摘要:

Young's modulus, the shear modulus, and Poisson's ratio have been determined for pure polycrystalline chromium as a function of temperature and thermal history. Both sonic and mechanical measurements were made, and it was found that all of the above properties show anomalous behavior near 37°C. The nature of the anomalies is such that Young's modulus and Poisson's ratio drop rather sharply over a narrow temperature range while the shear modulus increases slightly. The temperature at which this occurs seems to be fixed for a fixed composition and stress condition, although the extent of the anomalies is strongly influenced by thermal history. It is believed that this behavior is a result of an antiferromagnetic to paramagnetic transition, and that it is influenced by both internal and applied stresses. A model is developed to explain the observed behavior. Since Poisson's ratio is very nearly zero in the temperature range of the magnetic transition, it becomes necessary to consider the volume changes occurring under stress. When this is done, the anomalous behavior in Young's modulus is shown to be a necessary consequence of the anomaly in Poisson's ratio, which is described in terms of magnetostrictive versus elastic strain energy.

ISSN:0021-8979    

DOI:10.1063/1.1714591

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Observations on both electromigration and the Soret effect in tungsten have been recorded using silhouette electron microscopy and electron microscan techniques. The surface structure developed when a tungsten wire is heated by a current density of 3.3×104A/cm2depends on whether the current is direct or alternating. An alternating current produces a smooth surface structure while a direct current produces a steplike structure due to electromigration of tungsten ions. The direction of the electromigration of tungsten ions is toward the cathode in agreement with the theories of Huntington and Fiks.Soret effect diffusion has been observed in tungsten wires when subjected to a temperature gradient of 5000°C/cm. Either electromigration or Soret effect diffusion can produce pronounced changes in the original geometry of the conductor resulting in large current density variations over a short wire segment.

ISSN:0021-8979    

DOI:10.1063/1.1714592

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Reflectivities of silver and gold as measured by Bennett and Ashley are compared to the equations of Dingle for free electrons, including the anomalous skin effect. At a wavelength of about 5 &mgr;, the measurements are consistent with Dingle's equations with about half of the electrons specularly reflected from the metal surface. At lower wavelengths the measured reflectivities are lower than the theoretical ones; the origin of this deviation is not clear.

ISSN:0021-8979    

DOI:10.1063/1.1714593

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A new etchant for GaAs consisting of CrO3, HF, AgNO3, and H2O is described which selectively attacks dislocations on the following planes: Ga {111}, As {111}, {100}, and {110}. Dislocations normal, inclined, and parallel to the plane of observation are revealed. The etching figures were correlated with dislocations by equating (a) the etch pits produced on {111} surfaces with those produced by a known dislocation etchant, (b) the {111} etch pits with the linear structure appearing on {100}, and (c) the pits on two matched {110} cleavage planes. Supporting evidence obtained from plastic indentation experiments on {111} and {100} is also presented. It is observed that long, straight dislocations tend to lie in ⟨110⟩ and ⟨112⟩ directions. It was established by reverse bending experiments that the etchant produces pits only at As or &bgr; dislocations, if no impurity segregation has occurred. If decoration of the dislocations has occurred, as in Bridgman‐grown GaAs, pits are produced at both &agr; (Ga) and &bgr; dislocations.The relative etching rates for the {100}, Ga {111}, {110}, and As {111} faces are 1.0, 0.71, 0.69, and 0.50, respectively.Stacking faults on {100} are also revealed by the etchant on epitaxial films. A second etchant is reported which reveals stacking faults on the As {111} faces of GaAs. This etchant is the same as the dislocation etchant but with the CrO3absent.

ISSN:0021-8979    

DOI:10.1063/1.1714594

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A rotating x‐ray camera is described which yields lattice constants of single crystals with a possible error of 0.00007kX.Measurements of expansion may be made with a precision of 0.00002kX.The design of the camera permits accurate specimen alignment at any specimen temperature and requires that few corrections be made. Lattice constants of pure Al, Au, CaF2, Cu, Ge, and Si at 25°C and of pure Ar and Ne at 4.3°K are reported and critically compared with values from the literature.

ISSN:0021-8979    

DOI:10.1063/1.1714595

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The volume compressibilities of BeO, ZnS, CdS, CdSe, and CdTe have been measured to 45 kbar. Solid‐solid transitions were observed in CdS, CdSe, and CdTe at 17.5, 21.3, and 31.8 kbar, respectively, with corresponding volume changes of 16.0%, 16.4%, and 16.4%.

ISSN:0021-8979    

DOI:10.1063/1.1714596

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An absolute low‐angle light scattering photometer is described which is used for the quantitative evaluation of the light scattering exhibited by shock‐cooled isotactic polypropylene films. Following Stein and Wilson the supermolecular order is considered to be describable in terms of a density correlation function &ggr;(r) and an orientation correlation functionf(r), which are both dependent only upon the magnitude of the distancerbetween individually scattering volume elements. By means of Fourier transformations performed upon the horizontally and vertically polarized components of the scattered light under polarized incident light, these functions can be obtained. It is found that &ggr;(r)=exp(−r2/a2), witha≅40 000 Å andf(r)=Bexp(−r2/b2)+Cexp(−r2/c2), withB=0.544,b=4500 Å,C=0.456, andc=17 000 Å. The density correlation thus reaches much further than the orientation correlation. This is ascribed to the poorly developed spherulitic crystallization due to the shock cooling of the sample. This meaning of the splitting up off(r) into two Gaussian distributions needs to be explored further. The occurrence of a Gaussian density correlation function &ggr;(r) rather than the simple exponential function &ggr;(r)=exp(−r/a) found for amorphous polymers by Debye and Bueche, might be ascribed to the spherical crystalline aggregates in the sample, which are visible under the polarizing microscope. Calculation shows that a collection of spheres will indeed give a scattering pattern approximately describable by &ggr;(r)=exp(−r2/a2). Further work on samples with varying thermal history will have to reveal the connection between the correlation functions and the molecular processes leading to specific supermolecular arrangements.

ISSN:0021-8979    

DOI:10.1063/1.1714597

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Variational principles of anisotropic elasticity have been applied to aggregates of randomly oriented pure‐phase polycrystals having hexagonal symmetry and trigonal symmetry. The bounds of the effective elastic moduli obtained in this way show a considerable improvement over the bounds obtained by means of the Voigt and Reuss assumptions. The Hill average is found to be in most cases a good approximation when compared to the bounds found from the variational method. The new bounds reduce in their limits to the Voigt and Reuss values.

ISSN:0021-8979    

DOI:10.1063/1.1714598

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Techniques were developed to grow single‐crystal films of a magnetic garnet (yttrium iron garnet) on a nonmagnetic garnet substrate. Y3Al5O12, Y3Ga5O12, and Gd3Ga5O12substrates were investigated. Single‐crystal YIG films were grown by flux and vapor deposition. The perfection, optical transmission, surface characteristics, and thickness of these films were investigated.

ISSN:0021-8979    

DOI:10.1063/1.1714599

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An open‐tube vapor deposition process has been used to grow GaP epitaxially on GaAs seeds. The overgrowths generally contain large numbers of defects including dislocations, stacking faults, impurity striae, and local strains. The stacking faults and impurity striae may be eliminated by growing on (1¯1¯1¯)‐plane seeds under carefully controlled conditions. The mobility of electrons inn‐type GaP is found to increase from approximately 120 cm2/V sec at 300°K to approximately 600 cm2/V sec at 77°K. Undoped GaP layers are invariablyn‐type with carrier concentration in the range 1015–1017/cm3.

ISSN:0021-8979    

DOI:10.1063/1.1714600

出版商:AIP    

年代:1965

数据来源: AIP