摘要:

We describe experiments for a neon tandem-puffZpinch modified with a small-diameter, high-Zwire target (i.e., pinch-on-wire). The radiative yield for photon energies in the range of 1–100 keV is measured. With a copper-wire target the integral yield (J) between 0.9 and 1.5 keV increases by a factor of 1.5 compared to the pinch without a target; the yield is unchanged or slightly increased for higher-Zwires. The high-energy integral yield, above 6 keV, increases by a factor of 2 or more with a copper target and as much as a factor of 5 with a tungsten target. This behavior cannot be accounted for by simple hydrodynamic compression of a hot plasma and suggests yield enhancement by a nonthermal mechanism. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365036

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The magnitude and relative phase of the time varying magnetic field in an inductively coupled discharge have been measured with twodB/dt(B-dot) probes: OneB-dot probe was enclosed by a dielectric tube (as is commonly used indB/dtmeasurements) while the other, a thin wire probe, was immersed directly into the plasma. Each probe was used to measure the radial and axial component ofdB/dt. A comparison of rf electric fields and currents obtained by the two probes showed essentially different results. The disagreement is interpreted to be due to a large local disturbance of the plasma density and current caused by the dielectric tube. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365026

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A novel scheme that employs the use of an auxiliary discharge has been shown to reduce markedly anode sheath potentials in a transverse discharge. An 8.8 A low-pressure argon discharge in the presence of a transverse magnetic field was used as the plasma source in this study. In such discharges, the transverse flux that is collected by the anode is severely limited due to marked reductions in the transverse diffusion coefficient. Findings of this study indicate that the local electron number density and the transverse flux increase when the auxiliary discharge is operated. Changes in these parameters are reflected in the measured anode sheath voltage. Anode sheath potentials, estimated by using Langmuir probes, were shown to be reduced by over 33&percent; when the auxiliary discharge is operated. These reductions in anode sheath potentials translated into significant reductions in anode power flux as measured using water calorimeter techniques. The reductions in anode power flux also correlate well with changes in the electron transverse flux. Finally, techniques implementing these positive effects in real plasma accelerators are discussed.

ISSN:0021-8979    

DOI:10.1063/1.365038

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of the electron temperature(Te)on charging potentials that develop in trenches during plasma etching of high aspect ratio polysilicon-on-insulator structures is studied by two-dimensional Monte Carlo simulations. Larger values ofTecause the potential of the upper photoresist sidewalls to become more negative; thus, more electrons are repelled back and the electron current density to the trench bottom decreases. The ensuing larger charging potential at the bottom surface perturbs the local ion dynamics so that more ions are deflected towards the polysilicon sidewalls causing (a) more severe lateral etching (notching) and (b) larger gate potentials, thereby increasing the probability of tunneling currents through the underlying gate oxide. The simulation results capture reported experimental trends and offer new insight into the nature of charging damage. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365039

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Diamond crystals nucleate in the centers of spherical concentric-shell graphitic particles where high pressure prevails under electron irradiation at specimen temperatures above 900 K. The diamond crystals grow under further irradiation until the graphitic particles have wholly transformed to diamond. Hence, the conversion of the graphitic structure to diamond starts at high pressure and proceeds at decreasing, possibly even at zero, pressure. The experiment is carried out in a transmission electron microscope which enables us to monitor this phase transformationin situon an atomic scale. It is shown that the graphite/diamond system under electron irradiation is highly dissipative. This suggests that the phase transformation at low pressure occurs via self-organization under nonequilibrium conditions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365040

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Positron lifetime investigations were done on a series of InP samples irradiated to various doses with 2.5 MeV electrons. Inn-type materials, positron lifetimes of 265±5 and 338±15 ps are attributed to indium vacancy–interstitial complexes and divacancy–interstitial complexes, respectively. Inp-type materials these defects were not observed. Thermal annealing took place up to 200 °C for both defect types. Introduction rates were estimated to be 0.1cm−1forVIn⋅InIand ∼0.05cm−1for the divacancies. The divacancies showed a temperature dependence of the trapping rate, which suggests a thermally activated process. No evidence forVPvacancies could be found in neitherp-type norn-type materials. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365041

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A detailed analysis of the electon paramagnetic resonance line shape was performed on amorphous Si samples obtained by Kr+ion implantation. The Lorentzian character and behavior upon annealing was explained via a strong exchange interaction, leading to a cluster model for the spin density distribution. The saturation measurements are shown to be a convenient method to study structural changes caused by thermal annealing. The spin density distribution (as described with the cluster model) imposes a clear difference between amorphous Si material obtained by ion implantation and one obtained by evaporation and/or chemical vapor deposition. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364704

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Experimental and theoretical results are presented on the evolution of large elastic deformation, non-uniform curvature, shape changes and geometric instability in substrates of Si wafers with metal films. The critical diameter and thickness of the Si wafer, for which large deformation and shape instability occur, are identified, as functions of the line tension in the film (which is the product of the biaxial stress in the film and the film thickness). Observations of the curvature and shape variations along the wafer diameter and geometry-dependence of the shape instability compare favorably with those predicted by detailed finite element analyses. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365042

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

ZnS1−xTex(0<x<1)alloys grown on (100) GaAs substrates by molecular beam epitaxy are investigated using the x-ray diffraction and Raman scattering. The frequencies of long wavelength ZnTe-like and ZnS-like longitudinal optical phonons determined from Raman scattering show linear variation with the compositionx. The frequency of the zone-center optical phonons as a function ofxof theZnS1−xTexmixed crystal shows a typical two-mode behavior, which is in good agreement with the theoretical results from a modified random-element isodisplacement model.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365043

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Phonon dispersion and Fro¨hlich interaction in coupled quantum-well structures are derived by using a modified image–charge ansatz that shows that the mode symmetry in the surface phonon dispersion of single quantum-well (QW) structures is modified by the addition of a thin inner barrier. The electron–phonon scattering rates are evaluated for phonons in the entire coupled QW configuration and compared with the corresponding rates calculated for phonons in the separated-single QW approximation. Our calculations show that the separated-single QW phonon model provides reasonable estimates of the electron–phonon scattering rates except for intersubband processes when the quantized energy separation between the initial and final electron states is in resonance with the polar optical phonon energy. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365044

出版商:AIP    

年代:1997

数据来源: AIP