bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Intensity Transmission X-Ray Topography of Homogeneously Bent Crystals
Authors: Meieran E. S. , Blech I.A.
Published: February 2004

Homogeneously elastically curved regions of otherwise perfect crystals are shown to give rise to area contrast images of the bent regions in transmission x-ray topographs of the crystals. In addition, the homogeneous bending causes contrast asymmetries in the localized images of defects or other small-strain fields in the Lang topographs of crystals. This intentional elastic bending of crystals containing defects will thus often provide a number of advantages over taking topographs of unbent crystals. For example, the exposure times may be reduced by more than an order of magnitude with little loss in resolution or contrast. Secondly, the sense of strain or Burgers vectors of defects may be determined even for thin or nonabsorbing crystals by using the intentionally bent portion of the crystal as a reference strain.
Annealing Effects on the Structure and Resistivity of Ni–P Films
Authors: Pai S. T. , Marton J. P. , Brown J. D.
Published: February 2004

Structural and electrical properties of electroless Ni–P thin films deposited on glass substrates were studied. Upon heating the as-deposited films in vacuum, the resistivity was observed to change drastically, accompanied by structural transformation of the film from a single-phase fcc Ni structure to a two-phase structure of fcc Ni and tetragonal Ni3P. The mechanism responsible for the changes can be described quantitatively by two different thermally activated processes. One is the annihilation of grain boundaries which decreases the resistivity, and the other process is the formation of Ni3P which tends to increase the resistivity. Results show that a large proportion of Ni3P is formed only above 300 °C. The activation energy of the processes was found to be both temperature and film-thickness dependent.
Behavior of Simple Screw Dislocation Arrays under an Applied Stress
Authors: Sadananda K. , Marcinkowski M. J.
Published: February 2004

A detailed numerical analysis has been made of the behavior of passing screw dislocation arrays on parallel slip planes as a first step in the development of a computer model of workhardening. It is found that in the absence of frictional forces, dislocations cannot pass one another since they form dipoles and become unstable. The introduction of frictional forces shows that for each dislocation there is a range of positions within which it is stable, and the actual position of the dislocation depends on its initial position as well as its direction of motion. The frictional-force concept is extended to determine the equilibrium separation of superlattice dislocations and to determine the relaxation of a pile-up in the absence of an applied stress. In order to determine unique positions for passing dislocations under an applied stress and a frictional stress, a model has been postulated in which the dislocations are generated from distant sources. Equilibrium configurations are determined as a function of the applied stress for a single source, as well as for two opposite sources on parallel slip planes. The stress-strain curves are developed for both cases, and the results are discussed in detail.
Atomic Mismatch on Closure of Controlled Partial Splits in Silicon
Authors: Khokhar R. U. , Haneman D.
Published: February 2004

It was previously shown that lattice restoration (``atomic healing'') was possible in the base regions of small partial splits produced in Ge and Si by a particular technique (``mating''). The upper portions of the split did not heal, presumably due to a degree of lattice mismatch on closing the split. In this work, x-ray moiré-type fringes have been measured in transmission topographs taken through mated Si structures. These indicate that very slight shear does take place, of about 0.6 sec of arc. This corresponds to a relative displacement of the two sides of the split of 30 Å at the entrance, and correspondingly less, deeper down the split. The measurements reveal why it is possible to obtain lattice restoration in the base of of the split, due to the negligible shear displacement in this region.
A New Analysis of Space-Charge-Limited Emission between Concentric Spheres and Concentric Cylinders
Authors: Porter J. H. , Franzen W. , Wenstrup R. S.
Published: February 2004

Space-charge-limited current flow between a small spherical cathode and a concentric spherical anode has been reexamined, taking into account the full energy and angle distribution of the emitted thermoelectrons. A similar analysis has been carried out for concentric cylindrical electrodes. On the basis of the theory thus developed, self-consistent iterative computations have been carried out to determine the variation of the potential and the space charge with radius at various cathode temperatures and fixed anode potential. The important effect of the initial angular motion of the thermoelectrons is demonstrated, and a comparison with other calculations is presented.
Spatial Depth and Density of Charge in Electrets
Authors: Sessler G. M.
Published: February 2004

A new method for determining the mean spatial depth and the density of charges trapped in charged dielectrics (electrets) is suggested. The method is based on (i) a measurement of the initial induction charge on a metal plate in proximity to the electret and (ii) a measurement of the displacement current obtained for discharge of the electret between contacting electrodes. The method can be used if charge carriers of positive and negative polarity are trapped in proximity to the two surfaces of the electret, respectively (mean depth of the charges less than about 20% of the foil thickness), if the retrapping time of both types of charge carriers is short compared to their transit time through the dielectric, and if dipole polarization is negligible. The method offers the possibility of determining charge depths in a wide variety of materials for which such data could not be obtained before. In addition, the method should also be useful for obtaining information about the retrapping kinetics in various dielectrics.
Measurement of Sputtered-Particle Velocity Spectra
Authors: Cowell G. K. , Smith Harold P.
Published: February 2004

A time-of-flight technique was employed to determine the velocity distributions of particles sputtered from polycrystalline copper targets by a 1- to 5-keV pulsed Cs+-ion beam. Velocity spectra were obtained for sputtered atoms having velocities greater than 2×106 cm/sec and for sputtered ions having velocities less than 3×106 cm/sec. In all cases, the target surface normal bisected the 64° angle between the detector and the incident ion beam, the target temperature was 20°C, and the flight path was 40 cm. Analytical models were fitted to the time-of-flight data. High-velocity emission was found to be described best by binary collisions at the target surface and low-velocity emission by Maxwellian distributions with temperatures predicted by C. H. Townes's theory of sputtering. It is proposed that the binary collisions (high-velocity particles) are responsible for preferred angular emission along close-packed crystallographic directions and that the low-velocity particles are responsible for the cosinusoidal component of the angular distribution.
Internal Friction in Copper Subjected to Neutron Irradiation and Fatigue
Authors: Strible Fred C. , Cady James R.
Published: February 2004

The internal friction of pure (99.999%) annealed polycrystalline copper has been studied as a function of fatigue and neutron irradiation. The fatigue was applied to wire specimens in rotating bending and the internal friction was measured at selected fatigue intervals by means of a torsional pendulum. The internal friction of unirradiated copper was found to change significantly with fatigue and the changes can be related by Granato-Lücke theory to dislocation generation, mobility, and interaction. These in turn can be related to present fatigue theories of slip zone development, dislocation pileup, and microcrack formation. The internal friction of copper subjected to fatigue after neutron irradiation is reduced due to dislocation pinning by irradiation-generated point defects, principally vacancies. Dislocation pinning in irradiated copper remains effective, in most instances, throughout the fatigue life. However, the fatigue strength of copper is not greatly changed by irradiation which suggests that the improvement in fatigue usually expected from the irradiation-induced reduction in dislocation mobility may be offset by other damaging effects of the neutron irradiation.
Optical Spectra and Laser Action of Neodymium in a Crystal Ba0.25Mg2.75Y2 Ge3O12
Authors: Miller J. E. , Sharp E. J. , Horowitz D. J.
Published: February 2004

Crystals of the garnet structured germanate Ba0.25Mg2.75Y2Ge3O12 have been grown doped with 2% Nd3+. The absorption, fluorescence, and excitation spectra have been measured at 300°K. The lifetime of the 4F3/2 state of the neodymium ion is 305 μsec at 300°K. Laser action was achieved at 1061.5 nm at room temperature.
Spacing of Photocurrent and External Emission Spectra Maxima in Electroluminescent Diodes
Authors: Eisencraft Marcus , Anderson R. L.
Published: February 2004

Expressions are derived relating the photon energy corresponding to the external emission peak of an electroluminescent diode to that of the photocurrent peak of the diode when used as a photodetector. The results are expressed in terms of the derivatives of the logarithms of the absorption coefficient and the internally generated emission spectrum with respect to photon energy. The predictions based on these relations are in reasonable agreement with the 0.01-eV peak spacing obtained for Zn-doped GaAs diodes. The 0.04-eV spacing observed for Si-doped units is thought to result from degraded emission and absorption edges resulting from the high degree of compensation.
Hot-Electron Impact Excitation of Tb3+ Luminescence in ZnS: Tb3+ Thin Films
Authors: Krupka D. C.
Published: February 2004

It is experimentally demonstrated in a new and direct manner that electroluminescence in thin films of ZnS: Tb3+ is excited by the direct impact of hot electrons on the Tb3+ ions. The scheme consists of monitoring as a function of applied voltage across the structure studied-a ZnS: Tb3+, Ta2O5 sandwich-the ratio of fluorescence intensities I(5D3)/I(5D4) originating from the 5D3 and 5D4 levels of Tb3+ at 3.25 and 2.54 eV, respectively. As the electron energy distribution is shifted to higher energies by increasing the voltage across the structure, I(5D3)/I(5D4) grows. The Tb3+ ion thus acts as a probe for the electron distribution in these films. By comparing the results obtained to simple theory, it is concluded that in considering low-energy losses of the electrons in the active layer, inelastic scattering by low-lying 7F levels of Tb3+ can not be the sole energy-loss mechanism at the Tb concentration of interest. The optical phonons of ZnS must also be taken into account.
Dielectric Properties of Semiconductors at Low Temperatures
Authors: Smakula A. , Skribanowitz N. , Szorc A.
Published: February 2004

The dielectric constant κ′ and the dielectric loss κ″ of p-type, n-type, and compensated Si have been studied at frequencies from 103 to 109 Hz and temperatures from 4.2 to 300 °K. At frequencies above 107 Hz, the κ′ decreases with temperature from 12.1 at 4.2 °K to 11.94 at 300 °K. In this frequency region, electronic polarizability of Si only is observed. At frequencies below 107 Hz the atomic polarizability of dopants (or impurities) is predominant. In this frequency range the κ′ and κ″ show strong variation with temperature and depend on the matrix material, the dopants, and frequency. At lowest temperatures the dopants are inactive and the κ′ corresponds to that at high frequency. By increasing the temperature, dipoles are activated and correspondingly, κ′ and κ″ are changed. Within about 10 °K, the κ′ reaches a maximum value and then remains constant, while the κ″ shows a relatively sharp maximum at the temperature where the κ′ curve goes through inflection. The temperature of κ″ maxima are for Sb, 18.0, 19.5, 21.5, and 23.5 °K; for B, 22, 24, 27, and 29 °K; for P, 25, 29, 33, and 38 °K; for B + P (compensated), 27, 31, 36, and 42 °K. The °K numbers correspond to the frequencies 103, 104, 105, and 106 Hz. The variation of κ′ and κ″ with frequency and temperature is explained by the Debye relaxation theory. From the relation of frequency and temperature of κ″ maxima, the following activation energies have been obtained: for Sb, 0.0431 eV; for B, 0.0410 eV; for P, 0.0427 eV; for B + P, 0.0431 eV. Our activation energy data correspond quite closely to the published data obtained by optical activation for the same dopants. In a very pure sample, 30 000 Ω cm, three κ″ maxima have been observed which may correspond to three excited levels. Some preliminary results for Ge, GaAs, and CdS are also given. Our results indicate that dielectric measurements are very suited for the study of semiconductors.
Direct Measurement of Impurity Distribution in Semiconducting Materials
Authors: Gupta Dinesh C. , Chan Joseph Y.
Published: February 2004

Differential capacitance-voltage measurements are commonly used to determine the impurity distribution in a semiconducting material whereby a Schottky or a diffused junction is reverse biased by a dc voltage. If the biased junction is driven by an ac current, the voltage generated by the diode contains first and second harmonics of the frequency of the driving current. The first harmonic is proportional to the depletion width and the second harmonic to the inverse of the impurity density, thus providing an absolute representation of the impurity distribution without any computations. The ratio of the amplitude of the second harmonic to the amplitude of the first harmonic, is, however, very small and separation of the second harmonic from the first harmonic requires a carefully designed circuit. The method and the electrical circuit is described in detail. Limitations of the technique and the methods for eliminating these limitations are also discussed.
Use of Ultrasonic Attenuation to Study Photoconduction and Optical Properties in CdS
Authors: Lomnes R. K. , Weichman F. L.
Published: February 2004

The photosensitive ultrasonic attenuation that is observed in CdS is examined as a possible tool for studying photoconduction and optical properties in piezoelectric semiconductors. The theory of Hutson and White, describing the acoustic attenuation due to the interaction of low-frequency lattice vibrations and mobile charge carriers, is adapted to fit the geometry of an experiment in which the change in the ultrasonic attenuation is measured when highly absorbed light is incident normal to the surface at which the acoustic wave is reflected. The equations developed predict that by measuring the photosensitive ultrasonic attenuation at different ultrasonic frequencies, calculations can be carried out to yield values for both the conductivity and the optical absorption coefficient. Some experimental results for the ultrasonic attenuation in CdS are reported. From these results, values for the optical absorption coefficient and the photoconductivity as a function of the wavelength of incident light are calculated and compared with similar results obtained by other methods.
Spin Configurations Induced by Strong Anisotropic Ions in Yttrium-Iron-Garnet
Authors: Hansen P.
Published: February 2004

The spin canting of Fe3+ ions induced by strong anisotropic ions such as 4d and 5d transition-metal ions in yttrium-iron-garnet has been calculated in a simple classical model. Strong deviations of the spins of the nearest neighbors from the direction of the average magnetization can occur in the case that the spin-orbit coupling of the anisotropic ion is larger than its exchange coupling to the Fe3+ neighbors. This especially implies a modification of the anisotropy contribution of the anisotropic ions. The canting will further cause a decrease in the saturation magnetization which becomes in addition anisotropic.
Comments on ``Measurement of NO and SO2 Raman-Scattering Cross Sections''
Authors: Reiss Nathan M.
Published: February 2004

The step-by-step procedure is presented whereby Raman-backscatter cross sections for gases are determined from electric polarizability, depolarization ratio, and the ratio of Raman intensity to Rayleigh intensity for 90° observation. Computations for N2 indicate a Raman-backscatter cross section of 1.9×10−30 cm2sr−1.
Electron Mobility in Hg1−xCdxTe
Authors: Scott Walter
Published: February 2004

The electron mobility in Hg1−xCdxTe has been obtained from Hall and resistivity measurements for x as high as 0.6, and in samples with carrier concentrations generally less than 2×1015/cm3. The room-temperature mobility was found to increase uniformly, as x was varied from CdTe, to a maximum value at the semiconductor-semimetal transition. With further reduction in x the mobility drops uniformly again to the HgTe value. Estimates are made of the contributions of various scattering mechanisms to the room-temperature mobility. The effects of optical-mode scattering were calculated for a nondegenerate parabolic band and were the right order of magnitude for compositions as low as x=0.20, but failed to fit the measured results accurately. The ionized impurity scattering mobility was also calculated, and the model of singly ionized donor scattering centers accounts very well for the low-temperature mobility. The results indicate that n-type Hg1−xCdxTe is not compensated to any large extent over a large range in compositions.
Domain Wall Mobility Enhancement Through X-Ray Irradiation Compared With Thermal Annealing
Authors: Shumate P. W. , Eisenberger P. M.
Published: February 2004

Flux-grown platelets of Sm0.55Tb0.45FeO3, cut perpendicular to the orthorhombic c axis, were irradiated with Mo x rays. Identical platelets were also thermally annealed in O2. Measurements of the room-temperature domain wall mobility as a function of exposure time or annealing temperature show remarkable similarities as the mobility is first increased 27% and then falls below its initial (as-grown) value.
Piezoelectric Effect in Teflon Cable
Authors: Zook J. D. , Liu S. T.
Published: February 2004

Preliminary measurements of the piezoelectric effect in commercially produced Teflon cables have been performed using simple static methods. The effective piezoelectric constants for both uniaxial strain and torsional strain were determined. The effect, though 2–3 orders of magnitude smaller than those of good piezoelectric materials, is potentially useful as the basis of inexpensive but sensitive strain transducers.
Epitaxial Growth of Pb0.918Sn0.082Se Films on CaF2 and BaF2 Substrates
Authors: Tao T. F. , Wang C. C.
Published: February 2004

Single-crystal (111) Pb0.918Sn0.082Se films have been deposited on cleaved (111) BaF2 substrates by both the flash and the one-boat evaporation methods. On cleaved (111) CaF2 substrates, single-crystal (111) films were obtained only when one-boat evaporation was used. At 87°K, mobilities up to 1.3×104 cm2/V sec have been obtained.
Piezoeletric Current from x-Cut Quartz Subjected to Short-Duration Shock-Wave Loading
Authors: Graham R.A. , Ingram G. E.
Published: February 2004

When an x-cut quartz disk is subjected to an impulsive load, the piezoelectric current in an external short circuit is ordinarily an accurate time-resolved replica of the stress history at the input electrode. Recently, it has been observed that stress pulses whose durations are less than the shock-wave transit time through the disk sometimes produce anomalous current-vs-time responses. In the present work, x-cut quartz disks are subjected to stress pulses of six different durations and with amplitudes from 9 to 29 kbar. Carefully controlled accurately known pulses are applied to the samples by the impact of projectile-mounted quartz disks of various thicknesses. The piezoelectric current accompanying each stress pulse is continuously monitored as the pulse propagates through the sample disk. It is found that the anomalous current is a consequence of shock-induced conductivity in the region of the quartz disk that has been shock loaded and subsequently unloaded to a lower stress value. The threshold for conductivity is found to depend upon both stress amplitude and pulse duration. The threshold is further determined to be controlled both by a critical unloading stress value and by a critical electric field value. The critical unloading stress value is found to be 11.2±0.7 kbar, and the critical electric field is found to be (2.8±0.3) ×105V/cm.
Existence of Dislocations at Domain Tips in Ferroelectric Crystal KH2PO4
Authors: Bornarel Jean
Published: February 2004

An analysis is made of the mechanical defects in KH2PO4 compatible with the crystal symmetry. With the theory of crystal dislocations, one can explain several experimental results on domain equilibrium states, domain velocities, and the critical electric field to move the domains in the plane perpendicular to the ferroelectric axis c. The most important result is the possible explanation in terms of mechanical phenomena of the long-range interaction between domains, and domain freezing at low temperatures.
Propagation of Electromagnetic Pulses in a Magneto-Ionic Medium
Authors: Hill David A.
Published: February 2004

Using the known steady-state solution for transmission of a plane wave normally incident on a magneto-ionic half-space, the time-dependent waveforms for an impulsive incident field are calculated by use of a numerical inverse Fourier transform. Curves are presented which show the dependence of the parallel and cross-polarized components on the static magnetic field and the distance from the interface.
Continuum Measures of Spall Damage
Authors: Davison Lee , Stevens A. L.
Published: February 2004

Following the introduction of the concept of continuous spall damage as a replacement for the customary discrete description, existing spall criteria are generalized to continuous measures of damage and are classified according to their dependence on the history of the continuum field variables. A compound-damage-accumulation theory is proposed in which the rate of damage accumulation depends on the existing damage, in addition to the applied stress. Several examples of the application of the new theory to the correlation of existing data are given.
Computer Generation and Identification of Kikuchi Projections
Authors: Young C. T. , Lytton J. L.
Published: February 2004

Computer programs were developed to provide for computer plotting of standard stereographic Kikuchi projections of any desired orientation and projection sphere radius for fcc (Al), bcc (Fe), diamond cubic (Si), and hcp (α-Ti) crystals. The programs also provide for automatic identification of Kikuchi poles as well as identification of individual Kikuchi lines. Indexing of observed patterns becomes a matter of comparison between the experimental patterns and the projections. Coates projections for scanning electron microscopy and transmission Kossel or pseudo-Kossel projections for x-ray diffraction studies can also be generated simply by changing the input wavelengths. The matrix algebra employed in producing the projections is presented, and the details of the computer programs are described.
Compressibility of Hexagonal Selenium by X-Ray and Neutron Diffraction
Authors: McCann D. R. , Cartz L. , Schmunk R. E. , Harker Y. D.
Published: February 2004

In order to resolve reported differences in the compressibility of hexagonal selenium, lattice parameters have been measured at pressures up to 140 kbar. Independent measurements have been made by neutron time-of-flight and by x-ray diffraction. The results from these methods are in good agreement. The a axis is found to contract, but the c axis expands with increasing pressure. Values obtained for the average volume, a-axis, and c-axis zero-pressure compressibilities are 49.7±15, 31.9±7, and −14.3±4×10−4 kbar−1, respectively. These results compare favorably with a correlation of bulk modulus and cohesive energy. The expansion of the c axis under pressure is comparable to the contraction of the c axis with increase of temperature.
Bragg Imaging with Finite Amplitude Ultrasonic Waves
Authors: Martin F. D. , Adler Laszlo , Breazeale M. A.
Published: February 2004

Light passing through ultrasonic waves of finite amplitude at the angle at which Bragg diffraction is dominant produces diffraction orders which contain images of the ultrasonic wavefront, with multiple images appearing in the higher orders. These multiple images are attributed to multiple scattering of light by the fundamental ultrasonic wave. The harmonics of the ultrasonic wave arising from nonlinearity of the propagating medium are isolated by use of a transmission filter plate. The images produced by them are larger than those produced by the fundamental.
Response of Interdigital Acoustic Surface Wave Grids
Authors: Daniel Michael R.
Published: February 2004

Using a basically simple model whereby an interdigital surface wave grid is allowed to transmit a fixed fraction of an incident surface wave per finger pair, expressions are obtained to describe the electrical output from the receiver grid of a delay line as a function of the number of rf cycles applied to the transmitter, the number of finger pairs, and the transmission coefficient per finger pair. Additionally, the variation of insertion loss for the delay line with the number of finger pairs on the receiver is computed. Agreement between these calculations and experiments performed on quartz and lithium niobate is good. The predicted envelope of the receiver signal is in poorer agreement with measurements.
Relativistic Solution of Maxwell's Equations in a Class of Conservative Flow Fields
Authors: Pogorzelski R. J.
Published: February 2004

Maxwell's equations are solved in spherically and cylinderically symmetric regions containing a dielectric medium moving radially with constant velocity. The solutions are correct to all orders in v/c and are obtained by appropriate modification of the corresponding solutions for zero velocity.
Optical Properties of MgO and MgF2 in the Extreme Ultraviolet Region
Authors: Hanson W. F. , Arakawa E. T. , Williams M. W.
Published: February 2004

Measurements of the optical properties of MgO and MgF2 have been extended from 29 to 80 eV. Reflectance and emission spectra were obtained for single crystals and transmittance spectra for thin films. The extinction coefficients for single crystals of MgO and MgF2 are relatively large (>0.07 up to 80 eV), and sum-rule calculations show the values to be reasonable. Structures in the extinction coefficients are identified as due to interband transitions from the core electron states to the conduction bands and to excitons associated with the Mg 2p to conduction-band transitions in the two materials. The optical constants are used to identify the nature of characteristic energy losses reported in the literature. The extinction coefficients of thin films of MgO and MgF2 are less than for the single crystals.
Ellipsometric Study of Ni–P Film Surfaces
Authors: Marton J. P. , Chan E. C.
Published: February 2004

Ellipsometric measurements were performed on the surfaces of freshly deposited, hydrogen annealed, and thermally oxidized electroless Ni–P deposits. Conventional interpretation of the parameters ψ and Δ for the oxidized samples, in terms of a homogeneous surface oxide film, was found possible only for a certain class of samples. For the remainder, the results suggested that changes of the surface region of the metal were caused by absorption and desorption of gases, rather than by a surface oxide formation. To facilitate better interpretation of ψ and Δ for all samples, the spectral reflectance of both surfaces of the deposits were measured with a spectrophotometer in the photon energy range 0.5–4 eV. An attempt was also made to establish the optical constants and the film thickness of totally oxidized films, to be used as a check on the ellipsometer results, without success. The results suggest a rather complicated oxidation process for Ni–P deposits with an inhomogeneous surface oxide film.
Brillouin and Rayleigh Scattering in Aprotic Laser Solutions Containing Neodymium
Authors: Pappalardo R. , Lempicki A.
Published: February 2004

Rayleigh and Brillouin scattering spectra have been measured at 6328 Å in aprotic laser solutions of neodymium containing SeOCl2 and POCl3. The intensity of the scattered radiation was mainly concentrated in the Rayleigh component of the scattering spectrum. The Rayleigh line was quite intense, while the intensity of the Brillouin line was comparable to that of benzene and other common liquids. The POCl3 laser solutions were generally stronger scatterers than the SeOCl2 solutions. Values of the scattering coefficients in the laser solutions have been obtained by comparison with the scattering spectra of benzene. This made it possible to derive values of the scattering losses at 1.06 μm. The values obtained are of ≃ 0.02%/cm. SeOCl2-based laser solutions exhibit Rayleigh-wing scattering. The width of the line indicates molecular reorientation times of the order of 50–100 psec. In POCl3-based solutions such processes appear to be much slower.
Theory of a Gas Laser with Internal Absorption Cell
Authors: Greenstein Howard
Published: February 2004

A single-mode gas laser containing an internal absorption cell is described theoretically, with special emphasis on those properties that make this configuration appropriate as a frequency standard. No use is made of perturbation theory, since its applicability to this problem is of restricted validity. Primary attention is devoted to (a) the ``inverted Lamb dip,'' the conditions for its existence, and its size, width, and shape, (b) the frequency ``self-stabilization'' effects, which are a consequence of the dispersive properties of the absorption medium, and (c) the nature of the solutions to the gain equation, including the hysteresis and ``hard-excitation'' effects. The parameter that measures the relative saturability of the absorption and gain media plays a central role in the theory, and it is found that those properties of interest from the point of view of frequency stabilization are generally optimized if the gain and absorption media saturate at comparable rates.
Barrier Energies in MIM Structures from Photoresponse: Effect of Scattering in the Insulating Film
Authors: Lewicki G. , Maserjian J. , Mead C. A.
Published: February 2004

Scattering of electrons photoexcited into the insulator conduction band prevents photoresponse from following the Fowler relation in MIM structures. However, barrier energies can be obtained without specific knowledge of the scattering process either by measuring the threshold for photoresponse directly, or by applying sufficiently large voltages across the insulator.
Stimulated Emission of Polaritons
Authors: Mahr Herbert , Tang C. L.
Published: February 2004

The gain of optically pumped CdS lasers is calculated assuming that stimulated emission occurs with photonlike polaritons created in inelastic exciton-exciton collisions; it is shown that gain constants of the recently observed magnitude can be expected from this mechanism.
Growth of High-Purity Single Crystals of Magnesium
Authors: Hayden S. C. , Faust J. W. , Brickwedde F. G.
Published: February 2004

An apparatus is described for the growth of magnesium crystals of extreme purity and perfection. The technique involves vapor growth by sublimation under high-vacuum conditions using magnesium itself as a getter. Crystals two orders of magnitude better than the best commercially available have been grown.
Thermostimulated Conductivity and Trapping Centers in Irradiated MgO
Authors: Mallard W. C. , Crawford J. H.
Published: February 2004

Thermostimulated conductivity (TSC) measurements, reinforced on occasion by thermoelectric power measurements, have been made on gamma-irradiated MgO crystals from several sources after a variety of thermal treatments. It has been confirmed that the TSC peak near 90°C is associated with the escape of holes from V− centers. In addition, a persistent electron current extending to below 200°K was observed in relatively high-purity (low-iron) crystals which appears to be associated with shallow electron traps. The free electrons responsible for it are inhibited from recombining with holes in V− centers by Coulomb repulsion. Annealing and air cooling from 1400°C eliminates this electron current and suppresses the over-all amplitude of the thermally stimulated current. The cause of this suppression and the relative insensitivity of the TSC curve to thermal treatment below this temperature are examined on the basis of a simple kinetic model.
Effect of Secondary Infrared Irradiation on the Photoelectron Energy Distribution Curve of Cesiated Silicon
Authors: Ebina Atsuko , Sakaue Tatsuo , Takahashi Tadashi
Published: February 2004

Effects of secondary ir irradiation of which photon energy is slightly higher than the indirect band-gap energy on photoemissive properties of cesiated Si crystals are given. Measurements were made for p+-, p-, and n-type cesiated Si. In the case of the samples which had absorbed metallic cesium by the ampoule method, it was observed that the ir irradiation had little or no effect on the quantum yield of the photoemission for all types of samples, but did cause a shift of the photoemitted EDC (energy distribution curve) towards higher electron energy and at times narrowing of EDC for p+- and p-type samples. ir irradiation had no effect on the n-type sample. Maximum shift of the low-energy cutoff of EDC was observed for the ir of 1.25 eV, and it was about 0.4 eV. By the analysis of the ir effect on the photoemitted EDC, the electron escape length was estimated to be about 65–75 Å for photoelectrons excited by a light of 2.6–3.4 eV.
Quasistatic Deformation of Solids with Pressure
Authors: Schock R. N. , Duba A. G.
Published: February 2004

The stress-strain behavior of several solids as a function of confining pressure to 4 kbar is determined by applying a fluid pressure of up to 5 kbar to the ends of cylindrical samples, thereby eliminating nonuniform stress fields that result from loading with a solid piston. The initial shear modulus μ of Pyrex glass is determined to be 255 kbar with δμ/δP=−2.15. Data are also presented on the deformation of Armco iron, polymethylmethacrylate, Westerly granite, and Solenhofen limestone. Hysteresis in the granite axial stress-strain data is attributed to the influence of elongate cracks that are closed with increasing confining pressure. The stress-strain curves for the limestone as a function of confining pressure show evidence of microfracturing from the distortion of the anisotropic calcite grains.
Approximate Method for the Motion of Dislocations among Random Obstacles in the Presence of Viscous Drag
Authors: Das E. S. P. , Gururaj P. M. , Richman M. H.
Published: February 2004

The motion of dislocations among random obstacles in the presence of a viscous drag is studied using techniques based on von Kármán's integral method for fluid flow problems. An approximate method is developed for the case of a dislocation bowing between two discrete obstacles, and examples are presented to illustrate its application to various arrays of obstacles with a continuous force field (both attractive and repulsive) of random strengths. The approximate method gives sufficiently accurate values for such parameters of interest as average velocity, total strain, strain rate, penetration distance, and breakthrough time at a given obstacle.
Dynamics of High-Velocity Jet Generation with Compressible Liquids
Authors: King Walter F. , Politzer Jay L.
Published: February 2004

A one-dimensional analysis of gas-driven accumulators capable of generating high-velocity water jets is presented. An equation of motion is derived for a model that approximately accounts for nozzle profiles and compressibility of the liquid. Numerical results are given for two accumulator configurations.
Moduli of Crystalline Polymers Employing Composite Theory
Authors: Halpin J.C. , Kardos J.L.
Published: February 2004

Crystalline polymers are hypothesized to behave, with respect to their physical properties, as a multiphase composite solid. Two experimental model systems are employed to illustrate this concept. Illustrative calculations are then presented which employ the micromechanics and macromechanics available in composite theory to develop a property-structure calculation for the influence of supermolecular structures on stiffness properties. Additional formal comments are then made upon the permissible theoretical techniques in obtaining sensible estimates of the mechanical properties of a heterogeneous material.
Thermal Modulation of HgS Edge Absorption
Authors: Abkowitz M. , Pfister G. , Zallen R.
Published: February 2004

The propitious location and temperature dependence of the absorption edge of trigonal HgS have been exploited for thermal modulation of the 6328-Å He–Ne laser line.
10.6-μm Laser Beam Absorption by a Particulate Cloud
Authors: Leib Kenneth G.
Published: February 2004

Absorption effects on a laser beam due to crosswind have been observed by using particulate clouds. The results support workers in the field who established the criteria for crescenting and beam movement into the wind. Fluidized particulate Ca(OH)2 was found to have an absorption four orders of magnitude greater than the fluidizer CO2 used alone.
Addendum to the Paper ``Tunnel Effect in Al–Al2 O3–Al Junctions: Inclusion of Short-Range Forces''
Authors: Sarnot S. L. , Dubey P. K.
Published: February 2004

It is remarked that the tunnel thickness of Al–Al2O3–Al junctions (and in general MIM junctions) should be calculated from capacitance measurements using the static value of the dielectric constant and that, therefore, the correction factor for thickness (i.e., Kopt/Kstat) used in the above-titled paper should be dropped.
Oxidation of n-Type Silicon in the 10–1400-Å Oxide Thickness Range
Authors: Smith Tennyson , Carlan A. J.
Published: February 2004

The oxidation of the (111) surface of n-type silicon in oxygen and in steam has been followed by ellipsometry in the film thickness region of 10 to about 1400 Å. For very thin films (<300 Å), the real part of the complex index of refraction proves to be 4.08±0.02 as compared to 4.05 for films >300 Å. Oxidation between 30 and about 60 Å follows a logarithmictime relationship. As the film thickens above this the rate accelerates then decreases and the data do not follow any of the usual thickness-vs-time relationships. As a first approximation the average rate of oxidation (up to about 500 Å) is proportional to the square root of the oxygen partial pressure. Between about 890 and 1100°C the activation energy proves to be about 22 kcal/mole.
Reply to ``Comment on `Temperature Dependence of Hole Velocity in p GaAs' ''
Authors: Dalal V. L. , Dreeben A. B. , Triano A.
Published: February 2004

It is shown that our experimental data on hole mobility in p GaAs are self-consistent and are not influenced significantly by impurity scattering, contact resistance, or light-hole magnetoresistance.
Thermal Expansion of Iridium at High Temperatures
Authors: Halvorson J. J. , Wimber R. T.
Published: February 2004

The linear thermal expansion of iridium was measured in the range 891–2221 °C. The following equation was found to fit selected earlier results and the present results over the temperature range 30–2221 °C: 100(Lt−L0)/L0=616.7×10−6t+151.9×10−9t2−28.16×10−12t3+14.63×10−15t4for t expressed in °C. Thermal expansion coefficients and average coefficients of expansion were calculated.
Ultrasonic Elastic Constants of Carbon Fibers and Their Composites
Authors: Smith Robert E.
Published: February 2004

The elastic constants of carbon-fiber-reinforced composites have been measured with an ultrasonic immersion technique. Both carbon and graphite fibers were studied. These fibers were derived from both rayon and polyacrylonitrile (PAN), and had Young's moduli ranging from 6 to 80×106 psi. The composite elastic constants varied with fiber modulus and fiber type (carbon or graphite) but not with the fiber-matrix bond. The fiber elastic constants c11 and c66, corrected for porosity, varied with fiber modulus but not with fiber type. The fiber constants c44 and c13 were independent of fiber modulus but varied with fiber type.
Measurement of Arc Electrode Temperatures and Reignition Characteristics
Authors: Murooka Y. , Hearne K. R.
Published: February 2004

The electrode temperatures of graphite during the arc and post-arc periods associated with the recovery characteristics in argon were measured. The photoelectric pyrometer used was sensitive to ir rays (corresponding to 1000–4000°K), but insensitive to the rays radiated from the arc plasma. The anode drop relating to the anode temperature was derived as 2.9 V for the quiet arc where the evaporation and radiation losses were considered to be small, and the electron current density derived from the arc-root diameter at the cathode was found to be much larger than that derived from the Dushman-Richardson equation, and had to be considered even in case of refractory electrode F-T (field and thermionic) electron emission mechanism. On the other hand, the polarity effect on the reignition tests suggests that when the cathode temperature increases above about 1600°K, Paschen's law will fail.
Space-Charge Flow with Unrestricted Variation of Current Density and Energy Range
Authors: Hart Philip J. , Wolford Dan L.
Published: February 2004

A fast but accurate relativistic method for determining the time variation of potential and field distributions, electron trajectories, and space-charge-limited current between parallel conducting walls is described. No limit is placed on how broad the energy spectrum of the emitted electrons may be, or in what manner the energy distribution and intensity may vary with time. A major simplification results from performing the basic calculations in terms of scalar potentials rather than vector fields. The emission of a group of charge sheets representing the existing energy spectrum is assumed for each closely spaced time interval. The incremental advance of each sheet is found from its starting velocity and acceleration as functions of the momentary potential distribution curve and of its past variations by a procedure which also compensates for ``self-field'' effects. The new sheet positions define a new potential curve and the process is repeated. Trajectories calculated for monoenergetic electrons agree with previous analytic solutions. For the first time trajectories are calculated for electrons injected with rapidly varying current density and a broad energy range. The method was developed for electron emission resulting from energetic photons but has general applicability.
Laminar Elastico-Viscous Source Flow between Parallel Porous Disks
Authors: Roy Jyotirmoy Sinha , Das Jatin , Mishra Shankar Prasad
Published: February 2004

The steady-state laminar source flow of an incompressible elastico-viscous liquid between stationary infinite porous disks is considered. The suction or injection velocities at the disks are assumed to be uniform. The flow phenomenon has been characterized by the nondimensional parameters S (elastic number), R (wall Reynolds number), and Re* (reduced Reynolds number). The solution obtained is in the form of a perturbation from the creeping flow solution and is valid for small values of R and also for small values of Re*. The effects of the above parameters on the velocity distribution, shear stress, and the radial pressure variation have been studied.
Radial Distribution Studies of Glassy GexS1−x Alloys
Authors: Rowland S. C. , Narasimhan Subha , Bienenstock A.
Published: February 2004

X-ray diffraction radial distribution studies of glassy GexS1−x alloys, with x=0.33 and 0.42, have been performed. The interatomic distances in the x=0.33 sample, 2.2 and 3.55 Å, are consistent with those in the covalently bonded crystalline GeS2. The distances in the x=0.42 sample, 2.3 and 3.65 Å, are also consistent with covalent bonding, and show no relationship to those found in crystalline GeS. No evidence of a previously proposed octahedral coordination of Ge can be found. A tentative explanation for the existence of two separated glass-forming regions in this system is put forth.
Electron Trapping in Neutron-Irradiated Silicon Studied by Space-Charge-Limited Current
Authors: Quat Vu Thuong , Nicolet Marc-A.
Published: February 2004

The trapping and detrapping of electrons is studied through measurements of space-charge-limited current in the temperature range 77≤T≤293°K in high-purity silicon after irradiaton with 14-MeV neutrons at a dose of about 1.2×1011 neutrons/cm2. A model is developed which describes most of the results quantitatively and self-consistently, including dc characteristics. Two distinct trap levels exist: The ``fast'' levels lie at Etf=0.14±0.005 eV below the conduction band, with a concentration of Ntf≃1.4×1012 cm−3 and a capture cross section of σf≃4×10−17 cm2 at 77°K. The ``slow'' levels lie at Ets=0.47±0.01 eV below the conduction band, with a concentration of Nts≃1.6×1012 cm−3 and a capture cross section of σs≃1.4×10−14 cm2 at 293°K. At 77°K, injected free electrons are initially captured by the fast 0.14-eV traps and then sink into the deep 0.47-eV traps, predominantly without being reemitted into the band. Above approximately 110°K, the detrapping rate from the shallow traps becomes so fast that the deep traps dominate. The results also offer a direct verification of the simple model of space-charge-limited current dominated by shallow and deep traps. Some pertinent unresolved questions are also formulated.
Dielectric Relaxation in Insulating Layers on Contaminated Langmuir Probes
Authors: Olson Robert A.
Published: February 2004

Measurements have been made of the low-frequency admittance of contaminated Langmuir probes in a mercury-vapor plasma. It was found that the probe admittance components were frequency dependent and could be represented by an equivalent electrical circuit corresponding to a metal-insulator-plasma configuration. The frequency dispersion of the admittance components is described by the empirical equation Y=G∞−(G∞−G0)/ [1+(G0/G∞) (jωτ0)1−h], where Y is the complex admittance, G0 and G∞ are the static and infinite-frequency values of conductance, τ0 is a relaxation time constant, and h is a parameter with values between 0 and 1. The complex-plane locus of the admittance is a circular arc from which the resistance of the insulating layer on the probe surface, the plasma-sheath resistance, and the value of h are derived. The susceptance-voltage characteristic of a probe is shown to be a sensitive indicator for the presence of insulating material on the probe surface. The susceptance-voltage curve for an insulator-contaminated probe has a peak in the vicinity of plasma potential which disappears upon removal of the insulating material by sputtering.
Correction for Defocusing in the Schulz Technique for Pole Figure Determination
Authors: Segmüller Armin
Published: February 2004

The intensity of the diffracted x-ray beam captured by the receiving slits is calculated as a function of the angle the sample is tilted out of the position parallel to the diffractometer axis around the bisectrix of incident and diffracted x-ray beams. Only the experimental determination of the line profile of the untilted sample and simple numerical computations are required.
Punched-Out Dislocation Rosettes in Low-Dislocation-Density Copper
Authors: Miura Yasuhiro
Published: February 2004

Copper single crystals of extremely low dislocation density have been obtained through a thermal cyclic annealing. Ball indentation in the dislocation-free area of (111) surface produced large dislocation rosettes, each arm extending in the 〈110〉 cystallographic orientations consisted of a row of prismatic dislocation half-loops. Half-loops of a diameter larger than 20 μ were easily produced in regular shape and they seemed much less mobile than independent dislocations under glide shear stress.