摘要:

In this paper we use straight‐line models of observed extrinsic nodes to estimate extrinsic stacking‐fault energies. Using isotropic elasticity theory and neglecting interactions, we find simple expressions for the energy in terms of the inscribed radii of the nodes. We apply the results to observed extended nodes in a silver—8 at.% tin alloy and find a ratio of extrinsic to intrinsic stacking‐fault energy of about 3.

ISSN:0021-8979    

DOI:10.1063/1.1708954

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

GaAs injection lasers were prepared by an epitaxial solution growth method and their properties compared with those of diffused junctions. The optical gain factor &bgr; was up to a factor of 7 higher for the epitaxial diodes at 300°K. This resulted in threshold current densities as low as 26 000 A/cm2(3.8×10−3cm length) at 300°K. At 77°K, gain factor and loss numbers were similar for the two laser types. The spontaneous line‐width of the epitaxial lasers was unusually large (∼300 Å at 77°K) and increased with decreasing junction voltage. The internal quantum efficiency of epitaxial diodes drops from 100% at 4.2°K to 40% at 300°K. The vertical beam spread was found to be between 20°–30° half‐width at 77°K as well as at 300°K. Diffused diodes frequently show a delay between the current pulse and the stimulated emission of up to 30 nsec, dependent on the current value at higher temperatures. No such delay was observed in epitaxial lasers.

ISSN:0021-8979    

DOI:10.1063/1.1709010

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A new method is proposed to demonstrate the existence of a true polarization threshold field in materials that demonstrate ferrielectric properties. The detection of small changes in the Bragg diffraction angles of a diffracter x‐ray beam has been used to show the existence of a true polarization threshold field in one such material, namely bismuth titanate (Bi4Ti3O12). It is shown that the x‐ray diffraction method effectively establishes the polarization threshold field of bismuth titanate at 3 kV/cm. This value of polarization threshold field agrees with that found previously using direct electrical methods. Prior to this work, the demonstration of a true polarization threshold field has been shown only by direct electrical methods.

ISSN:0021-8979    

DOI:10.1063/1.1708938

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

An analysis of thermoionic converters operating in the extinguished mode is presented. Expressions for the forward and reverse saturation output current densities, and for the open circuit voltage are derived for the first time from a single set of transport equations and boundary conditions. Agreement between theoretical and experimental results is established. It is shown that the output current density cannot exceeed a certain upper limit which depends only upon the emitter temperature and the interelectrode spacing, and is independent of the emitter work function and the cesium pressure. It is shown that, under certain operating conditions, measurements of the forward and reverse saturation output‐current densities and of the open circuit voltage can be used to infer values of the emitter temperature, emitter work function, collector work function, and electron and ion mobilities.

ISSN:0021-8979    

DOI:10.1063/1.1708942

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

In the generation of plane waves in metal plates by detonation of contact explosives, the pressures reached can be sufficiently high to produce finite elastic and plastic strain components, and appreciable changes in temperature due to thermomechanical coupling effects. A theory of elastic—plastic deformation is developed to include these conditions. Finite elastic and plastic deformations are represented in terms of the initial and final configurations of the body, and an unstressed configuration subject only to plastic flow. In general, this configuration cannot be represented by a continuous displacement function. The analysis of the kinematics of these three states is carried out for general deformation history. The discussion of the application of finite deformation thermoelastic theory is limited to the conditions in a plane wave with fixed principal directions. Plasticity theory with the consideration of variable temperature is also restricted to the plane‐wave situation. The influence of the thermodynamic irreversibility of plastic flow is included in an entropy production term which modifies the temperature variation. Application to the plane‐wave propagation problem is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1708953

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Electrodeless discharges in coaxial tubes, capable of holding a laser crystal in the center, have been studied to obtain a measure of the energy coupled into the tube, to understand the dynamical processes, and to quantitatively determine the radiation emitted by the tube. The energy coupling and emitted radiation have been found to depend on the voltage stored on the capacitor, the primary coil dimensions, the fill gas and fill‐gas pressure, and the tube dimensions. The dominant dynamical processes are those due to strong cylindrically imploding shock waves. Radiation emitted is found to be due to particles liberated from tube walls as well as that of the fill gas. Curves of radiation intensity vs wavelength, as well as spectral pictures and calculations of spectral matching coefficients, indicate the possibility of pumping very high powers into ruby crystals.

ISSN:0021-8979    

DOI:10.1063/1.1708969

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A new negative‐resistance device, the semiconductor—insulator—semiconductor or SIS structure, is analyzed. The effect is due to quantum‐mechanical current transmission through a thin insulator barrier and leads to anN‐shaped current—voltage characteristic similar to that of the tunnel or Esaki diode. A highly qualitative analysis using general current equations is used to predict the major characteristics. Among these is the fact that the height and shape of the potential barrier, as created by the insulator, influence the current—voltage characteristics significantly—the former controls the amount of diffusion current and the latter the shape of the tunnel‐current characteristic. Diffusion currents should be negligibly small as compared to those in the conventional tunnel diode because the barrier height is very high (∼5 eV) for most typical insulators. These and other features, such as wider adjustment of the negative‐resistance cutoff voltage through variation in impurity concentration, give the SIS structure enormous versatility in terms of current—voltage shape adjustment through material control. A crude calculation, using the Wannier formalism, is used to derive an expression for the current in a simple, closed analytic form. This analysis shows that, at low temperatures, the slope of current characteristic (dJ/dVA) is a function of the insulator energy gap, &Dgr;I, and will usually be less than that for the equivalent tunnel diode. The general conclusion reached is that realization of the SIS diode is perhaps just beyond the scope of current semiconductor technology. Nevertheless, if developed properly, this structure could conceivably find wide application in current MOS integrated circuits.

ISSN:0021-8979    

DOI:10.1063/1.1708982

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The equations of motion for an elastic nonisotropic solid are reduced to a form useful for determination of third‐order elastic constants by means of ultrasonic pulse distortion measurements. Values of the coefficients in the reduced equations of motion are tabulated for two cubic materials. The tables are used to show that for cubic materials one should be able to measureC111,C112, andC166with reasonable accuracy. An argument is given which shows that the equations of motion for a single plane wave in a cubic crystal depend on the five parametersC111,C112,C166, (2C144+C123), and (½C144+C456) instead of all six third‐order elastic constants.

ISSN:0021-8979    

DOI:10.1063/1.1709006

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Electron‐scattering mechanisms in SiC polytypes are discussed. It is shown that the mechanism which limits mobility from 300° to 800°K inn‐type SiC is probably intervalley scattering (in relatively pure samples). The dependence of electron mass on polytype enables one to study the scattering mechanisms by a comparison of Hall mobilities in two polytypes.

ISSN:0021-8979    

DOI:10.1063/1.1709007

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Electron mobilities were measured in a number ofn‐type SiC samples selected and prepared in such a way as to ensure that they were single polytype specimens of 6H, 15R, or 4H. In the purest samples from the same growth preparation the ratio of 15Rto 6Hmobilities was found to be about 1.7 with both polytypes having a temperature dependence of mobility nearT−2.4between 300° and 800°K. Room‐temperature mobilities of these specimens were about 300 and 500 cm2V−1sec−1, respectively, for 6Hand 15R. Only two 4Hsamples were measured, but these showed even higher mobilities than 15Rpolytype samples.

ISSN:0021-8979    

DOI:10.1063/1.1709008

出版商:AIP    

年代:1967

数据来源: AIP