摘要:

Small‐angle x‐ray scattering from oriented voids in pyrolytic graphite has been studied. The scattering is found equivalent to that from a dilute dispersion of ellipsoids of revolution called ’’Guinier spheres’’ of radius of gyrationR=[(3/5)H]1/2=[(3/5)(a2 sin2&ggr;+b2 cos2&ggr;)]1/2, where &ggr; is the angle between the common axis of revolution (semiminor axisb) and the scattering vector h. Analysis of the data using Hamzeh and Bragg’s theory provides values ofa,b, anda/bfrom the ’’Guinier’’ and the ’’Porod’’ regions, independently, with good agreement. The theoretically predicted angular dependence ofHusing ’’best‐fit’’ values ofaandbis in good agreement with the experimentally determined value ofH, &ggr; varying from 0° to 180°.

ISSN:0021-8979    

DOI:10.1063/1.325177

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The measured birefringence of ultrathin AlxGa1−xAs‐GaAs multilayers grown by molecular beam epitaxy is shown to result from the difference in the effective refractive indices for transverse electric and magnetic polarizations and from the quantum‐size effect of the one‐dimensionally confined carriers in the GaAs potential wells.

ISSN:0021-8979    

DOI:10.1063/1.325178

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Measurements of composition of multilayer semiconductor laser wafers were performed with the aid of photoluminescence spectra. Reliable depth profiling of composition is difficult in as‐grown wafers, even at low temperature, because the excess‐carrier diffusion length is comparable to the layer thicknesses. With adequate reduction of the diffusion length, which in our case was done with ion implantation, the origin of photoluminescence could be restricted to a narrow region close to the excited surface. Samples were prepared for profiling by an angle‐etching technique, leaving a controlled angle as small as 0.01° across the wafer, which greatly simplifies profiling measurements. Results from composition profiling of a conventional five‐layer GaAs‐AlxGa1−xAs DH‐laser wafer with a depth resolution better than 0.1 &mgr;m are presented.

ISSN:0021-8979    

DOI:10.1063/1.325179

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The nature of the origin of the color in anodized aluminum colored by ac electrolysis in electrolytes containing nickel, copper, silver, gold, and molybdenum salts is investigated. The measured specular reflectance spectra in the region 350–750 nm can be adequately explained by assuming that small metallic particles are incorporated in the anodic film as a colloid. By calculating the optical constants of such a system, specular reflectance spectra can be deduced. A detailed comparison of the calculated and experimental reflectance spectra yields good agreement. It is concluded that metals which do not possess interband transitions or plasma resonance absorptions in or near the visible region of the spectrum will produce brown or bronze colored anodic films when incorporated as a colloid.

ISSN:0021-8979    

DOI:10.1063/1.325153

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

It is shown that the strain‐induced dipole‐dipole interaction gives a major contribution to the elasto‐optic effect and can explain the opposite signs of the two shear coefficients observed in most alkali halides and alkaline‐earth fluorides.

ISSN:0021-8979    

DOI:10.1063/1.325180

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Experimental results of plasma diagnostic measurements taken during the early development of laser‐supported‐detonation (LSD) waves in TEA‐CO2laser irradiations of solid surfaces in air are reported. Photographic and sample examination results for irradiations of practical aluminum surfaces indicate that the initiation process is highly local at surface features which are heated preferentially. The intensity dependence of time to plasma initiation was measured using target‐electron emission, target‐hole transmission, and electrostatic‐probe response as indicators of the initiation event timing. The initiation time for aluminum was found to be in the range 25–70 nsec for peak‐power densities in the range 0.4 to 4×108W/cm2. Emission‐spectroscopy results indicate the presence of neutral aluminum vapor at late times in the pulse, but no ionized aluminum was detected at atmospheric pressure. The experimental results for aluminum are found to be consistent with a simple theoretical model, wherein electrons are thermionically emitted at preferentially heated surface features. The emitted electrons serve as priming electrons in a cascade air breakdown. A limited amount of data on metals other than aluminum are also presented.

ISSN:0021-8979    

DOI:10.1063/1.325181

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The equilibrium cation distribution and the valence state on tetrahedral or octahedral sites in copper ferrites Cu1−&dgr;Fe2+&dgr;O4have been derived by taking account of site exchange not only of cationic nuclei but also of valence electrons. The calculated cation distribution has shown satisfactory agreement with experimental results for the composition range &dgr;?0.5. Two nonequilibrium valence states accompanied by the transposition of valence electrons from the equilibrium sites were expected and they corresponded well to the positive and negative regions in the observed Seebeck coefficient of quenched Cu1−&dgr;Fe2+&dgr;O4.

ISSN:0021-8979    

DOI:10.1063/1.325136

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

MIS structures on GaN consisting of Au‐NaI‐GaN or Au‐Al2O3‐GaN with insulator thickness <100 A˚ have been fabricated with the aim of producing light‐emitting diodes with emission in the uv and blue spectral region at low bias.I‐Vcharacteristics are consistent with a tunneling carrier transport mechanism, and light emission typically occurs for voltages 2–3 V. The spectral behavior of electroluminescence (EL) is in good agreement with photoluminescence (PL) data in the uv and blue spectral region. Suggestions for further work to improve radiant power output from such devices are presented.

ISSN:0021-8979    

DOI:10.1063/1.325137

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

By numerical calculations of the differential‐difference sine‐Gordon equation, we have discussed the discrete Josephson‐junction transmission lines which are constructed of a series of small‐area Josephson junctions connected by superconducting strips. It is shown that the discrete Josephson lines containingDlines,Nlines,Tturning points, andSturning points are elementarily characterized by the discreteness parameter (2&pgr;LIc/&Fgr;0)1/2. On the discrete Josephson logic circuits there exists a region of forbidden propagation in the (2&pgr;LIc/&Fgr;0)1/2‐&ggr; (bias‐current parameter) plane for single flux quanta. A single flux quantum can be stuffed in a small area of the discrete Josephson logic circuits. The discrete circuits can be conveniently and easily linked to each other, in a practical fabrication of a Josephson network.

ISSN:0021-8979    

DOI:10.1063/1.325138

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The conduction mechanism of non‐Ohmic ZnO ceramics is investigated. In order to explain the non‐Ohmic property, a new energy‐band model composed of a thin intergranular layer with traps sandwiched between Schottky barriers formed opposite each other is proposed. According to the newly proposed energy‐band model, the non‐Ohmic property of ZnO ceramics is mainly governed by field emission for the reverse‐biased Schottky barrier in the voltage region above the threshold voltage in theV‐Icurve and by thermionic emission in the voltage region below the threshold voltage. The energy‐band model and the conduction mechanism discussed in this paper are appropriate for the explanation of experimental results, not only those presented in previous papers, such as the effect of additives, theV‐Icurve and its temperature dependence, but, additionally, the dielectric properties, the asymmetrical degradation of theV‐Icurve, and the thermally stimulated current.

ISSN:0021-8979    

DOI:10.1063/1.325139

出版商:AIP    

年代:1978

数据来源: AIP