摘要:

Dislocations formed during the growth and deformation of BeO single crystals were studied with x‐ray and electron microscopy. The stresses for slip on the systems (0001) ⟨112¯0⟩, {101¯0} [0001], {101¯0} ⟨112¯0⟩, and {112¯2} ⟨112¯3⟩ are approximately 3.5×108, 1.1×109, 4.9×108, and >2.5×109dyn/cm2, respectively, at 1000°C. Slip directions in deformed specimens were shown with x‐ray microscopy. Defects in the specimens were shown to interfere with slip. Dislocation pinning and elastic interactions were observed in electron micrographs. These observations are correlated with theory.

ISSN:0021-8979    

DOI:10.1063/1.1709112

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A scanning electron microscope using a quadrupole doublet as the focusing lens is described. The optical properties of an unsymmetrical, ``pseudostigmatic'' (unequal magnifications in perpendicular planes) doublet are summarized, and rotational misalignment of the elements is discussed. Experimental studies were made to determine the dependence of the final image size on lens aberrations and construction defects. A computer was used to fit the experimental data to a generalized spot size equation. Separate experiments were made on both magnetic and electrostatic doublets, and the smallest experimental image size (which appears to be limited by astigmatism) was 150 by 450 Å using either quadrupole system. Experimental results agree with recent computer predictions for these doublets, and further calculations indicate that the use of quadrupoles and octupoles in a scanning microscope may be advantageous.

ISSN:0021-8979    

DOI:10.1063/1.1709113

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Multiplication and noise measurements on InSb avalanche photodiodes have been made from 77° to 125°K. For the diodes studied, the electron ionization rate is much larger than the hole ionization rate and depends only weakly on the field for fields between 5×103and 104V/cm. The electron ionization rate increases and the breakdown voltage decreases with increasing temperature. The dependence of the ionization rate on field and temperature is explained by the weak dependence of the distribution function on field for high fields. The noise measurements are consistent with McIntyre's theory providing that the electron ionization rate is much greater than the hole ionization rate. A current‐controlled negative resistance is observed in InSb avalanche diodes at breakdown.

ISSN:0021-8979    

DOI:10.1063/1.1709114

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Propagation of piezoelectric and elastic surface waves on the basal plane of hexagonal piezoelectric crystals has been investigated theoretically. Variations of the piezoelectric field and the particle displacement with the distance from the surface have been derived and compared with Stoneley's result for nonpiezoelectric crystals.The results are applied to hexagonal CdSe, CdS, and ZnO. For CdSe and CdS, the surface waves are pure Rayleigh modes. However, for ZnO which has relatively large piezoelectric coupling coefficients, the surface waves are found to have the form of a general surface wave defined by Synge. Velocities of surface waves propagating on the basal plane of CdSe, CdS, and ZnO are computed to be 1.470×105, 1.7306×105, and 2.70×105cm/sec, respectively, which are in good agreement with measured values.

ISSN:0021-8979    

DOI:10.1063/1.1709115

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Velocities, particle displacement, and piezoelectric field associated with surface elastic waves in CdS, ZnO, and lead‐titanate zirconate (PZT‐4) have been computed for two cases, with and without metallic coating on the surface. Compiled are data for CdS, ZnO, with theircaxis normal to the surface, and PZT‐4, poled in the direction normal to the surface. The velocity of propagation is found to be slightly lowered by the presence of metallic coating. Such change in velocity is applied to conduct an experiment which shows strong Bragg's reflection of elastic surface waves by metallic thin‐film gratings. It has been pointed out that the previously reported surface wave velocities inferred from the response of interdigital transducer are believed to be slightly lower than the actual velocity of propagation.

ISSN:0021-8979    

DOI:10.1063/1.1709116

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The effects of hydrostatic pressures up to 13 kbar on the stress dependence of the velocity of screw dislocations in single crystals of lithium fluoride at room temperature have been determined. The shear stresses to move the dislocations were introduced by means of a three‐point bending device incorporating a load‐cell and operated entirely within a fluid medium at constant pressure and temperature. The range of velocities observed was from 10−5to 10−2cm/sec. Both high‐purity and impurity‐doped crystals were studied.At all the pressures examined, the dislocation velocity was found to vary with the applied shear stress &tgr; in accordance with the empirical relationshipv = v*·e−A/&tgr;(wherev* is a terminal velocity andAis a drag stress) suggested by Gilman for one‐atmosphere behavior. However, the stress required to move a dislocation at a given velocity in increases rapidly with pressure, by a factor of approximately 3 at 10 kbar. Correspondingly, the dislocation velocity at constant applied shear stress decreases by several orders of magnitude. Based on the magnitudes of the activation volume measured for the high‐purity and doped crystals, the effects are interpreted in terms o the mobility of jogs as the mechanism controlling dislocation velocity at pressure.The measured decrease in dislocation mobility has been used to compute the expected change in stress—strain behavior in LiF as a function of pressure.

ISSN:0021-8979    

DOI:10.1063/1.1709117

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The current oscillations which are observed in piezoelectric semiconductors, such as cadmium sulfide, are often accompanied by a high field domain which moves through the sample at the velocity of sound. These domains may be a result of the negative differential conductivity which is produced in the material by a large component of acoustoelectric field. This field opposes the applied field when the drift velocity exceeds the velocity of sound. We determine from the linear theory a threshold condition for the onset of the negative differential conductivity and show that this model is in agreement with the experimental observations reported here on CdS and elsewhere on GaAs.

ISSN:0021-8979    

DOI:10.1063/1.1709118

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

This paper reports the results of an experimental determination of the secondary‐emission characteristics of glycerol layers on copper surfaces. This work has as its motivation the use of glycerol as a working fluid in electric thrustors for spacecraft.Secondary‐emission coefficients for glycerol are reported as a function of incident primary‐electron energy. Primary‐electron energy was varied from 200–900 eV and glycerol secondary‐emission coefficients were found to vary from 2.5 to about 1.0. These results are compared with values for clean copper surfaces found by using the same apparatus.

ISSN:0021-8979    

DOI:10.1063/1.1709119

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Sputtering of aluminum oxide (sapphire) by 2.5 to 10 keV cesium ions has been investigated using neutron activation analysis. The sputtering yield (aluminum atoms/ion) was measured as a function of ion energy, target temperature, andR, the ratio of background oxygen molecular flux arriving at the target surface to the sputtered aluminum and oxygen flux leaving the surface. Positive‐charge accumulation on the dielectric surface was neutralized by electron flooding of the ion‐beam area while the ion current was measured by a periodic beam deflection technique. In all measurements the ion beam was normal to the target surface and the (001) crystallographic plane. The yield increased monotonically from 0.40 (aluminum atoms/ion) at 2.5 keV to 0.52 at 10 keV and was unaffected forR<0.1. The yield decreased slightly asRwas increased, and forR>10 it approached the saturation value of monocrystalline aluminum. The yield exhibited a temperature dependence decreasing from 0.55 at 77°K to 0.48 at 475°K. The results were reproducible to within 5%.

ISSN:0021-8979    

DOI:10.1063/1.1709120

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The effective shear moduli, dislocation line energies, dislocation widths, and relative ease of gliding have been calculated for the (0001) [112¯0], (11¯00) [112¯0], (11¯01) [112¯0], (112¯2) [112¯3¯], and (hk.0) [0001] slip systems in each of the hexagonal close‐packed metals Cd, Zn, Mg, Co, Zr, Ti, and Be by applying anisotropic elasticity theory of dislocations. Except for the case of Be, the results correctly explain the choice of prevailing slip systems among the three with a common slip vector ⅓ [112¯0]. The second‐order pyramidal slip, frequently observed in Cd and Zn, cannot be accounted for in terms of its calculated relative ease of gliding. It seems that the extended nature of a dislocation, hence the stacking‐fault energy, may affect the ease of gliding of the dislocation.

ISSN:0021-8979    

DOI:10.1063/1.1709121

出版商:AIP    

年代:1967

数据来源: AIP