摘要:

The five independent elastic constants of single crystals of the hexagonal allotrope of thallium have been determined by the ultrasonic pulse‐echo technique over the temperature range, 4.2°–300°K. The values at 300°K in units of 1011dyn/cm2areC11=4.080,C33=5.280,C44=0.726,C12=3.54, andC13=2.9. The compressibility derived from these elastic constants is in good agreement with the compressibility obtained by Bridgman from hydrostatic measurements on polycrystalline samples.

ISSN:0021-8979    

DOI:10.1063/1.1729531

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Pyrolytic graphite was cleaved in a high vacuum to obtain clean surfaces, and the secondary electron emission properties of these surfaces were determined. Pyrolytic graphite has a maximum secondary emission yield of 1.0 at 300‐eV primary electron energy for electrons incident normal to the basal plane. The most probable energy of the emitted secondaries is 2 eV, with one‐half of the secondaries having energy in excess of 8 eV. A maximum secondary emission yield of 0.75 at 350‐eV primary energy was measured for normal incident electrons on a face that was perpendicular to the basal plane. The backscattered fraction for pyrolytic graphite was found to be 0.05. No differences were observed in the secondary electron emission properties of single‐crystalline pyrolytic graphite and pyrolytic graphite that was less well ordered.

ISSN:0021-8979    

DOI:10.1063/1.1729532

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The electron density of a pure InSb crystal has been synthesized using very accurate x‐ray diffraction intensities. After subtracting the electron density of the palladium core from both kinds of atoms, the distribution of the valence electrons was determined. By this means it was established that, on the average, 0.45±0.05 electrons are transferred from the Sb atoms to In atoms, as compared to a transfer of 0.34 or 0.42 electrons deduced from infrared absorption measurements. The effective ionic charge to be used in polar‐scattering calculations for InSb was calculated to be 0.17±0.02 e based on the electron density, as compared to 0.18 e or 0.16 e determined from electron mobility measurements.

ISSN:0021-8979    

DOI:10.1063/1.1729533

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Utilization of the Hall effect in the frequency conversion of microwaves with gain was investigated. A conversion gain which seemed to be feasible was found to be dependent on the control sensitivity of the conversion system. A high control sensitivity can be achieved through use of a high‐mobility Hall sample, like InSb, an efficient coupling of a modulating field to the sample, and a suitable high‐energy pump source.The high‐power test was performed by using a pulsed microwave pump. Conversion gains were measured as a function of the pumping power and showed some ``saturation'' effects. These effects were explored and explained, based on the behavior of carriers in the sample under high‐power microwave fields. In particular, a breakdown field beyond which the saturation seemed to disappear was found.The presentSband experimental model still suffered a conversion loss of 25 to 30 dB. Results have, however, revealed the possibility of a practical microwave Hall converter with gain.

ISSN:0021-8979    

DOI:10.1063/1.1729534

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A theoretical study has been made of the transmission of a monochromatic, well‐collimated beam of radiation normally incident on idealized material containing only two energy levels. The nonlinear partial differential equations governing the variation of population and photon density in space and time have been solved exactly for arbitrary initial conditions under the assumption that spontaneous emission and thermal relaxation from the excited state can be neglected. These conditions are satisfied in practice when the radiation is in the form of a pulse whose duration is short compared with the characteristic times of these relaxation processes. Two cases are considered in detail: (a) when all atoms are in the ground state and the material absorbs; and (b) when there is a population inversion and the material amplifies. In case (a), the radiation, with a characteristic velocity, ``bores'' its way through an optically dense substance emerging delayed in time and leaving the material in a perfectly transparent or saturated state. In case (b), an incoming pulse is amplified and sharpened—to a degree determined by the gain of the medium. In addition to these cases, the dependence of the apparent spontaneous emission lifetime on the size and population distribution of the material is mentioned.

ISSN:0021-8979    

DOI:10.1063/1.1729535

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The quantum theory of an atomic beam machine is set up in matrix form. A new method is then used to derive the Bloch‐Siegert shift in the resonance. The results are extended to the case of Ramsey‐type excitation. Finally the Bloch‐Siegert shift is computed for the present atomic beam frequency standards and found to be well below the accuracy of measurement.

ISSN:0021-8979    

DOI:10.1063/1.1729536

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The effect of slow frequency modulation of the exciting radiation on the Ramsey line shape observed in an atomic beam experiment is formulated theoretically. It is shown that the presence of second harmonic in the modulation can introduce measurable frequency shifts, whether observed directly or with a servo system.

ISSN:0021-8979    

DOI:10.1063/1.1729537

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Previously, five phonon energies were used to explain 16 peaks in the measured lattice absorption spectrum of GaAs. It is shown here that the five phonon energies are not unique and that a different set of values is also compatible with the available infrared data both with respect to the absorption peak positions and the temperature dependence of the absorption. A similar difficulty is also noted for some previously published work on CdS. It is suggested that difference band absorption measurements might show which sets of phonon energies are correct.

ISSN:0021-8979    

DOI:10.1063/1.1729538

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Observations of Bitter patterns were carried out for two varieties of Ni&sngbnd;Fe alloy thin films electrodeposited without magnetic field onto mechanically polished copper substrates. These two sorts of films were composed of 80Ni‐20Fe ``Film 1'' and 82.5Ni‐17.5Fe ``Film 2'' and were Fe‐rich and Ni‐rich from the composition of 81.5Ni‐18.5Fe with minimum coercive force. The behavior of magnetic domains was examined during various magnetic processes and under externally applied stress. It was found that: (i), in ``Film 1,'' the easy axis is parallel to the scratches on the substrates and the domain walls fall into those scratches; and (ii), in ``Film 2,'' an averaged easy direction is induced perpendicular to the scratches in several films, whereas in the other films it was not well‐established. These results are well explained, being consistent with the hysteresis characteristics, by assuming that magnetostriction is positive in ``Film 1'' and negative in ``Film 2'' and that magnetoelastic and shape anisotropies both are induced, accompanying the scratches on the surface of the substrates.

ISSN:0021-8979    

DOI:10.1063/1.1729539

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Space‐charge, field, and potential distributions in inhomogeneously doped crystals are determined by a nonlinear differential equation which requires numerical computation in order to be solved. By means of numerical computation an attempt is made to obtain the potential, field, and space charge throughout the crystal. For exponential impurity distributions bounding curves can be obtained which allow one to obtain the complete distributions. A few examples are computed which demonstrate the difficulties encountered in obtaining solutions.

ISSN:0021-8979    

DOI:10.1063/1.1729540

出版商:AIP    

年代:1963

数据来源: AIP