摘要:

Glass‐coated bismuth films were deposited onto a glass substrate at room temperature and their Hall coefficients and electrical resistivities were measured between 77 and 300°K. Scanning electron micrographs revealed that the films prepared in this way were more polycrystalline than those deposited onto a heated mica substrate. Interesting features were found in the temperature dependence of the Hall coefficient: the thinner films with thicknesst<500 Å wereptype at higher temperatures and becamentype below a critical temperatureTc, whereTcincreased with the increase int, whereas the thicker ones witht>500 Å were alwaysntype over the temperature ranges studied. Hall mobility and magnetoresistance data are also presented here and the experimental results are discussed qualitatively.

ISSN:0021-8979    

DOI:10.1063/1.1663458

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The phenomena of the formation of stacking faults and the enhanced diffusion during the oxidation of silicon are shown to be closely related and to have a common cause. A model is presented which at once can consistently explain various aspects of both phenomena; in particular, it is capable of explaining the crystal‐orientation dependence of these phenomena and the parabolic growth of stacking faults. The model envisages a small incompleteness (∼ 10−3) of oxidation, producing silicon interstitials. A concept is introduced that these excess interstitials, as they supersaturate the lattice, will undergo surface regrowth. The rate of interface regrowth is proportional to the density of surface kinks, which is in turn dependent on the surface orientation. The dependence is described. Quantitative analyses are given for the excess interstitials, the growth of stacking faults, and the enhancement of diffusion. The analyses also show that the stacking‐fault embryos are formed within a very short time of the start of oxidation, usually less than 1 sec, consequently leading to uniform stacking‐fault size. The occasionally observed variation in the size of bulk stacking faults is attributed to a continuous formation of stacking‐fault nuclei (e.g., oxide clusters and precipitates). The absence of a surface regrowth would predict a 1/4 power law of stacking‐fault growth, in contradiction of the experiments.

ISSN:0021-8979    

DOI:10.1063/1.1663459

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Bulk acoustic waves at frequencies up to several hundred megahertz and acoustic powers down to the nanowatt range have been visualized via acousto‐optic Bragg diffraction. Using double‐optical and electrical‐heterodyne mixing, the acoustic wavefronts have been displayed over several wavelengths along the propagation path. Possible applications of the reported experiments are briefly reviewed.

ISSN:0021-8979    

DOI:10.1063/1.1663460

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Below‐gap optical absorption, above‐gap reflectivity, photoluminescence, and He ion channeling backscattering measurements are reported for ion‐bombarded GaP. Each of the four experiments provides a measure of disorder. A one‐to‐one correspondence exists between the absorption, reflectivity, and backscattering measurements, and all three exhibit comparable sensitivity to damage. Photoluminescence is ∼ 100 times more sensitive. The absorption results suggest that every implanted ion species produces amorphous regions associated with each projectile and that these regions have properties very much like those of cold‐deposited amorphous films. The results are interpreted in terms of a model which ascribes these amorphous regions to localized melting followed by rapid quenching to a glassy (amorphous) state in which short‐range tetrahedral order remains intact. The damaged volume per bombarding ion as determined from absorption data is ∼6 times larger than that determined from channeling measurements. Although the annealing experiments show considerable scatter, the damage‐induced changes in absorption and reflectivity can be largely removed by annealing at ∼600°C for 30 min. Some anomalies are observed in the photoluminescence annealing results.

ISSN:0021-8979    

DOI:10.1063/1.1663461

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A method for calculating stress‐strain fields around edge dislocations in smectic‐Asamples is discussed. In large part the method is isomorphic with the formalism for calculating magnetic fields around lines of electric current. The force law between dislocations that follows from the analogy is equivalent to the accepted force law between dislocations in crystals. In addition to rederiving the expression for the strain field surrounding an isolated edge dislocation that was first given by de Gennes, we present the solutions for the stress‐strain fields surrounding dislocations near one or two boundaries and also the strain field surrounding an edge dislocation that is curved to form a circular loop. The stress‐strain fields surrounding other defects with the same symmetries and boundary conditions can be expressed in terms of the above‐mentioned solutions using Green's function techniques. The relative stability of dislocations in samples with different types of boundaries and also the effects of dislocations on the elastic properties of smectic samples are also discussed in some detail. We comment briefly on the relation between the analogy discussed here and an earlier one developed by de Gennes.

ISSN:0021-8979    

DOI:10.1063/1.1663462

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Bismuth titanate (Bi4Ti3O12) crystals grown from ``high‐purity'' melts are shown to have significantly lower activation fields than those reported previously when switching times are > 1 &mgr;sec. Controlled doping experiments demonstrate that the switching characteristics of Bi4Ti3O12are controlled by the crystal impurity content. Specifically, the pseudothreshold for switching is not intrinsic to the material. A model is proposed for the activation‐field control which invokes the anisotropic conductivity due to the combination of impurity content and crystal structure.

ISSN:0021-8979    

DOI:10.1063/1.1663463

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Differential thermal analysis has been performed on barium sodium niobate single crystals. A thermal effect is detected for the first time at the 260°C ferroelastic transition. A large thermal peak is also observed at the 570°C Curie point. For both transitions an estimate of the latent heat is obtained by comparison with thermal effects recorded in gadolinium molybdate and quartz single crystals. The results for the first‐order 570°C transition is in good agreement with existing dielectric data. First order is also assigned to the lower ferroelastic transition whose features are discussed in the framework of the available thermodynamic theory.

ISSN:0021-8979    

DOI:10.1063/1.1663464

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The effects of fast‐neutron‐induced defects on the dislocation internal friction and modulus defect of copper crystals were studied by two procedures: (i) irradiation at 20°K followed by measurements during heating at a constant rate to room temperature and (ii) measurements during and after irradiations at various constant temperatures between 90 and 410°K. The measurements were made at low enough strain amplitude so that breakaway of dislocations from pinning points did not occur. Samples of known dislocation density were used in many of the experiments so that the ``vibrating‐string'' model of dislocation motion could be used to calculate approximate absolute values for the densities of radiation‐defect pinning points obtained at various temperatures. These were characterized by the ratiogof pinning points collected to freely migrating radiation defects created in the samples, assuming that on the average 20 defects can migrate away from the cascade region of each primary recoil. For the lower‐temperature pinning processes which showed no time delay, values ofgincreased monotonically from 10−6–10−5at 60°K to 10−4–10−3at 204°K. The higher‐temperature process is known to have a broad delay‐time distribution; by collecting all pinning points available at 410°K agvalue of ∼0.1 was obtained. Because of uncertainty as to the validity of the vibrating‐string model, pinning‐point densities were obtained primarily from the modulus‐defect data. The damping data often implied the same densities but sometimes disagreed seriously with the modulus‐defect results.

ISSN:0021-8979    

DOI:10.1063/1.1663465

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The objective of this work was to determine the Cu diffusion coefficient in silver thin films as a function of temperature, and Cu electromigration velocity as a function of electric current density and to test whether linearity between electromigration and current density was preserved at high current stress. An Ag stripe was doped with Cu in a limited region, and the movement of Cu out of this region under temperature and current stressing was measured by electron probe. The experiment was conducted at 200, 250, and 300°C and at current densities of 106, 2×106, and 3×106A/cm2. From the copper concentration profile, the diffusion coefficientDand the electromigration velocityVwere calculated. Results show that the diffusion of Cu in Ag films obtained by extrapolation to use conditions (D=10−15cm2/sec at 55°C) is about 2 orders of magnitude greater than bulk, and that electromigration under ∼106−A/cm2stress is negligible when compared to thermal diffusion of Cu, even at ambient temperature. At high current density (3×106A/cm2), the electromigration velocity becomes much greater than the value predicted on the basis of linearity betweenVandJ. This indicates a departure from the Nernst‐Einstein relationship of ion shift in a field.

ISSN:0021-8979    

DOI:10.1063/1.1663466

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Transmission electron microscopy has been used for the observation of polytypes of SiC having very long periods. The periodicity of these structures can be observed from the direct resolution of structural lattice periods and from the diffraction patterns. The actual structures can be determined from the intensity distribution in the diffraction pattern, and this has been done for two of the structures. These have been identified as [(33)1632]3or 303Rand [(33)634(33)434]3or 222R, two hitherto unknown structures. A mechanism for conveying the long‐distance information concerning the stacking order which leads to stabilization of the long‐period structures in SiC is suggested. This mechanism essentially involves a transformation from a basic structure of short period to accommodate a constraint from the surroundings.

ISSN:0021-8979    

DOI:10.1063/1.1663467

出版商:AIP    

年代:1974

数据来源: AIP