Negative Differential Resistance Effect Research Articles

Spin transport properties in zigzag silicon carbide nanoribbon nanojunctions by asymmetric hydrogenation and BN doping

Based on asymmetric edge hydrogenation of zigzag silicon carbide nanoribbons (ZSiCNRs), the nanojunction with the boron and nitrogen impurity are constructed. The spin transport properties of nanojunction are calculated in different magnetic configurations by using the non-equilibrium Green’s function method and density functional theory. Our findings show the N atom prefers to substitutes for C site while the B atom prefers the Si site. The obtained I–V characteristics indicate that the spin-down and spin-up states filtered in parallel and antiparallel configurations, respectively, which can be used for designing spintronic devices. Moreover, the spin-resolved negative differential resistance (NDR) effect occurs in the spin-polarized currents.

The electronic transport properties in graphyne and graphyne-like carbon-nitride nanoribbons

By applying nonequilibrium Green’s functions in combination with density-functional theory, we investigate the electronic transport properties of graphyne nanoribbons (GYNR) and graphyne-like carbon nitride nanoribbons (GYCNNR). Our results show that GYNR is a semiconductor and the current across the GYNR system is almost forbidden at low bias voltages, while GYCNNR has a similar metallic band structure and the current shows an obvious negative differential resistance effect. Moreover, the results also show that the Lorenz conductance ratios, namely the ratio of electron thermal conductance and electric conductance against temperature, have different chemical-potential dependence for GYNR and GYCNNR.

Spin transport properties of single molecule magnet Mn(dmit)2 devices with phosphorene electrodes

Multiple-effect molecular devices have been constructed by single molecule magnet Mn(dmit)2 and phosphorene electrodes. First-principle quantum transport calculations show that the devices present excellent spin-filtering, spin-switching and negative differential resistance effects, which can be explained by the frontier molecular orbitals, the projected density of states and evolution of the transmission spectra. These excellent spin transport properties are better than the performance of the devices constructed by Au or graphene electrodes, which suggest that the one-dimensional devices with phosphorene electrodes are promising candidates for future applications of phosphorene-based multi-functional spintronics devices.

Electronic and transport properties of zigzag phosphorene nanoribbons doped with ordered Si atoms

Using density functional theory (DFT) and the nonequilibrium Green's function method, we explored the electronic structures and transport properties of zigzag phosphorene nanoribbons (ZPNRs) with ordered doping of Si atoms. Our results show that both pristine and Si-doped ZPNRs exhibit metallic properties and the conductance of the doped ZPNRs nanoribbons can be modulated effectively by changing doping positions and concentrations. As different doping positions, different transmission currents can be obtained even with the same doping concentration. Moreover, current amplification factors vary with the doping concentrations. In addition, compared with the pristine system, negative differential resistance effect can also be observed in doped system (Si3), which occurs in lower bias range.

The spin-transport properties of single edge oxidized zigzag MoS2 nanoribbon

Abstract Based on density functional theory and combined with non-equilibrium Green's function, we investigate the electronic, magnetic and transport properties of zigzag MoS2 nanoribbons which is passivated by oxygen atoms at the single Mo edge (ZMoS2ONRs). At ferromagnetic ground magnetic state, the magnetic moment is found to concentrate on the non-passivated edge. Due to the oxygen passivation, the negative differential resistance effect discovered in the bare zigzag MoS2 nanoribbons disappears. Besides, the electron transport pathway is located at the passivated side and the transport current is mainly contributed by spin-down channels. The findings provide more possibilities for its application in spintronics and nanoelectronic devices.

Half-metallicity modulation of zigzag BC2N nanoribbons by transverse electric fields: A first principles study

We performed density functional theory calculations to investigate the electronic and magnetic properties of H-terminated zigzag BC2N nanoribbons (ZBC2NNRs) with the atoms arranged as B-C-N-C along zigzag lines. The ribbons can be classified into three groups according to the profiles of band structures and edge atoms: BN-BN, CC-CC and BN-CC. Among them, CC-CC and BN-CC ZBC2NNRs behave magnetic ground states. The results show that the CC-CC ZBC2NNR is an antiferromagnetic (AFM) semiconductor. Under the transverse electric field, the half-metallicity of 16-CC-CC ZBC2NNR can be achieved with electric field in the range of 0.2∼0.45 VÅ−1. Interestingly, the intrinsic half-metallicity exists in BN-CC ZBC2NNRs when the ribbon width is smaller than ∼29.2 Å. For larger ribbon width (∼33.5 Å), the system could be converted from ferromagnetic metal to half-metals at a very low critical field of E=0.02 VÅ−1. Meanwhile, it is also shown that the I–V characteristic of BN-BN ZBC2NNRs shows a negative differential resistance (NDR) effect. These ample electronic and magnetic properties might open great opportunities for BC2N materials in spintronics and nanoscale device in the future.

Single ultrathin WO3 nanowire as a superior gas sensor for SO2 and H2S: Selective adsorption and distinct I-V response

In order to take insight into the gas sensing performance of single ultrathin WO3 nanowire, we performed first principles calculation to investigate the gas adsorption properties and used non-equilibrium Green function (NEGF) to investigate the electron transport properties of WO3 nanowires with gas adsorption. Our investigation indicated that the WO3 nanowires with/without oxygen vacancies are both sensitive to H2S due to the large adsorption energies and distinct charge transfer. Besides, we found that the WO3 nanowire with Oa type oxygen vacancies is highly selective to SO2. We supposed that the high chemical activity and the small molecular volume of H2S and SO2 are the main reasons of the selectivity. Finally, the negative differential resistance (NDR) effect of single ultrathin WO3 nanowire and the gate voltage were proposed to benefit the application of WO3 nanowires gas sensors. We also supposed two ways to take advantage of the NDR effect of single ultrathin WO3 nanowire in gas sensing applications. It should be noted that this is the first theoretical investigation of WO3 nanowires gas sensors considering the electron transport properties. Our work highlighted the possibility to use the single ultrathin WO3 nanowire as superior gas sensors for SO2 and H2S.

Immobilization of doped TiO2 nanostructures with Cu or In inside of macroporous silicon using the solvothermal method: Morphological, structural, optical and functional properties

Copper (Cu) and Indium (In) doped titanium dioxide (TiO2) obtained by a solvothermal method was confined in Porous Silicon (PS) prepared by Metal-Assisted Chemical Etching -MACE-, a low-cost and versatile method to investigate the morphological, structural, optical, and electrical properties of the TiO2:X/PS/Si structure (X = In, Cu, 0). According to Scanning Electron Microscopy, different morphologies were found, such as small particles (without dopant) or well-defined geometries such as cubes (indium-doped) and micro-flowers (copper-doped) that covered the PS surface depending on the kind of dopant elements. Cross-section images showed that the TiO2 nanoparticles decorated and filled the macroporous silicon and that they can even form conformal deposits.Raman spectroscopy and x-ray diffraction patterns revealed the crystalline phase structure of the In and Cu-doped TiO2 materials, which correspond to anatase and rutile, respectively. Furthermore, the lattice parameters corroborated the incorporation of the dopant elements. The photoluminescence (PL) spectra show broad-bands around 2.8 eV, which can be related to oxygen vacancies. Additionally, a blue shift was observed in the PL spectra when the dopant changed from Cu to In. Diffuse reflectance and the Kubelka-Munk plots were used to determine the optical bandgap of the TiO2 structures with and without dopant. Bandgap reduction was observed due to the dopant changes. Current-voltage curves showed a rectifying behavior for negative voltages; however, a negative differential resistance effect was observed for positive voltages in all the samples. Finally, current-voltage curves showed a rectifying behavior for negative voltages; however, it was observed a negative differential resistance effect for positive voltages in all the samples. Besides, these current voltages curves were carried out under dark and illumination conditions, which revealed a photocurrent effect.

Electronic structure, strain effects and transport property of armchair graphene nanoribbon with variously possible edge oxidation

Graphene and related 1D structures have been investigated intensely so far. Here, to consider expanding their potential applications and explore their more underlying physics, we construct armchair graphene nanoribbon models with variously possible edge oxidation, and their geometrical stability, electronic properties, carrier mobility, strain effect, and device properties of are studied systematically, based on the first-principles method. The calculated edge formation energy and molecular dynamics simulations show that these ribbons are quite stable, and the calculated Gibbs free energy suggests that they likely exist in different O-atom concentration environment. Different oxidation leads to different hybridization subbands, making rich and versatile electronic structures, in particular causing various differences in the band gap for ribbons. Large carrier mobility and significant carrier polarization are predicted as well. Under applied strain conditions, some ribbons exhibit flexibly tunable band gaps and the transition of electronic phases, which promises a potential application for developing nanoscale mechanical switches reversibly working between different electronic phases. In addition, the edge oxidation can improve the related ribbon device behavior, such as producing significant negative differential resistance effects. Therefore, the structures proposed here might have important potential applications for developing future on-demand nano devices.

Designing of spin filter devices based on zigzag zinc oxide nanoribbon modified by edge defect**Project supported by the National Natural Science Foundation of China (Grant Nos. 61664008 and 11604286) and the Scientific Technological Innovation Team of Yan’an City, China (Grant No. 2017CXTD-01).

The spin-dependent electronic transport properties of a zigzag zinc oxide (ZnO) nanoribbon are studied by using density functional theory with non-equilibrium Green’s functions. We calculate the spin-polarized band structure, projected density of states, Bloch states, and transmission spectrum of the ZnO nanoribbon. It is determined that all Bloch states are located at the edge of the ZnO nanoribbon. The spin-up transmission eigenchannels are contributed from Zn 4s orbital, whereas the spin-down transmission eigenchannels are contributed from Zn 4s and O 2p orbitals. By analyzing the current–voltage curves for the opposite spins of the ZnO nanoribbon device, negative differential resistance (NDR) and spin filter effect are observed. Moreover, by constructing the ZnO nanoribbon modified by the Zn-edge defect, the spin-up current is severely suppressed because of the destruction of the spin-up transmission eigenchannels. However, the spin-down current is preserved, thus resulting in the perfect spin filter effect. Our results indicate that the ZnO nanoribbon modulated by the edge defect is a practical design for a spin filter.

Spin-polarized transport properties and spin molecular Boolean logic gates in planar four-coordinate Fe complex-based molecular devices with carbon nanotube bridges and electrodes

Based on density functional theory combined with Keldysh non-equilibrium Green’s function formalism, we investigate the spin-polarized transport properties of planar four-coordinate Fe complexes-based molecular devices with carbon nanotube bridges and electrodes. The results show that these systems can exhibit perfect spin filtering, large giant magnetoresistance and low-bias negative differential resistance effects with the external magnetic field modulation. The underlying mechanism is analyzed by spin-resolved transmission spectra, projected density of states, and spatial distributions of corresponding molecular projected self-consistent Hamiltonian orbitals. On the basis of these intriguing transport properties, we further design basic spin molecular Boolean logic gates, such as YES, NOT, AND, NAND, XOR, NXOR, OR and NOR logic gates.

Interfacial charge transfers and interactions drive rectifying and negative differential resistance behaviors in InAs/graphene van der Waals heterostructure

Vertical heterostructures of two-dimensional (2D) materials are excellent candidates for designing next-generation electronic devices with superior performance. By using both ab initio electronic calculations and quantum transport simulations, we investigated the electronic and transport properties of InAs/graphene heterostructure. The results reveal that electrons and holes accumulate at different layers after the adsorption of InAs layer, forming the built-in electronic field at the interface. The electrostatic potential energy of InAs layer is higher than that of graphene, and it favors more electrons transferring from InAs to graphene layer. Comparing the comment methods by introducing impurity and carriers' injection, rectifying and negative differential resistance behaviors can also be realized by the combined effects of electron-hole distribution, interfacial hybridization, and contact barrier in InAs/graphene heterostructure device. It shows that the rectifying ration gradually increases with bias voltage, and the negative differential resistance effect happens at either positive or at negative bias voltage regions. Electrostatic potential distribution and contact barrier play important roles in determining transport properties. Increasing interfacial hybridization is helpful for transmission enhancement in the weak interlayer interaction van der Waals heterostructure.

A novel steep slope hybrid InGaZnO TFT with negative DIBL improvement based on the Ag/HfO2 threshold switching device

We present a steep slope hybrid thin film transistor (TFT) that integrates an Ag/HfO2 based threshold switching (TS) with a ferroelectric HfZrO gated InGaZnO TFT. The hybrid TFT shows a minimum subthreshold swing of 16 mV decade. The negative differential resistance effect (NDR) was observed during the switching process of the TS. And the InGaZnO TFT shows a negative drain-induced barrier lowering (DIBL) effect. Furthermore, a Verilog-A model is developed to simulate the hybrid TFT. All of these suggests the as-fabricated hybrid TFT is suitable for low power TFT based applications.

Rectification and negative differential effects of Si2C2 clusters: An ab initio study

By combining the density functional theory (DFT) with the nonequilibrium Green’s function, we studied the transmission properties of Si2C2 clusters (the linear form M1 and the rhombic form M2). The result shows that the I-V characteristics of the cluster are closely related to the structure of the cluster. The change in the structure of the cluster causes a change in the coupling process between the cluster and the electrode, resulting in a change in its transmission characteristics. Compared with the linear form M1 system, the rhombic form M2 system has obvious rectification and negative differential resistance (NDR) effects, which makes it more advantageous as a candidate for molecular devices.

Modulation of Electronic Behaviors of InSe Nanosheet and Nanoribbons: The First‐Principles Study

AbstractRecently, InSe monolayer, a new member added to the 2D materials, has been extensively studied in theories and experiments. Here, the electronic structures of the tunable band‐gap semiconductor of 2D InSe nanosheets and the band structure and electronic transport properties of quasi‐1D InSe nanoribbons (ISNs) are presented by using the first‐principles method. The calculated band structures show that an enlarged indirect band gap appears in 2D InSe nanosheet by external strain, and the gap reduces monotonically as the strain changing from the compression to stretch independent of the zigzag or armchair direction. Moreover, the band structures of quasi‐1D ISNs show that armchair ISNs are all nonmagnetic semiconductors, and the zigzag ISNs (zISNs) exhibit metallic regardless of the ribbon width or magnetic states. The non‐equilibrium Green's function calculation reveals the electronic transport properties of zISNs with different widths. An obvious negative differential resistive (NDR) effect is found in the current–voltage curves independent of the ribbon width due to the bias‐dependent transmission within the voltage window. The tunable band‐gap semiconductor behavior of 2D InSe nanosheet and the novel NDR effect in quasi‐1D zISNs indicate a very promising application of InSe‐based nanomaterials in electronic nanodevices.

Low bias negative differential resistance with dual-peaks based on octacene molecular device

Based on non-equilibrium Green's function and density functional theory, a first-principles study of the transport properties of a molecular device is performed. This device is composed of two octacene molecules separated by a ethyl barrier, which are then linked to Ag leads through thiolates. The device shows low bias negative differential resistance effect with dual-peaks, which may be useful for designing molecular devices with low power-dissipation and multi-function in the future.

Spin induced inverter circuit with trinuclear chromium complexes

Density functional theory is used in conjunction with the non-equilibrium Green's functions approach to explore the spin polarized charge transport properties of homo-nuclear tri‑chromium and hetero-nuclear chromium‑ruthenium metal-string complexes. The metal strings comprise Cr-Cr-Cr, Cr-Cr-Ru, Cr-Ru-Cr, and Cr-Ru-Ru metal centers that are sandwiched between two Au (111) nano-electrodes. As deduced from the results, the Cr-Cr-Cr metal-string junctions could potentially be exploited in designing an inverter logic circuit to transfer the data at nanoscale. Considerably It also turns out that, among these single molecular junctions, Cr-Cr-Ru and Cr-Ru-Ru exhibit significant spin-up filtering with about 100% efficiency. More importantly, the Cr-Ru-Ru metal string complex demonstrates the negative differential resistance (NDR) effects in addition to its spin filtering properties. To analyze these phenomena, we examine the respective transmission spectra along with the potential drop across all the four metal-string junctions.

The Magnetism and Transport Properties of Bare and Hydrogenated Borophene Nanoribbons

In this paper, we have investigated the magnetism and transport properties of borophene nanoribbons by using the first-principles calculations based on density functional theory. It can be seen that the hydrogenated borophene nanoribbons are more stable than the bare borophene nanoribbons. The magnetism of borophene nanoribbon can be modulated by the edge’s hydrogenated. Interestingly, with regard to the hydrogenated armchair borophene nanoribbons, the current increases with the increase of bias voltage when V ≤ 1.0 V, and then the current decreases with the increase of bias voltage when V > 1.0 V, namely, it appears negative differential resistance effect. It is hoped that borophene may be useful for the design and application of spintronic devices.

Multifunctional 2D CuSe monolayer nanodevice

In a very recent experimental work (Gao et al 2018 Adv. Mater. 30 1707055), a graphene-like CuSe monolayer (ML) was realized. Motivated by this success, we performed first-principles calculations to investigate its electronic transport and photoelectronic properties. We find that the CuSe ML shows a strong electrical anisotropy, and its current–voltage (I–V) curves along the zigzag and armchair directions are noticeably different. The CuSe ML also displays a useful negative differential resistance (NDR) effect along the both directions when the bias is beyond 1.0 V. Moreover, it has a large photon absorption to orange light. Our study suggests that CuSe ML is a multifunctional material and has various potential applications in electrical-anisotropy-based, NDR-based, and even optical nanodevices.

Multiple slopes in the negative differential resistance region of NbOx-based threshold switches

Niobium oxide devices exhibit threshold switching behavior which enables their use as selectors in memory arrays or as locally active devices for neuromorphic computing. Among the basic dynamical phenomena appearing in non-linear circuits, the oscillations generated in a relaxation oscillator, which is making use of the negative differential resistance (NDR) effect of a threshold switching device, are of special significance for the design of neuromorphic electronic systems. Here, the necessary requirements for the emergence of oscillations of this kind in a simple relaxation oscillator circuit and their influence on the shape of the measured quasi-static I– characteristic of the threshold switch are examined. In the corresponding experiments multiple NDR regions were found to appear in the quasi-static I– characteristic of the threshold switch concurrently with the occurrence of oscillations. The observed ‘multiple NDR phenomenon’ is therefore merely a measurement artefact due to the averaging effect associated to the operating principles of the source measure unit (SMU) utilized to measure the device current and voltage. In this work, we analyzed how the emergence of oscillatory behavior in the relaxation oscillator depends upon the device layer stack composition. The probability of the appearance of oscillations within a large current range can be increased by decreasing the oxygen content in the sub-stoichiometric bottom layer of a niobium oxide bi-layer stack. It is shown that this trend is caused by the resulting decrease in the value of the product between thermal capacitance and thermal resistance of the threshold switching device. Furthermore, the changed stack composition reduces the variability and changes the forming voltage, which goes hand in hand with a change of the threshold voltage.