Uniform Transverse Electric Field Research Articles

Direct measurement of the viscoelectric effect in water

The viscoelectric effect concerns the increase in viscosity of a polar liquid in an electric field due to its interaction with the dipolar molecules and was first determined for polar organic liquids more than 80 y ago. For the case of water, however, the most common polar liquid, direct measurement of the viscoelectric effect is challenging and has not to date been carried out, despite its importance in a wide range of electrokinetic and flow effects. In consequence, estimates of its magnitude for water vary by more than three orders of magnitude. Here, we measure the viscoelectric effect in water directly using a surface force balance by measuring the dynamic approach of two molecularly smooth surfaces with a controlled, uniform electric field between them across highly purified water. As the water is squeezed out of the gap between the approaching surfaces, viscous damping dominates the approach dynamics; this is modulated by the viscoelectric effect under the uniform transverse electric field across the water, enabling its magnitude to be directly determined as a function of the field. We measured a value for this magnitude, which differs by one and by two orders of magnitude, respectively, from its highest and lowest previously estimated values.

Electro-optical properties of zigzag and armchair boron nitride nanotubes under a transverse electric field: Tight binding calculations

The electro-optical properties of zigzag and armchair BNNTs in a uniform transverse electric field are investigated within tight binding approximation. It is found that the electric field modifies the band structure and splits band degeneracy where these effects reflect in the DOS and JDOS spectra. A decrease in the band gap, as a function of the electric field, is observed. This gap reduction increases with the diameter and it is independent of chirality. An analytic function to estimate the electric field needed for band gap closing is proposed which is in good agreement with DFT results. In additional, we show that the larger diameter tubes are more sensitive than small ones. Number and position of peaks in DOS and JDOS spectra for armchair and zigzag tubes with similar radius are dependent on electric field strength.

The transient dynamics of a liquid column in a uniform transverse electric field of small strength

Abstract The transient behavior of a leaky dielectric liquid column under a uniform transverse electric field of small strength is investigated analytically. It is shown that for small distortion from a circular shape, the column boundary deforms to an ellipse and the deformation time history, D − t , is D = D ∞ [ 1 − exp ( − t / τ ) ] , where D ∞ is the steady state deformation and τ = a ( μ i + μ o )/ γ is the characteristic time, a , γ , and μ ˜ = μ i / μ o being the drop radius, the surface tension, and ratio of the drop viscosity to that of the ambient fluid, respectively.

Destruction of quasi-Landau levels in nanographene ribbons by the external electric fields

Our study reveals that the magneto-electronic properties of the zigzag nanographene ribbons are tuned by the external electric fields. The spatially modulated electric field (the uniform transverse electric field) converts the dispersionless Landau levels into subbands with the sinusoidal (linear) energy dispersions. The energies of the band-edge states are affected by the electric potentials. The localization positions and the spatial symmetry of the Landau wave functions are altered. The modulated electric potential with shorter periodic length has stronger influence on the quasi-Landau levels. The magneto-optical absorption spectra are expected to be changed by the external electric fields.

Uniform-field transverse electroreflectance using a mode-locked laser and a radio-frequency bias

We describe a technique for transverse electroreflectance that uses broadband optical pulses from a mode-locked laser and a rapidly oscillating bias with a frequency near half the laser repetition rate. Since the electrodes are electrically isolated from the sample, highly nonuniform trap-enhanced fields do not occur. Because the time-averaged electric field is zero, space charges do not build up. Experimental results are presented for semi-insulating GaAs. The technique is also useful in ultrafast experiments that require a uniform transverse electric field.

The EHD-driven fluid flow and deformation of a liquid jet by a transverse electric field

The aim of this study is to investigate the effect of a uniform transverse electric field on the steady-state behavior of a liquid cylinder surrounded by another liquid of infinite extent. The governing electrohydrodynamic equations are solved for Newtonian and immiscible fluids in the framework of leaky-dielectric theory and in the limit of small electric field and fluid inertia. A detailed analysis of the electrical and hydrodynamic stresses acting on the interface separating the two fluids is presented, and an expression is found for the interface deformation for small distortions from a circular shape. The electrical stresses acting on the interface of two leaky-dielectric liquids are compared with those acting on an interface separating a perfect dielectric or infinitely conducting core fluid cylinder from a surrounding perfect dielectric fluid. A comparison is made between the results of this study and those of a similar study for fluids with permeable interfaces and the classical results for liquid drops.

Electronic and optical properties of single-walled carbon nanotubes under a uniform transverse electric field: A first-principles study

A systematic study on the effect of a transverse electric field on the optical properties of carbon nanotubes has been performed using density-functional calculations. The band gaps of the zigzag tubes decrease significantly as the electric field is increased. In the case of armchair tubes, the metallic band energy dispersion relation develops multivalleys at the Fermi level at high fields. The electric-field-induced changes in band dispersions lead to changes in optical properties as manifested in the dielectric functions. Some of the changes are not obvious. For example, a significant field-induced change in band gap can lead to small changes in dielectric functions in some special cases. Our results show that the armchair carbon nanotubes can be a promising material for electro-optical modulation device applications.

Negative bias–temperature stress in non-self-aligned p-channel polysilicon TFTs

The electrical instabilities in p-channel polysilicon TFTs induced by negative bias temperature stress (NBTS) and self-heating have been investigated. From NBTS experiments performed at different temperatures and gate bias, we derived an empirical relationship that provides the T and electric field dependence of the interface state generation. To explain the device instability related to self-heating we considered a spatially non uniform interface state distribution, as a non uniform transverse electric field is present during bias stress. The interface state distribution can be deduced using the empirical relationship, determined from NBTS experiments, and considering the spatial distribution of the oxide electric field, obtained from numerical simulations. Using the so determined interface state distribution it was possible to perfectly reproduce not only the transfer characteristics but also the asymmetry observed in the output characteristics, when source/drain contacts are reverted after bias stress.

Competition between intertube interactions and external electric fields on a pair of narrow-gap carbon nanotubes

A uniform transverse electric field is applied to a pair of narrow-gap carbon nanotubes with intertube interactions, and the electronic structures at low energy are studied within the tight-binding model. Unlike a single nanotube, the band structures of an aligned pair vary with not only the strength of the electric field but its direction. When the transverse field is applied along the plane containing both tube axes of the pair, the low energy bands are found to have significant changes with the field strength higher than 0.01 V / A ˚ , only a tenth of the order for a single tube. A small energy gap could be opened by the intertube interactions, nevertheless, the hybridization of atomic wave functions between tubes is suppressed by increasing the electric field. By contrast, a field perpendicular to the plane of tube axes alters the band structures at the same level as for a single tube, and the electronic states between tubes are still strongly coupled.

Band structure and absorption spectrum of double-walled zigzag carbon nanotubes in an electric field

The electronic structure of the (9, 0)–(18, 0) double-walled zigzag carbon nanotubes in the presence of a uniform transverse electric field is studied by the tight-binding model. The electric field could induce the semiconductor–metal transition, change the direct gap into the indirect gap, alter the subband curvatures, destroy the double degeneracy, produce the new band-edge states, make more subbands group around the Fermi level, and widen the π-band width. Such effects are directly reflected in density of states and optical excitation spectra. The absorption spectra exhibit a lot of prominent peaks, mainly owing to the rich one-dimensional energy subbands. The intensity, the number, and the frequency of absorption peaks are strongly modulated by the electric field. The modulation of electronic and optical properties is amplified by the parallel magnetic field. The predicted electronic and optical properties can be, respectively, verified by the conductance measurements and the optical spectroscopy.

Dielectric screening for carbon nanotubes in a gating electric field

We use the sp 3 tight-binding model to calculate electronic structures of single-walled carbon nanotubes. All the π and σ electrons would take part in charge screening. As a result of the cylindrical symmetry, the momentum ( q) and angular momentum transfer ( L) are conserved in the electron–electron Coulomb interactions. The static dielectric function ε ( q, L), which determines the charge screening ability, is evaluated from the random-phase approximation. ε of L = 1 at long wavelength limit ( q → 0 ) is very important in understanding the dielectric screening in the presence of a uniform transverse electric field E ⊥ . ε ( q = 0 , L = 1 ) hardly depends on the chiral angle, and the dependence on the nanotube radius is weak. It quickly grows as the Fermi level increases, that is, the screening response is largely enhanced by the increasing free carriers.

Charge screening of single-walled carbon nanotubes in a uniform transverse electric field

Charge screening of single-walled carbon nanotubes in a uniform transverse electric field

Particle acceleration at an X‐type reconnection site with a parallel magnetic field

The acceleration of charged particles at a two‐dimensional magnetic reconnection site is investigated. The magnetic field has an X‐type neutral point, while reconnection is driven by a uniform transverse electric field; the effect of including a uniform magnetic field component parallel to the driving electric field and transverse to the plane of the X point is studied. We focus on the adiabatic motion of strongly magnetized particles, a valid assumption everywhere for sufficiently strong parallel magnetic fields but one which excludes a region around the neutral point for weaker fields. The regime of interest is fast driven reconnection, in which the electric drift is strong. The trajectories of particles and their dependence on the magnitude of the parallel magnetic field component are investigated. Particles can be accelerated along the magnetic field lines both because of the coupling of the perpendicular electric drift with the parallel motion, which occurs in an inhomogeneous magnetic field, and the direct acceleration by the electric field. The energy spectra of particles leaving the reconnection site are also calculated.

Interaction forces of dielectric cylinders in electric fields

The electric field configuration and forces in a dielectric system of two long circular cylindrical bodies is studied in detail. The cylinders are parallel to each other and situated in a uniform transverse electric field. The cylinder bodies and surrounding medium have arbitrary and different permittivities. The origin of the forces in the piecewise-homogeneous material under study is polarization in the dielectrics. The local forces on the surfaces of the cylinders are examined. It is shown that the cylinders exert forces on each other. The total forces and torques depend on the dielectric materials, the geometric parameters of the system, and the orientation of the applied electric field. Under these conditions the problem has a complete analytic solution.

Investigation of internuclear axis alignment with projectile direction in recoil ion production from ion-molecule collisions

We have developed an experimental system to measure the dependence of the cross section for the production of recoil fragments from molecular targets on the alignment of the internuclear axis of the molecule with respect to the beam. Recoil N q+ ( q = 1–5) ions, produced by a 19 MeV F 9+ beam on an N 2 target, are extracted in a uniform transverse electric field and allowed to fall onto a two-dimensional position-sensitive channel-plate detector. The flight time of each recoil is used to determine its charge state. The beam is charge-state-analyzed and coincidences between recoils and projectiles are measured. Information on the alignment of the molecule prior to its Coulomb explosion is extracted from the spectrum of positions with which the recoil fragments strike the recoil detector. Clear alignment effects are seen for the highest and lowest recoil charge states.