摘要:

The energy distribution of positive ions incident on a grounded surface in a low‐pressure argon planar rf glow discharge system has been measured as a function of excitation frequency from 70 kHz to 13.56 MHz for both capacitive and direct coupling of the rf power to the excitation electrode. The results are interpreted by taking into consideration both the transit time for the ion to traverse the sheath relative to the period of the rf excitation voltage, and the resistive or capacitive characteristics of the sheaths. The importance of system geometry and of the dc potential of the excitation electrode (as determined by external circuitry) on the maximum energy of ions incident on grounded surfaces is shown.

ISSN:0021-8979    

DOI:10.1063/1.335797

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The underlying mechanisms involved in the heat loading on the accelerator grids and plasma chamber components of multimegawatt ion sources are experimentally identified. Utilizing numerical techniques, a new accelerator geometry is designed to minimize the heat loading on various source components and maximize the beam brightness. Measurements on an ion source employing this accelerator geometry, during extraction of quasi‐steady‐state beam pulses of 3.2‐MW power, show significantly reduced heat loadings on all its components.

ISSN:0021-8979    

DOI:10.1063/1.335798

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We are investigating surface discharges as XUV photon sources forinsitucleaning and preionizing of anode surfaces in light‐ion‐fusion accelerators. In these experiments the surface discharge was formed by discharging a capacitor bank across a spark gap which consisted of two copper electrodes attached to an insulator and facing each other across a 5.5‐mm gap. The surface discharge and its power feeds were constructed in a stripline configuration to minimize overall system inductance. When the surface discharge was driven by a 2.9‐&mgr;F, 45‐kV capacitor bank, the peak current thru the discharge was ∼250 kA. When driven at these levels, a single discharge radiated with a peak power of over 80 MW of 10–70 eV photons and had a total extreme ultraviolet output energy of 60 J per pulse.

ISSN:0021-8979    

DOI:10.1063/1.335799

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Isochronal and isothermal annealing results for peroxy radical defects induced in Suprasil W1 by &ggr; irradiation are reported. The activation energy for annealing is estimated to be ∼2 eV and argued to be due to OO bond dissociation rather than gaseous interstitial or network diffusion. The results are shown to be consistent with those obtained from annealing/reactivation studies on oxygen vacancy defect centers.

ISSN:0021-8979    

DOI:10.1063/1.335800

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We analyze in this paper the effect of thermal treatment on structural properties of GaAs/InGaAs strained‐layer superlattices grown by molecular beam epitaxy. The superlattices are analyzed using double‐crystal x‐ray rocking curves. In order to model the satellites intensity variation as a function of the heat treatment time at a temperature of 850 °C, we have calculated the structure factors of the superlattices, taking into account both composition and lattice spacing modulation. The latter is found to be more influent in the calculation in this particular case. The deduced values of the diffusion coefficient, about 2×10−18cm2/s, is discussed and compared to those determined on GaAs/AlAs structures.

ISSN:0021-8979    

DOI:10.1063/1.335780

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Substrates of Al, Si, Al2O3, and GaAs were implanted with 100 to 420‐keV Al, Ar, Mn, Ni, Zn, Te, and Xe ions at low temperature of about 100 K. The reduced energies range from 0.2 to 4. The implantation energies were calibrated accurately using a nuclear resonance reaction of19F( p,&agr;&ggr;)16O. The depth distributions of the implanted ions and the induced damage were determined by means of backscattering (including channeling) combined with computer‐simulated spectrum analysis. The results are compared with the theoretical predictions given by Gibbonsetal. (GJM) and Winterbonetal. (WSS). For the latter theory, optimum WSS parameters are determined to give a good fit to the experimental data. The systematic investigation reveals that the reduced projected range and damage depth are proportional to reduced energy &egr; for Al, Si, and Al2O3, whereas they are expressed in the form &egr;2/3for GaAs substrates.

ISSN:0021-8979    

DOI:10.1063/1.335754

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The phase and microstructure of Ni, Co, and Fe impurities found in synthetic diamonds have been characterized in some detail using a combination of extended x‐ray absorption fine structure (EXAFS) utilizing intense synchrotron radiation as a light source, and conventional transmission electron microscopy (TEM), x‐ray diffraction, and fluorescence analyses. In all three cases, the metal impurity exists as an fcc metallic phase dispersed in the diamond matrix. The particles are submicron in size and not facetted. There was no evidence of a metal carbide phase in these systems. Quantitative simulations of the first‐shell EXAFS signal showed that the Co and Ni particles contain, respectively, 2.3 and 1.5 at. % of carbon in solution.

ISSN:0021-8979    

DOI:10.1063/1.335755

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

High‐speed optical pyrometry has seen increasing application in the measurement of shock temperatures in initially transparent solids and liquids; however, the information contained in the time‐dependent intensity of the emitted light has frequently been overlooked. A model has been developed for this time dependence in the observed intensity of light emitted from materials undergoing high‐pressure shock loading. Most experimental observations of this time dependence can be explained on the basis of geometric effects only, without having to invoke intrinsic time dependences of the source intensity (due to changes in temperature, emissivity or shock‐wave structure). By taking advantage of this fact, observed time dependences can be used to determine the absorption coefficient of shocked materials and their effective emissivities, thereby providing more precise temperature measurements. The model is invoked under various limiting conditions to explain time dependences previously observed in NaCl, CaO, Mg2SiO4(forsterite), SiO2(quartz), MgO, and CaAl2Si2O8(anorthite) glass. As an example, the linear absorption coefficient at 650 nm of NaCl shocked to 75 GPa is found to be 13 cm−1, close to previously published values based on a similar but less general model.

ISSN:0021-8979    

DOI:10.1063/1.335756

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Crack tip opening displacement of a crack lying parallel to a free surface is calculated by counting the number of dislocations emitted into the plastic zone from a crack tip. A discrete dislocation model was used to simulate the crack, while varying the strength of dislocations so as to satisfy the boundary condition. The result coincides numerically with the predictions made in a previous paper, in which the stress intensity factor appearing in a theory of bulk materials was replaced with the one which includes the surface correction.

ISSN:0021-8979    

DOI:10.1063/1.335757

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A light gas gun has been used to measure the unreacted Hugoniot of both pressed and cast Composition B‐3. Transmitted stress and wave speeds were determined from quartz gauges placed on the rear surface of explosive disks. Both pressed and cast Composition B‐3 exhibited elastic–plastic behavior. Good agreement was found between the elastic and plastic shock wave speeds and those determined ultrasonically. The elastic constants for pressed Composition B‐3 were evaluated ultrasonically. Apparently, reaction in Composition B‐3 has not occurred in the Hugoniot measurements described in this work.

ISSN:0021-8979    

DOI:10.1063/1.335758

出版商:AIP    

年代:1985

数据来源: AIP