摘要:

Glancing angle x‐ray diffraction photographs are used in the evaluation of the quality of epitaxial silicon overgrowths. Comparisons are made between the results obtained from high quality growth and highly polycrystalline and slightly nonepitaxial structures. The method is a reliable technique for detecting the presence of randomly oriented silicon in amounts exceeding the equivalent of 5 &mgr; in thickness.

ISSN:0021-8979    

DOI:10.1063/1.1728949

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Theory is given for current‐carrier transport in nondegenerate semiconductors with anisotropic electron and hole mobilities and diffusivities. Two perpendicular principal directions are considered along each of which mobility of one carrier is maximum and mobility of the other minimum. This anisotropy might be obtained by elastic strain of a cubic semiconductor, or might occur without strain in certain semiconductors of noncubic structure. The ``photopiezoresistance effect'' in a slab with strongly absorbed radiation incident on one surface is analyzed in detail. Short‐circuit current and open‐circuit voltage between and electrodes are calculated, as well as efficiency of the transducer with an external load resistance. In the small‐signal range, the current, voltage, and efficiency are proportional to photon absorption rate. In the large‐signal range, with load matched for maximum power, similar proportionality holds for the current, while the voltage and efficiency have limiting large‐signal values. For maximum power there is an angle of optimum orientation of the principal directions relative to the surface of the slab. It is determined by the ratio of the maximum relative mobility variations for the respective carriers. Maximum attainable efficiency, the large‐signal value for pronounced anisotropy, is about 0.4 times thermal energy divided by the average energy required to produce one electron‐hole pair; the numerical factor is the root of a simple transcendental equation. This efficiency is about 0.4% for germanium at room temperature, and is consistent with an estimate from small‐signal theory with mobilities that are probably obtainable in strained material.

ISSN:0021-8979    

DOI:10.1063/1.1728950

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The total hemispherical absorptivity of electroplated silver at 75.8°K has been measured as a function of blackbody radiation temperatures from 268°K to 367°K. The measurements were made in a Dewar‐like calorimeter. The total hemispherical absorptivity is found to increase with decreasing blackbody radiation temperature. Assuming a simple relationship between hemispherical absorptivity and normal absorptivity, the normal absorptivity increases with increasing mean wavelength.

ISSN:0021-8979    

DOI:10.1063/1.1728951

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Using a high frequency cw mechanical resonance technique, the adiabatic elastic constants of single crystals of molybdenum and tungsten were measured between 77° and 500°K.

ISSN:0021-8979    

DOI:10.1063/1.1728952

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A special problem involving the passage of a beam of gamma rays through air is examined. The effect of Compton scatterings on the sharpness of the gamma‐ray beam is discussed. Other mechanisms whereby the beam is softened are not included because the interest is only in the component of the beam which suffers little energy loss.The problem of interest is similar, in some respects, to multiple scattering of electrons with negligible energy loss. The mathematical expression for the collision process is different, however. A method used by Fermi in regard to multiple scattering of electrons is also used here. The Klein‐Nishina cross section for Compton scatterings is introduced into the present problem in order to obtain scattering probabilities.Some numerical results are obtained which can be applied to cobalt‐60 gamma rays. The results are presented in graphical form.

ISSN:0021-8979    

DOI:10.1063/1.1728953

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The strongest emission in the helium‐neon gas maser corresponds to transitions between the 2s2and 2p4states of neon which have angular momenta of 1 and 2, respectively. These levels split up in a magnetic field and the maser output contains differently polarized radiations of slightly different frequencies. In particular, for a small magnetic field parallel to the maser axis two circularly polarized components of different frequency are emitted. Their superposition may be described as linearly polarized light where the plane of polarization is rotating at half the difference frequency. A polarizer in the beam gives rise to amplitude modulated light. Interesting effects may be observed when the various Zeeman components resonate in different cavity modes of the Fabry‐Perot interferometer.

ISSN:0021-8979    

DOI:10.1063/1.1728954

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The two‐beam dynamical theory of electron diffraction (Laue case) with attenuation is treated using imaginary potentials and a damping vector &agr; in the Schro¨dinger equation. Explicit formulas are obtained for centrosymmetric crystals when the Bragg condition is realized relating the damping vectors for the two wave fields with the mean imaginary inner potentialP0and the imaginary Fourier coefficientPg.Using a simplified model, the imaginary Fourier coefficients are expressed in terms of the imaginary potentialPffor nearly free electrons (plasma) andPcfor bound atom cores. It is shown that the imaginary potentials can be directly related to the total inelastic collision cross sections and absolute numerical values so calculated. The values computed in this way are sufficiently near experimental results reported in the literature to warrant confidence in the approach. For 105‐V electrons, the damping vectors &agr; are around 10−3Å−1, and the imaginary potentialPf≅0.6 V.The question of anomalous transmission or an electron ``Borrmann effect'' is considered on the basis of the results obtained. It is concluded at this stage that the effect will not be large for metals but will increase with atomic number and may become significant forZ>30. Uncertainties in both plasma and core electron cross sections make such predictions unreliable except for a few elements.A calculation of the contribution of those electrons that have lost energy toE1<Eindicates that theE1electrons also can produce an ``anomalous transmission.'' A velocity filter will be necessary to distinguish thisE1effect from a true anomalous transmission.

ISSN:0021-8979    

DOI:10.1063/1.1728955

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Measurements are made of the wavelengths, linewidths, and fluorescent efficiencies of the fluorescentR1andR2lines in ruby, in the temperature range 300° to 500°K. The results are used to explain the degradation of ruby optical maser performance at elevated temperatures.

ISSN:0021-8979    

DOI:10.1063/1.1728956

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A study has been made of the inhibition of emission from barium‐activated tungsten dispenser cathodes and adjoining molybdenum electrodes which can be produced by carburization. X‐ray diffraction and metallographic techniques have been employed coupled with emission measurements as a function of time, temperature, and arrival rate of Ba+BaO. Performance characteristics including the extent of the emission suppression and its time dependence are presented. It is concluded that the emission inhibition results from greatly reduced activator coverage of the surface of the carbide relative to that of the metal owing to much weaker adsorption forces. Return of emission coincides with disappearance of the carbide layer from the surface via diffusion.

ISSN:0021-8979    

DOI:10.1063/1.1728957

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Grain boundaries in indium antimonide with misfit angles of 6° have been prepared which, according to the dislocation model for grain boundaries, consist of rows of &agr; or &bgr; dislocations. Current flow across these boundaries inn‐ andp‐type material has been studied. Alpha boundaries were found to present a barrier to current flow inn‐ andp‐type material, &bgr; boundaries only inp‐type material. This indicates for &agr; dislocations donor behavior inp‐type material, acceptor behavior inn‐type material and for &bgr;‐dislocations donor characteristics. A theoretical model for the boundary states is proposed.

ISSN:0021-8979    

DOI:10.1063/1.1728958

出版商:AIP    

年代:1962

数据来源: AIP