differential Resistance (NDR) is reported in purely polymeric systems. A tri-layer thin film system of PEDOT:PSS, P3HT and PCBM was prepared using spin coating method on ITO substrates and Al contact was deposited on other side using thermal vacuum evaporation. Current –Voltage (I-V) measurements were carried out at room temperature where NDR behaviour was observed which was repeatable only qualitatively for as-prepared device. On annealing at 40 °C for 2 h, the NDR became stable however at the cost of peak broadening and was even repeatable quantitatively within reasonable percentage of errors. On further annealing at higher temperatures (60° & 80° C), the NDR disappeared most likely due to isolated networks and disconnected domains of P3HT/PCBM. Simple construction, robust NDR and large current shown by these devices make them potential candidate for the development of organic memory elements.

Time-Resolved Imaging of Negative Differential Resistance on the Atomic Scale.

Negative differential resistance remains an attractive but elusive functionality, so far only finding niche applications. Atom scale entities have shown promising properties, but the viability of device fabrication requires a fuller understanding of electron dynamics than has been possible to date. Using an all-electronic time-resolved scanning tunneling microscopy technique and a Green's function transport model, we study an isolated dangling bond on a hydrogen terminated silicon surface. A robust negative differential resistance feature is identified as a many body phenomenon related to occupation dependent electron capture by a single atomic level. We measure all the time constants involved in this process and present atomically resolved, nanosecond time scale images to simultaneously capture the spatial and temporal variation of the observed feature.

Charge and spin transport in single and packed ruthenium-terpyridine molecular devices: Insight from first-principles calculations.

Using first-principles calculations, we study the electronic and transport properties of rutheniumterpyridine molecules sandwiched between two Au(111) electrodes. We analyse both single and packed molecular devices, more amenable to scaling and realistic integration approaches. The devices display all together robust negative differential resistance features at low bias voltages. Remarkably, the electrical control of the spin transport in the studied systems implies a subtle distribution of the magnetisation density within the biased devices and highlights the key role of the Au(111) electrical contacts.

First principles design of divacancy defected graphene nanoribbon based rectifying and negative differential resistance device

We have studied using density functional theory and non-equilibrium Green’s function based approach, the electronic structures of 555-777 divacancy (DV) defected armchair edged graphene nanoribbons (AGNR) as well as the transport properties of AGNR based two-terminal devices constructed with one defected electrode and one N doped electrode. Introduction of 555-777 DV defect into AGNR results in shifting of the π and π∗ bands towards the higher energy value indicating a downward shift of the Fermi level. Formation of a potential barrier, analogous to that of conventional p-n junction, has been observed across the junction of defected and N-doped AGNR. The two terminal devices show diode like property with high rectifying efficiency for a wide range of bias voltages. The devices also show robust negative differential resistance with very high peak-to-valley ratio. Shift of the electrode energy states and modification of the transmission function with applied bias have been analyzed, in order to gain an insight into the nonlinear and asymmetric behavior of the current-voltage characteristics. Variation of the transport properties on the width of the ribbons has also been discussed.

Homostructured negative differential resistance device based on zigzag phosphorene nanoribbons

Robust negative differential resistance as well as quite large currents are observed in zigzag phosphorene nanoribbon homostructures.

Negative Differential Resistance and Spin-Filtering Effects in Zigzag Graphene Nanoribbons with Nitrogen-Vacancy Defects

We explore the electronic and transport properties of zigzag graphene nanoribbons (GNRs) with nitrogen-vacancy defects by performing fully self-consistent spin-polarized density functional theory calculations combined with non-equilibrium Green's function technique. We observe robust negative differential resistance (NDR) effect in all examined molecular junctions. Through analyzing the calculated electronic structures and the bias-dependent transmission coefficients, we find that the narrow density of states of electrodes and the bias-dependent effective coupling between the central molecular orbitals and the electrode subbands are responsible for the observed NDR phenomenon. In addition, the obvious difference of the transmission spectra of two spin channels is observed in some bias ranges, which leads to the near perfect spin-filtering effect. These theoretical findings imply that GNRs with nitrogen-vacancy defects hold great potential for building molecular devices.

Tuning electron transport through a single molecular junction by bridge modification

The possibility of controlling electron transport in a single molecular junction represents the ultimate goal of molecular electronics. Here, we report that the modification of bridging group makes it possible to improve the performance and obtain new functions in a single cross-conjugated molecular junction, designed from a recently synthesized bipolar molecule bithiophene naphthalene diimide. Our first principles results show that the bipolar characteristic remains after the molecule was modified and sandwiched between two metal electrodes. Rectifying is the intrinsic characteristic of the molecular junction and its performance can be enhanced by replacing the saturated bridging group with an unsaturated group. A further improvement of the rectifying and a robust negative differential resistance (NDR) behavior can be achieved by the modification of unsaturated bridge. It is revealed that the modification can induce a deviation angle about 4° between the donor and the acceptor π-conjugations, making it possible to enhance the communication between the two π systems. Meanwhile, the low energy frontier orbitals of the junction can move close to the Fermi level and encounter in energy at certain biases, thus a transport channel with a considerable transmission can be formed near the Fermi level only at a narrow bias regime, resulting in the improvement of rectifying and the robust NDR behavior. This finding could be useful for the design of single molecular devices.

Resonant transport and negative differential resistance in the graphene and graphyne quantum dots

The electronic transport properties of graphene and graphyne quantum dots embedded in zigzag-edged graphene nanoribbons are studied. The results show that the quasi-bound states in the quantum dots induce resonant transmission around the Fermi level in the transmission spectrums. While the resonant peaks lead to robust negative differential resistance (NDR) behaviors. Moreover, the resonant transmission and NDR behavior are very sensitive to the size of the quantum dots. As the size of quantum dots increases, the number of resonant peaks increases and shift to the Fermi level, correspondingly the NDR phenomena shift to lower bias. Compared with graphene quantum dots, graphyne quantum dots show more amazing transport properties. These interesting findings could offer useful guidelines for the design of electronics associated with resonant and NDR phenomenon.

Pressure Sensing and Electronic Amplification with Functionalized Graphite–Silicone Composite

AbstractA flexible yet electronically active composite that mimics mechanoreceptor neurons in the human skin is synthesized, generating voltage oscillations whose frequency increases with pressure. By encoding pressure into frequency, the sensor achieves a high pressure sensitivity (<10 Pa). The ability to sense pressure and to amplify signals arises from the robust negative differential resistance of functionalized graphitic flakes in silicone.

Negative differential resistance and spin polarization of metal-C6H6 multidecker complexes

We investigate the electronic properties of one-dimensional metal-C6H6 multidecker complexes: chromium(Cr)-benzene(Bz), benzene(Bz)-chromium(Cr)-benzene(Bz)-iron(Fe) wires and CrnBz2 (n = 1, 2, 3) and CrBz2Fem (m = 1, 2) clusters by applying nonequilibrium Green's functions combined with the density-functional theory. We predict that the ground state of the FeBzCrBzFe cluster is 100% spin-polarized. The density of states shows metallic for the spin-up electrons, while a semiconductor gap merges for the spin-down electrons (half-metallic). It is found that there is 92%–97% spin polarization of the electron transmission for the five sandwich molecular junctions constructed by the multilayer metal-benzene organometallic CrnBz2 (n = 1, 2, 3) and CrBz2Fem (m = 1, 2) clusters, which coupled to gold electrodes. In deed, these clusters will perform as nearly perfect spin-filters via the electron transport calculations. The current increases with the cluster length and depends on the bias and spin-up current-voltage characteristics for three kinds of sandwich molecular junctions (Bz2Cr, BzCrBzFe, and Bz2Cr3). It also shows robust negative differential resistance behavior, which is closely related with the evolution of the transmission spectrum under applied bias.

Doped GNR p–n Junction as High Performance NDR and Rectifying Device

On the basis of density functional theory and nonequilibrium Green’s function technique, we have presented theoretical results on transport properties of B- and N-doped aGNR p–n junction. The current–voltage characteristic of this system indicates robust negative differential resistance (NDR) behavior of it. Meanwhile, that p–n junction diode can be utilized as a highly efficient voltage rectifier. The calculations also reveal that the voltage rectifying efficiency can be highly enhanced by forming a tandem diode by connecting two single diodes in series. The variation of transport properties on the width of aGNR is also investigated. The NDR phenomena as well as the rectifying property can be well explained on the basis of relative shifting of discrete energy states of the conjugate system with applied bias, which in turn explains very strong coupling between the p and n regions of the diode.

Theoretical Study of the Properties of Si Nanowire Electronic Devices

Electron-transport properties of three terminal field-effect devices based on both pure and doped Si nanowires with diameters less than 1 nm are theoretically studied. The results indicate that some devices possess electronic functions, such as current amplification and robust negative differential resistance accompanied with large on–off ratios. Three kinds of mechanisms are proposed to interpret different negative differential resistance phenomena of some devices investigated in this paper. Not only structures of nanowires but also applied bias can change the mechanism of negative differential resistance. Furthermore, the performance of these devices is mainly dependent on the doping and atomic arrangement of Si nanowires. This work provides a deep insight into the electron-transport properties of functional electronic nanodevices.