摘要:

The defect morphology of Se‐doped GaAs grown by CVD on undoped 100‐oriented GaAs substrates has been studied by transmission electron microscopy. Two types of samples are discussed: The first is nearly saturated,n≅NSe≅ 4 × 1018cm−3; the second is supersaturated,n≅ 1.5 × 1019cm−3,NSe≅ 4 × 1019cm−3. The nearly saturated samples exhibit an array of small features (probably Frank loops) near the original interface and have a density of misfit relieving dislocations≲103 cm−1. The supersaturated samples show a large number of Frank loops, whose density decreases monotonically with distance away from the original interface while their diameterincreasesin this direction. The loops seem to be invariably connected with one or more very small precipitate particles of Ga2Se3. Most of the Frank loops are of the intrinsic type; these are sometimes accompanied by closely neighboring loops of extrinsic nature. Pure edge misfit relieving dislocations with a density ≅ 104cm−1are observed at the interface, running in one of the⟨011⟩directions, but not in the orthogonal direction. A model is proposed to explain these results. Among the ingredients of this model are the notions (i) that misfit dislocations are asymmetrically introduced well away from the original interface and climb to that interface; (ii) that the solubility of Se in GaAs is a function of the imposed strain; and (iii) that the precipitation of Ga2Se3in GaAs is accompanied by the formation of both As vacancies and interstitial Ga in the matrix.

ISSN:0021-8979    

DOI:10.1063/1.1663773

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Measurements have been made of the nonlinearly generated harmonics and attenuation of Rayleigh acoustic surface waves at microwave frequencies on crystalline quartz. The Rayleigh waves were generated using an interdigital transducer deposited on thex‐zsurface of the quartz crystal aligned so that the surface wave propagates in the pure‐modexdirection. Attenuation coefficients &agr; were measured using the laser diffraction technique at frequencies of ∼160, ∼280, and ∼492 MHz with resulting typical values of &agr;=0.083 dB/&mgr;sec, &agr;=0.206 dB/&mgr;sec, and &agr;=0.812 dB/&mgr;sec, respectively. These results agree with previously reported values and with theoretical predictions. The growth and decay of nonlinearly generated harmonics of Rayleigh waves with a fundamental frequency of 281 MHz were observed also using the laser probe technique. A description of the variation of the Rayleigh waves' intensity for each of the three harmonics observed is provided by a set of coupled amplitude equations modified to include dispersion effects. It was not possible to describe the data using the coupled amplitude equations without including terms containing dispersion. Surface imperfections are assumed to be responsible for the dispersion as well as to contribute to the residual values for the attenuation coefficients. The small amount of dispersion needed for a good fit is determined. The nonlinearities are characterized by a set a nonlinear coefficients &Ggr;. A computer program was written in order to solve the coupled amplitude equations and to determine a set of &Ggr; values which provide a best description of the experimental data.

ISSN:0021-8979    

DOI:10.1063/1.1663774

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Several configurations of pyroelectric optical‐radiation detectors are mathematically modeled to determine their frequency response and current response to step‐function heat inputs. Included in the analysis are heat losses by conduction and reradiation, effects of absorptive coatings, and an experimentally observed nonuniformity of polarization through the thickness of polymer pyroelectric films. Roll‐off of the frequency response at both low and high frequencies is carefully examined. Curve fitting to response data allows a quantitative determination of the pyroelectric coefficient and the degree of nonuniformity of the polarization. The thermal conductivities of gold blacks used as absorbers are determined from the high‐frequency data together with independent measurements of the black thicknesses and densities. The total emissivity of evaporated nickel films sometimes used as absorbers can be estimated from the low‐frequency data. The difference in response to optical and electrical heat inputs is examined as a part of our effort in fabricating electrically self‐calibrating optical detectors.

ISSN:0021-8979    

DOI:10.1063/1.1663775

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The reaction rate of vacuum‐evaporated films of V of the order of 1000 Å thick is investigated by MeV He backscattering spectrometry. On substrates of single‐crystal Si and for anneal times up to several hours in the temperature range 570–650°C, VSi2is formed at a linear rate in time. The activation energy of the process is 1.7±0.2 eV. The presence of oxygen in amounts of 10% can significantly decelerate the reaction. On substrates of SiO2in the temperature range 730–820°C and anneal times of several hours or less, V3Si is formed at a square‐root rate in time. The activation energy of this process is 2.0±0.2 eV.

ISSN:0021-8979    

DOI:10.1063/1.1663776

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Changes of ultrasonic transit times in compression‐annealed pyrolytic graphite (CAPG) were measured as a function of temperature (4–300°K at atmospheric pressure) and of pressure (0–20 kbar at 295°K). From the low‐temperature results, obtained for five independent acoustic modes, the temperature variations of all five elastic constants were calculated using the thermal expansion data of Bailey and Yates. From the high‐pressure data, taken for four independent modes, the changes of all five elastic constants and of the unit cell dimensions with pressure were calculated under the assumption that the smalla‐axis compressibility is independent of pressure. The initial pressure derivatives ofC33andC44are, respectively, about 25 and 35% lower than those obtained by Greenet al.for CAPG. The pressure dependences of the volume andc‐axis compressibilities are in good agreement with measurements on natural graphite crystals by Lynch and Drickamer and by Bridgman, and in less satisfactory agreement with data of Kabalkina and Vereshchagin. The results support the contention that CAPG has bulk elastic properties very similar to those of single‐crystalline graphite.

ISSN:0021-8979    

DOI:10.1063/1.1663777

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Cross‐sectional views of epitaxial structures yield much information when examined by transmission electron microscopy. Since the growth direction then lies in the plane of observation, rather than normal to it (as is usual), the overgrowth, original growth interface, and substrate can be imaged either simultaneously or individually. A realization of the suitable technique for preparing thin cross‐sectional samples is described. Applications to continuously graded GaAsxP1−x/GaAs and step‐graded InxGa1−xP/GaP are shown.

ISSN:0021-8979    

DOI:10.1063/1.1663778

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Using propane‐air mixtures, it is shown that the minimum ignition energy corresponds precisely to the amount that produces, in the discharge channel, the electron density (1017cm−3) that changes the discharge from a cold streamer to a hot incipient arc. This electron density together with the minimum quenching distance are suggested as a physically meaningful criterion for ignition. The procurement of the critical electron density is also studied using a polyester film and water as examples of solid and deformable dielectric electrodes. It is found that thermalization is controlled by the rate of supply of charge into the discharge channel and that a stored minimum energy value applies only when two metal electrodes are involved. Ignition capability can be determined by the characteristics seen in the oscilloscope recordings of the current in the discharge. Electrode conduction effects are studied by varying the conductivity of a saltwater solution. It is found that either surface‐charge accumulation or resistive effects may prevent ignitions depending on the conductivity of the solution. Also, that except for metals, ignitions are always invariably associated with nonuniform electric fields and the procurement of electrons by cold‐streamer discharges. In the better dielectrics, surface charges prevent ignition independently of the energy supply. However, these same charges may be stored for a long time (days) and produce ignitions at very low voltages with polarity reversals. Finally, local thermalization is suggested as a necessary requirement for the propagation of long sparks characterized by stepping.

ISSN:0021-8979    

DOI:10.1063/1.1663779

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Tellurium films were deposited on glass substrates and maintained in vacuum during the course of the measurement of electrical conductivity. The films were found by electron microscopy to have polycrystalline structure with a grain size dependent on deposition parameters. The electrical conductivity increased with increasing thickness, with increasing rate of deposition, and with the transition from the nonannealed to the annealed state. The increase in deposition rate from 100 to 1000 Å/min led to an increase in both grain size and number of surface defects. Annealing resulted in a further increase in grain size but in a decrease in the number of defects. The conductivity could further be explained in terms of mobility and carrier concentration, the former increasing with increasing grain size and decreasing defects, and the latter increasing with increasing defects. A comparison of quenched and annealed films confirms the dependence of mobility on the number of defects.

ISSN:0021-8979    

DOI:10.1063/1.1663780

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

At low primary‐electron beam energies, Auger and loss transitions frequently interfere. The distinction between the two types can be accomplished easily by modulating the crystal. Auger peaks, which shift with crystal bias, are spread in energy and thus are effectively removed from the spectra whereas the loss peaks are relatively unaffected. The spreading functions are treated mathematically, and computer‐generated results agree with experimental data.

ISSN:0021-8979    

DOI:10.1063/1.1663781

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The electronic charge transfer during the TiNi martensitic transition is pictured as a shift of thesband relative to thedband. Such a description not only is consistent with the earlier postulate that a portion of the valence electrons behaves covalentlike in TiNi II and metallike in TiNi III, but also gives a good account of the low‐temperature specific heat, magnetic susceptibility, enthalpy, and Hall coefficient changes observed during the transition. The strength of electron correlation is calculated to be 1.1 eV; the work‐function change during the transition is also about 1.1 eV.

ISSN:0021-8979    

DOI:10.1063/1.1663782

出版商:AIP    

年代:1974

数据来源: AIP