Tens Of Volts Research Articles

A technique for measurement of electrical potential of a balloon-borne gondola

During electrical conductivity measurements using balloon-borne probes, the gondola was observed to acquire an electrical potential of the order of a few tens of volts. Such an effect was found to occur mainly during balloon ascent and also to a lesser extent during balloon float and descent periods. A technique has been developed at the Physical Research Laboratory (Ahmedabad, India) for the direct measurement of potential acquired by the gondola during the course of its flight. Such measurement has relevance when we interpret the data obtained from the balloon-borne conductivity and electric field probes.

Boundary-layer effect on railgun muzzle voltage

Measured values of railgun muzzle voltage exceed those predicted from simple armature models by several tens of volts. This excess voltage is called the contact potential and may represent a substantial fraction of the power dissipated in the armature. A simple two-dimensional model for the conductivity and velocity boundary layers has been used to calculate the electric field in the region near the rail surfaces. Calculations were performed for parameters characteristic of the University of Tennessee Space Institute (UTSI) 1-cm square-bore railgun. These calculations showed that the electric field decreased across the boundary-layer thickness and predicted contact potentials from 12.5 to 88.7 V, depending on the choice of boundary-layer parameters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Current-to-voltage amplifier with a high voltage isolated input

The measurement of very low currents collected on electrodes held at high voltages is a commonly encountered experimental problem, since a commercial electrometer’s input can usually be floated only at a few tens of volts. We have run into this problem when attempting to measure the gain of the first dynode of an electron multiplier of the type used on cesium-beam atomic clocks. In order to solve it, we have designed, built, and tested a current-to-voltage (transresistance) amplifier whose input can be floated up to ±2000 V, while providing a ground-referenced low-impedance output capable of driving a voltmeter or chart recorder. This very flexible instrument can measure currents in the 10−12 –10−7-A range, has a 1-Hz bandwidth, and it can be built at a cost of a few hundred dollars.

Variation of the soft-mode frequency in ferroelectric semiconductors in a static electric field

The action of a static electric field on the soft-mode frequency in narrow-gap ferroelectric semiconductors, as a result of the contribution of the electron subsystem, is investigated within the framework of the vibronic mechanism. It is shown that the frequency of the soft mode varies directly as the square of the electric field strength under the action of the field, and the soft-mode frequency is determined in the vibronic model by the electron distribution function, whose parameters also vary under the action of the electric field. The effect is stronger for crystals with a one-dimensional electron spectrum than for those with an isotropic three-dimensional spectrum; according to estimates for ferroelectric semiconductors of the type Pb1−xGexTe, a frequency variation of the order of the soft-mode frequency itself is attained in fields of the order of tens of volts per centimeter.

Exposure of calcium fluoride resist with the scanning tunneling microscope

The scanning tunneling microscope (STM) can be used to generate very fine beams of very low energy electrons (below 100 eV). Under optimum conditions the beam diameter is proportional to beam voltage and hence, when using such a beam as an exposure tool it is desirable to employ the thinnest possible resists. The metal halides in general have several properties that make them attractive candidates for use in a scanning tunneling microscope. They are easily evaporated as thin films of thickness from 10 to 100 nm. It is important that an insulating resist film be thin so that the electrons can penetrate it and the tip does not crash into it. Thicker films require a higher accelerating voltage and this degrades resolution. The sensitivity of the metal halides is on the order of 1 C/cm2, which coincides with the dose range most readily obtainable in our instrument. Finally, the exposure voltage threshold of the metal halides is thought to be in the range of a few tens of volts. This is low enough to take advantage of the very fine low energy beams available from the STM, but high enough to exclude secondary electrons from contributing to the exposure process. The calcium fluoride was thermally evaporated onto a silicon substrate. When exposed to a beam of electrons, the fluorine dissociates and the calcium converts to calcium oxide, which can be dissolved in water. We have demonstrated the ability of the STM to expose lines in CaF2 with linewidths from tens to hundreds of nanometers and have shown the degradation of resolution as beam voltage increases.

Experimental investigation of the molecular ions of the xylenes

AbstractA mass spectrometric method of distinguishing between molecular ions of the three isomeric xylenes (dimethylbenzenes) was sought, in light of recent findigs that photoexcited ions could be distinguished via measurements of kinetic energy release accompanying expulsion of a methyl radical. Provided the molecular ions are formed with low internal energies, reproducible differences were found between relative intensities of collision induced reactions of higher critical energies, than for methyl expulsion. These differences exist both for collision energies in the kilovolt range (double focusing mass spectrometers) and in the range of a few tens of volts (triple quadrupole instrument). Though statistically significant, these differences were small. The mechanism of isomerization and fragmentation was investigated via isotopic labelling studies and measurements of kinetic energy release. Most of the present findings can be rationalized in terms of the most recent version of established mechanisms for reactions of ionized methylbenzenes.

400-Channel commutator for laser-radiation energy-distribution measurement

We shall examine the results of experimental studies of a 400-channel commutator for a measurement system for the transverse energy distribution of pulse laser radiation. The commutator is designed for step-by-step feeding of electrical signals from 400 channels to the input of a precision digital voltmeter. The electrical signals from the channels are constant (during switching) voltages of from units to tens of microvolts to units to tens of volts [i]. The dynamic range of the signals entering the commutator during one channelinquiry cycle can reach several thousands for a signal-to-noise ratio of ~ i0, which means that the switching elements as well as the voltmeter must be carefully selected. The eommutator can be used in other multichannel DMS for which its characteristics are suitable. Stepping relays with palladium-plated contacts are used as the switching elements. An Shch68003 digital voltmeter [3] is used with the commutator. Stepping relays of type ShIS0/4 make it possible to switch electrical signals over a wide dynamic range on the order of several tens to hundreds of thousands for a minimum signal value of a few tens to hundreds of microvolts. The possibility of switching weak signals makes it possible to reduce the gain of the channels and , therefore, to reduce the power consumption, dimensions, and weight of the system, which are important economic considerations for multichannel systems. The Gate numbers Channel

Si and SiO2 Etching under Low Self-Bias Voltage

Si and SiO2 reactive ion etching and the associated radiation damage were investigated employing CF4 in the low self-bias voltage region (less than 100 V). The etching was carried out using the substrate tuning method. In the low self-bias voltage region, both Si etching and SiO2 etching proceed accompanied by the polymerization of CFx (x=0–3) radicals generated from the dissociation of CF4. The polymer deposited on the surface is decomposed by the subsequent ion bombardment to form F and CFx radicals, which take part in the etching and the polymer formation reaction again. The radiation damage induced in the Si by energetic fluorocarbons depends strongly on the magnitude of the self bias. However, the damage induced by tens of volts can easily be removed.

New micromechanical display using thin metallic films

A new mechanical display is described, working on a simple electrostatic principle and yielding good contrast ratio (20-25), low power consumption, and short response time (1 ms). The device, which relies on the torsion of thin Al straps and works at some tens of volts, is fabricated using standard IC technology.

Impact induced plasma during a cometary fly-by

GIOTTO, the probe which is presently developed by the European Space Agency, will encounter comet Halley in March 1986 with a relative velocity of 69 km/s. The fore section of the surface will be submitted to the bombardment of dust grains and neutral molecules in the final phase of the mission, like that of an Earth orbiter during atmospheric re-entry. These particles have a kinetic energy of 24 eV per a.m.u.; they produce secondary ions and electrons which form a plasma cloud around the body and control the electric potential of its surface. This paper is a review of the work which has been performed on the subject by dedicated study groups; the purpose of their action was to gather information and produce new findings which might have an influence on the design of the spacecraft and help in the interpretation of the data collected by the scientific payload. The effect of impact induced plasma may already be significant at 10 5 km from the comet nucleus; at a distance of 1000 km the flux of ions and electrons produced by cometary dust and neutrals will possibly exceed that of the ambient plasma by more than three orders of magnitude. It is expected that the spacecraft surface potential will be positive and will reach at least a few tens of volts; coating the leading surface of the spacecraft with a thin layer of gold or silver will help reducing the emission of ions from neutral gas. Computer simulation models are used to predict the structure of the charged particle density distribution in the vicinity of the surface. Effects associated with the wake and differential charging are also discussed. The significance of these results is conditioned by the validity of the models and the largest source of uncertainty seems to be associated with the plasma generated by dust impact.

Effects of an electric field on the growth of CdS crystals

CdS crystals were grown from the vapor under an electrostatic field. When the potential of a central electrode was kept at a value less than minus several tens of volts, crystals grew preferentially in the + c-direction on the central electrode placed in the growth zone, but they grew preferentially in the - c-direction when the potential was kept at a higher value than that value. These growth features are the same when crystals were grown on the polar surface of a CdS substrate fixed on the central electrode. These results suggest that the electrostatic field accelerates the preferential deposition of one of the ionized constituent atoms onto the growth surface and causes a difference in the growth rate between two polar surfaces.

Temperature Dependence of Magneto-Electric Effect of Magnetite (Fe3O4) at about 10 K

Magneto-electric effect was measured in a temperature range between 4.2 and 30 K on a plate of Fe 3 O 4 cut parallel to (110) referred to the cubic axes. The voltage as high as several tens of volts was observed to be induced across a 1.45 mm thick specimen when the magnetization is rotated in the (110) plane at 4.2 K. The effect changes drastically as the temperature is increased towards 10 K, at which a specific heat anomaly had been reported.

Low-voltage cathodoluminescence of ZnS single crystals

Bright blue and green cathodoluminescence from low resistivity ZnS crystals has been observed under the excitation of low-energy electron beams of several tens of volts; i.e., 40 fL at 50 V. Properties of the surface of the crystals are studied by the dependence of current and brightness on applied voltage and by the spectra of cathodoluminescence and photoluminescence.

The floating potential of a metal surface under bombardment of ions from a cold cathode grid

When a wire mesh is used as a cold cathode ion source, the ion beam is mixed up with neutral atoms, sputtered material and electrons. Measurements of the floating potential of a metal surface bombarded by such an ion beam are presented. The floating potential is shown to be within a few tens of volts of the cathode potential, if the discharge current is not too low. The total ion and electron currents are estimated.

Electroforming in point-contacted silicon oxide layers: Low frequency characteristics for devices with gold anodes and with carbon anodes

SiO x films of 50 nm thickness, deposited on an aluminium base electrode, were electroformed using point-contact anodes of gold and of carbon. Forming voltages of 50–150 V were required; this is interpreted as the voltage required to initiate current flow in a comparatively perfect region of the film. The electroformed devices can pass currents of up to a few milliamps in an area of less than 25 microm 2 with only a few volts applied. The usual behaviour of electroformed SiO x is observed, but after a number of voltage cycles step-like behaviour is observed which shows various features best interpreted in terms of a filamentary model. One unusual feature is that turn-off can occur at applied potentials of up to several tens of volts. The high current density and high forming voltage suggest that in normal large-area devices current flows at major defect and/or impurity sites. The method has considerable possibilities for refinement.

Acoustic-surface-wave convolver using nonlinear interaction in a coupled PZT-Si system

Efficient acoustic-surface-wave convolution, using 14.5-MHz Bleustein-Gulyaev waves, has been observed in a coupled PZT-Si system. It has been found that the magnitude of the phenomenological nonlinear coupling constant of the convolver was four times as large as that of the basal plane of PZT-8. The convolution output was controlled by the application of a voltage of several tens of volts.

Voltage Hash in Low-Current DC Vacuum Arcs

The nature and mechanism of the high-voltage pulses in the anode region of copper-vapor arcs have been investigated. Arcs are drawn between a 1.3-cm-diameter anode and a 5-cm-diameter cathode in the dc range of 30-400 A. Prior to anode spot formation and at constant current, the arc voltage exhibits HF pulses superposed on the dc voltage. The amplitude and frequency of repetition (= 500 kHz) of these pulses is highly erratic, and the total instability is evidenced as voltage hash. The hash amplitude increase with both arc current and contact spacing and, at 2.5 cm, varies from several tens of volts at 30 A to several hundreds of volts at 400 A. The hash is attributed to fluctuations in vapor and plasma density in the anode region. Although these fluctuations appear unrelated to the gross motion of the cathode spots, streak photographs indicate a time-variant cathode evaporation that may contribute to the hash phenomenon. A second contributory mechanism is suggested from experience of hash in the anode region of fluorescent lamps, and involves quasi-periodic emission from the anode.

Enhanced photoemission into n hexane

A gap between a photocathode and the liquid into which charge emission is directed considerably enhances the magnitude of photocurrent normally obtained. It also makes the process relatively insensitive to electronegative contaminants such as oxygen, even at stresses as low as a few tens of volts per centimetre.

Cathode Region of a Vapour Arc

THE total potential across a short arc discharge is normally a few tens of volts, and the cathode and anode falls, the regions of high field close to the electrodes, account for a large proportion of this. The small thickness and high current density in the cathode and anode fall sheaths make measurements of potential in these regions very difficult. In the past, the sum of the electrode potential falls has been found either by extrapolating voltage-length plots to zero length, or by measuring the arc voltage on an oscilloscope just before approaching electrodes contact1, but it has not been possible to determine their individual contributions unambiguously. The thickness of these regions has also remained a matter of conjecture.

Differential minority-carrier-storage circuit for fast-pulse generation

A balanced system of minority-carrier-storage diodes, energised from avalanche-pulse generators, is described, which delivers fast-rise/fast-fall pulses of adjustable length. Nanosecond risetime is obtained with step-recovery diodes; readily available charge-storage coupling diodes may be used to achieve 5 ns rise and fall times and amplitudes of some tens of volts into 50 Ω.