摘要:

Elastic constants of single crystals of the cubic Laves phases CaAl2, YAl2, LaAl2, and GdAl2have been measured over the temperature range 4.2–300 K. The ferromagnetic transition in GdAl2near 170 K is evident by changes in slope in plots of the three independently measured elastic constants of GdAl2as functions of temperature. Debye temperatures at 0 K were evaluated as 474 K for CaAl2, 484 K for YAl2, 374 K for LaAl2, 399 K for magnetically disordered GdAl2, and 406 K for magnetically ordered GdAl2. It was inferred from the data that the valence electron distributions in nonsuperconducting YAl2and GdAl2are much alike, but the valence electron distribution in superconducting LaAl2is significantly different. Thus the results support a theoretical calculation indicating an admixture of 4fcharacter into the valence bands of LaAl2.

ISSN:0021-8979    

DOI:10.1063/1.1663118

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A method is proposed to detect the presence of a uniaxial stress component in samples belonging to the cubic system, pressed in a tungsten carbide anvil x‐ray camera unit. The method is based on fitting the experimental data to an expression of the form&egr;w(hkl)=&egr;wp−m t(C11+4C12−2C44)/2 (C11+2C12)(C11−C12+3C44)+n t [S12+(S11−S12−S44/2) &Ggr;(hkl)], where &egr;w(hkl) is the strain calculated from the shift of the diffraction line (hkl) at a loadwapplied between the anvils,&egr;wpis the strain arising from the hydrostatic component of the stressp, tis the uniaxial stress component, and &Ggr;(hkl)=(h2k2+k2l2+l2h2)/ (h2+k2+l2)2. If the state of stress continuity in the crystallites is assumed, thenm=0 andn=1; andm=1 andn=0 if the state of strain continuity in the crystallites is assumed. The experimental data for Si atw= 1400 kg and for NaCl atw= 510 kg indicate a linear dependence of &egr;w(hkl) on &Ggr;(hkl) as is expected forn≠0. The slope of the &egr;w(hkl) versus &Ggr;(hkl) plot is negative for Si and positive for NaCl; this is in agreement with the theory as the value of (S11−S12−S44/2) is positive for Si and negative for NaCl, andt, being a compressive stress, is negative by convention. The lowest estimates oft, made from the slope of the &egr;w(hkl) versus &Ggr;(hkl) plot, is obtained ifm=0 andn=1 are assumed. The slope of the &egr;w(hkl) versus &Ggr;(hkl) plot shows a considerable variation from run to run. For Si, for example, the lowest estimate oftvaried between 21±4 and 32±4 kbar in the four runs made atw= 1400 kg. For NaCl, the lowest estimate fortvaried between 4.2 ± 1.5 and 5.5 ± 1.5 kbar in the six runs made atw= 510 kg.

ISSN:0021-8979    

DOI:10.1063/1.1663119

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Photostimulated exoelectron emission produced by tensile deformation is much more intense than that produced by compressive deformation. This result is demonstrated for a number of metals and apparently is quite general. The strain required for the onset of emission is not appreciably different for either mode of deformation. However the intensity of emission increases rapidly with increasing tensile strain, whereas additional compressive strain has little further effect. In both cases the natural surface oxide cracks to reveal a fresh metal surface of lower work function, thereby increasing the photoelectric yield. The differing effects of tensile and compressive deformation can be correlated with the geometry of the slip steps as observed by scanning electron microscopy.

ISSN:0021-8979    

DOI:10.1063/1.1663120

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A kinetic theory is developed for diffusion of an interstitial solute in a dilute ternary fcc alloy. The development includes kinetic interpretations for off‐diagonal terms in the matrix of diffusion coefficients and a concentration‐dependent heat of transport for thermal diffusion and effective charge for electromigration. The associated chemical potential is shown to reflect the tendency towards interstitial and interstitial‐substitutional pair formation.

ISSN:0021-8979    

DOI:10.1063/1.1663121

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Stacking‐fault energies can be determined by measuring the positions and profiles of x‐ray diffraction lines. Use of this method has been hampered by the uncertainty of the relationship between stacking‐fault energy and the ratio of microstrain to stacking‐fault probability. Microstrains and stacking‐fault probabilities have been determined for five fcc metals by x‐ray diffraction line profile analysis. For these metals, Ag, Au, Cu, Al, and Ni, stacking‐fault energies have been estimated from a comprehensive updated review of the experimental literature. A linear correlation does exist between &ggr; and⟨&egr;502⟩111/&agr;and thus, the x‐ray technique can be applied more confidently. The possible role of elastic anisotropy is also considered.

ISSN:0021-8979    

DOI:10.1063/1.1663122

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A free‐space and in‐waveguide dielectric constant measurement facility at 10 and 35 GHz is described. Results are presented for the dielectric constant and loss of both fresh and sea ice at these frequencies, and are interpreted in terms of a dielectric model of sea ice. Suggestions are made for possible improvements in the model and the measurement technique.

ISSN:0021-8979    

DOI:10.1063/1.1663123

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A new liquid‐crystal alphanumeric display device is described. The device is of the guest‐host type and involves the orientational change of a pleochroic dye (guest) in a cholesteric liquid‐crystal mixure (host) by the application of an external electric field. The cholesteric nature of the host permits the operation of the device in the reflective mode with excellent brightness since no external polarizers are required. Good contrast ratios have been obtained for new pleochroic dyes (guests) which have higher optical order parameters than those previously employed. The theory of light absorption in a cholesteric liquid crystal having both homogeneous and homeotropic boundary conditions is developed and aspects of contrast ratio and its relation to human perception are described.

ISSN:0021-8979    

DOI:10.1063/1.1663124

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Irradiation of dielectrics with nonpenetrating electron beams has been used for practical purposes, e.g., manufacturing of electrets, and as a research tool, e.g., the investigation of induced conductivity and transport properties. The present paper develops some aspects of the theory of charge transport and storage and radiation‐induced conductivity in irradiated dielectrics. It is assumed that the dielectric is kept in short circuit and that the range of the incident electron beam is smaller than half the sample thickness. The treatment applies only to dielectrics which have a very low dark conductivity and contain a great number of deep traps.

ISSN:0021-8979    

DOI:10.1063/1.1663125

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Misfit accommodation in epitaxially grown GaAs1−xPxwas examined by x‐ray topography which shows crosshatch contrast and by transmission electron microscopy which reveals individual misfit dislocations. Of these misfit dislocations 80% are glissile 60° dislocations and the remainder are perfect edge dislocations. Contrast considerations show that the x‐ray images are fully compatible with the actual dislocation structure although they cannot resolve the individual dislocations.

ISSN:0021-8979    

DOI:10.1063/1.1663126

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

To improve the performance and reliability of heterostructure GaAs lasers, it is important to reduce stress in the epitaxial layers caused by lattice mismatch between GaAs and AlxGa1−xAs. More precise measurements than previously available have been made on the lattice mismatch of binary layers of GaAs&sngbnd;Al0.24Ga0.76As1−yPyand GaAs&sngbnd;Al0.36Ga0.64As1−yPyfrom radius‐of‐curvature measurements. The heterostructures were grown by LPE, with various atom fractions of P, on (100) and (211) GaAs substrates. Liquidus values of P concentration at 780°C growth temperature to achieve room‐temperature lattice matching have been determined to ±4%. The threshold value of the lattice mismatch and layer thickness product on (211) substrates necessary to avoid misfit dislocations is given.

ISSN:0021-8979    

DOI:10.1063/1.1663127

出版商:AIP    

年代:1974

数据来源: AIP