摘要:

Thermal expansion of the wurtzite phase of ZnS was measured using a back‐reflection Debye‐Scherrer x‐ray camera. Experimental results indicate that retrograde behavior is exhibited both perpendicular and parallel to thecaxis at 60°±5°K. The molar volume decreases approximately 0.30% from 300° to 60°K and then increases slightly upon further cooling. Lattice parameters obtained at 25°C area0=3.8226±0.0003 Å andc0=6.2605±0.0015 Å.

ISSN:0021-8979    

DOI:10.1063/1.1709718

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Exact expressions of the stress components and dilatation of a straight dislocation, lying in a ⟨111⟩ direction in a cubic crystal, have been obtained analytically. The transitions in the contours of stress and dilatation fields are found to be controlled by an elastic anisotropy parameterR. For bcc crystals, the transition of &sgr;23contours of a screw dislocation takes place atR=(32)1/2and that of &sgr;13contours atR=3 (for W, Ta, V, Cr, Mo, Nb, and Fe,R<(32)1/2; for Na, K, Li,(32)1/2<R<3). The results of the stress analysis are useful in treating the dissociation of screw dislocations in the bcc lattice.The dilatation contours of a [111] dislocation of the mixed type with Burgers vectora/2[111¯] are illustrated. The differences in shape of the contours for the anisotropic and isotropic cases are greater for the pure edge dislocation than for the mixed‐type dislocation.

ISSN:0021-8979    

DOI:10.1063/1.1709719

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A study was made of the shock‐induced phase transformation in bismuth at 25 kbar. A quartz pressure‐gauge technique was used to obtain the experimental data. A previously reported disagreement between the dynamic and the static transition pressure is due in part to a strength‐of‐material correction. The remaining discrepancy is probably due to a systematic error in the earlier dynamic study. The observed dynamic transition pressures corrected for strength‐of‐material effects and corrected to 25°C were 25.4 kbar for isotropic bismuth, and 25.9 kbar for cast bismuth. These values agree nicely with the value 25.4 kbar obtained by static compression. Hugoniot elastic limits of 2.4 to 3.1 kbar were observed for the different types of samples.

ISSN:0021-8979    

DOI:10.1063/1.1709720

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A derivation for the steady‐state currentJproduced by a large homogeneous electric fieldE0in the presence of a concentration gradient is presented which includes explicitly the effects due to lattice discreteness. The resulting equation isJ=4a&ngr;exp(−W/kBT)sinh(ZeE0a/kBT)[C(L)−C(0)exp(ZeE0L/kBT)]/[1−exp(ZeE0L/kBT)],whereC(0) andC(L) are the boundary concentrations of the diffusing species at the interfaces of the planar film at positionsx=0 andx=L;e, the electronic‐charge magnitude;Ze, the charge per particle of the diffusing species; 2a, the distance between adjacent potential minima;v, the frequency at which the ion attempts energy barriers which have heightWin zero field;kB, the Boltzmann constant; andT, the absolute temperature. A derivation valid in the limit of a continuum model is also presented, and the results are compared numerically. The equations for the discrete and continuum models reduce to the results predicted by the ordinary linear diffusion equation for electric fields below approximately 105V/cm. The relevance of the equations to the phenomena of anodic and thermal oxidation and to thin‐film current‐voltage devices is briefly described.

ISSN:0021-8979    

DOI:10.1063/1.1709721

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Crystalline defects have been studied in silicon crystals grown by the vapor‐liquid‐solid (VLS) technique. Most of these crystals are highly perfect. However, some crystals contain defects such as dislocations, stacking faults, and second‐phase regions. An elastic stress field, resulting from differential thermal contraction was found near the tip of every crystal. The formation and prevention of these defects and their relation to the VLS growth mechanism are discussed in detail. The morphology of the prismatic side faces of the crystals depends on deposition temperature, and is primarily due to vapor‐solid deposit. This deposit is perfect even at deposition temperatures as low as 700°C.

ISSN:0021-8979    

DOI:10.1063/1.1709722

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The reflection of electrons by standing light waves, i.e., the stimulated Compton scattering proposed by Kapitza and Dirac, has been treated by applying the Born approximation. The probability that an electron will be reflected is derived, for light waves that are not too intense, as a function of the electron beam orientation and of the coherence properties of the light waves. It is shown, among other things, that the original formula of Kapitza and Dirac is not directly applicable to representative studies using lasers. More general formulas are given along with a discussion intended to serve as a practical guide in the design of experiments.

ISSN:0021-8979    

DOI:10.1063/1.1709723

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

In analogy with the free‐space solution of Maxwell's equations, the excitations which are set up in an anisotropic, macroscopically neutral plasma by an arbitrary current can be described by potentials. The equations which the one vector and two scalar potentials must satisfy are first obtained for a relatively general physical situation. Due to the complexity of the mathematics, however, one cannot expect to obtain analytic solutions to this set of coupled equations without first making some realistic simplifications. One particular case that can be solved without an inordinate amount of difficulty is that of the point charge moving with uniform velocity parallel to a strong magnetic field. It is shown that the propagating waves which arise in this situation are electroacoustic in nature but very different from those created by a moving charge in an isotropic plasma.

ISSN:0021-8979    

DOI:10.1063/1.1709724

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Microtwin lamellae and tri‐pyramid defects often form in {111} silicon epitaxial films and these are affected by impurities within the substrate and system. The tri‐pyramids, which are doubly twinned with respect to the substrate surface, result when three oblique pyramids sprout from a triangular twinned deposit which forms on the (111) substrate surface. Twinning enhanced by adsorbed impurities could account for the initial twinning, but since it is a random process, cannot explain the second twinning operation for all three pyramids. The results also show that SiC platelets are not unique or necessary for tri‐pyramid formation. A reentrant twin mechanism is proposed to account for this as the twinned islands join up with correct ones. This mechanism can also account for the formation of microtwin lamellae which often accompany the tri‐pyramids. It is also shown that oblique microtwin lamellae can propagate directly from the twinned deposits and that multiple twin lamellae can result when the twinned deposit has steps in it.

ISSN:0021-8979    

DOI:10.1063/1.1709725

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The artificial viscosity method of von Neumann and Richtmyer is used to calculate the flow field for a shocked, elastic‐plastic‐relaxing solid; particular material parameters are chosen to represent the rate‐dependent behavior of iron. The constitutive relation is based on the dislocation model for plastic flow. Dislocation velocity is assumed to be a unique function of shear stress as given by Gilman and Johnston. Two models for dislocation multiplication are studied. The first is the multiple‐cross‐glide model discussed by Gilman, and the second is one in which pinned dislocations become sources of new mobile dislocations in the sense of the Frank‐Read multiplication process. Artificial viscosity calculations yield precursor amplitudes which are sometimes considerably different from those obtained from characteristic theory of precursor decay. These differences are believed to be due to the finite width of the elastic wave front provided by the viscosity. With proper choice of mesh size in the artificial viscosity calculations, a decrease in stress can be seen immediately behind the elastic precursor. This agrees qualitatively with experimentally determined shock profiles in iron.

ISSN:0021-8979    

DOI:10.1063/1.1709726

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Measurements of dislocation damping as a function of static biasing stress and during deformation have been carried out on single‐crystal, high‐purity tantalum. The results show that the dislocation mobility for small periodic stresses is orders of magnitude greater than for large constant stresses. The change in flow stress &Dgr;&sgr; due to the application of a small periodic stress &sgr;vis proportional to &sgr;v2. This second‐power dependence of &Dgr;&sgr; on &sgr;vis shown to result from thermal activation of the deformation. Calculations of activation energies and volumes using the point‐defect theories of Gilman and Fleischer give reasonable values.The large difference in dislocation mobility between the periodic type motion and the unidirectional motion indicates that the thermal component of the flow stress is not due to a Peierls‐type mechanism, but to discrete dispersed barriers to dislocation motion.

ISSN:0021-8979    

DOI:10.1063/1.1709727

出版商:AIP    

年代:1967

数据来源: AIP