bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrostrictive effect in lead magnesium niobate single crystals
Authors: Uchino K. , Nomura S. , Cross L. E. , Jang S. J. , Newnham R. E.
Published: February 2003

Transverse and longitudinal elastic strain have been measured for electric fields applied along the 〈100〉 direction in single crystals of lead magnesium niobate [Pb(Mg1/3Nb2/3)03], using a bonded strain gauge technique. A quadratic electrostrictive relation holds between induced elastic strain and electric polarization for temperatures near the low-frequency dielectric maximum. The electrostriction coefficients are almost temperature independent with values Q11=2.50×10−2 m4/C2 and Q12=−0.96×10−2 m4/C2. To check the direct measurements, the hydrostatic Q coefficient was determined independently by measuring the pressure dependence of the dielectric permittivity. The value Qh =0.60×10−2 m4/C2 obtained is in good agreement with that calculated from the direct measurements.
Saturation of transmitted intensity of CO2 laser pulses in germanium
Authors: Yuen S. Y. , Aggarwal R. L. , Lax B.
Published: February 2003

The transmission behavior of 90-ns CO2 laser pulses through germanium has been studied at high intensities up to 20 MW/cm2. With increasing incident intensity, the transmitted intensity was observed to saturate quite abruptly at a level which decreased with increase in crystal length. The saturated level of transmitted intensity was found to be higher at lower temperatures. The observed transmission behavior is interpreted in terms of multiphoton absorption across the direct band gap, followed by absorption by the excess carriers thus generated. By fitting experimental data to a phenomenological model, a room-temperature seven-photon absorption coefficient of 1.5×10−9 (cm2/MW)6 cm−1 is obtained for germanium in the 10-μm region.
Effect of hydrogen on the temperature dependence of the elastic constants of vanadium single crystals
Authors: Ko C. R. , Salama K. , Roberts J. M.
Published: February 2003

The changes in the absolute values of the elastic constants C′, CL and C44 by the ultrasonic technique over the temperature range 144–320 K with varying amounts of hydrogen in Vanadium up to 1.5 at.% have been determined. In the α phase, the changes in the absolute values of C′ and CL were found to be linear with negative slopes of 2.0% and 0.5%/at.% H, respectively. The changes in C44 in the α phase varied between 0 and 0.5 or 0.9% H. The bulk modulus and Voight-Reuss average Young’s modulus in that phase were found to decrease 0.70% and 0.65%/at.% H, respectively. The elastic constants in the temperature range of the α phase exhibited no change in their temperature dependences by the addition of hydrogen. The present results are compared to the results of other published investigations. The anharmonic effects are discussed in the light of the volume expansion due to H in V upon the elastic constants, the possible electronic effect by suggesting the addition of H to V is analogously similar electronically to adding Cr to V and finally the Snoek relaxation effect. It is concluded that the Snoek relaxation best describes the ΔC′ effect observed when hydrogen is present in the α phase. This effect yields an asymmetric distortion energy parameter [3(A−B)/(A+2B)] of the order of 0.47.
Role of atmosphere in the crystallization of amorphous plasma-sprayed Sm-Co deposits
Authors: Kumar K. , Das D. , Williams R.
Published: February 2003

Thick, machinable, and amorphous 1Sm-5Co plasma-sprayed deposits show a high resistance to magnetization and demagnetization at room temperature. This behavior is believed to be related to large internal stresses and variations in chemical composition present in the as-sprayed material. Thermal treatments of these deposits, in argon, at temperatures substantially lower than those required for crystallization, produce little change in their magnetic behavior. Similar treatments in hydrogen, however, result in an easy approach to saturation and very low coercivity values. This different response of the material to hydrogen has been attributed to an increased mobility of the atoms in hydrogen, which permits sufficient rearrangement of the atoms so that high magnetization and low coercivity are achieved in the amorphous state. Use of a hydrogen atmosphere also results in a considerable increase in the temperature required for crystallization. Whereas crystallization occurs at about 500 °C in argon, temperatures of about 700 °C are needed to produce similar effects in hydrogen. The suppression of the crystallization processes in hydrogen has been attributed to a deposit-hydrogen chemical interaction at the low temperatures. The results of this study indicate that amorphous 1Sm-5Co is probably more suited for use as a means for storing hydrogen than is crystalline SmCo5 material.
Influence of phosphorus-induced point defects on a gold-gettering mechanism in silicon
Authors: Lecrosnier D. , Paugam J. , Richou F. , Pelous G. , Beniere F.
Published: February 2003

Deep-level transient spectroscopy (DLTS) and neutron-activation analysis have been applied to measure the gold distribution after a phosphorus gettering step. It is found that the gettering mechanism is able to operate without induced dislocations but depends mainly on the surface phosphorus concentration. For example, when Cs=1021/cm3, the gold concentration is reduced by a factor 103 over the whole thickness of a wafer. This Au trapping phenomenon is attributed to the presence of a phosphorus-induced point defect and related to the emitter push effect mechanism.
Edge emission in zinc sulphide
Authors: Gezci S. , Woods J.
Published: February 2003

The cathodoluminescence emission spectra of a number of cubic ZnS crystals have been measured at 8 K. Two series of LO-assisted bands were observed with their zero-order components at 3360 and 3395 A. were prominent at 3300 and 3330 A.
Gas-flow-controlled arcs for power collection
Authors: Klapas D. , Hackam R. , Benson F. A.
Published: February 2003

Arcs in axial, free or constricted, gas flows were found to be promising as a means of contactless power collection for high-speed ground transportation vehicles. Satisfactory current collection at speeds up to 250 km/h has been achieved with a 6-mm gap. Higher speeds or larger gaps, however, may require partial aerodynamic shielding or magnetic trapping of the arc column.
Blue-band emission in LiInS2 crystals
Authors: Kamijoh T. , Kuriyama K.
Published: February 2003

A new material, LiInS2 (β-NaFeO2 type: wurtzitelike structure), for blue-light emission is proposed. A deep blue-band emission is observed by photoluminescence measurements at 77 K. The peak value is 453 nm for colorless as-grown crystals. From the annealing studies in a sulfur atmosphere, sulfur vacancies are responsible for the blue-band emission.
Photoinduced chemical changes in obliquely deposited amorphous Se-Ge films
Authors: Singh Bhanwar , Rajagopalan S. , Chopra K. L.
Published: February 2003

A large photoinduced change in the chemical solubility of obliquely deposited a-Se1−xGex films has been observed. The effect is a function of composition of the film, angle of deposition (obliqueness), annealing, exposure kinetics, and temperature of etching solution. The occurrence of large photochemical effects in obliquely deposited films is related to the creation of metastable defect centers on illumination. The effect has been utilized to obtain micron-resolution photolithographic patterns.
Photostructural change in the Urbach tail in chalcogenide glasses
Authors: Utsugi Yasushi , Mizushima Yoshihiko
Published: February 2003

Absorption properties in the Urbach tail range were studied in relation to the photostructural change (PSC) or the photodarkening effect in amorphous-chalcogenide semiconductors. A reversible absorption change in the Urbach tail of amorphous-chalcogenide films due to photoirradiation and heat treatment is first reported. The Urbach tail is relaxed by photoirradiation and recovered by heat treatment, an effect which is associated with the effect of the photoenhanced far-infrared band broadening in amorphous-chalcogenide films. Temperature dependence of the absorption is found to be closely associated with the frequency of the dominant far-infrared absorption of the vibration mode. It is indicated that optically excited randomness, due to the photostructural change, contributes to the photoenhanced relaxation of the exponential tail slope. Analysis of the tail slope parameter reveals strong electron-phonon couplings at the Ge-Se (S) or As-Se (S) bond. The photostructural change physical mechanism is discussed, and the frozen-in fictive temperature concept is found adequate.
Angular and energy distributions of H and He atoms backscattered from gold
Authors: Verbeek H. , Eckstein W. , Bhattacharya R. S.
Published: February 2003

A clean Au target was bombarded with H and He ions with primary energies between 5 and 16 keV at normal incidence. The energy distributions of the backscattered particles at exit angles between 25° and 90° were measured. The angular distributions derived from these were cosine within the experimental errors. The experimental results were compared with computer simulations with the new TRIM program. There is satisfactory agreement between the measured and computed energy and angular distributions, but a considerable difference in the reflected intensities.
Double-etching technique for the fabrication of submicron channels on a GaAs wafer and its application to laser fabrication
Authors: Chen Chung-Yih , Wang Shyh
Published: February 2003

We demonstrate in this paper a simple, reproducible, uniform, and reliable double-etching technique which enables us to make submicron channels on a GaAs wafer from a photomask of considerably larger dimension. Only conventional photolithographic process and preferential etching are required. The technique consists of stripping the photoresist after a first-step preferential etching and then immersing the wafer back into the etchant to perform the second etching. As a first example, we have applied this technique to the fabrication of a channeled-substrate planar laser using liquid-phase epitaxy. The surface morphology of the LPE layers and the performance of the laser are shown to be of superior quality.
Design parameters for reducing radiation confinement errors and the spatial dependence of the emission delays in light-emitting diodes
Authors: Cancellieri G. , Mezzetti M.
Published: February 2003

The generic multilayer structure under the top emitting surface of a Burrus-type LED is considered as a radial transmission multiline system. By this model, which gives results in good agreement with experimental measurements, it is possible to explain radiation confinement errors and the spatial dependence of the emission delays. This model allows one to obtain also the optimum numerical values of a set of design parameters in order to reduce these two undesired effects.
Shear strength of some semisintered oxides at high pressure
Authors: Onodera Akifumi , Suito Kaichi , Ogo Yoshiaki , Okuri Yasuhiro
Published: February 2003

The shear strength of semisintered MgO, ZrO2, Al2O3, and Fe2O3 has been measured up to 30 kbar using an opposed anvil shear device. The shear strength of each oxide increases quite linearly with increasing pressure.
Dependence of thermal diffusivity on organic content for Green River oil shales—Extension of the modified Cheng-Vachon model to the parallel heat-flow case
Authors: Wang Y. , Rajeshwar K. , DuBow J.
Published: February 2003

In an earlier paper [J. Appl. Phys. 50, 2776 (1979)], the modified Cheng-Vachon model was found to give good agreement with experimental data on the variation of thermal diffusivity with organic content for Green River oil shales. Calculations using the model were carried out for the case where heat flows in directions perpendicular to the shale stratigraphic planes. In the present paper, the above model is modified to account for experimental trends in the parallel heat-flow case. The modified model provides a self-consistent explanation for the lower degree of anisotropy (relative to theory) that has been experimentally observed for the thermal diffusivity of Green River oil shales.
Electrical conductivity of a seeded H2/O2 system
Authors: Sawhney B. K. , Hussain S. Q. , Swithenbank J.
Published: February 2003

A H2/O2 system is suggested as a working fluid for an open-cycle MHD generator, and the conductivity of seeded combustion products of such a system has been investigated.
Comment on ’’High coercivity, isotropic plasma sprayed samarium-cobalt magnets’’
Authors: Buschow K. H. J. , den Broeder F. J. A.
Published: February 2003

It is shown that the experimental results obtained by Kumar et al. on plasma-sprayed Sm-Co alloys, which seem to refute the existence of a eutectoid decomposition of SmCo5, can actually be taken as further experimental evidence in favor of the presence of the decomposition reaction.
Reply to ’’Comment on ’High coercivity, isotropic plasma sprayed samarium-cobalt magnets ’ ’’
Authors: Kumar K. , Das D.
Published: February 2003

The alternative interpretation of x-ray results of Kumar et al. by Buschow and den Broeder, suggesting possible support for eutectoid decomposition of SmCo5, is questioned in view of the large body of published experimental evidence that clearly demonstrates that the SmCo5 phase must be stable at the low temperatures.
Band-edge photoluminescence of ZnSe using far-below band-gap excitations
Authors: Shing Y. H. , Walsh D.
Published: February 2003

Band-edge photoluminescent spectra of ZnSe were measured at 2 K using blue, green, and red krypton laser excitations. These results indicate the presence of a deep level whose binding energy is stronger than those for previous reported acceptor states. The nonlinear photoluminescent intensity dependence for the red excitation suggests that a two-photon excitation process takes place.
Electrical transport in ZnCdS films deposited by spray pyrolysis
Authors: Chynoweth Trevor A. , Bube Richard H.
Published: February 2003

Electrical transport has been analyzed by thermoelectric power measurements on thin films of ZnxCd1−xS deposited by spray pyrolysis for values of x between 0 and 0.35. The electron density decreases exponentially with x in the as-deposited films, and the observed more rapid increase of resistivity between 0.10 and 0.20 is caused by a decrease in electron mobility. The mobility activation energy Eμ measured by the difference (Eσ−ES) is essentially constant for x=0 to x=0.27 in as-deposited films with Eμ of about 0.14 eV. Heat treatment in H2 is effective in reducing the resistivity, primarily through an increase in electron mobility for low x, and primarily through an increase density for high x. A resistivity of 4.0×102 Ω cm has been obtained for x=0.35.
The Josephson device with a matched rf source
Authors: Longacre Andrew
Published: February 2003

Analog simulation of a resistance-shunted ac Josephson junction coupled to an rf source with matching impedance reveals (1) added structure in the device’s V-I curve even when the source is quiescent and (2) rf-induced steps with peak amplitudes between those produced by voltage and current rf sources. Both results are consistent with experimental data.
Nonlinear dynamic response of piezoelectric polyvinylidene fluoride
Authors: Reid W. M. , Steel M. R.
Published: February 2003

A film of piezoelectric polyvinylidene fluoride (PVF2) under a stress of 3.5×106 N m−2 was subjected to a periodic driving force for a range of frequencies through a fundamental resonance. Shifts in frequency and discontinuous jump phenomena were observed by monitoring the generated voltage. The results are shown to correspond to a nonlinear Young’s modulus Y=[(2.9±0.2) ×109−(2.1±0.3) ×1014S2] N m−2 where S is the dynamic strain.
Wavelength-modulated photocapacitance spectroscopy
Authors: Kamieniecki E. , Lagowski J. , Gatos H. C.
Published: February 2003

Derivative deep-level spectroscopy was achieved with wavelength-modulated photocapacitance employing MOS structures and Schottky barriers. The energy position and photoionization characteristics of deep levels of melt-grown GaAs and the Cr level in high-resistivity GaAs were determined. The advantages of this method over existing methods for deep-level spectroscopy are discussed.
Formation of silicon nitride compound layers by high-dose nitrogen implantation
Authors: Tsujide T. , Nojiri M. , Kitagawa H.
Published: February 2003

This study is concerned with physical and electrical properties of nitrogen-implanted silicon. Ellipsometric analysis and sheet-resistivity measurements of the retained silicon surface were made. Sheet resistivity was found to increase with increasing anneal time, in spite of silicon surface crystallinity recovery. Also, an in-depth morphological observation of silicon to buried silicon nitride transition layers was made, using optical and scanning electron microscope and electron diffraction. Dendritic growth of silicon nitride precipitates was observed for 3×1017/cm2 implanted and 1200 °C annealed samples.
One-carrier thermally stimulated currents and space-charge-limited currents in naphthalene crystals
Authors: Campos M. , Mergulhão S.
Published: February 2003

Electron trapping in naphthalene is studied by analysis of the space-charge-limited and thermally stimulated currents as a function of applied voltage and temperature. The two methods are used on naphthalene single crystals, with continuous electron injection from a silver contact. The use of the two techniques allows a quantitative determination of the characteristics of deep and shallow traps. Three monomolecular current peaks were observed. Activation energies of 0.5, 0.79, and 1.1 eV, and cross sections of 8.8 × 10−20, 6.9 × 10−16, and 1.0 × 10−18 cm2, were calculated for the corresponding discrete trapping levels of the charge carriers. The behavior observed for space-charge-limited current was a current-voltage characteristic of a single set of traps, with an activation energy of 0.71 eV, and a cross section of 7.1 × 10−16 cm2. The results showed that the use of only space-charge-limited current is not good enough for a characterization of the traps of the material.
Electronic processes in SnO2- (n-type) InP heterojunctions
Authors: Pande K. P. , Hsu Y.-S. , Roberts G. G.
Published: February 2003

An examination is made of the electrical and photovoltaic characteristics of SnO2-InP heterojunctions which were fabricated by chemical vapor deposition of SnO2 onto the surface of epitaxial layers of n-type InP. The dark current and capacitance of these devices were measured as a function of voltage at several temperatures and analyzed in terms of existing theories, considering the presence of an interfacial oxide layer. The devices exhibited ideality factors of 1.40 and saturation current densities of ∼10−5 A cm−2 at room temperature. The dark currents in the devices were found to be mainly dominated by tunneling of carriers via interface states. The analysis of the electrical characteristics yielded a thickness of the interfacial layer between 19 and 36 Å. Under AM1 illumination, the devices exhibited photovoltaic effect with an open-circuit voltage of 265 mV, short-circuit current of 19.10 mA cm−2, and a fill factor of 0.56.
Thermoelectric power of bcc transition-metal alloys of the second period
Authors: Lin A. C. , Brotzen F. R. , Loftin R. B.
Published: February 2003

The absolute thermoelectric power of Nb-rich Zr, Mo-Nb, and Mo-rich Re alloy crystals was measured between 4.2 and 300 K. The composition of these alloys covered the entire composition range in which a continuous solid solution of bcc structure prevails. The diffusion component of the thermopower as a function of composition is generally proportional to the change of the density of states at the Fermi level with respect to composition. The curves exhibit two extrema: a minimum at 5.35 and a maximum at 6.1 valence electrons per atom. The phonon-drag component of the thermopower is positive for all the alloys and is attenuated by the addition of alloying elements to Nb. The phonon-drag component of Mo is particularly sensitive to alloy content.
A theoretical treatment of charge transfer via surface states at a semiconductor-electrolyte interface: Analysis of the water photoelectrolysis process
Authors: Nishida Masahiko
Published: February 2003

Considerable experimental work has recently been reported on semiconductor-electrolyte interfaces in connection with the photoelectrolysis of water by illuminated n-type semiconductors. It is believed that surface states play an important role in charge transfer at the interface. In this paper the nature of that role of surface states is analyzed theoretically in the context of the photoelectrolysis of water. Conditions resulting in the improvement of charge transfer efficiency at the interface are particularly noticed. The semiconductor-electrolyte junction is treated as a metal-insulator-semicondutor (MIS) structure with the metal and insulator replaced, respectively, by the electrolyte and Helmholtz layer, and the interface current is analyzed in some detail using this model. It is shown that efficient charge transfer observed in the O2 evolution process on n-TiO2 photoanodes is ascribed to the existence of almost completely occupied surface states whose occupation is determined by the electrolyte. Then, such surface states act simply as current flow sites for holes transferred across the interface instead of acting as recombination centers for semiconductor carriers. Further, it is found that the requirement of efficient charge transfer via surface states tends to be incompatible with that of a large band bending in the surface barrier region. Charge transfer accompanied by H2 evolution on a p-type GaP photocathode is also discussed in relation to the presence of surface states at a GaP-electrolyte interface.
Measurements of device parameters on large arrays of Josephson interferometers
Authors: Basavaiah S. , Greiner J. H. , Zappe H. H. , Singer S. J.
Published: February 2003

Measurements on large arrays of Josephson interferometers were carried out to obtain individual device parameters and their spread. Each array contained 784 identical interferometers with junction diameters of 5 and 7 μm and was deposited on a 6.35×6.35-mm Si chip. Threshold currents Im(0), subgap resistances Rj, and Vm —the product of Rj and Im(0) —were investigated. Statistical analysis indicated that the standard deviation σ of Im(0) and Rj ranged between 6 and 18% and that of Vm ranged between 5 and 7%. A systematic spatial dependence of Im(0) and Rj on the chips was obtained which is attributed as being due to nonuniformities in the rf oxygen discharge used to form the tunnel barrier. With improvements in the process, namely, eliminating these nonuniformities, the standard deviation in Im(0) (and Rj) can be reduced to about 5%. From the observed variations in the junction areas it is estimated that the random variation in the Josephson current density is about 4%. Large scale applications of these interferometers in the design of computer memory and logic thus seem feasible.
Crystallographic texturing in Nb3Sn multifilamentary superconducting composites
Authors: Cogan Stuart F. , Rose Robert M.
Published: February 2003

Crystallographic texturing in Nb3Sn composites, fabricated by both the external diffusion and the commercial bronze processes, has been investigated. In the external-diffusion-processed composite the as-drawn texture of the copper matrix contained ca. 55% 〈111〉 and 45% 〈100〉; after recrystallization at 650 °C for 16 h this changed to 70% 〈111〉 and 30% 〈100〉. Tin plating and reaction heat treatment for 40 h at 650 °C eliminated most of the texturing. In a commercial bronze-processed composite a 〈211〉 or 〈221〉 texture was obtained in the as-drawn bronze matrix, and after a reaction heat treatment at 700 °C for 30 h a diffuse 〈100〉 texture was developed. In both composites the Nb3Sn reaction layer exhibited no preferred orientation.
Nb3Al thin-film synthesis by electron-beam coevaporation
Authors: Kwo J. , Hammond R. H. , Geballe T. H.
Published: February 2003

Nb3Al thin films have been prepared and characterized with varying deposition parameters, including substrate temperature, deposition rate, gas doping, and epitaxial growth. Nb-Al samples made with the optimum substrate temperature have lattice constants following the prediction of Geller radii and a systematic Tc increment with Al composition, namely, a ΔTc/ΔC of 1.9 K/at% Al. Employment of the self-epitaxial method results in extending the A15 phase boundary by 1 at% Al and an enhancement of Tc by 2.4 K at a given substrate temperature. By extrapolating from Tc =16.7 K, the highest transition temperature observed in this work, stoichiometric Nb3Al is predicted to have an Tc onset of 20.7 K.
Optical properties of polycrystalline anthracene in the 3.2–9.3-eV spectral region
Authors: Painter L. R. , Riedinger T. S. , Birkhoff R. D. , Heller J. M.
Published: February 2003

The optical functions of polycrystalline anthracene films have been determined in the spectral region between 3.2 and 9.3 eV. Conventional reflectance techniques using the semicylinder method were used to obtain the optical and dielectric functions for our sublimed films. In general the maxima in our data occur at energies comparable to those where maxima occur in single-crystal data. However, the magnitudes are frequently quite different. Our data indicate that the a and b axes of the crystallites tend to lie in a plane parallel to the surface of the substrate.
Photoacoustic signal variations with chopping frequency for ZnSe laser windows
Authors: Fernelius Nils C.
Published: February 2003

Experimental photoacoustic (PA) signal amplitude and phase angle data were obtained as a function of chopping frequency on a 10.6-μm antireflective coated ZnSe window using a CO2 laser. The PA signal amplitude had an f−n frequency dependence with n=1.04. The PA phase angle varied by 20° between 1000 and 50 Hz; 7° between 1000 and 100 Hz. Theoretical calculations were made using the Bennett-Forman, Rosencwaig-Gersho, and two-layer Rosencwaig-Gersho theories. No theory yielded a 20° phase change between 1000 and 50 Hz. The homogeneous sample Rosencwaig-Gersho theory did not fit either amplitude or phase angle data. Assuming a 1-μm-thick ThF4 layer on top of the ZnSe, the two-layer Rosencwaig-Gersho theory yielded a coating optical absorption coeffficient, βc =2.7 cm−1 to give a 7° phase change. This then gave an amplitude dependence of n?1.03. The Bennett-Forman theory agreed with PA amplitude results for r=βsurface /βbulk ≳0.05 cm. A 7° phase change was obtained for r=0.03 cm. The best fit of the Bennett-Forman and two-layer Rosencwaig-Gersho theories gave very similar amplitude and phase results.
X-ray diagnostics of a high-Z plasma produced by a laser—Experimental
Authors: Sinha B. K. , Gopi N.
Published: February 2003

Experiments were conducted on a planar aluminum target using a 50-MW 60-ns ruby laser to estimate the scaling law of the plasma temperature against laser flux in a purely collisional regime for laser plasma interaction. The laser flux density was varied between 5×1010 and 5×1011 W/cm2 and the plasma temperature was estimated from recombination continuum using coronal equilibrium for ionization states. The variations of x-ray intensity and plasma temperature showed approximately a φ2.4 and φ0.6/9 dependence, respectively, on the laser flux. In the range of the laser intensity variation, the plasma temperature was observed to vary from 116 to 135 eV with an accuracy of ±5 eV.
Atomic data and level populations of highly ionized Ti for tokamak plasmas
Authors: Bhatia A. K. , Feldman U. , Doschek G. A.
Published: February 2003

We present calculations of electron impact collision strengths and spontaneous radiative decay rates for titanium ions of the Li I through F I isoelectronic sequences for transitions between levels of the 2s22pk, 2s2pk+1, and 2pk+2 configurations. From these atomic data, excitation-rate coefficients are calculated as well as level populations for the above-mentioned three configurations. The calculations of level populations include the effects of proton excitation, and are carried out at electron temperatures and densities typical of tokamak plasmas. Wavelengths of forbidden and intersystem lines are given, and a synthetic spectrum is presented for a typical temperature and density.
Determination of the amorphous content of superconducting films by x-ray diffraction and its relation to transition temperature
Authors: Vander I. , Cadieu F. J.
Published: February 2003

A method has been developed for the determination of the amorphous content of superconducting films (niobium-germanium) based on x-ray analysis. Measurements are made in reflection using a standard diffractometer which includes a silicon semiconductor counter. The intensity of the diffraction line of the substrate was measured at an angle outside the amorphous halo region of the films to calibrate their surface density. The second angle of measurement was chosen to be within the region of the amorphous halo but away from the diffraction lines of the substrate or crystalline components of the films under investigation. Expression have been derived for calculation of the amorphous content. For the set of films investigated, a direct correlation of the amorphous concentration and the superconducting transition temperature has been observed.
The solution of iron in silicon
Authors: Weber E. , Riotte H. G.
Published: February 2003

The solution of iron in silicon has been examined by instrumental neutron activation analysis (NAA) and EPR of quenched samples. It was possible to obtain the total iron concentration and the concentration of interstitial iron for each specimen as a function of temperature. During the heat treatment of any silicon sample, iron from random sources diffuses into the silicon in a two-step process; the second step can be suppressed by the use of a nonreducing atmosphere. At 1100 °C iron-coated samples show saturation of the iron concentration already after about 30 min. The NAA and EPR of samples saturated with iron lead to the same slope of concentration versus 1/T. From this, it is concluded that most likely both experiments measure the interstitial iron species so that the substitutional solubility has to be lower than that for the interstitial with 2.90.05 eV being the enthalpy of formation of a neutral interstitial iron atom in silicon.
H2O in berlinite detected by Raman scattering
Authors: Shand M. L. , Chai B. H. T.
Published: February 2003

Raman scattering (RS) is used to measure the concentration of H2O in berlinite. Sample size and scattering geometry variations are eliminated by normalizing to an internal standard. The H2O concentration (in ppm by weight) is 1.2×106 (RS at 3400 cm−1)/RS at 1112 cm−1). The spectra indicate that hydrogen in berlinite is present only in the form of H2O and not OH−.
The effect of stress on the temperature dependence of ultrasonic velocity
Authors: Salama K. , Ling C. K.
Published: February 2003

The effects of applied elastic stress on the temperature dependence of ultrasonic velocity has been investigated in commercial aluminum and copper. Velocities of 10-MHz longitudinal and shear waves as a function of temperature were measured when specimens of these metals were subjected to external compressive stresses applied in a plane perpendicular to the direction of propagation. In all measurements, the velocity increased linearly as the temperature was lowered in the range between 280 and 200 K. The slopes of the linear relationships of the longitudinal velocities were found to decrease linearly as the amount of stress was increased within the elastic limit of the specimen. The maximum decrease in the temperature dependences of the longitudinal velocities of aluminum and copper were, respectively, 23 and 6%. These occurred at applied stresses of 96 and 180 MPa. The temperature dependence of the shear velocity in aluminum, however, remained unchanged with the application of stress.
On the microhardness of mixed crystals
Authors: Shrivastava U. C.
Published: February 2003

The Kataoka-Yamada model for highly concentrated solid solutions has been used to calculate the microhardness of NaCl-NaBr, KCl-KBr, and KBr-KI systems. The extra hardness in mixed crystals is computed from the amount of hindrance in the transport of ion pairs in the fluctuating stress field produced by the random distribution of anions of different sizes. The theoretical results are in very good agreement with available experimental data.
Hypersonic sound velocity in liquid and rubbery polymers
Authors: Kondo Shingo , Igarashi Takashi
Published: February 2003

The hypersonic sound velocities in liquid and rubbery polymers were studied in connection with the degree of polymerization n and the cross-link density ν of linear polymers by adopting lattice model for three congregation states. The elastic modulus M defined by the product of the density and the square of the sound velocity depends on 1/n in uniform mixing of molecular chains, on (1/n)1/3 in not uniform mixing of molecular chains, and on ν in uniform mixing of molecular chains with ν cross-link points. The hypersonic sound velocity in linear polydimethylsiloxanes (PDMS) and chemically cross-linked polydimethylsiloxanes (PDMSR) were measured by Brillouin spectroscopy. The modulus M of PDMS varied according to (1/n)2/3 in a region of low molecular weight and that of PDMSR depended linearly on ν. Since these treatments based on lattice model are thought to explain successfully behaviors of propagation of hypersonic sound, it is suggested that the energy elasticity plays a significant role here.
Clarification of the Hashin-Shtrikman bounds on the effective elastic moduli of polycrystals with hexagonal, trigonal, and tetragonal symmetries
Authors: Watt J. Peter , Peselnick Louis
Published: February 2003

Bounds on the effective elastic moduli of randomly oriented aggregates of hexagonal, trigonal, and tetragonal crystals are derived using the variational principles of Hashin and Shtrikman. The bounds are considerably narrower than the widely used Voigt and Reuss bounds. The Voigt-Reuss-Hill average lies within the Hashin-Shtrikman bounds in nearly all cases. Previous bounds of Peselnick and Meister are shown to be special cases of the present results.
Infrared absorption bands induced by Si-related defects in GaAs: Absorption cross sections
Authors: Chen R. T. , Rana V. , Spitzer W. G.
Published: February 2003

Silicon is an amphoteric impurity in GaAs and is present in different defect configurations. This work reports measurements of the infrared absorption cross sections for some of the localized vibrational mode bands related to the Si defects. Heavily doped melt-grown samples are used to measure the free-carrier density ne and the integrated absorption of all bands attributed to electrically active defects. The resulting data are analyzed by using a least-squares-fitting procedure employing two different models. A set of absorption cross sections is given for each model. These results differ from others reported recently. Using the two sets of cross sections to interpret the absorption spectra of p-type liquid-phase epitaxial samples seems to reaffirm a previously reported interpretation in which an additional Si-related acceptor defect of unknown nature is present.
Growth and phase stability of epitaxial metastable InSb1−xBix films on GaAs. I. Crystal growth
Authors: Zilko J. L. , Greene J. E.
Published: February 2003

Epitaxial metastable InSb1−xBix films with InBi concentrations up to 12 mole % have been grown on (110) GaAs substrates by multitarget rf sputtering. Tetragonal InBi is a semimetal whose equilibrium solid solubility in zinc blende structure InSb is 2.6 mole %. Low-energy ion bombardment of the growing film was used to modify the elemental Sb and Bi incorporation probabilities σSb and σBi through preferential resputtering in order to maintain overall stoichiometry and to allow the growth of single-crystal extended solid solution alloys at elevated temperatures. The effects of the Bi to Sb impingement flux ratio JBi/JSb, film growth temperature TS, and the Ar sputtering pressure PAr on the composition and structure of the as-deposited films as well as their metastable solid solubility, were also investigated. Holding all growth variables except one constant in a given set of experiments, the ratio σBi/σSb was found to decrease with increasing JBi/JSb, increasing TS, and decreasing PAr . The metastable solid solubility limit increased with decreasing PAr . Single-phase metastable films were n-type semiconductors with the 100 °K carrier concentration increasing from 1.8×1017 to 4.5×1017 cm−3 as the mole % of InBi was increased from 3 to 12. Electron mobilities at this temperature ranged from a few hundred to ∼1000 cm2/V sec. The mobility increased with increasing temperature yielding an activation energy of 0.02 eV. The optical band gap decreased with increasing InBi concentrations indicating a semiconductor-semimetal transition at ∼11 mole % InBi at 20 °K.
Grain boundary diffusion of aluminum in polycrystalline silicon films
Authors: Hwang J. C. M. , Ho P. S. , Lewis J. E. , Campbell D. R.
Published: February 2003

Grain boundary diffusion of Al in poly-Si films has been measured by an Auger sputter profiling technique in a temperature range of 350–425 °C. The Al atoms were observed to diffuse through Si grain boundaries, then accumulated near a poly-Si/SiO2 interface. By concentrating on the initial stage of diffusion, the diffusion problem was analyzed using a simple model in which a steady-state flux of Al though Si grain boundaries is accumulated by an effectively infinite sink at the poly-Si/SiO2 interface. Auger measurements yielded quantitative information regarding the concentration gradient in the middle of the poly-Si layer and the amount of accumulation near the poly-Si/SiO2 interface. From this information, the grain boundary diffusion coefficient of Al in Si Db was determined. The temperature dependence of Db fits an Arrhenius-type relation with D°b =1.3×107 cm2/s and Qb =2.64 eV. The measured activation energy was found to be consistent with that of the grain boundary diffusion of P and B as well as the dislocation diffusion As in Si.
Steady-state diffusion of zinc and manganese at high concentrations in fcc Cu-Zn-Mn ternary alloys
Authors: Ki Dong Eue , Park Tong Soo
Published: February 2003

Diffusion phenomena under substitutional steady-state conditions in a Cu-Zn-Mn system were investigated at 800 °C, using vapor-solid couple, in order to evaluate the atomic mobility of zinc and manganese in the α phase region. The experimental diffusion cell consisted essentially of a thin membrane of copper of negligible vapor pressure and a high-vapor-pressure source of zinc alloy chips that was charged on one side of the copper membrane, while the other side was charged with one of the following: Cu-Mn alloy chips, fine manganese powder, or manganese powder mixed with manganese chloride in order to accelerate the movement of manganese atomic vapor. Five series of steady-state diffusions were obtained by this experiment, and the atomic mobilities of zinc and manganese calculation were made along each of the steady-state diffusion path concentration profiles. From these calculated atomic mobilities, a contour map of the isomobility lines of zinc and manganese was formed in the high-alloy-content region of the α phase in Cu-Zn-Mn ternary alloy system.
Silicide formation in thin cosputtered (tantalum + silicon) films on polycrystalline silicon and SiO2
Authors: Murarka S. P. , Fraser D. B.
Published: February 2003

Formation of tantalum silicides has been investigated by cosputtering tantalum and silicon on polycrystalline silicon and oxidized silicon wafers. Alloys with as-deposited Si/Ta atomic ratios of 0.6 to 3 are sintered in hydrogen or argon ambient in the temperature range 400–1000 °C. It is found that for alloys with Si/Ta?1.0 and sintered at temperatures <700 °C, only Ta5Si3 is formed. At higher temperatures and in presence of polycrystalline silicon TaSi2 is formed. In the absence of polycrystalline silicon (i.e., on oxide) only Ta5Si3 is formed at all temperatures. For alloys with Si/Ta ratios ?2 only TaSi2 is formed. In all cases the resistivity decreases as a result of sintering, ending up in a value as a low as ∼50 μΩ cm after 1000 °C/30 min sintering. The stress in the silicided films is found to be nearly 1×1010 dyn/cm2, tensile. The results have been explained on the basis of the fact that in cosputtered films interaction occurs locally which leads to smaller grain size, higher resistivities, lower stress, and smoother surface.
Study of surface recombination in GaAs and InP by picosecond optical techniques
Authors: Hoffman C. A. , Gerritsen H. J. , Nurmikko A. V.
Published: February 2003

We report results of measurements for surface recombination velocity in GaAs and InP under varying material conditions. The experimental method permits direct observation of the time-resolved decay of excess electron-hole pairs near a semiconductor surface.
GaAs homojunction rib waveguide directional coupler switch
Authors: Carenco A. , Menigaux L.
Published: February 2003

An electro-optic directional coupler switch has been fabricated with a GaAs homojunction structure and tested at 1.15 μm. Each single mode guide is made in a n-LPE layer grown on a n+ substrate, the p+ rib used to confine the light being obtained by Zn diffusion and chemical etching. A calculation of the losses in the planar approximation roughly yields the large values of attenuation measured for TE and TM modes (∼8 cm−1). By reversely biasing the ’’stepped Δβ’’ junctions with less than 17 V, more than 13 dB power isolation has been achieved for both switching states on a 6.3-mm-long device. Large improvements of the characteristics are expected from the additional design parameters provided by GaAs-GaAlAs double heterostructure.
Phonon-assisted recombination and stimulated emission in quantum-well AlxGa1−xAs-GaAs heterostructures
Authors: Holonyak N. , Kolbas R. M. , Laidig W. D. , Vojak B. A. , Hess K. , Dupuis R. D. , Dapkus P. D.
Published: February 2003

Extensive data are presented on various photopumped multiple-quantum-well AlxGa1−x As-GaAs heterostructures, grown by metalorganic chemical vapor deposition, showing the variety of laser operation that can be observed one and two phonons below the lowest (n=1, n′=1′) confined-particle electron-to-heavy-hole (e→hh, n) and electron-to-light-hole (e→lh, n′) recombination transitions. These experiments are performed on small cleaved rectangular samples that, because of two identifiable sets of orthogonal coupled modes, permit unambiguous identification of laser operation on LO-phonon sidebands below the confined-particle transitions. For a small number (two) of closely coupled (∼50 Å) GaAs quantum wells of size Lz ∼50 Å laser operation occurs on multiples of h/ωLO from one phonon below transition n=1 (E1) to within a phonon or two of the L indirect band edge. AlxGa1−x As-GaAs heterostructures with more coupled GaAs quantum wells readily permit observation of laser operation two phonons below the lowest confined-particle transitions. Besides the use of size to reduce carrier scattering to lower energies in a GaAs quantum well, high Zn doping is used to screen and reduce the electron-phonon interaction and thus reduce the carrier scattering to lower energies. The strong phonon participation in the laser operation of these quantum-well heterostructures, which are not superlattices, demonstrates that the electron-phonon interaction observed in this work is a true two-dimensional effect (and not, e.g., the effect of Brillouin-zone folding). An analysis and arguments are presented justifying this statement and, in addition, leading to the important conclusion that stimulated phonon emission is possible and might play (or likely plays) a role in the quantum-well heterostructures of this work.
Unidirectional magnetic gradiometers
Authors: Karp P. , Duret D.
Published: February 2003

The response of a magnetic gradiometer to various types of magnetic sources is analyzed. Both semiquantitative and quantitative methods for determining the noise immunity and the spatial sensitivity of the gradiometer are presented. A new class of magnetic gradiometers with unidirectional properties is introduced.
Generalized concepts in large-scale laser isotope separation, with application to deuterium
Authors: Vanderleeden J. C.
Published: February 2003

Optical laser isotope separation (LIS) and chemical process concepts are developed that arise in the large-scale application of LIS processes with continuous process streams. The discussion applies to one-photon, two-photon and multiphoton LIS and the separation of a multiple-component mixture. It is partly based on a novel reaction chamber which provides throughout its volume a constant energy fluence or power density. Concepts discussed are the isotopic depletion, isotopic and process selectivity, isotopic abundances, abundance quotients α* and β*, the photon utilization factor, and the material balance equations in the LIS plant. An expression is derived that gives the total process cost per unit separated product in terms of the isotopic selectivity, the isotopic depletion, and the natural abundance of the desired species. A total-cost minimization is carried out which gives the optimum isotopic depletion of the process as a function of isotopic selectivity, photon cost parameters, and parameters characterizing the photochemical reaction and the feed costs. The expressions are applicable to ’’closed cycle’’ as well as ’’once through’’ feed processing. The results are used to estimate the cost per kg of heavy water as a function of laser efficiency and isotopic selectivity, for a formaldehyde-based deuterium separation method.
Transition radiation as a source of x rays
Authors: Chu A. N. , Piestrup M. A. , Barbee T. W. , Pantell R. H.
Published: February 2003

The generation of transition radiation resulting from the passage of relativistic charged particles through a periodic structure can produce intense and highly directional x rays. An optimization analysis accounting for material properties, multiple scattering, and statistical random errors in foil thicknesses is used to design an x-ray emitter. The results demonstrate that transition radiation sources can be comparable in brightness to synchrotron emitters.
Photorefractive effects and light-induced charge migration in barium titanate
Authors: Feinberg Jack , Heiman D. , Tanguay A. R. , Hellwarth R. W.
Published: February 2003

We propose a new theoretical model for the light-induced migration of charges which mediates the ’’photorefractive effect’’ (light-induced refractive index change) in barium titanate and other crystals. We also present experimental results of various effects of this light-induced charge migration in a single-domain crystal of barium titanate, specifically, (1) energy transfer between two intersecting optical beams, (2) optical four-wave mixing and optical-beam phase conjugation, (3) erasure of spatial patterns of photorefractive index variations, and (4) photoconductivity. The theoretical model predicts the observed dependences of these effects on (1) beam intensities, directions, and polarizations, (2) crystal orientation, and (3) on an externally applied dc electric field. Time dependences of transients as well as steady-state magnitudes are predicted. In this model, identical charges migrate by hopping between adjacent sites, with a hopping rate proportional to the total light intensity at the starting site. The net hopping rate varies with the local electric potential that is calculated self-consistently from the charge migration pattern. In barium titanate the charges are positive with a density of (1.90.2) ×1016 cm−3 at 514 nm. The origin of the charges and sites is at present unknown. The hopping rate constant determined from optical beam interactions is used to predict the observed photoconductivity of 1.3×10−10 cm Ω−1 W−1 at 514 nm.