bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Dependence of the Elastic Constants
Authors: Lakkad Subhash Chandra
Published: February 2004

This analysis presents a new approach to the problem of temperature dependence of elastic constants, which leads to a simple expression. A phenomenological model is assumed to explain and estimate the temperature dependence of elastic constants. The model consists of the usual harmonic oscillator with the applied force term plus a third-order term representing the anharmonicity of the oscillator. The state function ψ is evaluated in terms of the Hermitian polynomials using perturbation methods. The average mean displacement of the mass points (atoms or molecules) is obtained by using the state function and Maxwell-Boltzmann distribution. Consequently, the expression for the elastic constant and also for the coefficient of the thermal expansion is obtained. The result is again averaged over the range of frequencies, using Debye spectrum. The final expression shows good agreement with experimental results and other theories.
Metastable fcc Fe–Rh Alloys and the Fe–Rh Phase Diagram
Authors: Chao Clinton C. , Duwez Pol , Tsuei Chang C.
Published: February 2004

Single-phase metastable fcc Fe–Rh alloys have been obtained by rapid quenching from the liquid state over a wider range of compositions than formerly reported. Lattice spacings and Mössbauer spectra of Fe57 of these alloys have been measured at room temperature. Both lattice parameters and isomer shifts are found to vary smoothly with rhodium concentration. These experimental findings suggest the existence of a continuous γ field at high temperatures. A tentative phase diagram based on the results of the present investigation is proposed.
High-Pressure α⇄ε Martensitic Transformation in Iron
Authors: Giles P. M. , Longenbach M. H. , Marder A. R.
Published: February 2004

A study of the high-pressure transformation in iron using an opposed-anvil x-ray diffraction apparatus and high-pressure light metallography has shown that the 130-kbar transformation is martensitic. The bcc and hcp phases were found to coexist over a large pressure range, and there is a large hysteresis between the forward and reverse transformation-start pressures. A room-temperature equilibrium pressure for the bcc and hcp phases of 107 ± 8 kbar is proposed, and discrepancies in the current P-T equilibrium diagram for iron are discussed.
Conductivity Tensor and Hall Effect in Magnetic Semiconductors
Authors: Saleh N. , Qureshi A. H.
Published: February 2004

The Boltzmann transport equation is solved taking into consideration the skew scattering of carriers in a magnetic semiconductor. The conductivity tensor is derived and used in the study of the spontaneous Hall effect. The effect of anisotropic scattering and spin-orbit interaction usually present in magnetic metals is accounted for.
Magnetic Properties of GdxTh1−xCuAl and Nuclear Magnetic Resonance in GdCuAl
Authors: Buschow K. H. J. , van Diepen A. M. , de Wijn H. W.
Published: February 2004

The magnetic properties of the intermetallic compounds GdxTh1−xCuAl (0.2≤x≤1.0) are reported for temperatures between 2.1 and 300 K. These compounds become ferromagnetic at low temperatures. Curie temperatures and magnetic moments are derived. The paramagnetic Curie temperature varies quite anomalously with x. The variation is compared with that calculated in terms of the Ruderman-Kittel-Kasuya-Yosida theory. In GdCuAl, the 27Al Knight shift was measured between 190 and 300 K. For the effective exchange constant Γ and the Fermi wave vector kF, values of +0.5 eV and 1.13 Å−1, respectively, were estimated.
Isochronal Recovery of the Shape of the Normal Magnetization Curve of Nickel Shocked at 400 kbar
Authors: Crowe C. R. , Rose M. F.
Published: February 2004

The recovery of the shape of the normal magnetization curve of high-purity polycrystalline nickel shock loaded to 400 kbar has been studied using an isochronal annealing technique. It was found that gross shape recovery occurs after annealing at temperatures in excess of 400°C. Lower-temperature annealing does not effect the shape of the normal magnetization curve significantly but lower-temperature annealing processes are reflected in the value of the field strength associated with the maximum susceptibility.
Effects of Foreign Co2+ and Fe2+ Ions on the Magneto-Optical Properties of Gadolinium Iron Garnet
Authors: Egashira K. , Manabe T. , Katsuraki H.
Published: February 2004

Ferrimagnetic single crystals derived from gadolinium iron garnet by cosubstitution with cobalt and germanium, Gd3Fe5−2x3+Cox2+Gex4+O12, are shown to exhibit a drastic change of the visible Faraday rotation. This effect is attributed to a spin-allowed crystal field transition in tetrahedrally coordinated Co2+ ions. Another system, Gd3Fe5−2x3+Fex2+Gex4+O12, was studied also, and it was found that the Faraday rotation is suppressed by formation of Fe2+ ions. It is suggested that certain transition-metal ions like Co2+ are useful in achieving materials of improved magneto-optical performances.
Mössbauer Line Positions and Hyperfine Interactions in α Iron
Authors: Violet C. E. , Pipkorn D. N.
Published: February 2004

The 57Fe Mössbauer spectrum of NBS standard reference material 1541 α-iron foil has been determined at 298±2 and 4.2±0.1°K, using a palladium source at 298±2°K. Line positions at 298 and 4.3°K were determined for the calibration of Mössbauer spectrometers. The magnetic splitting, in mm/sec, of the 57Fe ground state and first excited state are g0=(3.9098±0.0008), g1=(2.2342±0.0008) at 298°K and g0=(4.0117±0.0010), g1=(2.2931±0.0010) at 4.3°K. The center shift is − (0.1748±0.0008) mm/sec at 298°K and − (0.0556±0.0012) mm/sec at 4.3°K; the temperature shift is − (0.1192±0.0014) mm/sec. The hyperfine magnetic field is − (330.4±0.3) kOe at 298°K and − (339.0±0.3) kOe at 4.3°K. The 57Fe magnetic moment ratio is μ1/μ0=−1.7145±0.0005. The magnetic moment of the first excited state is μ1=−0.1547±0.0001 nm. The hyperfine magnetic field ratio is H(298°K)/H(4.3°K)=0.9746±0.0001. The electric quadrupole effect in terms of ε, the shift of the ±32 levels, is 4ε=+0.0023±0.0015 mm/sec at 298°K and 4ε=+0.0088±0.0025 mm/sec at 4.3°K. At 298°K, the quadrupole coupling is never between +0.0023±0.0015 mm/sec and −0.0046±0.0030 mm/sec. At 4.3°K, it is never between +0.0088±0.0025 mm/sec and −0.0176±0.0050 mm/sec. The 57Fe Mössbauer transition in palladium is more energetic than in sodium nitroprusside by 0.4361±0.0009 mm/sec.
Self-Healing Breakdown Measurements of Pyrolytic Aluminum Oxide Films on Silicon
Authors: Carnes J. E. , Duffy M. T.
Published: February 2004

Self-healing breakdown techniques are employed to study dielectric breakdown in pyrolytic aluminum oxide films on silicon substrates. The Al2O3 is prepared by chemical vapor deposition at low temperature (300–600°C) using Al isopropoxide as source material. Both weak-spot breakdown and intrinsic breakdown in the absence of weak spots using Au–Al2O3–Si test capacitors are investigated. Intrinsic breakdown field strengths of 7.5×106 V/cm for Si+ on p-type substrates and 6.9×106 V/cm for Si − on n-type are observed and found to be independent of Al2O3 thickness and temperature. Weak-spot breakdown is found to be associated with contamination of the silicon surface.
Hall Mobility in Chemically Deposited Polycrystalline Silicon
Authors: Kamins T. I.
Published: February 2004

Hall-mobility measurements have been performed on polycrystalline silicon films deposited on a silicon oxide surface by the thermal decomposition of silane. Samples with doping impurities added during deposition or by diffusion from a doped vapor-deposited oxide showed similar behavior. For both n-type and p-type samples approximately 5 μ thick, the mobility reached a maximum value of about 40 cm2/V sec at a free carrier concentration of about 1018 cm−3 and decreased for both higher and lower carrier concentrations. The observed Hall mobility was generally higher in p-type samples than in n-type samples. The decrease in observed mobility with decreasing carrier concentration is attributed to the effects of high resistivity space-charge regions surrounding grain boundaries in the polycrystalline material. The mobility was seen to increase as the film thickness increased for samples with similar doping, indicating a more ordered structure in thicker films.
Photoinjection Studies of Charge Distributions in Oxides of MOS Structures
Authors: Powell R. J. , Berglund C. N.
Published: February 2004

Determination of the nature and distribution of oxide charge in MOS structures is important to an understanding of oxide charging phenomena. In addition to their relevance to device failure mechanisms, it appears that charging phenomena may be used to advantage in memory device applications. The physical mechanism dominating the voltage dependence of photoinjected currents in SiO2 is the scattering of electrons in the region of the oxide between the injecting electrode and the image force potential maximum. Since the spatial position of the potential maximum depends on the electric field resulting from space charge in the oxide as well as the field due to the applied voltage, analysis of the V-I characteristics of photoinjected currents can provide information about the spatial location of oxide charge. Presented in this paper are the results of an analysis of the effects of oxide space charge on the voltage dependence of photoinjected currents. It is shown that effective charge distributions in SiO2 can be nondestructively profiled over a range from about ten to several hundred angstroms from the injecting electrode. Since photoinjection V-I characteristics depend on electric field at the potential maximum in the oxide, whereas C-V characteristics depend on the field just inside the semiconductor, analysis of both characteristics permits distinction between charge in the oxide a distance greater than about 10 Å and charge located at the interface. The results of experiments on Au–SiO2–Si structures in which charge has been purposely introduced into the oxide are presented, and it is shown that the interface fixed charge and the charge associated with fast surface states extend no further than about 20 Å into the oxide from the Si–SiO2 interface.
Tunneling through Fatty Acid Salt Monolayers
Authors: Mann Bernhard , Kuhn Hans
Published: February 2004

Sandwiches of monolayers of Cd salts of fatty acids CH3(CH2)n−2COOH of different chain lengths between metal electrodes show the exponential decrease of conductivity vs thickness predicted by the tunnel theory. The electron work function from metal to dielectric is obtained. The current-on-voltage dependence is predicted and it is found to be in good agreement with experiment. The effects of changing the electrode material are quantitatively predicted from the differences between the vacuum work functions of the metals used (Hg, Al, Pb, and Au). The good agreement between theory and experiment can be taken as an extremely sensitive test for the uniformity of the monolayers obtained by the monolayer assembling technique used in this investigation.
Doping Dependence of Hole Lifetime in n-Type GaAs
Authors: Hwang C. J.
Published: February 2004

The bulk hole lifetimes τ at 300 and 77°K are determined by a phase-shift technique for several Te-doped melt-grown GaAs crystals with electron concentrations n ranging from 2×1016 to 6.5×1018 cm−3. The phase-shift technique measures the phase lag φ of band-to-band photoluminescence relative to the excitation which is intensity modulated at some radio frequency ω. An expression relating τ and φ is derived taking into account hole diffusion and the reabsorption of emitted radiation. If the diffusion length is greater than the absorption length, the the usual simplified relation φ=tan−1 ωτ yields a poor approximation. It is also shown that the reabsorption can cause a wavelength-dependent phase shift along the spectrum of the band-to-band recombination. Apparatus used to measure φ is described. Values of τ are obtained from the measured φ using the previously determined diffusion length. At 300°K, τ=1.9×10−8 sec and is constant for n<1.5×1018 cm−3, indicating that recombination processes other than the band-to-band transitions are dominant in these lightly doped crystals. The hole lifetime begins to decrease at n=1.5×1018 cm−3 but decreases more rapidly for n>3×1018 cm−3. This shows that the band-to-band process is competitive with other processes beginning at n=1.5×1018 cm−3 and that additional hole-capturing processes exist in crystals with n>3×1018 cm−3. At 77°K, the behavior is similar, but the decrease from a constant lifetime of 1×10−9 sec for lightly doped crystals now occurs at n=8×1017 cm−3.
High-Field Diffusivity of Electrons in Silicon
Authors: Persky G. , Bartelink D. J.
Published: February 2004

The diffusivity of electrons in silicon transverse to a high electric field has been measured with precision by a beam-spreading technique. The measurements were carried out on 306-μm-thick double-Schottky-barrier structures fabricated from nearly intrinsic Si in which the applied field depleted the Si and was uniform to within ± 250 V/cm. It was found that the transverse diffusion coefficient D⊥ decreases monotonically from the known zero-field value of 35 cm2/sec for E 1 kV/cm to 22 cm2/sec at 11.5 V/cm, the upper field limit of the measurements. Monte Carlo calculations of the diffusivity tensor were carried out for a simplified band model and yielded D⊥ values in good agreement with the experimental results, thereby lending credence to the calculated values of the longitudinal diffusion coefficient.
P-N Junction Formation during Molecular-Beam Epitaxy of Ge-Doped GaAs
Authors: Cho A. Y. , Hayashi I.
Published: February 2004

Germanium was used to dope both the n and p layers of GaAs grown when molecular beams containing Ge, Ga, and As2 simultaneously impinged on the substrate surface. The formation of n- or p-type layers is dependent on the ratio of As2/Ga in the molecular beam and the substrate temperature. We describe the process used for the doping as well as the photoluminescence spectra from these layers.
Low-Energy Electron-Diffraction and Surface Conductance Studies of Surface Reaction of Germanium with Oxygen
Authors: Margoninski Y. , Feinstein L. G.
Published: February 2004

The oxidation process of clean germanium (100), (110), and (111) surfaces was studied by simultaneously measuring the beam and background intensities of the low-energy electron-diffraction (LEED) pattern and the surface conductance during exposure of the surface to oxygen. Two distinct and separate phases of oxidation were observed. During the first phase and for the (100) and (110) surfaces, the intensity of the beams (half-order and integral) as well as that of the background decreased and reached a minimum at about 15×10−7 Torr min. The surface resistance decreased also and its minimum almost coincided with that of the beam (or background) intensity. The second phase of the oxidation was marked by an increase in resistance and beam and background intensities. Results for the (111) surface were similar, but here the minimum of surface resistance was reached after an oxygen adsorption of 200×10−7 Torr min and therefore did not coincide with the minimum of the LEED intensities. There are indications that inelastic electron processes are important and that the changes in surface conductance are related to these inelastic processes and not to the structural changes occuring at the surface during the oxidation.
Tracer Study on the Decrease of Emission Density of Osmium-Coated Impregnated Cathodes
Authors: van Stratum A. J. A. , Kuin P. N.
Published: February 2004

Investigations have been performed on osmium-coated dispenser cathodes. The dispenser cathode consisted of a tungsten matrix impregnated with barium-calcium-aluminate. The coating was supplied by sputtering osmium on top of the tungsten matrix. The origin of the decrease in emission density with life was studied. This decrease is strongly temperature dependent and related to interdiffusion of the osmium and the tungsten substrate, resulting in the formation of a layer of OsW2 during life.
Theory of Transverse Cavity Mode Selection in Homojunction and Heterojunction Semiconductor Diode Lasers
Authors: Butler J. K.
Published: February 2004

A discussion of the transverse electromagnetic modes in single and double heterojunction lasers is presented. Three basic structures are analyzed: a laser with single heterojunction and optical cavity defined by the (p+-p) heterojunction and p-n junction; a double heterojunction laser with the second heterojunction at the p-n junction; and another double heterojunction unit which can have a large range of optical cavities because the second heterojunction is in the n region spaced a controlled distance from the p-n junction. Since the dielectric discontinuity at a heterojunction is an order of magnitude larger than at a p-n junction, these double heterojunction lasers can have high-order transverse modes. To model the observed radiation fields and, in particular, the preference for high-order modes, the optical properties of the junction region are treated as a five-layer dielectric slab. The two outer regions are bulk p+ and n+ (AlGa)As in the double heterojunction structures and p+(AlGa)As and n+ GaAs in the single heterojunction structures. The section between the p+ heterojunction and the p-n junction, which is customarily treated as the active section of the laser, has here been partitioned into two regions: a gain region adjacent to the p-n junction where recombination occurs and a lower gain region adjacent to the p-p+ heterojunction. In fact the latter region may be absorbing. The width of the first gain region is associated with the electron diffusion length in heavily doped p-type GaAs. For a suitable partition the modal gain of the high-order modes becomes larger than for the low-order modes, resulting in the highest mode reaching threshold first. In contrast, were the region between the n-p junction and the p-p+ heterojunction uniformly inverted, the laser would operate in the fundamental mode, contrary to experimental observation. Machine calculations indicate that structures radiating high-order modes have a gain region narrower than 1 μm.
Mode Reflectivity and Waveguide Properties of Double-Heterostructure Injection Lasers
Authors: Reinhart F. K. , Hayashi I. , Panish M. B.
Published: February 2004

It is shown that the mirror reflectivity for tightly confined planar waveguide modes becomes a function of both the waveguide and mode parameters. This dependence of the mirror reflectivity plays the dominant role in the selection of the oscillating transverse modes and explains why room-temperature cs-type double-heterostructure lasers tend to lase in higher-order TE modes. Experimental investigations show that the waveguide and mode parameters are qualitatively consistent with a dielectric step waveguide which is mainly perturbed by small gradients of the optical dielectric constant arising from impurity segregation.
Observation of Cylindrical Cavity Modes in Circular Josephson Weak-Link Junctions
Authors: Bermon Stuart , Mesak R. M.
Published: February 2004

We report the observation of self-induced step structure in the I-V characteristic of bulk-Hg/C/Sn multiple weak-link Josephson junctions formed by freezing a small drop of mercury onto the surface of a carbon covered tin film. The voltages at which steps appear are found to correspond to the frequencies of the resonant modes of the open-sided cylindrical rf cavity formed by the circular bottom of the mercury drop and the tin film. The effect of temperature and applied magnetic field on the junction critical current and on the step behavior is explored. The observation of such cylindrical cavity modes is contrasted with the situation for rectangular Josephson junctions where only the ``strip-line'' resonances have been observed.
Investigation of Gallium Arsenide Emission Diode Characteristics with Transistor Structures
Authors: Ashley K. L. , Doerbeck F. H.
Published: February 2004

Transistor structures were fabricated from amphoteric solution-grown Si-doped GaAs emission diodes. The ``collector'' was obtained with a sulfur diffusion into the p-type surface of the solution-grown wafers. The collector current and emission (intensity) were measured over a wide range of diode (emitter) current and temperature. The radiative and collector currents are shown to be associated with the same component of diode current (diffusion) at 300 °K but to be separate components at 77 °K. At 77 °K it was determined that the radiative current (nkT,n≃2) did not participate in transistor action and the collector current was that due to diffusion (kT). The same data were obtained with the sulfur-diffused diode as the emitter with results qualitatively similar in most respects. The ratio of collector and emitter currents was used to calculate an electron diffusion length Ln≃6–7 μm.
Collective Effect Acceleration of Electrons in Electron Beams
Authors: Coutu A. , Heese N. R. , Raudorf W. R.
Published: February 2004

Owing to a dynamic space-charge effect, a cylindrical stream of electrons, advancing in an evacuated metal tube continued by a plastic tube, is reflected at the junction of the tubes apart from the electrons constituting the front portion of the beam which become accelerated to many times their original energies.
Minority Carrier and Lithium-Ion Drift Mobilities and Oxygen Concentration in p-Type Germanium
Authors: Sher A. H. , Thurber W. R.
Published: February 2004

No correlations have been experimentally observed between electron drift mobility and lithium drift mobility nor between electron drift mobility and oxygen concentration in p-type germanium single crystals, as had been previously suggested.
Smooth, Detachable, (111) Monocrystalline Ag Films
Authors: Koch F. A. , Vook R. W.
Published: February 2004

A method for obtaining atomically smooth (111)-oriented single-crystal films of Ag on specially prepared (111) monocrystalline NaCl films has been developed. The latter, approximately 100 Å thick, were prepared by vacuum deposition onto air-cleaved mica at 25 °C in pressures of around 10−6 Torr. Ag films deposited on these NaCl films at 270 °C were (111)-oriented monocrystals with atomically smooth surfaces that compared well with those formed directly onto heated mica. The Ag/NaCl/mica films can be removed easily from their substrates for subsequent transmission electron microscopy by dissolving the intermediate layer in water.
Nd:YAlG–Ba2 NaNb5O15 0.66-μ Harmonic Source
Authors: Karr M. A.
Published: February 2004

Second harmonic generation (SHG) using a continuously pumped Nd:YAlG laser operating at a fundamental wavelength of 1.32 μ is described. Ba2NaNb5O15 is used for intracavity conversion to 0.66 μ. A cw output power at 0.66 μ of 77 mW in a TEM00 mode with a conversion efficiency of 70% was obtained. Repetitively Q switching the laser with an acousto-optic loss modulator yielded an output power of 28 W in a TEM00 mode at 1 kHz.
Laser-Stimulated Thermoluminescence in Glass
Authors: Ginther R. J. , Claffy E. W.
Published: February 2004

Thermoluminescence has been investigated as a tool for the detection of damage precursors in laser glass samples exposed to 1.06-μ laser radiation. Exposure which did not produce visible damage gave very small thermoluminescence yields. Damaged glasses produced stronger thermoluminescence, but in even those the effect is not large enough to provide a convenient materials test. A quenching action due to neodymium was noted. The emitting centers are believed to be impurities in the glass.
High-Mobility Epitaxial Layers of PbTe and Pb1−xSnxTe Prepared by Post-Growth Annealing
Authors: Holloway H. , Logothetis E. M.
Published: February 2004

Postgrowth annealing has been found to give layers of PbTe and Pb1−xSnxTe (with x ≈ 0.2) with much larger low-temperature Hall mobilities than as-grown layers. At temperatures down to about 50 °K the Hall mobilities are close to those of good bulk crystals. Below 50 °K there is a tendency to saturation at values greater than 105 cm2 V−1 sec−1. Structural studies indicate that both as-grown and annealed specimens are single crystals with about the same concentration of low-angle grain boundaries as the BaF2 substrates. It is suggested that the annealing process removes an excess of native defects.
Magnetostriction of Mn Ferrites at 293 K
Authors: Brabers V. A. M.
Published: February 2004

Magnetostriction constants of MnxFe3−xO4 at room temperature are reported and related to the cation distribution in these spinels. Octahedral Fe2+ ions give a positive contribution to λ111. The contribution to λ100 of octahedral Mn3+ ions is negative in this system and is not a linear function of the Mn3+ concentration, which may be caused by local stresses in the crystal.
Stable Superconducting Point-Contact Weak Links
Authors: Buhrman R. A. , Strait S. F. , Webb W. W.
Published: February 2004

Mechanically stable, room-temperature—helium-temperature-cyclable insulated double and single point contacts have been obtained by use of an insulating glass with thermal expansion matching that of the niobium superconductor. When two of these contacts are connected in parallel, the resultant device works quite well as a cyclable dc-biased magnetometer.
Cathodoluminescence Efficiency of Tm+3 in Zinc Sulfide
Authors: Shrader R. E. , Larach S. , Yocom P. N.
Published: February 2004

The power efficiency of ZnS : Tm under cathode-ray excitation was determined as 0.216 W/W, the highest yet reported for any rare-earth-activated phosphor. The unusual power distrition among the three emission manifolds concentrates the major portion of the luminosity in a single narrow blue band, yielding an unusual, highly saturated, nearly monochromatic, efficient source.
A New Method for Isolating Q-Switched Lasers
Authors: Mallozzi P. J. , Epstein H. M. , Walters C. T. , Applebaum D. C. , Gallagher W. J. , Dennis J. E.
Published: February 2004

A laser-isolator device capable of protecting Q-switched lasers from target backscatter has been designed and tested. The technique is readily applicable to lasers of any aperture.
Hole Theory of Liquids and Glass Transition
Authors: Somcynsky Thomas , Simha Robert
Published: February 2004

A recently elaborated theory of the p-V-T properties successfully describes the behavior of amorphous polymers above the glass temperature. The improvement over earlier results arises from the introduction of a vacancy fraction which is obtained as a function of volume and temperature by a maximization of the partition function. We now explore a possible application of this theory to the glassy state by introducing an assumption following a frequently used idea, namely, the freezing of one parameter, (or more), for example, an unoccupied volume ratio. The natural quantity to consider is the vacancy fraction and its effect on the thermal expansion coefficient at the glass temperature. Experimental data at atmospheric pressure on a series of polymers, encompassing a wide range of Tg's, are examined and compared with theoretical predictions. The computed expansivities αg at T=Tg are uniformly smaller than is observed. We suggest as the primary reason for this discrepancy the assumption of a complete freezing of the hole fraction at the glass temperature, which should be replaced by a decreased dependence on volume and temperature as compared with the liquid. Additional factors are discussed.
Crystal Structure of Alpha Poly-p-Xylylene
Authors: Kubo S. , Wunderlich B.
Published: February 2004

A crystal structure of α poly-p-xylylene is proposed with the help of data of oriented crystals grown during polymerization. The unit cell is monoclinic, a=8.57 Å, b=10.62 Å, c=6.54 Å (chain axis), β=101.3°. Four repeating units per cell lead to a calculated density of 1.185 g/cm3 and a packing density of 0.71. The probable space group is P21/m.
Light Scattering and Electron Microscopic Characterization of Amylose Films
Authors: Borch J. , Muggli R. , Sarko A. , Marchessault R. H.
Published: February 2004

The anisotropic morphology of amylose films is described by solid-state light-scattering analysis. A wide range of supermolecular structures was found, varying from ``rodlike'' texture for water-cast films to ``ringed spherulitic'' texture for those cast from dimethyl sulfoxide (DMSO). After treatments, such as alcohol swelling or prolonged exposure at high relative humidity, the DMSO-cast films undergo significant textural modification which is best characterized by the observed changes in the scattering envelopes. Electron microscopy is, in general, in accord with these observations, although the advantage of the light-scattering method over electron and simple polarization microscopy for characterizing such systems is clearly shown.
Intercrystalline Links: Critical Evaluation
Authors: Keith H. D. , Padden F. J. , Vadimsky R. G.
Published: February 2004

Previous electron microscopic studies have demonstrated the presence of intercrystalline links between thin lateral edges of chain-folded lamellar crystals in spherulitic polymers. We now present evidence that links also connect broad faces of superimposed neighboring lamellae. The latter links have been observed by electron microscopy of polyethylene lamellae standing normal to the surface of uniaxially drawn Mylar on which they had been crystallized epitaxially. Links of this kind are similar to those observed in the first instance and are evidently produced by the same mechanism. We consider also, in a critical way, the formation of intercrystalline links and tie molecules, and their important influence on mechanical properties, in bulk polymers crystallized either from quiescent or flowing melts. We show that links and tie molecules are formed mostly during primary crystallization, and few additional ones are produced during later stages. We examine, finally, a variety of ways in which links and tie molecules strengthen adhesion between crystals to promote ductile, rather than brittle, response to applied stress.
Strain-Induced Crystallization of Isotactic Polystyrene from the Glassy and ``Rubbery'' States
Authors: Yeh G. S. Y. , Lambert S. L.
Published: February 2004

In a continuing effort to extend our understanding of the strain-induced crystallization mechanism we have examined the morphology of oriented isotactic polystyrene (IPS) crystallized from the glassy and ``rubbery'' states under a variety of experimental conditions (elongation, annealing temperature and time, and sample geometry) by means of a wide variety of experimental techniques using Au decorations, solvent etching, electron diffraction, and bright- and dark-field electron microscopy. The oriented morphology is found to be strongly dependent on the original strained state and other experimental variables; it can be either lamellar, fibrillar, or a combination of the two. A fine texture is found to exist in both the lamellar and fibrillar crystals. Extended-chain line nuclei were also sought. Our results, including darkfield studies of highly stretched samples and samples which have been Au decorated or elutriated with solvent, do not reveal any crystallites of length greater than about 100 Å along the stretch direction, thus essentially ruling out their presence in IPS crystallized under strain. The observations are in complete agreement with the strain-induced crystallization mechanism suggested by Yeh and can also account for such phenomena as stress decay and melting temperature increase.
Yielding Behavior of Glassy Amorphous Polymers
Authors: Brady T. E. , Yeh G. S. Y.
Published: February 2004

The effect of thermal history on yielding behavior of atactic polystyrene, isotactic polystyrene, polycarbonate, and polymethyl methacrylate was examined by correlating the deformed microstructure with measured density changes and compressive stress-strain studies. Electron micrographs of bulk polymers and thin films demonstrate the tendency for well-annealed materials to undergo localized shear deformation at 100–1000-Å interspacings, and density measurements show an over-all density increase of about 0.15% upon plastic deformation. Rapid cooling from the melt decreases both the material density (about−0.04%) and the tendency for plastic strain to localize into narrow bands. Compressive stress-strain studies in which the strain rate, test temperature, and thermal history were systematically varied show a semilogarithmic relationship between nominal strain rate and yield stress. These data were analyzed according to an Eyring-type exponential model where the ``shear activation volume'' and the ``activation energy'' were calculated and compared for the ranges of variables studied.
Effect of Water Content on Stress Aging of Nylon 6–10
Authors: Bubeck Robert A. , Kramer Edward J.
Published: February 2004

The kinetics of stress aging are markedly increased by H2O additions to nylon. This increase in rate is taken as evidence that the aging process takes place in amorphous regions of the polymer. The breakup of the stress-aged structure is also greatly accelerated by H2O. The activation enthalpy ΔH* and shear activation volume V* for breakup are constant up to ∼0.7 wt% H2O, and then decrease to about one-half their dry values at ∼2.0 wt% H2O. These changes in the activation parameters are consistent with the activated step in breakup being the synchronous shear of stress-induced microcrystals, the size of microcrystals which nucleate during stress aging being limited by the average spacing between H2O molecules in the amorphous regions.
Internal-Friction Study of High-Purity Single Crystals of n Eicosane (C20H42)
Authors: Crissman J. M. , Passaglia E.
Published: February 2004

Large pure single crystals of n eicosane (C20H42) with [210] growth axes have been prepared by slow crystallizations from the melt. Internal-friction measurements covering temperatures from 100 to 300 K at ≃ 1 kHz reveal that in the as-grown single crystals both the α and γ loss peaks characteristic of polycrystalline n alkanes of less purity are absent, from which we conclude that, in polycrystals, these processes are a result of impurities and/or crystal defects. Two very weak loss maxima of obscure origin were observed at about 270 and 287 K for all the crystals studies. In one single crystal progressive stages of light cold work induced a complex spectrum of small loss maxima between 200 and 300 K. These maxima were found to be highly sensitive to aging. We believe that the observed behavior provides evidence for dislocation motion in crystals of this type. No detectable γ peak resulted from the cold work. Data are also included for one single crystal which was irradiated with γ rays.
Reaction-Rate Model for Fracture in Polymeric Fibers
Authors: DeVries K. L. , Lloyd B. A. , Williams M. L.
Published: February 2004

Electron paramagnetic resonance (EPR) techniques were used to determine the number of free radicals produced during deformation leading to fracture of nylon 6 fibers. A reaction-rate molecular model is proposed to explain some of the deformation and bond-rupture behavior leading to fracture. High-strength polymer fibers are assumed to consist of a sandwich structure of crystalline-block and amorphous-flaw regions along the fiber axis. In the flaw regions, tie chains connecting the crystalline blocks are assumed to have a statistical distribution in length. These chains are, therefore, subjected to different stresses. The length distribution was determined by EPR. The probability of bond rupture was assumed to be controlled by reaction-rate theory with a stress-aided activation energy and behavior of various loadings determined by numerical techniques. The model is successfully correlated with experimental stress, strain, and bond-rupture results for creep, constant-rate-of-loading, and cyclic-stress tests.
Dynamic Mechanical Properties of a Number of Elastomers and Related Polymers from 4 to 250 °K
Authors: Morgan R. J. , Nielsen L. E. , Buchdahl R.
Published: February 2004

Young's modulus and mechanical damping have been measured down to 4 °K for cis- and trans-polybutadienes, cis- and trans-polyisoprenes, butyl rubber, and random SBR copolymers. Trans-polybutadiene has two large damping peaks below Tg, trans-polyisoprene one peak, while the cis-polymers and butyl rubber show either no damping peaks or only very small ones below Tg. The low-temperature damping peaks of the trans-polymers might be explained by a type of crankshaft motion and by a special motion of the trans-monomeric unit which involves a simultaneous libration and bond angle deformation. The high Young's moduli of the polybutadienes compared to the polyisoprenes and the SBR copolymers are explained by the good molecular packing of the polybutadienes.
New Relaxation Phenomena in Linear Polyethylene at Cryogenic Temperatures
Authors: Papir Yoram S. , Baer Eric
Published: February 2004

The internal friction of linear high-density polyethylene (LPE) at cryogenic temperatures was investigated using an inverted free-oscillating torsion pendulum (1–3 Hz). The results show that LPE is not viscoelastically inactive below its γ peak as had been previously contended. Two new relaxation peaks, δ at 48 °K and ε at 20 °K, were observed. The characteristics of these loss maxima are identical to those of the cryogenic relaxations observed for polyethylene terephthalate and polyoxymethylene. A mechanism consisting of the motions of dislocation jogs and their interactions with specific conformational kink defects is proposed. This mechanism is consistent with all the experimental data in that it accounts for the effects of orientation and thermal histories on the relaxation strength of the δ and ε internal-friction peaks.
Scattering of Electrons by Vacancies through an Order-Disorder Transition in Vanadium Carbide
Authors: Shacklette L. W. , Williams Wendell S.
Published: February 2004

In nonstoichiometric vanadium carbide the carbon-atom vacancies can be either ordered or disordered at certain compositions. It is likely that these vacancies in the disordered carbide are important electron scattering centers and produce the observed large residual resistivity. On the other hand, band-structure effects in the transition-metal carbides are sensitive to composition so it is difficult to evaluate the contribution of vacancies to the electrical resistivity. Since vacancy scattering should vanish in the ordered phase, the change in resistivity through the ordering temperature for VC0.83 → V6C5 should be a useful measure. We have performed such an experiment. Though electron scattering by domain boundaries and by super-lattice defects is important, the results show that vacancy scattering is indeed significant at low temperatures, but of lessening importance as temperature increases.
Thermal Conductivity of BeO Single Crystals
Authors: Slack Glen A. , Austerman S. B.
Published: February 2004

The thermal conductivities of three single crystals of BeO have been measured from 2 to 300 K. Phonons carry the heat at all temperatures. At 300 K the conductivity is 3.7 W/cm K, which is slightly less than that of copper. In the purest sample the maximum conductivity occurs at 45 K where it is 137 W/cm k, and at temperatures below 10 K the conductivity is limited by boundary scattering. The anisotropy in the conductivity of this hexagonal material is 20% or less.
Correlations between Dislocation Character and Lithium Precipitation Kinetics in Germanium
Authors: Calzecchi F. , Gondi P.
Published: February 2004

The lithium precipitation kinetics have been examined in germanium containing dislocations with different character and density. The experimental data have been interpreted on the basis of existing growth theories by considering solute transfer coefficients from the matrix to the precipitates on the dislocations different for each dislocation type. The behavior of the 60° dislocations can be explained by assuming that they are surrounded by mobile vacancy clouds and by space-charge cylinders where the lithium concentration remains negligible.
X-Ray Topography with Chromatic-Aberration Correction
Authors: Chikawa Jun-ichi , Fujimoto Isao , Asaeda Yuhko
Published: February 2004

A new scanning topographic technique has been devised to superimpose images due to x rays with different wavelengths. This method is named ``chromatic-aberration-correction'' (CAC) topography and provides the following advantages in comparison with the usual scanning topography with only Kα1 radiations: (i) A high resolution is obtained even with both the Kα1 and Kα2 radiations. The effect of the CAC technique on resolution is remarkable for higher-order reflections for which high-resolution topographs are not obtained easily by the usual technique. (ii) The exposure time is reduced to ⅔ by using both Kα1 and Kα2 radiations. (iii) Uniform topographs of warped crystals such as semiconductor devices can be obtained with a high resolution by the combination of the CAC recording and a simple crystal-orientation-tuning device. These advantages are demonstrated by some observations of Si wafers.
Resolution Effects in the Measurement of Phonons in Sodium Metal
Authors: Werner S. A. , Pynn R.
Published: February 2004

In the course of making a detailed study of the phonons in Na metal using a triple-axis neutron spectrometer we have observed anomalous, asymmetric, and, in some cases, extraordinarily broad or split resonances. In this paper we account for these effects quantitatively by performing a complete resolution analysis. This analysis includes fully the combined effects of vertical resolution, a highly anisotropic dispersion surface, the variation of the polarization vectors and the temperature factor inside the resolution volume, and the sample mosaic spread. The application of this calculation to the measurement of phonons in other materials is straightforward.
Surface Self-Diffusion of Ag+ on AgBr by a New Radiotracer Technique
Authors: Tan Y. T. , Perkett W. , Powell R.
Published: February 2004

The tracer diffusion coefficient of radioactive silver 110 on thin epitaxial layers of silver bromide has been determined for temperatures in the range 95–160 °C. These layers were formed by vacuum deposition of AgBr onto mica substrates which resulted in epitaxial layers having a 〈111〉 surface and a thickness ranging from 0.1 to over 1.0 μ. At each temperature, the diffusion coefficient along the surface of layers having different thicknesses was determined by autoradiography. The results for different layers were then extrapolated towards zero thickness to give a surface diffusion coefficient. An activation energy for surface diffusion of 0.34 eV was obtained. This technique makes possible, for the first time, a determination of the surface self-diffusion coefficient of ionic solids without the need for assuming an arbitrary surface layer thickness as required by other tracer diffusion methods.
Defect Centers in Boron-Implanted Silicon
Authors: Chan W. W. , Sah C. T.
Published: February 2004

Deep-level defect centers in the upper half of the energy gap, created by 70-keV and subsequent 150-keV boron ions implanted into n-type (111)-oriented silicon crystals at room temperature, have been investigated using the dark capacitance transient technique. Two independent centers with thermal ionization energy for electrons of 241 ± 8 and 558 ± 6 meV are found. Thermal emission rates of electrons at these centers depend slightly on the applied field. For annealing temperature up to 450 °C, the post-implantation annealing rates vary from 10−4/cm to 10−3/cm for both levels (defect concentration ∼ 1012 to 1013/cm3). The defects are annealed out (<10−4/cm) above 600 °C. The thermal activation energy and the preexponential factor in the emission rate are essentially independent of annealing temperature and no new centers are detected after each annealing step. Low junction leakage (0.2 μA/cm2 at −10 V) is observed for all samples obtained prior to and after annealing
Sputtering of Niobium by Niobium, Hydrogen, Deuterium, and Helium Ions in the 10- to 80-keV Energy Range
Authors: Summers A. J. , Freeman N. J. , Daly N. R.
Published: February 2004

Sputtering coefficients of niobium for bombardment by Nb, H, D, and He ions in the 10- to 80-keV range have been measured and compared with theory. The light-ion measurements were obtained by sputtering through a thin film (600 Å) of niobium deposited on a zirconium substrate. Penetration of the film was observed by the appearance of substrate ions in the mass spectrum of sputtered ions from the target.
On Electron-Cyclotron Wave Resonance in Inductively Coupled hf Discharges
Authors: Szuszczewicz Edward P.
Published: February 2004

The theory of Pfeiffer on electron-cyclotron wave resonance phenomenon in inductively coupled hf ring discharges has been extended by Sager to include electron temperature, nonuniform density distributions, and the finite dimensions of a plasma of rectangular cross section. A scheme is herein proposed for adapting Sager's results to the experimentally important case of circular cross section. In order to test the scheme, an experiment was conducted in a low-pressure hf (27 MHz) argon discharge of cylindrical geometry with plasma densities in the range (1.0–3.5)×1011/cm3 and static magnetic fields less than 60 G. The agreement between theory and experiment is found to be good and lends credence to the scheme as a means for predicting resonance values of the magnetic field in cylindrical hf discharges.
Development of a New Plasma Diagnostic Technique Using Slow Positrons
Authors: Lohnert Gunter H. , Schneider Richard T.
Published: February 2004

Interaction of positrons with a plasma allows investigations of plasma parameters such as density, temperature, and velocity distribution of the electrons. In order to obtain detectable effects for the positron-plasma interactions, a beam of slow positrons has to be used. The measurement of positron lifetime in the plasma and measurement of the angular correlation of the annihilation radiation yield information on electron density and temperature. A parallel beam of slow positrons injected into a plasma is spread into an angle 〈α〉 after leaving the plasma due to the cumulative effect of small-angle scattering of the positrons with the microfield of the plasma. In measuring 〈α〉, the microfield, and hence the electron density, can be found. A rigorous derivation of the average scattering angle of the positrons as a function of the electron density and gas pressure is developed. The theoretical results are applied to a special test plasma. A device was designed and constructed which is capable of producing a beam of slow positrons. Both 22Na and 58Co are possible commercially available positron sources. Employing a 22Na source of 2 mCi, the device produces 1850 slow positrons per second, at a beam radius of 1.9 mm. In order to verify the theoretical expression for the beam spread and to demonstrate the feasibility of the new plasma diagnostic technique, a He plasma (14-cm diameter) was used as a test object. The slow positrons were injected into the plasma from a high-vacuum system into the plasma chamber through an ultrathin window (200 Å). The results of the beam-spread measurements were compared with spectroscopic and probe measurements. Good agreement was found.
Bidirectional Scattering of Electromagnetic Waves from Rough Surfaces
Authors: Leader J. C.
Published: February 2004

A general bidirectional expression is derived from the Stratton-Chu-Silver integral for the scattering of electromagnetic waves from rough surfaces. This expression is then expanded in a power series of surface slope terms for the special case of scattering in the plane of incidence. The results of this expansion are then compared with other models and closed-form solutions are obtained for comparison with experiment.