摘要:

An x‐ray emission computed tomographic technique has been demonstrated to diagnose the laser implosion uniformity of spherical targets. Three‐dimensional images of compressed core were reconstructed from five pinhole camera images obtained at different viewing directions by using an iterative algorithm. Good agreement between the experimental results and two‐dimensional hydrodynamic simulations showed that the uniformity of initial target shell thickness has a significant influence on implosion symmetry.

ISSN:0021-8979    

DOI:10.1063/1.346677

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The deposition of diamond films by microwave plasmas has been studied in gaseous mixtures of methane, hydrogen, and noble gases. Plasma diagnostic results are compared with growth rates and Raman spectra of the films. The noble gases, which influence the degree of excitation or reactant molecules by energy transfer or charge transfer from their excited and ionic states, are active in the deposition process by inducing additional ion‐molecule and excited atom‐molecule reactions. As a result, enhanced deposition rates have been observed. Small oxygen additions along with the noble gases can suppress the formation of nondiamond carbon phases, leading to an effective way to rapidly deposit diamond films at high methane concentrations while still retaining minimal nondiamond carbon components in the films.

ISSN:0021-8979    

DOI:10.1063/1.346679

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An analysis is made of the relations determining the electron drift velocity in the oscillating boundary between plasma and space‐charge region at the electrode surface of an rf‐driven parallel‐plate discharge. The resulting set of equations is solved directly to yield an expression for the rf power dissipation in the plasma. Similarly, the dissipation in the space‐charge region is derived from the equations for mobility‐limited and free‐fall movement of positive ions to the wall. This model is applied to existing data for the electrical discharge properties in a 13.56‐MHz dry etch reactor. The calculated total power dissipation is shown to agree with published transfer efficiencies for the applied rf power. It appears that the electron dissipation term is dominant at high pressure and low rf power, while the ions determine the power input at low pressure and high power. The same set of equations is used to calculate the rf current wave form, the displacement of the plasma boundary with time, and the averaged plasma density. Also here, the model is in agreement with published simulations and experimental work.

ISSN:0021-8979    

DOI:10.1063/1.347155

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A self‐consistent continuum model is presented for glow discharges based on the moments of the Boltzmann transport equation. The resultant set of governing equations consist of continuity and momentum equations for electrons and ions, an energy conservation equation for electrons and Poisson’s equation. An efficient numerical scheme to solve the set of coupled equations is presented. Results from case studies of dc discharges are used to illustrate the model. A parametric study varying the cathode voltage, gas pressure, and secondary electron emission coefficient predicts many of the well‐known features of dc discharges.

ISSN:0021-8979    

DOI:10.1063/1.346652

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The spatial distribution of ground‐state scandium atoms in a high‐pressure metal‐halide discharge has been measured by saturated laser‐induced fluorescence (LIF). Sc atoms were excited at 402.4 nm (y2D05/2←a2D5/2) and the laser‐induced fluorescence was detected at 399.7 nm (y2D05/2→a2D3/2). The LIF signals were corrected for the optical depth of the fluorescence. The LIF measurements were made under saturated conditions to minimize the spatial dependence of the fluorescence quantum efficiency. In the radial plane the Sc density was a maximum at reduced radii of 0.6–0.7 with a local minimum at the arc center. The shape of the radial profile and the magnitude of the LIF signals were sensitive to the axial position in the discharge and to variations in discharge power. The radial Sc profile was independent of the ac phase angle. LIF signals were also observed at wavelengths corresponding to fluorescence from they2D03/2,y2F05/2,7/2, andy2P01/2,3/2states. The radial dependence of the LIF signal at 393.3 nm (y2F05/2→a2D5/2) was compared with the radial dependence of the LIF signal at 399.7 nm.

ISSN:0021-8979    

DOI:10.1063/1.346653

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The electrical and optical properties of radio frequency (rf) air plasma process‐induced defect states in 50 &OHgr; cmn/n+epitaxial silicon are investigated by junction capacitance techniques. Capacitance‐voltage measurements reveal the presence of a thin oxide layer of about 180 A˚ on the 30‐min plasma treated silicon sample. Deep level transient spectroscopy shows the existence of various defects in the sample. These consists of a dominant bulk electron trap labelled asE(0.46) at 0.46 eV below the conduction band, as well as continuously distributed interface states. The spectral dependence of the optical cross section for the defect levels were measured by deep level optical spectroscopy. A simple analysis indicates that a phonon mode (ℏ&ohgr;p=28 meV) couples to the defectE(0.46). Its electron‐phonon coupling strength is rather weak with a Franck–Condon shift of 0.04 eV. DefectE(0.46) anneals out at a fairly low temperature of about 120 °C. Etching off the oxide layer in a diluted HF solution was found to eliminate theE(0.46) defect level. This is tentatively explained as due to passivation of the defectE(0.46) by hydrogen from the HF solution.

ISSN:0021-8979    

DOI:10.1063/1.346627

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Misfit dislocation glide velocities have been measured in Si1−xGex/Si heterostructures. Dislocations were deliberately introduced at sites of crystalline damage, the samples were then annealed, and dislocation propagation distances measured using defect selective chemical etching. A number of different sample configurations were investigated with different layer thicknesses and alloy compositions. The measured velocities were found to depend on a number of factors including anneal temperature, an activation energy (which was found to depend on the Ge mole fraction), the effective misfit stress (which is a function of the Ge mole fraction and layer thickness), and the length of the threading arm of the misfit dislocation. Si/Si1−xGex/Si buried‐layer structures typical of the heterojunction bipolar transistor were also studied. Two possible relaxation mechanisms, involving two‐ and three‐segment dislocation configurations, are considered and an evaluation of the most likely mechanism for a range of different structures is presented. A complete quantitative analysis is made of all the results and expressions have been derived for the misfit dislocation glide velocity as a function of layer thickness and alloy concentration for all types of layer configuration.

ISSN:0021-8979    

DOI:10.1063/1.346628

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Novel results on defect annealing behavior and minority‐carrier lifetime control in electron irradiated siliconp+‐njunctions are presented. Two mechanisms are found to be involved in the annealing process of the divacancies; one dominates in the lower temperature range (from 240 to 300 °C) and the other dominates in the higher temperature range (from 320 to 360 °C). A defect labeld as E3with an energy level at 0.37 eV below the conduction band is found to be an efficient recombination channel responsible for minority carrier lifetime control. The activation energy for dissociation of the defect E3obtained from the annealing study is 1.7 eV, and the frequency factor is 2.8×109s−1. Annealing of electron irradiated samples at about 300 °C, or performing the electron irradiation at a similar high temperature is found to increase the concentration of the defect E3, and stabilize the carrier lifetime. These processes might be useful to improve the thermal stability of devices like high‐voltage rectifiers and thyristors.

ISSN:0021-8979    

DOI:10.1063/1.346629

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Thin films of InN and AlN/InN bilayers have been deposited on (0001) sapphire at a variety of substrate temperatures by reactive rf‐magnetron sputtering. For all films, thecaxis of the metal nitride film parallels thecaxis of the sapphire substrate, and the transmission x‐ray precession method has been employed to study the nature and azimuthal coherence of the in‐plane heteroepitaxy. For the InN films, a mixture of textured and epitaxial grains persists up to ∼200 °C and solely epitaxial grains are observed at higher substrate temperatures, to a maximum adherence temperature of 525 °C. In contrast, the AlN/InN bilayers are epitaxial at substrate temperatures of 50 °C and above, and a uniform deposition can be retained up to 650 °C. These fundamental differences in adhesion, structure and morphology of the InN films and the AlN/InN bilayers on (0001) sapphire are also clearly reflected, for example, in the variation in electrical mobility with substrate deposition temperature.

ISSN:0021-8979    

DOI:10.1063/1.346630

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Y3Fe5O12samples have been irradiated by Kr ions with incident energies between 9 and 37 MeV/A and Xe ions between 9 and 25 MeV/A. In this way a range of electronic stopping power between 7 and 28 MeV/&mgr;m has been explored. The irradiated samples have been etched chemically. A homogeneous track etching radius is observed after xenon irradiation but not after krypton irradiation. This result indicates that at an electronic stopping power value (dE/dx) of 17±3 MeV/&mgr;m a change in the damage morphology occurs: above this value the latent track becomes continuous cylinder. This value of stopping power is markedly higher than thedE/dx(8±1 MeV/&mgr;m) at which we have previously observed a change in the latent track damage rate and in the damage morphology from spherical to cylindrical shape of the defects.

ISSN:0021-8979    

DOI:10.1063/1.346631

出版商:AIP    

年代:1990

数据来源: AIP