bluuebunny/crossref_metadata_2025 huggingface dataset:
Cathodoluminescence of Ruby
Authors: Levine M. W. , Subramanian M.
Published: April 2005

The results of a series of experiments on the fluorescence of ruby excited by medium-energy (<25 keV) electrons are reported. Fluorescence output increases linearly with voltage after an initial ``dead voltage'' region. The radiation in the R lines reaches saturation at a current density of approximately 5 mA/cm2. The measured light output and efficiency are 500 W/cm3 and 1%, respectively. The spectrum obtained by electronic excitation is identical to the one obtained by optical excitation. The difference in the measured relaxation times between the optical and electronic excitations is presented. Based on the measurements made, the feasibility of laser action in ruby by electronic excitation is discussed.
Comparison of Langmuir Probe and Spectrometric Electron Temperature Measurements
Authors: Powers Robert S.
Published: April 2005

Langmuir probes, because of their convenience and their ability to give time-resolved measurements, are often used for temperature measurements in plasmas. Since probe results are subject to suspicion, we compare probe and spectrometric electron temperature measurements in a particular low-temperature plasma in which this is possible. We find probe temperatures to be significantly higher over an electron temperature range (measured spectrometrically) of at least 410° to 820°K.
Rotational Model for Constricted Magnetic Hysteresis Loops in Cubic Crystallographically Textured Materials
Authors: Hagedorn F. B.
Published: April 2005

Magnetic hysteresis loops are calculated in detail for cubic, crystallographically textured, magnetic materials. The assumptions required for this calculation are (1) magnetization reversal occurs only by irreversible rotation and (2) the magnetostatic and exchange interactions are sufficiently strong so that the magnetization direction does not change appreciably in going from one crystalline orientation to another within the textured material. It is found that constricted hysteresis loops result from this calculation for certain types of crystallographic texture which are similar to textures that are known to occur in hard-rolled magnetic materials. The nature of the loops depend sensitively on the texture. For example, a (11̄0) [112] type of texture implies a square loop, but a (11̄0) [113] type of texture leads to a highly constricted loop with zero remanence. Although no experimentally observed loops are known to be well described by this model, it is expected that conditions may be found to which the present model will apply, and the calculated loop properties are presented in a way to make them generally useful. In addition to certain textured materials, it is shown that these calculations pertain to single-crystal magnetic materials in which an induced uniaxial anisotropy exists. Constricted loops are thus predicted under certain conditions for single-crystal Permalloy thin films.
The Inert Thermometer
Authors: Erdmann Joachim C. , Jahoda James A.
Published: April 2005

A thermometer in contact with a test specimen is inert, if its heat capacity is not small compared with the heat capacity of the specimen. The response of the thermometer to a transient temperature of the specimen can then be described by a transfer function. This transfer function has been determined for the single thermometer and the differential thermometer in contact with a slab whose ends are at zero temperature. Significant simplifications arise, if the inertia of the thermometer is large. Some applications of the theory to calorimetric measurements are discussed.
Wake Fields of a Pulse of Charge Moving in a Highly Conducting Pipe of Circular Cross Section
Authors: Morton P. L. , Neil V. K. , Sessler A. M.
Published: April 2005

Expressions are presented for the electric and magnetic fields due to a pulse of charge, which may be oscillating transversely while moving down an infinitely long, highly conducting pipe of circular cross section. The expressions are evaluated at large distances from the pulse and the fields are shown to decrease algebraically in the distance behind the pulse. In the absence of transverse oscillations the longitudinal electric field varies as the inverse three-halves power of the distance; in the presence of oscillations the dominant field component is the transverse magnetic field, which decreases as the inverse one-half power. In the long-range limit the amplitude of the fields is proportional to the square root of the wall resistivity. The phase of the field associated with the oscillating pulse is shown to be the phase of the pulse at the time when it passed the point of observation.
Dislocation Structures in Cleaved Magnesium Oxide
Authors: Robins J. L. , Rhodin T. N. , Gerlach R. L.
Published: April 2005

Surface structures produced during cleavage of magnesium oxide are described and interpreted in terms of the production and motion of dislocations. The usefulness and applicability of the nucleation decoration technique to obtain high-resolution micrographs of surface structures is presented. The observed surface structures are described in terms of production and termination of line pairs associated with the cutting of screw components, the interaction of dislocation half-loops with the surface, and the occurrence of cross-glide and of dislocation multiplication.
Low-Temperature Excess Heat Capacity in Glassy Polymers
Authors: Reese William
Published: April 2005

Measurements of the velocity of longitudinal and transverse sound waves in polymethyl methacrylate and polystyrene are presented from room temperature to about 140°K. Using these values and values deduced from low-temperature elastic modulus measurements, it is shown that the measured heat capacity of these polymers is considerably larger than is predicted by Debye theory. This is interpreted as evidence of a low-temperature heat capacity anomaly similar to that observed in several other disordered solids.
Anisotropic Relaxation Functions and Strength of Oriented Solids
Authors: Moghe S. R. , Hsiao C. C.
Published: April 2005

Mechanical properties of a solid, especially a high-polymer solid, are formulated in terms of microscopic behavior as a result of deformation and orientation. The relaxation behavior of the oriented solid is obtained by considering statistically the viscoelastic microbehaviors. It is found that various anisotropic relaxation functions can be expressed as a single time-dependent function under certain conditions. The time-dependent macroscopic fracture strength is also analyzed for the oriented system using known results for a completely oriented system.
Light-Scattering Characterization of Polyvinyl Acetate Latex Films
Authors: Wilkes Garth L. , Marchessault R. H.
Published: April 2005

Light scattering from solid films of polyvinyl acetate latices was studied as a function of particle size distribution, surfactant and stabilizer content, as well as temperature of film formation. The two basic structural parameters from the Debye-Bueche theory were obtained: 〈η2〉, the mean square fluctuation in dielectric constant, and a, the average distance between fluctuations. It was shown that 〈η2〉 was due only to density fluctuations and increased with polyvinyl alcohol stabilizer content. Generally, increasing the temperature of film formation also caused 〈η2〉 to increase. When stabilizer was present the a parameter was of the same order of magnitude as the particle diameter. Over the range of film-forming temperatures, a was relatively constant for a given latex sample. For two of the four systems studied a distinct maximum in the angular scattering was observed. By means of surface replication and electron microscopy, observed packing periodicities in the films could be correlated with the first-order spacings calculated for the angular maxima from the Bragg equation. The data indicate that 〈η2〉 is a useful measure of latex film texture. The polymeric stabilizer seems to form a continuous matrix in which particles are embedded. It is a major factor determining film heterogeneity.
Scattering of Light by Films Having Nonrandom Orientation Fluctuations
Authors: Stein R. S. , Erhardt P. F. , Clough S. B. , Adams G.
Published: April 2005

A theory is developed for the scattering of light by a two-dimensional solid having correlated fluctuations in density and in the optic axis orientation of anisotropic scattering elements. The case of nonrandom orientation correlations is considered where the probability of a given angle between two optic axes depends upon the separation of the scattering elements r and the angle β which the optic axis makes with the interconnecting vector. It is shown that in addition to the density correlation function γ(r), three correlation functions T0(r), [T2(r) − S2(r)], and [T4(r) − S4(r)] are usually sufficient to describe the orientation correlations. The values of the latter two characterize the kind and amount of dependence of the scattered intensity upon the polarization directions ψ1 of the incident and ψ2 of the scattered light, while the dependence of these functions upon r characterizes the dependence of scattered intensity upon the angle θ between the incident and scattered beam.
Crystallization in Thin Films of Isotactic Polypropylene
Authors: Padden F. J. , Keith H. D.
Published: April 2005

Microstructure of spherulites of the monoclinic modification of isotactic polypropylene has been studied in thin films by transmission electron microscopy and electron diffraction. Centers of spherulites are found to consist invariably of complex arrays of intercrossing lamellae. Radiating from the central regions are frondlike growths which constitute the coarse arms that are visible by optical microscopy. Each of the fronds is composed of a cluster of ribbonlike leaders, each of which, in turn, is covered with dense arrays of lamellar branches. Electron diffraction shows that constituent lamellae of both central and frondlike regions are chain-folded single crystals. Diffraction from the central regions confirms a model proposed by Khoury in which parent and daughter branches intersect at an acute dihedral angle of 80° 40′. Morphological evidence suggests that the same branching relation is preserved in the fronds and indicates that branching is initiated on the thin (010) faces of the lamellae.
Kinetics of Crystal Nucleation in Molten Isotactic Polypropylene
Authors: Burns Joanne R. , Turnbull D.
Published: April 2005

The crystallization of polypropylene droplets was investigated with the optical microscope. It is found that the droplets will undercool approximately 100 deg (Tm0=178°C). The undercooling attained for most of the droplets is increased by 1.43 deg when the cooling rate is increased by a factor of 10. An isothermal experiment indicates that the droplets crystallize sporadically in time, and nucleation frequency of 1.5 (107) cm−3 sec−1 is found at 79.9°C. Conventional analysis of this data yields a value of Kv, the pre-exponential factor of the nucleation frequency, of the order of 1050, which is much higher than expected from the paraffin data. Analysis which treats the free energy of formation of the nucleus as a discontinuous function of the nucleus size yields the more reasonable value of Kv of the order of 1030, and a value of the surface energy perpendicular to the chain axes, δe, between 60 and 95 erg/cm2.
Solution Crystallization of Poly-3,3-Bis(Chloromethyl)-Oxacyclobutane
Authors: Garber C. A. , Geil P. H.
Published: April 2005

Poly-3,3-bis(chloromethyl)-oxacyclobutane crystallizes isothermally from dilute solution in the form of lamellar single crystals, whose shape and thickness depend on the crystallization temperature, along with a globular material of distinctly different morphology. The variation in crystal shape with crystallization temperature is suggested to arise from the presence of two different types of folds in a given fold domain, the relative number depending on the temperature. The globular material is believed to arise from a phase separation occurring during rapid quenching of the hot polymer solution to the crystallization temperature, the polymer-rich phase crystallizing as globules and the polymer-poor phase as single crystals.
Crystallography of Poly-p-Xylylene
Authors: Niegisch W. D.
Published: April 2005

Poly-p-xylylene prepared by the vapor-phase pyrolysis of di-p-xylylene affords a linear high-purity polymer whose crystalline transitions were characterized by x-ray and electron diffraction, mechanical creep studies, and differential thermal analysis (DTA). Two of the three endotherms observed by DTA correspond to the known alpha and beta polymorphs of poly-p-xylylene. The third, occurring at 270°C, is a reversible transition which is regarded as a smectic mesomorphic transition of the stable beta modification. Hence: α→ lim 220∘Cβ1⇋ lim 270∘Cβ2→Tm 420∘C (decomposition).Single crystals precipitated from alpha-chloronaphthalene were instrumental in characterizing the alpha and beta unit cells. The alpha modification is best represented by an orthorhombic cell with a=21.3, b=33.6, c=6.58 Å, for which the theoretical density is 1.141 g·cm−3 at 23°C. The beta modification is hexagonal, with a=20.52±0.05 Å and c=6.581±0.020 Å, having a theoretical density at 23°C equal to 1.153±0.005 g·cm−3. The fiber repeat distance consists of one chemical repeat unit in a fully extended configuration for both modifications. The high positive birefringence, particularly for the beta modification, reveals that the planes of benzene rings in neighboring molecules are steeply inclined to one another.
Thermal Initiation of Screw Dislocations in Polymer Crystal Platelets
Authors: Peterson James M.
Published: April 2005

It is shown that thermal fluctuations coupled with an applied shear stress can possibly yield a workable mechanism for the initiation of screw dislocations in polymer platelets. The activation energy of such a process lies at about 1 eV within the present knowledge of crystal elastic and dislocation parameters. This is approximately the energy required for such a mechanism to be successful.
Lamellar Crystallization and Melting of Polyoxymethylene
Authors: Carter D. R. , Baer Eric
Published: April 2005

Polyoxymethylene has been crystallized isothermally from the melt and from solution, and has been analyzed for the lamellar fold period as related to the melting behavior. The melt-crystallized samples gave intense low-angle x-ray and DTA peaks, and in addition produced weak x-ray reflections and shoulders on the DTA melting peaks. The strong peaks yielded Tm0(s)=210±10°C, and two independent methods of calculating δe(s) place its value at 150 erg/cm2 with a maximum variation of ±40 erg/cm2. A method of plotting the data is proposed which allows a determination of δ from the experimental data of about 14 erg/cm2. The weak peaks, although not as accurate as the strong ones, yielded Tm0(w)=182°±2°C and δe(w)=37±10 erg/cm2.

Dried single-crystal mats gave a single low-angle x-ray reflection which when plotted with the appropriate melting point caused the data to lie with the weak bulk data. A second, higher temperature endotherm appears upon slow melting of the single crystals. It has not yet been fully explained, but it appears to be related to an abrupt increase in fold period.
X-Ray Source-Image Distortion Technique for the Study of Crystal Distortion and Vibration
Authors: Young R. A. , Wagner C. E.
Published: April 2005

A technique is described which permits graphic display and quantitative determination of ultrasonic oscillation amplitudes, and of warping and other macroscopic strains, in crystals. An x-ray ``source image'' appears superimposed on the crystal image formed by one diffracted beam from a stationary crystal. ``Source-image'' distortion (SID) occurs on reflection from distorted regions of the crystal. X-ray sources ranging from 100-μ spots to 15-mm line sources interrupted by Soller slits have been used. The latter experimental arrangements bear some similarities to those described by Cullity and Julien, by Barth, and by Carlson and Wegener. Lattice tilts of ∼1′ and lattice strain variations (Δd/d) of ∼10−4 can be routinely detected and separately identified. The underlying crystal image often contains useful topographic information of limited quality.

SID photographs showing distortion produced in quartz plates by mounting clips, cements, cracks, and piezoelectric oscillations are presented. An example of direct measurement and mapping of vibrational amplitudes, e.g., 650±25 Å in one case, in piezoelectrically oscillating crystals is given. Oscillation mode characterization has been aided by the SID demonstration of a 180° phase relation in some cases and by both SID and topographic display of the pattern of vibrational activity.
The Cooperative Diffusion Effect
Authors: Lawrence J. E.
Published: April 2005

The mechanisms governing the abnormal diffusion of base dopant impurities (boron and phosphorus) in shallow double-diffused structures in silicon have been investigated. The cooperative diffusion effect is manifest in an enhanced or retarded penetration of the base region beneath a diffused emitter. The enhanced diffusion of acceptors in npn structures has been identified earlier as the emitter dip effect. The retarded diffusion effect and the enhanced diffusion of donor impurities in pnp structures have not been previously reported. The abnormal diffusion of base impurities appears to be governed by a physical interaction between the base atoms and the effects of lattice stress created by emitter impurities. The enhanced diffusion of base impurities is attributed to excess vacancies in the base region generated by dislocations moving away from the emitter. The retarded penetration of a base region is attributed to base impurities precipitating at the lattice disorder formed to relieve the emitter-impurity stress.
Laser Saturation of Photoconductivity and Determination of Imperfection Parameters in Sensitive Photoconductors
Authors: Bube Richard H. , Ho Ching-Tao
Published: April 2005

Saturation of photoconductivity is a valuable technique in the determination of imperfection parameters in sensitive photoconductors. Measurements of saturation of photoconductivity using high-intensity excitation from a ruby laser have been made on a single crystal of Cd(S0.5—Se0.5), selected for its band gap to give appreciable but approximately homogeneous excitation, as a function of temperature between 80° and 400°K. The density of sensitizing centers can be obtained directly from such measurements, together with information about the densities and depths of traps that influence the saturation process. For the crystal investigated, the density of sensitizing centers is 7×1015 cm−3. Knowledge of the density of sensitizing centers permits a direct determination of both photon absorption and electron-capture cross sections for these centers. Values obtained in this way are in good agreement with values independently determined.
Near-Ultraviolet and Visible Radiation from a Dynamic Pinch
Authors: Görög I. , Singer J. R.
Published: April 2005

The utility of a magnetically compressed plasma as a high-intensity light source was experimentally investigated in a dynamic pinch. The motion of the confined plasma column was studied both experimentally and theoretically throughout a wide range of parameters. It was found that the peak intensity of the emitted light in the 2000–6000 Å spectral region is maximum when the plasma reaches minimum radius at times comparable to the quarter cycle period of the discharge current. When the parameters are adjusted to give this mode of operation, a single high-intensity pulse, lasting approximately 2×10−6 sec, is emitted. The peak intensity was greatest with xenon as the filling gas. The absolute intensity of the light emitted from helium, air, argon, and xenon plasmas was also measured. The results indicate that a dynamic pinch arrangement can be employed to obtain peak intensities significantly greater than those available from conventional flashlamps. The time-integrated intensity, however, is limited by the inherently unstable nature of the pinched plasma, which restricts the pulse duration to a few microseconds.
Chemisorbed Oxygen Structures on the Rhodium (110) Surface
Authors: Tucker Charles W.
Published: April 2005

Eight different chemisorbed structures formed by oxygen on the (110) face of Rh are analyzed and discussed. Three are high-coverage coincidence lattices with rows of oxygen atoms parallel to the close-packed direction of the substrate and with O/Rh atom ratios of 5/4, 7/8, and 5/6. Two of the structures are formed by oxygen entering the open structure of the surface causing a rearrangement of the Rh atoms to form a combined oxygen and Rh lattice. The necessary Rh atom motions are small (0.7 Å) and the resultant structures form rows of O and Rh atoms, in the ratio of 1:2, normal to the Rh close-packed rows in a coincidence-lattice configuration. The remaining three structures are simple low-coverage structures formed at the end of depletion of the Rh lattice of its oxygen content produced by the original oxygen treatment of the surface. A wide variety of O–O contacts in chemisorbed structures formed on Rh and Pt surfaces is discussed relative to O–O distances observed in three-dimensional ionic crystals and in covalently bound radicals. The great majority of O–O contacts in the chemisorbed structures fall in the range of O–O ionic contacts. Two fall in the shortest range of covalently bound O–O contacts. When the variation in size with coordination number is considered, it is concluded that the observed O–O contacts fall in the range of, but do not distinguish between, ionic and covalent O-metal bonds.
Differential Step Response of Unipolar Space-Charge-Limited Current in Solids
Authors: Baron R. , Nicolet M-A. , Rodriguez V.
Published: April 2005

The small signal step response of unipolar space-charge-limited current in solids is analyzed for planar structures and for media in which the drift velocity of the charge carriers is either proportional to the electric field (thermal charge carriers) or is independent of the electric field (hot charge carriers). Results are reported in analytical and graphical form. Their features are discussed in terms of the underlying physical phenomena, as well as in the perspective of experimental applications. Cylindrical and spherical structures are not accessible to closed-form solutions by the approach.
Optical Density and Thickness of Graphite Lamellae
Authors: Myers G. E. , Montet G. L.
Published: April 2005

The optical densities of various thicknesses of graphite lamellae have been measured for light of wavelength λ=578 mμ. The thicknesses of the lamellae studied were determined by a shadowing technique followed by examination in the electron microscope. A value of ∼1.15 was obtained for the extinction coefficient k.
Elastic Interaction between Dislocations and Tetragonal Defects in Anisotropic Sodium Chloride
Authors: Graham L. J. , Sines G.
Published: April 2005

The elastic interaction energies between a calcium-cation vacancy pair and both a screw and an edge dislocation in a sodium chloride lattice are calculated using isotropic, semi-anisotropic, and anisotropic elasticity theory. The defect pairs considered have their axes along the 〈100〉 directions, the cation vacancy occupying a next-nearest neighbor position to the calcium impurity. They produce a tetragonal strain field in the lattice which interacts elastically with the stress field of both kinds of dislocations. The semi-anisotropic method introduces the single-crystal elastic constants by considering the defect pair as a force dipole. The interaction of the stress arising from this force dipole with the strain field of a dislocation as determined by isotropic elasticity theory is then calculated. For the other two methods of calculation the stress field of a dislocation in an isotropic and in an anisotropic medium are used. Dislocations in sodium chloride lie along certain high-symmetry directions thus enabling closed-form solutions for their stress fields in anisotropic materials to be obtained. Results of the calculations indicate good agreement between the isotropic and anisotropic cases and poor agreement between these two cases and the semi-anisotropic case. A comparison is made between the results of these calculations and the analogous situation of the interaction of dislocations with carbon interstitials in iron for which calculations have been made previously using isotropic and semi-anisotropic elasticity theories.
Filamentary Injection in Semi-Insulating Silicon
Authors: Barnett A. M. , Milnes A. G.
Published: April 2005

Double injection in semi-insulators causes a negative resistance regime. The voltage across the bulk material drops from the value necessary for the onset of negative resistance to a value that may remain fairly constant while the current increases by an order of magnitude or more. This region exists because the double-injection occurs initially along a filament in the bulk material. Its current growth is marked by a constant voltage region followed by an I vs V1.5–1.9 relation, somewhat similar to the V2 region predicted by Lampert and others.

The existence of filamentary breakdown has been inferred by very indirect evidence up to now, although Ridley has shown that it might be expected from considerations of energy. The present study shows the development and growth of double-injection filaments in semi-insulating silicon, by photographing them with their own recombination radiation. The silicon used was approximately 104Ω·cm at 77°K and contained 6×1016 cm−3 indium atoms as the deep acceptor responsible for the semi-insulating character.

A theoretical model is presented for the current density within the filament. The current densities observed by densitometer studies of the recombination radiation photographs are in reasonable agreement with this model. Experimental V−I characteristics are also predicted by the theoretical study.
Unipolar Space-Charge-Limited Current in Solids with Nonuniform Spacial Distribution of Shallow Traps
Authors: Nicolet M-A.
Published: April 2005

Models and analyses of unipolar space-charge-limited current (sclc) in the presence of traps usually assume that the distribution of the traps is uniform in space. It is demonstrated here that this assumption can be a critical one. Simple models with shallow traps are analyzed in detail to establish the fact. Planar, cylindrical, and spherical geometries receive equal attention. The results show that traps in the bulk of the base outside of the immediate vicinity of the emitter are of little significance to the V−I characteristic. The origin of this effect is discussed. A simple approximate treatment is derived. The results imply that the dc characteristic alone is an ambiguous tool for characterizing traps and their physical origin. Included as a byproduct are complete solutions of the V−I characteristics of trap-free sclc in all five distinct cases of the planar, cylindrical, and spherical geometries. Results are given both analytically as well as graphically.
Response of Si and GaP p-n Junctions to a 5- to 40-keV Electron Beam
Authors: Czaja W.
Published: April 2005

This paper reports the use of the scanning electron beam technique for a determination of diffusion lengths in Si and GaP p-n junctions and of the recombination cross section of dislocations in n-type Si. This determination is based on the measurement of the current generated in reverse-biased Si and GaP p-n junctions by an electron beam of 5–40 keV energy. After applying corrections for backscattered and secondary emitted electrons the junction current determined experimentally is compared with calculated values using known principles of charge collection in p-n junctions. Diffusion lengths on both sides of the depletion region enter the calculations as free parameters which are adjusted to fit the experimental data. The experiments described are directly related to the display of lattice defects previously investigated by the same technique.

Si p-n junctions: The experiments lead to a diffusion length profile in the phosphorus diffused n region which qualitatively can be understood from the concentration profile in the same region. An upper limit of the cross section for recombination at dislocations in n-type silicon has been determined as 1.9×19−12 cm2. The results support the mechanism of contrast creation in the scanning electron beam display of dislocations as proposed earlier.

GaP p-n junctions: Diffusion lengths on both sides of the space-charge region have been found to be at least in order of magnitude agreement with values determined by other experimental techniques.
Elastic Moduli of the Lead-Thallium Alloys
Authors: Alers G. A. , Karbon J. A.
Published: April 2005

The adiabatic elastic moduli of single crystals of lead containing 1%–17% thallium have been measured using the ultrasonic pulse echo technique. Data at room temperature, 77°, and 4.2°K were obtained. It was observed that increasing the thallium content decreased all the moduli in spite of the fact that the interatomic distance decreases with thallium additions. Values of the Debye θ0 parameter were calculated from the 4.2°K modulus values.
Thermal Behavior of Stacking Faults in Graphite Platelets
Authors: Major Schwab S. , Grosskreutz J. C.
Published: April 2005

Stacking faults were observed in graphite platelets by transmission electron microscopy over the temperature range 170° to 890°K. From measurements of fault widths w at various temperatures T, it was found that (1/w)(∂w/∂T)=+(2.6±5.2)×10−4(∘K)−1.This value was used to obtain the estimate (Kbp/γ)(∂/∂T)(γ/Kbp)=−(2.6±5.2)×10−4(∘K)−1,where γ is the stacking fault energy, K the elastic coefficient of the fault, and bp the magnitude of the partial Burgers vector. The essential temperature dependence of γ in graphite is of the same order as that of K, that is, (1/γ) (∂γ/∂T)∼(1/K) (∂K/∂T).
Transition Probabilities between Laser States in Carbon Dioxide
Authors: Statz H. , Tang C. L. , Koster G. F.
Published: April 2005

Radiative transition probabilities were investigated between certain vibrational levels of carbon dioxide. The number of levels studied was restricted to those that are directly or indirectly involved in the observed laser action. Vibrational wavefunctions were determined by diagonalizing large Hamiltonian matrices (up to 30×30). In the Hamiltonian, nonlinear forces were included and the potential energy contained terms up to fourth order in the normal coordinates. The dipole moment as a function of the normal coordinates was determined by comparing certain observed and calculated absorption coefficients. Reasonable agreement is obtained between theory and experiment for most transitions where experimental information is available. The radiative lifetimes of most vibrational levels were calculated to be rather long. Thus, radiative processes cannot account for relaxation times observed in laser action. Relaxation probably takes place during collisions with other molecules or light atoms. From gain measurements it is possible to determine the population difference between laser levels. In Q-switching experiments, half the energy stored in the upper maser state can be emitted in a short pulse. In thin tubes the energy content of a pulse can be 10−5 J/cm3 of gas used.
Optical Avalanche Laser
Authors: Young C. G. , Kantorski J. W. , Dixon E. O.
Published: April 2005

A neodymium-glass laser device is described which employs amplified spontaneous emission in a nonresonant system to obtain a high brightness output pulse. The spontaneous avalanche obtained was in a 70-nsec pulse of approximately 1-GW power confined to a 1-mrad-full-angle beam. The output brightness was sufficient to produce unfocused air breakdown. Included are design criteria and an analysis of the characteristics of the avalanche pulse.
Barium Vapor Activation of Oxide Cathodes
Authors: Springer R. H. , Anderson D. E.
Published: April 2005

Experimental results are presented for (BaSr)O cathodes exposed to a heated barium-covered surface. These results indicate that there is a maximum in the steady-state level of pulsed thermionic emission as a function of increasing barium source temperatures, when the oxide is at a much higher temperature. Analysis of these results in terms of nonequilibrium thermodynamics leads to the development of a model for the barium activation of oxide cathodes. This model considers the chemical reaction rate of barium with the surface of the oxide in terms of the entropy transferred when a barium atom reacts with the oxide. This leads to a time-dependent differential equation which is solved for steady-state conditions, for some of the transient behavior obtained in this study, and for the complete time response of a few alloy-based chemical reduction systems.
Random-Line and Hard-Sphere Models
Authors: Greet R. J.
Published: April 2005

The random placement of segments on an infinite one-dimensional line has been used as a model for several physical situations, including polymer crystallization and liquid and glassy-state structure. The average density of the end state of such a random configuration has been known for some time. The distribution of end-state densities is derived here. It is shown that the distribution of segment spacings is similar to a distribution of free volume which has been derived for a system of hard spheres. The configurational entropies predicted by the random-line and free-volume distributions are compared. A technique for including consideration of the vibrational entropy of a real system is identified. Experimental results with hard-sphere systems are compared with predictions of the random-line density-distribution function.
Dislocations in Silicon due to Localized Diffusion
Authors: Schwuttke G. H. , Fairfield J. M.
Published: April 2005

Dislocations generated by localized diffusions in silicon are investigated through x-ray diffraction microscopy. It is shown that dislocations are produced at the interface of diffused and undiffused silicon as a consequence of elastic strains resulting most likely from steep lattice-constant gradients. From the device point of view these dislocations are undesirable because their axes lie outside the diffusion plane; consequently they can cause device failure.
Electron Transfer Processes through Tantalum—Tantalum-Oxide Diodes
Authors: Flannery W. E. , Pollack S. R.
Published: April 2005

The electron transfer processes in thin-film diode structures of Ta–Ta2O5–Au have been studied. The structures were prepared by electron beam evaporation of tantalum at 10−6 Torr followed by plasma oxidation of the tantalum film to the desired thickness. The counterelectrode metal was then evaporated without breaking the vacuum. Current—voltage—temperature characteristics of these structures were studied. Tunnel emission was observed when the tantalum electrode was biased positively and Schottky emission was observed for the tantalum electrode biased negatively. Trapezoidal energy barrier models have been used by many authors to explain electron injection and transfer through extremely thin insulating films. Such a model is proposed here for the tantalum—tantalum-oxide system, and as is shown, it provides a self-consistent framework for describing both Schottky and tunnel emission electron transfer processes in these structures. Using this model, it was found that the barrier height at the parent tantalum oxide interface is 1.1 eV and the built-in voltage with a gold counterelectrode is 0.5 eV.
311 and 31̄1 Damped Spherical Ferrimagnetic Resonance Modes
Authors: Van Sant Oscar J.
Published: April 2005

The technique employed by Fletcher and Bell to obtain the potential functions of the various modes in undamped ferrimagnetic spheres has been extended to the damped case. Solutions for the potential functions, induced magnetic-moment vectors, and the power absorbed by the sphere in the 311 and 31̄1 modes are given when the Gilbert equation of motion is used to obtain the effects of damping. Sketches of these modes are shown along with graphs which describe the motion of the rf magnetic-moment vectors induced in the sphere.
Minimum-Energy Trajectory Method for Constructing Hysteresis Loops for N Coupled Films
Authors: Fulcomer E. , Chang H. , Finzi L. A.
Published: April 2005

By following the minimum-energy trajectory, stable and critical states can be calculated and M—H loops constructed for two coupled films in a more simple and direct manner than by the conventional methods. Furthermore, the method is shown to be applicable to a system of multiple films.
Electron and Ion Emission from Iridium in Lithium Vapor
Authors: Wilson R. G. , Wolf E. D.
Published: April 2005

The electron and ion emission characteristics of the adsorption system lithium on iridium are reported in the range of lithium arrival flux from 1013 to 1018 atoms/cm2·sec. The electron emission S curves exhibit a 2.80-eV heavily lithium-covered work function, no minimum in the composite work function, a 5.35-eV bare iridium work function, and a stronger dependence on lithium flux than for cesium. The surface ionization of lithium on iridium exhibits ionization efficiencies from 10%–35% and a critical temperature envelope, the slope of which yields 2.10 eV for the desorption energy of lithium ions from iridium at critical coverage.
Perturbation of Electron Energy Distribution by a Probe
Authors: Waymouth John F.
Published: April 2005

In order to determine electron-energy distribution in a plasma, the electron current to a probe is measured as a function of potential on the probe. If the rate of removal of high-energy electrons by measurement is comparable with the rate of replenishment by the various plasma processes, serious perturbation of the electron-energy distribution will result as a consequence of the act of measurement. A criterion for deciding when this effect may be ignored is presented herein. It is based on the hypothesis that when the depletion time constant τd of electrons of a particular energy by a given probe in a given plasma is large compared with the time for electrons to fill out a Maxwellian tail by Coulomb collisions as given by Montgomery and Tidman, perturbation of the electron-energy distribution is negligible. The depletion time constant is τd = 2.9V (mv2 / 2kTe) / (Ap·v), where V is plasma volume, Ap is the probe area, v is electron velocity, and Te is electron temperature. The criterion for no perturbation of the electron-energy distribution then becomes N»1.5 × 104 T2 Ap, in which N is the total number of electrons in the plasma, T is the temperature in degrees Kelvin, and Ap is the probe area in square centimeters. It is shown that even if the criterion is not satisfied, probe measurements of the electron-energy distribution may still be made by using a pulsed or transient system with pulses of length τp, provided 1/ωp « τp « τd, where ωp is the electron plasma frequency.
Some Surface Current Phenomena in Type II Superconductors
Authors: Ullmaier H. A. , Gauster W. F.
Published: April 2005

For a cylindrical sample of an imperfect type II superconductor in an external field Hext parallel to its axis, it is found that in the mixed state no flux enters or leaves the specimen within an interval Hext±ΔH; the positive or negative sign applies when Hext is reached in a decreasing or increasing field, respectively. Similarly, when the sample is cooled in a field Hext, an increase of the external field less than ΔH does not change the trapped flux.

ΔH depends only on Hext and not on B, the bulk flux density, which itself depends on the magnetic history of the specimen and its defect structure (flux pinning, bulk critical current). ΔH is affected by various surface treatments, such as machining and chemical polishing, but not significantly by metal plating.

The results can be explained in terms of an intrinsic surface critical current, and comparison with existing theoretical calculations yields reasonable agreement.
Thin-Film Piezoelectric Transducers used as Generators and Detectors of Microwave Phonons, with some Attenuation Measurements in SiO2
Authors: De Klerk J.
Published: April 2005

The manner in which thin-film piezoelectric transducers are used is determined by their intended application. Attenuation measurement transducers should be capable of independent generation of each of the three pure acoustic modes and should exhibit low electromechanical conversion efficiency, whereas device transducers should exhibit maximum possible electromechanical conversion efficiency. Multilayer transducers offer increased power handling capabilities and higher electrical impedances than single-layer transducers at high frequencies. An anomalous behavior of quartz in the presence of CdS is discussed. Attenuation measurements of the L, T1, and T2 modes along the X1 axis of synthetic quartz are presented.
Theory of Grain Growth in Porous Compacts
Authors: Nichols F. A.
Published: April 2005

Following a suggestion by Kingery and Francois, the theory of grain growth in porous compacts controlled by the migration of pores with the boundaries is developed for all possible transport processes. Contrary to the assumption of these authors, it is shown that the cubic rate law reported for both UO2 and Al2O3 compacts, if it is due to pore migration, must be interpreted as being controlled by vapor transport through the pore with the pressure maintained at 2γ/r, where γ is the surface tension and r the pore radius. Available data for UO2 and Al2O3 are analyzed according to this model and found to give satisfactory agreement, with the calculated activation energies being reasonably close to the heats of vaporization for the two oxides. An interesting prediction of the model is that the compact should in fact show a decrease in density during grain growth. This behavior has been observed in the case of UO2 but apparently has not yet been reported for Al2O3.
Damping Peaks in Deformed Nickel
Authors: Sommer Alfred W. , Beshers Daniel N.
Published: April 2005

The internal-friction spectrum of zone-refined nickel [R(273°K)/R(4.2°K)=600] has been examined at 30 kc/sec, in the temperature range 77°-350°K. Plastic deformation produces two prominent relaxation peaks, each the sum of several simple peaks. At 30 kc/sec, one peak, which occurs at 138°±7°K, has been identified as the Niblett and Wilks peak, and the other, which has its maximum at 248°±40°K, has been shown to be the Bordoni peak. Both peaks have been studied as a function of cold work, grain size, state of annealing, and strain amplitude.

One major result of these studies is a demonstration that the Bordoni peak is only large at low-to-moderate flow stresses and vanishes at high flow stress (greater than 50 000 psi) with the Niblett and Wilks peak being the predominant feature of the damping spectrum at the higher-flow stresses (greater than 30 000 psi). Moreover, the present results in Ni show such similarity to results obtained on deformation-induced peaks in bcc metals that, if the definition of the Bordoni peak given by Niblett and Wilks is broadened to include Ni, then the peaks in bcc metals can also be included under the definition. Arguments are presented to show that the Bordoni relaxation is best described by the Seeger—Paré hypothesis.
Upper Bound to the Energy of Cross-Tie Walls
Authors: Aharoni Amikam
Published: April 2005

A simple mathematical model is suggested for the magnetization variation inside a cross-tie domain wall in ferromagnetic films. The exchange and anisotropy energies are calculated analytically for this model. The magnetostatic self-energy is overestimated by adding essentially the contribution of volume charge at an infinite film thickness to the contribution of the surface charge at zero film thickness, and this gives an upper bound of about 10 erg/cm2 for the total wall energy at any thickness. Neglecting the volume charge yields an energy of 0.27 erg/cm2 for zero thickness, while neglecting the surface charge yields 7.7 erg/cm2 for an infinite thickness. The latter should be an upper bound for the energy in any thickness, if the energy is a monotonic increasing function of the thickness. The radius of a Bloch line is found to be of the order of 100 Å, while the distance between crosses is found to be of the order of 10-4 cm in Permalloy, which is of the order of experimentally observed values.
Thermodynamics and the Manley—Rowe Equations
Authors: Penfield Paul
Published: April 2005

An unproved hypothesis is made: a physical system obeys the Manley—Rowe frequency-power formulas if, and only if, it is reversible in the thermodynamic sense. A general proof of this hypothesis is not available, and the exact conditions under which it is true are not yet known, but it is demonstrated for a three-frequency upconverter pumped sinusoidally and exchanging noise at the other two frequencies.
Ultrasonic Attenuation in Cadmium Sulfide from 1.8° to 300°K
Authors: Lord A. E. , Truell R.
Published: April 2005

Ultrasonic attenuation measurements have been made at 12, 30, and 46 Mc/sec and from 1.8°K to room temperature on a cadmium sulfide specimen. The specimen had a dark room temperature conductivity of about 10-2 (Ω·cm)-1. A very large attenuation peak was observed in the neighborhood of 15°-20°K. Conductivity values showed that the peak is undoubtedly due to relaxation effects in the space-charge bunching caused by the acoustic wave, the mechanism proposed by Hutson and White.
Ballistic Demagnetizing Factor in Uniformly Magnetized Cylinders
Authors: Joseph R. I.
Published: April 2005

A simple, closed-form expression is obtained for the ballistic demagnetizing factor of a uniformly magnetized cylinder. Detailed comparison is made between the present results and both the previously derived series expansion (in which the radial variation of magnetization is neglected), valid for p(=length/diameter) ≥10, and the numerical extrapolation of the latter to the range 0≤p≤100. An alternate derivation of a result for the magnetometric demagnetizing factor of a uniformly magnetized cylinder is presented. Detailed comparison is made between the demagnetizing factors in the uniformly magnetized cylinder (ballistic, magnetometric) and the demagnetizing factor of an inscribed ellipsoid of revolution.
Impurity Effects on the Basal Plane Solidification Kinetics of Supercooled Water
Authors: Michaels Alan S. , Brian P. L. T. , Sperry Peter R.
Published: April 2005

Growth rates of ice on the basal plane from pure water and from dilute solutions of selected ionic salts, surfactants, and water-soluble polymers were measured by an improved technique of capillary crystallization for supercoolings ranging from 0.03° to 0.2°C. The corresponding velocities ranged from 10-6 cm/sec to 5×10-4 cm/sec. Corrections for bulk mass transfer and heat transfer effects were applied to the kinetic data.

The kinetic data for pure water, although in agreement with those of Hillig near supercoolings of 0.07°C, diverge from the earlier results toward lower velocities at both lower and higher supercoolings. The data nonetheless support the general conclusion of Hillig that growth of undamaged ice crystals on the basal plane proceeds by two-dimensional nucleation.

Both growth-rate enhancements (up to a factor of about five) and retardations (up to a factor of about three) were observed during crystallization in the presence of additives. The type of effect and its magnitude were dependent on the nature of the additive, its concentration, and upon the degree of supercooling. Certain effects of ionic salts appear related to freezing potential phenomena reported by several earlier workers. Growth acceleration, found to occur to varying degrees with all classes of additive, may have been a consequence of dislocations introduced in the crystal by the additive during growth.