bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous increase in strength of i
n s
i
t
u formed Cu-Nb multifilamentary composites
Authors: Bevk J. , Harbison James P. , Bell Joseph L.
Published: February 2003

Cu-Nb wire composites with 0.105, 0.148, and 0.182 volume fraction of Nb filaments were produced in situ and their mechanical properties measured as a function of filament size and interfilament spacing. The yield stress and the ultimate tensile strength increased with both niobium volume fraction and overall composite reduction. At room temperature, the ultimate tensile strength of the Cu–18.2 vol% Nb composite reduced by 99.999% in cross-sectional area (100–200 Å filament thickness) reached the value of 2230 MN/m2 (323 ksi) and further increased to 2850 MN/m2 (413 ksi) when measured at 77 °K. These values are higher by a factor of 4 than the values predicted by the rule of mixtures based on the highest reported strength of both niobium and copper. The composite strength is as high as that of the best copper whiskers and is shown to closely approach the theoretical strength of the material. The anomalous increase in strength despite the low volume fraction of reinforcing filaments suggests that the filaments act primarily as barriers to the motion of matrix dislocations and that the strength of the filamentary material is only of secondary importance. This hypothesis is supported by microstructural obsevations (transmission and scanning electron microscopy) which reveal the deformation modes during composite fabrication and mechanical testing. The excellent transport properties (in both the normal and superconducting state) make these composites attractive as conductors for high-stress applications.
Vibrating-reed measurements of the ΔE effect and internal friction of the higly magnetostrictive alloy Fe2(Tb0.2Dy0.22Ho0.58)
Authors: Berry B. S. , Pritchet W. C. , Savage H. T.
Published: February 2003

The large ΔE effect exhibited by the alloy Fe2(Tb0.2Dy0.22Ho0.58) has been measured dynamically at low frequencies under conditions which closely approach quasistatic equilibrium. It is found that, in common with several other materials, Young’s modulus E passes through a distinct minimum as a function of magnetizing field. The modulus minimum is most apparent during initial magnetization, but occurs with reduced prominence and with typical hysteresis as the material is cyclically magnetized. The origin of the minimum is reviewed in terms of the behavior of the macroscopic ΔE effect, and the frequency above which the minimum is expected to disappear from the measured response is discussed in terms of the theory of stress-induced macroeddy currents. The magnetoelastic internal friction exhibits unexplained features which indicate a need for further study of these alloys.
Analysis of transient temperature distribution in oil shale due to heat source propagating in retort
Authors: Wilhelm H. E. , DuBow J. B. , Hong S. H.
Published: February 2003

The initial-boundary-value problem for the transient temperature fields in oil shale, which is heated by a propagating combustion flame in an in situ retort chimney, is formulated and solved analytically. The heat source of the flame is represented by a Gaussian distribution, which models the average statistical variations in radial and axial flame extensions, and is assumed to build up to maximum strength in accordance with a temporal relaxation process. The transient temperature fields in the oil shale surrounding the retort are calculated and discussed with respect to their spatial variations and dependence on the flame relaxation time. The theoretical temperature distributions are shown to be consistent with those observed experimentally. The high-temperature core extends less than a retort radius into the surrounding shale bed. This result has implications for (i) the in situ retort design and (ii) the environmental impact of in situ retorts. It appears that the spacing between neighboring retorts can be reduced and that the thermal effects of retorts on the environment are less severe than previously anticipated.
The evaporation rate from the cathode spot on base metal electrodes in vacuum arcs
Authors: Kubono Takayoshi
Published: February 2003

The rate of metal evaporation from the cathode spot in a vacuum arc is calculated and expressed in approximate formulas as a function of arc current by use of estimated values of its radius and temperature on the basis of the cathode mechanism theory proposed recently. As the evaporation rate is in good agreement with the experimental erosion rate, these formulas for the radius, temperature, and rate of evaporation on the cathode spot as a function of arc current are very useful in the industrial field.
Laser fluorescence spectroscopy of three-level systems
Authors: Müller K. G. , Stania M.
Published: February 2003

In common laser fluorescence spectroscopy a quasi-instantaneous distribution of the laser-coupled levels according to their statistical weights is assumed. This saturation case can only be achieved by a fast rising laser pulse of sufficient intensity. Otherwise, losses from the laser-pumped levels and the time dependence of the laser pulse have to be taken into account. In this paper a model including losses is investigated. Normalized fluorescence curves result which are characterized by one fit parameter. Into this parameter the rise time of the laser pulse, the overlap of the laser line and of the corresponding atomic line and its oscillator strength enter. The influence of the loss processes on the peak of the fluorescence curve can be shown. The model is applied to measurements at a nonthermal neon plasma of a microwave discharge. Transitions from the levels 2p5 3s 3P0, 3P1, 3P2 to a common upper level 2p5 3p 3P1 have been pumped. Evaluation of the fluorescence signal (2p5 3p 3P1→2p5 3s 1P1) leads to relative populations of the lower levels. The agreement between the theoretical and the experimental fluorescence curve proves the applicability of our model. By this method the range of applicability of laser fluorescence spectroscopy can be extended to nonsaturation cases.
Energy removed from vibration in V-V collisions between SF6 and helium or argon
Authors: Woodroffe J. A. , Kivel B.
Published: February 2003

We have measured the amount of vibrational energy transferred to translation in V-V collisions between SF6 and helium or argon. We used precise mass-spectrometric measurement of the change in SF6 density in a flow of He or Ar and SF6 through a focused cw CO2 laser beam under conditions where the number of collisions in the beam was much less than the collision number for V-T deactivation. We have determined the ratio of energy lost Δ? to the number of collisions for V-V relaxation ZVV to be Z−1VVΔ? =13±6 cm−1/collision for helium and 4±2 cm−1/collision for argon. These values are independent of temperature over the range 150–300 K.
Ionized beam doping in molecular-beam epitaxy of GaAs and AlxGa1−xAs
Authors: Matsunaga Nobutoshi , Suzuki Toshihisa , Takahashi Kiyoshi
Published: February 2003

Molecular-beam epitaxy (MBE) with ion beams as dopants is proposed, and experiments with Zn ions in GaAs and AlxGa1−xAs are reported. In conventional MBE, impurities with low sticking coefficients have not been used because doping into MBE layers involves simultaneous evaporation. In this paper, a method of ionizing the dopant molecular beam and increasing its effective sticking coefficient is proposed. By means of ionization, an effective sticking coefficient of ∼0.03 for Zn ions in GaAs and AlxGa1−xAs is obtained as compared with a value of ∼10−7 for neutral Zn. This value does not vary even with the mole fraction of AlAs in the system AlxGa1−xAs. A strong ion acceleration is not essential for increasing the sticking coefficient, and ionized dopants arriving at the substrate even without enough kinetic energy for penetration beneath the surface react and bond with the surface atoms sufficiently to prevent reevaporation. Crystallographic characteristics of ion-doped GaAs and AlxGa1−xAs films are as good as for undoped MBE layers and the Hall mobilities are comparable to those of LPE and VPE p-type layers. Other electrical and optical characteristics are reported here, and the results show that this modification of MBE can be applied to many other dopants and is a useful method to fabricate various electron devices, especially with complicated structures.
Characterization of (Al,Ga)As injection lasers using the luminescence emitted from the substrate
Authors: Hartman R. L. , Koszi L. A.
Published: February 2003

The spontaneous radiation generated in the active region of (Al,Ga)As double-heterostructure (DH) proton-delineated stripe-geometry lasers has been studied by measuring the luminescence (Ls) emitted from a window fabricated in the metallization on the substrate. Observations of the intensity of this luminescence with an image converter provide an effective means for detecting growth-, processing-, and aging-induced defects. In addition, these measurements provide a simple procedure for separating changes in optical loss from changes in radiative-recombination efficiency. Thus, Ls observations are useful for quality control and laser-aging analysis. For lasers with 8% aluminum in the active region, Ls is shown to be principally radiation reemitted from a very thin layer of GaAs substrate at the interface with the n-type ternary layer. Reasonably high spatial resolution (∼3 μm) of the radiation from the active stripe region is retained in this absorption-reemission process. For devices with no aluminum added to the active layer, the luminescence is mostly single pass radiation from the active region. Quantitative current and spatial dependences of Ls have been obtained which probe the carrier concentration in the active volume. It has also been shown that the threshold current is easily measured by an abrupt change in dLs/di (saturation) and that this slope also characterized the slope of the intensity of the stimulated emission (L) above threshold. In addition, abrupt changes in dLs/di at threshold current have been measured near the edges of the stripe showing that saturation-induced effects are observable over the entire stripe width. In the current increment in which near-field examination of L showed spatial motion of a filament significant spatial changes in Ls were observed (although only for lasers without aluminum in the active layer). Thus, spatial motion of lasing filaments can be correlated with changes in the steady-state spatial carrier-concentration profiles. Many lasers exhibited a decrease in Ls above threshold, most pronounced about the central axis of the lasing stripe. This decrease in the steady-state carrier concentration does not seem to be consistent with a model based on saturable optically absorbing traps.
Angular multiplexing as a technique for short-pulse amplification in a high-gain xenon amplifier
Authors: Sandoval Robert P.
Published: February 2003

It has been proposed that the technique of angular multiplexing could provide an efficient scheme for extracting short pulses from a high-gain laser with a high degree of spatial and temporal control of the extracted laser beam. The scheme of angular multiplexing proposes to amplify short laser pulses (∼1 nsec) by sequentially passing these pulses through the amplifier at slightly different angles. The intensity of each pulse must be sufficient to control amplified spontaneous emission and to extract a significant fraction of the available energy. The experimental demonstration of this technique on the high-gain xenon laser is described here. The measurements were made for a two-pulse train with each pulse width shorter than the amplifier gain period. The results of this experiment indicate that for an optimum pulse separation and input pulse intensity, a major fraction of the available laser energy could be extracted efficiently by the pulse train without significant pulse distortion.
Effect of radial expansion in the laser heating of short plasma columns
Authors: Lai C. S.
Published: February 2003

Plasmas heated uniformly by inverse bremsstrahlung are found to approach a constant electron-ion temperature difference as a function of only the laser intensity and wavelength. A quasistatic model is employed to account for the radial expansion of plasmas. Analytic solutions up to the first order in β are obtained for the electron and ion temperatures.
Crystalline and magnetic properties of an ion-implanted layer in bubble garnet films
Authors: Komenou K. , Hirai I. , Asama K. , Sakai M.
Published: February 2003

Crystalline properties of Ne+-implanted garnet films with varying implantation energies and dosages have been studied by means of the double-crystal x-ray-diffraction method, and it was found that when implantation-induced damage was low, Pendellösung interference was observed which is directly related to crystal perfection, and a layer with large microscopic strain was found to become amorphous. The damage profiles were determined by measuring changes in x-ray rocking curves after etching the implanted layers. Based on these experimental results, an implanted layer model was derived. The influences of the crystalline properties on the magnetic properties were also investigated from the viewpoints of the flux keeper and hard-bubble-suppression effects. For high implantation dosage the amorphous layer becomes magnetically inactive. This phenomenon is ascribed to randomly oriented micro-magnetic-domains with zero net magnetization caused by large microscopic strain in the amorphous layer. The effect of annealing is also discussed.
The redistribution of implanted dopants after metal-silicide formation
Authors: Wittmer M. , Seidel T. E.
Published: February 2003

The redistribution of implanted As and Sb following metal-silicide formation of Pt, Pd, and Ni has been studied. The phases of the silicides used were PtSi, Pd2Si, and NiSi. Investigations with Rutherford backscattering analysis showed that after the formation of the silicides, the Sb was always found in the silicide layer near the surface of the samples, whereas PtSi and Pd2Si caused a partial rejection of As for implanted doses of 2×1015 cm−2 and higher. No rejection of As was found after the formation of NiSi. The results are discussed in terms of solid solubilities and impurity-metal compound formation. The data presented has implications in the fabrication of Ohmic contacts and the adjustments of the heights of Schottky barriers on silicon.
Distorted twisted nematic liquid-crystal structures in zero field
Authors: Scheffer T. J.
Published: February 2003

Leslie’s differential equations describing the orientation of the optic axis through a twisted nematic layer are solved for the case where there is a nonzero tilt bias angle. Three classes of solutions are investigated: the simple solution of constant tilt angle through the layer with uniform twist, symmetric solutions where the tilt angle in the middle of the layer has an extreme value, and antisymmetric solutions where the tilt angle in the middle of the layer is identically zero. These solutions and their corresponding elastic deformation energies are compared for typical values of the splay, twist, and bend elastic constants of nematic liquid crystals. For 90° twisted nematic layers the antisymmetric solution always has a higher elastic energy than the symmetric solution. This result explains why regions of reverse twist are suppressed in twisted nematic display devices which have finite tilt bias angles at both boundaries. Reverse-twisted domains can also be avoided by adding chiral dopants to the nematic mixture and by making layers having total twist angles of less than 90°. The effectiveness of these three techniques is discussed in terms of a comparison of the elastic energy difference between the oppositely twisted configurations.
Surface inhomogeneities on arsenic-implanted silicon
Authors: Vale R. , Dobson P. S.
Published: February 2003

Patterns have been observed on the surfaces of silicon epitaxial layers grown on annealed-silicon substrates which had been implanted with arsenic at high doses and high dose rates. The patterns take the form of bands which lie parallel to the scanning direction of the ion beam and which contain a large density of pits. X-ray topography reveals that the bands are present immediately after the slice had been annealed and the band contrast is sensitive to the diffraction conditions employed. Transmission electron microscopy shows that the bands contain a high density of dislocation loops, as well as the pits which always contain a small precipitate at their center. These results are discussed in terms of temperature variations in the slice during the implantation process which lead to inhomogeneities in the damage and impurity distribution.
Use of heavy doping effects to calculate the electrostatic field acting on the impurity atoms
Authors: Jain R. K.
Published: February 2003

Considering the heavy-doping and high-temperature effects, the electrostatic field acting on the phosphorus atoms into silicon during their diffusion at high temperatures is calculated. It is found that our theory predicts a smaller field than the classically expected results. This anomaly is explained basically by the fact that the Debye length decreases with the increase in the impurity concentration, which ultimately reduces the electric field produced.
Superconducting wires of PbMo5.1S6 by a powder technique
Authors: Luhman Thomas , Dew-Hughes D.
Published: February 2003

Wires of PbMo5.1S6 have been prepared by drawing sintered and powdered ternary sulfide in a metal sheath. Subsequent annealing at high temperatures (850–1000 °C) is necessary to restore Tc to its maximum value ∼14.4 K. The sheath material must not react with and reduce the sulfide, and of the common metals this limits the choice to silver. Critical fields Bc2 (4.2 K) ?51 T of these wires are the same as for the best powder samples, but current densities, Jc (4.2 K, 4 T) ∼ (1–5) ×107 A/m2, are disappointingly low.
The penetration depth of 0.5–3-keV electrons in solid hydrogen and deuterium
Authors: Schou J. , So/rensen H.
Published: February 2003

The mirror-substrate method was used for measuring the penetration depth of 0.5–3-keV electrons in solid hydrogen and deuterium. The penetration depth was found to be 0.53×1018E1.72 molecules/cm2 with the energy given in keV. There was satisfactory agreement with other data. The measurements also showed that the escape depth for true secondary electrons from solid deuterium is less than 50 Å, which agrees well with the small values for the secondary-electron-emission coefficient found for solid deuterium. Results were furthermore obtained for the electron-reflection coefficient for the gold substrate, i.e., the number of electrons that are reflected with high energies. The electron-reflection coefficient agrees well with other results, both with respect to magnitude and energy dependence.
Effects of photodecomposition on the electrophotographic properties of amorphous As2Se3
Authors: Hillegas W. J. , Neyhart J. H.
Published: February 2003

Selenium-arsenic alloys undergo a photochemical reaction when exposed to radiation of band-gap energy or greater. The influence of this photoinduced reaction on the electrophotographic photosensitivity of amorphous arsenic triselenide films was studied. A progressive change in the short-wavelength photoresponse was seen in films which were exposed to intense light. The characteristics of the change depend upon the substrate temperature during the vacuum deposition of the film. Films prepared at substrate temperatures below Tg initially showed an increase in sensitivity, possibly due to structural relaxation or molecular rearrangement within the film. The initially measured spectral sensitivity of films prepared below Tg was always lower than that for films prepared near Tg. All films eventually showed a reduction in short-wavelength sensitivity. The rate of this change increased at elevated temperatures. The photolytic reaction itself does not affect the photosensitivity. The reduction in photosensitivity is a result of the oxidation and subsequent depletion of arsenic at the surface of the photoconductor which is enhanced by the prior photodissociation of the arsenic triselenide.
Catalysis and quenching of N2 afterglows by SF6
Authors: Sutton D. G. , Melzer James E. , Heidner III R. F.
Published: February 2003

Spectra are presented from flowing afterglows in N2 produced by a microwave discharge. The luminescence from pure N2 discharges can be characterized as a typical Lewis-Rayleigh afterglow with no molecular emission in the ultraviolet. Trace amounts of SF6 added upstream of the discharge greatly enhance the first-positive emission from the afterglow and produce intense emission from the N+2 first-negative system and the appearance of N2 second-positive emission. Further SF6 addition downstream of the microwave discharge quenches the N+2 first-negative bands but causes no appreciable change in the emission from the N2 second-positive bands. Increasing the SF6 added prior to the discharge by a factor of 15 results in complete quenching of all N2 ultraviolet emission which is replaced by NS B-X luminescence.
Auger electron analysis of oxygen contamination in sputter-deposited Nb films
Authors: Schwanebeck J. C. , Buitrago R. H. , Toth L. E. , Goldman A. M. , Cantor R.
Published: February 2003

Oxygen contamination in sputter-deposited Nb films was measured as a function of background pressure and other sputtering variables using Auger electron spectroscopy. Significant variables affecting purity were the degassing rate and the ultimate background pressure prior to sputtering. Serious contamination occurred even when the background pressure was in the 10−10-Torr range. Getter sputtering within a cryogenically cooled container with the appropriate sputtering variables can reduce contamination to a level nearly identical to that of the target material.
The distribution of vibrationally excited states in resonant radiation and the rate of photodissociation
Authors: Steverding B. , Dudel H. , Gibson F. P.
Published: February 2003

The distribution of vibrational states which are excited by resonant radiation and deactivated by a relaxation process is strongly influenced by the anharmonicity of the molecule and the red shifting of the resonant frequency. Steady-state distribution curves are calculated for the BCl3 molecule, the ν3 mode of which is resonant to CO2 laser light. A flux of states is defined for these distribution functions which is recognized as the rate for photochemical reactions. Some results are given for photodissociation, which show that proper detuning of the light can increase the rate of photodissociation by several orders of magnitude.
A SQUID device for ac current measurements down to 10−14 A
Authors: Barbanera S. , Carelli P. , Modena I. , Romani G. L.
Published: February 2003

A new method for measurements of ultralow currents in the audio-frequency range (from dc up to over 104 Hz) has been developed. The combined use of a ferromagnetic current transformer and of a superconducting flux transformer together with a rf-biased SQUID allows measurements of currents as low as 10−14 A. A detailed circuital analysis and considerations on the input impedance of the device are presented. The agreement between predictions and experiments is quite good. The measured noise level beyond the low-frequency region keeps at values typical of commercial SQUID’s.
A lower bound for the length of an autoresonant accelerator
Authors: Proctor W. A. , Genoni T. C.
Published: February 2003

A lower bound is derived for the length of an autoresonant accelerator designed to produce relativistic positive ions of a given energy. The ion kinetic energy is found to scale as the 2/3 power of the distance along the accelerator in the nonrelativistic limit and as the 1/3 power in the ultrarelativistic limit. For protons trapped in a negative-energy Doppler-shifted cyclotron wave that enters the accelerator with a phase velocity of 0.05c, we estimate that GeV energies can be attained only if the accelerator length exceeds 75 m, which is roughly 10 times greater than previous estimates made by the authors of this collective acceleration scheme.
A quick method for determining the characteristics of a step index optical waveguide
Authors: Chartier Germain H. , Jaussaud Pierre C.
Published: February 2003

We show how the characteristics (index and thickness) of an optical step index waveguide can be determined very easily, no calculations being necessary. The method is compared to some results published in the literature, and the agreement is found to be better than 5×10−3 with other methods.
Generation of MeV and GeV ions by relativistic self-focusing from laser-irradiated targets
Authors: Hora H. , Kane E. L. , Hughes J. L.
Published: February 2003

The short-range shrinking of a laser beam in a solid by relativistic self-focusing generates intensities which accelerate highly charged ions to MeV energies in agreement with experiments. Limitations at higher energies due to ionization, relativistic limits, and Debye length are given.
Propagation along a dielectric-rod waveguide embedded in a magnetoplasma
Authors: Basu J. , Das S. K.
Published: February 2003

This paper presents a study of the dispersion relation for propagation in the TM0m mode along a dielectric-rod waveguide immersed in collisionless plasma with a strong static magnetic field in the direction of the rod axis. Dispersion characteristics, covering all plasma densities, are plotted for a typical value of the dielectric constant (εd) of the rod. A discussion of how the characteristics would change if εd is varied is also presented. In particular, the special case in which εd=1 and the dielectric rod is replaced by a vacuum channel is investigated in detail.
The Hall and the magnetoresistive effect of amorphous Fe-Si films
Authors: Shimada Y. , Kojima H.
Published: February 2003

Measurements on the Hall and the magnetoresistive effect in Fe-Si amorphous films are described. The spontaneous Hall constant Rs increases as the Si content increases. A sensitive irreversible change of Rs was observed by annealing. Rs increases by crystallization. The magnetoresistive effect Δρ/ρ is low but Δρ is comparable to those of Fe-Ni crystalline alloys.
On the efficient calculation of magnetic bubble functions
Authors: Hegedüs C. J. , Della Torre E.
Published: February 2003

The various magnetic bubble stability functions as well as the field due to a bubble are all expressed in terms of a single generalized complete elliptic integral. This integral can be computed efficiently to arbitrary accuracy using the Bartky transformation.
On the effects of thermal expansion in metal-matrix composites
Authors: Wang Frederick E. , Sutula Raymond A.
Published: February 2003

Based on a qualitative argument, it is shown that the detrimental effect due to differential thermal expansion existing between fiber and metal-matrix in MMC (metal-matrix composite) is minimized for shorter fibers. The ’’ideal’’ aspect ratio for fibers found experimentally in MMC is also justifiable within the same argument.
Diffusion of Ag110 into single-crystalline copper in a temperature gradient
Authors: Shih S. , Stark J. P.
Published: February 2003

Silver-110 was diffused into the cold end of copper single crystals exposed to a temperature gradient to determine the presence of over-equilibrium vacancy concentrations as has been shown previously for aluminum. For these experiments, the hot end of all nonisothermal experiments was 1000 °C, with the temperature of the cold end between 790  and 1000 °C for various anneals. A least-squares fit of these data yields D0=0.57 cm2/sec and Q′=191.9±1.7 kJ/mol. Isothermal measurements on this system from this research may be described by D0=0.79 cm2/sec and Q=195.2±2.5 kJ/mol, which compares favorably with the previous results of Tomizuka where Q=194.4 kJ/mol. The agreement between the activation energies implies that vacancies follow an equilibrium distribution in copper to within the accuracy of this determination. This may be contrasted to recent results in single crystals of aluminum, where a major withdrawal from equilibrium was determined, and with silver, which demonstrated a lesser withdrawal as a consequence of nonisothermal conditions.
Shear strain at corners and edges of epitaxial silicon on sapphire
Authors: Abrahams M. S. , Blanc J. , Buiocchi C. J. , Ham W. E.
Published: February 2003

Silicon on sapphire composites into which notches and ’’islands’’ were formed were studied by transmission electron microscopy. Shear strains are found near edges in both 7- and 0.6-μm-thick Si. Their magnitude can exceed that of the grown-in compressive strains by an order of magnitude. The shear strain is a maximum (?2%, corresponding to 1.5×1010 dyn/cm2) at the corner of the silicon/sapphire interface and decreases in an exponential-like manner both along and normal to the interface. These shears are believed to result from transformation of the compressive strains in regions of the Si which are mechanically free to relax. An approximate model giving reasonable agreement with the fractional change of the shear strain with distance along the interface is presented. Experimentally, the shear strain in silicon on sapphire varies along the interface as γ?0.02 exp(−x/bT), where bT is the total overgrowth thickness and x is measured from the corner position. Mechanical, electrical, and chemical effects of this shear strain on devices are considered. Similar effects can be expected in all semiconductor composites with grown-in strain.
Magnetic field dependence of far-infrared spectra of NdF3
Authors: Bäuerle D. , Borstel G. , Sievers A. J.
Published: February 2003

The Zeeman splitting of the lowest Kramers level of the 4I9/2 ground state in NdF3 has been measured by far-infrared techniques. The principal components of the g tensor, gx=1.72, gy=1.03, and gz=3.02, were derived. A line at 18 cm−1, which is induced by the magnetic field, but does not shift, was observed.
Dielectric-relaxation currents in cadmium borosilicate glasses
Authors: Manfredo Louis J. , Pye L. David
Published: February 2003

A dielectric-relaxation model has been proposed by Simmons and Taylor to explain anomalous currents in silicon nitride thin films. In this study, similar currents are observed in certain cadmium borosilicate glasses. The presence of a color center and of composition indepedence of the activation energy for electronic conduction (1.42±0.02 eV) indicate that these glasses possess identifiable defect energy states which are required by the dielectric-relaxation model. The glass compositions range from 57.5 to 67.5 mol% cadmium oxide with the B2O3/SiO2 mole ratio held constant at 2.25. The results are experimental verification of the dielectric-relaxation phenomena in a bulk noncrystalline solid.
Trapped-electron doping of photovoltaic sandwich cells containing microcrystalline chlorophyll a
Authors: Corker G. A. , Lundström I.
Published: February 2003

Cr‖Chla‖Hg sandwich cells with microcrystalline chlorophyll a exhibit rectifying I-V characteristics, whereas Au‖Chla‖Hg cells show Ohmic behavior. We present a comparative study of their ac and dc electrical properties. The impedances of both structures increase with age. The aging process can be reversed by light, suggesting that a trapped space charge controls the impedance levels. The results are consistent with an interpretation that the space charge is trapped electrons which function like a dopant in the Chl layer. The results with the Cr cells show the presence of an interfacial barrier region at the Cr-Chl contact which is responsible for the photovoltaic activity of these cells. The extent of this region is governed by the negative space charge. In a cell with approximately 7×1016 electrons/cm3, the width of the barrier is about 450 Å.
Charge injection and storage in thin films of chlorophyll a
Authors: Lundström Ingemar , Corker Gerald A. , Stenberg Manne
Published: February 2003

Chlorophyll a microcrystals can be electroplated from a suspension in an organic solvent. The optical-absorption spectra of the resulting films indicate an interaction between the porphyrin rings of different molecules. It is shown that these films can store electronic charge. The charge storage was studied by plating the chlorophyll on silicon and using the well-known C (V) technique. It is also shown that monomeric films, made by heating the microcrystalline films at about 100 °C, have different charge-storage properties. The charge-injection and charge-storage properties of the chlorophyll films are discussed in terms of the molecular arrangement of the films. The results are also compared with ac- and dc-conductivity measurements of the films.
The accuracy of Schottky-barrier-height measurements on clean-cleaved silicon
Authors: van Otterloo J. D. , Gerritsen L. J.
Published: February 2003

Schottky-barrier diodes have been realized by cleaving n-type Si in ultrahigh vacuum (UHV) in a stream of evaporating metal atoms. The properties of these Al, Mg, and Fe diodes are studied by means of standard I-V, C−2-V, and photoemission threshold measurements in the same UHV. With an error analysis it is shown that the barrier height is most accurately obtained from C−2-V measurements. This is in contrast to the prevailing opinion that the barrier height from photoemission measurements is the most reliable measure of the barrier height. It will be shown that a correct value from the photoemission experiments is obscured by the difficulty in determining the exact number of absorbed photons in the metal (back illumination). Finally, reported large systematic discrepancies between barrier heights from photoemission measurements and those from C−2-V measurements were not observed. All observed differences remain within the experimental error.
Thermal stability of superconductors with large surface barriers to flux entry: Superconducting power-line conductors
Authors: Kim S. , Howard R. E. , Beasley M. R.
Published: February 2003

The effect of surface barriers to flux entry on the stability of superconductors at low fields is considered theoretically in the context of the usual critical-state model. The presence of such a barrier is found to greatly reduce overall stability unless a thin normal-metal overcoat is used to stabilize the superconductor. The relevance of these results to superconducting power transmission lines is discussed.
Pyroelectric induced optical damage in LiNbO3
Authors: Schein L. B. , Cressman P. J. , Cross L. E.
Published: February 2003

Laser-induced changes in the extraordinary index of refraction (optical damage) in ferroelectrics are caused by macroscopic charge separation produced during laser illumination. If the sample is heated in the vicinity of the laser beam, pyroelectric fields are produced in ferroelectrics which can also produce macroscopic charge separation. We report the observation of the continuous transition in LiNbO3 between macroscopic charge separation associated with optical damage and pyroelectricity. Macroscopic charge separation due to pyroelectricity represents a second source of optical damage in ferroelectrics which can occur whenever the temperature of the sample is raised significantly (32 °C for LiNbO3).
Transmittance and reflectance of a coated substrate with application to index measurement of thin films
Authors: SooHoo J. , Henry R. D.
Published: February 2003

Equations are derived for the transmittance and reflectance of a coated substrate of finite thickness. These equations are valid for thick substrates and thin films whose surfaces are specularly reflecting. It is found that the results are in good agreement with spectrophotometer readings of corresponding laboratory samples. Based upon the present results, a simple technique for calculating the refractive index of thin films from photometer readings is given.
Repetitive self-Q-switching in a continuously pumped ruby laser
Authors: Szabo A.
Published: February 2003

We report the observation of repetitive self-Q-switched pulses from a continuously operating ruby laser pumped by an argon ion laser. 500-W pulses of 2 nsec width at a 3-kHz rate are observed. It is tentatively concluded from the pulse characteristics and other data that the phenomenon can be explained by a saturable absorber mechanism.
Optically pumped taper-coupled GaAs-AlxGa1−xAs laser with a second-order Bragg reflector
Authors: Miller Robert C. , Nordland W. A. , Logan R. A. , Johnson L. F.
Published: February 2003

Optically induced laser action has been achieved at room temperature with a structure consisting of a pumped double-heterostructure (DH) GaAs active layer taper coupled to a low-loss passive AlxGa1−xAs waveguide incorporating a second-order Bragg-reflection grating which served as a feedback component. In terms of injection pumping, the lasing threshold is equivalent to approximately 8 kA/cm2. In contrast to optically pumped conventional DH GaAs-AlGaAs lasers, the output has a spectral width reduced to 2 Å, its wavelength is insensitive to the pumping geometry, and the lasing always occurs in time at the peak intensity of the pump. Additional relevant active and passive data are also given.
A high-efficiency tunable picosecond dye laser
Authors: Huppert D. , Rentzepis P. M.
Published: February 2003

A picosecond dye laser system has been developed which utilizes the 265-, 355-, and 530-nm pulse harmonics of a mode-locked Nd+3 glass laser to pump transversely several dyes which emit tunable picosecond pulses from 340 nm to near infrared. The psec dye laser pulses are amplified in a specially designed dye cell pumped by a Q-switched Nd/glass laser to energies of ∼4 mJ per picosecond pulse with a pulse width of 7 psec.
Gain measurements at 4416 Å on ArXeF* and Kr2F*
Authors: Hunter R. O. , Oldenettel J. , Howton C. , McCusker M. V.
Published: February 2003

Recent measurements of radiation from certain rare gas–halogen mixtures have indicated the efficient production of broadband emitters in the visible. This paper reports a gain measurment at 4416 Å in mixtures containing the two emitters tentatively identified as Kr2F* (λmax=4000 Å and FWHM=900 Å and ArXeF* (λmax=4600 Å and FWHM=900 Å). Attenuation of the 4416-Å probe laser during electron-beam and electron-beam-sustained discharge excitation of 2–3 atm pressure mixtures of argon-krypton-fluorine and argon-xenon-fluorine indicates absorption only. The fluorescence signals from ArXeF* and XeF* (Ar/Xe/F2 mixture), and KrF* and Kr2F* (Ar/Kr/F2 mixtures) were monitored simultaneously with the absorption of the probe laser. Since the absorption was not proportional to the fluorescence of these species, it is tentatively concluded that it is due to another transient species. Typical absorptions of 10−3 cm−1 were observed at pump levels of 105 W cm−3. A knowledge of the absorption mechanism will be required to assess the efficiency with which such lasers can be made to operate, if at all.
Intensity of the low-pressure high-current cadmium vapor discharge in the middle ultraviolet
Authors: Johnson Peter D.
Published: February 2003

The intensities of the Cd 2288- and 2981-Å and Cd+ 2144- and 2265-Å lines have been measured as a function of Cd vapor pressure in the Cd-Ar discharge. Except for the 2981-Å line, the intensities are highest at Cd vapor pressures in the range 5–30 mTorr. The 2981-Å line increases in intensity with increasing Cd vapor pressure in the 5–200-mTorr range. Absolute radiant flux densities have been determined by calibrating the spectrometer response using a low-pressure mercury discharge.
Analysis of surface waves using orthogonal functions
Authors: Datta Supriyo , Hunsinger Bill J.
Published: February 2003

A simple noniterative method using an orthonormal basis for expressing field distributions has been developed for obtaining surface-wave solutions in piezoelectric crystals. Velocity and field distributions are obtained for YZ LiNbO3 that agree with earlier works. The boundary conditions are incorporated in a manner that is easily adapted to layered structures. Dispersion curves are obtained for surface waves in LiTaO3 with a SiO2 layer at the surface; the results are in good agreement with those published earlier.
High-efficiency low-energy x-ray spectroscopy in the 100–500-eV region
Authors: Henke Burton L. , Perera Rupert C. C. , Gullikson Eric M. , Schattenburg Mark L.
Published: February 2003

The lead myristate multilayer analyzer has provided a basis for a relatively simple and efficient spectroscopy for the low-energy x-ray emissions in the 20–80-Å region (where conventional crystal spectroscopy and grazing incidence grating spectroscopy are generally inefficient). The percent reflectivity, the integrated coefficient of reflection, and the Bragg diffraction width of the lead myristate analyzer have been measured and found to be consistent with the predictions of a simple theoretical model for multilayer diffraction. This multilayer spectroscopy at large Bragg angles has a high efficiency (high instrument transmission) as compared to grazing incidence grating spectroscopy in this 20–80-Å region. However, the resolution is limited to that set by the diffraction width of the lead myristate analyzer of about 1 eV. Because the collimator-crystal broadening function can be precisely defined, a simple and effective deconvolution procedure can be applied with this multilayer spectroscopy to bring the resolution into the sub-electron-volt region. To demonstrate the efficiency of lead myristate spectroscopy in the 20–80-Å region, spectra were measured and analyzed from x-ray excited fluorescent sources which are characteristically of low intensity. (X-ray excitation yields a minimum of background spectra and of radiation damage.) These include the L2,3 atomic spectrum of argon and the C-K molecular spectrum of CO2, both in the gas phase, and the Cl-L2,3 and O-K spectra from solid lithium perchlorate. Many samples undergo appreciable radiation-induced chemical change during the exposure time that is required for measurement—even with an optimally fast spectrograph and with fluorescent excitation. A method has been developed to evaluate and to correct for radiation damage by distributing the exposure over an effectively large sample volume either by gas flow or by rotating through multiple samples during measurement. Several spectral scans were made on the LiClO4 using six samples. The total exposure time for each data point in each scan was recorded which permitted an extrapolation into a ’’zero’’ exposure spectrum. Finally, Fe-L2,3/O-K spectrum (from Fe2O3) in the 17–25-Å region is presented to illustrate the effectiveness of the lead myristate analyzer in third-order diffraction. For this multilayer, the third-order diffraction efficiency is one-third that of the first order and is nearly twice that of the second order for this wavelength region.
Relief-exposure characteristics of radiographs in relief
Authors: Mardix S. , Keene M. , Swyt D. A. , Teague E. C.
Published: February 2003

Highly exposed radiographs are utilized in microradiography in order to increase the signal-to-noise ratio. Relief radiography enables the evaluation of these microradiographs. Relief-exposure characteristics are shown to follow a relationship of the type R=Rm[1−exp(−E/Em)], where R is the relief height, E is the exposure, and Rm and Em are constants. The density of developed silver in Ilford L-4 nuclear emulsion is found from the value of Rm to be 2.86. The constant Em is shown to give the exposure for maximum contrast. The experimental results are discussed and compared to those found in the literature.
uv photoion density measurements using a high-pressure Langmuir probe
Authors: Santiago J. , Robinson A. M.
Published: February 2003

Volume ionization produced in Ar by uv photoions was measured using a fast rotating Langmuir probe. The uv radiation was obtained from an electric discharge and collimated to produce a cylindrical plasma. Measurements were performed for pressures of 100, 200, 400, and 600 Torr and distances of 2.5–10.2 cm from the discharge. Plasma decay was observed from 50 to 350 μs after the discharge was fired and was attributed to radial expansion by ambipolar diffusion and volume recombination. By an extrapolation process, the initial photoion density can be obtained; its distance dependence suggests two-photon ionization of Ar. The results are also compared to other measurements found in the literature.
Analysis of the cathode fall in high-voltage low-current gas discharges
Authors: Neuringer Joseph L.
Published: February 2003

An analytic investigation is made of the cathode-fall region in high-voltage low-current gas discharges. Explicit expressions for the variation of electric field, voltage drop, charge density, Joule heating, and cathode-fall thickness are obtained as functions of pressure, current density, gas properties, and distance from cathode. To first order, it is shown that the former two quantities depend on the two-thirds power of the ratio of the current density to pressure squared, that the electric field varies linearly in the cathode-fall region, and that the fall thickness is independent of the operating current and varies inversely with pressure. To illustrate the order of magnitudes involved, a numerical calculation is made using helium as the working gas.
Temporal growth of filamentation instability in plasmas
Authors: Sodha M. S. , Sharma J. K. , Sharma R. P. , Kaushik S. C.
Published: February 2003

In this paper we have derived an expression for the growth rate of filamentation instability, valid for arbitrary intensity of the electromagnetic wave and upto plasma resonance (ωp?ω0 here ωp and ω0 are the field free plasma frequency and EM wave frequency respectively). In a collisionless plasma and on the short time scale (tτε, τε being the energy relaxation time) in a collisional plasma, the nonlinearity arises on account of pondermotive force and consequent depletion of electrons in regions of large wave amplitude. On the time scale of energy relaxation time in a collisional plasma, the dominant nonlinearity arises on account of preferential heating electrons. It is found that (i) maximum growth rate attains it’s maximum for an optimum intensity of the beam (ii) filamentation is predicted in the over dense plasmas (ωp≳ω0).
Uniform doping of channeled-ion implantation
Authors: Nishi H. , Inada T. , Sakurai T. , Kaneda T. , Hisatsugu T. , Furuya T.
Published: February 2003

This paper describes an apparatus designed to obtain spatial uniformity of channeled-ion implantation using a parallel-scanning system. Descriptions of the special sample holder which can be tilted in two directions and a detecting scheme for channeling alignment are also included. This apparatus implanted channeled B ions along the [110] axis of silicon (Si). The variations of the implanted profiles and the breakdown voltages of the fabricated diodes in a wafer are compared with those obtained by random implantation and by channeled-ion implantation using an angular-scanning system. High doping uniformity comparable to that of random implantation is obtained reproducibly, proving that channeled-ion implantation using a parallel-scanning system can provide a controlled technique for device fabrication.
Effect of bias voltage on the hardness of {101̄0} ZnO surfaces immersed in an electrolyte
Authors: Ahearn J. S. , Mills J. J. , Westwood A. R. C.
Published: February 2003

Recent work has demonstrated that the hardness of the (0001) ZnO surface is sensitive to surface charge (controlled by an applied voltage in an electrolytic cell), maximum hardness being produced by a slightly positive surface charge. The uniqueness of these findings was examined in the present work by measuring the hardness of {101̄0} ZnO surfaces as a function of applied cell voltage. The results are similar to those reported earlier. A mechanism involving charge exchange between donor levels and the conduction band near moving dislocations, used to interpret the data for the (0001) surface, is applied to the results from {101̄0} surfaces. To obtain agreement with the experimental results, an upward distortion of the conduction band of ∼+200 meV near basal dislocations must be assumed. This contrasts with the downward band distortion of ∼−50 meV near prismatic dislocations assumed to explain the earlier data.