摘要:

A model for theJ‐V‐Pcharacteristics for the dc diode sputtering discharges had already been developed. Here we analyze this model and show that theJ‐Vlaw is independent of the specific form of the electric field distribution and of the distribution functions of the velocities with which the ions reach the target. The distribution functions have an influence on theJ‐Vcoefficient and on the pressure dependence only. We also show two equivalent possible ways for developing the model: one based on the average velocity of the ions and the other on the average velocity of the electrons. A generalized model which is valid for both discharges: diodes and magnetrons is described herein. Its’J‐Vlaw is a superposition of the termsV3/2andV2. Experimental results are given to support the model.

ISSN:0021-8979    

DOI:10.1063/1.336841

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In the magnetized plasma of a hollow cathode arc the longitudinal and rotational drift velocities of ions have been measured, together with the electron and neutral densities and the temperatures of ions, electrons, and neutrals. The radial and longitudinal gradients of these quantities have been established. The ions drift against the electric field towards the anode with velocities between about 500 and 2500 m/s, driven by the plasma pressure gradient which is balanced by viscous deceleration and by friction against the surrounding neutral gas. The classical theory of the momentum balance with a turbulent contribution to the viscosity provides a good description of the longitudinal ion transport and explains direction and magnitude of the occurring drift velocity.

ISSN:0021-8979    

DOI:10.1063/1.336842

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Cross‐field injection of an intense ion beam has been proposed and tested as a method of creating rotating ion layers. Approximately 7% of a proton beam injected (90 keV, 300 A) is found to be trapped in a magnetic field of 5 kG through collective processes and to stay there in the form of a rotating, dilute ion layer for a time several times as long as the ion gyroperiod. The maximum azimuthal current density of trapped ions is 0.3 A/cm2. The trapped ions have a rather wide distribution along the magnetic field because of field‐aligned expansion of the injected beam.

ISSN:0021-8979    

DOI:10.1063/1.336843

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The nanosecond time‐scale developing mechanisms of positive and negative corona streamers on the insulation surface are investigated using a square pulse generator and the Lichtenberg figure technique. The developing length of the corona streamers in air is measured at a pulse duration of 3 ns, an applied voltage of 7–20 kV, and a gas pressure of 150–760 Torr. The results are compared with those obtained in the time range of 5–920 ns. The ratio of the developing length obtained at a certain pressure and that obtained at atmospheric pressure becomes a constant value irrespective of the magnitude of the applied voltage, and it increases as the gas pressure is reduced. The time lag of corona streamer inception increases with decreasing pressure. The time lag for the negative corona streamer obtained at a voltage of 20 kV is 0.1 ns at atmospheric pressure and 0.35 ns at a pressure of 150 Torr, while that for the positive corona streamer obtained at the same voltage, is 0.55 ns at the atmospheric pressure and 1.0 ns at the pressure of 150 Torr. From the results of the developing length and the time lag, the velocity of corona streamer development is estimated. The observed maximum velocity of the negative corona streamer is 8.4×108cm/s at the conditions of 20 kV and 150 Torr and that of the positive corona streamer is 1.5×109cm/s at the same conditions except for the polarity of the voltage.

ISSN:0021-8979    

DOI:10.1063/1.336844

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have probed the spin reorientation transition in Er2Fe14B by neutron powder diffraction. Our data and Rietveld analyses of them indicate that the transition is centered near 330 K, as magnetization measurements have shown, but extends over an interval of approximately 50 K. It occurs by coherent rotation of the moments from the basal plane at low temperatures to thecaxis above ∼350 K. We find no evidence for any noncollinear arrangement of the Er and Fe moments.

ISSN:0021-8979    

DOI:10.1063/1.336845

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Recent research on silicon grain boundaries has confirmed the typical features known from earlier work on grain boundaries in germanium and III‐V compound semiconductors. However, there is less clarity with respect to the role of the ‘‘dangling bonds’’ when testing for electrical activity. In silicon a pronounced double barrier with its space‐charge layer and a low leakage current rarely forms. Here the Cottrell atmospheres in conjunction with impurity complexes such as SiO, SiO2, and SiO4can strongly influence the electrical properties in a material with an exceptionally high self‐diffusivity. Conditions for the measurability of the longitudinal impurity band‐type conduction through space‐charge layers in silicon grain boundaries are outlined. It is concluded that in those cases where electrical activity is measured, the conduction parallel to the grain‐boundary plane should be apparent for pure material and at low temperature. Experiments are proposed to further our understanding of the properties of grain boundaries in silicon.

ISSN:0021-8979    

DOI:10.1063/1.336846

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The lattice location of deuterium has been investigated by channeling in fcc, hcp, and bcc metals. Implanted deuterium is studied in the range 15 K up to the release temperature and its site is compared to that of dissolved deuterium (&agr; phase). After implantation, the octahedral and tetrahedral sites are distorted and deuterium can be displaced inside these cells. This distortion explains why implanted deuterium occupies a displaced site within the tetrahedral cell in bcc metals and not the pure tetrahedral site as for dissolved deuterium. The vacancy‐deuterium interaction cannot account for all the experimental results. The trapping of implanted deuterium is described in terms of the stress induced by extended implantation defects.

ISSN:0021-8979    

DOI:10.1063/1.336850

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Cross‐sectional transmission electron microscopy and Raman spectroscopy have been used to study the defect structure and intermixing of annealed ion‐implanted Al0.3Ga0.7As/GaAs superlattices. The results show clearly that the amount and depth of superlattice layer intermixing depends on the ion mass. In superlattices that retain their structure after implantation and annealing, the distribution of defect clusters (primarily interstitial loops) is inhomogeneous; most defect clusters are nucleated in the GaAs layers. Examination of unannealed superlattice samples reveals that ion beam damage occurs preferentially in the GaAs layers.

ISSN:0021-8979    

DOI:10.1063/1.336852

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In plate impact experiments, the elastic precursor is attenuated as it propagates through the shocked specimen due to plastic straining at the shock front. However, the plastic strain rates required to explain the observed precursor decay are much higher than the strain rates that are predicted for known initial dislocation densities in the unshocked specimen, regarded as homogeneous. This anomaly, which poses a significant difficulty for the acceptance of the micromechanical theory of plasticity, has motivated this investigation of the effects of dislocation generation at surfaces and subgrain boundaries on precursor decay in single crystals of high‐purity LiF. Surface damage effects have been minimized by preparing damage‐free surfaces and by using fluid layers to protect the specimen surfaces during impact. These precautions reduce the precursor decay significantly compared to the decay measured for lapped crystals impacted directly (normal stresses of 5 kbars). However, computer simulation of the experiments based on subsonic dislocation motion, a linear viscous drag model, and nonlinear elasticity (assuming a homogeneous specimen), does not predict the measured wave profiles within experimental uncertainty. When dislocation generation at the surfaces is included in the computation, the calculated precursor amplitudes are comparable with measurements only for thin (3‐mm) specimens. Reexamination of recovered specimens from plate impact experiments suggests that subgrain boundaries are important sources for dislocation generation in precursor decay experiments. When subgrain boundaries are included as additional sources for dislocation generation, the computed velocity‐time profiles at 3 and 6.6 mm are in good agreement with measured profiles. Thus, it appears that the inclusion of dislocation generation at impact surfaces and subgrain boundaries provides a means for explaining the precursor decay anomaly, at least for high‐purity LiF.

ISSN:0021-8979    

DOI:10.1063/1.337044

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A new equation of state (EOS) has been produced for aluminum, which accurately reproduces experimental data for both the liquid and solid states. It also has a melting transition that reproduces measurements of the temperature vs pressure along the melt line. The liquid part of the EOS was calculated with the soft‐sphere model for liquid metals, and the solid EOS is based upon a Birch‐equation cold curve and Gru¨neisen thermal contributions. The range of the table extends from room temperature to 1.6 eV and from densities of 10−3–103g/cm3.

ISSN:0021-8979    

DOI:10.1063/1.336853

出版商:AIP    

年代:1986

数据来源: AIP