摘要:

A retarding potential technique has been employed to select electrons for extraction from a hollow cathode discharge. In ‘‘normal’’ operating pressures, the electron distribution function is Gaussian like with a superthermal tail. At low operating pressures, the electron distribution function has an additional distinct component of electrons with a very low thermal spread of 0.13 eV and an energy corresponding to the cathode potential.

ISSN:0021-8979    

DOI:10.1063/1.345770

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The rate constants of low‐energy electron attachment to BCl3diluted in N2are measured as a function ofE/Nat 1–11 Td, corresponding to mean electron energies at 0.4–1.0 eV. The negative ions produced by hollow‐cathode discharges of either pure BCl3or mixtures of BCl3in N2are mass analyzed to identify the products of electron attachment to BCl3. Only Cl−ion is found in the discharge media, although BCl−3is observed at the applied voltage significantly lower than the breakdown voltage. The electron attachment processes of BCl3are discussed.

ISSN:0021-8979    

DOI:10.1063/1.345771

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The electron distribution function is calculated for a plasma created when a high‐current, high‐energy (∼MeV) electron beam enters nitrogen gas. No spatial dependence is considered for the distribution function and the velocity is expanded in the two‐term approximation. Time dependence is retained. Benchmark calculations are presented that compare code output with experimental results of electron deposition studies and swarm studies in nitrogen. Production efficiencies are given. The effect of inner‐shell processes is discussed. An example illustrates the importance of the beam‐induced electric field on the plasma generation and behavior. It shows that considerable ohmic energy deposition can be involved and that, consequently, production of certain species can be greatly enhanced.

ISSN:0021-8979    

DOI:10.1063/1.345772

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The combination experiments of ac and dc (as the thermally stimulated polarization current) suggest that, by the dc process, there appeared the positive and negative ion‐depleted region at the interface between glass bulk and the positive ion‐depleted region near the anode. This may be the ionic analog for ap‐njunction under reverse bias of a semiconductor. The relaxation in polarized glass would take place by the annihilation of the positive and negative ion‐depleted region by back‐diffusion of oxygen ions from the positive ion‐depleted region and of sodium ions from the bulk.

ISSN:0021-8979    

DOI:10.1063/1.345773

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

By using a nanoprobe electron beam 4 A˚ in diameter, the [001] nanodiffraction patterns of AlGaAs‐GaAs multiple‐quantum‐well structures have been formed and the epitaxial relationship between AlGaAs and GaAs is confirmed. The intensities of the (200) diffraction disk, monitored by a spot detector, are displayed in two ways: (1) the (200) dark‐field scanning transmission electron microscopy (STEM), which shows the layers of AlGaAs and GaAs in contrast, and (2) the (200) line‐scan profile, which reveals the (200) intensity distribution of a specimen region of uniform thickness. The thickness and the absolute Al concentration of AlGaAs layers are, respectively, determined from the contrast of, and the (200) thickness contour position in, the (200) dark‐field STEM images. The microanalysis on the (200) line‐scan profile is used to find the local Al concentrations in AlGaAs layers and to study the interface boundary between the layers of AlGaAs and GaAs. Diffusion of the Al atoms from the AlGaAs layer into the GaAs layer is also reported.

ISSN:0021-8979    

DOI:10.1063/1.345774

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Correlated self‐diffusion in a screw dislocation in a face‐centered‐cubic crystal is treated with a vacancy mechanism using matrix functions that are generated to permit the length of the dislocation to approach infinity for the tight‐binding approximation. The correlation factorffor positive vacancy binding to the dislocation is found to lie in the range 0.819≥f≥0.516. Previous calculations for a screw dislocation in a simple cubic structure are in the range 0.74≥f≥0.52, and are viewed as representing the differences associated with the core structure. Comparable calculations of the diffusion coefficient suggest that it becomes indefinitely large in the limit where the vacancies are tightly bound to the dislocation core but with a finite concentration in the surrounding lattice which is in agreement with similar limits for other dislocations.

ISSN:0021-8979    

DOI:10.1063/1.345775

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The formation of mixed metastable phases as a result of ion‐beam mixing of the Al‐Fe‐Mn system with 100‐keV Ar+ions and their subsequent transformations upon thermal annealing have been studied. The mixed state is comprised of both binary (Fe‐Al, Fe‐Mn, Mn‐Al) and ternary (Al‐Fe‐Mn) metastable phases. Conversion‐electron Mo¨ssbauer spectroscopy and low‐angle x‐ray diffraction studies reveal the formation of disordered phases upon ion beam mixing, which acts as a precursor for the growth of the equilibrium phases upon thermal annealing via lowering of kinetic barrier for the reactions.

ISSN:0021-8979    

DOI:10.1063/1.345776

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Spall at ultra high strain rate (107s−1) was investigated using short pulsed laser‐induced shock waves in copper and aluminum foils. The intensities of the 3.9‐ns Nd:Glass laser were in the range of 1010–1012W/cm2, and the foil thickness was in the 100–600 &mgr;m range. The laser‐generated shock wave pressure was in the range of a few hundred kilobars (kb). The shock wave traversed the foils in a few tens of nanoseconds. The controlled stepwise increase in laser energies allowed the stages of damage evolution from incipient to complete perforation of the target foils to be found. The energy threshold for spall and the spall width at that energy was measured as a function of the foil thickness for both materials. At threshold energy conditions, spall width of 25–65 &mgr;m for Al and 15–45 &mgr;m for Cu were obtained for foil thicknesses of 100–600 &mgr;m. Computer simulations of the laser‐induced spall were performed, including the laser absorption, shock wave travel through the foil, and the spall phenomena. The simulations were based on the one‐dimensionalmedusacode, which was expanded to include the spall phenomena, using simple spall criteria. An estimate of the strain rate was derived from the simulations and it was shown that the strain rates in the present experiments are about an order of magnitude larger than those obtained in spall experiments using other methods. The experimental results of energy threshold for spall and spall width at this energy were compared with the numerical simulations. The experimental results are in good agreement with the simulation results, indicating that spall strength for both materials, Al and Cu, are in the −50 to −60 kb regime.

ISSN:0021-8979    

DOI:10.1063/1.345777

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Wave propagation phenomena in two magnetoelastic, initially stressed, conducting, homogeneous, and isotropic media are discussed. The coefficients of reflection and refraction are obtained in cases of the incidentPwave and incident shear wave incident obliquely at a plane interface between two welded, magnetoelastic media. Energy relations in both cases are also derived. Total internal reflection for an incident shear‐horizontal (SH) wave is analyzed. The equation of caustic for the SH wave is obtained. The velocities of the SH waves in both media are calculated. Analysis of the results are carried out by drawing graphs between the initial pressure and critical angle and the initial pressure and velocity of the SH wave. The equation of caustic is also analyzed by determining the values of distances of the points on the caustic for different values of the angles of incidence. Taking the initial stress and magnetic field to zero the results obtained are in compliance with those results in elastic homogeneous isotropic media.

ISSN:0021-8979    

DOI:10.1063/1.345778

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Thermal expansion coefficients and biaxial elastic moduli of the sputtered W, WNx, WSi0.45, and WSi0.67N0.10thin films, used as refractory gate in the self‐aligned metal‐semiconductor field effect transistors on GaAs, were determined byinsitustress measurements during heating and cooling of the films on GaAs and Si substrates in the temperature range of 20–450 °C. For the WNxfilms the average values of thermal expansion coefficients increased with the nitrogen content, and varied from 4.5×10−6 °C−1for tungsten to 5.80×10−6 °C−1for WN0.43. For the WSi0.45and WSi0.67N0.10films, the measured values of coefficients of thermal expansion (6.55×10−6and 6.37×10−6 °C−1, respectively) were close to that of GaAs (6.40×10−6 °C−1, respectively). Thus by using these films as refractory gates, the stress‐induced interdiffusion and interaction at the interface with GaAs can be substantially reduced.

ISSN:0021-8979    

DOI:10.1063/1.345779

出版商:AIP    

年代:1990

数据来源: AIP