摘要:

The expansion flow of helium plasma in the end loss region of a theta pinch has been studied. The accuracy of several spectroscopic techniques for determining plasma properties in the transient, inhomogeneous plasma has been evaluated. Plasma at a location of 2.5 cm outside the end of a 25‐ cm long theta‐pinch coil is characterized byNe∼1016cm−3,Te∼6 eV. Radial electron density profiles were obtained by: (1) Abel inversion of plasma continuum emission from chords across the plasma column to produce relative radial electron density profiles, with normalization by a new technique, whereby a theoretical He II 4686‐A˚ spectral profile is calculated and compared to that observed experimentally being emitted across the diameter of the plasma column; and (2) direct prediction of an absolute electron density profile by Abel inversion of He II 4686‐A˚ spectral profiles obtained by viewing chords across the plasma column. Electron temperatures were obtained from spectroscopic measurements across the diameter of the plasma flow by: (1) measurement of the ratio of the He II 4686‐A˚ line intensity to the underlying continuum intensity; and (2) measurement of the absolute intensity of the He II 4686‐A˚ line. The accuracy of these spectroscopic techniques in a pulsed discharge, with plasma undergoing flow expansion, will be indicated by comparison of the results with those from Thomson scattering.

ISSN:0021-8979    

DOI:10.1063/1.331235

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

This paper is concerned with experimental and analytical/numerical studies of the anode region of an atmospheric pressure argon arc in a current range from 100 to 300 A. The arc arrangement allows unobstructed viewing of the entire anode region, including the anode itself, and it is also suitable for simulating short as well as long arcs. Depending on the flow situation in the anode region, two different types of stable arc roots are observed. The diffuse anode arc root, characterized by a strong flow impinging on the anode surface, is well known from free‐burning, short arcs. The second type reveals a more or less vevere constriction in front of the anode, caused by the entrainment of gas into the arc, resulting in an anode jet. Measurements of the induced flow at the cathode of such an arc show a linear increase of the induced mass flow rate with increasing current. This correlation can be confirmed by a simple analysis. A fast‐scanning, computer‐controlled system has been used for spectrometric measurements of the temperature distribution for both modes of anode arc roots, assuming local thermodynamic equilibrium (LTE) in the arc. The maximum temperatures in the arc core compare favorably with calculated temperature distributions of the constricted mode. The calculated isotherms, however, show a substantial shift which is probably due to the chosen boundary conditions at the end of the constrictor tube.

ISSN:0021-8979    

DOI:10.1063/1.331236

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The microstructure of ac‐thin film electroluminescent devices was studied by transmission electron microscopy (TEM) of cross‐sectional specimens, and was correlated to electro‐optical characteristics of the devices. The cross sections reveal the microstructure of the BaTiO3/ZnS:Mn/BaTiO3layer structure as a function of film depth. The rf‐sputtered BaTiO3films are amorphous; the electron‐beam evaporated ZnS films are polycrystalline. The first‐to‐grow region of the ZnS layers always exhibits a very small grain size. With increasing film thickness the growth of larger columnar grains is observed. At higher substrate temperatures the grains have a more conical shape. The Mn‐concentration, measured by x‐ray microanalysis on the cross‐sectional specimens in a scanning TEM, shows an overall increase with growing ZnS film thickness, because the ZnS was evaporated from a single ZnS:Mn source. Annealing at 550 °C improves the electro‐optic characteristics of the samples considerably, without changes in microstructure being observable. Annealing at 850 °C induces strong recrystallization. The initial fine‐grained region disappears and the grains extend from the bottom to the top of the ZnS film.

ISSN:0021-8979    

DOI:10.1063/1.331237

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The microgeometry or texture of a porous medium determines its physical properties, e.g., the electromagnetic, acoustical, and fluid dynamic properties of sedimentary rock. Unified functional models of texture are clearly needed to test and provide insight for texture‐dependent theories relating different properties or explaining empirical observations. A class topological models of sedimentary rock is introduced, together with the necessary topological concepts. Each sample is modeled by two 3‐D networks, pore and grain, together with a set of measured parameters such as integranular contact areas or pore/throat ratios (of which any given application may use only a subset). An intuitive example of thin modeling process is provided. A description is given of data acquisition and image analysis procedures used for measurements from reconstructed serial rock sections. Preliminary observations of grain and pore statistics are presented, with comparisons to other related data. The ’’connectivity’’ of the pore (or grain) system of Berea is lower than the connectivities of regular monosized sphere packs with similar porosities and the same mean grain ’’diameters’’. A wide distribution of sizes, aspect ratios, and coordination number were also found for Berea. Illustrative applications of this kind of modeling to nuclear‐magnetic resonance, fluid flow, and frame modulus are given.

ISSN:0021-8979    

DOI:10.1063/1.331238

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Infrared transmission spectra of a series of silicon dioxide (SiO2) films grown on silicon wafers from a HCl and O2gas mixture at 850 °C, have been studied for film thicknesses down to 28 A˚. The validity of Lambert‐Bouguer’s Law for such thin films has been confirmed, and the apparent absorption coefficient calculated for the absorption at 1065 cm−1is in good agreement with previously published data for thicker, vapor‐deposited, and thermally grown films. A continuous shift of the absorption near 1065 cm−1has been found, moving from an asymptotic limit maximum of ∼1070 cm−1for thick films towards smaller wave numbers for thinner films. Various possibilities for the origin of this shift are discussed.

ISSN:0021-8979    

DOI:10.1063/1.331239

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Reversible hysteresis behavior of capacitance and ac conductance of amorphous Se:As alloy films (alloy range 0–4% As) below the glass transition temperature (Tg) is observed when measurements are carried out at fixed frequency in the temperature scan mode over an experimental range encompassingTg. In this measurement mode, annealing effects which follow either cycling or film formation by evaporation can be continuously monitored, via film capacitance, as the film undergoes kinetically arrested isothermal relaxation toward a quasistable state. Arsenic addition to amorphous Se alters many of its physical properties. For example, in a previous study of the same series of films, it was found that both the dielectric increment measured just above their respectiveTg’s and the widths of the associated relaxation distribution function varied significantly with composition. In the present study, dielectric and thermodynamic measurements indicate that arsenic addition to amorphous Se significantly slows the rate of structural relaxation near room temperature (?15 K below respectiveTg’s). However, it is found that the shape of the capacitance relaxation function, associated in this case with structural relaxation belowTg, is relatively insensitive to alloy composition. The changes in room temperature relaxation, reflected in capacitance measurements, can in fact be adequately accounted for, phenomenologically, solely in terms of the shift inTginduced by arsenic alloying. It is suggested (1) that dielectric relaxation in the melt aboveTgand structural relaxation during annealing belowTgare controlled by a different set of dynamic processes or (2) progressive arsenic alloying skews the relaxation distribution function so that the very low frequency‐spectral components which dominate relaxation belowTgremain unaffected.

ISSN:0021-8979    

DOI:10.1063/1.331240

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Field evaporation events in time‐of‐flight atom‐probe analyses were treated as Markov chains. Both the random chain and the chain with a given distribution of cluster sizes were considered. The validity of the analysis was checked with a set of atom‐probe data of iridium. The data agree with a random distribution of the two isotopes. Two sets of atom‐probe data were collected from Pt‐Rh alloys, and were analyzed and compared with these models. It is found that the experimental distributions fit best with the distributions including slight degrees of clustering in the field evaporation events. Thus, microclustering of Rh and Pt atoms occurs in Pt‐Rh alloys, which are generally believed to be complete random solid solutions over the entire composition range. From the atom‐probe data, however, we are not yet able to estimate the cluster size distribution of Rh and Pt atoms in the alloys. Our atom‐probe data of a metallic glass agree well within the statistical uncertainty of the data with a random distribution of the constituents. If microclustering occurs, it is still beyond the sensitivity of the method as constrained by the amount of data available.

ISSN:0021-8979    

DOI:10.1063/1.331241

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Neutron energy dependence of the initial dislocation pinning rate was studied from 67 keV to 1 MeV on a copper sample. By comparing the initial pinning rates of 0.5‐MeV electron irradiations and the neutron irradiations and using the defect production rate for electron bombardments, an estimate of the free interstitial production cross sections for neutrons was made. Comparison with the Norgett‐Robinson‐Torrens production cross section for the total number of defects was made to estimate the fraction of defects surviving as free interstitials. Previous data covering the neutron energy range of 2–24 MeV showed this fraction to be a constant. However, the present lower energy data show that the survival fraction increases at low energies, from 0.7% at 1 MeV to 2% at 67 keV. The entire data set is compared with two additional models, one which considers experimental data and computer models supporting a recoil energy dependent displacement efficiency and one which yields the number of free vacancies after short‐term annealing. Our results are best described by the latter. It is concluded that the surviving fraction of defects in displacement cascades is a function of primary knock‐on energy in the few keV range and that this behavior must be considered in modeling radiation effects.

ISSN:0021-8979    

DOI:10.1063/1.331242

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A molecular dynamics simulation has been used to investigate the sensitivity of atom ejection processes from a single‐crystal target to changes in the atom‐atom potential function. Four functions, three constructed from the Gibson potentials with Anderman’s attractive well, and a fourth specifically developed for this investigation, were investigated in the Cu/Ar+system over a range of ion energies from 1.0 to 10.0 kev with the KSE‐B ion‐atom potential. Well depths and widths also were varied. The calculations were done at normal incidence on the fcc (111) crystal orientation. Computed values were compared with experimental data where they exist. Sputtering yields, multimer yield ratios, layer yield ratios, and the ejected atom energy distribution vary systematically with the parameters of the atom‐atom potential function. Calculations also were done with the modified Moliere function. Yields and other properties fall exactly into the positions predicted from the Born‐Mayer function analysis. Simultaneous analysis of the ejected atom energy distribution and the ion energy dependence of the sputtering yield curve provides information about the parameters of both the wall and well portions of the atom‐atom potential function.

ISSN:0021-8979    

DOI:10.1063/1.331243

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The stresses of thermally grown as well as chemically vapor deposited (CVD) silicon dioxide were measured by the cantilever beam technique using x‐ray diffraction. Thermally grown oxide shows reversible stress changes upon heating or cooling of the films. The linear thermal expansion of such films is similar to that of bulk vitreous silica, 5×10−7 °C−1, the biaxial elastic modulus was found to be 6.3×1011dyn/cm2. CVD oxides show extensive hysteresis in the stress‐temperature curves when tested in ambient air. From stress measurements of such films, deposited on Si and GaAs, it was concluded that their average linear thermal expansion coefficient in the temperature range of −170–115 °C is 4×10−6 °C−1, much higher than that of thermally grown oxide, while their biaxial elastic modulus is only 4.6–5.1×1011dyn/cm2. The stress in such films was found to increase when the films were exposed to a dry ambient or vacuum. The time constant for this change was found to be several minutes at room temperature.

ISSN:0021-8979    

DOI:10.1063/1.331244

出版商:AIP    

年代:1982

数据来源: AIP