Mechanism Of Current Transfer Research Articles

Physics of Spotless Mode of Current Transfer to Cathodes of Metal Vapor Arcs

A fresh attempt is made to clarify the physics of the diffuse, or spotless, mode of current transfer that may occur on cathodes of vacuum arcs if the average cathode surface temperature is high enough, about $2000 \operatorname {K}$ . It is shown that in the case of chromium cathode the usual mechanism of current transfer to arc cathodes cannot sustain current densities of the order of $10^{5}$ – $10^{6}~\operatorname {A}{\cdot }\operatorname {m}^{-2}$ observed in the experiment, the reason being that the electrical power deposited into electron gas in the near-cathode space-charge sheath is insufficient. It is hypothesized that the electrical power is supplied to the electron gas primarily in the bulk plasma, rather than in the sheath, and a high level of electron energy in the vicinity of the sheath edge is sustained by electron heat conduction from the bulk plasma. Estimates of the current of ions diffusing to the sheath edge from the quasi-neutral plasma gave values comparable with the experimental current density, which supports the above hypothesis. On the contrary, the spotless attachment of vacuum arcs to gadolinium cathodes may be interpreted as a manifestation of the usual mechanism of current transfer to arc cathodes. Results given for gadolinium cathodes by a model of near-cathode layers in vacuum arcs conform to available experimental information.

Experimental study of the domain of existence of intensive non-self-sustained discharge in crossed fields

A set of experiments was performed on the breadboard model of the Hall thruster with the anode layer. Use of the thermoemission cathodes as the cathode-compensators made it possible to determine the domain of existence of the non-self-sustained type of discharge in the crossed electric and magnetic fields at different values of the anode voltage, the magnetic field, and the working body mass flow rate. According to the electron current transfer mechanism and the current oscillation character, two modes of the discharge are distinguished burning strictly differing, even visually: the “accelerative” and the “stochastic” ones.

Sub-National Revenue Mobilization in Latin America and Caribbean Countries: The Case of Venezuela

This paper analyzes the high fiscal dependence of Venezuelan states and municipalities on the central government and the political economy process embedded in the interaction between the central government and sub-national entities. Also explored is whether there is scope to increase sub-national governments’ revenues, improve the current intergovernmental transfer system, and reduce horizontal imbalances; of particular importance is analyzing the impact of current transfer mechanisms on sub-national governments’ revenues volatility. Following a presentation of Venezuela’s economic background, public sector and fiscal variables, the paper describes the process of decentralization, inter-governmental transfer mechanisms and revenue volatility, and local governments’ own revenues. Subsequently presented are sub-national governments’ fiscal dependence and its determinants, followed by options for revenue mobilization and improving the transfer mechanism. The paper concludes with a summary and policy recommendations.

Schottky emission effect in surface topography: method and application

Presented here is an application of Schottky emission effect in surface topography. Since using current transfer mechanism can detect the metal or semiconductor surface structures in high resolution without contact, the tendency of Schottky emission in surface metrology is obvious. In this study, Schottky emission property in practical condition is compared both theoretically and practically into detail with tunnelling effect and field emission in order to distinguish the observed phenomena. A new developed probing system holding a thick electrical probe is exemplified to demonstrate the Schottky emission effect application in surfaces study. Future prospects of applying Schottky emission to manufacturing metrology are overviewed.

RESTRUCTURING DEFECT SURFACE-BARRIER STRUCTURES Bi-Si-Al STIMULATED ACTION RADIATION

In this work the surface-barrier structures based on p-Si with different resistivity (ρ1 =24 Ohm∙sm, ρ2 = 10 Ohm∙sm) were made and their electrophysical characteristics were investigated under the influence of X-rays. It is shown that depending on the defect structure of silicon substrate, the action of irradiation leads to generation of new defects or changing of charge state of existing defects. Consequently, the mechanism of current transfer in irradiated structures changes.

Accounting for the market and non-market values of multifunctional outputs in evaluating water transfers to non-agricultural uses: empirical evidence from Taiwanese rice production

Increased demand for water for municipal and industrial uses throughout Taiwan has intensified the pressure to re-allocate water from agricultural to non-agricultural uses. The full policy implications of such water transfers must not only account for the value of lost agricultural production and income, but also any loss in the social value of multifunctional benefits from agricultural production. Focusing on two northern irrigation associations in Taiwan, this paper empirically assesses the changes in rice production and multifunctional values under the scenario of transferring water from agricultural to non-agricultural uses. We also compare these combined multifunctional values of land in agricultural production with the per hectare compensations for water transfer in 2002 to evaluate the current water transfer mechanism. The empirical results have significant policy implications. Despite substantial reductions in production and farm income, the compensation levels in both irrigation regions exceed those required to compensate farmers for the losses in net farm revenue, and do so by substantial margins.

Electrical properties of photodiodes based on p-GaSb/p-GaInAsSb/N-GaAlAsSb heterojunctions

We have studied the electrical characteristics of photodiodes based on p-GaSb/p-GaInAsSb/N-GaAlAsSb heterojunctions and investigated the mechanisms of current transfer in these heterostructures at various temperatures. A comparison of the theoretical results and experimental data showed that the tunneling charge transfer mechanism dominates at low temperatures (T < 150 K) under both forward and reverse bias conditions. The tunneling current becomes a determining factor at an electric field strength in the p-n junction of no less that 105 V/cm, which is related to a small bandgap width of the materials studied and low effective masses of electrons and holes.

Mechanisms of dc-current transfer in tris(acetylacetonato)iron(III) films

Thin tris(acetylacetonato)iron(III) films were prepared by sublimation in vacuum on p-Si substrates for electrical investigation. The prepared films were characterized by X-ray diffraction (XRD) which shows the material to exhibit polycrystalline orthorhombic structure. Thin films of the complex were prepared as a gate-insulator for metal/insulator/Si (MIS) device. The capacitance-gate voltage, C( V g) characteristics of the constructed MIS device were measured, from which the relative permittivity and the density of the charges in the sample were extracted. The dc-electrical conduction in the complex film was studied at room temperature and in the temperature range of (293–353 K). It was found that the data follow a Poole–Frenkel (PF) mechanism for low voltages and a trap-charge-limited space-charge-limited conductivity (TSCLC) mechanism for higher voltages. The switching observed between the two mechanisms was explained. The characteristic parameters both mechanisms were also determined. It was concluded that the dc-conduction can be described by hopping between structural defects that form trap levels in localized states near the bottom of the mobility band. Therefore, the density of structural defects in the film, which are controllable by the method of preparation, is critical in determining the mechanism of current transfer.

Acoustic wave corrected current-voltage characteristics of GaAs-based structures with Schottky contacts

The effect of ultrasonic treatment (UST) on the current-voltage (I-U) characteristics of Au-TiBx-n-n +-GaAs diode structures has been studied. Upon acoustic loading with an intensity below 2 W/cm2, the character of the UST-induced changes in the reverse branches of I-U curves depends on the predominating mechanism of current transfer. UST at a power density above 2.5 W/cm2 increases the reverse current by one or two orders of magnitude. It is shown that UST favors a significant increase in the homogeneity of the characteristics of devices manufactured using integral heat sink technology.

Mechanisms of current transfer and photosensitivity in Zn/CuInSe2 Schottky diodes

Photosensitive Schottky barriers have been obtained for the first time by electrolytic deposition of zinc onto p-type CuInSe2 crystals. The capacitance-voltage and current-voltage characteristics of these structures have been studied at liquid nitrogen temperature and in the interval from 238 to 330 K. For a direct bias voltage, the current transfer in the system studied is characterized by the Ohm law, with space-charge-limited current and thermionic emission. Reverse-biased structures also obey the Ohm law and simultaneously exhibit soft breakdown. The relative quantum efficiency spectrum of photocurrent in the Zn/CuInSe2 barriers has been measured.

Interface characteristics and mechanisms of current transfer in metal-tunnel-thin rare earth fluoride-silicon structures

We have studied the electrical properties of metal-tunnel-thin insulator-silicon (MIS) structures with dysprosium, cerium and neodymium fluorides as insulating layers. The characteristics of interfaces (energy distributions of the density of surface states, surface potential) were determined and mechanisms of the current transfer in these MIS structures were studied.

Asymmetric Current Transfer in Isotype n-In[sub 2]Se[sub 3] ∕n-InSe Heterocontacts

We have studied the mechanisms of current transfer and the capacitance-voltage characteristics of a radiation-resistant isotype n-In2Se3/n-InSe heterocontact in which the region depleted of major charge carriers is localized predominantly in a relatively low-ohmic semiconductor—the α-type In2Se3 with a large density of defects. The spectrum of the relative quantum efficiency of photoconversion in this structure depends on the thickness of the In2Se3 layer and on the geometry of illumination of the heterocontact.

Synthesis and characterization of n-ZnO:Al/CoPc/p-Si structures

Photosensitive structures of the n-ZnO:Al/CoPc/p-Si type were synthesized for the first time using vacuum sublimation of cobalt phthalocyanine (CoPc) and magnetron sputtering of a ZnO:Al target. The maximum photoresponse is observed when the structure is illuminated from the side of the ZnO layer and amounts to ≅400 V/W at T = 300 K. Mechanisms of current transfer and peculiarities of the photosensitivity spectrum are considered. It is suggested that the new photosensitive structures can be used in multiband photoconverters of natural radiation with a broad working spectral range.

Model for arc cathode regionin a wide pressure range

A one-dimensional model for the near-cathode region of electric arcsis applied to define the current, heat and mass transfer mechanisms in theelectrontemperature range of 10-40 kK and the pressure range of 104-107 Pa.The model considers details of the space charge zone, the ionization zone andevaporation of the cathode material.A copper-tungsten cathode is investigated, and it is found thatevaporation is an important cooling mechanism of the cathode and shouldnot be neglected. The plasma near the cathode is constituted ofevaporated contact material in the main part of the investigatedpressure-temperature domain.The results show that Schottky-enhanced thermoionic emission, togetherwith the present model for the near-cathode layer, explains the currenttransfer mechanism for a wide range of pressures and temperatures and forrefractory and non-refractory cathode materials.

Silicon diffused diodes with nearly ideal current-voltage characteristics

It is shown that nearly ideal current-voltage characteristics (I-V curves) can be obtained for small-area, shallow silicon diffused p-n junctions irradiated with 60Co gamma rays in the dose range 103–5×105 Gy. In the irradiated diodes the current transfer mechanism is observed to shift from generation-recombination to diffusion. The nonideality factor on the forward branch of the I-V curve decreases from 1.68 in the unirradiated diode to 1.17 in a diode irradiated to a dose of 5×105 Gy. A saturation current is observed on the reverse branch of the I-V curves of irradiated diodes at room temperature.

Time-spatial structure of an electric arc anode region

This paper studies the anode region of an eroding anode with a nonstationary arc-root attachment. High-current free-burning short as well as long arcs at atmospheric pressure are investigated. A technique to study the anode region of the arc is suggested. An anode moving perpendicular to the arc axis was used for estimating parameters of the anode jets at a given moment of their development. The mechanism of current transfer in the anode region is considered on the basis of electrophysical and optical-spectroscopic investigations of the arc attachment traces and plasma parameters both of the anode jet and arc column. The anode jet was found to be of importance in the stationary arc operation. The near-anode plasma parameters depend on the effect of the cathode jet. In short arcs (L/sub a//spl sim/2 mm), the plasma temperature at the anode exceeds 20000 K, while in long arcs (L/sub a/>50 mm), it falls below 7000 K. At plasma temperature T/sub a/>11000 K, the total arc current in the anode region is transferred through the arc plasma, while at lower temperatures, both the arc column and the anode jet take part in the current transfer.

Electrical and photoelectric properties of a Pd-p 0-Si-p-Si structure with a disordered intermediate p 0 layer

The electrical characteristics and the photovoltage on Pd-p 0-Si-p-Si diode structures with a disordered (porous) p 0 layer of Si have been measured. The current-transfer mechanism is assumed to be double injection of electrons and holes into the p 0 layer. In a hydrogen atmosphere, the photovoltage increases by a factor of 20 and the reverse current falls by a factor of 3–4. The increase of the photovoltage is associated with the growth of a Pd-p 0-Si Schottky barrier, while the decrease of the dark current is attributable to the variation in the amount of injected electrons. The relaxation of the photovoltage after turning off the H2 flow has two time intervals, with lengths of about 130 and 420 sec. It is shown that these features of the relaxation are associated with heterogeneity of the structure of the p 0 layer, which includes unanodized sections and porous sections. These regions of the structure each contain their own set of deep traps and recombination centers. This set of traps and recombination centers can vary as a result of the introduction of hydrogen which creates induced “temporary” deep levels.

Thin-film ZnSe xTe 1-x/ZnSe oxygen sensitive structures

An investigation of the electrical parameters of semiconductor ZnSe xTe 1-x films with high sensitivity to oxygen is presented. A correlation was observed between the adsroption-desorption processes and the current transfer mechanism of the ZnSe xTe 1-x films. A non-monotonous dependence on temperature is explained by the influence of charge in the adsorbed oxygen on potential barriers in the films. The values of potential of the intercrystalline barrier and also the concentration of chemisorbed oxygen equal to NO(O 2=10 17 m −2 were calculated.

Perturbation region near a biased body in a flowing collision-dominated plasma with low ionization density. Current–voltage chracteristics of a langmuir probe

The asymptotic theory of flows of high-pressure plasmas past biased bodies (electrostatic probes) is extended to relatively low charge densities, where the Debye radius h is comparable to or exceeds the thickness ▴ of the viscous near- probe boundary layer. Various orders of magnitude of h with respect to a dimension of the probe and various ranges of the probe potential are considered. The governing physical mechanism of current transfer in the perturbation region is identified in each regime, and simple formulae for the probe current–voltage characteristic are obtained whenever possible. In particular, it is shown that an earlier conclusion, valid for h ≪ Δ, on the existence of a linear segment on the electron branch of current-voltage characteristic with a slope depending on the electron density, is also valid in the present situation. It h ≫ Δ, a similar conclusion holds for the ion branch; at large enough probe potentials the jon branch saturates —although for a different physical reason than in the case h ≪ Δ

Mechanism of current transfer in oxidized iron ore minerals

Mechanism of current transfer in oxidized iron ore minerals