摘要:

First, we present formal aspects of the scattering of plane elastic waves by a single elastic cylindrical inclusion or a cavity of an arbitrary cross section embedded in an isotropic homogeneous elastic medium of different properties. An integral equation is used to derive expressions for the displacement field valid in the entire domain. Thereafter the Born approximation for the solution is derived. Formulas for the scattered amplitudes and the scattering cross sections are presented. The validity of the approximation is examined by comparing the results with those of the simple bodies for which the exact solutions are available in the literature. Some new results for the corresponding three‐dimensional case are also presented.

ISSN:0021-8979    

DOI:10.1063/1.331245

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A technique is described for measuring torsional wave velocity in (nonferromagnetic) wire with diameters of less than 1 mm. Transduction is noncontacting, via Lorentz forces acting across a gap between transducer and wire, so that velocity can be ’’scanned’’ along the length of the wire. A double‐receiver approach permits the scan to be made in a ’’point‐by‐point’’ fashion. The wires are a metal‐matrix composite of 6061 aluminum and pitch mesophase graphite. Some data are presented, together with a discussion of the effects of metal‐matrix‐composite parameters, such as graphite content and porosity, on torsional velocity. An extrapolation of our metal‐matrix‐ composite data yields a value forc44, of the graphite fiber, that was within 1% of a value determined from data of Fischbach and Scrinivasagopalan. Good predictions of experimental results were obtained through use of theory of Hashin and of Achenbach and Herrmann. Some differences, and their implications, between torsional and longitudinal waves propagating in metal‐matrix‐composite wire are described.

ISSN:0021-8979    

DOI:10.1063/1.331246

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Nuclear resonance profiling was used to measure the distributions of hydrogen incorporated into dry SiO2films by thermal treatments in steam. Thermal oxides were grown on silicon to a thickness of 260 nm in dry O2and were subsequently treated in steam at temperatures of 320 and 500 C for periods lasting between 390 and 6×105s. The concentrations of hydrogen carried in by permeating water were then profiled with 6.4 MeV15N ions using the resonant nuclear reaction1H(15N, &agr;&ggr;)12C. Water was seen to penetrate the films rapidly and to slowly react with the SiO2uniformly throughout the films. Two distinct stages were observed in the buildup of H, indicating that the water/SiO2reaction involves at least two concurrent processes rather than a single‐stage process.

ISSN:0021-8979    

DOI:10.1063/1.331247

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Residence lifetimes of Mg on GaAs surfaces were observed using 10 KV reflection electron diffraction and Auger electron spectroscopy to decrease from ∼120 s at 550 °C to ∼1 s at 600 °C. The electrical incorporation coefficient is ∼0.3 at and below 500 °C decreasing to ∼3×10−4at 600 °C at the expense of desorption. Hole mobilities of uniformly Mg‐doped samples are as good as those for equivalently Be‐doped GaAs samples. Calcium does not behave as a shallow acceptor in GaAs grown by molecular‐beam epitaxy.

ISSN:0021-8979    

DOI:10.1063/1.331248

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Monolithic electroluminescence devices require planar growth of isolated devices on a substrate. Planar growth has been realized by selective‐area molecular beam epitaxy (MBE). Selective‐area growth of ZnSe thin films by MBE has been successfully achieved over a GaAs substrate partially coated with SiO2film, where active device positions are defined by windows in SiO2layers. Extensive characterization has been carried out for both monocrystalline and polycrystalline materials. It is found that the device‐quality single‐crystal layer is isolated by the insulating polycrystalline layer. The difference in the etch rate of polycrystalline layers from that of monocrystalline layers enables the fabrication of three‐dimensional structures. Schottky barrier electroluminescence diodes have been fabricated by aninsituprocess. The diodes show white emission for applied voltages as low as 6 V.

ISSN:0021-8979    

DOI:10.1063/1.331249

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

We have developed a one‐dimensional model for thermal‐wave depth profiling that provides expressions for the temperature at the surface of the sample and for the thermoelastic response beneath the surface. The model shows that elastic wave interference effects produce significant differences between samples with mechanically free and constrained surfaces, and that thermal‐ wave images of thermal conductivity variations are obtainable from the thermoelastic signal only if the front surface is mechanically free. We have also considered the case of subsurface heating and found that for heating occurring at depths of more than a few thermal diffusion lengths, the thermoelastic signal becomes independent of thermal conductivity variations. This has important implications for thermal‐wave image range and resolution.

ISSN:0021-8979    

DOI:10.1063/1.331250

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Traps in semi‐insulating InP:Fe and InP:Cr have been studied by Photo‐Induced Current Transient measurements for the first time. Hole emissions to the valence band with activation energy &Dgr;ET= 0.69±0.01 and 0.96±0.01 eV from the Fe and Cr levels, respectively, have been identified. These values of &Dgr;ET, on comparison with Hall measurement data for 350⩽T⩽600 K, indicate negligible coupling of the Fe and Cr levels with the lattice. Electron traps with &Dgr;ET= 0.68±0.01 eV, probably related to native defects, and hole traps with &Dgr;ET= 0.50±0.005 and 0.67±0.01 eV have also been detected. The thermal capture cross section related to the various electron and hole emissions have been estimated.

ISSN:0021-8979    

DOI:10.1063/1.331251

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A scanned cw Ar ion laser was used to recrystallize polycrystalline and amorphous silicon films.N‐channel metal‐oxide‐semiconductor transistors were fabricated on these recrystallized films and used for electron field effect mobility measurements. The electron conduction in the samples which had polycrystalline silicon substrates and were annealed at higher power (⩾12 W) was dominated by the lattice scattering mechanism. Other relatively minor factors, such as the scattering by surface imperfections, impurities, and very small intercrystalline potential barriers, altered the magnitude and the temperature dependence of the measured mobilities. For the unannealed and lower power (⩽11 W) annealed polycrystalline samples, scattering at the intercrystalline potential barrier dominated the electron conduction. The role of additional phosphorus doping in the substrate is also discussed. In the higher power annealed polycrystalline devices, the scattering caused by the ionized phosphorus atoms not only lowered the magnitude but also reduced the negative temperature coefficient of the mobility. For the lower power annealed devices, the segregation of the phosphorus atoms to the grain boundary regions may be responsible for the lack of increase of the positive temperature coefficient in the mobility measurements. The unannealed and annealed (10–15 W) amorphous silicon samples also showed that the electron conduction was dominated by scattering at the intercrystalline potential barrier.

ISSN:0021-8979    

DOI:10.1063/1.331252

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Trapping of light‐generated holes in copper‐doped CdS is important to the operation of the thin‐film CdS/Cu2S solar cell. Consequently, there is interest in determining the distribution of the hole traps both in energy and inx, the depth from the junction. Capacitance transients are a useful probe of the depth dependence of trapped hole density,pT(x), since capacitance can be related by electrostatic theory to depletion layer width and charge density. It is shown from variation of capacitance in 1‐cm2thin‐film CdS/Cu2S solar cells, prepared at the Institute of Energy Conversion with temperature, heat‐treatment time, infrared quenching, and illumination intensity, that the observed photocapacitance is characteristic of copper impurity centers in CdS. Measurements of photocapacitance decay in these cells following abrupt shutoff of intense blue light show a time dependence different from that predicted by the usual theoretical treatment ofp–njunctions. This starts from the assumption of a uniform fixed‐charge density and leads to a prediction thatC2−C2∞decays exponentially with time, whereC∞is the dark capacitance. The theoretical relations have been rederived using apTvarying as exp(−x/d), wheredis a distance characteristic of the depth dependence. The resulting expressions predict thatpTshould vary asC−2∞−C−2. It is shown that this relation is closely satisfied by the measured photocapacitance transient data for temperatures from 77.5 K to ∼190 K, for times up to several tens of seconds, and for shorter times at higher temperatures. It is pointed out that some other dependence which confines the trapped hole density near the junction could equally well be used to fit the data. Possibilities for the physical origin of this depth dependence are discussed. It is shown that the relation of electric field at the junction to the measured capacitance derived from this model gives better agreement with measurements of the variation of collection efficiency with illumination intensity.

ISSN:0021-8979    

DOI:10.1063/1.331253

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The line spread function, crosstalk, and modulation transfer function (MTF) are computed for stripe geometries, assuming the absorption length is greater than the detector resolution element size. It is assumed that the radiation incident surface is antireflection coated and that the reflectivity of the exit face is a parameter. Numerical computations are carried out to find the optimal focal‐plane depth (least crosstalk), and the crosstalk is calculated at this optimal focal‐plane depth as a function of both absorption coefficient and detector width. The MTF is then calculated for various detector widths.

ISSN:0021-8979    

DOI:10.1063/1.331254

出版商:AIP    

年代:1982

数据来源: AIP