Volume 35, Issue 9, 01 September 1964
Index of content:
35(1964); http://dx.doi.org/10.1063/1.1713799View Description Hide Description
Micron‐sized particles (0.3 to 15 μ in radius) of metals such as aluminum, carbonyl nickel,molybdenum;semiconductors such as magnetite and zirconium hydride; and insulators such as aluminum oxide, silicon oxide, and eccospheres are charged by contact electrification in electric fields up to 8000 V in a 0.3‐cm gap. The charges are measured with a drift‐tube detector and a quadrupole mass spectrometer and compared with a theoretical value which includes the contact potential and the electric field. Experimentally, the contact charge is quite important for particles less than one micron in radius, but relatively unimportant for larger particles. The experimental values are in good agreement with the calculated values for the range of materials and particle sizes studied.
35(1964); http://dx.doi.org/10.1063/1.1713800View Description Hide Description
A method for determining electron density in cylindrical plasma columns uses surface wave resonances which occur when the length of plasma column is an integral multiple of the half‐wavelength of the surface wave. One type of resonance is in an axially symmetric mode, the other in a dipolar mode. A theory is given for the relation of resonance frequency to electron plasma frequency. Experiments were carried out with both propagation modes excited simultaneously; the axially symmetric resonances are at much lower frequencies than the electron plasma.
35(1964); http://dx.doi.org/10.1063/1.1713801View Description Hide Description
Previous work by the authors indicated that the penetration depth of krypton ions into the molybdenumcathode of a glow discharge tube operated at 150 V was the order of 104 Å after a 24‐h bombardment (C. Y. Bartholomew and A. R. LaPadula, J. Appl. Phys. 31, 445 (1960)]. Additional results indicate that this penetration depth increases with time of operation of the discharge. A diffusion‐like process appears to be dominant in the initial period of bombardment, but later the removal of surface layers by sputtering becomes dominant. The penetration reaches a steady‐state condition after a sufficient period of bombardment.
35(1964); http://dx.doi.org/10.1063/1.1713802View Description Hide Description
Properties of a moving striation in the positive column of a dc glow discharge are investigated using a pulsed microwave technique. The electron density and the power absorption in various portions of the striation are determined from the time‐resolved resonant curves of a microwave cavity containing the discharge, and the variation of the electron temperature is inferred from the absorption measurement. The results of the measurement show a large degree of variation of both the temperature and the density within one cycle of the striation. The variation of the light intensity measured with a photomultiplier tube is observed to be in phase with the temperature. These results are consistent with the Langmuir probe data and results of other microwave measurements previously reported.
35(1964); http://dx.doi.org/10.1063/1.1713803View Description Hide Description
Protons,electrons, and primary x rays were used to excite characteristic x radiation from individual specimens of Ti, Cr, Fe, Cu,Ge, Zr, and Au. X‐ray yield expressed as (photons /sr)/ quantum increased with quantum energy in a similar manner for protons in the range about 1 MeV and electrons in the range about 50 keV. For primary x‐ray excitation, the yield decreased with increasing quantum energy, a relationship opposite to that for proton or electron excitation. It appears that the relative values of photo‐electric absorption and scattering must be quite different for x rays and electrons to account for their opposite relationship of yield vs energy.
35(1964); http://dx.doi.org/10.1063/1.1713804View Description Hide Description
This paper investigates problems associated with multimode oscillations in semiconductor lasers. In particular, even in semiconductors there can exist a spatially nonuniform distribution of excess electrons and holes because a given mode de‐excites electrons most strongly at antinodes and not at all at nodes of the electric vector. This nonuniform distribution encourages the oscillation of other modes which have a different distribution of the electric field vector and which, in particular, have finite electric fields at nodes of the first oscillating mode. Diffusion of electrons and holes tends to wipe out nonuniform carrier distributions. For low temperatures, this diffusion is relatively slow, and for current densities only moderately above the threshold, several modes may oscillate simultaneously. At higher temperatures the suppression of additional modes is much more effective. Because of the complexity of the calculations, the present work had to be restricted to Fabry‐Perot type modes and relatively low power levels. Comparisons are made between theory and experiments.
35(1964); http://dx.doi.org/10.1063/1.1713805View Description Hide Description
The emission of electrons from metals can be excited through a variety of treatments and stimulated by thermal energy and as shown only recently, by high‐intensity ultrasound. Investigations were carried out on disks of 99.999% pure aluminum and aluminum 6061, exposed to acoustic irradiation up to 100 W/cm2 at 20 kc/sec. The peak emission at certain intensity levels of the acoustic field is presented, compared with emission from thermal stimulation, and discussed from the viewpoint of acoustic activation of lattice defects in metal crystals.
35(1964); http://dx.doi.org/10.1063/1.1713806View Description Hide Description
An analytical model is described in which the time‐averaged charge of adsorbed particles is a function of the energy of transition between atomic and ionic states, as in a thermally ionized gas. This relation is used to determine the dipole moment of the adsorbed layer, including the effect of depolarization by adjacent charges. An expression is obtained which relates the emission properties to the temperature, degree of surface coverage, and basic properties of the substrate and adsorbate. Through estimation of the atom adsorption energy, a relationship is obtained which gives a good correlation of most available data for the emission properties of surfaces immersed in cesium vapor.
35(1964); http://dx.doi.org/10.1063/1.1713807View Description Hide Description
The optical transmission of a xenon flashtube has been measured at wavelengths from 2500 to 10 000 Å and at currents up to 5000 A/cm2. It is found that the absorption increases with current and with wavelength. Above about 5000 Å and a current of 4000 A/cm2, a discharge tube 1 cm thick is nearly opaque. At shorter wavelengths or lower currents, the discharge is fairly transparent.
Compositional and Thickness Dependence of the Ferromagnetic Anisotropy in Resistance of Iron‐Nickel Films35(1964); http://dx.doi.org/10.1063/1.1713808View Description Hide Description
Experiments are reported in which (1) the resistivity has been measured as a function of the angle between the magnetic field direction and the current direction and as a function of the thickness in 82% Ni‐18% Fe thin films, (2) the ferromagneticresistanceanisotropy in these films has been measured as a function of thickness, (3) the anisotropy in the fractional magnetoresistance has been measured as a function of thickness in these films, and (4) the anisotropy in the fractional magnetoresistance of films ranging in composition from 65% Ni‐35% Fe to 92% Ni‐8% Fe has been measured. The angular dependence of the resistivity agreed with theoretical predictions, provided suitable values are assumed for the mean free path and bulk resistivity of the films. The ferromagneticresistanceanisotropy appears to be independent of film thickness in the range from 75 to 2500 Å. The anisotropy in fractional magnetoresistance is lower than in bulk due to an abnormally high value for the resistivity of the zero magnetostrictive films studied. Nonzero magnetostrictive films also exhibit anomalies when the anisotropy in fractional magnetoresistance is compared with that in bulk material. A simple analytic expression relating these resistance anomalies to the magnetostriction parameter for the films is explained in terms of the magnetostriction of the films and the fact that they are attached to the substrate.
35(1964); http://dx.doi.org/10.1063/1.1713809View Description Hide Description
Measurements of the temperature dependence of the conductivity of single crystals of ammonium dihydrogen phosphate are described. Impurities introduced in known amounts as substituents in the lattice enable the activation energy for mobility to be separated from the total energy in the Boltzmann factor for conduction. With Ba++ as impurity, the activation energy is 10.1 kcal/mole, with SO4 −− 10.9; the average, 10.5 kcal/mole, is taken to be the activation energy for mobility in this crystal. It ls proposed that activation for mobility in this solid is due to the simultaneous breaking of two hydrogen bonds independently. The σ0 factors, both for intrinsic conduction and for impurity conduction, agree reasonably well with the values expected from the theory of ionic conduction.Measurements on crystals enclosed in an evacuated space show that hydrogen gas is generated by the electrolysis of the crystal. According to Faraday's law the theoretical yield for a univalent ion leading to a diatomic molecule (H2) as product is 0.5 mole/F; the observed yields ranged from 0.3 to 0.7 moles/F. It is inferred that the conduction is ionic and that the migrating particle is probably the proton. From the conduction data for the pure crystal, the energy required for the formation of ions within the crystal is calculated to be 19.8 kcal/mole. The mobility process in this crystal shows a strong resemblance to that in ice. Both appear to be referable to the breaking of two hydrogen bonds simultaneously and to the tunneling of protons between equivalent sites. Both crystals have hydrogen bonds as an important part of their structure.
35(1964); http://dx.doi.org/10.1063/1.1713810View Description Hide Description
The systematic errors inherent in the numerical evaluation of the various moments of an experimental paramagnetic resonance line are discussed as a function of the choice of the shapes and the arbitrary cutoff of wing contributions. Lorentzian and Gaussian first derivative shapes are used as models. Expressions for the zeroth, second, and fourth moments of these shapes are derived in generalized coordinates with an arbitrary cutoff. The generalized coordinates, which contain parameters related to easily measured experimental quantities, permit application of the results to any line of the Lorentzian or Gaussian shape.
Experimental Determination of the Drift Velocity of Low‐Energy Electrons in Ar, N2, CO2, Several Ar–N2 Mixtures, and Several Ar–CO2 Mixtures35(1964); http://dx.doi.org/10.1063/1.1713811View Description Hide Description
An experimental determination of the drift velocity of low‐energy electrons in argon, nitrogen, carbon dioxide, several mixtures of argon and nitrogen, and several mixtures of argon and carbon dioxide used a pulsed ionization chamber with alpha particles as the source of ionization. The experimental data for the single gases serve to verify the experimental technique. The results and a detailed estimation of the possible experimental errors are presented.
35(1964); http://dx.doi.org/10.1063/1.1713812View Description Hide Description
The locations of domains appearing on the surface of a BaTiO3 crystal have been observed by repeated partial switching and etching to determine how frequently the domains appear at the same location on successive applied pulses. The ratio of the number of repeating locations to that of all locations is (10±1.6) % for a series of six pulses at 20 kV/cm on crystals with a positive internal bias and (28±5) % on crystals with a negative bias. The simplest interpretation of the results is that new domains can nucleate at points in the crystal remote from imperfections. This interpretation is in rough agreement with Landauer's calculation of the probability of thermally activated new domains for a 180° wall energy of 0.4 erg/cm2.
35(1964); http://dx.doi.org/10.1063/1.1713813View Description Hide Description
The shifts of the (111) and (200) x‐ray diffraction lines have been measured by both the centroid and the peak method. From these measurements the stacking fault probability α and the twinning fault probability β can be obtained on powdered samples prepared by filing. These results show a parabolic type of dependence of α with composition, whereas the stacking fault probability α obtained from previous measurements using the same technique on Cu‐Zn and Ag‐Cd alloys had a linear dependence with composition.
By means of a simple argument the relative stacking fault energies for these alloys can be deduced and compared with those obtained on similar Cu‐Ge alloys by Howie using thin‐film electron microscopy and by Haasen and King using tensile tests.
35(1964); http://dx.doi.org/10.1063/1.1713814View Description Hide Description
The temperature dependence of ferromagnetic resonance losses was measured for single‐crystal samples of lithiumferrite and yttriumirongarnet that were treated to increase or decrease the state of order of the atomic structure. The maximum linewidth, at low temperatures and caused by residual impurity ions, is much greater for the more ordered state as contrasted to the more disordered state. An explanation of these observations is given in terms of expected changes in the energy levels of the impurity ions with changes in the state of order.
35(1964); http://dx.doi.org/10.1063/1.1713815View Description Hide Description
The recently developed method of etching fission fragment tracks in mica appears to be applicable to the measurement of neutron exposures in irradiation tests. The sensitivity of the method depends on the concentration of fissile elements. The naturally occurring uranium which is present in trace quantity can be used to measure thermal neutron exposures of 1016 to 1021 neutrons/cm2. Deposition of fissionable material on the mica would increase the sensitivity to permit measurement of 106 to 1011 neutrons/cm2. Density counts are reproducible to approximately 5% by using simple laboratory techniques.
35(1964); http://dx.doi.org/10.1063/1.1713816View Description Hide Description
The ordinary‐ray index of refraction at 5893 Å in BaTiO3 was measured in the range 20°–160°C by a refined Chaulnes' method with an average error of 0.35%. Two BaTiO3 crystals were studied and the results indicate a constant index of 2.368 from 20° to 105°C; above the Curie point the ordinary index increased by 1.3% to 2.398 and remained constant to 160°C.
35(1964); http://dx.doi.org/10.1063/1.1713817View Description Hide Description
Hysteresis loop measurements were conducted on several commercial iron‐nickel alloys during neutron irradiations at 90°K and at temperatures up to 175°C, in both zero and saturating magnetic fields. Isochronal annealing tests were also performed on the alloys after irradiation. The low‐temperature irradiation results indicated that magnetic properties are affected not by the point defects themselves but by their motion and eventual disposition. The radiation‐induced changes appeared similar in many ways to those observed in these alloys upon magnetic annealing.
Experiments on the alloys at temperatures from 70° to 175°C in a saturating magnetic field showed that the activation energy of the radiation‐induced process was 0.3 eV. In all cases the radiation‐induced changes were annealed out at temperatures below the usual ordering temperature for Ni3Fe. This recovery process appeared to be dependent upon the state of the magnetization of the sample.
35(1964); http://dx.doi.org/10.1063/1.1713818View Description Hide Description
Ultrasonic propagation in Al2O3 at low temperatures and high frequencies (to 3000 Mc/sec) is discussed in terms of the relations given by Woodruff and Ehrenreich. Phononrelaxation times calculated from thermal conductivity measurements are used. The measured low‐temperature attenuation values at 1315 Mc/sec agree with the calculated values. A comparison of attenuation as a function of frequency is made among Al2O3, Ge, Si, and quartz. On comparing experimental values of attenuation for pure Al2O3 and impure Al2O3(ruby) it is found that impurities lead to an increase in the attenuation as would be predicted from the corresponding effect of impurities on the thermal phononrelaxation time.