Positive External Electric Field Research Articles

A resilient type-III broken gap Ga2O3/SiC van der Waals heterogeneous bilayer with band-to-band tunneling effect and tunable electronic property

The potential of van der Waals (vdW) heterostructure to incorporate the outstanding features of stacked materials to meet a variety of application requirements has drawn considerable attention. Due to the unique quantum tunneling mechanisms, a type-III broken-gap obtained from vdW heterostructure is a promising design strategy for tunneling field-effect transistors. Herein, a unique Ga2O3/SiC vdW bilayer heterostructure with inherent type-III broken gap band alignment has been revealed through first-principles calculation. The underlying physical mechanism to form the broken gap band alignment is thoroughly studied. Due to the overlapping band structures, a tunneling window of 0.609 eV has been created, which enables the charges to tunnel from the VBM of the SiC layer to the CBM of the Ga2O3 layer and fulfills the required condition for band-to-band tunneling. External electric field and strain can be applied to tailor the electronic behavior of the bilayer heterostructure. Positive external electric field and compressive vertical strain enlarge the tunneling window and enhance the band-to-band tunneling (BTBT) scheme while negative electric field and tensile vertical strain shorten the BTBT window. Under external electric field as well as vertical and biaxial strain, the Ga2O3/SiC vdW hetero-bilayer maintains the type-III band alignment, revealing its capability to tolerate the external electric field and strain with resilience. All these results provide a compelling platform of the Ga2O3/SiC vdW bilayer to design high performance tunneling field effect transistor.

Elucidating the dissociative and associative mechanisms on the surface-anchored Fe3 cluster under the effect of external electric field

In the Haber-Bosch process, the direct dissociation of the N-N bond requires harsh reaction conditions. Three-atom metal clusters exhibit excellent catalytic performance in ammonia synthesis under mild conditions. They are considered potential catalysts to promote the associative hydrogenation of NN*. Moreover, it has been reported that electric fields can be a powerful tool for enhancing the performance of heterogeneously catalyzed reactions. Whether electric fields can further promote ammonia synthesis on three-atom metal clusters and its regulation mechanism needs to be investigated. In this work, we illustrate the effects of the electric fields on the N2 adsorption process, the NN* associative hydrogenation process, the N-N bond direct dissociation process, and the NNH* dissociation process for Fe3 cluster. The results show that the positive external electric field promotes the N2 adsorption process and activates the N-N bond of the NN* and NNH* species. With the increase of electric fields, the initial and final states of the N2 adsorption and NNH* dissociation processes become more stable. In addition, the electric field impedes electron transfer during the N2 adsorption process and the NN* associative hydrogenation process. This research will guide future work on applying electric fields to ammonia synthesis catalyzed by three-atom metal clusters.

Tunable Schottky barrier of WSi2N4/graphene heterostructure via interface distance and external electric field

Improving the electric transport of field-effect transistors based on heterostructure (HTS) is a stern challenge by the reduction of the interfacial barrier. Herein, the electronic properties of WSi2N4/graphene HTS with different interface distance or external electric field are researched in detail using the first-principles approach. The result shows that a stable vdW HTS can be produced between WSi2N4 and graphene. In the interface, the tunable range of Schottky barrier height by external electric field exceeds that by interface distance, although both of two prominent approaches can modulate the energy band structures of WSi2N4/graphene HTSs. The transformation of Schottky contact from p-type to n-type, eventually into Ohmic contact can appear under external electric field. Predictably, the positive external electric field strength of 0.55 V·Å−1 can generate the largest carrier concentration 2.73 × 1013 cm−2 of graphene in the HTS. Verifiably, the redistribution of interface charge density determines the Schottky barrier height and contact type in the HTS. These findings present the potential of WSi2N4/graphene HTS as high sensitive Schottky field-effect transistors.

Tunable Schottky contacts in graphene/XAu4Y (X, Y = Se, Te) heterostructures.

Graphene-based (G-based) heterostructures have recently attracted considerable research interest in the field of two-dimensional nanodevices owing to their superior properties compared with those of separate monolayers. In this study, the electronic properties and Schottky barrier heights (SBHs) of G/XAu4Y (X, Y = Se, Te) heterostructures were systematically analyzed through first-principles calculations. G/SeAu4Se, G/SeAu4Te, and G/TeAu4Se are n-type Schottky contacts with Φn = 0.40, 0.38, and 0.55 eV respectively, whereas G/TeAu4Te is a p-type Schottky contact with Φp = 0.39 eV. In G-based heterostructures consisting of SeAu4Te that has a 0.22-Debye intrinsic dipole moment, the intrinsic dipole moments in different directions enhance or weaken the interfacial dipole moments corresponding to the charge transfer at the interface, resulting in different Φn values of G/SeAu4Te and G/TeAu4Se. Furthermore, vertical strain and external electric field, which influence charge transfer, are applied to G/XAu4Y heterostructures to modulate their SBHs. Taking G/TeAu4Te as an example, the p-type contact transforms into an almost ohmic contact with decreasing vertical strain or positive external electric field. The findings of this study can provide insights into the fundamental properties of G/XAu4Y for further research.

Regulation of external electric field on the high-energy polynitrogen compound 1,5-diaminotetrazole-4N-oxide.

The external electric field (EEF) tends to have a significant impact on chemicals, especially energetic materials. Molecular structure, electrostatic potential (ESP), electron density difference, density of states (DOS), and frontier molecular orbitals (FMOs) of 1,5-diaminotetrazole-4N-oxide (SYX-9) are calculated by density functional theory (DFT) at B3LYP/6-311G+(d, p) and M062X/def2-TZVP under external electric field. Calculated results reveal that EEF has definite influence on the trigger bond of SYX-9, especially in positive direction, and the shortening of the trigger bond caused by it can effectively reduce the sensitive of SYX-9. In addition, EEF has an effect on the electron density of SYX-9. The positive EEF can reduce the HOMO-LUMO gap. From the perspective of components of energy variation and the force on atoms, the factors of structural deformation are specifically investigated. The aromaticity of SYX-9 makes its structure stable under the influence of EEF, which is verified by the method of the iso-chemical shielding surface (ICSS).

Electric Field-Induced Specific Preconcentration to Enhance DNA-Based Electrochemical Sensing of Hg2+ via the Synergy of Enrichment and Self-Cleaning.

Efficient preconcentration is critical for sensitive and selective electrochemical detection of metal ions, but rapid specific enrichment with depressed absorption of interfering ions at the electrode is challenging. Here, we proposed an electric field-induced specific preconcentration to boost the analytical performance of DNA-based electrochemical sensors for Hg2+ detection. As for such preconcentration, a positive external electric field was first used to enrich Hg2+ at an electrode assembled with T-rich DNA, thus boosting T-Hg2+-T recognitions. The following applied inverse electric field strips the nonspecifically absorbed Hg2+ and other interfering ions, thus depressing matrix interferences via self-cleaning. Based on this principle, we designed a portable device to realize programmable control of electric fields; a T-Hg2+-T recognition-based electrochemical sensor was thus fabricated as a model platform to assess the feasibility of electric field-induced preconcentration. The experimental results revealed that such a strategy decreased the time of T-Hg2+-T-based recognition from 60 to 20 min and led to detection with better reproducibility by depressing the influence of free Hg2+ as well as interfering ions. This strategy offered Hg2+ detection limits of 0.01 pM─three-fold better than that without preconcentration─within 22 min. The proposed preconcentration strategy offers a new way to enhance the analytical performance of sensing at the solid-liquid interface.

Modulation of MoSH/WSi<sub>2</sub>N<sub>4</sub> Schottky-junction barrier by external electric field and biaxial strain

In view of the newly synthesized two-dimensional (2D) semiconductor material WSi<sub>2</sub>N<sub>4</sub> (WSN) and the 2D metal material MoSH (MSH), a metal-semiconductor MSH/WSN Schottky-junction is constructed in this work. In practical applications of metal-semiconductor contact, the presence of the Schottky barrier degrades the device performance severely. Therefore, it is crucial to obtain a smaller Schottky barrier height or even an Ohmic contact. Here, the first-principles calculations are used to investigate the variation of the Schottky barrier in MSH/WSN Schottky-junction under an external electric field and a biaxial strain. The results show that both external electric field and biaxial strain can effectively modulate the Schottky barrier of the MSH/WSN Schottky-junction. The dynamic switching between the p-type Schottky contact and the n-type Schottky contact can be achieved under the action of positive external electric field in the MSH/WSN Schottky-junction. Under the action of negative external electric field, the MSH/WSN Schottky-junction can be modulated to realize the transition from the Schottky contact to the Ohmic contact. The large biaxial strain can also induce the MSH/WSN Schottky-junction to realize the transition between the p-type Schottky contact and the n-type Schottky contact. This work may provide theoretical guidance for the WSN semiconductor based Schottky functional devices and field-effect transistors.

Electronic and transport properties of GaAs/InSe van der Waals heterostructure

Recently, the GaAs/InSe heterostructure was synthesized experimentally, and the spatial redistribution of charge and motion of energy-resolved photoelectron was imaged. To gain more insight into the detailed electronic structure and expand knowledge to transport behaviors and physical field tuning effects, we here construct the GaAs/InSe van der Waals heterostructure theoretically and perform investigations in depth, especially focusing on the comprehensive understanding and mechanism analysis of results, trying to create new predictions. The results show that such a heterostructure holds a typical type-II band alignment and its band gap is narrowed significantly as compared with its each component, and the indirect-direct band gap transition is realized, which holds great potential applications in developing excellent photovoltaic materials and new photo-electronic devices. Particularly, the carrier mobility of heterostructure is predicted to be enhanced dramatically to μ > 104 cm2 V−1 s−1, greatly overcoming the intrinsic weakness of InSe monolayer with a very low hole mobility, ~101 cm2 V−1 s−1. Meanwhile, we find that the electronic structure of the heterostructure is flexibly controllable. Under higher compressive strain and whole tensile strain, its band-gap size drops linearly. While by applying an external electric field, the band offset is increased significantly, and the type-II band alignment is well preserved and the band gap drops significantly under positive external electric field, These flexibly tunable properties are more favorable to design the photovoltaic materials and photo-electronic devices.

Contact barriers modulation of graphene/β-Ga2O3 interface for high-performance Ga2O3 devices

The ultra-wide-gap β-Ga2O3 has been regarded as a promising material for next-generation power electronic and deep-ultraviolet (UV) photodetectors. Exploring a suitable electrode is vital for realizing high performance β-Ga2O3 based nanodevices. Herein, the structural and contact properties of graphene/Ga2O3 interfaces are tuned and investigated by using the first-principles calculations. Results show that the small n-type Schottky barrier of about 0.07 eV for the graphene/Ga2O3 interface with weak interlayer interaction is irrespective of the interface stacking arrangement. Moreover, the intrinsic electronic property of Ga2O3 is well preserved in the interface. More interestingly, the n-type Schottky barrier to Ohmic contact transition can be obtained by shorting the interlayer distance, or increasing the graphene layers or applying a negative external electric field for the interface. Moreover, applying a large positive external electric field can realize the p-type Schottky barrier to Ohmic contact transition for graphene/Ga2O3 interface. These results are uncovered by analyzing the interfacial dipole and potential step of graphene/Ga2O3 interface, and expected to enhance the application potential of graphene electrode in the β-Ga2O3 based electronic and optoelectronic devices.

Tuning Schottky barrier in graphene/InSe van der Waals heterostructures by electric field

The contacts between semiconductor and metal are vital in the fabrication of nano electronic and optoelectronic devices. The contact type has a great influence on the function realization and performance of the device. In order to prepare multifunctional devices with high performance, it is necessary to modulate the barrier height and contact type at the interface. First-principles calculations based on the density functional theory (DFT) are implemented in the VASP package. The generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA-PBE) with van der Waals (vdW) correction proposed by Grimme (DFT-D3) is chosen due to its good description of long-range vdW interactions. It is demonstrated that weak vdW interactions dominate between graphene and InSe with their intrinsic electronic properties preserved. We find that the n-type ohmic contact is formed at the graphene/InSe interface with the Fermi level through the conduction band of InSe (<i>Φ</i><sub>Bn</sub> < 0). The Fermi level of graphene/InSe heterostructure moves down to below the Dirac point of graphene layer, which results in p-type (hole) doping in graphene. Moreover, the external electric field is effective to tune the Schottky barrier, which can control not only the Schottky barrier height but also the type of contact. With the negative external electric field varying from 0 to –1 V/nm, the conduction band minimum of InSe below the Fermi level declines gradually but the n-type ohmic contact is still preserved. Nevertheless, with the positive external electric field varying from 0 to 0.8 V/nm, the conduction band minimum of InSe shifts upward and across the Fermi level, the conduction band minimum of InSe is closer to the Fermi level than the valence band maximum, which indicates that the n-type Schottky contact is formed. The Fermi level moves from the the conduction band minimum to the valence band maximum of InSe when the positive external electric field increases from 0.8 V/nm to 2 V/nm. The n-type Schottky barrier height exceeds the p-type Schottky barrier height gradually, which demonstrates that the positive external electric field transforms the n-type Schottky contact into the p-type Schottky contact at the graphene/InSe interface. When the positive external electric field exceeds 2 V/nm, the valence band of InSe moves upward and cross the Fermi level (<i>Φ</i><sub>Bp</sub> < 0), the ohmic contact is obtained again. Meanwhile, p-type (hole) doping in graphene is enhanced under negative external electric field and a large positive external electric field is required to achieve n-type (electron) doping in graphene. The external electric field can control not only the amount of charge transfer but also the direction of charge transfer at the graphene/InSe interface.

Remarkable Rashba spin splitting induced by an asymmetrical internal electric field in polar III-VI chalcogenides.

Herein, the Rashba spin orbit coupling (SOC) of polar group III-VI chalcogenide XABY (A, B = Ga, In; X ≠ Y = S, Se, Te) monolayers is investigated based on density functional theory. The different electronegativities of X and Y atoms lead to an asymmetrical internal electric field in the XABY monolayer; this implies that the internal electric field between A and X is not equal to that between B and Y. Mirror symmetry breaking in the XABY monolayer induces a remarkable Rashba spin splitting (RSS) at the conduction band minimum (CBM). Moreover, it is demonstrated that an external electric field and an in-plane biaxial strain can affect the internal electric field by varying the charge distribution, and this further manipulates the RSS. Under a positive external electric field and tensile strain, the RSS at the CBM exhibits a near-linear increasing behavior, whereas under a negative external electric field and compressive strain, the RSS displays a monotonous decreasing pattern. In addition, we explored the influence of interlayer coupling and substrate on the RSS. The stacking pattern of bilayer structures has a significant impact on the RSS. The investigation of SInGaSe on the Si(111) substrate suggests that the Rashba band is situated inside the large band gap of the substrate. Overall, our investigations suggest that the polar group III-VI chalcogenides are promising candidates for future spintronic applications.

Theoretical study of methane adsorption and C─H bond activation over Fe‐embedded graphene: Effect of external electric field

The effect of an external electric field (EF) on the methane adsorption and its activation on iron-embedded graphene (Fe-GPs) are investigated by using the M06-L density functional method. The EF is applied in the perpendicular direction to the graphene in the range of -0.015 to +0.015 a.u. with the interval of 0.005 a.u. The effects of EF on the adsorption, transition state and product complexes of the methane activation reaction are revealed. The binding energies of methane on Fe site in Fe-GPs are increased from -12.9 to -15.3, -18.1 and -21.5 kcal/mol for the negative EF of -0.005, -0.010 and -0.015, respectively. By applying positive EF, the activation barriers for methane activation are reduced in range of 3-8 kcal/mol (around 12-31%) and the reaction energies are more exothermic. The positive EF kinetically favors the reaction compared to the system without EF. The adsorption and activation of methane on Fe-GPs can be easily tuned by adjusting the external electric field for various applications. © 2019 Wiley Periodicals, Inc.

Piezoelectrically tunable resonance properties of boron nitride nanotube based resonators

Resonance properties such as the resonance frequency, the sensitivity, and the intrinsic dissipation of boron nitride nanotube (BNNT) based resonators are investigated in this work based on molecular dynamics simulations together with density functional theory calculations. A remarkable resonance property comparable to their carbon nanotube (CNT) counterparts is found in the present BNNT based resonators. Moreover, due to the unique piezoelectric characteristic of BNNTs, the resonance properties of BNNT based resonators can be efficiently tailored by external electric fields. It is found that when a negative electric field is applied, the resonance frequency and the sensitivity of BNNT based resonators can be significantly enhanced. This effect is attributed to the fact that due to the inverse piezoelectric response the applied negative electric field will induce a residual tensile stress in BNNTs and thus enhance their equivalent stiffness. Meanwhile, it is also found that the intrinsic dissipation of BNNT based resonators can be mitigated by a positive external electric field, since under this condition the thermoelastic dissipation and the phonon-phonon scattering of BNNTs are both reduced by the piezoelectric effect. Such unique piezoelectrically tunable resonance properties in BNNT based resonators render them have a broader spectrum of applications than their conventional CNT counterparts.

The studies on the physical and dissociation properties of chlorobenzene under external electric fields

Chlorobenzene is one of the Persistent Organic Pollutants (POPs) threatening human health. It is significant to study the degradation mechanism under external electric fields. Based on the density functional theory, the physical and dissociation properties including C–Cl bond length, total energy, dipole moment, frontier orbital energy, energy gap, IR spectrum, UV-vis absorption spectrum and potential energy curve are studied under external electric fields. According to these results, it is found that the C–Cl bond length becomes longer and tends to break with the increase of external electric field and the energy gap decreases with the increase of positive as well as negative external electric field. Moreover, the dissociation barrier in potential energy curve decreases and equilibrium bond length increases with increase of positive external electric field. And when external electric field reaches 0.040 atomic units ([Formula: see text], 1 atomic [Formula: see text], the dissociation barrier disappears which means that degradation of chlorobenzene occurs under strong external electric field due to the breakage of C–Cl bond. These results provide important references for studying the degradation mechanism of chlorobenzene under strong external electric fields.

Interlayer coupling and electric field tunable electronic properties and Schottky barrier in a graphene/bilayer-GaSe van der Waals heterostructure.

In this work, using density functional theory we investigated systematically the electronic properties and Schottky barrier modulation in a multilayer graphene/bilayer-GaSe heterostructure by varying the interlayer spacing and by applying an external electric field. At the equilibrium state, the graphene is bound to bilayer-GaSe by a weak van der Waals interaction with the interlayer distance d of 3.40 Å with the binding energy per carbon atom of -37.71 meV. The projected band structure of the graphene/bilayer-GaSe heterostructure appears as a combination of each band structure of graphene and bilayer-GaSe. Moreover, a tiny band gap of about 10 meV is opened at the Dirac point in the graphene/bilayer-GaSe heterostructure due to the sublattice symmetry breaking. The band gap opening in graphene makes it suitable for potential applications in nanoelectronic and optoelectronic devices. The graphene/bilayer-GaSe heterostructure forms an n-type Schottky contact with the Schottky barrier height of 0.72 eV at the equilibrium interlayer spacing. Furthermore, a transformation from the n-type to p-type Schottky contact could be performed by decreasing the interlayer distance or by applying an electric field. This transformation is observed when the interlayer distance is smaller than 3.30 Å, or when the applied positive external electric field is larger than 0.0125 V Å-1. These results are very important for designing new electronic Schottky devices based on graphene and other 2D semiconductors such as a graphene/bilayer-GaSe heterostructure.

Molecular dynamics simulation of the response of bi-disperse polyelectrolyte brushes to external electric fields**Project supported by the National Natural Science Foundation of China (Grant No. 21374052).

Langevin dynamics simulations have been performed to investigate the response of bi-disperse and strong polyacid chains grafted on an electrode to electric fields generated by opposite surface charges on the polyelectrolyte (PE)-grafted electrode and a second parallel electrode. Simulation results clearly show that, under a negative external electric field, the longer grafted PE chains are more strongly stretched than the shorter ones in terms of the relative change in their respective brush heights. Whereas under a positive external electric field, the grafted shorter chains collapse more significantly than the longer ones. It was found that, under a positive external electric field, the magnitude of the total electric force acting on one shorter PE chain is larger than that on one longer PE chain, or vice versa. The effects of smeared and discrete charge distributions of grafted PE chains on the response of PE brushes to external electric fields were also examined.

Response of bi-disperse polyelectrolyte brushes to external electric fields — A numerical self-consistent field theory study

The self-consistent field theory has been employed to numerically study the response of bi-disperse flexible polyelectrolyte (PE) brushes grafted on an electrode to electric fields generated by opposite surface charges on the PE-grafted electrode and a second parallel electrode. The numerical study reveals that, under a positive external electric field, the shorter and negatively charged PE chains are more responsive than the longer PE chains in terms of the relative changes in their respective brush heights. Whereas under a negative external electric field, the opposite was observed. The total electric force on the grafted PE chains was calculated and it was found that, under a positive external electric field, the magnitude of the total electric force acting on one shorter PE chain is larger than that on one longer PE chain, or vice versa. The underlying mechanism was unraveled through analyzing the total electric field across the two oppositely charged electrodes.

Electric field induced modification of magnetism in platinum tripod on pt (111) surface

Pt (111) hexagonal surface with tripod geometry constructed from four Pt atoms is investigated by first principle calculation. Interestingly, appreciable spin magnetic moment of 0.11μB per Pt tripod atom and 0.9μB per unit cell is observed without application of external electric field (EF). Further, the magnetic moment per Pt atom and/or unit cell can be tuned using EF of ±0.5V/Å. Negative EF enhances the spin magnetic moment of tripod Pt atom and unit cell up to 0.137μB and 1.29μB, respectively. Positive EF reduces the spin magnetic moment of tripod Pt atom and unit cell down to 0.087μB and 0.45μB, respectively.

Interface characteristics of thin liquid films in a charged lubricated contact

The interface characteristics of liquid films confined within a nanogap between a steel ball and a smooth glass disk after exposing to an external electric field (EEF) are reported in the paper. The emergence of micro-bubbles induced by the EEF has been found to be closely related with the electric current flow at both a positive EEF and a negative EEF. The polarity effect of the variation in the electric current flowing through a polar liquid film over time is more pronounced than that through a nonpolar liquid film. The surface of the contacting pair with the polar liquid film confined after the removal of the EEF is more severely damaged at a negative EEF, while no indication of damage has been observed on the surface contacting the nonpolar liquid film at either polarity. The bubbles generated under a positive EEF can collapse more readily than those generated under a negative EEF. Different mechanisms of these experimental phenomena have been discussed in the paper. Copyright © 2014 John Wiley & Sons, Ltd.

Intersubband Transitions in Asymmetric Quantum Wells with External Electric Field

The quantum-confined Stark effect on the optical absorption of intersubband transitions in an asymmetric AlxGa1-xN/In0.3Ga0.7N/GaN quantum wells is investigated by means of the density matrix formulism. The built-in electric field generated by the piezoelectric and spontaneous polarizations competing against to the external electric fields is considered. As the result, the influences of the built-in and external electric fields on the energy potentials and the eigen stares are discussed in detail. When the positive external electric field is applied, the peak values of the absorption coefficients from 3-2, 2-1 and 3-1 transitions are reduced and moved to the lower photon energy levels. With the negative field, the exactly opposite results can be obtained. Moreover, it is indicated that the results of the wavelengths from the 3-2, 2-1 and 3-1 transitions are reduced by the positive external electric field and increased by the negative field.