bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of accelerating lens system in field-emission scanning electron microscope
Authors: Kuroda Katsuhiro , Suzuki Tatsuro
Published: February 2004

This paper is composed of five sections. Section III analyzes the Butler-type and flat-plate lenses of the accelerating lens system in the scanning electron microscope (SEM) using a field-emission gun. Section IV presents the result of an analysis of some new accelerating lens systems when three anodes are present. The lens systems described in sec. IV are designed particularly for the low-energy SEM. Their major advantage is that the accelerating voltages can freely be changed in a wide range (from 300 V to about 100 kV) by merely adjusting the control voltages between the tip and the second anode without changing the focal point, etc. The resolution of the system and the beam current on the specimen seem to have the possibility of reaching 1000 Å and 10−8 A respectively, at accelerating voltages higher than 3 kV. Therefore, these lens systems also seem appropriate for the scanning Auger electron microscope.
Contact area dependence of minority-carrier injection in Schottky barrier diodes
Authors: Clarke R. A. , Green M. A. , Shewchun J.
Published: February 2004

A general theory of the Schottky barrier diode capable of incorporating geometrical effects is shown to predict the widely different minority-carrier injection properties of planar and point contact metal-semiconductor structures.
Injection electroluminescence in phosphorous-ion-implanted ZnSe p-n junction diodes
Authors: Park Y. S. , Shin B. K.
Published: February 2004

Electroluminescence has been obtained from phosphorus-implanted ZnSe p-n junction diodes at room temperature. In forward bias, the diodes exhibit an electroluminescence spectrum similar to the red photoluminescence spectrum with a peak at 6300 Å giving an external quantum efficiency of 0.01%.
On resultant force due to a screw dislocation in an anisotropic two-phase medium
Authors: Chou Y. T. , Pande C. S.
Published: February 2004

It is shown that, for a straight screw dislocation in an anisotropic two-phase medium, there is no resultant force exerted on any closed curve inside the medium. The resultant force on an infinite plane, if it intersects the interface, can be finite in an anisotropic medium, but it vanishes as isotropy is approached.
Characteristics of effused slab waveguides in LiNbO3
Authors: Wood Van E. , Hartman N. F. , Verber C. M.
Published: February 2004

Concentration profiles for LiNbO3 surface optical-waveguiding layers formed by diffusion-controlled evaporation of Li2O are calculated on the assumption that the evaporant flux is small and proportional to the available lithium ion concentration at the surface. The calculated profiles are found to agree reasonably well with the index-of-refraction changes observed by Kaminow and Carruthers. The apparent concentration dependence of the diffusion coefficient is discussed qualitatively. Approaches to design of waveguiding layers of specified characteristic are described.
Temperature dependence of gas diffusion in glass
Authors: Shelby J. E. , Keeton S. C.
Published: February 2004

Previous studies of gas diffusion in glass have suggested that the activation energy is a continuous function of temperature. Several models have been offered to explain this departure from the Arrhenius behavior commonly observed in diffusion studies. These models are compared with each other and with a new model which allows for the unique properties of vitreous materials. It is shown that this new model adequately describes the diffusion process.
Optical second harmonic generation in Ba2NaNb5O15: Simultaneous presence of growth inhomogeneities and self-induced thermal effects
Authors: Chakravarti A. K. , Phadke U. P.
Published: February 2004

We have theoretically investigated the effects due to the simultaneous presence of growth inhomogeneities (stratification/striae) and thermally induced inhomogeneities on optical second harmonic generation (SHG) in Ba2NaNb5O15 at low conversion efficiencies. The main result is the prediction of a double-humped SHG-vs-temperature curve due to the combined influence stratification and thermal effects.
Mobility of electrons in Hg1−xCdxTe
Authors: Chattopadhyay D. , Nag B. R.
Published: February 2004

Electron mobility in semiconducting Hg1−xCdxTe at room temperature has been calculated in the range 0.2 ≤ x ≤ 1.0 by an iterative solution of the Boltzmann equation incorporating the two-mode nature of the polar optical scattering and the nonparabolicity of the conduction band. The effects of the deformation potential acoustic, ionized impurity, and electron-hole scattering have also been considered. The calculated results agree with the measured values to within a factor of 2 for x = 0.6 and 0.4, whereas for x = 0.2, 0.8, and 1.0 the agreement is within a factor of 1.4.
On the calculation of surface energies from phonon frequencies
Authors: Purushothaman S. , Burton J. J.
Published: February 2004

Caglioti, Rizzi, and Bilello have recently proposed a method for calculation of surface energies from phonon frequencies and other experimentally accessible quantities such as the melting temperature. We apply their expressions to a number of simple solids and obtain results which are contradictory to experiment.
A new method for fabricating niobium oxide barrier Josephson junctions
Authors: Hansma Paul K.
Published: February 2004

Niobium oxide barrier junctions of excellent quality can be easily and reliably fabricated on unheated glass substrates by using a newly available hollow-cathode sputtering source. These junctions have survived both thermal cycling and room-temperature storage without degradation.
Etch pitting of fresh dislocations in C-doped nickel
Authors: Boah John K. , Winchell P. G.
Published: February 2004

Dislocations in nickel single crystals with carbon levels near 100 ppm have been reliably etch pitted on their {111} plane using a chemical (phosphoric acid, nitric acid, ferric chloride) etch for 30 min at room temperature. Carbon doping is found to be necessary for the etch pitting, but fresh dislocations are found to be pitted even though the etching time is less than one-millionth of the mean time of stay for carbon diffusion in the nickel lattice.
Determination of relevant parameters of the dopants Zn and Te from C-T measurements in GaP |Zn,O| p-n junctions
Authors: Ferenczi George
Published: February 2004

Using the single time constant approximation of the small ac signal capacitance of the reverse-biased GaP |Zn,O| p-n junction, a good agreement with the experimental C-T dependence in the 77–110 K temperature range was found at high frequencies. The important parameters of the dopants Zn and Te-activation energy, concentration, degree of compensation, and thermal capture coefficient-are determined applying this model.
Study of effective Debye temperature for germanium
Authors: Kor S. K. , Mishra P. K. , Pandey S. K.
Published: February 2004

The second-order elastic constants of germanium have been used to evaluate the temperature and pressure dependence of effective Debye temperature Θ and maximum Debye frequency vm, theoretically, from two different approaches. Good agreement is found between the results obtained from both methods used. As usual, the Debye temperature Θ decreases with increasing temperature while with increasing pressure it does otherwise.
Incidence angle and polarization dependence of light diffracted by acoustic surface waves
Authors: Alippi A. , Palma A. , Palmieri L. , Socino G.
Published: February 2004

A theoretical analysis of the diffracting effects produced by ASW on light beams contained on the sagittal plane of the wave is presented. The separate contributions have been explicitly studied, produced by periodical changes of the refractive index and by corrugation of the surface in cases of x- and y -cut crystalline quartz and y -cut LiNbO3 for both states of polarization of the incident light. In all cases analyzed, measurements of light-deflection efficiency have been performed as a function of the angle of incidence in light-transmission experiments.
Excess vacancy generation mechanism at phosphorus diffusion into silicon
Authors: Yoshida Masayuki , Arai Eisuke , Nakamura Hiroaki , Terunuma Yukio
Published: February 2004

Phosphorus is diffused into silicon at 900 °C from a phosphorus-doped silicon-dioxide layer. Since a profile of phosphorus concentration is expressed by a function of x/t, where x is the distance from a surface and t the diffusion time, diffusion coefficients are determined by the Boltzmann-Matano method. They are larger than the intrinsic diffusion coefficient and are dependent not only on the concentration (the concentration effect) but also on some unknown condition at a surface (the surface effect). The surface effect extends more than 20 μ deep into a bulk of silicon, and is stronger than the concentration effect. All of phosphorus atoms are located at substitutional sites. Diffusion-induced dislocations are not found. A new mechanism for the generation of excess vacancies is suggested. The new mechanism consists of the following: (i) Phosphorus diffuses by a vacancy mechanism. The diffusion of phosphorus occurs only through the diffusion of E centers. (ii) When phosphorus atoms enter from a surface into a bulk, they should be in a form of E centers. Affected by a surface, a large amount of E centers is formed per unit time at a surface. (iii) The E centers flow into a bulk. (iv) By their dissociations, excess vacancies are generated. The surface effect and the emitter dip effect are attributed to excess vacancies.
Diffraction of light by two orthogonal sound waves
Authors: Mahajan Virendra N. , Gaskill Jack D.
Published: February 2004

The diffraction of a light beam by two orthogonal sound waves is described. The Raman-Nath equation for the diffracting system is derived and is shown to separate into two Raman-Nath equations, one for each of the two sound-wave components. Thus it is shown that diffraction by two orthogonal sound waves present simultaneously in a medium is equivalent to diffraction by the two waves present successively. Analytic solutions of the Raman-Nath equation are obtained in the Raman-Nath and Bragg regions of diffraction. Practical applications of the diffraction effect in the Bragg region are outlined.
Extension of the unified theory of grain boundaries. I. Structure of the boundaries
Authors: Sadananda K. , Marcinkowski M. J.
Published: February 2004

The structures of both low- and high-angle grain boundaries are examined from a dislocation approach, and it is shown that coincidence-site lattice theory can adequately account for the structure of boundaries of any angle. For simplicity, the structures of symmetric tilt and twist boundaries in simple cubic structures are analyzed. The concepts that are developed, however, are quite general and can be applied to more complex crystal structures. In particular, it is shown that any grain boundary can be considered to arise from some suitable combination of crystal lattice dislocations associated with each one of the two grains comprising the boundary. Although the analysis is done with rigid models, the conclusions reached are independent of any atomic relaxations that occur at the boundary. The results developed from the dislocation approach are compared with those of Bollmann's O-lattice theory, and it is shown that the relatively complex O-lattice theory may not be necessary for an understanding of the dislocation structure of grain boundaries. Also, concepts such as the Burgers circuit are rationalized, and it is shown that the defect content described by a given circuit depends directly on its reference lattice whereas the strain fields are related to the relaxations that occur around the defect.
Optical and channeling studies of ion-bombarded GaP
Authors: Wemple S. H. , North J. C. , Dishman J. M.
Published: February 2004

Below-gap optical absorption, above-gap reflectivity, photoluminescence, and He ion channeling backscattering measurements are reported for ion-bombarded GaP. Each of the four experiments provides a measure of disorder. A one-to-one correspondence exists between the absorption, reflectivity, and backscattering measurements, and all three exhibit comparable sensitivity to damage. Photoluminescence is ∼ 100 times more sensitive. The absorption results suggest that every implanted ion species produces amorphous regions associated with each projectile and that these regions have properties very much like those of cold-deposited amorphous films. The results are interpreted in terms of a model which ascribes these amorphous regions to localized melting followed by rapid quenching to a glassy (amorphous) state in which short-range tetrahedral order remains intact. The damaged volume per bombarding ion as determined from absorption data is ∼6 times larger than that determined from channeling measurements. Although the annealing experiments show considerable scatter, the damage-induced changes in absorption and reflectivity can be largely removed by annealing at ∼600°C for 30 min. Some anomalies are observed in the photoluminescence annealing results.
Impurity control of domain switching in ferroelectric bismuth titanate
Authors: Luke T. E.
Published: February 2004

Bismuth titanate (Bi4Ti3O12) crystals grown from ``high-purity'' melts are shown to have significantly lower activation fields than those reported previously when switching times are > 1 μsec. Controlled doping experiments demonstrate that the switching characteristics of Bi4Ti3O12 are controlled by the crystal impurity content. Specifically, the pseudothreshold for switching is not intrinsic to the material. A model is proposed for the activation-field control which invokes the anisotropic conductivity due to the combination of impurity content and crystal structure.
Temperature and time dependence of dislocation pinning-point density in fast-neutron-irradiated copper crystals
Authors: Paré V. K. , Guberman H. D. , DeNee P. B.
Published: February 2004

The effects of fast-neutron-induced defects on the dislocation internal friction and modulus defect of copper crystals were studied by two procedures: (i) irradiation at 20°K followed by measurements during heating at a constant rate to room temperature and (ii) measurements during and after irradiations at various constant temperatures between 90 and 410°K. The measurements were made at low enough strain amplitude so that breakaway of dislocations from pinning points did not occur. Samples of known dislocation density were used in many of the experiments so that the ``vibrating-string'' model of dislocation motion could be used to calculate approximate absolute values for the densities of radiation-defect pinning points obtained at various temperatures. These were characterized by the ratio g of pinning points collected to freely migrating radiation defects created in the samples, assuming that on the average 20 defects can migrate away from the cascade region of each primary recoil. For the lower-temperature pinning processes which showed no time delay, values of g increased monotonically from 10−6–10−5 at 60°K to 10−4–10−3 at 204°K. The higher-temperature process is known to have a broad delay-time distribution; by collecting all pinning points available at 410°K a g value of ∼0.1 was obtained. Because of uncertainty as to the validity of the vibrating-string model, pinning-point densities were obtained primarily from the modulus-defect data. The damping data often implied the same densities but sometimes disagreed seriously with the modulus-defect results.
Direct observation and identification of long-period structures of SiC by transmission electron microscopy
Authors: Sato H. , Shinozaki S. , Yessik M.
Published: February 2004

Transmission electron microscopy has been used for the observation of polytypes of SiC having very long periods. The periodicity of these structures can be observed from the direct resolution of structural lattice periods and from the diffraction patterns. The actual structures can be determined from the intensity distribution in the diffraction pattern, and this has been done for two of the structures. These have been identified as [(33)1632]3 or 303R and [(33)634(33)434]3 or 222R, two hitherto unknown structures. A mechanism for conveying the long-distance information concerning the stacking order which leads to stabilization of the long-period structures in SiC is suggested. This mechanism essentially involves a transformation from a basic structure of short period to accommodate a constraint from the surroundings.
Analysis of mode coupling in piezoelectric waveguides
Authors: Sugimoto Mitsunori , Makimoto Toshio
Published: February 2004

A perturbed piezoelectric waveguide is constructed from a reference waveguide, which is specified by the eigenvalues and eigenfunctions, by the coordinate transformation, or other methods. In the perturbed waveguide, coupling occurs between normal modes of the reference waveguide. Coupling phenomena are analyzed by transforming Maxwell's and Newton's equations into the variational expression of the phase constant of the normal mode and then by applying the Rayleigh-Ritz method. As an example, the couplings between purely elastic waveguide modes are discussed; and then the two-mode approximation is applied in the case when two modes are degenerate or nearly degenerate. Mode conversion phenomena are discussed and from the viewpoint of the network theory, the mode transfer matrix relating the complex amplitudes of the two modes along the waveguide is defined and developed.
Properties of a dielectric-rod waveguide immersed in plasma
Authors: Maiti J. N. , Basu J.
Published: February 2004

The paper presents a study of various aspects of propagation in the TM01 mode along a dielectric-rod waveguide immersed in plasma. Expressions are derived and characteristics obtained for the dispersion relation, phase and group velocities, as well as power flow in and around the guide in the loss-free case of propagation. The dispersion relation reveals that the TM01 mode is the dominant one with backward wave characteristics for low negative values of εp/εd, where εp and εd are the dielectric constants of the plasma and the rod, respectively. The phase velocity is found to be always greater than the velocity of a plane wave in the rod medium if εp is positive, while for its negative values the phase velocity can be either greater or less. From the point of view of power concentration, the structure acts as a very good surface waveguide, particularly for high negative values of εp/εd. The attenuation coefficient is subsequently derived by the standard perturbation method, assuming that both the plasma and the rod are slightly lossy. Finally, the possibility of using the waveguide as a plasma diagonostic tool is discussed, and it is shown how the results reported in the paper can be employed for determining the electron density and electron collision frequency for momentum transfer in a plasma.
Dynamics of intense relativistic electron beams in toroidal fields
Authors: Benford James , Guillory John , Stallings Charles
Published: February 2004

Intense relativistic electron beams were propagated around a 180° toroidal sector to study beam dynamics in toroidal fields. The major beam drift under conditions for neutralization of self-fields was along - R × B and scaled as γZ/Bt, where Z is the propagated distance, Bt the toroidal field, and γ the relativistic factor. This is indicative of curvature and ∇B drifts. Use of conducting walls caused an additional F × B drift around the chamber due to image current forces. Analysis of the distortion of a propagating rectangular beam shows that beam electrons follow field lines. Preliminary experiments on counterstreaming beams show inefficient reflection of beams from opposing diodes. Application of these results to beam injection and confinement in toroidal magnetic fields is discussed.
Interdiffusion and compound formation in Ta–Au thin-film couples
Authors: Tisone T. C. , Lau S. S.
Published: February 2004

An investigation of the interdiffusion between sputter-deposited bilevel films of bcc Ta–Au, β-Ta–Au, and Ta2N–Au has been carried out by using x-ray diffraction, electron microscopy, and electrical resistance measurements. In all three systems only the TaAu phase was observed to form. The temperature range of formation of the TaAu phase for the systems considered increased in the order β-Ta, bcc Ta, and Ta2N. The resistance change for a given temperature increased in the order Ta2N, bcc Ta, and β-Ta. It was concluded that the change of resistance occurred by three mechanisms: (1) diffusion of Ta into the Au grain boundaries, (2) diffusion of Ta into the Au bulk, and (3) transformation of the Au into a high-resistivity TaAu phase. From the resistance measurements the kinetics of the formation of the TaAu phase were found to be diffusion controlled with the diffusion species moving through the TaAu phase grain boundaries.
Space-charge-perturbed discharge characteristics of poly-n-vinylcarbazole
Authors: Sato Hisanao , Ono Shusuke , Ando Eiji
Published: February 2004

Photoinduced discharge characteristics of the photoreceptors consisting of a poly-n-vinylcarbazole (PVK) layer sensitized with a thin carrier-generation layer have been analyzed theoretically. The electric field in the PVK layer has been calculated by solving the three basic equations: the law of hole conduction with neglect of diffusion, the continuity equation with no trap, and Poisson's equation. After long time from light-on, the surface voltage is determined by the hole charges drifting in the PVK layer; it decreases with time t as (3/4)(tT0/t)1/3, where tT0 is the hole transit time across the PVK layer at the initial electric field. The theory has been compared with measurements on the photoreceptors in which the carrier-generation layer consists of amorphous Se or amorphous Se0.86Te0.14. The hole mobility in the PVK layer has been estimated to be 10−5 cm2/V sec at an electric field of 106 V/cm. When illuminated with a tungsten light, the Se0.86Te0.14-PVK photoreceptors have shown an emission-limited discharge current which is nearly proportional to the surface voltage and is 4 times as large as that of the Se-PVK photoreceptors at 106 V/cm.
The solenoid which gives the desired value of magnetic field for the smallest possible volume of conductor
Authors: Miklavc Adolf
Published: February 2004

We derive the shape which a solenoid must have to give, for the smallest possible volume of conductor, the desired value of magnetic field at a point z0 on its axis. To get a somewhat more complete picture of the field produced by the solenoids of such shape we study its behavior away from point z0 in the case of the cylindrical ``frame'' of radius r0=2 cm and for a few values of the conductor volume.
Radial flow of conical beams of charged particles
Authors: Bosi G.
Published: February 2004

The usual geometry of a spherically symmetric radial-flow Pierce-type gun is criticized and some shortcomings are underlined. The general equation defining the family of field forms ensuring third-order radial flow is carried out and a particular solution is selected. The shape of electrodes providing the chosen field form is calculated in a simple and reliable way.
Study of prebreakdown phenomena in a liquid using a gas bubble chamber
Authors: Murooka Y. , Toriyama Y.
Published: February 2004

A gas bubble chamber was used to study the prebreakdown mechanism in diethyl ether. The liquid was saturated with CO2 gas at a pressure of 9–13 kg/cm2 and then further compressed to a pressure of 40–45 kg/cm2. The liquid was then rapidly expanded 4–6% in volume, causing it to become temporarily supersaturated. At that time an impulse voltage of about 33 kV/was applied between two needle electrodes (gap length 3.2 mm) in the liquid. The resultant bubble figures, which represent electron emission from the cathode, were recorded photographically. The time lag from the application of the impulse voltage to the growth of bubbles of observable size was about 0.8–1.0 msec. This value agrees with the results obtained by using an ordinary bubble chamber.
Elastic constants of niobium-rich zirconium alloys between 4.2 K and room temperature
Authors: Hayes D. J. , Brotzen F. R.
Published: February 2004

The adiabatic elastic constants were determined for niobium and for its alloys containing 1.4, 3.6, and 6.0 at.% zirconium. The c11, c12, and c44 constants as well as the shear constant C′ = (1/2)(c11 − c12) and the bulk modulus were tabulated between 4.2 and 290 K. The unusual temperature dependence of the shear constant c44 found in niobium was also observed in the alloys. The Debye temperatures were computed from the constants at 4.2 K.
Crystallization of Ge and Si in metal films. II
Authors: Sigurd D. , Ottaviani G. , Arnal H. J. , Mayer J. W.
Published: February 2004

Heat treatment of evaporated Si in contact with Ag films and Ge in contact with Al films results in the formation of precipitates of the semiconductor in a metal matrix. The structure of these precipitates was studied by transmission electron microscopy and diffraction (TEMD) and MeV 4He ion channeling techniques. TEMD studies showed that the semiconductor precipitates were crystalline in nature. Channeling techniques showed that the crystallites did not have a simple orientation relationship with the underlying single-crystal substrate.
Light-emitting mechanism of ZnTe–CdS heterojunction diodes
Authors: Ota Tadahisa , Kobayashi Kikuo , Takahashi Kiyoshi
Published: February 2004

ZnTe–CdS heterojunction LED, which was prepared on the ZnTe substrate by CdS vapor growth, showed the red light emission at 300°K. The EL spectra had a peak at 1.78–1.80 eV at 300°K, and two peaks at about 2.10 and 1.55 eV at 77°K. The existence of the ZnxCd1−xTe mixed crystal with a graded band structure at the heterojunction interface was shown from the results of the photovoltage spectra and transmittance analysis of the heterojunction. The formation of the mixed crystal was found to be due to Cd diffusion into the ZnTe substrate during the epitaxial growth. From photoluminescence measurements, it is concluded that the red emission of ZnTe–CdS LED may originate from the ZnxCd1−xTe mixed crystal layer. Thus, efficient red emission could be obtained in our ZnTe–CdS heterojunctions on account of the mixed crystal layer, which reduced high-energy barriers for electrons and holes.
Glow-discharge mass spectrometry—Technique for determining elemental composition profiles in solids
Authors: Coburn J. W. , Taglauer E. , Kay Eric
Published: February 2004

Glow-discharge mass spectrometry, in which an rf glow discharge is used both to sputter etch the sample undergoing analysis and to ionize the neutral sputtered species, is shown to be a promising new technique for the elemental analysis of thin solid layers or bulk solids. A description of the method is given followed by some examples of its application to composition profiling. The influence of some parameters is shown and opinions as to the advantages and disadvantages of the method are given.
HF laser initiated by a 300-keV electron beam
Authors: Patterson E. L. , Gerber R. A. , Blair L. S.
Published: February 2004

An intense electron beam has been used to initiate HF lasing in mixtures of SF6 and C2H6. Parametric studies of this highly superradiant chemical-laser system were performed to determine optimum composition of the SF6/C2H6 mixture. The maximum laser energy measured was 5.5 J in a pulse width (FWHM) of 45 nsec. The efficiency for conversion of deposited electron-beam energy to laser energy was approximately 4%. The chemical reactions and the limits on the production of fluorine atoms and of vibrationally excited HF are discussed.
Interface-state generation by gold diffusion through SiO2 films on silicon: MOS and neutron-activation results
Authors: Schmidt P. F. , Adda L. P.
Published: February 2004

Diffusion from a metallic gold source into SiO2 films on (100) silicon substrates at 1000 °C for 15 min leads to large negative shifts in the C-V curves and distortion of the C-V characteristics. Annealing in hydrogen in the temperature range 300–450 °C, in argon at 1100 °C, or short exposure to steam at 950 °C is only partially effective in reversing these changes. Gold from a metallic source appears to diffuse in SiO2 mostly or exclusively as metallic gold and to cause the generation of a very large density of interface states. Most of the negative C-V shift is due to these interface states and not due to a laterally uniform fixed oxide charge, as claimed by other researchers. The magnitude of the effect depends in the thickness of the gold film, and hence directly or indirectly on the amount of gold diffused into the SiO2 film because thicker gold films result in larger amounts of gold diffusion in uniform fashion into the SiO2. The total amount of gold in the SiO2 film after diffusion, however, is insufficient by several orders of magnitude to account, on a one-to-one basis, for either the supposed oxide charge or the interface-state density. It must be concluded that gold diffusion in SiO2 films leads to the formation of interface states by an entirely new and unexplained mechanism.
GaAs : Si double-heterostructure LED's
Authors: Hsieh J. J. , Rossi J. A.
Published: February 2004

The spontaneous-emission spectra of liquid-phase-epitaxial grown double-heterostructure light-emitting diodes with a Si-doped GaAs active region and Ga1−xAlxAs barrier regions have been measured as a function of the Si concentration in the growth solution and the thickness of the active region. The results indicate that a graded band-gap region is probably formed at the GaAs–Ga1−xAlxAs interface. The double-heterostructure light-emitting diodes are compared with homojunction diodes as potential excitation sources for upconverting phosphors.
A Sm2 (Co,Fe)17 magnet with (BH)max = 12 MG Oe
Authors: Heinrich John P. , Garrett Harold , Allen Richard P.
Published: February 2004

A sample of sputtered Sm2(Co0.7Fe0.3)17 was found to have mHc=5600 Oe and (B H)max=12 MG Oe after heat treatment. These are both record values for 2:17 alloys, and the energy product is a record value for an isotropic magnet. This material is the first 2:17 alloy to exhibit useful permanent-magnet properties.
A chemical approach to superconductivity
Authors: Gualtieri Devlin M.
Published: February 2004

Correlations of the important parameters of the BCS theory of superconductivity are developed with respect to the number of d-shell electrons per atom of the transition elements predicted by the Engel-Brewer theory of alloys. The importance of ``bonding'' on the d level as a generalized electron-electron interaction is demonstrated; and the total attractive potential V of the BCS equation for the critical temperature Tc is shown to arise from both the phonon-induced potential, Vph, and a large attractive potential Vb, due to bonding and having a maximum at the half-filled d shell. The present theory is consistent with the recent data of amorphous superconductors if their electron density of states at the Fermi level, No, is a constant or a shallow function of the electron-per-atom ratio. The anomalous isotope effect of some elements is also discussed, as well as the fundamental instability of high-Tc superconductors and the incompatibility of ferromagnetism and superconductivity.
Measurement of x-ray absorption coefficients of some common metals for the 1.5–3-keV range
Authors: Singman Leif
Published: February 2004

The x-ray absorption coefficients of the metals Al, Ti, Fe, Ni, Cu, and Zn have been measured for radiations in the 1.5–3-keV range. Monochromatic x rays were obtained by diffracting characteristic x-ray lines with a crystal. Freedom from fluorescent radiation was ensured by using crystals of low-Z material. The absorber thicknesses as well as the time distributions between measuring I and I0 were optimized. The average of nine transmission measurements taken with the absorber in nine different positions was used in computing the absorption coefficients for each element. Comparison of absorption coefficients obtained with different absorbers of the same element indicates an experimental uncertainty of 1–4%.
Does backscattering of 4He ions by nuclei obey the Rutherford cross-section formula?
Authors: Ziegler J. F. , Baglin J. E. E.
Published: February 2004

Implicit in the use of nuclear backscattering as a quantitative analytic tool is the accuracy of calculating cross sections using a classical Coulombic scattering formula (Rutherford cross section) which includes recoil effects, but ignores spin, nuclear size, electron screening, hard-sphere scattering, and any nuclear-force effects. The Rutherford cross section has not previously been verified experimentally for ions of 4He (1–2.5 MeV) for targets of 16O, 27Al, and 28Si. For 14N, agreement has been found with an accuracy of about 5%. Our experimental results show that 27Al and 28Si have the Rutherford formula value (±1%), and 16O is Rutherford from 1.4 to 2.4 MeV. 14N appears to deviate by about 2% at energies from 1.2 to 2.2 MeV and by more beyond this energy band.
Characterization of incomplete activation of high-dose boron implants in silicon
Authors: Schwettmann F. N.
Published: February 2004

The incomplete activation observed when high doses of boron (2×1015−2×1016 ions/cm2) are implanted in silicon is characterized by a maximum concentration of electrically active boron that is independent of both the dose and anneal time and well below the solid solubility value. An Arrhenius plot for this concentration-temperature dependence yields an activation energy of 0.31 eV. It is suggested that the incomplete activation is due to interactions between the implanted ions. Whether the defect structure is a simple B–B pair or a cluster involving residual damage is not clear at this time.
Different diffusion behavior of copper in epitaxial and in bulk GaAs
Authors: Hasegawa Fumio
Published: February 2004

A considerable difference in the diffusion behavior of copper was found between epitaxial GaAs and bulk GaAs. The carrier concentration of epitaxial GaAs scarcely decreased (much less than 1×1015 cm−3) with copper diffusion at around 500°C, while carrier concentration of undoped bulk GaAs decreased about (3–5)×1016 cm−3 with the diffusion under the same conditions. The diffused-copper concentration in the epitaxial GaAs, measured by radioactive copper Cu64, was less than that in the bulk GaAs by more than one order of magnitude. These differences in the copper diffusion can be understood by the difference in the amount of defects, and therefore, by the difference in solubility of substitutional copper between epitaxial and bulk GaAs.
Visualization of vibration and sound using scanning and holographic methods
Authors: Hannon Robert J. , Watson E. Eugene
Published: February 2004

Two scanning techniques are now being used to determine the vibrational patterns and far-field sound radiation of complex vibratory systems. One technique is a near-field scanning apparatus which scans the vibrator and gives a three-dimensional display on graph paper of the nodal patterns. The other scanning technique uses the principles of holography to locate far-field sound sources on the vibrator. These two methods, coupled together, have demonstrated a unique capability to locate acoustic sources and hot spots on vibratory systems.
Neutron- and proton-induced defects in SiGe alloys: Optical absorption
Authors: Stein H. J.
Published: February 2004

The effects of neutron ([inverted lazy s]300 K) and ion bombardment ([inverted lazy s]85 K), and subsequent isochronal annealing, on the near-infrared transmittance of SixGe1−x alloys (x=0.24, 0.44, and 0.73) have been investigated and compared to those for similarly bombarded Si and Ge. Defect absorption bands are observed in all three alloy compositions and can be separated into Ge-like and Si-like centers. Energy positions for the bands increase linearly with Si fraction. Damage-induced near-edge absorption is also observed in all three alloy compositions. Results for the Ge-like center are consistent with the previous assignment of a 2.4-μm band in Ge to divacancies. Growth of the Si-like center between 200 and 300 K is consistent with Si stabilization of divacancies formed from vacancies initially trapped by Ge. Annealing loss of the Si-like center is also consistent with the thermal stability expected for Si–Si bonding through a divacancy. The formation rate for Si-like centers by bombardment near 300 K can be explained by Si–Si bonding through divacancies in a random alloy when two Si atoms are in the same plane as the divacancy and are nearest neighbors to the divacancy. Neutron-induced hole-removal rates approaching those for p-type Si are indicated by free-carrier absorption measurements on the x = 0.44 and 0.73 alloys.
Compressional waves in fluid-saturated elastic porous media
Authors: Garg S. K. , Nayfeh Adnan H. , Good A. J.
Published: February 2004

This article discusses the propagation of compressional waves in fluid-saturated elastic porous media. Both harmonic and transient pulses are considered. In general, two modes of wave propagation exist. In the case of a transient pulse, these modes lead to a two-wave structure. It is not possible to obtain closed-form solutions for the general case of transient loading, but considerable insight may be obtained from certain limiting cases (e.g., no viscous coupling, large viscous coupling) for which analytical solutions are derived by means of Laplace transform techniques. Strong viscous coupling leads to the coalescence of the two wave fronts into a single front; in this case the material behaves like a single continuum with internal dissipation. Solutions for the general case are obtained both by numerical inversion of the Laplace transforms and by direct finite-difference methods.
Thermally activated deformation. I. Method of analysis
Authors: Hanley T. O'D. , Krausz A. S.
Published: February 2004

To understand the processes which control the rate of plastic deformation it is necessary to determine the atomic parameters and in particular the activation volume. The true activation volume can be identified only if the stress dependence of deformation rate is described by a valid expression. To determine this expression a kinetics analysis has to be carried out, often for a system of parallel and consecutive energy barriers. This is an intricate procedure which has to be carried out in well-defined steps and in the order of increasing complexity of barrier combinations. Furthermore, the validity of the numerical values obtained in the analysis has to be established. This process of deformation kinetics analyis is elucidated and the method is described fully.
Neutron diffraction by vibrating ADP crystals
Authors: Parkinson T. F. , Gürmen E. , Loyalka S. K. , Muhlestein L. D.
Published: February 2004

The intensity of neutrons diffracted from ADP crystals is enhanced when the crystals are vibrated in their fundamental piezoelectric modes. The neutrons are also modulated at a frequency approximately twice that of the crystal frequency. These effects can be explained by the dynamical theory of diffraction and are similar to the effects of neutrons diffracted by piezoelectric quartz crystals.
Thermally activated dislocation glide through a random array of point obstacles: Computer simulation
Authors: Morris J. W. , Klahn Dale H.
Published: February 2004

This paper reports results obtained through computer simulation of the thermally activated glide of an idealized dislocation through a random array of point obstacles. The array size is fixed at 999, and the dislocation-obstacle interaction is taken to have a simple step form. The variables governing glide are then the resolved shear stress, the temperature, and the obstacle strength, which may be phrased as dimensionless parameters. The principal subjects studied are (1) the stress required for athermal glide at a given obstacle strength and the characteristics of the obstacle configurations which determine this stress, (2) the glide path taken by the configuration and the characteristics of the obstacle configurations encountered along this glide path, (3) the velocity of glide and its dependence on the stress, the temperature, and the obstacle strength.
Sliding electrification of Teflon by metals
Authors: Wåhlin A. , Bäckström G.
Published: February 2004

The electrification of a system consisting of a metal and Teflon (polytetrafluoroethylene) has been investigated in vacuum under relative motion. A plane strip of Teflon was moved in relation to a metal electrode connected to an electrometer, which permitted the electrification charge to be continuously recorded. The electrification current was found to be closely proportional to the velocity, and it was practically independent of the radius of curvature of the tip of the electrode. The normal force was also varied, and the linear charge was found to be proportional to the square root of this force. Electrodes of Al, Au, Cu, Dural, Mg, Ni, and Pt were used, and the charge deposited was found to be linearly dependent on the metal work function, except for a large anomaly in the case of Cu. For a given metal the charge was shown to be closely proportional to the area swept out by the electrode on the insulator surface. The linear dependence of charge on metal work function and the short charging time (0.06 s) observed indicate that electrons from the metal fill empty surface states in the insulator up to a level corresponding to the Fermi level of the metal. The surface-state density of Teflon was found to be 7×1010 eV−1 cm−2.
Instability in a counterstreaming plasma with a magnetostatic field
Authors: Seshadri S. R.
Published: February 2004

The instability of an electromagnetic wave propagating obliquely to a counterstreaming plasma is investigated for the case in which the magnetostatic field is normal to the plane containing the wave vector and the stream direction. The stream direction normal to the wave vector is a singular case for which, if the magnetostatic field is less than a critical value, the instability occurs for wave numbers exceeding a minimum value, the maximum growth rate being attained for very large wave numbers. An increase in the magnetostatic field increases the minimum wave number and reduces the growth rate. For all other stream directions unstable waves exist between two limiting wave numbers for all values of the magnetostatic field. The maximum growth rate is found to be practically the same for all stream directions other than normal to the wave vector. An increase in the magnetostatic field reduces the range of wave numbers for which there is instability, causes the region of instability to shift to shorter wavelengths, and decreases the maximum growth rate. The dependence of the growth rate on the stream direction with respect to the wave vector and the validity of the quasistatic approximation in predicting the nature of this instability are also examined.
Investigation of the energy and impurity content of a crossed-field plasma gun
Authors: Baker C. C. , Forsen H. K.
Published: February 2004

The downstream energy and impurity content of the plasma produced by a pulsed crossed-field source is investigated. With a positive center electrode and an optimum neutral gas loading, the source ionizes and accelerates 7×1017 protons containing 140 J of energy to the end of a 2-m-long axial magnetic guide field. This energy is distributed equally between axial motion and gyromotion. The dominant acceleration method is the −μ·∇B force resulting from a gradient in the axial magnetic field within the source. Impurities, in the form of C2+ and O2+ ions, account for about 10% of the plasma. Reversing the source polarity results in a lower energy efficiency and the appearance of Fe2+ ions in the downstream plasma.
Current continuity in dense plasma
Authors: Mills Carroll B.
Published: February 2004

The equations of current continuity have been solved for high-density (nion>1012 cm−3) gaseous plasma as a problem associated with electron-beam-controlled electrically excited pulsed laser energy sources. The procedure used first-order numerical approximations to the space and time development of current and potential gradients. The results of a laser plasma study are (a) the total electron current is not very sensitive to electron emission at the cathode because (b) the sheath multiplies both secondary electrons and cathode current by a large factor and adjusts to current requirement set by electron mobility and density in the plasma. Small changes in the sheath thickness and potential drop satisfy the variable-current condition set by gas ionization and ion recombination: I=new=ew (S/α)1/2. The potential drop in the sheath of an STP plasma is 400–2000 V for plasma currents of 1–10 A/cm2, and the sheath thickness is d≃0.003 cm.
Electron effects in sputtering and cosputtering
Authors: Chapman B. N. , Downer D. , Guimarães L. J. M.
Published: February 2004

We had previously observed, when cosputtering from a single target, that the deposited film was far from uniform, even showing a pattern resembling that of the target. Having subsequently made some energy and power measurements of the negative particles bombarding the anode in a sputtering system, we have concluded that the patterning is due to fast secondary electrons from the target. These secondary electrons are of importance in all types of sputter deposition, since a significant number of them travel in straight lines to the anode without collision. They are responsible for almost all of the power input into the anode and can dominate the growth of a thin film on a substrate at the anode.
Laser-target interactions
Authors: Hoffman C. G.
Published: February 2004

Metallographic and microscopic techniques have been applied to the study of laser targets of various materials. Optical microscopy and scanning electron microscopy of foils and wires that had been irradiated by a 10-J laser (wavelength 1.06 μm) were followed by sectioning through the holes both longitudinally and transversely. Foils of gold and titanium show considerable melting and splatter on the front surface, a hole through the foil, and spalling from the rear surface. Polyethylene shows tensile fracture on the front surface, clouds of large and very small bubbles around the hole near the entering surface, and evidence of the ejection of molten material from the rear surface. In addition, a lenticular void appears near the center of the film. Gold wires, in addition to being ruptured, show a lanceolate void along the axis of the wire extending to well outside the supposed area of influence. As yet only hypotheses for this behavior exist.
Determination of Fermi-level effect on Si-site distribution in GaAs : Si
Authors: Kung J. K. , Spitzer W. G.
Published: February 2004

Silicon-site distribution in GaAs under the influence of a second dopant was studied by measuring the Si localized vibrational modes and the carrier concentrations of a series of samples. Each sample had the same total Si concentration, [Si], but with different concentrations of a second dopant. Semiquantitative results give a relationship between [SiGa]/ [SiAs] and the concentration of the second dopant which is compared with a calculation based on the thermodynamically predicted Fermi-level effect as formulated by Longini and Greene.
Improvement of Raman spectroscopy by quenching the fluorescence
Authors: Kato Daisuke
Published: February 2004

Fluorescence owing to organic impurities in a Raman spectroscopic sample is quenched by the photochemical reaction, which improves the Raman spectroscopy. The quenching technique is demonstrated in the Raman spectroscopy of liquid methanol.
On breakdown fields of a superconducting niobium cavity at S band
Authors: Kneisel P. , Stoltz O. , Halbritter J.
Published: February 2004

The influence of several surface preparation techniques on both Q0 values and peak rf fields has been studied in a welded beam hole cavity between 2 and 4 GHz. In the TE011 mode peak rf fields up to 810 G at Q0≈1011 have been obtained, whereas, in modes subject to electron loading, the limitations are below 400 G, corresponding to E≲30 MV/m. The significant difference in the breakdown field of modes with and without electron loading show that the observed frequency dependence of Hcrit can easily be explained by electron loading and radiation damage.