Large Negative Differential Resistance Research Articles

Large magnetoresistance and spin negative differential resistance in photoisomers-based molecular spin valves

By using non-equilibrium Green's functions in combination with density functional theory, the spin transport properties of photoisomers-based molecular spin valves constructed by salicylidene methylamine connected with two cobalt- dibenzotetraaza[14]annulene (Co-DBTAA) complex molecules via acetylene linkers are explored. A large magnetoresistance (MR) effect with a MR ratio larger than 104 can be observed in the molecular spin valves whether salicylidene methylamine is in the cis-enol form or the trans-keto form. Moreover, spin negative differential resistance (NDR) effects are also observed in the photoisomers-based molecular spin valves. The spin transport mechanisms are explored for MR and spin NDR effects observed in the molecular spin valves.

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.

Regulation and mechanism of graphene electrode bending on negative differential resistance of 2-phenylpyridine molecular devices

Combining non-equilibrium Green’s function with density functional theory, we study the electronic transport properties of the molecular devices comprised of 2-phenylpyridine and zigzag graphene nanoribbon (ZGNR) electrodes. The <i>I-V</i> characteristics and transmission coefficients under external voltage biases are analyzed, and the results show that the negative differential resistance (NDR) is effectively adjusted by the bending of ZGNR electrode, which reduces the peak voltage (<i>V</i><sub>p</sub>) and increases the peak-valley ratio (PVR) of the device. When the electrode bending angle is 15°, the PVR of device M2 is a maximum value of 12.84 and <i>V</i><sub>p</sub> is 0.1 V, which is low enough for practical applications. The transmission spectra, the density of states and the real-space scattering state distribution at <i>E</i><sub>f </sub> of device under zero bias explain that the weaker coupling between the molecules and the electrodes is caused by the bending of the ZGNR electrode, which might be responsible for the adjustability of NDR. The analysis shows that the bending of the electrode changes the electronic structure between the 2-phenylpyridine molecule and the ZGNR electrode, and then changes the wave functions overlap between them, the coupling between the molecule and the electrodes gets weaker. An external bias can induce the level to shift. The transmission coefficient for the weaker coupling between the molecules. The electrodes can fluctuate wildly from level to level, and large NDR effect under very low bias is obtained with the variation of external bias. Therefore, for highly symmetric molecular devices, the electronic transport properties can be effectively adjusted by changing the coupling between the central molecule and the electrodes. Our investigations indicate that the 2-phenylpyridine molecular device with ZGNR electrodes may have potential applications in the field of low-power dissipation molecules device.

Large negative differential resistance in triangular and square cyclopropyllithium derivative molecule

Different from hexagon-based carbon structures, the recently synthesized cyclopropyllithium derivative molecule of [{μ-c-CSiMe3C2H4}Li]4 possesses both triangular and quadrilateral rings, which is expected to exhibit interesting electronic features. Based on first-principles calculations, the electronic transport of this molecule contacted with carbon linear chain electrodes is investigated. Large negative differential resistance (NDR) phenomenon is observed. Moreover, the NDR is found to be robust to the doping on side branches which are perpendicular to the transport direction, but sensitive to the doping on main branches, which has a great influence on the NDR. NDR is found in all the doping cases, suggesting it is the intrinsic feature of such systems. Further analysis shows that, it is the suppression of the transmission peak induced by the change of energy states from delocalization to localization around the Fermi level that triggers the NDR. Our findings may throw light on the development of future molecular devices.

Electroluminescence of atoms in a graphene nanogap.

Here, we report light emission from single atoms bridging a graphene nanogap that emit bright visible light based on fluorescence of ionized atoms. Oxygen atoms in the gap shows a peak emission wavelength of 569 nm with a full width at half maximum (FWHM) of 208 nm. The energy states produced by these ionized oxygen atoms bridging carbon atoms in the gap also produce a large negative differential resistance (NDR) in the transport across the gap with the highest peak-to-valley current ratio (PVR = 45) and highest peak current density (~90 kA/cm2) ever reported in a solid-state tunneling device. While tunneling transport has been previously observed in graphene nanogaps, the bridging of ionized oxygen observed here shows a low excess current, leading to the observed PVR. On the basis of the highly reproducible light emission and NDR from these structures, we demonstrate a 65,536-pixel light-emitting nanogap array.

Redox-mediated Negative Differential Resistance (NDR) Behavior in Perylenediimide Derivative: A Supramolecular Approach.

Deaggregated perylenediimide (PDI) derivatives exhibit exceptionally high quantum yields, photostability and appropriate molecular features for organic electronics. This work demonstrates a metal-dye-metal framework with a large and stable negative differential resistance (NDR) at ambient conditions, built using a supramolecular strategy. The deaggregation achieved through the encapsulation of the bay-substituted phenyl groups of aggregated (l/d)-Phe-PDI dyes by the β-CD macrocyclic host is validated through detailed spectroscopic and imaging techniques. The host-guest interaction resulted in a dramatic enhancement in the emission yield from 0.28 to 0.90. In the thin film deposits, the β-CD/(l/d)-Phe-PDI complex displayed well-connected sheet-like morphology, whereas the uncomplexed (l/d)-Phe-PDI dye remained as scattered lumps. The large and reversible I-V characteristics displaying strong NDR behavior is attributed to the oxidation/reduction processes involving the rigid π-rich PDI core and is stable at least for about six months at ambient conditions, a promising system for organic electronics applications.

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.

Large negative differential resistance behavior in arsenene nanoribbons induced by vacant defects

We have studied the electronic structures of arsenene nanoribbons with different edge passivations by employing first-principle calculations. Furthermore, the effects of the defect in different positions on the transport properties of arsenene nanoribbons are also investigated. We find that the band structures of arsenene nanoribbons are sensitive to the edge passivation. The current-voltage characteristics of unpassivated and O-passivated zigzag arsenene nanoribbons exhibit a negative differential resistance behavior, while such a peculiar phenomenon has not emerged in the unpassivated and O-passivated armchair arsenene nanoribbons. The vacant defects on both top and bottom edges in unpassivated armchair arsenene nanoribbon can make its current-voltage characteristic also present a negative differential resistance behavior. After expanding the areas of the top and bottom defects in unpassivated armchair arsenene nanoribbon, the peak-to-valley ratio of the negative differential resistance behavior can be enlarged obviously, which opens another way for the application of arsenene-based devices with a high switching ratio.

Spin-dependent resonant tunneling and magnetoresistance in Ni/graphene/h-BN/graphene/Ni van der Waals heterostructures

Abstract Future development of spintronic devices urgently requires an advanced control method of spin current. Combining graphene with other various characteristic two-dimensional crystals in different ways can produce a new class of functional materials, which offers a unique platform for spintronics. A specific van der Waals heterostructure consisting of graphene and hexagonal boron nitride (h-BN) as the barrier layer in magnetic tunnel junctions (MTJs) is proposed in this paper. This heterostructure device combines the strong spin filtering effect of graphene/ferromagnet interface and the resonant tunneling effect of graphene/h-BN/graphene van der Waals heterostructure. We demonstrate an effective approach to control spin current based on the bias tunability of the spin resonance tunneling transport. Theoretical research unambiguously reveals that spin resonance appears when the electronic spectra of spin electron in two graphene layers are aligned, which results in a large magnetoresistance and negative differential resistance in the device. The efficient bias controllability of spin current, combined with the excellent magnetoresistance behavior, can be the key building blocks in future spin-based magnetic detection and high-frequency logic devices.

Large negative differential resistance effect induced by boron-doping in zigzag phagraphene nanoribbon junctions

By applying nonequilibrium Green’s function in combination with the density-functional theory, we investigate the electronic transport properties of boron or nitrogen doped zigzag phagraphene nanoribbon junctions. Our calculated results show that the negative differential resistance effect could be observed in zigzag phagraphene nanoribbon junction. Moreover, the peak to valley ratio of the negative differential resistance significantly increase from 1.6 to 111.32, when the junction is doped by boron atoms. We rationalize the mechanism leading to negative differential resistance by providing a detailed analysis of transmission spectra and transmission pathways.

Spin-Conserving Resonant Tunneling in Twist-Controlled WSe2-hBN-WSe2 Heterostructures.

We investigate interlayer tunneling in heterostructures consisting of two tungsten diselenide (WSe2) monolayers with controlled rotational alignment, and separated by hexagonal boron nitride. In samples where the two WSe2 monolayers are rotationally aligned we observe resonant tunneling, manifested by a large conductance and negative differential resistance in the vicinity of zero interlayer bias, which stem from energy- and momentum-conserving tunneling. Because the spin-orbit coupling leads to coupled spin-valley degrees of freedom, the twist between the two WSe2 monolayers allows us to probe the conservation of spin-valley degree of freedom in tunneling. In heterostructures where the two WSe2 monolayers have a 180° relative twist, such that the Brillouin zone of one layer is aligned with the time-reversed Brillouin zone of the opposite layer, the resonant tunneling between the layers is suppressed. These findings provide evidence that, in addition to momentum, the spin-valley degree of freedom is also conserved in vertical transport.

Large negative differential resistance in graphene nanoribbon superlattices

A graphene nanoribbon superlattice with a large negative differential resistance (NDR) is proposed. Our results show that the peak-to-valley ratio (PVR) of the graphene superlattices can reach 21 at room temperature with bias voltages between 90–220 mV, which is quite large compared with the one of traditional graphene-based devices. It is found that the NDR is strongly influenced by the thicknesses of the potential barrier. Therefore, the NDR effect can be optimized by designing a proper barrier thickness. The large NDR effect can be attributed to the splitting of the gap in transmission spectrum (segment of Wannier–Stark ladder) with larger thicknesses of barrier when the applied voltage increases.

Large Negative Differential Resistance and Rectification from a Donor-σ-Acceptor Molecule in the Presence of Dissimilar Electrodes.

A multifunctional spin quantum device obtained by sandwiching 11-mercaptoundeca-2,4,8,10-tetraenenitrile, a donor-σ-acceptor molecule, between gold and iron electrodes is proposed. The device can act as a spin rectifier at lower bias and also exhibits negative differential resistance (NDR) after attaining a bias of 1.3 V. The rectification feature is quite prominent in the spin-up channel, with an appreciable rectification ratio of 68, whereas the NDR indicator, that is, the peak to valley ratio (≈10) of the current-voltage characteristics after 1.3 V, is also quite significant. To understand the origin of this in silico observation, nonequilibrium green's function based DFT calculations have been performed. Analyses reveal that both properties originate from the bias-independent energy offset between the frontier orbitals and electrode Fermi levels, popularly known as Fermi-level pinning. More precisely, rectification results from the Fermi-level pinning of the HOMO and LUMO with the gold and iron electrodes, respectively; the Fermi-level pinning forces a HOMO-LUMO crossover that helps to explain the origin of the NDR.

Charge Effect on Current-Voltage Characteristics of MoS2 Nanoribbon

Charge effect on I-V characteristics of single layer zigzag nanoribbon MoS2 (Z-NR-MoS2) have been studied using first-principles quantum transport calculations. We show that the internal electric polarization is strongly dependent on dominating edge atoms; hence, two structures with different edge atoms are investigated. Our calculations show that due to this internal polarization a large negative differential resistance (NDR) has been observed.

Multifunctional Homogeneous Lateral Black Phosphorus Junction Devices

We demonstrate a controllable doping technique of few-layer black phosphorus (BP) via surface charge transfer using an ionic liquid mixture of EMIM(C6H11N2+):TFSI(C2F6NO4S2–) [EMIM:TFSI, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide]. A wide range of hole carrier densities, from 1011 cm–2 (nondegenerate) to 1013 cm–2 (degenerate), can be obtained by controlling the weight percentage of the ionic liquid mixture. The doping method we proposed in this paper can be applied to make a multifunctional homogeneous lateral p–n junction device. By doping a fraction of the BP sample and by applying a gate voltage to the other fraction of the BP, we obtain homogeneous lateral p+–p, p+–n, p+–n+ junction diodes in a single BP channel. The homogeneous lateral BP p+–p and p+–n junctions display ideal rectifying behavior and a much stronger photoresponse due to the built-in potential. Furthermore, at high positive gate voltages, the interband tunneling enables the homogeneous lateral p+–n+ junction transistors to provide both a negative differential resistance (NDR) and a negative transconductance (NTC) in the current–voltage characteristics at room temperature. On the basis of our results, it is possible to build novel devices utilizing the large NDR and NTC in BP such as amplifiers, oscillators, and multivalued logic systems.

Imperfect two-dimensional topological insulator field-effect transistors

To overcome the challenge of using two-dimensional materials for nanoelectronic devices, we propose two-dimensional topological insulator field-effect transistors that switch based on the modulation of scattering. We model transistors made of two-dimensional topological insulator ribbons accounting for scattering with phonons and imperfections. In the on-state, the Fermi level lies in the bulk bandgap and the electrons travel ballistically through the topologically protected edge states even in the presence of imperfections. In the off-state the Fermi level moves into the bandgap and electrons suffer from severe back-scattering. An off-current more than two-orders below the on-current is demonstrated and a high on-current is maintained even in the presence of imperfections. At low drain-source bias, the output characteristics are like those of conventional field-effect transistors, at large drain-source bias negative differential resistance is revealed. Complementary n- and p-type devices can be made enabling high-performance and low-power electronic circuits using imperfect two-dimensional topological insulators.

Insight into negative differential resistance in polyphenylene molecular device with graphene electrodes

The organic molecule deposited between gaphene electrodes to form a molecular device has been demonstrated experimentally. Motivated by this case, devices consisting of the polyphenylene molecule bonded covalently with armchair-edged graphene nanoribbon (AGNR) electrodes are constructed and the selective doping with N atom is considered theoretically. Our modeling calculations show that such devices hold the nonlinear and doping-site-dependent transport properties, prominently with multi-peak NDR (negative differential resistance) effect. And, for a peculiar doping site, a very large NDR can be observed, which could be attributed to interactions of the molecular core and doped AGNR electrodes, namely, these hybridized wave functions hold distinctly different delocalization in different benzene rings of the polyphenylene molecule when the applied bias is altered. Also shown is that this large NDR is robust regarding the length increasing and rotation of molecule.

S-parameter characterization and lumped-element modelling of millimeter-wave single-drift impact-ionization avalanche transit-time diode

Five silicon (Si) p++–n−–n++ samples were grown at various doping concentrations (1.0 × 1017–2.2 × 1017 cm−3) in an n− layer by using the reduced-pressure CVD technique. By using these samples, 30 × 2 µm2 single-drift (SD) impact-ionization avalanche transit-time (IMPATT) diodes were processed with Si-based monolithic millimeter-wave integrated circuit (SIMMWIC) technology.,) The samples within a small process window exhibited a large negative differential resistance at approximately the avalanche frequency, as confirmed by small-signal S-parameter characterization. A model based on depletion width was given to explain the conditions for the appearance of the negative differential IMPATT resistance, which is the basis of millimeter-wave amplifier and oscillator applications. Furthermore, a measurement-based small-signal lumped-element model was established to describe the IMPATT functionality from the circuit component aspect. This lumped-element model shows a negative differential resistance within a well-defined range in the given element parameters, which can explain the experimental observations.

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.

Design molecular rectifier and photodetector with all-boron fullerene

Abstract All-boron fullerene B 40 is a highly stable molecule, which has been successfully synthesized in recent experiment. In this paper, with Au as two electrodes, the single-molecule device Au–B 40 –Au was investigated by using density functional theory and non-equilibrium Green׳s function method. The results show that the device can exhibit large rectification ratio and significant negative differential resistance. More importantly, the photocurrent of the device has different responses in the infrared, visible and ultraviolet regions. The excellent optoelectronic properties ensure that the device can be used as photodetector.