Wire Dimensions Research Articles

Calibration of magnetic force microscopy tips by using nanoscale current-carrying parallel wires

Experimental results on the characterization of commercially available magnetic force microscopy (MFM) thin film tips as a function of an external magnetic field are presented. Magnetic stray fields with a definitive z-component (perpendicular to the substrate) and a magnetic field strength of up to Hz=±45 Oe are produced with current carrying parallel nanowires with a thickness of t=60 nm, which are fabricated by electron-beam lithography. The magnetic fields are generated by electrical dc-currents of up to ±6 mA which are directed antiparallel through the nanowires. The geometry and the dimensions of the nanowires are systematically varied by choosing different wire widths w as well as separations b between the parallel wires for two different sets of samples. On the one hand, the wire width w is varied within 380 nm<w<2460 nm while the separation b≈450 nm between the wires is kept constant. On the other hand the separation b between the parallel wires is varied within 120 nm<b<5100 nm, while the wire width w=960 nm is kept constant. For all the geometrical configurations of parallel wires the resulting magnetic contrast is imaged by MFM at various tip lift-heights. By treating the MFM tip as a point probe, the analysis of the image contrast as a function of both the magnetic field strength and the tip lift height allows one to quantitatively determine the effective magnetic dipole and monopole moments of the tip as well as their imaginary locations within the real physical tip. Our systematic study quantitatively relates the above point-probe parameters to (i) the dimensions of the parallel wires and (ii) to the characteristic decay length of the z-component of the magnetic field of parallel wires. From this the effective tip-volume of the real thin film tip is determined which is relevant in MFM-imaging. Our results confirm the reliability of earlier tip calibration schemes for which nanofabricated current carrying rings were used instead of parallel wires, thereby proving that the tip calibration equations depend on the underlying stray field geometry. Finally, we propose an experimental approach which allows one to measure the magnetization of nanoscale ferromagnetic elements with an in-plane orientation of the magnetization, quantitatively, by using a calibrated MFM-tip.

An Improved Model of Cored Wire Injection in Steel Melts

Mathematical models for tracking the melting of cored wire during its injection into the steel bath have been developed in the past though important aspects of the formulations have not been discussed in sufficient detail. As a result, it is difficult to use the results of these models to derive benefits for a specific steel melting shop. A general purpose mathematical model has been developed at R & D, Tata Steel, using the finite difference approach with a fully implicit scheme to simulate the process of cored wire injection taking into account the different operating practices encountered in the steel shop. Numerical simulation of this kind of problem, involving moving boundary, typically suffers from the limitation that the progressive solidification of frozen layers that takes place is not made part of the thermal balance till it attains the size of a full and thus the heat gained or lost by this partial node is not accounted for till such time. An alternative numerical formulation has been developed to rectify this. Owing to the difficulty in making a direct validation, this model has been verified through a novel approach. This work suggests that the use of different wire dimensions (13-18 mm diameter and 0.4-0.6 mm casing), depending on the steel grades to be processed, is necessary in order to extract the maximum benefit.

Optical Properties of Excitons in Quantum Well Wires Under the Magnetic Field

The binding energy of excitons in quantum well wires of GaAs surrounded by Ga 1-x Al x As was calculated in an effective mass approximation with the use of the variational approach. Results obtained show that the exciton binding energies depend on the sizes of the wire and the strength of the magnetic field. The exciton theory was then used to calculate the linear absorption coefficient of HH1–C1 excitons by varying the wire dimensions and magnetic field values.

Intersubband absorption in V-groove quantum wires

This article describes intersubband optical transitions in V-groove quantum wires and the resulting absorption. It is demonstrated that the optical absorption spectrum can be modified and controlled by varying the quantum wire dimensions. In addition, the importance of the conduction band nonparabolicity in calculating the absorption spectrum is pointed out. Finally, a possible application of this structure as a converter to the far-infrared wavelength range is discussed.

Optical Cavity Effects in ZnO Nanowire Lasers and Waveguides

Wide band gap semiconductor nanostructures with near-cylindrical geometry and large dielectric constants exhibit two-dimensional ultraviolet and visible photonic confinement (i.e., waveguiding). Combined with optical gain and suitable resonant feedback, the waveguiding behavior facilitates highly directional lasing at room temperature in controlled-growth nanowires. We have characterized the nanowire emission in detail with high-resolution optical microscopy. The waveguiding behavior of individual zinc oxide (ZnO) nanowires depends on the wavelength of the emitted light and the directional coupling of the photoluminescence (PL) to the emission dipoles of the nanowire. Polarization studies reveal two distinct regimes of PL characterized by coupling to either guided (bound) or radiation modes of the waveguide, the extent of which depends on wire dimensions. Pumping with high pulse energy engenders the transition from spontaneous to stimulated emission, and analysis of the polarization, line width, and line spacing of the laser radiation facilitates identification of the transverse and longitudinal cavity modes and their gain properties. Interpretation of the lasing spectra as a function of pump fluence, with consideration of ZnO material properties and ultrafast excitation dynamics, demonstrates a transition from exciton (fluence 1 IJ/cm 2 ) and gain saturation behavior (fluence > 3 IJ/cm 2 ) modified by the constraints of the nanoscale cylindrical cavity.

Multi-component behavior of the photoluminescence lifetime in porous Si

The photoluminescence lifetimes have been calculated within effective mass approximation for porous Si modeled as a system of wires with dispersion in their sizes and in their crystallographic directions. It comes out that the magnitude of the PL lifetime depends considerably on the wire crystallographic orientations and the wire dimensions. This dependence may be connected with the multicomponent exponential decay law of the PL observed experimentally in some samples of porous Si.

Theoretical Thermal Conductivity of Periodic Two-Dimensional Nanocomposites

ABSTRACTA phonon Boltzmann transport model is established to study the lattice thermal conductivity of nanocomposites with nanowires embedded in a host semiconductor material. Special attention has been paid to cell-cell interaction using periodic boundary conditions. The simulation shows that the temperature profiles in nanocomposites are very different from those in conventional composites, due to ballistic phonon transport at nanoscale. The thermal conductivity of periodic 2-D nanocomposites is a strong function of the size of the embedded wires and the volumetric fraction of the constituent materials. At constant volumetric fraction the smaller the wire diameter, the smaller is the thermal conductivity of periodic two-dimensional nanocomposites. For fixed silicon wire dimension, the lower the atomic percentage of germanium, the lower the thermal conductivity of the nanocomposites. The results of this study can be used to direct the development of high efficiency thermoelectric materials.

Magnetoelastic anisotropy of amorphous microwires

Anisotropy constants of amorphous microwires with positive, negative, and nearly zero magnetostriction, are calculated as function of wire dimensions starting from the distribution of internal stresses induced during preparation. Some basic aspects of their magnetic behavior are subsequently discussed, in correlation with earlier experimental results.

Free-carrier absorption in semiconducting quantum well wires for alloy-disorderscattering

A theory of free-carrier absorption is given for quasi-one-dimensional ternarysemiconducting structures when the carriers are scattered by alloy disorder andthe radiation field is polarized along the length of the wire. The free-carrierabsorption coefficient is found to be an oscillatory function of the photonfrequency and of the area of the cross-section of the wire. It is found that theabsorption coefficient increases with decreasing transverse dimension of thequantum wire. The results obtained are compared with those from the quantumtheory of free-carrier absorption in quasi-two-dimensional structures. In addition,it was found that in quantum wire the electron–alloy-disorder interaction gives agreater contribution to the absorption than the electron–acoustic phononinteraction.

Luminescence properties of Zn nanowires prepared by electrochemical etching

We have prepared samples of Zn wire structures by electrochemical anodization and measured their photoluminescence spectra at various temperatures. Scanning electron micrographs (SEM) were also taken on these samples. It was found that the dimension of the Zn wires has a definite influence on the photoluminescence (PL) spectra. Specifically, large wire dimensions exhibit a blue/violet luminescence. In addition to this blue/violet luminescence, nanowires of Zn about 20 nm in diameter exhibit a PL peak at 379 nm, which is the characteristic of ZnO. Low-temperature PL measurements on these Zn nanowires reveal three distinct excitonic emission peaks similar to high-quality ZnO. These results strongly suggest that high-quality ZnO nanowires can be formed by electrochemical etching of Zn.

Strategic flat rolling of Ag/BSCCO-2223 tapes

In the process of single-step flat rolling of multifilament Ag/BSCCO-2223 wire to tape previous work has shown the optimum strategy giving maximum critical current density to be a balance between the length and width strain, so they are of equal size i.e. so, that the logarithmic strain ratio, LSR, reaches zero. In order to investigate the possible improvements by using multistep flat rolling, a new strategy to control the LSR in each individual step, i.e. to control the differential logarithmic strain ratio DLSR, has been investigated. The present paper shows that appropriate choice of the processing conditions may be used to reach DLSR=0 in each step, and suggests dimensionless parameters applicable to transfer the results to other wire dimensions. The tapes produced engineering current densities of up to 7.6 kA/cm 2 with an average of 7.2 kA/cm 2.

Fabrication of Bi-2212 ROSATwire with reduced silver content

Bi-2212 rotation symmetric arranged tape-in-tube wires (ROSATwires) with small anisotropy and accurate wire dimensions are promising for the practical applications such as magnets for NMR and MRI. In this study, we show the preliminary results of a new fabrication method for Bi-2212/Ag ROSATwire with a reduced silver content, that improves the transport performance and cost effectiveness. Improved flatness between the Bi-2212 and the silver interface is also obtained. The silver to core ratio was reduced to 1.3. An engineering critical current density ( J e) of the present ROSATwire with reduced silver content reached 105 A/mm 2 at 4.2 K and 24 T for a round shaped wire, and >200 A/mm 2 for a rectangular shaped wire, showing an increase of 40% compared to the conventionally processed wire.

A database-oriented eddy current loss estimation for the reactor windings of HVDC filters

In the design of reactors, it is desired to develop a practical estimation method of eddy current loss in conductors under the field of arbitrary direction. In this paper, a database-oriented estimation technique is proposed by using the eddy current losses of standard conductor obtained by the finite element method. It is shown that the estimated eddy current losses at arbitrary dimensions of wire, spatial angle and frequency of flux density are in good agreement with measured ones. The practical estimation technique described here is utilized in the design of large power filters for the HVDC (High Voltage DC) project in Japan.

Erratum to “A Unified Look at Berenger's PML for General Anisotropic Media”

To better understand the effect of wire thickness and width on the TWT small-signal gain, two 3-D charts are also presented. The average small-signal gain in the frequency band as a function of the wire width and thickness, expressed as a percentage value with respect to the nominal value, is Ž . plotted in Figure 3 a . The figure shows that the variation due to the wire thickness is more remarkable than the variation Ž due to the wire width. The small-signal gain flatness percentage variation between the higher and lower gain value in . the 10 13 GHz frequency band as a function of the wire Ž . width and thickness is plotted in Figure 3 b . It can be observed that both of the dimensions affect the gain flatness behavior, and this effect is more evident for a smaller value of wire thickness. This study shows that the tolerance of the wire dimensions must be carefully considered in the framework of a good TWT design.

Stability and control of electrodynamic tethers for de-orbiting applications

Electrodynamic tethers provide a very promising propulsion system for de-orbiting of spent upper stages or LEO satellites. In this application, the Lorentz force generated by the interaction between the current in the wire and the geomagnetic field produces an electrodynamic drag leading to a fast orbital decay. The attractiveness of tether system lies especially in their capability to operate with uncontrollable satellites and in the modest mass requirement. The need for significant along-track forces leads however to the onset of an undesirable torque which, if not controlled, may drive the system into a dangerous instability. The electrodynamic torque determines in-plane and out-of-plane librations whose amplitude depends upon the current in the wire, mass distribution and system dimensions. Even more important, this torque is modulated along the orbit due to the changing magnetic field and ionospheric plasma density, giving rise to forced oscillations. The counteracting (and stabilizing) gravity-gradient torque is generally to small to ensure stability in typical, strongly non-symmetrical mass distributions, where a massive satellite or upper stage is attached at the lower end and a light electron collecting device (or passive ballast mass) is deployed a few kilometers above. Reducing the electron current or increasing the mass at the upper end are both unattractive solutions. In this paper we show how the electrodynamic torque pumps energy into the system (finally leading to large librations angles) and indicate that many proposed configurations are intrinsically unstable. Our results point out the need for a control strategy. Fortunately, the librations amplitudes can be limited by acting on the current flowing in the wire. Our model of a rigid, conductive tether shows that a control based upon timely current switch-off, using energy criteria, is indeed effective and simple to implement. The resultant duty-cycles are satisfactory and affect only marginally the de-orbiting times.

半導体のトランスファー成形工程における金線変形予測手法の検討 第３報 ＢＧＡパッケージとＱＦＰでの共通パラメーターの構築

A practical method for predicting gold-wire deformation during the transfer molding process of semiconductor devices has been developed. In this study, common parameters for estimating values of wire deformation of the BGA (Ball Grid Array) package and the QFP (Quad Flat Package) used in previous reports were investigated. First, we examined the parameter λ, which was already derived as a function of resin velocity component perpendicular to the center of each wire, resin flow time at the center of each wire, apparent resin viscosity in the mold cavity, gold wire dimensions such as loop height, actual length and diameter, and Young's modulus for the gold wire. In the case of the BGA package, the maximum horizontal displacement, δmax, was found to be a linear function of λ up to around δmax=0.4mm with an intersection at the origin of the coordinate axes, On the other hand, for the QFP, a deviation from linearing was found for δmax exceeding 0.16mm. Next, both δmax and λ were divided by the actual length of each gold wire, and these values were defined as new parameters ζ and φ, respectively. By introducing these parameters, all the data were found to fit well by a straight line up to around ζ=8% with a subsequent a saturation curve. Three empirical models to represent the relationship between ζ and φ were obtained. Using these models, values of ζ were accurately calculated.

Ongoing innovations in biomechanics and materials for the new millennium.

Material innovations are reviewed within the context of ongoing biomechanical developments that relate the critical contact angle of second-order angulation (theta c) to the overall resistance to sliding (RS). As a science in its embryonic stage of development, RS is partitioned into classical friction (FR), elastic binding (BI), and physical notching (NO). Both FR and BI are defined in terms of normal forces (N) and kinetic coefficients (mu k). The angulation at which NO occurs (theta z) is introduced as a second boundary condition to theta c. Given this scientific backdrop, material modifications are sought that reduce RS. Approaches include minimizing mu k or N within the context of FR and theta < theta c, as, for example, by surface modifications of arch wires and brackets or by engineering novel ligation materials. Stabilizing theta at theta approximately equal theta c should provide more efficient and effective sliding mechanics by developing innovative materials (eg, composites) in which stiffness (EI) varies without changing wire or bracket dimensions. Between the boundaries of theta c and theta z (ie, theta c < theta < theta z), BI may be reduced by decreasing EI or increasing interbracket distance (IBD), independent of whether a conventional or composite material is used.

Size effects in the electrical resistivity of polycrystalline nanowires

Grain-boundary and surface scattering are known to increase the electrical resistivity of thin metallic films and wires. The length scale at which these produce appreciable effects is of the order of the electronic mean free path. For the well-studied case of thin films, both mechanisms can, in principle, be used to explain the observed thickness dependence on resistivity. In order to evaluate which of these mechanisms is more relevant, we have carried out an experimental study of the width dependence of the resistivity of narrow thin-film polycrystalline gold wires (nanowires), and computed the expected behavior on the basis of both surface and grain-boundary scattering mechanisms independently. We find that the resistivity increases as wire width decreases in a manner which is dependent on the mean grain size and cannot be explained adequately by either model alone. We propose a modification to the well-known model of Mayadas and Shatzkes, incorporating the variation of mean grain size on wire dimensions.

Torquedrehmomentübertragung zwischen Vierkantdraht und Bracket als Funktion von Maß-, Form- und Härteparametern

The aim of the study was to investigate the influence of cross section, edge geometry and structural hardness on torque transmission between square wire and bracket. For this purpose, 5 different brands of stainless steel square wire in 3 dimensions (0.016" x 0.016", 0.016" x 0.022" and 0.017" x 0.025") were inserted into edgewise brackets with a slot size of 0.018" and loaded with different torques (1 and 3 Ncm). The slot and wire geometries were analyzed by computer on ground specimens before and after loading. In addition, the Vickers hardness and micro-hardness of the unstressed and stressed metal surfaces were determined. While the slot size was very accurately maintained, the wire dimensions deviated downwards by an average of 10%. Torque transmission led to notching and bending-up phenomena on the bracket slot flanks. A torque loading of 3 Ncm increased the torque play of 0.016" x 0.022" wires by 3.6 degrees, and of 0.017" x 0.025" wires by 3.7 degrees. In the case of 0.016" x 0.016" wires, an effective torque transmission was no longer possible. The average Vickers hardness of the wires was 533 kp/mm2, and that of the brackets 145 kp/mm2. The micro-hardness in the deformation area of stressed internal slot walls increased with increasing load transmission from 204 to 338 kp/mm2. As a result of excessively small wire dimensions and plastic deformation of the brackets, a relatively large torque play occurs. Deformation and notching in the area of the internal slot walls are inconsistent with demands for recycling brackets. A standardization of bracket wire systems stating the actual torque play would be desirable.

Photochemical Etching of Silicon

Silicon that was immersed in hydrofluoric acid can be etched photochemically by laser, and it was found to produce long and regular columnar structure, if the laser power density is greater than 10 mW/mm2. Another criterion is that the laser wavelength should be at the blue end of visible spectrum. Fine wires with diameter 300–200 nm were also observed at the top of these columns. The dimension of these fine wires is near to quantum confinement dimension, thus can be taken as supporting evidence for quantum confinement. The photoluminescence spectra full width half maximum was narrower than that from porous silicon fabricated from conventional anodisation method. The narrower full width was attributed to the uniformity of the porous silicon structure. A physical model is proposed to explain the observed strong directional etching. The model showed that once the etch sites have randomly initiated, the etching rate becomes directional under the influence of laser. The intensity of laser controls the etching direction such that silicon columns are formed if the intensity of the laser is strong enough.