摘要:

90° ferroelectric domain boundaries were observed by direct transmission electron microscopy in single crystals of pure BaTiO3and (Ba,Pb)TiO3solid solutions. Domain‐wall thickness measurements were made from electron image plates by a densitometer‐trace‐curve‐fitting technique. Boundary widths varied from 50 to 150 Å. These results are compared with theoretical estimates of 90° domain‐wall thicknesses and correlated with the relative purity levels of the crystals. The temperature variation of the 90° wall thickness is reported for the (Ba,Pb)TiO3solid solutions.

ISSN:0021-8979    

DOI:10.1063/1.1663523

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Excitation of Lamb waves in the five lowest‐order modes is demonstrated on polarized plates of PZT by using interdigital transducers. It is shown that in this structure the nonlinear interaction of noncollinear phonons can produce sum‐ and difference‐frequency beams at arbitrary angles. This is accomplished by interacting waves propagating in various combinations of the many available Lamb modes and by selecting frequencies and wave vectors that satisfy energy and momentum conservation. The phenomena described may have applications to acoustic signal processing.

ISSN:0021-8979    

DOI:10.1063/1.1663524

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The influence of thermocompression bonding condition on the gradual degradation of a Gunn diode, accompanied by an increase of the low‐field resistance, was studied. It was found that the diodes bonded with a higher pressure or at a higher temperature degrade in a shorter aging period. Many dislocations are easily induced into the GaAs chip by thermocompression bonding. Dislocations are also induced into the GaAs chip during aging, if mechanical strain remains in the GaAs chip after the bonding. The presence of many dislocations accelerates copper diffusion in GaAs and increases the acceptor concentration due to diffused copper in the epitaxial GaAs layer. It was concluded from these results that gradual degradation of the Gunn diode in question originates from the dislocations induced at the thermocompression bonding or during the aging, although it has not been clear yet whether the contamination by copper through the dislocations or the multiplication of dislocations during the aging is the dominant process.

ISSN:0021-8979    

DOI:10.1063/1.1663525

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A considerable difference in the diffusion behavior of copper was found between epitaxial GaAs and bulk GaAs. The carrier concentration of epitaxial GaAs scarcely decreased (much less than 1×1015cm−3) with copper diffusion at around 500°C, while carrier concentration of undoped bulk GaAs decreased about (3–5)×1016cm−3with the diffusion under the same conditions. The diffused‐copper concentration in the epitaxial GaAs, measured by radioactive copper Cu64, was less than that in the bulk GaAs by more than one order of magnitude. These differences in the copper diffusion can be understood by the difference in the amount of defects, and therefore, by the difference in solubility of substitutional copper between epitaxial and bulk GaAs.

ISSN:0021-8979    

DOI:10.1063/1.1663526

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Diffusion, at constant surface concentration, with coefficient varying to the positiventhpower is considered. It is shown that the diffusion equation for these cases has a unique solution whose leading term is concentration ∝Z1/n, where z = 1−(x/x+),xbeing the distance from the surface andx+the distance at which the concentration just reaches zero. Numerical solutions can be obtained by standard methods of solution; explicit expressions are given forn= 1, 2, and 3. It is also shown that plots of log(concentration) versus logz give rapid reliable estimates ofnfrom usual diffusion profiles. These methods are applied to previously analyzed data for diffusion of Zn in GaAs at 1000 °C. This reanalysis suggests that (i) the diffusion coefficient for Zn in GaAs is accurately given by the ``interstitial‐substitional'' mechanism at thesurfaceof GaAs, (ii) for surface concentrations ofZn⪞5×1019 cm−3, the diffusion is influenced by a limited flux of gallium vacancies from the surface, and (iii) the diffusion coefficient for gallium vacancies is roughly 5×10−9cm2/sec at 1000°C. It is suggested that ``double'' profiles, often found for surface Zn concentration⪞1020 cm−3, are due to dual vacancy sources: the free surface and a dislocation net occurring at positions of large Zn gradient.

ISSN:0021-8979    

DOI:10.1063/1.1663527

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Two scanning techniques are now being used to determine the vibrational patterns and far‐field sound radiation of complex vibratory systems. One technique is a near‐field scanning apparatus which scans the vibrator and gives a three‐dimensional display on graph paper of the nodal patterns. The other scanning technique uses the principles of holography to locate far‐field sound sources on the vibrator. These two methods, coupled together, have demonstrated a unique capability to locate acoustic sources and hot spots on vibratory systems.

ISSN:0021-8979    

DOI:10.1063/1.1663528

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The effects of neutron ([inverted lazy s]300 K) and ion bombardment ([inverted lazy s]85 K), and subsequent isochronal annealing, on the near‐infrared transmittance of SixGe1−xalloys (x=0.24, 0.44, and 0.73) have been investigated and compared to those for similarly bombarded Si and Ge. Defect absorption bands are observed in all three alloy compositions and can be separated into Ge‐like and Si‐like centers. Energy positions for the bands increase linearly with Si fraction. Damage‐induced near‐edge absorption is also observed in all three alloy compositions. Results for the Ge‐like center are consistent with the previous assignment of a 2.4‐&mgr;m band in Ge to divacancies. Growth of the Si‐like center between 200 and 300 K is consistent with Si stabilization of divacancies formed from vacancies initially trapped by Ge. Annealing loss of the Si‐like center is also consistent with the thermal stability expected for Si&sngbnd;Si bonding through a divacancy. The formation rate for Si‐like centers by bombardment near 300 K can be explained by Si&sngbnd;Si bonding through divacancies in a random alloy when two Si atoms are in the same plane as the divacancy and are nearest neighbors to the divacancy. Neutron‐induced hole‐removal rates approaching those forp‐type Si are indicated by free‐carrier absorption measurements on thex= 0.44 and 0.73 alloys.

ISSN:0021-8979    

DOI:10.1063/1.1663529

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A technique is described for the measurement of the refractive indexnof static or flowing lossy polar liquids in the 10‐GHz region and in the presence of magnetic fieldsH. Measurements ofnas a function ofHwere performed on static and flowing H2O containing various concentrations of ionic impurities. The application ofH(up to 7300 Oe) to liquids flowing with velocitiesv(up to 200 cm/sec) yielded the following result: &Dgr;n/n≤6×10−4for all concentrations. This result indicates that Umanskii's observed change in dielectric constant &egr;′ (roughly 100% change in &egr;′ forH= 1500 Oe andv= 50 cm/sec) is probably a spurious instrumental effect.

ISSN:0021-8979    

DOI:10.1063/1.1663530

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A method is presented of estimating the stacking‐fault energies in alkali halide crystals using creep data. Using this procedure, the stacking‐fault energies of NaCl, KCl, and LiF are estimated to be 235, 135, and 390 erg/cm2, respectively, in good agreement with the theoretical predictions for dissociation on {110} planes.

ISSN:0021-8979    

DOI:10.1063/1.1663531

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

This article discusses the propagation of compressional waves in fluid‐saturated elastic porous media. Both harmonic and transient pulses are considered. In general, two modes of wave propagation exist. In the case of a transient pulse, these modes lead to a two‐wave structure. It is not possible to obtain closed‐form solutions for the general case of transient loading, but considerable insight may be obtained from certain limiting cases (e.g., no viscous coupling, large viscous coupling) for which analytical solutions are derived by means of Laplace transform techniques. Strong viscous coupling leads to the coalescence of the two wave fronts into a single front; in this case the material behaves like a single continuum with internal dissipation. Solutions for the general case are obtained both by numerical inversion of the Laplace transforms and by direct finite‐difference methods.

ISSN:0021-8979    

DOI:10.1063/1.1663532

出版商:AIP    

年代:1974

数据来源: AIP