摘要:

It is demonstrated that with proper analysis of the diffusion profiles, the effective charge and diffusivity for grain‐boundary electromigration can be separately measured. Electromigration profiles are analyzed based on Fisher‐type approximations for an equiaxial and perfectly textured grain structure. Electromigration profiles were obtained for Cu in Al at 255°C by measuring the spreading of a Cu cross‐stripe subject to a direct current; the results were checked by annealing experiments performed under similar conditions. Cu was observed to migrate in the direction of electron flow. Results obtained from analysis of the anode and annealing profiles are −16.8±1.2 for the effective charge and (1.75±0.12) × 10−14cm3/sec for the diffusivity parameter &agr;Db&dgr;. The over‐all consistency of the results is better than 5%. Whipple analysis gives a more exact value of (2.74±0.16) × 10−14cm3/sec for &agr;Db&dgr;.

ISSN:0021-8979    

DOI:10.1063/1.1663763

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The dielectric anisotropy &Dgr;&egr; and threshold voltageVthfor electrically controlled birefringence have been measured for a series of nematic liquid crystals (binary mixtures of MBBA and PEBAB) with different negative &Dgr;&egr; values. The threshold voltage varies as |&Dgr;&egr;|−1/2, in agreement with theoretical predictions. The bend elastic constantK33evaluated from these experiments is in order‐of‐magnitude agreement with recent measurements for pure MBBA.

ISSN:0021-8979    

DOI:10.1063/1.1663764

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A phenomenon observed in homeotropically aligned liquid‐crystal cells after prolonged excitation in dynamic scattering is presented. The phenomenon, because of its visual appearance, is called texturing and is found to be associated with the induction of a metastable configuration in the liquid crystal. A model for the metastable configuration which is consistent with the experimental observations is proposed. Texturing is undesirable in display applications and has been found to occur in matrix‐addressed liquid‐crystal cells.

ISSN:0021-8979    

DOI:10.1063/1.1663765

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Binding energies and atomic configurations for small xenon‐vacancy clusters in &agr;‐iron have been computed using a model based on a two‐body potential between the interacting atoms. Various clusters were placed near the center of a sphere containing about 150 iron atoms initially at regular positions in bcc configuration. The results of these calculations are of importance for the interpretation of hyperfine interaction measurements on implanted radioactive sources.

ISSN:0021-8979    

DOI:10.1063/1.1663766

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Exact formal solutions of the transport equations which govern the flow of current in a mosaic crystal set at a Bragg condition are given. These solutions are applied to a crystal cut in the shape of a parallelepiped. A formula is derived for the extinction coefficient for this crystal shape. We call this result the ``AB‐extinction formula''. It will provide the experimentalist with an approximate method to correct for anisotropic extinction resulting from a crystal shape anisotropy. It is suggested that the exact results of the dynamical diffraction theory for slabs should be used to correct for primary extinction. The mathematical and conceptual errors in the theory given by Zachariasen are pointed out.

ISSN:0021-8979    

DOI:10.1063/1.1663767

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Calculations have been made for the surface‐wave velocity and the piezoelectric coupling constant in the multilayered system consisting of an Al2O3film and a piezoelectric ZnO film on a silicon substrate. It was found that the addition of an Al2O3film to the ZnO‐on‐Si configuration substantially reduced the surface‐wave dispersion over a range of normalized acoustic wave numbers. A specific example considered gives phase‐velocity variations of less than 0.8% over a 40% acoustic bandwidth, and less than 0.08% over a 10% acoustic bandwidth.

ISSN:0021-8979    

DOI:10.1063/1.1663768

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The enhancement and modulation of x rays diffracted from two planes of an ammonium dihydrogen phosphate crystal have been measured with the crystal driven in its fundamental piezoelectric vibration mode. Both effects are qualitatively similar to results obtained with neutrons diffracted from ADP and from quartz crystals.

ISSN:0021-8979    

DOI:10.1063/1.1663769

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

This paper describes a model for insulator surface charging in high‐voltage ceramic vacuum diodes. The model involves electron emission from the insulator‐cathode‐vacuum junction followed by electron avalanches on the insulator surface which leave the wall positively charged. Experiments were performed to measure (i) the triple‐junction (cathode‐vacuum‐insulator interface) emission and its relation to the initiation of the avalanche, (ii) the dynamic current in the avalanche, and (iii) the saturated surface charge resulting from the avalanche. The experimental results were interpreted by computer simulation in terms of the model and were found to be in close agreement with the predictions.

ISSN:0021-8979    

DOI:10.1063/1.1663770

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Thermally activated polarization (TAP) and thermally activated depolarization (TAD) effects resulting from impurity‐vacancy dipole reorientation occur in Mg‐doped and undoped lithium fluoride in the temperature region 200–250°K. These polarizations appear related radiation‐induced thermally activated depolarization (RITAD) effect in the same samples. We measure reorientation rate activation parameters of activation energyEa=0.44±0.03 eV and preexponential factorW0=108.5±1.5sec−1for simple divalent impurity‐vacancy dipole reorientation. Conversion to a second polarization phenomenon, stabilizing atEa=0.86±0.03 eV andW0=1019±1.5sec−1is observed during annealing for several days at room temperature. This seems to be caused by aggregation into dipolar complexes for which the activation energy becomes significantly temperature dependent.

ISSN:0021-8979    

DOI:10.1063/1.1663771

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

n‐type single crystals of lead sulfide, PbS, have been grown by a novel chemical vapor deposition method of potential importance for growing a variety of chalcogenide crystals. A reduced‐pressure flowing system was developed based on the following chemical reactions: Pb+Cl2→PbCl2and PbCl2+H2S→PbS+2HCl. Additional Cl2is used for fine control of the growth rate. The optimal growth conditions are a temperature of 650 to 750°C and a pressure of 8 Torr. Important to the furnace design is a quartz concentric gas injection arrangement which prevents premature mixing and reacting of the gases.n‐type single crystals of PbS having carrier concentrations of the order of 1019cm−3and Hall mobilities of 600 cm2/V sec at 300°K and as high as 14 000 cm2/V sec at 77°K have been grown. An isothermal anneal at 850°C for 15 days will convert the crystals toptype. Possible extensions of the technique to mixed lead‐tin salts, including tellurides and selenides, and to other chalcogenides are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1663772

出版商:AIP    

年代:1974

数据来源: AIP