摘要:

X‐ray diffraction profiles from four compositions of &agr;‐phase Ag‐Ga alloys containing 3.55, 9.45, 13.05, and 15.90 at.% of solute gallium have been recorded in a Geiger‐counter x‐ray diffractometer for both the cold‐worked and fully annealed states of the samples, and a detailed analysis of the line shifts, line asymmetry, and Fourier line shapes has been performed considering recent improvements made in such studies. The line‐shift analysis from 111, 200, 220, and 311 reflections has shown the prominent effect of net stacking‐fault density &agr;=&agr;′−&agr;″(&agr;′ and &agr;″being intrinsic and extrinsic fault densities, respectively) over the residual stresses and this has also been observed from the shifts in the lattice parameter values (&Dgr;ahkl). The logarithmic dependence of &agr; with the solute concentrationXhas been examined using the semiempirical expressions of the forms log&agr;=log&agr;0+K‖&Dgr;Z‖Xand log&agr;=log&agr;0+K&agr;[C/(1+C)]. Combining the results of all the methods of analysis, the individual stacking‐fault densities &agr;′, &agr;″, and &bgr; (twin‐fault density) have been evaluated, which indicates the increased presence of intrinsic fault with a total absence of twin fault in the deformed structures. An over‐all analysis suggests that the extrinsic fault may also occur in very small concentrations in the these alloys. The values of the dislocation density &rgr; and the parameter &ggr;/&mgr; (&ggr; is the stacking‐fault energy and &mgr; is the shear modulus) have also been calculated for these alloy compositions. From the logarithmic dependence of &ggr;/&mgr; with solute concentrations, &ggr;0, the stacking‐fault energy for pure silver has further been estimated.

ISSN:0021-8979    

DOI:10.1063/1.322662

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The Weinreich relation expressed in differential form is used as the basis for determining the dc electric field set up along the acoustic path of a piezoelectric semiconductor. This field results from the streaming of the charge carriers as they are carried along in the direction of a propagating surface wave by the electric fields associated with that wave. Two nonlinear effects are considered. The first is the saturation of the charge modulation or bunching. The second is the change in the surface wave attenuation coefficient due to the acoustoelectric current. The return loop for this current may be through the substrate or through an external resistor connected to electrodes on the surface. The output dc voltage as detected by these two electrodes is calculated as a function of the input rf signal. Experimental results obtained on CdS agree with the theoretical predictions in both the linear and nonlinear regions.

ISSN:0021-8979    

DOI:10.1063/1.322663

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A statistically homogeneous and iostropic two‐phase composite is considered. The constituents are dielectrics with low loss factors. Bounds are found on the dielectric behavior of the composite utilizing the fact that the imaginary part of the complex permittivity is small compared to the real part. The bounds on loss factor are found generally (with one exception) to be the best possible based only on volume fractions and constituent properties. Further, it is shown that for dielectric constituents whose dielectric constants are nearly unvarying with frequency, the loss factor of the aggregate is simply a linear combination of the loss factors of the constituents.

ISSN:0021-8979    

DOI:10.1063/1.322664

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A proof is developed that for a given direction of propagation on the free surface of a half‐infinite anisotropic crystal, a surface‐wave solution with a certain phase velocityvR<vL, wherevLis the limiting velocity, will always exist, except in the special case when the bulk wave defining the limiting velocity satisfies the condition of a free surface. The proof is in terms of the surface impedance, which relates the amplitude at the surface of a surface wave with the external forces needed at the surface. The properties of the impedance as a function of phase velocity determines whether a surface wave not requiring external forces at the surface exists for a certain phase velocity. The proof is valid also in the case of degeneracies in the eigenvalue problem entering the analysis.

ISSN:0021-8979    

DOI:10.1063/1.322665

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The pressure derivatives of the adiabatic elastic moduli of single‐crystal Nb and Ta have been measured ultrasonically at 25 °C. The results are in good agreement with shock compression data but differ, particularly for Nb, with previous ultrasonic work. Experimental evidence is presented which indicates that the discrepancy in results may be due to nonideal specimen‐transducer geometries which cause an apparent dependence of the observed pressure derivatives on the ultrasonic carrier frequency.

ISSN:0021-8979    

DOI:10.1063/1.322666

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

From heat‐balance considerations at the growing interface and an assumption of predominantly radiative heat loss from the surface, an expression for the maximum growth rate of melt‐grown ribbon‐shaped crystals has been derived. For a given material and a large width‐to‐thickness ratioW/t, the maximum growth rate varies ast−1/2and is independent ofW. A comparison of the maximum cylindrical and ribbon growth rates is made for the silicon system. Some representative values at 7.5 cm diameter or width are 45 cm/h or 2000 cm3/h, for a cylindrical Czochralski‐grown crystal and 625 cm/h or 95 cm3/h for a 0.02‐cm‐thick ribbon.

ISSN:0021-8979    

DOI:10.1063/1.322667

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A technique for the liquid‐phase epitaxial growth of thin GaAs layers has been developed. This technique uses supercooled solutions free from GaAs precipitates. With the amount of the initial supercooling in the range of 1–10 °C, very smooth surfaces with a roughness smaller than 0.01 &mgr;m are obtained for layers thinner than 1&mgr;m. The layer thickness data agree well with the diffusion theory equation by assuming that the diffusion coefficient of As in Ga is 4×10−5cm2/sec at 800 °C. The thickness uniformity within a wafer is better than ±5%, and the thickness reproducibility among different runs is within ±7%. The carrier concentration is also well controlled.

ISSN:0021-8979    

DOI:10.1063/1.322668

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The results of a theoretical study of diffusion‐controlled dissolution of planar, cylindrical, and spherical precipitates are presented. Graphical relationships between the precipitate size and the dissolution time are developed for a constant diffusion coefficient. The validity of various approximate solutions is considered and it is shown that the invariant‐interface treatment provides the best approximation. In this development the composition profile is considered independent of the movement of the phase interface. For concentration‐dependent diffusion coefficients, the same dissolution curves can be used, but the time axis must be multiplied byDe, an effective diffusion coefficient taken from the plot of diffusion coefficient vs composition. All three precipitate shapes haveDeequal to the interface value of the diffusion coefficient at very high saturations. At low saturationsDeis equal to ?, the weighted mean coefficient for spherical precipitates, to ?, the first moment of the diffusion coefficient about the matrix composition for planar precipitates, and to (?+?)/2 for cylindrical precipitates. Procedures for determiningDeat other values of saturation are discussed.

ISSN:0021-8979    

DOI:10.1063/1.322669

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The Orowan‐Polanyi approach to the calculation of surface energy is modified to incorporate information on interplanar force constants derived from phonon frequencies. Models using interatomic interactions to second and first nearest neighbor respectively for bcc and fcc crystals are found adequate to give acceptable results for dispersion curves and surface energies.

ISSN:0021-8979    

DOI:10.1063/1.322618

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The core configuration and energies of the two symmetric configurations of an (a/2) [110] edge dislocation in a model MgO crystal were calculated atomistically using a point‐ion or shell model with a rigid boundary region. Two short‐range potentials and one set of shell‐model parameters used in the present calculation were developed by Catlow, Faux, and Norgett who employed them to calculate Schottky defect energies and volumes of formation in MgO. The two symmetric dislocation configurations investigated turned out to have unequal energies, but which dislocation configuration had the higher energy depended on the particular version of the short‐range potential. The shell model yielded dislocation strain energies which were approximately 0.24 eV/repeat distance lower than the corresponding strain energies for the point‐ion model. The atomistically calculated energy factors derived from a strain‐energy–vs–lnrplot were, in all cases, larger than the corresponding values derived from anisotropic elasticity theory. The Peierls energy barrier separating two equal‐energy dislocation configurations was calculated using a linear interpolation technique. These calculations showed that the higher‐energy symmetric dislocation configuration was situated either in a small local minimum or on top of a very flat‐topped ’’Peierls hill’’. The maximum value of the Peierls barrier varied between 0.012 and 0.042 eV/repeat distance, depending on the method and the potential used to calculate it. The Peierls stress derived from the Peierls energy calculations ranged between 162 and 383 MPa.

ISSN:0021-8979    

DOI:10.1063/1.322670

出版商:AIP    

年代:1976

数据来源: AIP