Negative Differential Conductance Phenomenon Research Articles

H/O edge passivated B/N co-doped armchair graphene nanoribbon field-effect transistors, based on first principles

This study employs the nonequilibrium Green’s function method in conjunction with density functional theory to fabricate and analyze a Graphene Nanoribbon Field-Effect Transistor (GNRFET). The co-doping of B and N creates built-in electric fields, thereby reducing leakage current. The results demonstrate effective control performance of planar gates, as evidenced by an increase in IDS with rising gate voltage. Furthermore, a negative differential conductance phenomenon is observed at bias voltages exceeding 0.7 V, exhibiting correlation with transmission spectra and energy band structures. To precisely illustrate the electron distribution within the doped scattering region, calculations involving transport paths, the molecular projection self-consistent Hamiltonian (MPSH), and the emission eigenvalues and eigenstates of the device are conducted. This research provides a reference for exploring and developing smaller and more energy-efficient AGNR field effect transistor designs and implementations. The principal objective of this paper is to investigate the potential applications of these smaller, more energy-efficient devices.

Electrical conductance of conical nanopores: Symmetric and asymmetric salts and their mixtures.

We have studied experimentally the electrical conductance-voltage curves of negatively and positively charged conical nanopores bathed in ionic solutions with monovalent, divalent, and trivalent cations at electrochemically and biologically relevant ionic concentrations. To better understand the interaction between the pore surface charge and the mobile ions, both single salts and salt mixtures have been considered. We have paid attention to the effects on the conductance of the cation valency, the pore charge asymmetry, and the pore charge inversion phenomena due to trivalent ions, both in single salts and salt mixtures. In addition, we have described how small concentrations of multivalent ions can tune the nanopore conductance due to monovalent majority ions, together with the effect of these charges on the additivity of ionic conductance and fluoride-induced negative differential conductance phenomena. This compilation and discussion of previously presented experimental data offers significant insights on the interaction between fixed and mobile charges confined in nanoscale volumes and should be useful in establishing and checking new models for describing ionic transport in the vicinity of charged surfaces.

Giant Spin Current Rectification Due to the Interplay of Negative Differential Conductance and a Non-Uniform Magnetic Field.

In XXZ chains with large enough interactions, spin transport can be significantly suppressed when the bias of the dissipative driving becomes large enough. This phenomenon of negative differential conductance is caused by the formation of two oppositely polarized ferromagnetic domains at the edges of the chain. Here, we show that this many-body effect, combined with a non-uniform magnetic field, can allow for a high degree of control of the spin current. In particular, by studying all of the possible shapes of local magnetic fields potentials, we find that a configuration in which the magnetic field points up for half of the chain and down for the other half, can result in giant spin-current rectification, for example, up to for a system with only 8 spins. Our results show clear indications that the rectification can increase with the system size.

Local magnetic moments and electronic transport in closed loop quantum dot systems: A case of quadruple quantum dot ring at and away from equilibrium

We apply the non-equilibrium functional renormalization group approach treating flow of the electronic self-energies, to describe local magnetic moments formation and electronic transport in a quadruple quantum dot (QQD) ring, coupled to leads, with moderate Coulomb interaction on the quantum dots. We find that at zero temperature depending on parameters of the QQD system the regimes with zero, one, or two almost local magnetic moments in the ring can be realized, and the results of the considered approach in equilibrium agree qualitatively with those of more sophisticated fRG approach treating also flow of the vertices. It is shown that the almost formed local magnetic moments, which exist in the equilibrium, remain stable in a wide range of bias voltages near equilibrium. The destruction of the local magnetic moments with increasing bias voltage is realized in one or two stages, depending on the parameters of the system; for two-stage process the intermediate phase possesses fractional magnetic moment. We present zero-temperature results for current-voltage dependences and differential conductances of the system, which exhibit sharp features at the transition points between different magnetic states. The occurrence of interaction induced negative differential conductance phenomenon is demonstrated and discussed. For one local moment in the ring and finite hopping between the opposite quantum dots, connected to the leads, we find suppression of the conductance for one of the spin projections in infinitesimally small magnetic field, which occurs due to destructive interference of different electron propagation paths and can be used in spintronic devices.

Negative differential conductance in nano-scale normal metal/superconductor/normal metal junctions featuring Fe1 + y Te1 − x Se x

Iron-based superconductors have been the subject of intensive study due to their high transition temperature and intriguing physical mechanisms. We describe a unique experimental approach to fabricate nano-scale normal metal/superconductor/normal metal junctions involving microcrystals of Fe1 + y Te1 − x Se x , for which we have observed a distinct phenomenon of negative differential conductance (NDC) dips along with multiple plateau features in differential conductance spectra. The evolution of the NDC dips and the plateau features is further explored as a function of both temperature and magnetic field, and their physical origin is discussed.

Numerical simulation of amplification of space charge waves in n-InP films

a b s t r a c t The non-linear interaction of space charge waves including the amplification in microwave and millimeter wave range in n-InP films, possessing the negative differential conductance phenomenon, is investigated theoretically. Both the amplified signal and the generation of harmonics of the input signal are demon- strated, which are due to non-linear effect of the negative differential resistance. It is possible to observe an amplification of the space charge waves in n-InP films of submicron thicknesses at essentially higher frequencies f <70 GHz, when compared with n-GaAs films f < 44 GHz. The increment observed in the gain is due to the larger dynamic range in n-InP than in n-GaAs films. © 2011 Elsevier B.V. All rights reserved.

Investigation of Resistance Switching Properties in Undoped and Indium Doped SrTiO3 Thin Films Prepared by Pulsed Laser Deposition

AbstractIn this paper, the undoped SrTiO3 (STO) and Indium doped STO (SrTi1-xInxO3: STIO) thin films were grown on Pt/Ti/SiO2/Si substrates by pulsed laser deposition with low substrate temperature. For undoped STO film, the influences of the forming processes on their resistive switching properties were studied by current and voltage controlled I-V sweeps, respectively. An obvious current controlled negative differential conductance phenomenon was found in both polarities of the electrical field. However, for low Indium doped STIO (x=0.1), the filament related resistance switching was observed in both the current and voltage I-V sweeps. And for high Indium doped STIO (x=0.2), a resistance switching with a reverse direction change to that in undoped STO can be obtained by a proper forming process. Based on these results, the reversible change of the Schottky like barrier at the grain boundary by the migration of oxygen vacancies were proposed to interpret the mechanism of the resistance switching.

Effect of hydrogen molecules on the electronic transport through atomic-sized metallic junctions in the superconducting state

In this paper the interaction of hydrogen molecules with atomic-sized superconducting nanojunctions is studied. It is demonstrated by conductance histogram measurements that the superconductors niobium, tantalum, and aluminum show a strong interaction with hydrogen, whereas for lead a slight interaction is observed and for tin and indium no significant interaction is detectable. For Nb, Ta, and Pb the subgap method is applied to determine the transmission eigenvalues of the nanojunctions in hydrogen environment. It is shown that the behavior of Nb and Ta nanojunctions is strongly modified by hydrogen molecules as reflected by the pronounced changes in the conductance histogram, the appearance of extremely long conductance traces, and the observation of negative differential conductance phenomenon in the $dI/dV$ curve. Surprisingly the transport properties based on the measured transmission eigenvalues are similar to those of pure junctions. Our results imply that in Nb and Ta the interaction with hydrogen causes a plastic, ductile behavior and the formation of long nanoscale necks, but no well-defined single-molecule contacts are formed, and the transport properties are still dominated by Nb and Ta.

The Synthesis of Molecular Rods with a Transversal Push‐Pull System

AbstractThe design and synthesis of the molecular cruciforms 1–4 consisting of an oligophenylene‐ethynyl backbone with an acetyl‐protected sulfur anchor group on one end and a crossing oligophenylene cross‐bar with terminal trifluoromethyl and dimethylamino groups as transversal push‐pull system are reported. These cruciforms 1–4 are model compounds to investigate electronic potential‐dependent switching properties of molecular junctions. While the oligophenylene‐ethynyl backbone is responsible for the electronic transport properties, the transversal push‐pull system should alter the tilt angle of the rod upon alignment in an electric field. As the tunnel distance at the rods end to the opposite electrode depends on the tilt angle of the rod, a considerable dependence of the transport current on the tilt angle is expected. The investigation of such transport mechanisms with the model compounds 1–4 may unravel the origin of negative differential conductance phenomena in devices consisting of sandwiched self assembled monolayers between two electrodes. The reported cruciform structures display limited stability features in the presence of acids. Their assembly is based on metal catalyzed cross coupling reactions with the chromatographic separation of two, on opposite sides monoprotected regioisomers as key step.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)

Numerical simulations of propagation of SCWs in strained Si/SiGe heterostructures at 4.2 and 77 K

The negative differential conductance phenomenon that occurs in strained Si/SiGe hetrostructures at low temperatures, have been used to perform numerical simulations of the propagation and amplification of space charge waves (SCWs). The 2D numerical simulations indicate that amplification of SCWs on the surface of the heterostructure may occur up to frequencies of 40 GHz when cooled down to 77 K, and up to 44 GHz at 4.2 K.

Synthesis of Macrocyclic Molecular Rods as Potential Electronic Devices

AbstractThe design and synthesis of the macrocycles 1 and 2 as model compounds for the investigation of negative differential conductance phenomena in molecular junctions are reported. The macrocycles 1 and 2 comprise a molecular rod subunit consisting of three ethynyl‐linked phenyl rings. While the rotational freedom along the rod axis of both terminal phenyl rings is limited by the macrocyclic frame, the central phenyl ring is revolving. The rod substructure is terminally functionalized with acetyl‐protected thiol groups to enable its immobilization between gold contacts. The central phenyl ring is functionalized with one and two nitro groups for 1 and 2, respectively. The nitro groups are of particular importance as i) both macrocycles are model compounds to investigate a hypothetical intramolecular interaction of the nitro group with the opposite macrocyclic subunits and ii) the nitro group(s) result in limited thermal stability of the compounds due to the intramolecular rearrangement to macrocycles comprising isatogen subunits. These highly functionalized macrocycles have been assembled by acetylene scaffolding strategies in combination with functional group transformation chemistry.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2006)

Two-dimensional simulations of amplification of space charge waves in a strained Si/SiGe heterostructure at 77 K

We theoretically investigated the propagation and amplification of space charge waves on the surface of a strained Si/SiGe heterostructure at 77K, using the negative differential conductance phenomenon. In this work, we also have done a comparison between the n-GaAs thin film and strained Si/SiGe heterostructure with respect to the propagation of space charge waves. We have obtained results in 2D of propagation and amplification of space charge waves in a strained Si/SiGe heterostructure until for frequencies f<40GHz.

Anomalous negative differential conductance in nanomechanical double barrier tunneling structures

Anomalous negative differential conductance (NDC) is observed along with a Coulomb staircase in the tunneling current-voltage curves of a nanomechanical double barrier tunneling structure consisting of a scanning vibrating probe/vacuum/colloidal Au nanodot/1,6-hexanedithiol/Au substrate. The peak voltages in the NDC phenomena when the sample voltage is applied correspond well with that of the probe voltage. We discuss a candidate mechanism of the NDC phenomena by taking into account the modulation of the tunneling rate between the scanning probe and an Au nanodot due to the nanometer-scale probe vibration.

Electromechanical single electron transistor in strong dissipative structure

In the experiment of electromechanical single electron transistor, two tunneling junctions are not the same completely because of manufacturing processes or quantum effects. We simplify these complexities as an asymmetric-junction device with two unequal initial capacitances. A model system of a single electron transistor with strong dissipation is investigated, where the metal cluster of mechanical motion is coupled to drain and source electrodes. This semiclassical system considers the difference between drain capacitor and source capacitor, simulated by using Monte Carlo methods. The voltage regions are distributed into the efficient-shuttle region and the non-shuttle region by the shuttle mechanism of the island. A symmetric-junction device only works in the efficient-shuttle region. However, both kinds of mechanisms occur in an asymmetric-junction device, where we observe restrained currents and negative differential conductance phenomena.

Sudden Suppression of Electron-Transmission Peaks in Finite-Biased Nanowires

Negative differential conductance (NDC) is expected to be an essential property to realize fast switching in future electronic devices. We here present a thorough analysis on electron transmission of a simple atomic-scale model consisting of two rectangular prisms, and clarify the detailed mechanism of the occurrence of NDC phenomenon in terms of the changes of local density of states upon applying bias voltages to the electrodes. On boosting up bias voltages, we observe the sudden suppression of transmission peaks which results in NDC behavior in the current–voltage characteristic. This suppression is explained by the fact that when the bias voltage exceeds a certain threshold, the conduction channels contributing to the current flow are suddenly closed up to deny the electron transportation.

Physical interpretations concerning nonlinear conductivity phenomena across no-load switching contacts

Data that aid physical interpretations concerning no-load switching contacts under high current density operation are presented. Measurements were performed on industrial switches with the following nominal values: isolation switches 400 V/100 A, isolation switches 20 kV/200 A, and fuse isolators 20 kV/100 A. It is shown that beyond a threshold field intensity (corresponding to smaller currents than the nominal values) nonlinear I-V relationships may develop, leading to bistability and negative differential conductance phenomena. This has been attributed to the dominating tunneling current component between oxidized (or nonideally contacted) metallic surfaces at high electric fields, resulting in an increased effective area of contact. The well-established metal-insulator-metal (MIM) theory, as well as that concerning nonlinear current voltage phenomena developing in insulating solids at high electric fields, provide the required theoretical basis for the interpretation of the obtained curves.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>