摘要:

SiC layers on silicon have been investigated by photothermal radiometry to study the influence of infrared emission spectra on the photothermal signal behavior. This was done by placing different band pass filters in front of the infrared detector. Because of the small amplitude of the obtained infrared signal, background contributions must be eliminated. A technique to correct the data with respect to background is presented and experimentally tested. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365789

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A particular problem in the field of shaped charge jet formation modeling concerns the collision of two fluid streams of different widths and speeds. It is commonly assumed that the flow is incompressible, and that the velocity of the fluid in any of the streams is constant across and normal to its cross section. Then the well-known classically indeterminate mathematical problem arises. In the shaped charge context the indeterminacy of the problem has been addressed by making three assumptions about the flow. Several models have assumed that conservation of kinetic energy holds, and have applied Bernoulli’s Law to equate the speeds of the jet and slug in a frame moving with the collision point. One natural choice for the third and final assumption is that the jet and slug lie in a straight line when viewed in this frame, the so-called straight line hypothesis. In this article the inclination of this line relative to the bisector of the two colliding streams is expressed as a function of the parameters of the incoming streams. It is shown that the angle between the jet and the incoming stream supplying momentum at the greater rate increases with the size of the angle between the incoming streams until it reaches a maximum value. It then decreases to zero. It is known that the straight line hypothesis is a good approximation for low values of the angle between the incoming streams, but becomes increasingly inaccurate as this angle increases. The above maximum appears to correspond to the limit of validity of the straight line hypothesis. Recommendations for the utilization of the existing formation models to achieve best accuracy are made, based on this limit.

ISSN:0021-8979    

DOI:10.1063/1.365854

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

High intensity discharge (HID) lamps are often initiated by the application of one or more short, high-voltage, breakdown pulses superimposed on a 50 or 60 Hz generator voltage. A successful transition from the breakdown event to steady-state operating conditions in HID lamps requires that the lamp-circuit system be adequate to sustain the plasma created during breakdown until the electrodes are heated to thermionic temperatures. In this article, we use a one-dimensional (in the axial direction) transient discharge model to study the conditions needed to sustain the cold-cathode discharge after a breakdown event has occurred. While the application of our one-dimensional model to real lamps is approximate, we find that the model predictions are consistent with experimental results in HID lamps, a few of which are presented here. The main conclusion from this work is that, after breakdown, the voltage necessary to sustain a glow discharge is dependent on the source impedance, the gas composition, and on the plasma density created by the breakdown event. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366274

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a quantitative study of the evolution of point defects into clusters and extended defects in ion-implanted Si. Deep level transient spectroscopy (DLTS) measurements are used to identify and count the electrically active defects in the damaged region produced by Si ion implantation at energies of 145 keV–2 MeV, and fluences from1×108to5×1013 Si/cm2.Analyses of silicon annealed in the temperature range 100–680 °C allow us to monitor the transition from simple point defects to defect clusters and extended defects that occur upon increasing the ion fluence and the annealing temperature. At low doses,<1010 Si/cm2,only about 2&percent; of the Frenkel pairs generated by the ion beam escape recombination and are stored into an equal number of interstitial and vacancy-type point defects. Thermal treatments produce a concomitant annealing of interstitial and vacancy-type defects until, at temperatures above 350 °C, only two to three interstitial-type defects per ion are left, and the DLTS spectra contain signatures of second-order point defects. Interstitial clusters atEv+0.29andEv+0.48 eVare found to dominate the residual damage of silicon implanted at higher fluences,1×1012–7×1013 Si/cm2,and at annealing temperatures,T⩾600 °C.These interstitial clusters have point defect capture kinetics and are not observable in transmission electron microscopy (TEM), suggesting that they are smaller than ≈50 Å. Finally, for silicon implanted at higher Si doses,⩾5×1013 Si/cm2,thermal treatments at 680 °C result in a strong decrease in the concentration of the interstitial cluster signatures and in the introduction of a different DLTS signal,Ev+0.50 eV,which exhibits logarithmic rather than exponential carrier capture kinetics, a feature typical of an extended defect. Comparison of the formation and dissolution of this extended defect signature with TEM analyses indicates that this level is a signature of the rodlike {311} defects that are known to store the interstitials responsible for transient enhanced diffusion. These results suggest that the small interstitial clusters are either the precursors of the {311} defects or that they compete with {311} defects as sinks for self-interstitials. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.365583

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

High resistivity silicon particle detectors will be used extensively in experiments at the future CERN Large Hadron Collider. The detectors will be exposed to particle fluences equivalent to∼1014(1 MeV neutrons)/cm2,causing significant atomic displacement damage. A model has been developed to estimate the evolution of defect concentrations and the electrical behavior of irradiated silicon detectors using Shockley–Read–Hall (SRH) semiconductor statistics. The observed increases in leakage current and doping concentration changes can be described well after60Co-gamma irradiation but less well after fast neutron irradiation. A possible non-SRH mechanism is considered, based on the hypothesis of charge transfer between clustered divacancy defects in neutron damaged silicon detectors. This leads to a large enhancement over the SRH prediction forV2acceptor state occupancy and carrier generation rate which may resolve the discrepancy between the model and neutron damage data. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365790

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Heavily silicon doped GaAs grown by molecular beam epitaxy using a single gallium isotope source(69Ga)has been studied by infrared absorption to reveal localized vibrational modes (LVMs) of Si complexes. The structure observed close to 367cm−1is the same as that present in normal GaAs:Si spectra and does not result from mixed Ga isotopes. The electron trapSi–Xgives three LVMs at 368.4, 370.0, and 399.6cm−1, typical of second neighbor donor-acceptor pairs, but inconsistent with a previous proposal that its structure is the planar defectVGa–SiAs–AsGa. It is now suggested that the defect is a perturbedSiGa–VGacenter, involving a second Si atom or a second vacancy. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365791

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Examining the effect of nonhydrostaticity on the shape of x-ray powder diffraction lines shows that a uniaxial stress field, as is generated in opposed-anvil type high-pressure apparatuses, can result in lines being split or having an asymmetric shape. The distribution of local stresses, generated by mismatches in shapes of neighboring grains within the specimen, results in orientation-dependent broadening: diffraction linewidths are generally proportional to1/E(hkl),whereE(hkl)is Young’s modulus for planehkl.Since anomalous diffraction patterns can be misinterpreted as indicating a phase transformation, the occurrence of new phases under nonhydrostatic pressure should be carefully confirmed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365792

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Structural properties of gradedSi(1−x)Gexlayers obtained on Si(100) by pulsed laser induced epitaxy were investigated by means of conventional powder x-ray diffraction and x-ray photoelectron spectroscopy. TheSi(1−x)Gexepitaxial layers were formed by pulsed KrF-laser driven rapid melting and crystallization of thin amorphous Ge layers deposited onto the Si(100). The experimental results showed that, by increasing the number of laser pulses, good quality and partially strained epitaxial layers could be attained. A Monte Carlo data evaluation algorithm is proposed, which is capable to determine, by the simultaneous fit of data obtained by x-ray diffraction and x-ray photoelectron spectroscopy, the strain level as a function of Ge concentration. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365793

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The metallic glassZr65Al7.5Cu27.5exhibits a wide temperature range in the undercooled liquid region. This offers the possibility of examining the phenomena that occur during glass transition. We investigated this glass by x-ray diffraction and x-ray absorption spectroscopy (XAS) at room temperature and at elevated temperatures below and above the glass transition temperature. The total number of nearest neighbors determined by x-ray diffraction remained unchanged. Using XAS irreversible changes in the short range order (SRO) towards the SRO of crystallineZr2Cuis observed in the nearest neighbor shell which is consistent with the x-ray diffraction results. The long range order was not affected by these changes. From the temperature dependence of the atomic mean-square relative displacements&sgr;2,Debye temperatures were determined and they compare well with low temperature specific heat measurements. AboveTgthe slope of&sgr;2increases drastically and is attributed to anharmonic effects. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365794

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The Rayleigh–Taylor (R-T) instability theory is usually applied to the acceleration of one fluid by a lower density one, but also becomes applicable to a solid accelerated by a fluid at very high pressure. Approximate analytic R-T stability criteria are derived for both finite and infinitesimal perturbations of the driven surface of an incompressible solid plate of a given thickness, shear modulus, and von Mises yield stress uniformly accelerated by a massless fluid. The Prandtl-Reuss equations of elastic-plastic flow are assumed for the solid. A single degree of freedom, amplitudeq, is assumed for thespatialdependence of the perturbation, which is approximated to be that of the semi-infinite half-plane ideal fluid linear R-T eigenfunction. Thetemporaldependence ofq, however, is determined self-consistently from global energy balance, following a previously published model. The (significant) effect of theunperturbedsolid’s stress tensor is included and related to the converging/diverging geometries of imploding/exploding cylindrical and spherical solid shells for which the model may be applied locally. Correlations with Phillips Laboratory’s quasispherical electromagetic implosions of solid shells are presented. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365795

出版商:AIP    

年代:1997

数据来源: AIP