Electrostatic Field Distribution Research Articles

Diminish the screen effect in field emission via patterned and selective edge growth of ZnO nanorod arrays

The authors report on the field emission from controlled selective grown zinc oxide (ZnO) nanorod arrays by hydrothermal reaction. With the combined effect from a ZnO seed layer and a passivation layer for nanorod growth, ZnO nanorods could only grow on the edge of a 4 μm diameter circle. The ZnO nanorods hollow arrays present excellent electron emission characteristics duo to its typical morphology which can significantly diminish the screen effect. By calculating the electrostatic field distribution, it was found that the electrostatic field of the ZnO nanorods hollow arrays is significantly higher than that of the solid arrays.

Design of a mirror aberration corrector and a beam separator for LEEM

A SPLEEM (spin polarized low energy electron microscope) has been designed with a numerical simulation of electrostatic and magnetic field distributions and electron ray trajectories. Highly (more than 90%) spin polarized electron source has been used. A Wien type spin manipulator and a magnetic lens type spin rotator are used to align spin direction. A magnetic field free objective lens is designed to observe magnetic domain structure of magnetic materials. High or low magnification mode can be selected by using a combined electrostatic and magnetic objective lens for a high spatial resolution and a wide imaging area observation. An electrostatic mirror aberration corrector is installed after the image forming objective lens. A double deflection 45° beam separator is used to bend the direction of electrons from the source to the objective lens and from the objective lens to the mirror aberration corrector.

The role of paper-nip interactions on electrostatic toner transfer forces in Xerographic printing

We present a new model that uses a 3D stochastic fibre networks to simulate the role of paper structure and paper-nip interactions on the process of toner transfer in Xerographic printing. Our simulations show that the surface properties of paper under deformation in the print nip are critical in establishing the electrostatic field responsible for transferring toner to paper. When the spatial distributions of simulated electrostatic transfer fields – established in the presence of paper surfaces in a state of z-compression – are compared to the distribution of toner experimentally printed onto laboratory handsheet, good agreement is found.

On the electrostatic equilibrium of granular flow in pneumatic conveying systems

AbstractAn analytical methodology involving the concept of “electrostatic equilibrium” is developed for granular flow in pneumatic conveying systems. The methodology can be used for estimation of the electrostatic field distribution at various sections of the system and explanation of the mechanisms involved for various electrostatic phenomena observed. For all cases conducted in the conveying system, there was a “charging time” required for the system to reach the state of “electrostatic equilibrium.” Experiments conducted at different sections of the system showed that the time required increased in the order: horizontal pipe, vertical pipe, and pipe bend. Through a physical analysis, it is deduced that electrostatic equilibrium is related to the granules' behavior and local flow characteristics. In general, a longer time duration taken to reach equilibrium corresponds to a process with more complicated granular flow patterns. In the electrostatic equilibrium state, the field distribution shows the highest electrostatic field strength near the pipe wall, and this field strength degrades from the pipe wall to the pipe center. At various pipe sections, the highest strength occurs at the bend, in accord with observations that electric sparking first occurs at that location within the entire pneumatic conveying system. In the vertical pipe, granular distribution was measured using electrical capacitance tomography (ECT), and granular velocities were cross‐referenced with those using particle image velocimetry (PIV). The electrostatic force at low air flow rates is found to be the primary cause for granules sticking to the pipe wall and results in the formation of the half‐ring or ring structure. The state of electrostatic equilibrium is physically influenced by several elements in conveying systems. In a cyclic conveying system, a new pipe (or low humidity or no antistatic agent) tends to expedite the process to reach electrostatic equilibrium and attain high magnitude of electrostatic current at the state. In a non‐cyclic horizontal conveying system, a thin film (pipe) is found to prolong the process duration to reach equilibrium, while the case with charged film (pipe) takes shorter duration to do so. © 2006 American Institute of Chemical Engineers AIChE J, 2006

A numerical method for the solution of 3D-integral equations of electro-static theory based on Gaussian approximating functions

In this work, numerical solution of 3D-integral equations of electro-static theory for an infinite homogeneous medium with a heterogeneous isolated inclusion is considered. Gaussian approximating functions are used for discretization of the integral equations of the problem. These functions essentially simplify construction of the matrix of the system of linear algebraic equations to which the problem is reduced after discretization. The developed method is meshfree, and only the coordinates of the nodes (centers of the Gaussian functions) in the region occupied by the inclusion are initial data required for the realization of the method. For acceptable precision of the numerical solutions of 3D-problems, the number of nodes (approximating functions) should be sufficiently large, and after discretization, the original integral equation is reduced to a system of linear algebraic equations with a non-sparse matrix of high dimension. The multipole expansion method is proposed for the iterative solution of this system. The comparison of the numerical and exact distributions of electro-static fields inside spherical inclusions with radially changing properties is presented and analyzed.

Electrostatic field distribution at the sharp interface between high density matter and vacuum

Ultrahigh intensity lasers are proven to be particularly suitable for ion acceleration to energies above hundreds of keV and even in the multi MeV range, due to their interaction with either planar thin solid foils, or spherically symmetric targets. With reference to these problems, a quasistationary model is developed, where the Poisson equation for the electrostatic potential distribution at the sharp solid target-vacuum interface is solved for a nonrelativistic Maxwellian distribution of trapped electrons. Analytical solutions are given and ion acceleration in the relevant electrostatic field configurations is discussed.

Diamond-like carbon overcoat for TFMH using filtered cathodic arc system with Ar-assisted arc discharge

The deposition system described for sub-30 Å and thicker carbon (ta-C) overcoat that includes two RF ion beam guns and Filtered Cathodic Arc (FCA) module mounted on a single vacuum chamber. The system is capable of flattening the Thin Film Magnetic Heads (TFMH) surface by ion beam etching; smoothing scratches, trenches, steps on boundaries of different materials, and enhancing the adhesion by ion assisted ion beam sputtering. It provides the highly controllable deposition of carbon using an FCA module with Ar-assisted arc discharge. Low-level particulates are achieved on the deposited film surface (<5/cm2 ). It was shown that crucial impact on filtering the particles with size <1 μm has the electrostatic field distribution across the plasma guide that can be controlled by duct bias. Mechanical and electrical properties, optical and Raman spectra of ta-C films were investigated as a function of Ar flow in the arc discharge area. At Ar flow rates 0–12 sccm, stress of the films was varied in a range 2.9–7.5 GPa while hardness and Young's Modulus stayed in ranges of 45–60 GPa, and 230–300 GPa, respectively. Density of the obtained films was greater than 2.8 g/cm3. Optical absorption and electrical conductivity of ta-C films showed a significant rise while stress came down with Ar flow. Raman G-peak was higher for ta-C films with lower stress and shifted to lower energy. The low stress films versus high stress films showed a few orders reduced electrical resistance and anisotropy of specific resistance with respect to substrate plane: ρ⊥≫ρ∥. In situ ellipsometric control of growing film thickness was implemented on the system. Run-to-run standard deviation was less than 1 Å for 20–25 Å thick films. High corrosion resistance of FCA coatings was exhibited. The impact of Ar gas–carbon plasma interaction on the deposition conditions and microstructure of ta-C films was discussed.

A Simple Method of the Electric/Magnetic Field Observation by a Conventional Transmission Electron Microscope

A novel method to observe the electrostatic field distribution with a conventional transmission electron microscope has been developed. The method allows measurements of a potential difference less than 1V/µm. This method can be performed in any kind of conventional transmission electron microscope and applied to the observation of the electric/magnetic field at the level of a specimen.

Nanoelectromechanics of piezoresponse force microscopy

To achieve quantitative interpretation of Piezoresponse Force Microscopy (PFM), including resolution limits, tip bias- and strain-induced phenomena and spectroscopy, analytical representations for tip-induced electroelastic fields inside the material are derived for the cases of weak and strong indentation. In the weak indentation case, electrostatic field distribution is calculated using image charge model. In the strong indentation case, the solution of the coupled electroelastic problem for piezoelectric indentation is used to obtain the electric field and strain distribution in the ferroelectric material. This establishes a complete continuum mechanics description of the PFM contact mechanics and imaging mechanism. The electroelastic field distribution allows signal generation volume in PFM to be determined. These rigorous solutions are compared with the electrostatic point charge and sphere-plane models, and the applicability limits for asymptotic point charge and point force models are established. The implications of these results for ferroelectric polarization switching processes are analyzed.

Characterization of a spiral‐shaped time domain reflectometry probe

Time domain reflectometry is one of the most common methods to determine water content in porous media. Transmission lines used to carry the electromagnetic pulse can take many different forms and shapes and can be tailored to specific needs. Here we describe the design and characterization of a miniaturized transmission line, specifically designed for applications in laboratory settings. The sensor consists of a spiral‐shaped Cu waveguide, which is constructed by etching techniques used in printed circuit board manufacturing. The waveguides are 0.508 mm wide and have a separation of 0.508 mm. The overall diameter of the spiral is 42 mm, and the overall length of the waveguide is 38 cm. The probe was tested experimentally in media of different dielectric properties using a Tektronix cable tester. The electrostatic field distribution of the probe was simulated using a two‐dimensional numerical solution of the Laplace equation. The numerical analysis was used to compute a weighting function of the measurement and to determine the equivalent dielectric permittivity. For the range of permittivities expected in environmental porous media, such as soils and sediments, the sampling area of the probe was not affected by the water content of the medium.

Electrostatic field and charge distribution in small charged dielectric droplets

The charge distribution in small dielectric droplets is calculated on the basis of continuum medium approximation. There are considered charged liquid spherical droplets of methanol in the range of nanometer sizes. The problem is solved by the following way. We find the free energy of some ion in dielectric droplet, which is a function of distribution of other ions in the droplet. The probability of location of the ion in some element of volume in the droplet is a function of its free energy in this element of volume. The same approach can be applied to other ions in the droplet. The obtained charge distribution differs considerably from the surface distribution. The curve of the charge distribution in the droplet as a function of radius has maximum near the surface. Relative concentration of charges in the vicinity of the center of the droplet does not equal to zero, and it is the higher, the less is the total charge of the droplet. According to the estimates the model is applicable if the droplet radius is larger than 10 nm.

Fields, Focusing, and Aberration in Electrostatic Accelerator Tubes

Electrostatic field distributions and particle trajectories have been computed using a standard software package for a number of geometries typical of the accelerator tubes used in modern electrostatic accelerators. The results have been used to confirm the validity of approximate formulae for the focusing action of the entrance and exit lens and to determine the effect of lens aberrations on the subsequent emittance and brightness of the beam. Nonuniform field distributions in the interior of the tube, due to finite electrode thickness, have been calculated for a range of parameters and the action of these fields on typical particle trajectories examined. Full three-dimensional finite-element calculations have been applied to the inclined-field geometries that are used to suppress secondary electrons in high-voltage systems. Particle trajectories through such tubes show the expected first-order deflections but higher order effects are shown to be small in typical designs.

Dynamic characteristics of shaped micro-actuators solved using the differential quadrature method

This study examined the dynamic characteristics of nonlinear electrostatic pull-in behavior for shaped actuators in micro-electro-mechanical systems (MEMS). The natural frequencies of a fixed–fixed shaped beam vibrating around its statically deflected position were calculated using the differential quadrature method (DQM). The proposed model included the nonlinear interaction between the curved electrostatic field force and the shaped micro-beam, as well as the mid-plane stretching, axial residual stress and electrical field fringing effect. Very good agreement existed between the results simulated using the proposed model and the measured data. This work also investigated the micro-beam and electrode shape effect on the natural frequencies of the actuator system. Analytical results indicate that the variation in the micro-beam and the electrode shapes might not only influence the electrostatic field distribution but also significantly alter the dynamic characteristics of the micro-actuator. Analytical results demonstrate that the shaped micro-beam with curved electrode can increase the working voltage range approximately six times compared to the rectangular micro-beam and flat electrode.

Improvement of magnetic field calculations by extrapolation

Magnetic field calculations by the boundary element method (BEM) are appropriate to particle optics simulation due to the inherent smoothness of field values, which is a consequence of the integral formulation of the problem. This allows the use of high-order and accurate ray tracing algorithms, as well as radial analytical continuation of axial data to obtain fields and potentials off axis with high accuracy in problems with radial symmetry. As shown for electrostatic field distributions in an earlier paper, magnetic field calculations can also be improved by orders of magnitude by extrapolation of a set of simulations with different numbers of boundary elements to arbitrarily fine discretisation. As examples for magnetic fields, in this paper we analyse a common magnetic lens with non-symmetric pole pieces and a lens with open magnetic circuit, which is a well-known test case in the literature. We will demonstrate how even artefacts, originating from insufficient numerical analysis or inherent difficulties of the BEM, can be suppressed by the extrapolation technique.

Transport properties of SINIS junctions with high-current density

We have fabricated Nb/Al/sub 2/O/sub 3//Al/Al/sub 2/O/sub 3//Nb devices with different current densities using a conventional fabrication process, varying pressure and oxidation time. Patterning of the multilayers was done using standard photolithography and electron-beam lithography. The current density of SINIS junctions was changed in the range from 0.5 kA/cm/sup 2/ to 20 kA/cm/sup 2/. We achieved characteristic voltages up to 0.35 mV. By fabricating sub-/spl mu/m junction with a width from 0.1 /spl mu/m to 0.5 /spl mu/m, we have studied the influence of the asymmetry of barriers on transport properties. By comparing the experimental and theoretical temperature dependence of the characteristic voltage we estimated the barrier transparency and its asymmetry. The comparison shows a good agreement of experimental data with the theoretical model of tunnelling through double-barrier structures in the dirty limit. A new approach for determination of the asymmetry of both barriers based on the measurement of the electrostatic field distribution in the SINIS structure has been developed.

Solution NMR Structure of Ribosome-binding Factor A (RbfA), A Cold-shock Adaptation Protein from Escherichia coli

Ribosome-binding factor A (RbfA) from Escherichia coli is a cold-shock adaptation protein. It is essential for efficient processing of 16 S rRNA and is suspected to interact with the 5′-terminal helix (helix I) of 16 S rRNA. RbfA is a member of a large family of small proteins found in most bacterial organisms, making it an important target for structural proteomics. Here, we describe the three-dimensional structure of RbfAΔ25, a 108 residue construct with 25 residues removed from the carboxyl terminus of full-length RbfA, determined in solution at pH 5.0 by heteronuclear NMR methods. The structure determination was carried out using largely automated methods for determining resonance assignments, interpreting nuclear Overhauser effect (NOE) spectroscopy (NOESY) spectra, and structure generation. RbfAΔ25 has an α+β fold containing three helices and three β-strands, α1-β1-β2-α2-α3-β3. The structure has type-II KH-domain fold topology, related to conserved KH sequence family proteins whose βααβ subunits are characterized by a helix-turn-helix motif with sequence signature GxxG at the turn. In RbfA, this βααβ subunit is characterized by a helix-kink-helix motif in which the GxxG sequence is replaced by a conserved AxG sequence, including a strongly conserved Ala residue at position 75 forming an interhelical kink. The electrostatic field distribution about RbfAΔ25 is bipolar; one side of the molecule is strongly negative and the opposite face has a strong positive electrostatic field. A “dynamic hot spot” of RbfAΔ25 has been identified in the vicinity of a β-bulge at strongly conserved residue Ser39 by 15N R 1, R 2 relaxation rate and heteronuclear 15N– 1H NOE measurements. Analyses of these distributions of electrostatic field and internal dynamics, together with evolutionary implications of fold and sequence conservation, suggest that RbfA is indeed a nucleic acid-binding protein, and identify a potential RNA-binding site in or around the conserved polypeptide segment Ser76–Asp100 corresponding to the α3-loop-β3 helix-loop-strand structure. While the structure of RbfAΔ25 is most similar to that of the KH domain of the E. coli Era GTPase, its electrostatic field distribution is most similar to the KH1 domain of the NusA protein from Thermotoga maritima, another cold-shock associated RNA-binding protein. Both RbfA and NusA are regulated in the same E. coli operon. Structural and functional similarities between RbfA, NusA, and other bacterial type II KH domains suggest previously unsuspected evolutionary relationships between these cold-shock associated proteins.

Nanoelectromechanics of Piezoresponse Force Microscopy: Contact Properties, Fields Below the Surface and Polarization Switching

ABSTRACTTo achieve quantitative interpretation of Piezoresponse Force Microscopy (PFM), including resolution limits, tip bias- and strain-induced phenomena and spectroscopy, knowledge of elastic and electrostatic field distributions below the tip is required. The exact closed form solution of the coupled electroelastic problem for piezoelectric indentation is derived and used to obtain the tip-induced electric field and strain distribution in the ferroelectric material. This establishes a complete continuum mechanics description of the PFM imaging mechanism. These solutions are reduced to the point charge/force behavior for large separations from contact, and the applicability limits and charge/force magnitude for these models are established. The implications of these results for ferroelectric polarization switching processes are analyzed.

Reactive ion etching of quartz and Pyrex for microelectronic applications

The reactive ion etching of quartz and Pyrex substrates was carried out using CF4/Ar and CF4/O2 gas mixtures in a combined radio frequency (rf)/microwave (μw) plasma. It was observed that the etch rate and the surface morphology of the etched regions depended on the gas mixture (CF4/Ar or CF4/O2), the relative concentration of CF4 in the gas mixture, the rf power (and the associated self-induced bias) and microwave power. An etch rate of 95 nm/min for quartz was achieved. For samples covered with a thin metal layer, ex situ high resolution scanning electron microscopy and atomic force microscopy imaging indicated that, during etching, surface roughness is produced on the surface beneath the thin metallic mask. Near vertical sidewalls with a taper angle greater than 80° and smooth etched surfaces at the nanometric scale were fabricated by carefully controlling the etching parameters and the masking technique. A simulation of the electrostatic field distribution was carried out to understand the etching process using these masks for the fabrication of high definition features.

Structural Proteomics of Eukaryotic Gene Families.

INTRODUCTION. Genome sequencing projects have already determined nearly complete genome sequences of several organisms, including human. The products of these genes are widely recognized as the next generation of therapeutics and targets for the development of pharmaceuticals. While identification of these genes is proceeding quickly, elucidation of their three-dimensional (3D) structures and biochemical functions lags far behind. In some cases, knowledge of 3D structures of proteins can provide important insights into evolutionary relationships that are not easily recognized by sequence alignment comparisons. Thus, structure determination by NMR or X-ray crystallography can sometimes provide key information regarding protein fold class, locations and clustering of conserved residues, and surface electrostatic field distributions that connect a protein sequence with potential biochemical functions. The resulting limited set of putative biochemical functions can then be tested by appropriate biochemical assays.

Modification of cell response to insulin by membrane-Acting agents in rat white adipocytes: analysis of structural features by computational simulation

The effect of membrane-acting agents, biscoclaurine alkaloids (cepharanthine, tetrandrine, isotetrandrine), carbobenzoxy-d-Phe-l-Phe-Gly (z-FFG), and tyrphostin AG17, on the insulin-involved fatty acid synthesis by an β-agonist (e.g., isoproterenol) in adipocytes was examined. The alkaloids dose-dependently enhanced the insulin-involved fatty acid synthesis in rat white adipocytes, stabilized the C6-NBD-PC (1-acyl-2-[6-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-caproyl]-sn-glycero-3-phosphatidylcholine) model membrane, and suppressed the phospholipase A2-induced phospholipid degradation. In contrast, z-FFG had no effect on the fatty acid synthesis or the membrane stability. Tyrphostin AG17 suppressed insulin action, but promoted the model membrane stabilization. In the same culture conditions as for the fatty acid synthesis assay, cepharanthine, z-FFG and tyrphostin AG17 had no effect on the transcript levels of glucose transporter isoforms (GLUT 1, 4) and hexokinase isozymes (HK I, II) in rat white adipocytes. Thus, these membrane-acting agents modify the insulin action via a change in the cell membrane condition, and do not directly act on the insulin-involved glucose metabolism. Then we analyzed the structural conformation of these membrane-acting agents by computational simulations. The alkaloids had an elliptic macrocyclic structure, and the order of ellipticity (cepharanthine>tetrandrine>isotetrandrine) agreed with that of the modifying ability for insulin action. The distribution of electrostatic potential fields of these alkaloids was essentially equal by turn in surrounding with the dipole moments. Both in z-FFG and tyrphostin AG17, the distribution pattern of electrostatic potential fields was different from that of the alkaloids. Judging from these results, we concluded that the electrostatic potential field is a good index of the modification of insulin action, and the elliptic structure in these alkaloids is regarded with the modification of insulin action.