bluuebunny/crossref_metadata_2025 huggingface dataset:
Electromechanical Behavior of Single Crystals of Barium Titanate from 25 to 160°C
Authors: Huibregtse E. J. , Bessey W. H. , Drougard M. E.
Published: April 2005

Dynamic piezoelectric resonance measurements have been made on single crystals of barium titanate in the temperature range from room temperature to 160°C. In the ferroelectric region (room temperature to 120°C) the material is spontaneously polarized and hence naturally piezoelectric. For this range of temperature results are presented for the elastic compliance coefficients s11E and s11P, the combination (2s12+s66) at constant field and constant polarization, and the piezoelectric coefficient d31 as functions of temperature. Above the Curie temperature (120°C) the piezoelectric resonances can be observed only by polarizing the crystal with an external field. From measurements of the resonant frequencies in crystals having their longitudinal axes along the (100) and the (110) direction, and the assumption of the validity of the Cauchy relation (c12=c44), the elastic coefficients at constant polarization have been determined as functions of temperature and polarization from the Curie point to 160°C. The strains induced by the polarization in a stress-free crystal are shown to be proportional to the square of the polarization, for values of polarization up to one-third of the spontaneous polarization at room temperature.
Contributions to Quantitative Electron Microscopy
Authors: Zeitler Elmar , Bahr Gunter F.
Published: April 2005

The effect of various parameters on contrast in an electron microscope image is analyzed and a simplified formula tested. The dependence of contrast on the weight per unit area, voltage, and aperture is in good agreement with the theory of electron scattering. The observed dependence of screening angle on atomic number deviates from the theory for higher atomic numbers, but carbon and elements of comparable atomic number are not affected. The application of quantitative electron microscopy to biological objects can be considered workable to ±10%.
Radiation Effects in Materials
Authors: Brooks Harvey
Published: April 2005

A review is given of the mechanisms of radiation damage, and of some of the resulting effects. The discussion is divided into three categories: (1) mechanisms of damage production, (2) nature and mobility of the imperfections produced, (3) effect of the imperfections on the measurement of the properties of the solid. Principal attention is given to metals, with related observations in semiconductors cited.
Some Consequences of Thermal Neutron Capture in Silicon and Germanium
Authors: Schweinler H. C.
Published: April 2005

The average value of the kinetic energy of recoil following thermal neutron capture and subsequent gamma-ray emission is 780 ev in silicon and 180 ev in germanium. For every neutron captured in silicon, 0.04 P31 atom (therefore, 0.04 excess electron) are formed by radioactive decay. For every neutron captured in germanium, 0.098 As75, 0.012 Se77 (therefore, 0.122 excess electron), and 0.304 Ga71 atom (therefore, 0.304 excess hole) are ultimately formed, in this time sequence. Analysis of an experiment of J. W. Cleland on the decay of irradiated n-type germanium gives 0.8 electron removed from the conduction band per initially recoiling germanium atom.
Diffusion-Controlled Reactions in Solids
Authors: Reiss Howard
Published: April 2005

This paper contains a discussion of those diffusion processes commonly referred to as diffusion-controlled reactions. Attention is focused on those aspects of the phenomena to which special care must be given in developing theoretical analyses. The discussion is documented with several experimental examples drawn from the chemical physics of semiconductors, e.g., annealing of radiation damage, ion pairing, precipitation, and the formation of complexes in solids.
High-Energy Electron Irradiation of Germanium and Tellurium
Authors: Van Lint Victor A. J. , Roth Harold
Published: April 2005

Tellurium samples in which current flowed parallel to the c axis were irradiated at 78°K with 20-Mev electrons. The conductivity increased linearly with a slope of 1.0×10−14 (ohm-cm)−1 per electron/cm2 up to at least 3×1014 electrons/cm2. Beyond 3×1015 electrons/cm2 the slope was approximately one tenth of the initial value. The reciprocal of the Hall coefficient decreased at first and then increased. Between 1×1013 and 5×1013 electrons/cm2 1/RH increases linearly from 3×10−5 to 6.3×10−5 coulomb/cm3. After irradiation, the samples showed no measurable conductivity changes during 14 hr at 78°K. After a day's anneal at 300°K the 78°K conductivity returned to its preirradiation value.

N-type germanium was irradiated with 20-Mev electrons at room temperature. Conductivity measurements indicated that the sample became intrinsic and then p type. However, the detailed dependence of conductivity on radiation dosage did not agree with a calculation based on four energy levels introduced into the gap. Carrier lifetime changes were also observed.
Annealing of Radiation Defects in Semiconductors
Authors: Brown W. L. , Augustyniak W. M. , Waite T. R.
Published: April 2005

Radiation induced defects studied through changes in conductivity and Hall coefficient have been observed to anneal in a number of different temperature ranges. Only those processes occurring above 80°K and involving defects created by electron irradiation have been considered in this paper. It has been found that the first annealing process in n-type germanium occurs at about 50°C and is structure sensitive, apparently to the original chemical donor impurity. Higher temperature annealing processes, observed at about 200°C and previously interpreted as due to direct annihilation of vacancies and interstitials must also be sensitive to other crystal defects. In p-type germanium there is a process of rearrangement of a defect center at about 200°K, exhibiting first order kinetics, but with a time constant which is strongly dependent upon the charge state of the defect. At about 120°C the defects in p type apparently anneal out completely, in striking contrast to the n-type case. Less extensive silicon measurements, showing lifetime recovery between 200 and 400°C again indicate through their kinetics the importance of other impurities or defects in the annealing process.
Electron Microscope Studies on the Etching of Irradiated Germanium
Authors: Noggle T. S. , Stiegler J. O.
Published: April 2005

Electron microscope and electron diffraction studies on the surfaces of CP-4 etched germanium specimens have shown that the changes in etching behavior induced by fast neutron irradiation occur as a result of a gross change in chemical behavior and cannot be due to local variations in the etching rate in the vicinity of the structural defects introduced by the irradiation. Observations on network structures which are produced under certain conditions of etching indicate that these arise as a result of mechanical preparation of the surfaces or from changes in the etching process and are apparently unrelated to any prior substructure in the material.
Cross Sections for Atomic Displacements in Solids by Gamma Rays
Authors: Oen O. S. , Holmes D. K.
Published: April 2005

Cross sections for the displacement of lattice atoms by gamma rays for energies up to 5 Mev have been calculated. The principal contribution is found to come from the Compton effect, in which the atoms are displaced by electrons produced by the incident gamma rays. The calculations have been based on the assumption of a sharp threshold energy for displacement, but cross sections have been computed as a function of the assumed threshold energy. Thus, from the present work it is relatively easy to obtain cross sections based upon other displacement functions.
Texture of Evaporated NiFe Thin Films
Authors: Verderber R. R.
Published: April 2005

The texture of 28 evaporated NiFe thin films, of various compositions, were determined by the Geiger counter x-ray reflection technique. The grain orientation of the thin films is described by one of the following three textures; random, [111] fiber axis, or a [311] fiber axis. The development of a texture was influenced by the temperature of the substrate during deposition. The coercive force and the selectivity, which is a measure of the slope of the sides of the hysteresis loop, of the films were measured on a 60-cycle hysteresis loop tracer. Only the selectivity was found to be related to the texture of the films. Films with a [311] fiber axis had a selectivity less than 0.5, while films with a [111] fiber axis had a selectivity of 0.5 or greater.
Some Criteria for the In Situ Combustion of Crude Oil
Authors: Cooperman P.
Published: April 2005

This paper presents a steady-state theory for the in situ combustion of oil in an underground reservoir. The hydrodynamic, chemical, and thermal aspects are treated in their relation with each other. The major results are three criteria for successful forward burning. These criteria state the minimum values for the oil saturation, the carbon-hydrogen ratio, and the volume flow rate.
Correlated Collisions in a Displacement Spike
Authors: Leibfried G.
Published: April 2005

The influence of correlated collisions due to lattice structure is investigated for f.c.c. lattices and discussed in detail for Cu. The model used is that of Silsbee in which the assumed exponential potential between atoms gives approximately hard core collisions. Two possibilities which may cause long-range effects are investigated; (1) focusing collisions which are suggested not to effect an interstitial transport. (2) crowdion-like collisions with interstitial transport. The number of such collisions as well as their range is calculated for given energy of a primary knock on. The result shows that the range should be determined by the focusing collisions only. The theoretical range (about 100 atom spacings) is in agreement with the experimental value derived out of the damping experiments in Cu. The effect of crowdion collisions on disordering is discussed for Cu3Au.
Elastic and Plastic Behavior in the Impact of Cylinders against Plates
Authors: Backman Marvin E.
Published: April 2005

A theory of the indentation of a thick plate from impact by a flat-ended elastic cylinder is derived from elastic and plastic theories and compared to experimental values for 2024-T4 aluminum alloy, half-hard-naval brass and Armco iron. Plastic conditions in plates of the aluminum alloy are considered in detail by assuming an exponential increase in hardness to a maximum value. These results are sensitive to projectile length and are compared to experimental results for five projectile lengths.
Pulse Technique for Probe Measurements in Gas Discharges
Authors: Waymouth John F.
Published: April 2005

A pulse technique for making Langmuir probe measurements in gas discharges has been developed. The basic procedure consists in operating the probe 40–50 v negative with respect to the discharge, and pulsing it positive at a repetition rate of 60 cps. The probe current-voltage characteristic during the positive-going pulse is presented on an oscilloscope and the resulting trace is photographed. The phase of the pulse may be varied, so that the method is useful for studying 60 cps ac discharges as well as dc discharges. Positive-ion bombardment while the probe is strongly negative tends to sputter away contamination and make it possible to keep the probe clean while making measurements within one mm of an oxide cathode at 1000°C, despite rapid evolution of contaminants from the cathode. Together with the small size of the probes that can be used, this permits meaningful measurements to be made in the negative glow of an oxide-cathode low-pressure discharge of the fluorescent-lamp type. Measurements on such lamps are described which demonstrate the presence of energetic primary electrons from the cathode as well as secondary electrons in the negative glow.
Effective Antenna Temperatures Due to Oxygen and Water Vapor in the Atmosphere
Authors: Hogg D. C.
Published: April 2005

Calculations of the effective noise temperature at the terminals of a high gain antenna due to oxygen and water vapor in the atmosphere are given for the frequency range 0.5 to 40 kmc. In the 1 to 10 kmc band, the effective temperature increases from about 3° to 100°K as the zenith angle is increased from 0° to 90°. Calculated values of the total attenuation through the atmosphere are given.
Diffusion of Aluminum, Magnesium, Silicon, and Zirconium in Nickel
Authors: Allison Herbert W. , Samelson Harold
Published: April 2005

The diffusion rates of aluminum, magnesium, silicon, and zirconium, alloyed as single additives in nickel, have been measured at temperatures between 800°C and 970°C. The method consisted of measuring the weight gain caused by surface oxidation of the additive in a wet hydrogen ambient. The surface oxides were identified by electron diffraction. Grain size was about 0.05 mm in Al–Ni, Si–Ni, and Mg–Ni but less than 10−3 mm in Zr–Ni. The composite volume and grain boundary diffusion coefficients are given by DAi→Ni = 1.1 exp(−59 500/RT); DMg→Ni = 2.3×10−5 exp(−31 300/RT); DZi→Ni = 10.6 exp(−64 800/RT); DZr→Ni = 1×10−5 exp(−26 700/RT). Stereo and photomicrographs indicate considerable grain boundary diffusion, particularly in Mg–Ni and Zr–Ni.
Some Effects of Fast Neutron Irradiation on Carrier Lifetimes in Silicon
Authors: Beck R. W. , Paskell E. , Peet C. S.
Published: April 2005

Single crystal specimens of silicon have been exposed to fast neutrons from a reactor source to determine the room temperature effects of irradiation on carrier lifetimes. For highly n- and p-type material the approximate lifetime damage constants, defined as 1/τ=1/τi+αφ, are found to be αn=4.4×10−7 (nvt)−1 × (sec)−1 and αp=1.2×10−6 (nvt)−1 (sec)−1. Two possible positions of the dominant recombination level are 0.36 ev below the conduction band or 0.33 ev above the valence band. Further agreement with the value of αp has been obtained by measuring high level lifetime in silicon junction diodes.
Solubility of Oxygen in Germanium
Authors: Kaiser W. , Thurmond C. D.
Published: April 2005

The infrared absorption band at 11.7 μ corresponding to a germanium-oxygen molecular vibration is quantitatively correlated to the chemically determined oxygen content of germanium crystals. The solid solubility of oxygen is determined as a function of temperature and the precipitation of the second phase GeO2 is observed. Crystals containing about 1017 atoms per cm3 of dissolved oxygen have been prepared. The maximum solubility appears to be 2×1018 atoms/cm2. The heat of solution is 1.2 ev. Silicon in a melt of germanium acts as a getter for oxygen, resulting in the formation of SiO2; this observation is in agreement with thermodynamical considerations.
Diffusion in a Liquid Indium-Tin Alloy at the Eutectic Concentration
Authors: Paoletti A. , Vicentini M.
Published: April 2005

Self diffusion coefficients for the two tracers In114 and Sn113 in the liquid alloy indium-tin at the eutectic composition have been measured as a function of temperature in the range 200°C–450°C. The customary Arrhenius equation is used to describe the experimental results. For indium as a tracer we obtained D=(42.5±5.7) 10−5 exp(−2771±158RT)cm2/sec,and for tin D=(11.7±1.7) 10−5 exp(−1380±156RT)cm2/sec. It is possible that the large difference between the two activation energies could be associated with properties of the eutectic composition.
Proposed Fiber Cavities for Optical Masers
Authors: Snitzer E.
Published: April 2005

The use of dielectric waveguides in the form of small fibers as the mode selector in optical masers is considered. The fibers consist of a core of index of refraction n1 which contains the maser material, surrounded by a cladding of lower index n2. A comparison is made with the Fabry-Perot interferometer used as a cavity. The principal advantages of the fiber for maser applications are the mode selection and the stronger mode coupling. It is shown that for core diameters just small enough to support only the two HE11 modes, the fraction of spontaneous emissions into the waveguide modes is given approximately by 1.4 (n1−n2)/(n1+n2). This could make maser action possible at much lower power levels. The major disadvantage is the difficulty of pumping into the small volume of the fiber. Schemes to overcome this difficulty are discussed.
Kinetic and Experimental Basis of Flash Desorption
Authors: Ehrlich Gert
Published: April 2005

Techniques are developed for deriving both qualitative and quantitative information on the kinetics of gas desorption from measurements at continuously changing temperature. First- and second-order processes can be distinguished immediately by the constancy of the end point of the former. Quantitative values for activation energy and frequency factors are deduced from the experimental time-temperature curve and the instantaneous slopes of the evolution curve, even for systems with concentration-dependent rate parameters. It is shown that for multiple desorption peaks, qualitative detection is simplified by slow heating, but may result in interconversion. The experimental basis of desorption measurements using the Bayard-Alpert gauge is also analyzed, together with artifacts arising from negative pressures, bistable gauge operation, formation of new species in the gauge, and the delay in sensing density pulses transmitted through tubes.
Pulse Method for the Measurement of Thermal Diffusivity of Metals
Authors: Woisard Edwin L.
Published: April 2005

A pulse method for measuring thermal diffusivitity of metals has been developed. The temperature in an effectively infinite rod is zero everywhere up to the time t=0, when a very short heat pulse is introduced in the plane x=0. The subsequent temperature histories of several points at different distances from x=0 are recorded, and from these data the thermal diffusivity may be calculated. Since an experimental run lasts less than one minute, the requirements on the stability of the ambient temperature are not as stringent as in previously reported methods. The present method saves time without sacrificing accuracy, a maximum error of ±4% being estimated. Although this work was all done at room temperature, the specimens were mounted in a vacuum furnace which should permit measurements at elevated temperatures. The method was tested on commercial ``A'' nickel, giving a result in excellent agreement with previous values. Results are reported for four new steels developed by the Bethlehem Steel Company.
Uniformity of Electrical Current Flow in Cylindrical Semiconductor Specimens with Cylindrical Metallic End Caps
Authors: Simon R. , Cahn J. H. , Bell J. C.
Published: April 2005

The distribution of current is computed in a cylindrical semiconductor specimen provided with cylindrical metallic end caps of the same diameter as that of the specimen and electrical lead wires of much smaller diameter. Nonuniformity of the longitudinal current density of 1% or less can be obtained in specimens with electrical resistivities at least 200 times greater than that of the end caps if the lengths of the specimens are at least equal to their diameters and if the length of each end cap is at least 0.3 diam.
Electrical Resistivities of Nickel-Niobium Solid Solutions
Authors: Arajs Sigurds
Published: April 2005

The electrical resistivities of nickel-rich nickel-niobium solid solutions have been determined from liquid-helium temperatures to 1000°K. The Matthiessen rule is not obeyed at any temperature. The addition of niobium to nickel increases its ideal electrical resistivity when the alloy is in the ferromagnetic state but decreases it in the paramagnetic region. Dissolved niobium in nickel at liquid-helium temperatures causes considerably larger perturbation for the conduction electron transport than either copper or palladium.
Likelihood Detection of Small Signals in Stationary Noise
Authors: Rudnick Philip
Published: April 2005

An approximation to the likelihood ratio which may be used in detecting a small signal in stationary noise is derived. The result contains only low-order moments of the signal and only stationary properties of the noise; hence it is applicable without change of form to any sufficiently long observation period. In the Gaussian case, with the signal also stationary and both signal and noise power spectra continuous, the result represents passage through a linear Eckart filter, followed by square law detection and equal-weight smoothing.
On the Macroscopic Analysis of the Conducting Electromechanical Solid with Application to Cylinders Subjected to Axial Electric Fields
Authors: Geldmacher R. C.
Published: April 2005

In the present work, the ambient to melting phase of the problem has been examined from the standpoint of intercoupled electrical, thermal, and mechanical effects in order to establish the foundations for a theoretical solution, and to establish the intervals over which the solution is valid. Thermoelectric and electromagnetic effects were considered relative to their influence on the distribution of temperature and electric field within the conductor. Body forces resulting from the electromagnetic field were also considered and the corresponding stresses worked out.

The principal analytic result obtained is that for the nonlinear problem resulting from electrothermal coupling through temperature-dependent electrical conductivity. General solutions have been obtained for conditions of no heat loss at the boundary, radiation at the boundary (Newton's law of cooling), and the boundary fixed at the initial temperature.

Various examples of engineering interest have been worked out and the results are compared with solutions obtained assuming constant electrical conductivity.

It has been found that significant electromechanical body forces may be present under certain circumstances and it is shown that these body forces may play an important part in the breakup of wires subjected to large, suddenly applied fields.
Phenomenological Elastomechanical Behavior of Rubbers over Wide Ranges of Strain
Authors: Carmichael A. J. , Holdaway H. W.
Published: April 2005

Relationships have been developed which permit a relatively good description of the elastomechanical behavior of natural rubbers over the full range of deformations. These relationships were obtained by development of a general relationship set forth by Mooney. A stress function was obtained from which principal stresses may be evaluated for any given set of compatible strains. This theory was tested by applying it to experimental results of Treloar. It is demonstrated that by the insertion of relatively simple ``exponential type'' functions, a very good fit was obtained over the whole range of Treloar's data. In this form, the properties of natural rubber can be described by three parameters, A, B, and β. It has been found (to be demonstrated in a later paper) that there are unique relationships between A and β, B and β, and between β and rubber hardness for a range of natural rubbers from pure gum vulcanizates to the hardest of commercial natural rubbers.
Tunneling Through Thin Insulating Layers
Authors: Fisher J. C. , Giaever I.
Published: April 2005

The resistance of thin aluminum-oxide films has been measured as a function of the voltage across the film and of the film thickness as calculated from its capacitance. All films showed ohmic behavior at low voltages, and exponential rise of current at higher voltages, in qualitative agreement with R. Holm's theoretical calculations for tunneling through thin vacuum layers. However, the resistance was several orders of magnitude lower than either the bulk value for Al2O3 or the calculated value for tunneling through vacuum. By making use of an effective mass in the oxide equal to about19 of the electron mass, the calculated values for tunneling can be brought into line with the experimental results.
Energy Dependence of Radiation Damage in Tungsten
Authors: Muss D. R. , Townsend J. R.
Published: April 2005

The rate of radiation damage in tungsten is shown experimentally to depend on the energy of the incident deuterons almost as 1/E. The small deviation from the 1/E dependence is in a direction opposite to that predicted by the hard sphere model for secondary defect production.
Sputtering of Vitreous Silica by 20- to 60-kev Xe+ Ions
Authors: Hines R. L. , Wallor R.
Published: April 2005

Experimental values for the sputtering of quartz by xenon positive ions at flux densities of 2×1015 ions/cm2 sec in a vacuum of 10−5 mm Hg are found by measuring the volume of the sputtered cavity by means of interference fringe contours. The sputtering ratios are 0.706±0.061 at 20 kev, 0.85±0.13 at 30 kev, 1.78±0.13 at 40 kev, 1.74±0.12 at 50 kev, and 1.31±0.09 at 60 kev. The technique of volume measurement by interference fringe contours has an accuracy of ±2×10−8 cc and is estimated to have an ultimate accuracy of ±10−10 cc.
Thermoelectric Behavior of p-n Junctions
Authors: Cutler Melvin
Published: April 2005

Equations are derived, on the basis of an emission model, for the flow of carriers and electronic heat which occurs when a temperature drop as well as an applied potential exists across a p-n junction. The application of the equations is discussed for small-signal situations, where the Onsager relation is obeyed, as well as for large-signal situations. In particular, the efficiency of p-n junctions for thermoelectric conversion is compared with that of homogeneous semiconductors and thermionic diodes.
Iron Whisker Surface Rearrangements Resulting from the Hydrogen Reduction of Oxides and from Thermal Etching
Authors: Laukonis J. V. , Coleman R. V.
Published: April 2005

The hydrogen reduction of high-temperature oxidation products grown on iron whiskers produces iron surfaces whose topography depends on the orientation of the surface that was oxidized. The different topographies for {100} and {110} surfaces are shown, and the dependence is further illustrated on the polycrystalline iron surfaces which result from the heating of a single-crystal α iron whisker through its transformation temperature of 910°C. Rearranged surfaces covered with parallel striations and unusual dendritic surface structures are shown and discussed. Both the striations and dendrites are the result of thermal etching of a ``polycrystalline'' iron whisker at temperatures between 800°–1200°C.
Dislocation Contributions to the Modulus and Damping in Copper at Megacycle Frequencies
Authors: Alers G. A. , Thompson D. O.
Published: April 2005

The three elastic moduli of 99.999+% pure copper and their associated internal frictions have been measured at Mc frequencies between 4.2 and 250°K both before and after fast neutron bombardment. The changes produced by the irradiation were used to determine the dislocation contributions to the damping and moduli as a function of frequency and temperature. The dislocation damping showed the maximum predicted by Granato and Lücke to arise from the heavily damped bowing of dislocation loops. By calculating the resolved shear stress factors and measuring the dislocation density by etch pit counts, it was possible to determine the coefficient B which describes the viscous drag on a moving dislocation as well as the effective loop length l. The factor B was found to be 8×10−4 d sec/cm2 at 300°K and to decrease linearly with decreasing temperature, as predicted by Leibfried. The effective loop length appeared temperature independent and had a value of 3×10−4 cm in the sample examined most carefully.

Cold-worked single crystals of the same copper were also studied. Two Bordoni type peaks in the damping vs temperature curves were located at 135 and 60°K at 10 Mc. Activation energies of 0.113 and 0.05 ev were determined by using low-frequency data taken from the literature.
Seesaw Maser Operation
Authors: Forrester P. A. , Mims W. B.
Published: April 2005

Cross relaxation between adjacent intervals may be used to secure an advantage in maser operation comparable to that obtained by ``push-pull'' pumping. Equations for the rate of change of populations in a scheme of four levels (A,B,C,D) when AC is pumped and cross relaxation takes place between BC, CD have been formulated, and the steady-state condition corresponding to various assumptions regarding lattice relaxation times is discussed. In an experimental investigation of maser operation based on this scheme and using ruby as the active material, an inversion of 0.9:1 was obtained at a signal frequency of 14.5 kMc when pumping at 24.5 kMc.
Interpretation of Experimental Characteristics of Cesium Thermionic Converters
Authors: Carabateas E. N. , Pezaris S. D. , Hatsopoulos G. N.
Published: April 2005

Experimental V–I curves have been obtained from a 150-w cesium thermionic converter. Two different kinds of V–I curves can be clearly distinguished. One, corresponding to a collision-free type operation, is obtained when the cesium mean free path is of the order of three or more times the interelectrode spacing. The other, corresponding to a sheath-type operation, is obtained when the spacing is of the order of 30 cesium mean free paths. In the first case the log I vs V plot has the familiar shape observed by Hernqvist et al. [K. G. Hernqvist, M. Kaneisky, and F. H. Norman, RCA Rev. 19, 244 (1958)]; it consists of two straight lines meeting at the breakoff point. From such an experimental curve the difference in emitter and collector work functions and the emitter temperature can be readily obtained. In the second case the V–I curve has the standard shape of a sheath curve which is smooth without breakoff point and which shows saturation in the current for both the high positive and high negative values of the voltage. In the present work a method is outlined by means of which the difference in emitter and collector work functions, as well as the emitter temperature, can be determined from an experimental V–I curve of the second kind. With this method experimental data from the above-mentioned converter in the sheath-type operation has been successfully analyzed, and good agreement has been obtained between experimental results and theoretical predictions.
Etch Effects from Oblique-Incidence Ion Bombardment
Authors: Magnuson G. D. , Meckel B. B. , Harkins P. A.
Published: April 2005

It has been found that metallic surfaces of Cu, Au, Al, W, Ta, Mo, and Ni when bombarded with 500-v Hg+ ions at angles of incidence other than zero, exhibit a definite surface structure or pattern. This pattern consists of hillocks or spires oriented parallel to the direction of the incoming ion beam. In Cu and Ni, steps oriented perpendicularly to the ion beam were also found. This surface pattern provides visual evidence that the sputtering process at low ion energies is a momentum transfer process. Since redeposition of sputtered atoms on the hillocks and steps could be quite large, angle of incidence yield measurements could be in error unless they are made before formation of the hillocks.
Fracture of Brittle Solids. II. Distribution Function for Fragment Size in Single Fracture (Experimental)
Authors: Gilvarry J. J. , Bergstrom B. H.
Published: April 2005

The theoretical results of Gilvarry for the size distribution of the fragments in single fracture have been verified experimentally by fracturing spherical glass specimens under compression. The fragments were contained by a gelatin matrix to inhibit secondary fracture and thus make conditions conform as closely as possible to single fracture. Experimental values of the probability of fracture as obtained by sieve analysis show the predicted linear variation with the mean dimension x of the particles, over reasonably large intermediate ranges of the variables. It is shown that a logarithmic-normal distribution does not represent the experimental results. The over-all data exhibit three local maxima in the differential probability of fracture as a function of x, whereas the theory permits only two. Agreement in the number of peaks is obtained by subtracting the contribution to the over-all probability of those fragments containing original surface of the specimen, which yields the true probability considered in the theory. In this manner, reasonably complete agreement between theory and experiment for single fracture is obtained. For plural fracture (carried out without use of gelatin), two additional peaks exist in the curve of the over-all differential probability vs x, as compared to the case for single fracture. The theory of Gilvarry is confirmed down to a fragment dimension of at least 1 μ by means of an electrical counting instrument, and checked by direct microscopic sizing to 5 μ. The results yield numerical values of internal flaw densities, and thus provide a tool to study the distribution of Griffith flaws existing internally in a solid.
Reactions of Oxygen with Pure Tungsten and Tungsten Containing Carbon
Authors: Becker J. A. , Becker E. J. , Brandes R. G.
Published: April 2005

Oxygen was made to flow at constant rates through a system consisting of a tungsten ribbon, an ion gauge, and a conventional mass spectrometer. The ion gauge recorded total pressures while the spectrometer recorded partial pressures of O2, CO, CO2, H2O, and other gases. From the way these pressures changed with filament temperature and time, we computed absolute rates at which O2 was converted to WO3, CO, CO2, and O or evaporated as O2. The data show that the sticking probabilities, the adsorption and desorption energies, and the rates of reaction change drastically when all the surface tungsten atoms have made first valence bonds with the adsorbed species; they change again after second valence bonds have been completed. Other conclusions are: (1) On a clean W surface consisting of 311 and 411 planes and for oxygen concentrations less than 4×1014 atoms/cm2, the sticking probability is 0.14, the desorption energy is 4.6 ev, and the evaporation rate is proportional to θ12; for concentrations between 5–9×1014 atoms/cm2, the sticking probability is 0.04, the desorption energy is 2.3 ev, and the evaporation rate is proportional to θ22. (2) In the temperature range 1200–1600°K the rate of formation and evaporation of WO3 increases with p(O2) and with T; the activation energy is 1.1 ev. (3) From 2000–2400°K the rate of WO3 formation increases as p(O2)32 and it decreases with T. (4) Less than about 4% of O2 molecules which strike the hot surface are converted to WO3. Most of the molecules evaporate as O2. Only above 2200°K is any oxygen evaporated as O. (5) No CO or CO2 is generated if the tungsten is carbon free. (6) If the tungsten contains carbon, CO and CO2 are formed if the surface is covered with a layer of oxygen and the temperature is high enough. Every carbon atom that diffuses to the surface is oxidized. The diffusion rate of carbon is proportional to the concentration gradient and increases exponentially with (1/T); the activation energy is 2.2 ev. (7) Tungsten can be made carbon free by glowing it at 2200°K in oxygen pressures near 10−6 mm for 10–60 hr.
Hot-Cathode Magnetron Ionization Gauge for the Measurement of Ultrahigh Vacua
Authors: Lafferty J. M.
Published: April 2005

In order to extend the low-pressure limit of the conventional hot-cathode ionization gauge it is necessary, at a given emission current, to increase the ratio of the ion current to the x-ray photo-current. This ratio may be increased by increasing the sensitivity of the ionization gauge. The gauge may be modified to permit the electrons to travel in long paths before they are collected by the positive grid or anode. Under these conditions the probability of the electrons' colliding with an ionizing a gas molecule will be enhanced, and the sensitivity of the gauge will be improved with no increase in x-ray photoemission. To accomplish this a magnetron with a cylindrical anode was selected for the ionization gauge and operated in a magnetic field with an intensity of 2.5 times the cutoff value. Two end plates maintained at a negative potential relative to the cathode collect the ion current generated in the magnetron and prevent the escape of electrons. Positive ion emission from the cathode is suppressed by mounting a hairpin filament on the axis of the cylindrical anode and well removed from the region of the negative ion collector. A very low level of electron emission is used to prevent instabilities in operation and to give a maximum ratio of ion current to x-ray photocurrent. Mearurements of sensitivity and x-ray photocurrent indicate that the magnetron gauge is linear down to a pressure of 4×10−14 mm Hg. Ability to measure low pressures with the gauge appears to be limited by the sensitivity of the circuit measuring the low ion currents. The ion pumping speed was found to be 0.003 liter/sec under normal operating conditions. Magnetron gauges have been built with ceramic metal envelopes.
Optical Spectrum of the Sonoluminescence Emitted by Cavitated Water
Authors: Srinivasan Devanatha , Holroyd Louis V.
Published: April 2005

The optical spectrum of the weak luminescence produced when water is irradiated by an intense ultrasonic beam has been determined. Water saturated with argon, helium, oxygen, or nitrogen was studied with the use of 800-kc radiation. The spectral distribution of the luminescence was measured with a spectrometer and photon counter combination in the interval 2800–5500 A. The spectra are continuous and correspond to that of a blackbody. For dissolved argon and helium the equivalent temperature is 11 000°K, whereas for dissolved oxygen and nitrogen the temperature is 8800°K.
Field Solution for a Thin-Film Superconducting Strip Transmission Line
Authors: Swihart James C.
Published: April 2005

By using Londons' equations, the two-fluid model, and the classical skin effect for the normal component of the current, a sinusoidal wave solution is found for a superconducting transmission line. This solution gives a slow mode of propagation which is dependent on the ratios of the dielectric and superconducting film thicknesses to the penetration depth. At low temperatures and frequencies where the losses are low, the velocity is dispersionless even though there is a component of electric field in the direction of propagation. The solutions for velocity and attenuation vary continuously as one passes through the critical temperature into the normal state. The solutions are interpreted in terms of lumped circuit characteristics.
Stable-Oscillation Conditions for the Magnetic-Film Parametron
Authors: Sanders Richard M.
Published: April 2005

A parametron can be constructed utilizing a single-domain magnetic film with uniaxial anisotropy as the core of a nonlinear inductor absorbing energy from an alternating pump field applied in the plane of the film and delivering energy to a signal winding coupled to the film. Conditions for stable oscillations in such a device are derived in a small-signal approximation for two cases: (1) pump field parallel to the easy axis of film magnetization and signal winding coupled to the hard axis; (2) pump field parallel to the hard axis and signal winding coupled to the easy axis. A dc bias field parallel to the pump field is considered separately from the film anisotropy field. The Gilbert equation, as specialized by Gillette and Oshima for film geometry, is used to describe changes in the angle θ of the film magnetization. Results are: (1) relations among the bias field, film and circuit parameters, and the amplitude and phase of the pump field for a given oscillation amplitude in θ; (2) the output-signal voltage, current, and power; (3) power dissipation by the film; (4) the approximate amplitudes of harmonics in the oscillating variables; and (5) modifications in circuit parameters to approximate the film gyromagnetic and damping effects. These results are expressed in terms of two functions, completely describing the influence of all circuit parameters through the effects of signal-winding current components in phase and in quadrature with oscillations in θ. When plotted as quadrature components of a phasor in a rotating coordinate system, these functions provide graphical means for determining stability conditions, amplitudes and phases of the oscillating variables, and the range of useful operating frequencies
Production and Analysis of a Large-Diameter Plasma Beam
Authors: Meckel B. B. , Harkins P. A.
Published: April 2005

A continuously operating low-velocity plasma accelerator is described which has a beam diameter of 3.6 cm. The beam is produced by extracting ions from a discreetly generated singly charged ion plasma in the following manner: A fine wire mesh placed so that one side is exposed to the plasma acts as a solid flat cathode when given a negative potential. Some of the ions which are attracted to the mesh pass between the wires and stream into the region behind the mesh where they enter a field of thermionically emitted electrons. The resulting beam consists of a stream of parallel-flowing ions with a compensated negative space-charge atmosphere of randomly moving electrons. Beam densities of 2×108 ions/cm3 of 100-ev Hg+ ions are obtainable 15 cm from the extractor. Gas pressures are maintained which provide mean free paths which are long compared to the tube dimensions. The diagnostic techniques used to analyze the beam parameters are described. The system is versatile and may be altered to permit the use of other gases, pressures and ion velocities.
High-Angle Tilt Boundary—A Dislocation Core Model
Authors: Li James C. M.
Published: April 2005

The dislocation model of a symmetric tilt boundary is modified to take into consideration the stress field of the cores of the dislocations. It is found that such modification enables discussion of many properties of high-angle tilt boundaries including porosity, strain energy, intergranular fracture, grain boundary shearing, void formation, preferential melting, preferential diffusion, boundary migration, segregation, precipitation, amorphous behavior, continuous and discontinuous transition, etc., in terms of the interaction among the cores of the dislocations and the properties of the cores themselves. This is a first attempt to devise a working model capable of interpreting all the properties of grain boundaries. Unlike other models which are designed to have a few particular properties in a limited angular range, this model has the advantage of reducing to the dislocation model at low angles and of providing for amorphous behavior at high angles. The characteristic of a grain boundary of behaving as an ordered liquid of lower density is pointed out. The picture of a high-angle boundary is that it contains an equilibrium number of jogs which control many mechanical as well as thermochemical properties.
Diffusion in a Liquid Indium-Tin Alloy at Several Concentrations
Authors: Paoletti A. , Vincentini-Missoni M.
Published: April 2005

Self-diffusion coefficients for both In114 and Sn113 as tracers have been measured in the liquid In-Sn alloy at several concentrations. The temperature range investigated is the range 200°–600°C. The dependence of diffusiveness on temperature at constant composition can be represented by the customary Arrhenius equation for all the compositions investigated. The variation of diffusiveness with composition at constant temperature is also examined, and it gives evidence of a large difference in the behavior of the two tracers.
Effects of Doping Additions on the Thermoelectric Properties of the Intrinsic Semiconductor Bi2Te2.1Se0.9
Authors: Bennett L. C. , Wiese J. R.
Published: April 2005

An alloy of 70 mol % Bi2Te3−30 mol % Bi2Se3, or Bi2Te2.1Se0.9, is the intrinsic semiconductor of the pseudobinary system Bi2Te3–Bi2Se3. This V–VI alloy was doped with lead (Group IV) and iodine (Group VII) separately and together. The effects of the dopants are analogous to those produced by Group III or Group V impurities in Group IV elemental semiconductors, the lower Group impurity producing a p-type material and the higher Group impurity an n-type material. Plots of the Seebeck coefficient, electrical conductivity, and thermal conductivity are given as a function of impurity concentration and show that the separate effects of the impurities are countered when the impurities are in the lattice together in the same amount.

Doping was also done with silver and iodine, separately and together. The results indicate that the silver is in the lattice interstitially (lead and iodine substitutionally) and that the type material produced is dependent also on how the impurity atom enters the lattice.
Measurement of Noise Power Spectra by Fourier Analysis
Authors: Akcasu A. Ziya
Published: April 2005

The theory of the direct Fourier analysis with finite sampled data is developed. Formulas for planning a measurement for a specified resolution and accuracy are obtained. A quantitative comparison with autocorrelation analysis is given. It is shown that direct Fourier analysis can be applied equally well to attain comparable resolution and accuracy with the same amount of data. The computer requirements are also comparable in both cases.
Propagation in a Plasma
Authors: Clavier P. A.
Published: April 2005

The boundary conditions for a radio signal incident normally on a layer of plasma are discussed. It is shown that 10 different modes must in general propagate in the layer, instead of the usually assumed six. The 10 modes are obtained when the Langevin form of the force is used in Boltzmann's equation.
Measurement of the Electrical Conductivity and Dielectric Constant without Contacting Electrodes
Authors: Ogawa Tomoya
Published: April 2005

A method is developed whereby electrical conductivity and dielectric constant of semiconducting and dielectric materials without contacting electrodes can be measured. The principle of this method is that a specimen suspended in a rotating field with a fine fiber is rotated by the torque proportional to the electrical conductivity or the imaginary part of its complex dielectric constant, and the torque exerted on it by a linearly polarized field is proportional to the real part of its dielectric constant.

An analysis of the method and some preliminary measurements of conductivity, photoconductivity, the dielectric constant of cadmium sulphate crystals and the dielectric loss of the lamella containing CdS powder are presented. The latter shows the photodielectric effect.
Response of a Thermocouple Circuit to Nonsteady Currents
Authors: Arai Thomas T. , Madigan John R.
Published: April 2005

The response of a thermocouple circuit functioning as a Peltier cooler to time-varying currents was determined by assuming that the current density could be represented by the sum of a dc and a time-varying component. The time-varying component took the form of either an impulse applied at time t0>0, a square pulse lasting from t0 to t1, a step increase in the current at time t0, or a sinusoidal ripple superposed on the dc current. The increased current results in an initial thermal cold spike at the cold junction but the time-average temperature difference between the junctions is reduced unless the dc current is well below the optimum value. The possibility of using such thermal spikes in a very long wavelength infrared communications system or in synchronous detection is discussed. In the case of a sinusoidal ripple the temperature difference between the junctions may either follow the fluctuations in current or may not, depending on the time constant of the couple and the frequency of the ac signal. In the latter case the only effect is a reduction in the temperature difference between junctions by the additional Joule heating due to the ac component.
Effect of Freezing Conditions on the Thermoelectric Properties of BiSbTe3 Crystals
Authors: Cosgrove G. J. , McHugh J. P. , Tiller W. A.
Published: April 2005

The thermoelectric parameters α, 1/ρ, and 1/(K−Ke) of oriented polycrystals increase as the freezing rate decreases and as the temperature gradient in the liquid at the interface increases. The effects are primarily attributed to the variation in the degree of microsegregation produced in the crystals as a function of the freezing conditions.