Volume 30, Issue 7, 01 July 1959

Diffusion of Copper in Cadmium Sulfide Crystals
View Description Hide DescriptionCopper was diffused in cadmium sulfide single crystals to determine diffusion coefficients using the radio‐active tracer sectioning technique. Over the temperature range of 450°–750°C, the relationship between temperature and diffusion coefficient was found to be D=1.5×10^{−3} e ^{−17600/RT } square centimeters per second for diffusion perpendicular to the C axis. For diffusion parallel to the C axis, the frequency factor and activation energy were found to be within the experimental accuracy of the corresponding values for perpendicular diffusion. There appears to be no appreciable diffusionanisotropy. Observed surface diffusion was a complicating factor in obtaining data on volume diffusion.

X‐Ray Method for the Differentiation of {111} Surfaces in A^{III}B^{V} Semiconducting Compounds
View Description Hide DescriptionMost of the A^{III}B^{V} semiconducting compounds have the zincblende crystal structure. This structure is noncentrosymmetric and as a consequence the modulii of F(hkl) and F(h̄k̄l̄), the geometrical structure factors, have different magnitudes. This difference results in a variation in the integrated intensities of certain x‐ray reflection from opposite sides of samples taken from crystals with the zincblende structure. X‐ray measurements of a series of {111} reflections from opposite sides of an InAssingle crystal have been made and related to the etching characteristics of these surfaces.

Effect of Thermal Motion on the X‐Ray Reflectivity of Quartz
View Description Hide DescriptionTwo characteristic temperatures for quartz were determined which, when substituted into the Debye‐Waller formula and then used to compute the ratios of temperature corrected integrated reflection coefficients of various pairs of sets of Bragg planes, gave results in best agreement with experimentally determined ratios. These temperatures are 508±16°K in the direction of the trigonal axis and 452±15°K in any perpendicular direction. Corresponding values obtained from an approximate formula relating characteristic temperatures with elastic constants were 448° and 398°K, respectively. The fairly good agreement between the characteristic temperatures obtained by the two methods seems to support the conjecture that the modification of the Debye theory used gives a fairly good approximate description of the effect of thermal motion on the x‐ray reflectivity of quartz. Calculations based upon the experimentally determined characteristic temperatures indicate that when Bragg spacings are less than about 0.7 A, the reflectivity of quartz at room temperature is reduced to less than half the value that would be obtained if the atoms were rigidly fixed.

Paraxial Formulation of the Equations of Electrostatic Space‐Charge Flow
View Description Hide DescriptionThe equations of electrostatic irrotational space‐charge flow are set up in a paraxial manner. Given an arbitrary trajectory, and the potential distribution along that trajectory, the variation of such quantities as potential and beam convergence in the vicinity of the specified trajectory are investigated. A detailed analysis is carried out for beams from a space‐charge‐limited cathode in the form of a cone. The agreement between the paraxial theory and the exact theory for particular beams is investigated. Numerical results are presented for beams from a conical cathode which predict beams with a microperveance of about 15 and a very large area convergence. It is felt that by use of this method much higher perveances and beam convergences could be obtained for hollow and sheet beams than have heretofore been possible.

Method for Calculating Simultaneous Resonance Conditions in a Three‐Level Ruby Maser
View Description Hide DescriptionIn operating a three‐level maser one wishes to know the external magnetic field and crystal orientation necessary to match a given pair of frequencies. In the case of Cr^{+++} a fourth‐degree secular equation determines four energy levels for each value of external fieldH and crystal orientation θ. Determination of the latter two variables, given two desired frequencies of operation, ordinarily involves either the solution of a tremendous number of fourth‐degree equations and extrapolation towards the required solution, or determination of the matching conditions by experimental methods. In the following a method is described, allowing direct calculation of H and θ for a three‐level rubymaser.

Dynamic Properties of the Polarizability in BaTiO_{3} Crystal
View Description Hide DescriptionThe second harmonic distortion by a BaTiO_{3} crystal of a small high‐frequency sinusoidal electric field, superimposed on a low‐frequency switching field, is studied by the filter method. From the phase relationship of the second harmonic distortion with respect to the measuring signal, together with the increase of the fundamental component of the capacitive current, it is concluded that the polarizability increases markedly for the backward direction during switching.

Spectrum of Thin Target Bremsstrahlung Bounded by a Forward Circular Cone
View Description Hide DescriptionThe Schiff expression for the cross section per nucleus, for thin‐target bremsstrahlung into the angular and energy ranges dθ _{0} and dk, is integrated analytically over angle from zero to θ̄ _{0}. Results are shown for the case Z=78, E _{0} − mc ^{2}=40 Mev and x̄=0.5, 1, 2, 4, and 8, where E _{0} − mc ^{2} is the kinetic energy of the incoming electron and x̄ is the reduced angle θ̄ _{0} E _{0}/mc ^{2}. The fraction of the total cross section included in a cone of angle θ̄ _{0} can be approximated to within 20% by x̄ ^{2}/(1+x̄ ^{2}). At x̄=1, or θ̄ _{0}=0.723°, the ratio of energy delivered by photons above (E _{0} − mc ^{2})/2 to that below is 9% greater than for the limiting spectral shape at θ̄ _{0}=0, or that given by the Schiff expression at θ _{0}=0, and 13% greater than for the spectrum integrated over all angles. For a target of finite thickness, multiple electron scattering should partially suppress the spectral dependence on x̄.

Ion Drag Pressure Generation
View Description Hide DescriptionA theory of pressure buildup under unipolar ion conduction is presented and verified experimentally. Constriction of the current flow leads to sizeable pressures in insulating liquids.

Magnetic Annealing in Perminvar. I. Structural Origin
View Description Hide DescriptionThis paper deals with the results of an electron diffraction investigation of the structure of soft magnetic materials which exhibit magnetic annealing. The property of heat treatment in a magnetic field has been found to depend upon the oxygen content present as an impurity and is associated with distinct diffraction phenomena. A structural model based on an interpretation of diffraction results, magnetic properties, and oxygen content is presented.
The pertinent conclusions from this study are:
1. The ability of soft magnetic alloys containing Fe, Co, and Ni to exhibit magnetic annealingproperties is due to oxygen present as an impurity.
2. An oxygen content of about 0.001% is sufficient to produce magnetic annealing with the proper heat treatment. An alloy containing only 0.0001% oxygen fails to respond to field heat treatment or is ``dead.''
3. The oxygen impurity produces magnetic activity in the alloy crystal (with proper heat treatment) by condensing into the (111) planes of the crystal, thus giving rise to a stacking disorder or fault. The term ``impurity fault'' has been introduced to describe this structural irregularity.
4. The oxygen impurity faults are presently thought to be aligned by magnetic annealing and are intimately connected with field heat treatmentproperties. If sufficient oxygen is available in the crystal, the faults thicken and organize to yield metal oxides.

Magnetic Annealing in Perminvar. II. Magnetic Properties
View Description Hide DescriptionPrevious work on Alnico single crystals(permanent magnetalloy) showed that magnetic torque reversals are associated with an inhomogeneous structure. More recently, it has been found that alloys of iron, nickel, and cobalt in the Perminvar region also exhibit these torque reversals although the alloys are considered to be solid solutions. An inhomogeneous structure occurs simultaneously with the torque reversals in some of these alloys. The inhomogeneous structure has been observed by means of electron diffraction, and the observations have been interpreted to mean that there are faults in the lattice normal to [111] directions. The faults form in the temperature region where the magnetic fieldheat treatment is effective and their density is roughly proportional to the response of the magnetic fieldtreatment. When the crystals are not heat treated in a field, the faults are arranged to have cubic symmetry and their magnetic anisotropy has cubic symmetry. When the crystals are heat treated in a magnetic field,electron diffraction indicates that the faults are usually affected also.
Evidence has been obtained that small amounts of oxygen as an impurity in Perminvar cause both the faulting and the heat treatment in a magnetic field. An extremely small amount of oxygen (0.0014%) is sufficient to cause such effects.
In a more detailed sense we feel that the magnetic anisotropy introduced by heat treatment in a magnetic field probably arises either from short range order within the faults or from the arrangements of the faults each of which is parallel to a (111) into regions whose shape anisotropy is along the direction of the magnetic field.

Transient Response of Grain Boundaries and Its Application for a Novel Light Sensor
View Description Hide DescriptionGrain boundaries in n‐type germanium and silicon carry a negative surface charge and constitute a potential barrier for electrons. The height of this barrier can be increased by applying an electrical pulse across the boundary or decreased by injecting holes. The relaxation time with which the perturbed barrier returns to its equilibrium value is for sufficiently low temperatures very large compared to the time necessary to change the barrier height. A theory of the transient response of a grain boundary to a pulse is given for the low temperature region. It is shown that the application of a pulse of given height results in a barrier height φ_{ s } which is practically independent of the barrier height φ_{ a } prior to the pulse. The transient current, however, depends markedly on φ_{ a }. A novel photosensor based on this phenomenon is described, and preliminary experimental results are reported.

Ferroelectric Properties of Colemanite
View Description Hide DescriptionThe ferroelectric properties of the calcium borate mineral colemanite are investigated in the ferroelectric and paraelectric temperature regions. It is shown that Devonshire's phenomenological theory may be applied successfully to account for the experimental measurements of spontaneous polarization and electrical susceptibility over a wide temperature range. The thermodynamic transition is confirmed to be of second order occurring for unbiased crystals at −7°C. It is shown, in general, that the temperature τ_{0} at which such a transition takes place depends upon the effective electric fieldE as τ_{0} = kE ^{⅔} where k is a constant evaluated from Devonshire's expansion. The effect of space charge fields are evaluated and a comparison is presented between the ferroelectric properties of colemanite and those of KDP.

Combustion Investigation in the Hypersonic Shock Tunnel Driver Section
View Description Hide DescriptionAn investigation was made of the combustion of stoichiometric mixtures of hydrogen and oxygen with a varying percent of helium in the constant volume driver section for a hypersonic shock tunnel. The pressure was measured as a function of time for a number of initial pressures, mixture ratios, and multiple sparks for ignition. The maximum pressures observed were close to that expected for smooth burning. When detonation was encountered, the ratio of the peak pressure to the initial pressure was about 50.

Some Characteristics of a Magnetically Focused Electron Beam
View Description Hide DescriptionThe detailed behavior of a solid cylindrical electron beam focused by a uniform magnetic field(Brillouin flow) has been studied experimentally. These studies include the influence of the optics of the electron gun on the beam‐focusing characteristics, the effects of transverse ``thermal'' velocities, the change in the internal beam dynamics with increasing values of magnetic focusing field, etc. A simple model of the beam is used to explain certain of the observed characteristics. It is found that an optically good electron gun will produce a focused beam which closely resembles the theoretical Brillouin‐flow model. A brief analysis of the electron motion in a magnetically focused beam is given in the Appendix.

Microplasma Fluctuations in Silicon
View Description Hide DescriptionThe electrical properties of a fluctuating bistable microplasma are specified by three parameters which, in general, are functions of voltage. For an ideal low impedance connection, these parameters are independent of time and thus yield simple forms for the pulse rate, average current, differential conductance, and noise spectral density. With a high impedance circuit the phenomenon is more complex, and only an approximate analysis is offered. Measurements on alloyed junctions with breakdown voltages between 7.9 and 10.5 v show that single breakdown regions sometimes occur at low currents. Multistable conduction as well as the simpler bistable conduction is observed. The multistable conduction is characterized by fluctuations among higher current levels which occur at a rate 10^{2}–10^{5} times faster than the ``on‐off'' fluctuations. Excellent agreement between measured and calculated current spectral density at low impedance is found. This justifies the assumptions of random events independent of previous ``on'' or ``off'' time and suggests that noise spectrummeasurements at low impedance be used as a tool for accurately determining the microplasma parameters. With a high impedance connection, the process is not Markoffian; thus the noise is not simply related to the noise at low impedance. The event which initiates breakdown is found to be field dependent suggesting that field emitted carriers are involved. It is shown that the results do not fully agree with those predicted by Rose's model of a microplasma.

InAs_{1‐x }P_{ x } as a Thermoelectric Material
View Description Hide DescriptionMeasurements of the electrical conductivity σ, the thermal conductivityK, and the Seebeck coefficient (thermoelectric power) α, of InAs_{1−x }P_{ x } have been made at high temperatures with x varying from 0 to 0.4. Between 450° and 800°C, the average thermoelectric figure of merit (z = α^{2}σ/K) increases moderately with x for small values of x, reaching a maximum near x = 0.1, and subsequently decreasing. Between 450 and 800°C, the average z for x = 0.1 is equal to 0.63 × 10^{−3}(°K)^{−1}, a 15% improvement over InAs. For the same figure of merit, the Seebeck coefficient and electric resistivity is higher in the ternary than in the binary InAs; this is advantageous for the design of thermoelectric devices. Previous values for the thermoelectric figure of merit of InAs are revised.

Microwave Techniques in Measurement of Lifetime in Germanium
View Description Hide DescriptionNew techniques are proposed for the measurement of lifetime in semiconductors by utilizing the absorption of microwave power by charge carriers. The densities of holes and electrons are varied by irradiation with light or the conduction mechanism. Agreement is found when the microwave absorption methods are compared with the more established photoconductivity decay techniques. One of the new methods offers an advantage in that electrode attachments are no longer required.

Ruby as a Maser Material
View Description Hide DescriptionThe reasons for the initial choice of ruby as a maser material are outlined and some measurements of the parameters in the spin Hamiltonian and of spin relaxation times are reported. The relative merits of single‐ and double‐pump modes of operation of a four‐level maser are discussed and measurements of the oscillator power for the two cases are included.

Synthesis of a (110) [001] Type Torque Curve in Silicon Iron
View Description Hide DescriptionThe orientations and sizes of all the grains in a polycrystalline disk specimen of high‐purity 3.25% siliconiron are measured to determine a calculated magnetic torque curve and the texture of the specimen. The torque results agree with the experimentally determined values. The curves approximate a (110) [001] single crystaltorque curve, which is reduced about 75%, and thus indicate a possible texture consisting of about 25% (110) [001] and 75% random. The true texture obtained from the orientation data is found to have more than ten components, none of which is (110) [001]. Illustrations showing how a (110) [001] type torque curve may be synthesized from non‐(110) [001] type components in the texture are given.

Polarization Reversal by Sideways Expansion of Domains in Ferroelectric Triglycine Sulfate
View Description Hide DescriptionAt fields in the range 30–35 v cm^{−1}, polarization reversal in liquid‐electrodedtriglycine sulfate crystals is accomplished by the formation and sideways expansion of a relatively few domains. While small, the domains are elliptical or lenticular in shape, but as they grow, they tend to become irregular before amalgamating with each other. In some cases, at least, the elliptical domains have approximately equilibrium shapes as determined by the wall energy. Some general results are given concerning the sites at which the domains form and the way in which domains contract when the field is reversed.