Parallel-plate Configuration Research Articles

The influence of metastables on the plasma-induced emission in a helium rf discharge

Space- and time-resolved emission spectroscopy is commonly used to investigate heating mechanisms in rf discharges (plane parallel plate configuration). The metastable density in these discharges is several orders of magnitude lower than the density of the ground-state atoms; however, the electron collision excitation cross sections of some helium levels out of the metastable levels exhibit values which are several orders of magnitude larger and have much lower thresholds than those for the ground state. It is therefore questionable whether stepwise excitation from metastable levels can be neglected in the interpretation of the spatiotemporal plasma-induced emission of rf discharges. To our knowledge only the excitation of ground-state atoms has been taken into account in model calculations to this date. With respect to the energy balance of such a discharge, this assumption is probably correct. However, with respect to the emission of light, our computational results show that some specific levels are excited significantly by electron collisions with metastables. We will show in this contribution, on the basis of our measurements, that this effect is responsible for the observed emission profiles of some lines. Consequently, the interpretation of the emission profiles in helium rf discharges has to take account of the role of metastables.

Cutoff frequencies of transmission lines consisting of pair of cylinders

The paper presents a method of evaluation of cutoff frequencies of higher-order modes of transmission line of parallel cylinders by transforming them into a parallel plate configuration using cotangent hyperbolic transformation. Application of the method of finite difference to the weighted Helmholtz equation leads to a set of simultaneous equations. The eigenvalues related to cutoff frequencies are determined from the characteristic equation expressed in terms of matrices obtained from the simultaneous equations. Numerical data are presented.

Investigation of E × B mass filters for focused ion beam systems

E × B mass filters have been investigated by 3-D simulations of electromagnetic field and ion trajectories, based on a 3-D boundary integral method. A new algorithm has been developed which enables the simulation of complex 3-D field configurations with less complicated data preparation. Five different shapes and arrangements of electrode/pole-piece, from parallel to non-parallel plates to curved inner surface, have been investigated in an attempt to find the optimum geometry of field configuration giving the least deterioration to the focused beam. The effect of beam energy spread has been studied by strictly 3-D simulation of ion trajectories under different focusing conditions. It has been found that the optimum geometry of an E × B mass filter is not the widely used parallel-plate configuration but the one with slightly curved inner surface in its electrode/pole-piece, which significantly reduces the astigmatic focusing effect. The beam dispersion caused by ion energy spread is the intrinsic feature of an E × B mass filter, which cannot be cancelled, as previously suggested, by arranging the beam crossover at the centre of an E × B mass filter.

Experimental Studies on 70 GHz Slow Surface Wave Propagation in Transversely Magnetized Partially Filled Ring-Form Solid-Plasma Waveguide

70 GHz slow wave propagation characteristics in a transversely magnetized partially filled ring-form solid-plasma waveguide have been studied experimentally employing n-type InSb ring at liquid nitrogen temperature as the plasma material. Obtained results were compared with those for the previously studied straight parallel-plate configuration. It is clearly shown that the surface wave resonance corresponding to the one observed in the straight plasma waveguide takes place also in the curved structure, and the propagation characteristics are quite similar to those of the straight configuration. Reduction of the resonant magnetic field is found with increasing the curvature of the waveguide.

Temperature dependence of surface impedance of pulsed-laser-deposited YBCO films

One promising application of HTS materials is as the reference resonator element for a stable frequency source. A high Q superconducting resonator operated at low reduced temperature (T/T/sub c//spl Lt/1) should offer excellent frequency stability due to its low temperature coefficient of resonant frequency. HTS planar resonators appear to be particularly promising since a reduced temperature of 0.1 may be readily achieved with a closed-cycle cryocooler. We report here microwave measurements made on YBCO films grown by pulsed laser deposition (PLD), using both a Nb cavity and a parallel-plate resonator configuration, with particular emphasis on the variation of resonant frequeney with temperature. We compare the data with simple theoretical models and find evidence from the low temperature data for a low energy gap parameter /spl Delta/(0)=6 meV. Some predictions of attainable frequency stability of planar resonator structures are also made.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Experimental Study of Very-High-Frequency Plasmas in H2 by Spatiotemporally Resolved Optical Emission Spectroscopy

A very-high-frequency (VHF) plasma at 100 MHz is experimentally investigated in parallel-plate configuration in H2 using spatiotemporal optical emission spectroscopy and current-voltage-power waveforms. The observed optical emission intensity and net excitation rate profiles have strong temporal and spatial variations. The VHF plasma is still capacitive, and is maintained by reflected electrons in the oscillating sheath next to the instantaneous cathode. The characteristics of VHF plasmas, that the excitation rate increases in proportion to the square of driving frequency, and that the minimum sustaining voltage and pressure decrease with increasing frequency, are experimentally confirmed at pressures, ranging from 0.01 to 2 Torr and at the frequency of 100 MHz .

FDTD modeling of noise in computer packages

In this paper, we discuss the electromagnetic modeling of the components of a computer package that contribute to noise on the signal lines in computer packages. We obtain equivalent circuits of coupled transmission lines, discontinuities in transmission lines, and a parallel-plate power plane configuration. These equivalent circuits allow one to use a circuit simulator to model the crosstalk, reflection, and simultaneous switching noises that are common in computer packages. The finite difference time domain (FDTD) algorithm is used to obtain the full-wave electromagnetic field solutions from which the equivalent circuits are determined. >

Electromagnetic Analysis of Eccentric Coaxial Cylinders

The paper presents method of evaluation of absolute values of equipotential boundaries of eccentric coaxial line using two types of conformal transformation. Cotangent hyperbolic transformation with appropriate normalizing constant transforms the line to a parallel plate configuration. Bilinear transformation expressed in terms of mutually inverse points transforms the same structure to a coaxial configuration. Numerical data on capacitance and charge distribution is presented.

Calculation of conductor loss in coplanar waveguide using conformal mapping

A quasistatic model for coplanar waveguide (CPW) including conductor loss has been developed. The CPW is conformally-mapped into a parallel plate configuration, where conductor loss is evaluated using a conductor surface impedance which is scaled by the conformal map. Both skin depth and current crowding in the CPW are accounted for. Comparison between experimental measurements on lowloss dielectric substrates and this model show excellent agreement.

Tmom modes in transversely magnetised semiconductor-filled coaxial waveguide and parallel plates

The behaviour of the TM/sub 01/ mode found in the azimuthally magnetised, semiconductor-filled, coaxial waveguide and the transversely magnetised parallel-plate configuration has been rigorously analysed. Investigation of the Poynting vector shows field displacement in both guides, with annular and laminar regions of negative average power density. The radial displacement of the electromagnetic fields in the coaxial waveguide gives rise to double-value phase constants below cut-off and nonreciprocal phase behaviour. This does not occur in the parallel-plate structure owing to its symmetry. Attenuation due to electron collisions was calculated for the TM/sub 0m/ modes in the parallel-plate case. This has implications for the attenuation expected on the TM/sub 0m/ modes in the coaxial-waveguide case. Gallium arsenide and indium antimonide proved promising in the frequency range 50-150 GHz when cooled to 77 K. For nonreciprocal devices in MMICs it appears that low doping concentrations will be required. >

Continuous arteriovenous hemodialysis: Effect of dialyzer geometry

Continuous arterio-venous hemodialysis (CAVHD) is an alternative to conventional hemodialysis for treating acute renal failure in critically ill patients [1, 2]. With this technique, a high flux dialyzer is connected to the arterial and venous blood circuit and dialysate is administered counter-current to the direction of blood flow [1, 2]. In this configuration, both diffusive clearance and ultrafiltration occur continuously but at relatively low blood and dialysate flow rates. Since CAVHD uses the patients' arterial blood pressure to circulate blood through the extracorporeal circuit, it is often better tolerated than standard hemodialysis in hemodynamically unstable patients [1]. Moreover, the large ultrafiltration capacity and diffusive clearances of CAVHD devices potentially permits control of fluid balance and biochemical manifestations of uremia [2]. A variety of high flux membranes of different composition are available in both parallel plate and hollow fiber configurations for use in CAVHD. Whereas the performance of parallel plates and hollow fiber dialyzers are roughly equivalent when used in high flow rate hemodialysis [3], dialyzer configuration may influence clearance during CAVHD. In particular, clearances could be limited in hollow fiber dialyzers, which have high flow resistance and consequently, a greater tendency for unstirred layers and/or flow mismatches between dialysate and blood at low flow rates [3]. Whether important differences exist between parallel plates and hollow fiber dialyzers with regard to performance in CAVHD is unknown. Thus, to evaluate the role of dialysis configuration in CAVHD, we performed a crossover study that sequentially used parallel plates and hollow fiber artificial kidneys in acute renal failure patients treated with CAVHD.

Modeling of a–Si:H deposition in a dc glow discharge reactor

PECVD reactors are increasingly used for the manufacturing of electronic components. This paper presents a reactor model for the deposition of amorphous hydrogenated silicon in a dc glow discharge of Ar–SiH4 The parallel-plate configuration is used in this study. Electron and positive ion densities have been calculated in a self-consistent way. A macroscopic description that is based on the Boltzmann equation with forwardscattering is used to calculate the ionization rate. The dissociation rate constant of SiH4 requires knowledge about the electron energy distribution function. Maxwell and Druyvesteyn distributions are compared and the numerical results show that the deposition rate is lower for the Druyvesteyn distribution. The plasma chemistry model includes silane, silyl, silylene, disilane, hydrogen, and atomic hydrogen. The sensitivity of the deposition rate toward the branching ratios SiH3 and SiH2 as well as H2 and H during silyl dissociation is examined. Further parameters that are considered in the sensitivity analysis include anode/cathode temperatures, pressure, applied voltage, gap distance, gap length, molar fraction of SiH4, and flow speed. This work offers insight into the effects of all design and control variables.

Spatially resolved optical emission and electrical properties of SiH4 RF discharges at 13.56 MHz in a symmetric parallel-plate configuration

A symmetric capacitively coupled SiH4 radio-frequency discharge at 13.56 MHz is analysed by spatially resolved optical emission spectroscopy and by measurements of the RF voltage and RF current and of the ion conduction current and energy distribution through the sheath. A transition between two discharge regimes is observed, either by increasing the pressure at a constant RF voltage, or by increasing the RF voltage at a constant pressure. This transition between two discharge regimes is attributed to different mechanisms by which electrons gain energy from the sheaths and in the plasma. For a gas temperature of 200 degrees C, at a fixed pressure of 0.185 Torr, the transition occurs as the RF voltage exceeds 140 V. When comparing both discharge regimes at the same pressure and RF voltage, the authors observe a drastic change of the RF current waveform. The power dissipated in the discharge, as well as the total intensity of the optical emission from the discharge, increases by a factor 3. Moreover the spatial distribution of the emission is completely modified. These results are discussed in relation to recent experimental and modelling studies of RF discharges.

Smoke Emission Factors from Medium-Scale Fires: Part 1

The concept of “nuclear winter” has been postulated with a number of assumptions regarding the smoke produced by post-nuclear-exchange fires. Whether nuclear winter would occur in the aftermath of a nuclear exchange depends largely on the quantity and character of smoke generated, its distribution in the atmosphere, and its optical characteristics. Since most of the current information is derived from small-scale experiments with little or no correlating data for larger scales on the order of actual buildings, a series of 11 medium-scale experiments with representative urban fuels, such as wood and asphalt roofing shingles, have been conducted. The effects of different combustion conditions resulting from differences in fuel composition, geometry, and ventilation have been investigated. The present state of knowledge regarding smoke production from building fires is briefly reviewed and placed into the nuclear winter framework. Plywood sheets were burned in a parallel plate configuration, a geometry in wh...

A novel X-ray transmission ionization chamber dosemeter for patient dose measurements in diagnostic radiology.

This paper describes an X-ray transmission ionization chamber diagnostic dosemeter for patient dose measurements and control. The chamber uses a commercially available radiofrequency screen as the wall material in a parallel-plate configuration. A digital varactor bridge electrometer serves to measure air kerma times area of fluoroscopic and radiographic beams. Detailed investigations on the characteristics of the chamber such as saturation, sensitivity, energy dependence (50-150 kV), response versus radiation field area, uniformity of response of the chamber, effects of distance and long-term stability have been carried out. The results demonstrate that the chamber meets all the requirements and can measure the incident patient dose with an overall uncertainty of +/- 11%. The chamber can be either mounted on the housing of the light beam diaphragm of the X-ray unit or used as a stand-alone system along with an image-intensifier TV monitor. It is inexpensive to build and is recommended particularly for hospitals in developing countries.

Electrokinetic dewatering and thickening. II. Thickening of ball clay

The electrokinetic thickening of a 20% slurry of ball clay over a range of pH values has been studied. By employing a cell utilizing a parallel plate configuration, together with a scraper and collector system to remove the electrophoretically thickened clay, a continuous thickening process has been devised. In addition to the electrophoretic anodic deposition process, water is simultaneously electroosmotically ‘pumped’ from the region of the cathode, the catholyte containing less than 0.3% solid. By employing this integrated design the cell can be operated with a steady-state clay concentration of about 15% from a 20% feed. At this operating concentration a thickened clay of 60–70% is obtained for energy consumption of 170 kW h per dry tonne of clay.

Casimir energy at finite temperature

We derive an integral representation for the temperature corrections to the Casimir effect between perfectly conducting parallel plates placed in the electromagnetic field for arbitrary dimension. The representation has the advantage that dependence upon the external constraints and thermal effects enter separately. The so-called mode sum function carrying the dependence on the boundaries is closely connected with the mode number density which is derived explicitly for the parallel plate configuration. The relation to local Green function methods is also pointed out.

Gate Oxide Damage in Dry Photoresist Stripping Environments

ABSTRACTThe effect of oxygen plasma stripping environments on the electrical properties of thin oxides has been studied. A barrel, parallel plate and downstream stripper are compared. Damage, measured by shifts in flatband voltage (Δ Vfb), increases in the density of interface traps (Dit), and degradation in minority carrier lifetimes, was observed in all plasma processed samples. Plasma treated wafers had 10–100 fold increases in Dit but recovered to nearly control levels after a 450 °C anneal. ΔVfb and lifetimes did not recover in all cases. Mobile ion contamination dominated in the high temperature (≥ 250 °C) downstream stripping tool. The mobile ion concentration was halved by decreasing the process temperature in the downstream etcher. Ion bombardment-induced damage appears to be most important in the parallel plate configuration. Lifetime results were poor for wafers etched in an unshielded barrel reactor and did not recover after anneal. Use of an etch tunnel improved results to control levels. Degradation of minority carrier lifetimes measured using the photoconductivity technique correlated well with changes in Vfb and Dit. This measurement provides a simple method for evaluating plasma-induced damage.

The influence of cell design and electrolysis parameters on the cathodic coupling of butadiene and carbon dioxide in acetonitrile. I. Undivided parallel plate configurations

The reduction of carbon dioxide in the presence of excess butadiene in acetonitrile leads to a mixture of carboxylic acids, pentenoic acids (two isomers), hexenedioic acids (two isomers) and decadienedioic acids (three isomers). The total current yield can exceed 60%. The current efficiency and the ratio of products are functions of both cell design and other electrolysis parameters. This paper reports studies of this coupling reaction in several undivided flow cells, where cyclindrical cathodes (lead-plated nickel gauze, reticulated carbon of various porosity, carbon felt) were surrounded by a platinum gauze anode. The electrolyte was ditetraethylammonium oxalate and/or tetraethyl-ammonium formate so that the counter electrode reaction was the oxidation of the anions to CO2 or CO2+H+, respectively. This choice avoids solvent decomposition or other unwanted reactions at the anode, and may be helpful to the cathode chemistry by replenishing the cathode active species, CO2, and possibly also creating a controlled supply of protons to the cathode.

Techniques for the viscometry of suspensions

AbstractTechniques are presented for the rotational viscometry of suspensions, using modified cone/plate and parallel plate configurations. For displaced cone‐and‐plate geometry an analysis considers the torque developed on the cone as a function of its angular velocity and the displacement at its apex. The two situations of constant angular velocity and of constant displacement present alternative methods for computing viscosity/shear‐rate data from torque/displacement or torque/angular velocity measurements. Neither method involves any assumption regarding the rheological properties of the test fluid and both can be extended to parallel plate geometry. An alternative and simpler approach uses an annular cone/plate configuration, in which conditions of uniform shear rate can be maintained with an operating gap of the order of 1 mm. The validity of the different techniques is tested by comparison with conventional cone‐and‐plate measurements, using a non‐Newtonian solution of polyisobutylene as a test fluid.