摘要:

Although the high‐intensity, free‐burning argon arc has been the object of many studies, modeling of the entire arc has been precluded because of complexities due to the interaction of electric, magnetic, fluid dynamic, and thermal effects, and the associated lack of realistic boundary conditions, in particular, close to the cathode. For establishing the most crucial boundary condition, which is the current density in the vicinity of the cathode, the maximum current density has been determined experimentally by measuring the size of the molten cathode tip (thoriated tungsten) for a given arc current. Calculated temperature profiles for a 100‐ and 200‐ A atmospheric pressure argon arc (electrode gap of 1 cm) are in good agreement with spectrometric measurements based on absolute line and continuum intensities. The arc current and arc current distribution are not only responsible for the temperature distribution in the arc, but also for the magnetohydrodynamics (MHD) pumping action in the cathode region, i.e., the arc behavior is mainly controlled by the current. In contrast to the sensitivity of the current density boundary condition on the results, the calculations show that variations of the boundary condition for the flow field are insignificant.

ISSN:0021-8979    

DOI:10.1063/1.332195

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The surface of a solid insulator in vacuum (and in a high gas pressure) becomes electrically charged when subjected to a high voltage stress. The surface charge density is proportional to the applied voltage. The magnitude of the surface charge density depends on the secondary electron emission characteristic, the geometrical shape, and the material of the insulator. The field enchancement, contributing to a lower withstand voltage of solid insulators in vacuum (and in high pressure gases), due to the presence of surface charge is computed along the surface of the solid insulator and at the triple electrode‐solid insulator‐vacuum junction near the anode and cathode. Different patterns of surface charge density distribution has been considered in order to evaluate their effects on the field enhancement. The polarity, the magnitude and the shape of the distribution of the surface charge density has been found to have a considerable effect on the field enhancement. The observed influence of the charge distribution patterns on the electric field suggests that in order to obtain the experimentally observed field enhancements, the insulator surface must possess a positive surface charge except in the region close to the anode, where it is negatively charged. The electric field and the potential distributions of the interfacial boundary between the solid insulator and vacuum is computed for different realistic surface charge distributions. The computed electric field at the triple junction for varying values of the dc applied field is then compared with the measured values reported in the literature. Good agreement is obtained. The effects of the magnitude of surface charge density, the applied field and the length of the solid insulator on the field enhancement at the triple junctions are also investigated. Nine different solid insulator materials having a relative permittivity in the range 2.1–13 and electron impact energies in the range 20–60 eV are examined. The effect of the surface charge on the withstand voltage of the insulating vacuum gap bridged by a solid insulator is discussed.

ISSN:0021-8979    

DOI:10.1063/1.332204

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A theoretical analysis is given of the induced current profiles at grain boundaries in polycrystalline solar cells, as obtained by light or electron beam excitation. The areaAand the variance &sgr;2of the contrast profile of a grain boundary are calculated for realistic generations as functions of the interface recombination velocityvsand the minority carrier diffusion lengthL. A graphical new procedure is proposed which allows the simultaneous determination ofvsandLfrom the measured values ofAand &sgr;. The evaluation of an experimental electron beam induced current profile illustrates the applicability of the theory.

ISSN:0021-8979    

DOI:10.1063/1.332205

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Single‐crystal samples of phosphorus‐doped Hg0.8Cd0.2Te were annealed at temperatures varying from 450 to 600 °C in different partial pressures of Hg. Hall effect and mobility measurements were performed on the samples cooled to room temperature. All the samples were found to beptype, with the hole concentration being much less than the total concentration of phosphorus present in the crystals. The hole concentration was found to increase with increase in partial pressure of Hg, in contrast to the behavior observed in undoped crystals. Also, the hole concentration obtained in the doped samples at low Hg pressures was less than that in undoped crystals. The 77‐K hole mobility of the doped samples was similar to that of undoped samples. All these inferences indicate that phosphorus behaves amphoterically in Hg0.8Cd0.2Te(s), acting as a single acceptor occupying interstitial and tellurium lattice sites at high Hg pressures, and as a single donor occupying Hg lattice sites at low Hg pressures; at intermediate Hg pressures, the majority of the phosphorus appears to be present as electrically neutral pairs formed from the association of the interstitial and substitutional phosphorus species. At low Hg pressures, a large fraction of the phosphorus appears to be present as positively and negatively charged pairs of substitutional phosphorus and vacancies of Hg. Thermodynamic constants evaluated for the incorporation of the various phosphorus species satisfactorily explain the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.332206

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Selective pair luminescence has been used to measure the exicted states of the shallow acceptors C, Zn, Si, and Ge in GaAs. Data for Ge are presented here for the first time while the sets of excited state energies of C, Zn, and Si are completed. These results show that the energies of thep‐symmetric impurity states are influenced by the impurity potentials. The germanium excited states are found to be shifted by 3 meV with respect to the valence band compared to the corresponding states in C, Zn, and Si.

ISSN:0021-8979    

DOI:10.1063/1.332207

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Secondary ion mass spectroscopy was used to measure phosphorus concentration profiles in TaSi2thin films deposited on P doped polycrystalline Si/SiO2/Si wafers by cosputtering. Fast redistribution of P in TaSi2takes place by its up‐diffusion from the polycrystalline Si layer. Radioactive assay of32P obtained by neutron activation confirmed the fast‐diffusion character of P in TaSi2. From preliminary results the temperature dependence of the diffusion coefficients over the temperature range of 664 °C‐913 °C can be expressed by the following relations:Dc=6.44×10−10 exp[−0.61/(kT)] andDa=2.0×10−8 exp[−0.76/(kT)], whereDcandDarepresent diffusion in the silicide film near and away from the surface, respectively.

ISSN:0021-8979    

DOI:10.1063/1.332208

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Measurements of surface free energy and surface tension of solid metals reported in the literature are collected and compared and preferred values are suggested. The basic criteria which determine the value of obtained results are shown.

ISSN:0021-8979    

DOI:10.1063/1.332209

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Changes in electrical resistance, light transmission, and mass were used to monitor thein‐situdegradation rate of thin Te films in room air and in an accelerated temperature‐humidity environment. The degradation resistance of Te films was found to depend strongly on the film deposition rate, film thickness, and the presence of a surface oxide layer. It was shown that, in addition to oxidation, weight loss through the formation of some unidentified volatile products also contributed to the degradation of thin Te films. The effects of deposition rate and film thickness were attributed to their influence on the film microstructure.

ISSN:0021-8979    

DOI:10.1063/1.332156

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A method of analysis has been developed by which the atomic composition of binary compound thin films can be determined, using Rutherford backscattering techniques. The advantage of the approach discussed in this paper is that the atomic concentration of the lighter material in the film can be deduced without taking into account the backscattering signals from the lighter element. This is of special importance whenever signals from the lighter element suffer from large statistical errors, or are not observable at all in a backscattering spectrum. A few examples of calculations, done with a developed computer program, as well as some experimental results are presented and discussed. It is shown that the atomic concentration of the lighter element in a compound film generally can be determined with an accuracy of about 5%.

ISSN:0021-8979    

DOI:10.1063/1.332157

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

In order to obtain good epitaxial growth,insitucleaning procedures are necessary. The procedures in use include argon ion bombardment and growth of an oxide passivation layer which is removedinsituby heat treatment. Several chemical cleaning procedures for InSb(100) have been compared, and a new technique based on growth of a chloride—rather than an oxide—over‐layer is proposed. The chloride is found to be easily removed at low temperatures (<350 °C), and carbon contamination is minimized. Procedures for growth of the chloride are described, including growth of an oxide followed by nucleophilic substitution by Cl−ions, and direct attack on the substrate by a Cl2plasma or Cl radicals in solution. In all cases, the film is composed of indium chlorides.In‐situdesorption of the chloride formed by the Cl2plasma is found to give the most reproducibly clean surfaces, as determined by x‐ray photoemission spectroscopy.

ISSN:0021-8979    

DOI:10.1063/1.332158

出版商:AIP    

年代:1983

数据来源: AIP