摘要:

Transmission characteristics of a rectangular waveguide with a perpendicularly inserted mercury‐vapor discharge tube, have been measured. The waveguide was excited in the TE01mode and the plasma column was either perpendicular or parallel to the electric vector of the waveguide mode. In the first case the transmission spectrum contains the well‐known Tonks‐Dattner resonances and some additional unexplained small peaks. In the second case the transmission spectrum has only small peaks superimposed on a smooth curve. Noise emission spectra were also measured for both polarizations and showed the same characteristics as the absorption spectrum.To explain these results, dispersion curves were measured for the symmetric, dipole, and quadrupole modes propagating on the plasma cylinder. In addition the dispersion curve for a new symmetric mode was measured. This mode is of the same nature as the fast dipole modes responsible for the subsidiary Tonks‐Dattner resonances. By combining these experimental results it has proved possible to gain an understanding of how the various peaks in the transmission spectrum are caused by coupling to plasma waves. In particular, the small previously unexplained peaks are due to coupling to slow plasma waves as also has been proved by direct measurement of the slow waves leaking out through the holes in the waveguide.

ISSN:0021-8979    

DOI:10.1063/1.1714515

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The possibility of observing collective effects of electrons and holes in InP under intense optical irradiation from GaAs lasers is examined. At 2°K, the exciton density at which a postulated Bose‐Einstein condensation might occur is 1.3×1015cm−3. It is shown that at this density another collective effect (shielding of the Coulomb potential) may cause excitons to dissociate. However, the criterion for exciton dissociation is too crude to resolve this question. The requisite light intensity to observe the effects discussed is estimated to be ∼5–100 W/cm2, whereas intensities ∼104W/cm2are available over a spot with diameter 0.1 mm.

ISSN:0021-8979    

DOI:10.1063/1.1714516

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Earlier calculations of the radiation intensity obtainable from lasers with homogeneous line broadening are generalized to include arbitrarily large loss fractions per pass. The conditions for maximum transmitted or internally dissipated power are derived, as well as the axial distribution of radiation within the active medium. The relevance of these calculations to high‐gain gas lasers is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1714517

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Effects of nonmagnetic scandium octahedral substitution in yttrium iron garnet were studied in a series of polycrystalline garnets having the unit formula Y3ScxFe2−xFe3O12wherexwas varied from 0 to 1.7. Measurements of the lattice parameters, spontaneous magnetization, Curie temperature, and the initial permeability as a function of frequency and temperature are reported. The lattice parameter varied linearly from 12.376±0.003 Å forx=0(YIG) to 12.495±0.005 Å forx=1.5 Sc3+. Single‐phase garnet was not obtained forx>1.5. The apparent spontaneous magnetization atT=0°K and the Curie temperature dependence on substitution are qualitatively explained using Gilleo's statistical theory of incomplete super‐exchange interactions. The initial permeability at room temperature is strongly affected by the addition of scandium, increasing from 120 (YIG) to a maximum value of 1934 (x=0.9 Sc3+) and then to unity for largerxvalues. The value of 1934 is the largest room‐temperature initial permeability reported in garnets to date; the corresponding Curie temperature is 320°K. The frequency spectra of the initial permeability forx≤0.7 Sc3+display the usual two characteristic loss peaks identified with domain wall motion and domain rotation mechanisms. The high‐frequency (domain rotation) peak appears only as a shoulder on the broad wall motion resonance. The wall motion peak does not exhibit electronic diffusion effects. In the absence of experimental anisotropy data on Sc3+substituted garnets, the temperature dependence of the initial permeability was used to deduceK1(T) by assuming that the rotational permeability contributes ∼20% to the total measured permeability. The rotational resonance frequencies calculated using the deduced anisotropy constants at room temperature agree quite well with experimental data. The derivedK1(T) seem to be in good agreement with the available single‐crystal experimental data.

ISSN:0021-8979    

DOI:10.1063/1.1714518

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The performance of the helium field‐ion microscope depends critically upon accommodating He atoms of 0.15‐eV kinetic energy to the specimen tip. The small accommodation coefficient requires the field‐trapped He atom to make several hundred contacts with the cold tip surface. The hopping He atoms diffuse preferentially to tip regions where the high local field permits ionization before full accommodation is reached. Improved accommodation is achieved with the provision of an intermediate collision partner in the form of adsorbed neon or, preferably, hydrogen or deuterium. Now a high‐resolution He ion image is obtained at 70% of the field used before. As the addition of hydrogen promotes field evaporation, its partial pressure must be carefully controlled to achieve image stability of the nonrefractory metals. Low‐field evaporation by the hydrogen reaction permits easy conditioning of the tip surface of the nonrefractory transition metals so that artifacts caused by yielding to He evaporation field stress are no longer a problem. The field evaporation end form obtained with hydrogen added to He more closely approaches the desirable spherical shape of the emitter than does field evaporation in vacuum or in a single imaging gas. As examples, ion images of niobium, nickel, iron, and high carbon steel are shown.

ISSN:0021-8979    

DOI:10.1063/1.1714519

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The third‐order elastic constants of germanium, magnesium oxide, and fused silica have been measured using the pulse superposition method for determining the ultrasonic velocity as a function of both uniaxial and hydrostatic pressure. From these measurements all six third‐order elastic constants were calculated by using the equations of Thurston and Brugger for MgO and Ge, and the three independent isotropic third‐order constants were calculated for fused SiO2.The results for Ge are in good agreement with the most recent data of McSkimin and Andreatch. The results for MgO agree in part quite well with theoretical data calculated from a Born‐Mayer potential. Drastic failure of the three Cauchy relations indicates the presence of many body forces. For fused silica, the remaining Cauchy relation is, as may be expected, not well fulfilled.

ISSN:0021-8979    

DOI:10.1063/1.1714520

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Results are reported of experimental investigations of the effect of uniaxial compression up to 1.8×1010dyn‐cm−2on grown Ge and Si junctions and of strongly inhomogeneous stress applied directly to the junctions. In Ge, agreement in sign and in magnitude within factors of about two and ten, respectively, was obtained between the currents induced by uniaxial stress in ⟨111⟩ and ⟨110⟩ directions and those predicted by a bandgap mechanism. No significant effect of uniaxial stress up to about 1.5×1010dyn‐cm−2on the reverse‐bias current was found in Si (111) junctions; however, changes in breakdown voltage and of forward‐bias current were observed. The presence of crystal defects is shown to enhance sensitivity to uniaxial stress and, in Si, was found to be a necessary condition for an effect on the reverse‐bias current. Defects introduced by strongly localized stress appear to play a similar role to those active in uniaxial stress effects. It is concluded that the bandgap mechanism proposed by Wortmanet al.applies both in Ge and in Si, but that it is partially masked in the latter by stress‐independent generation‐recombination currents. The plausibility of a generation‐recombination mechanism, possibly such as that proposed by Bernardet al., as an underlying cause of the effects of high localized stress is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1714521

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Ionization energy levels introduced in Te‐doped GaAs after conversion toptype by diffusion of64Cu have been measured by means of Hall effect. Levels at 0.145, 0.166, 0.20, and 0.44 eV are observed after various sequential heat treatments. The 0.145 and 0.44 eV levels are attributed to the two acceptor levels expected of Cu on a Ga site. The 0.20 eV level is assumed to arise from a Ga vacancy as previously reported, and the 0.166 eV level is interpreted as an ion pair between Cu on a Ga site and Te on an As site.

ISSN:0021-8979    

DOI:10.1063/1.1714522

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

General analytical expressions are given for the line shapes of Lorentzian signals broadened by modulation. The results are discussed for the cases of the first and second harmonic. The linewidths and the signal intensities have been calculated analytically as a function of the modulation amplitude.

ISSN:0021-8979    

DOI:10.1063/1.1714523

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Growth pips on epitaxial {111} silicon films result when growth occurs preferentially around tripyramid hillocks which nucleate on the substrate surface and propogate ahead of the film; whiskers sometimes propagate from these. The tripyramids are often associated with and are the mirror image of stacking‐fault triangles. The stacking‐fault tetrahedra are not always complete or necessary for tripyramid formation. The studies indicate that both stacking faults and tripyramids propagate from twinned triangular deposits, the mechanism for stacking‐fault nucleation being a twinned deposited layer model. This model also accounts for the presence of microtwin lamellae recently reported around tripyramids. The possible whisker growth mechanisms are discussed in relation to the observations. The results indicate that a re‐entrant twin mechanism for whisker growth may operate in some cases.

ISSN:0021-8979    

DOI:10.1063/1.1714524

出版商:AIP    

年代:1965

数据来源: AIP