Two-probe Device Research Articles

Gate controllable fully spin-polarized and pure spin current in γ-graphyne nanoribbon

Gate-controlled spin-dependent transport has paved the way for spintronic devices with tunable functionalities. In this study, we calculated the spin-dependent transport properties and photocurrent characteristics of a two-probe device based...

Doping-induced bandgap tuning in armchair graphene nanoribbons and its impact on electron transport properties on ZAPn – A DFT study

Graphene, sp2 hybridised-2D material has been widely reviewed for its fabulous structural, electronic, magnetic and optical properties. However, its employment in energy-related devices are controlled due to its semi-metallic nature. A quasi one-dimensional structure of graphene is called as graphene nanoribbon (GNR). Tuning the band gap of GNR based on its width can be achieved via doping. The present work envisages, the doping performance on the electronic properties of armchair graphene nanoribbon AGNR (N9) doped with Boron (B), Nitrogen (N) and Phosphorus (P) in a Z-shape. The effect of B, N, and P dopants in AGNR(N9) systems were analysed by varying the concentration from 0.75 % to 3.03 %. Our results predicts that the band gap has been reduced by the impact of dopants, and also ZAPn systems shows better results in lower concentration of dopants than ZABn and ZANn systems. Further, it is observed that, with the increase in the concentration of P dopants, their electronic structure is transformed from n-type to p-type. Transport calculations were performed for ZAPn systems, and their properties were analyzed with the help of transmission spectrum, device density of states (DDOS), and I-V characteristics. All the doped as well as the pristine two-probe device structures established non-linear current vs. voltage characteristics. The ZAP3 doped system achieved a maximum current of 60 µA. The present study will be established to construct AGNR(N9) based nano-electronic devices.

Vacuum barrier induced large spin polarization, giant magnetoresistance, and pure spin photocurrent in ferromagnetic zigzag graphene nanoribbons

Based on first-principle calculations combined with non-equilibrium Green’s function method, we investigate the spin-polarized transport properties of a two-probe device which consists of a vacuum barrier sandwiched between two semi-infinite ferromagnetic zigzag graphene nanoribbons (ZGNRs). It is well known that any vacuum barrier itself is not spin-polarized, and meanwhile, the infinite pristine ferromagnetic ZGNR presents no spin polarization in the transmission function around the Fermi level. However, our computational results indicate that robust large spin polarization is found in the proposed device. More interestingly, giant magnetoresistance up to can be obtained at low bias voltage. Furthermore, the photogalvanic effect-induced fully spin-polarized photocurrent or pure spin photocurrent can be generated in such device by illumination with polarized light, depending on the symmetry of structure. Consequently, our results indicate that vacuum barrier may show interesting spin-polarized transport properties in certain systems and should be taken into consideration in the construction of molecular junctions and spintronic devices.

Formaldehyde gas sensing properties of transition metal-doped graphene: a first-principles study

The formaldehyde gas sensing properties of transition metal-doped graphene have been systematically investigated by first-principles calculations. The optimized geometries of transition metal-doped graphene with and without HCHO adsorption, adsorption energies, charge transfers and magnetic moments are obtained for various doped graphene systems. The calculated results show that Co-, Ni-, Cu-, Zn-, Pd- and Ag-doped systems have moderate adsorption energies, implying their potential applications as HCHO sensors. The two-probe sensor devices consisting of the central scattering region and pristine graphene electrodes with the armchair or zigzag transport directions are built, and the spin-polarized current–voltage curves are calculated by the non-equilibrium Green’s function method within the framework of density functional theory. For the Cu-, Zn- and Ag-doped systems, the average sensor response is over 80%, 40% and 290%, respectively. In particular, the Cu- and Ag-doped graphene devices have the highest value of response over 200% and 900% at low voltages, indicating a short response time and high sensitivity of these devices. The present study provides a theoretical basis for exploring practical applications of the transition metal-functionalized graphene as superior HCHO gas sensors.

First-Principles Investigation of Pd-Doped Armchair Graphene Nanoribbons as a Potential Rectifier

A first-principles investigation is carried out on palladium (Pd)-doped armchair graphene nanoribbons (AGNRs) to investigate their structural, electronic and transport properties. The structural analysis of the considered Pd-doped nanoribbons reveals that single Pd doping at the edges of AGNRs results in the most stable configuration. The present findings reveal that the electronic transport properties are strongly dependent on the number of dopant atoms and their positions. Furthermore, it is noted that the proposed two-probe devices exhibit peculiar nonlinear I–V characteristics indicating potential for rectification behavior. Excellent high rectification ratio (RR) and reverse rectification ratio (RRR) are on the order of $$1.8\times 10^{5}$$ and $$9.7\times 10^{4}$$ , respectively, are found for center-Pd-doped 7-AGNRs. The interesting rectifying I–V behavior can be explained by the localization/delocalization effect of frontier orbitals along with the variation of the transmission spectra with the applied bias voltage. These findings indicate that Pd-doped armchair GNRs are a potential candidate for use in next-generation ultralow-power nanoscale switching devices.

Adsorption-site-dependent magnetic and electronic properties for single- or double-fluorine-atom adsorbed boron nitride nanotubes and their possible applications in spin filters

Here, by using the first-principles method, magnetic and electronic properties of (6, 0) boron nitride nanotubes fluorinated with single fluorine atom (SF-BNNT) or double fluorine atoms (DF-BNNTs) have been investigated. The numerical results show that the non-magnetic and semiconducting BNNT turns to be ferromagnetic and half metallic after a single fluorine atom adsorption. For DF-BNNTs, all the adsorption configurations show ferromagnetic features. However, the electronic properties of DF-BNNTs are closely dependent on adsorption sites of the F adatoms for DF-BNNTs. With different adsorption configurations, DF-BNNTs can be semiconductors, half metals or even conductors. The spin-dependent current-voltage curves of two-probe devices constructed by SF-BNNT or DF-BNNTs indicate that some of the devices manifest high spin filtering efficiency, which can be attributed to the overlap change for the spin-resolved energy bands of two electrodes. This work is helpful for applications of the BNNT in molecular spintronics.

First Principle Study of Adsorption Behavior of PF5 Gas Molecule on S and Mo Vacancy MoS2 Monolayer

The molybdenum disulfide monolayer (MoS2) is gaining more attention due to its attractive electronic property, and it is extensively used in different electronic applications. The presence of vacancies on the MoS2 monolayer leads to an increase in the conductivity of the material. In this work, we have investigated the adsorption behavior and estimated the gas-sensing properties of the S-vacancy (VS) and the Mo-vacancy (VMo) MoS2 monolayers and the two-probe MoS2 devices with phosphorus pentafluoride (PF5) gas molecule. To explore the sensing and electronic properties of VS and VMo MoS2 towards PF5 gas adsorption, the adsorption distance, adsorption energy, charge transfer, band structure, and density of the states have been analyzed using density functional theory in combination with Non-Equilibrium Green's Function. The results show that the PF5 gas molecule is allowed to adsorb on the S- and Mo-vacancy MoS2 monolayers through van der Waals interaction. The PF5 gas molecule shows adsorption distances of 3.3274 A and 2.8673 A, adsorption energies of − 0.1640 eV and − 0.3489 eV, and charge transfers of − 0.025 Q (e) and − 0.053 Q (e) on the VS/VMo MoS2 monolayers. To study the electron transport properties, the device density of the states, the transmission spectra, and the current–voltage characteristics of the VS/VMo MoS2 two-probe devices have been analyzed. The results predicted that the Mo-vacancy MoS2 device shows relatively more adsorption towards the PF5 gas molecule when compared with the VS MoS2 device.

Exploring the spin polarization and electronic transport properties for zigzag MoS2 nanoribbons with antisite defects

The spin polarization and electronic transport of zigzag MoS 2 nanoribbons (ZMoS 2 NRs) with two kinds of antisite defects are explored based on density functional theory and nonequilibrium Green's function . The study of the band structure indicates that the defective ZMoS 2 NRs keep the metallic property under antisite defects. From the transmission spectra under the zero bias voltage, it can be observed that the spin up and spin down transmission coefficients at the Fermi level become smaller for the defective two-probe devices when compared with the perfect ZMoS 2 NRs. It suggests that the antisite defects will suppress the transport ability. An obvious negative differential resistance (NDR) phenomenon can be seen from the spin-resolved current-voltage curves for the perfect and defective devices. Due to the antisite defects, the current flowing through the two defective devices is lower than that of the perfect counterpart. Besides, the reduced hop current and bond current in the spin down pathway cause the dramatic drop of the spin down current. An excellent spin filtering effect is found in the ZMoS 2 NRs with antisite defects than the perfect ZMoS 2 NRs. • The spin polarization and electronic transport properties of Z-SbNRs with antisite defects are investigated. • The spin up and spin down transmission coefficients at the Fermi level become smaller for the defective devices. • An obvious negative differential resistance phenomenon is observed from the spin-resolved current-voltage curves. • Excellent spin filtering effect is found in the ZMoS 2 NRs with antisite defects.

Simulation of gamma-ray distribution in rocks for determining the registration characteristics of measurement unit of horizontal borehole positional control system

Theoretical aspects of gamma-ray distribution in rock are described in the article. Information concerning the values of natural gamma radiation of rocks provides for the control of the drilling tool’s orientation during horizontal drilling. A simulation of gamma-ray distribution in rock, based upon the example of western Siberian fields, has been made in a COMSOL Multiphysics interactive environment. Test results for a prototype, two-probe device for horizontal borehole positional control are contained in this document. The maximum distance for the registration of changes in the natural gamma radiation of rocks was determined. The attenuation coefficient for the natural gamma radiation of rocks introduced by the influence of a nonmagnetic drill collar was calculated. Practical advice for improvements in the registration characteristics of the prototype device is provided.

Electronic transport properties of boron and nitrogen pair co-doped 6,6,12-graphyne nanosheet from first principles

The electronic transport properties of boron and nitrogen (B–N) pair co-doped 6,6,12-graphyne have been investigated comprehensively by means of the density functional theory combined with the non-equilibrium Green’s function method. In previous studies, the 6,6,12-graphyne represents a small carrier effective mass and high carrier mobility, and its limit in electronic application caused by the closed band gap can be broken through by B–N pair co-doping. It is found that the B–N pair co-doped 6,6,12-graphyne exhibits anisotropic current. The current along the armchair direction is much stronger than that in the zigzag direction. Intriguingly, the current–voltage characteristics generically exhibit a negative differential resistance effect, regardless of the B–N pair doping conformations. In addition, a current rectification effect is observed in the two-probe device models based on the B–N pair co-doped 6,6,12-graphyne. Our results reveal that both the current and rectification effect are intimately connected with the transmission peaks appearing near the Fermi level. These findings suggest that the B–N pair co-doped 6,6,12-graphyne is a promising material for microelectronic device design.

(Bz)n and (VBz)n covalent functionalized MoS2 monolayer: electronic and transport properties

Inspired by Benzene (Bz) derivatives dramatically enhancing MoS2 monolayer electronic properties (ACS Nano. 2015, 9, 6018–6030), we have investigated electronic and transport properties of (Bz)n/MoS2 and (VBz)n/MoS2, which are designed by grafting (Bz)n and (VBz)n arrays onto 2D monolayer MoS2 (ML-MoS2), respectively, using density functional theory (DFT) and non-equilibrium Green’s function (NEGF) methods. ML-MoS2 provides a perfect substrate for grafting (Bz)n and (VBz)n arrays upon its surface as a result of stable covalent binding energy with −3.841 eV and −1.953 eV for (Bz)n/MoS2 and (VBz)n/MoS2 respectively. From the electronic properties, we can find that grafting (Bz)n onto the ML-MoS2 surface turns ML-MoS2 from typical semiconductor to metallic properties because four wide bands coupled by (Bz)n and MoS2 in (Bz)n/MoS2 show better delocalization in heterointerface, resulting to these bands across the Fermi level (Ef). Furthermore, (VBz)n nanowire grafted on the ML-MoS2 further enhances the conductivities due to the introduction of metal V. Transport properties of ML-MoS2, (Bz)n/MoS2 or (VBz)n/MoS2 for two-probe devices are all studied in zigzag and armchair direction. By comparison the zigzag direction is the preferential pathway for electron transport. The ferromagnetic (VBz)n/MoS2 shows a spin polarized transport characteristic, spin-down state gives a higher conductivity than spin-up state. Finally this work suggests that the novel (VBz)n nanowire grafted on MoS2 should have potential application in low-dimensional magnetic nanoelectronic devices.

Transport and photogalvanic properties of covalent functionalized monolayer black phosphorus

Opposite responses of the transport and photogalvanic properties of the two-probe devices based on covalent functionalized black phosphorus.

Length-Dependent Electronic Transport Properties of the ZnO Nanorod.

The two-probe device of nanorod-coupled gold electrodes is constructed based on the triangular zinc oxide (ZnO) nanorod. The length-dependent electronic transport properties of the ZnO nanorod was studied by density functional theory (DFT) with the non-equilibrium Green’s function (NEGF). Our results show that the current of devices decreases with increasing length of the ZnO nanorod at the same bias voltage. Metal-like behavior for the short nanorod was observed under small bias voltage due to the interface state between gold and the ZnO nanorod. However, the influence of the interface on the device was negligible under the condition that the length of the ZnO nanorod increases. Moreover, the rectification behavior was observed for the longer ZnO nanorod, which was analyzed from the transmission spectra and molecular-projected self-consistent Hamiltonian (MPSH) states. Our results indicate that the ZnO nanorod would have potential applications in electronic-integrated devices.

Effect of C and O dopant atoms on the electronic properties of black phosphorus nanotubes

The electronic structures of the C and O-doped black phosphorene are investigated theoretically by using first-principles density functional theory (DFT). The results show that they are all metallic. And the black phosphorus nanotubes (BPNTs) rolled from the pure, C-doped and O-doped black phosphorene with different radii and chiralities are also studied. C and O atoms substitute for P atoms enable the armchair BPNT to have a metallic feature with several bands cross the Fermi level. Surprisingly, the number of the bands cross the Fermi level just equals the number of dopant atoms. But for the zigzag BPNT, when the O atoms decrease to 4, no band crosses the Fermi level and at which a minimal energy gap appears. Furthermore, the transport properties of two-probe devices fabricated by the pure A24 and Z34 BPNTs together with the C-doped A24 BPNTs are investigated theoretically. These calculated results show that the electronic transport properties of the A24 BPNT can be significant changed by C dopant atom and vary with the number of the doped atoms. The current-voltage curves of these BPNTs with C atoms substitute for P atoms present sinusoidal characteristics under low bias and negative differential resistance (NDR) properties. This study provides an effective route for tuning the electronic structures of black phosphorene and BPNTs and thus the transport properties of their electronic devices. And the unique properties of these black phosphorene and BPNTs also offer an inspiration for their subsequent experiments.

The electronic and transport properties of zigzag β-antimonene nanoribbons

The electronic and transport properties of zigzag β-antimonene nanoribbons (Z- SbNRs) are investigated based on density function theory (DFT) and non-equilibrium Green's functions (NEGF). The calculated band structure of Z-SbNRs shows a typical semiconductor characteristic. For Z-SbNRs, the band gap decreases monotonically with the increase of ribbon width. Moreover, it is found that the width and the length of central scattering region have a great effect on the electronic transport property of Z-SbNRs. The I-V curve of the two-probe device shows the current is almost zero when the bias voltage is lower than the threshold voltage of 2.0 V. However, when the bias voltage is higher than the threshold voltage, the transport channels are opened and the current increases quickly.

Carbon chain-based spintronic devices: Tunable single-spin Seebeck effect, negative differential resistance and giant rectification effects

Abstract Using the density functional theory combined with the Keldysh non-equilibrium Green's function methods, we investigate the thermally (or voltage)-induced spin transport properties of a two-probe device consisting of a carbon atom chain sandwiched between two zigzag graphene nanoribbon (ZGNR) electrodes. When the edge of one ZGNR electrode is partially doped by B atoms, the flowing direction of thermal single-spin current can be reversed in contrast with the undoped case. In addition, when a voltage is applied across the carbon-based device at room temperature, a giant rectification ratio of 10 4 is observed which mainly originates from the band-structure incompatibility between two ZGNR electrodes in the voltage window. Moveover, in the high-voltage region, a single-spin negative differential resistance is also observed in the carbon-based device. Our findings here suggest that the carbon-based systems can be used to design spintronic devices with multiple functions.

First principles study of electronic transport properties in novel FeB2 flake-based nanodevices

First-principles calculations can provide theoretical support for the promising applications of innovative two-probe devices based on FeB2 flakes at different temperatures. Results indicate that these FeB2-based devices not only exhibit a prominent transport capacity and a predictable strong current, but also possess outstanding electrical conductivity compared with many flake-based devices. Devices with FeB2 flakes at temperatures not above 1000 K have advantageous transmission and low-voltage current because of the delocalization of electronic states, essentially resulting from their undeformed flake structures. Importantly, Fe atoms are pivotal in the electron transport of FeB2-based devices. The edge effect of the flakes is also analyzed. These new-type FeB2 flakes can realize substantial value in nanoscale functional devices.

Negative differential resistance observation in complex convoluted fullerene junctions

In this work, we simulated the smallest fullerene molecule, C20 in a two-probe device model with gold electrodes. The gold electrodes comprised of (011) miller planes were carved to construct the novel geometry based four unique shapes, which were strung to fullerene molecules through mechanically controlled break junction techniques. The organized devices were later scrutinized using non-equilibrium Green's function based on the density functional theory to calculate their molecular orbitals, energy levels, charge transfers, and electrical parameters. After intense scrutiny, we concluded that five-edged and six-edged devices have the lowest and highest current-conductance values, which result from their electrode-dominating and electrode-subsidiary effects, respectively. However, an interesting observation was that the three-edged and four-edged electrodes functioned as semi-metallic in nature, allowing the C20 molecule to demonstrate its performance with the complementary effect of these electrodes in the electron conduction process of a two-probe device.

Impact of geometry on transport properties of armchair graphene nanoribbon heterojunction

Electron transport properties of undoped armchair Graphene Nanoribbon Heterojunction (GNRHJ) has been studied using semi-empirical extended Hückel method (EH). A two-probe configuration device utilizing armchair GNRHJ has been proposed. It is shown that a potential barrier was formed at the heterojunction interface between semiconductor and semi-metal, which resemble the conventional Schottky barrier at the interface of semiconductor/metal. Transmission spectrum was analyzed at finite bias; and current-bias voltage characteristic relations were established. Results show that the I–V characteristics of the heterojunction have rectifying nature, with its rectification ratio affected by the geometric asymmetry of the heterojunction.

Transport properties and device-design of Z-shaped MoS2 nanoribbon planar junctions

Based on MoS2 nanoribbons, metal-semiconductor-metal planar junction devices were constructed. The electronic and transport properties of the devices were studied by using density function theory (DFT) and nonequilibrium Green's functions (NEGF). It is found that a band gap about 0.4eV occurs in the planar junction. The electron and hole transmissions of the devices are mainly contributed by the Mo atomic orbitals. The electron transport channel is located at the edge of armchair MoS2 nanoribbon, while the hole transport channel is delocalized in the channel region. The I-V curve of the two-probe device shows typical transport behavior of Schottky barrier, and the threshold voltage is of about 0.2V. The field effect transistors (FET) based on the planar junction turn out to be good bipolar transistors, the maximum current on/off ratio can reach up to 1 × 104, and the subthreshold swing is 243mV/dec. It is found that the off-state current is dependent on the length and width of the channel, while the on-state current is almost unaffected. The switching performance of the FET is improved with increasing the length of the channel, and shows oscillation behavior with the change of the channel width.