Negative Differential Resistance Behavior Research Articles

Thermal rectification and negative differential thermal resistance behaviors in graphene/hexagonal boron nitride heterojunction

Thermal transport across graphene/hexagonal boron nitride (h-BN) nanoribbon interface is investigated using nonequilibrium molecular dynamics method. It is found that the heat current runs preferentially from the h-BN to graphene domain, which demonstrates pronounced thermal rectification behavior in this heterostructure. The observed phenomena can be attributed to the resonance effect between out-of-plane phonon modes of the graphene and h-BN domains in the low frequency region. In addition, we demonstrate that the optimum conditions for thermal rectification include low temperature, large temperature bias, short sample length and small interface densities. More interestingly, an unexpected negative differential thermal resistance (NDTR) behavior is also found at graphene/h-BN (CBN) nanoribbon interface with special edge geometry. Phonon spectra analysis reveals that the transverse acoustic wave plays an important role for the heat transfer at such interface.

Electronic transport properties of oligo phenylene ethynylene molecule modified by the (CH3)2 and (NH2)2 groups

The modification effects of the groups (CH3)2 and (NH2)2 on the oligo phenylene ethynylene (OPE) molecules with single and double S atoms connected to the two electrodes are investigated by the density functional theory and non-equilibrium Green function. The modified OPE molecule is optimized and used to build a two-probe system with Au electrodes. Then the two-probe system is fully relaxed to obtain a stable structure. The electronic transport properties of the two-probe system are also calculated with the non-equilibrium Green function method. The calculation results show that both the modified groups and the bridge atoms can lead to the switch effect, the negative differential resistance behavior, and the rectifying behavior for the two-probe system. When molecules are connected with single S atom at one end, both the (NH2)2-OPE and the (CH3)2-OPE molecules show the rectifying behavior. However, the (NH2)2-OPE also shows a switch effect at larger voltage because there is current when the negative bias is over 1.3 V, while the (CH3)2-OPE molecule demonstrates a complete rectifying behavior because it is hardly conductive in the whole positive bias area. The current of OPE molecule without modification group always increases with the increase of voltage. Therefore, it is only a resistance. These results are different from that of NO2-OPE-NH2 molecule which shows a negative differential resistance behavior. For the case of the molecule connected with S atoms at both ends, the (NH2)2-OPE(S) and (CH3)2-OPE(S) models show negative differential resistance behaviors in the negative bias range. It is found that both (NH2)2-OPE and (CH3)2-OPE molecules demonstrate the negative differential resistance behaviors when they are connected with S atoms bridge at both ends. However, the current of the molecule with one S atom at one end is about two-order magnitude lower than that of the molecule with S atoms at both ends. It is shown that S atom acting as a bridge can significantly affect the characteristic of current-voltage. The mechanisms for the various characteristics of the electronic transport properties are explored by analyzing the projection orbit electron distribution, the transmission spectrum, and the density of states under the different bias voltages. For (NH2)2-OPE molecule with a single S atom at one end in the negative bias range, only the lowest unoccupied molecular orbital (LUMO) can transfer electron with low bias, but both highest occupied molecular orbital (HOMO) and LUMO can be conductive with high bias, which results in the switch effect. In the positive bias range, both HOMO and LUMO cannot be conductive with low bias, while LUMO can be conductive with high bias, which results in the switch behavior. For the case of (NH2)2-OPE molecule with one S atom at each end, only the HOMO can transfer electron in the low bias range, while the LUMO can be conductive at high positive bias, but both HOMO and LUMO cannot be conductive in high negative bias range, which leads to the non-symmetric negative differential resistance effect in the whole bias range. A similar analysis of the difference between HOMO and LUMO can be used to understand the characteristics of the current-voltage of (CH3)2-OPE. Considering the fact that the different modification groups can lead to various current-voltage properties of OPE molecule, the modified OPE molecule is a promising candidate for designing molecule device.

Effects of line defects on spin-dependent electronic transport of zigzag MoS2 nanoribbons

The nonlinear spin-dependent transport properties in zigzag molybdenum-disulfide nanoribbons (ZMNRs) with line defects are investigated systematically using nonequilibrium Green’s function method combined with density functional theory. The results show that the line defects can enhance the electronic transfer ability of ZMNRs. The types and locations of the line defects are found critical in determining the spin polarization and the current-voltage (I-V) characteristics of the line defected ZMNRs. For the same defect type, the total currents of the ribbons with the line defects in the centers are lager than those on the edges. And for the same location, the total currents of the systems with the sulfur (S) line defect are larger than the according systems with the molybdenum (Mo) line defect. All the considered systems present magnetism properties. And in the S line defected systems, the spin reversal behaviors can be observed. In both the spin-up and spin-down states of the Mo line defected systems, there are obvious negative differential resistance behaviors. The mechanisms are proposed for these phenomena.

Tuning anisotropic electronic transport properties of phosphorene via substitutional doping.

Using first-principles calculations, we studied the anisotropic electronic transport properties of pristine and X-doped phosphorene (X = B, Al, Ga, C, Si, Ge, N, As, O, S, and Se atoms). The results show that doping different elements can induce obviously different electronic transport characteristics. Moreover, isovalent doping maintains semiconducting characteristics and anisotropic transport properties, while group IV and VI atoms doping can induce metal properties. Meanwhile, Al and Ga substituting P decrease the anisotropic behaviors of transport, and other atom doping still preserves anisotropic characteristics. Interestingly, obvious negative differential resistance behaviors can be observed in C, Si, Ge, O, S, and Se-doped phosphorene.

Axisymmetric All-Carbon Devices with High-Spin Filter Efficiency, Large-Spin Rectifying, and Strong-Spin Negative Differential Resistance Properties

We propose the perfect all-carbon axisymmetric spintronic devices consisting of a zigzag-edged trigonal graphene (ZTG) linked to left and right zigzag-edged graphene nanoribbons (ZGNR) electrodes via carbon atomic chains (CACs). To ensure the stability of the system, the edge carbon atoms are passivated by hydrogen atoms. The self-consistent density functional theory (DFT) calculations show that the simple all-carbon system possesses the prefect spin-filtering property at a wide voltage region from −1.0 to 1.0 V. More importantly, the proposed system can act as a perfect dual spin diode in the antiparallel (AP) spin configuration, and the single-spin rectifying ratio can reach 103. When we add the number of the CACs linked to the left ZGNR electrode, the device shows the obvious single-spin negative differential resistance (NDR) behavior, which originates from the appearance of the localized states in the region of the left ZGNR electrode and ZTG. Meanwhile, the perfect spin-filtering and dual spin-diode ...

Bias tuning charge-releasing leading to negative differential resistance in amorphous gallium oxide/Nb:SrTiO3 heterostructure

Negative differential resistance (NDR) and bipolar resistive switching (RS) phenomena were observed in Au/Ga2O3−x/Nb:SrTiO3/Au heterostructures fabricated by growing amorphous gallium oxide thin films on 0.7%Nb-doped SrTiO3 substrates using pulsed laser deposition technique. The RS behavior is reproducible and stable without the forming process. The NDR phenomenon happened during the course of RS from low resistance state to high resistance state and was dependent much on the applied forward bias. The bias dependent charge releasing from oxygen vacancies was considered to contribute to the NDR behavior. The results show that there is a very close relationship between NDR and RS.

Current controlled negative differential resistance behavior in Co2FeO2BO3 and Fe3O2BO3 single crystals

I–V curves showing negative differential resistance (NDR) are reported for single crystals of Co2FeO2BO3 at 315K and 290K and for Fe3O2BO3 at 300K, 260K and 220K. Resistivity measurements are presented for both systems, parallel and perpendicular to the c axis, in the range 315–120K. The high hysteretic behavior of the I–V curves in Co2FeO2BO3 around room temperature is discussed and the heat dissipated is estimated, suggesting an increase in the sample temperature of almost 22K for the I–V curve at 315K and a dominant contribution of Joule self-heating for the observed NDR. In contrast, insignificant hysteresis is observed on the I–V curves of Fe3O2BO3 around room temperature. The depinning of charge order domains is suggested as the main contribution to the NDR phenomenon for Fe3O2BO3. The high reproducibility of the NDR in the Fe3O2BO3 single crystal allows its use as a low frequency oscillator, as it is demonstrated.

Nitrogen Doping Position-Dependent Rectification of Spin-Polarized Current and Realization of Multifunction in Zigzag Graphene Nanoribbons with Asymmetric Edge Hydrogenation

The magnetic and spin transport properties of asymmetric edge-hydrogenated zigzag graphene nanoribbons (ZGNRs) selectively doped with nitrogen atoms were investigated using spin-polarized density functional theory and non-equilibrium Green’s function. Results show that the rectifying performance of spin-polarized current with a ratio higher than 105 can be modulated by changing the positions of the nitrogen dopant. Complete spin filtering (100%) and excellent negative differential resistance behaviors were observed in the ZGNR junctions. These doping position-dependent spin transport characteristics were further tested by shifting from the odd-numbered zigzag-shaped C chains (N Z) to the even-numbered N Z in ZGNRs. This study suggests that adopting a suitable nitrogen doping position could be an effective approach to significantly enhance the rectifying behavior of asymmetric edge-hydrogenated ZGNRs, which are promising materials for multifunctional spintronic devices.

Unipolar resistive switching in metal oxide/organic semiconductor non-volatile memories as a critical phenomenon

Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 1017 m−2. We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching.

Effect of electrode twisting on electronic transport properties of atomic carbon wires

We investigate the electron transport properties in atomic carbon wires between two zigzag graphene nanoribbon (ZGNR) electrodes by applying nonequilibrium Green's functions in combination with the density-functional theory. It shows that the ZGNR electrode twisting can modulate the conductance of the atomic carbon wire-graphene junctions remarkably. Typical currents of devices with odd carbon wires are much higher than currents of devices with even carbon wires to exhibit even-odd behavior. The negative differential resistance behaviors are only found in the devices with odd carbon wires. When the right ZGNR electrode is twisted, the curvatures of the current–voltage characteristics change remarkably upon twisted angles. The current will decrease by up to 5 orders of magnitude when the twisted angle reaches to 90°. That means the atomic carbon wire-graphene junctions can be made as a mechanical switching.

Negative differential resistance, rectifying performance and switching behaviour in carbon-chain based molecular devices

Using non equilibrium Green's function formalism coupled with density functional theory, we carry out electronic transport calculation in two types of molecular devices, one constructed by linear monoatomic carbon chain (···C–C–C–C ···) and the other by two carbon chains capped with a phenyl ring (···C–C–Ph–C–C···), sandwiched between two z-shape electrodes, constructed by zigzag-armchair-zigzag (zz-ac-zz) graphene nanoribbons (GNRs). The potential difference between the z-shape contacts can be varied by employing an external d.c. voltage source. Thus, one may observe the variation of conductivity through the channels. The current–voltage (I–V) characteristics of the proposed resistors show N-type negative differential resistance (NDR), within a particular voltage region. The figure of merit or PVR (peak to valley) ratio (Ipeak/Ivalley) gets significantly increased, on capping the chains with phenyl ring. A higher value of PVR in I–V characteristics enhances the possibility of applications utilizing NDR. The calculated I–V characteristic is asymmetric and the rectification ratio is found to be 7, in case of the linear carbon chain.The rectification ratio R(V) = I(V)/I(−V) is an important parameter which determines, its suitability as rectifying device. It has been demonstrated that on varying the conformation of the phenyl ring with respect to the plane of electrodes, the transport properties of the system can be modulated. Interestingly, I–V characteristics are asymmetric and show dual NDR peaks in perpendicular conformation of the phenyl ring, with respect to the electrodes in the (···C–C–Ph–C–C···) system. The figure of merit is found to be respectively 8 and 51 for the first and second NDR regions. The later value is extremely high, making it an excellent candidate for potential applications. Moreover, the multi peak NDR device may be widely used in multiple-valued logics. Only a limited number of multiple NDR peak molecular-based nano systems have so far been reported, which are quite complex; by contrast the present system seems to be quite simple. The physical phenomenon of NDR was explained in the light of molecular projected self-consistent Hamiltonian (MPSH) and also the evolution of the frontier molecular orbitals (HOMO–LUMO) as well as transmission under various external bias voltages.

Structurally Driven Enhancement of Resonant Tunneling and Nanomechanical Properties in Diamond-like Carbon Superlattices.

We report nitrogen-induced enhanced electron tunnel transport and improved nanomechanical properties in band gap-modulated nitrogen doped DLC (N-DLC) quantum superlattice (QSL) structures. The electrical characteristics of such superlattice devices revealed negative differential resistance (NDR) behavior. The interpretation of these measurements is supported by 1D tight binding calculations of disordered superlattice structures (chains), which include bond alternation in sp(3)-hybridized regions. Tandem theoretical and experimental analysis shows improved tunnel transport, which can be ascribed to nitrogen-driven structural modification of the N-DLC QSL structures, especially the increased sp(2) clustering that provides additional conduction paths throughout the network. The introduction of nitrogen also improved the nanomechanical properties, resulting in enhanced elastic recovery, hardness, and elastic modulus, which is unusual but is most likely due to the onset of cross-linking of the network. Moreover, the materials' stress of N-DLC QSL structures was reduced with the nitrogen doping. In general, the combination of enhanced electron tunnel transport and nanomechanical properties in N-DLC QSL structures/devices can open a platform for the development of a new class of cost-effective and mechanically robust advanced electronic devices for a wide range of applications.

Negative differential resistance and stable conductance switching behaviors of salicylideneaniline molecular devices sandwiched between armchair graphene nanoribbon electrodes

By applying nonequilibrium Green's functions in combination with the density-functional theory, we investigate the electron transport properties of the salicylideneaniline molecule sandwiched between two armchair graphene nanoribbon (AGNR) electrodes. It shows that the width of the AGNR electrodes plays a significant role in the transport properties of the salicylideneaniline molecular junctions. The current–voltage characteristics of the salicylideneaniline molecule sandwiched between 8AGNR electrodes can perform a stable conductance switching behavior at the bias region [1.2 V, 1.6 V] when the molecule translates between the trans-enol form and the trans-keto form. When the electrodes change to 7AGNR, a remarkable negative differential resistance behavior can be found in the salicylideneaniline molecular device at the trans-keto form. That means the salicylideneaniline molecule can perform different functions when it connects to the different AGNR electrodes.

Highly efficient spin polarizer based on individual heterometallic cubane single-molecule magnets

The spin-polarized transport across a single-molecule magnet [Mn3Zn(hmp)3O(N3)3(C3H5O2)3]·2CHCl3 has been investigated using a density functional theory combined with Keldysh non-equilibrium Green’s function formalism. It is shown that this single-molecule magnet has perfect spin filter behaviour. By adsorbing Ni3 cluster onto non-magnetic Au electrode, a large magnetoresistance exceeding 172% is found displaying molecular spin valve feature. Due to the tunneling via discrete quantum-mechanical states, the I–V curve has a stepwise character and negative differential resistance behaviour.

Reconstructed graphene nanoribbon as a sensor for nitrogen based molecules

The usage of reconstructed zigzag graphene nanoribbon (RZGNR) as a sensor for nitrogen based chemicals is being analyzed. The principle of sensing is based on reaction of nitrogen atom with the edge of RZGNR, which causes a measurable change in electrical properties of the nanoribbon. In order to characterize the RZGNR based sensor, reaction mechanisms of a graphene nanoribbon with an ammonia molecule (NH3) are analyzed in detail by using ab initio and DFT calculations. Ammonia molecule reacts with RZGNR via a two stage reaction. The first stage represents the rate limiting step of the entire reaction and produces a reaction intermediate. The reaction intermediate undergoes proton transfer as a second stage reaction in order to form energetically stable product. The negative differential resistance (NDR) behavior was noticed in our model of RZGNR. Upon reaction with the NH3 molecule, the electronic properties of RZGNR are significantly modified and the observed NDR behavior disappears. Present findings show that adsorption of guest NH3 molecule can be sensed by the change in current passing through the ribbons.

Current through fullerenes with calcium atom encapsulated

A theoretical study of quantum transport through Ca@C60 or Ca2+@C60 molecules is considered by using the non-equilibrium Green’s function (NEGF) formalism. The effects of gate and bias voltages, encapsulation, position and displacement of ion into the cage are important factors in endohedral molecular junction that are considered in the calculations of our study. The current value against the bias voltage, independent of the contacts strength, decreases when the calcium atom lies far from the cage center. Also, negative differential resistance (NDR) behavior is observed when it is in center of fullerene.

Effect of length and negative differential resistance behavior in conjugated molecular wire tetrathiafulvalene devices

The electronic transport properties of molecular devices constructed by conjugated molecular wire tetrathiafulvalene (TTF) have been studied by applying nonequilibrium Green’s functions in combination with the density-functional theory. Two molecular junctions with different wire lengths have been considered. The results show that the current–voltage curves of TTF devices can be modulated by the length of the molecular wire and negative differential resistance behaviors are observed in these systems. The mechanisms have been proposed for the length effect and negative differential resistance behavior.

Lithography-Free Fabrication of Core-Shell GaAs Nanowire Tunnel Diodes.

GaAs core-shell p-n junction tunnel diodes were demonstrated by combining vapor-liquid-solid growth with gallium oxide deposition by atomic layer deposition for electrical isolation. The characterization of an ensemble of core-shell structures was enabled by the use of a tungsten probe in a scanning electron microscope without the need for lithographic processing. Radial tunneling transport was observed, exhibiting negative differential resistance behavior with peak-to-valley current ratios of up to 3.1. Peak current densities of up to 2.1 kA/cm(2) point the way to applications in core-shell photovoltaics and tunnel field effect transistors.

The integrated spintronic functionalities of an individual high-spin state spin-crossover molecule between graphene nanoribbon electrodes

The spin-polarized transport properties of a high-spin-state spin-crossover molecular junction with zigzag-edge graphene nanoribbon electrodes have been studied using density functional theory combined with the nonequilibrium Green’s-function formalism. The molecular junction presents integrated spintronic functionalities such as negative differential resistance behavior, spin filter and the spin rectifying effect, associated with the giant magnetoresistance effect by tuning the external magnetic field. Furthermore, the transport properties are almost unaffected by the electrode temperature. The microscopic mechanism of these functionalities is discussed. These results represent a step toward multifunctional molecular spintronic devices on the level of the individual spin-crossover molecule.

Observation of room temperature negative differential resistance in solution synthesized ZnO nanorod

We report the observation of negative differential resistance (NDR) in solution synthesized ZnO nanorod. The ZnO nanorod was fabricated as a two terminal planar device using lithographically patterned Au electrodes. The measured current–voltage response of the device has shown a negative differential resistance behavior. The peak-to-valley current ratio of the NDR is found to be greater than 4. The mechanism of this observed NDR effect has been explained based on charge trapping and de-trapping at the nanoscale contacts. It is the first observation of negative differential resistance effect in solution synthesized ZnO nanorod.