bluuebunny/crossref_metadata_2025 huggingface dataset:
A class of cylindrically symmetric solutions to the force-free magnetic field equations with nonconstant α
Authors: Marsh Gerald E.
Published: July 2002

The general approach to cylindrically symmetric force-free magnetic fields first introduced by Lüst and Schlüter [Z. Astrophys. 34, 263 (1954)], is restricted to fields of the form H=[0,Hφ(r),Hz(r)], and subsequently used to determine a set of solutions to the force-free field equations with nonconstant α. The first element of the set is the well-known constant α solution of Lundquist [Ark. Fys. 2, 361 (1951)]. These solutions may have practical applications with respect to high-temperature superconductors.
Light guidance and mode conversion in magneto-optic buried channel waveguides
Authors: Pross E. , Dammann H. , Tolksdorf W.
Published: July 2002

The optical and magneto-optical properties of weakly guiding single-mode buried channel waveguides in substituted yttrium iron garnet have been investigated experimentally. The propagation constant difference Δβ of the two coupled TE and TM modes, which is of particular interest for waveguide isolator application, is found to be strongly dependent on waveguide geometry. Measured results can be explained by the specific growth of the top cladding layer, which occurs into different crystallographic directions around the etched waveguide core. This leads to a local variation of the refractive index, which effects the guidance of light, and to a local variation of birefringence, which effects Δβ. The measured variation of Δβ is shown to be primarily caused by growth induced birefringence. It is demonstrated that Δβ can be controlled to small values at selectable waveguide widths as required for waveguide isolator application simply by an appropriate setting of fabrication parameters.
Investigation on the quantum well structure of a GaAs/Al0.3Ga0.7As superlattice grown on a misoriented substrate
Authors: Jin Y. , Chen Y. , Zhu X. , Zhang S. L.
Published: July 2002

We analyzed the Raman spectra and x-ray diffraction of two GaAs/Al0.3Ga0.7As superlattices grown by molecular-beam epitaxy on a 4 ° misoriented (001) GaAs substrate and an exactly (001)-oriented GaAs substrate respectively. From the frequency shifts of the longitudinal-optical- (LO) confined phonons in the Raman spectra and the variation in linewidths of both the LO-confined phonons and the satellite peaks in x-ray diffraction, we found that the 4 ° misorientation of the GaAs substrate from (001) toward [110] direction improves the interface quality of the superlattices.
On the coupling of blast wave theory with atomic excitation in low-energy laser-induced plasmas formed in gases
Authors: Shah P. , Biswas A. , Armstrong R. L. , Radziemski L. J.
Published: July 2002

Time-dependent intensities of the spectral lines emitted by laser-induced plasmas generated in several gases are presented. The time-resolved and spatially varying intensities of two once-ionized nitrogen lines were used to calculate radial temperature distribution of temperature within the plasma. A modified blast wave theory, in which ionization was included through the Saha equation and the equation of conservation of charge, was used to calculate time-dependent intensities of several spectral lines of C, N, He, and Ar. The temporal profiles of the spectral lines appear to be dependent on the ionization potentials of the species in the plasma.
Absorption spectrum of EL2 defect in p-type GaAs
Authors: Skowronski Marek
Published: July 2002

Absorption of p-type GaAs crystals grown by horizontal Bridgman, liquid-encapsulated Czochralski, and liquid-phase electroepitaxy methods were measured at 4 K. The spectra of melt-grown crystals show a wide absorption band extending from 0.6 eV to the fundamental absorption edge. The comparison with the photocapacitance spectrum of EL2 defect and deep-level transient spectroscopy measurements allowed to interpret this absorption as due to transitions between the valence band and the doubly ionized EL2 level. Absorption can be bleached by intense illumination at temperatures below 60 K with the dark spectrum recovering upon heating with an activation energy of 55 meV.
Electrical resistivity of crystalline ZrC0.93, 1000–3000 K
Authors: Hinrichs C. H. , Hinrichs M. H. , Mackie W. A.
Published: July 2002

A four-point-probe technique was used to measure the dc electrical resistivity of single-crystal ZrC0.93 in the temperature range 1000–3000 K. A nonlinear temperature dependence was observed which is best described by an expression of the form ρ=ρ0+ρ1T+C exp(−T0/T), with ρ0=176.5 μΩ cm, ρ1=0.0552 μΩ cm/K, C=−650 μΩ cm, and T0=6900 K.
Persistent photoconductivity in SIMOX film structures
Authors: Mayo Santos , Lowney Jeremiah R. , Roitman Peter , Novotny Donald B.
Published: July 2002

Photoinduced transient spectroscopy (PITS) was used to measure the persistent photoconductive (PPC) response in n-type separation by implanted oxygen (SIMOX) film resistors. A broadband, single-shot, flashlamp-pumped dye laser pulse was used to photoexcite interband electrons in the film, and the excess carrier population decay was measured at temperatures in the 60–220-K range. The PPC signals exhibit nonexponential character and the conductivity transients are recorded as a function of temperature for variable periods up to 30 s. The photoconductive data are analyzed by using the Queisser and Theodorou potential barrier model, and a logarithmic time-decay dependence is confirmed for the first time in SIMOX material. The hole-trap density at the conductive-film–buried-silica interface is calculated to be in the high 1015 cm−3 to low 1016 cm−3 range. The sensitivity of PITS is demonstrated to be appropriate for characterization of the SIMOX interface structure and for material qualification.
Raman investigations of diamond films prepared by combustion flames
Authors: Harshavardhan K. S. , Vijayaraghavan M. N. , Chandrabhas N. , Sood A. K.
Published: July 2002

A detailed Raman analysis has been carried out to establish the mixed nature of carbon bonding in diamond films, deposited at atmospheric pressures in combustion flames. By monitoring the sp3 bonded 1334 cm−1 Raman signature of diamond and sp2 bonded 1350 and 1580 cm−1 signatures of graphite, it has been established that under optimum conditions of flow rates and substrate temperatures, the primary combustion zone provides an ideal situation for diamond growth. The study points out to an a-Si1−xCx like interface (0.5≤x≤1) and an amorphous diamondlike precursor phase. These investigations provide insights into the nature of the diamond films prepared by this technique in establishing their potential in various technological applications.
On a simplified analysis of the photoemission from quaternary alloys
Authors: Ghatak K. P. , Mondal M. , Biswas S. N.
Published: July 2002

An attempt is made to study the photo-emission from bulk specimens of quaternary alloys on the basis of three-band Kane model. It is found, taking In1−xGaxAsyP1−y lattice matched to InP as an example, that the photo-emission increases, with increasing carrier degeneracy and decreasing alloy composition respectively. The valence band splitting parameter influences significantly the numerical magnitude of the photo-emission in both cases. The corresponding well-known results of parabolic semiconductors having nondegenerate electron concentration have also been obtained as special cases from our generalized expressions, under certain limiting conditions.
Photoresponse of ion-beam-deposited Y-Ba-Cu-O thin films
Authors: Li K. , Hsiao R. , Tang C.
Published: July 2002

We report on the microstructure and photoresponse of ion-beam-deposited Y-Ba-Cu-O granular thin films. High-temperature superconductor thin films of the average composition YBa1.8Cu3.6Ox were ion-beam deposited onto yttria-stabilized zirconia and strontium titanate substrates from a composite target. Post-annealing processes were used to control the degree of granularity in these films, and led to films which varied in superconducting behavior. The microstructures of these films were studied by secondary electron microscopy and Auger analysis. Photoresponse and resistivity were measured as a function of temperature. We found that the degree of granularity in our films correlates with their resistivity and photoresponse which are similar to those of epitaxial or granular films.
Effect of nonparabolicity on free-carrier absorption in semiconductors at quantizing magnetic fields
Authors: Wu Chhi-Chong , Tsai Jensan , Lin Chau-Jy
Published: July 2002

Effect of the nonparabolicity on free-carrier absorption in nondegenerate semiconductors has been investigated at quantizing magnetic fields. The dominant scattering mechanism for electrons is assumed to be of the acoustic phonon scattering via the deformation-potential coupling. When the radiation is polarized parallel to a magnetic field, the absorption coefficient oscillates with the magnetic field in lower fields and then increases monotonically with the field. These oscillations of the abosrption coefficient with the magnetic field will be diminished with decreasing temperature and depend on the band gap of semiconductors.
van der Waals epitaxial growth of thin BiI3 films on PbI2 and CdI2 substrates by a hot wall method
Authors: Takeyama S. , Watanabe K. , Ichihara M. , Suzuki K. , Miura N.
Published: July 2002

A hot wall technique was applied to grow very thin BiI3 single crystals about 100–1000 Å thick by the achievement of low-temperature growth. The so-called van der Waals epitaxy became possible by employing layered materials such as PbI2 and CdI2 as substrate. BiI3 thin films grown with optimized conditions exhibited a sharp band-edge direct exciton absorption line of 30-meV half-width, which is much sharper than that of a single crystal grown by a conventional method reported so far. The transmission electron diffraction measurements were carried out on the films. It was revealed that highly perfect single crystals with a 4-mm diameter size were obtained.
Two-level fluctuations of in-plane current in a narrow lateral n-i-n junction
Authors: Takagaki Y. , Yuba Y. , Gamo K. , Namba S. , Takaoka S. , Murase K.
Published: July 2002

In-plane current through lateral n-i-n junction in GaAs-AlGaAs heterostructure is measured at low temperature. The junction consists of submicron wide narrow wires and an ion damaged insulating region where percolation is a dominant current-carrying mechanism. The current appears at a sufficiently high bias voltage, due to low temperature avalanche breakdown via impurity impact ionization. Time-dependent random-telegraph signals of 100% modulation in magnitude of the current through the i region are observed, which are caused by slow trappings and emissions of electrons at trap sites. The complete switching signals show a transition from normally off to normally on with increasing applied voltage.
Tunneling in planar-doped barrier diodes
Authors: Van Tuyen Vo , Szentpáli Béla
Published: July 2002

The effect of the thermionic-field emission mechanism on the I-V characteristics of planar-doped barrier diodes is investigated. The regions of temperature and of structural dimensions are given where this effect appears. The differences due to the different shapes of the potential barrier are pointed out between planar-doped barrier diodes and Schottky diodes.
The effect of the chemical vapor deposition of tungsten on shallow n+p and p+n junctions using titanium-tungsten as a barrier
Authors: Eshraghi S. A. , Georgiou G. E. , Liu R.
Published: July 2002

The effect of blanket chemical vapor deposition (CVD) of tungsten (SiH4 reduction) on shallow CoSi2 junctions using 450–1800 Å of titanium-tungsten (TiW) as a diffusion barrier has been investigated. Thermal stability of W/TiW and Al/W/TiW is studied by measuring the reverse leakage current at 25 °C anneal intervals. The Al/TiW structure has been used as a reference. W/TiW junctions with ≤700 Å of TiW are less stable than Al/TiW junctions. The addition of Al on top of CVD W enhances the junction degradation considerably. p+n junctions are more sensitive to the barrier failure. The effect of CVD W deposition temperature has been studied. Junctions exposed to 480 °C CVD W deposition temperature showed a lower leakage than those at 300 °C.
The operation of a uniformly insulated extraction applied-B ion diode
Authors: Slutz S. A. , Johnson D. J. , Crow J. T.
Published: July 2002

We present the first experimental results of a uniformly insulated extraction applied-B ion diode. The diode typically attained beam generating efficiencies of 70% at the time of peak beam power. This is a significant improvement over previous extraction applied-B ion diodes, demonstrating the importance of uniform insulation as suggested by theory [J. Appl. Phys. 59, 2685 (1986)]. Furthermore, we found that the beam current is nearly independent of the ion-emitting area down to a minimum area. At the minimum area, the beam current density was enhanced by 150 times the monopolar Child–Langmuir value. This data supports a recently proposed theory [Phys. Rev. Lett. 59, 2295 (1987)] that predicts large enhancements due to the electron diamagnetic effect on the virtual cathode.
The influence of Hg(63P2) population on emission processes in a low-pressure mercury-argon discharge
Authors: Maleki L. , Blasenheim B. J. , Janik G. R.
Published: July 2002

A low-pressure mercury-argon discharge is probed with a new technique of laser spectroscopy to determine the influence of the Hg(63P2) population on discharge emission. The discharge is excited with inductively coupled rf power. Variations in the intensity of emission lines in the discharge were examined as λ=546.1 nm light from a cw laser excited the Hg 6 3P2-to-7 3S1 transition. The spectrum of the discharge viewed in the region of laser irradiation showed increased emission in λ=546.1, 435.8, 404.7, 253.7, and 194.2 nm lines. Other lines in Hg i exhibited a decrease in emission. When the discharge was viewed outside the region of laser irradiation, all lines exhibited an increased emission. Based on these results we conclude that the dominant mechanism for the excitation of higher lying levels of mercury is the two-step electron impact excitation via the 3P2 level. The depopulation of the metastable level is also responsible for the observed increase in the electron temperature when the laser irradiates the discharge. We also conclude that the 3P2 metastable level of mercury does not play a significant role in the excitation of the 2P1/2 level of mercury ion.
Material properties of plasma-enhanced chemical vapor deposition fluorinated silicon nitride
Authors: Pai C. S. , Chang C.-P. , Baiocchi F. A. , Swiderski J.
Published: July 2002

The material and electrical properties of plasma-enhanced chemical vapor deposition fluorinated silicon nitride were studied. These films were deposited using SiH4-NF3-NH3-N2 chemistry. The concentration of fluorine in the films increases as the flow rate of NF3 increases during the deposition. The refractive index of the films was found to decrease as the concentration of the fluorine increases. The properties of the films, such as wet etch rates in various etching solutions, the reactive-ion etch rate, and the stress were measured. The concentration of SiH and NH bonds were also measured. Most of the material properties of the films were found to be strongly dependent on the concentration of fluorine in the films. It was also found that the refractive index of the fluorinated silicon nitride is determined by the concentration of fluorine. As a result, the refractive index of the fluorinated silicon nitride, which can be readily measured using an ellipsometer, is a useful monitor for process and quality control of film preparation in manufacturing. High resistivity and a frequency-independent dielectric constant were also observed from the fluorinated silicon nitride. The material and electrical properties of fluorinated silicon nitride with a refractive index in the range from 1.70 to 1.80, which shows promise for device applications, have been studied in detail.
Analysis of the hysteresis in the I-V characteristics of vertically integrated, multipeaked resonant-tunneling diodes
Authors: Kuo Tai-Haur , Lin Hung C. , Potter Robert C. , Shupe Dave
Published: July 2002

The hysteresis (extrinsic) and current-voltage (I-V) characteristics of the multiwell, vertically integrated, resonant-tunneling diode are analyzed. Our analysis shows that hysteresis in the vertically integrated diode I-V can result from interchanging the order in which the devices switch, depending if the bias is increasing or decreasing. Experimental results are presented that support this analysis.
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u, near-ideal epitaxial Al/AlxGa1−xAs Schottky barriers formed by molecular beam epitaxy
Authors: Missous M. , Truscott W. S. , Singer K. E.
Published: July 2002

The Schottky barrier height of in situ epitaxial aluminum on AlxGa1−xAs was measured as a function of aluminum mole fraction from x=0 to x=1, using I/V, C/V and activation energy plots of current-voltage dependence on temperature. The excellent electrical properties of the molecular beam epitaxy grown AlGaAs layers, with residual deep levels concentrations of less than 1014 cm−3 combined with the in situ deposition of single-crystal epitaxial aluminum resulted in extremely high quality Schottky diodes from x=0 (GaAs) to x=1 (AlAs) with accurately exponential current-voltage characteristics over up to 10 decades and with ideality factors less than 1.03. Both the C−2−V and activation energy plots were linear and yielded barrier heights in very good agreement with the I/V ones. The near-ideal characteristics of these diodes were compared with several models of Schottky barrier formation and the dependence of the Schottky barrier height on the aluminum mole fraction was found to agree with the anion vacancy model within 10–20 meV, with a maximum deviation of 46 meV.
Photocurrent spectroscopy of the CdHgTe/anodic oxide/ electrolyte junction
Authors: Berlouis L. E. A. , Peter L. M. , Fennell P. A. H.
Published: July 2002

Photocurrent spectroscopy is used to investigate the properties of the CdHgTe (CMT)/anodic oxide /electrolyte junction. The anodic oxide growth follows the high-field growth mechanism and the positive photocurrent response is found to originate from a thin layer close to the CMT/anodic oxide interface. The spectral response of this photocurrent indicates that the oxide is amorphous with a band gap of 2.8 eV. This value is considerably lower than has been previously reported. Electron photoemission also occurs at the CMT/anodic oxide interface, with an apparent threshold energy of ∼2.08 eV.
Thermoelastic response induced by a line thermal source located at the junction of two bonded materials
Authors: Tankovsky N.
Published: July 2002

A two-dimensional theoretical approach is developed to describe the thermal and elastic fields in the vicinity of a line thermal source located at the junction between two bonded materials. A modified system of thermoelastic equations is obtained and solutions are found. The temperature distributions give evidence for a depth-dependent transverse thermal flow. From the shape of the mechanical deformations at the interface, the ability of different pairs of materials to be applied as thermoacoustic transducers is qualitatively deduced.
Generalized buoyancy forces in dispersions
Authors: Zimmels Y.
Published: July 2002

Buoyancy forces in nonuniform dispersions are considered. Using a thermodynamic approach it is shown that Archimedes principle, which holds in cases of pure fluids and uniform dispersions, is incomplete in the case of nonuniform dispersions. For nonuniform dispersions the Archimedes force density must be augmented by two diffusion-type buoyancy force densities which are dependent on the expectation of particle size and density. The generalized buoyancy force consists of three vectors that may have different directions. It is shown that the effect of buoyancy diffusion is pronounced at diffusion fronts, being enhanced by aggregative motion of particles. Finally, the effect of buoyancy diffusion is expected to prevail over Brownian diffusion in the post-micron particle size range.
Performance characteristics of In0.6Ga0.4As/In0.52Al0.48As modulation-doped field-effect transistor monolithically integrated with In0.53Ga0.47As p-i-n photodiodes
Authors: Zebda Y. , Bhattacharya P. K. , Pavlidis D. , Harrang J. P.
Published: July 2002

Pseudomorphic In0.6Ga0.4As/In0.52Al0.48As 1 μm gate modulation-doped field-effect transistors have been monolithically integrated with In0.53Ga0.47As photodiodes for front-end photoreceivers using one-step molecular-beam epitaxy and lithography techniques. A 1-μm thick undoped In0.52Al0.48As layer is used to isolate the two devices. The transistors are characterized by gm(ext) =500 mS/mm and fT =9 GHz. The temporal response of the photodiodes is characterized by a linewidth of 60 ps. The eye pattern of the photoreceiver circuit for 1.7 Gbit/s pseudorandom optical signal is open and it is expected that the circuit can perform at bandwidths up to 2.5 GHz. Measured bandwidths of ∼6.5 GHz are obtained by using regrowth.
Measurement of the fundamental band gaps of a strained GaInAs layer
Authors: Reihlen E. H. , Birkedal D. , Wang T. Y. , Stringfellow G. B.
Published: July 2002

All three strain- and spin-orbit-split energy gaps of the Γ15v-Γ1c series are measured for the first time for a thin, strained Ga0.526In0.474As layer by a combination of transmission, photoreflectance (PR), and photoluminescence experiments at 10 and 300 K. Values of strain and composition of the layer are calculated from the splitting of the (J=3/2, mj=±3/2) and (3/2, ±1/2) valence bands and from x-ray data. Force balance calculations predict the strain in the layer to be relaxed while energy balance calculations predict the layer to be strained. The onset of generation of misfit dislocations at the InP/GaInAs interface has recently been reported to be well described by the force balance model. Nevertheless, the data reported in the present study show the degree of plastic strain relaxation for the sample under investigation to be so small that it can be neglected for the interpretation of the optical spectra. Almost identical PR spectra are measured when the sample is excited at photon energies larger and smaller than the InP band gap. In both cases, the PR signal originates from modulation of built in fields at the heterointerfaces, rather than the surface field.
O2 and CO2 glow-discharge-assisted oxygen transport through Ag
Authors: Outlaw R. A.
Published: July 2002

The permeation of oxygen through Ag normally occurs by a sequence of steps which include the initial dissociative adsorption of molecular oxygen at the upstream surface, the dissolution of the atoms into the bulk, and the subsequent migration of the atoms between octahedral sites of the lattice until they arrive at the vacuum interface downstream. The dissociative adsorption step, however, proceeds slowly, as indicated by the low sticking coefficient of O2 on Ag(10−6–10−3). The application of a dc field in 0.5 Torr of O2 (E/n∼10−14 V cm2) on the upstream side of a Ag membrane generated gas phase atomic oxygen that substantially enhanced the transport. The transport flux was observed to increase from a value of 4.4×1013 cm−2 s−1 to a glow discharge value of 2.83×1014 cm−2 s−1 at a membrane temperature of 650 °C. This suggests that the dissociative adsorption step limits the supply of oxygen atoms to the upstream side of the membrane. When the upstream O2 was replaced by an equal pressure of CO2, only a small permeation signal was observed, but the application of the glow discharge substantially increased the transport flux from 3.25×1012 cm−2 s−1 to 1.74×1014 cm−2 s−1. This method of separating O2 from a CO2 environment may be a possible mechanism for providing a supply of oxygen for astronauts in a manned mission to Mars.
Dependence of luminescence in five membered heterocyclic conducting polymers on molecular structure and temperature
Authors: Yoshino Katsumi , Manda Yasuhisa , Takahashi Hiroyuki , Nishioka Yoshinori , Kawai Tsuyoshi , Ohmori Yutaka , Onoda Mitsuyoshi
Published: July 2002

Dependencies of photoluminescence in five membered heterocyclic conducting polymers on heteroatoms and temperature are studied. Luminescence intensity of poly(3-alkylthiophene)s increases with temperature and luminescence intensity of poly(3-alkylfuran)s is slightly enhanced with increasing temperature. However, luminescence intensity of poly(3-hexylselenophene) is even suppressed with temperature. These difference of properties among heterocyclic conducting polymers with different heteroatoms can be interpreted in terms of the difference of steric hindrance effect between heteroatoms and alkyl side chain and the interchain interaction which influence on the dynamics of excited species and recombination.
Magnetic properties of Fe-based superlattices and sandwiches
Authors: Sellers C. , Hilliard J. E. , Ketterson J. B.
Published: July 2002

The coercivity and anisotropy of Fe-based superlattices have been found to be enhanced for Fe layer thicknesses from 3 to 30 atomic layers. Several nonferromagnetic metallic separation layers were used but the magnetic properties were found to be nearly independent of the material. Sandwich structures consisting of only one or two magnetic layers were prepared and it was found that size effects are important for dFe<60 Å. Magnetic coupling across large separations was also evident.
Properties of polycrystalline ZnSe thin films grown by ion-beam deposition
Authors: Kuroyanagi Akio
Published: July 2002

Polycrystalline ZnSe thin films were grown by ion-beam deposition on glass substrates. The crystallinity of ZnSe films grown by ion-beam deposition is affected by ionization. In particular, at a substrate temperature of 200 °C, there is an abrupt increase in the number of (311) oriented grains. Without ionization, the (111) oriented grains predominate. Transmittance of ZnSe films is improved by ion-beam deposition at substrate temperatures below 200 °C, in the wavelength range of 460–550 nm near the interband absorption edge. Ion-beam deposition has a heating effect on the film surface during deposition by ion bombardment, which controls the crystallinity and the optical properties of ZnSe films at low substrate temperature on noncrystalline substrates.
Background impurity dependence of redistributions of implanted gallium in silicon during annealing
Authors: Yokota Katsuhiro , Furuta Hiroshi , Ishihara Shinji , Kimura Itsuro
Published: July 2002

About 85% of Ga implanted into As doped Si, about 80% of that into Sb doped Si, and about 78% of that into P doped Si were lost into atmosphere during annealing at 950 °C for 30 min. The number lost depended on impurities in native oxide films on the Si surfaces.
Residual defects in AlGaAs co-implanted with Be and P or As
Authors: Magno R. , Shelby R. , Molnar B.
Published: July 2002

Deep-level transient spectroscopy (DLTS) and capacitance-voltage (C-V) measurements have been used to study the residual defects in n-type AlGaAs co-implanted with Be and either As or P. The co-implant procedure is being studied as a method for limiting Be diffusion during the rapid thermal annealing process used to activate the Be. The only defect found in the upper half of the band gap by DLTS measurements between 10 and 450 K has an activation energy of 0.88 eV. This defect undergoes photocapacitance quenching, which together with its activation energy suggests that it is similar to the EL2 defect found in GaAs. In an analysis of high-temperature C-V data, the defect manifests itself as a peak in the donor concentration. The donor concentration data were modeled by doing a double integration of Poisson’s equation assuming a Gaussian defect distribution and a uniform shallow donor distribution. This analysis indicates that the center of the Gaussian defect distribution is near the peak in the P or As distribution and that the peak concentrations are about 1×1017 defects cm−3 for the higher P and As fluences.
Path integral simulation of polarized solitons in optical fibers
Authors: Hayata K. , Saka K. , Koshiba M.
Published: July 2002

An efficient computational approach based on the path integral concept is described to solve nonlinear pulse propagation dynamics in realistic optical fibers. As model equations which can predict the propagation, we consider the perturbed (scalar) and the coupled (vectorial) nonlinear Schrödinger equations for monomode and birefringent fibers, respectively. With the equivalence between path integration and Fresnel transform, an efficient algorithm can be employed which has been developed for use in the field of wave signal processing of holographic data. After ensuring the validity of the method through the application to canonical soliton problems, results are shown for nonlinear pulse propagation under realistic conditions.
Forced thickness-extensional trapped energy vibrations of polarized ceramic plates
Authors: Shick D. V. , Tiersten H. F. , Sinha B. K.
Published: July 2002

An analysis of PZT-7A plates driven into thickness-extensional trapped energy vibrations by the application of a voltage to strip electrodes is performed. The plate waves in the unelectroded region that carry energy away from the trapped mode are included in the treatment. The solution consists of a sum of the driven thickness solution and the pertinent plate eigensolutions for shorted electrodes in the electroded region and for zero surface charge in the unelectroded region. Since the sum of the solutions in each region satisfies the differential equations and boundary conditions on the major surfaces exactly, the substitution into the appropriate variational principle of linear piezoelectricity yields integral conditions across the thickness of the plate at the edge of the electrodes. The resulting system of inhomogeneous linear algebraic equations yields the response from very low frequency to slightly above the first thickness-extensional frequency of the unelectroded plate.
Study of a cesium plasma as a selective emitter for thermophotovoltaic applications
Authors: Lowe R. , Goradia C. , Goradia M. , Chubb Donald L.
Published: July 2002

This experimental study evaluates the potential of a cesium plasma as an emitter for a thermophotovoltaic (TPV) energy conversion system. A cesium plasma, as a result of the ground-state transitions of its single outer-shell electron, produces large amounts of radiation in the 850–890-nm wavelength region. This would provide excellent coupling to silicon, gallium arsenide, and indium phosphide photovoltaic cells. Measurements of the radiative efficiency, the sum of the power at the 852 and 894 nm wavelengths relative to the total emitted power were made and correlated to the plasma operating variables. It was determined that for atomic density in the range (3–6)×1021/m3 and electron temperature in the range 2000–3000 K, radiative efficiencies in excess of 70% are attainable. This would indicate that a cesium plasma with its selective emission characteristics and low electron operating temperatures of 2000–3000 K would be an excellent candidate as an emitter in a TPV system.
Novel target configurations for selective ionization state studies in molybdenum
Authors: Ilcisin K. J. , Feldman U. , Schwob J. L. , Wouters A. , Suckewer S.
Published: July 2002

Details of experiments aimed at achieving low ionization state selectivity in molybdenum are presented. Targets are excited with a 10 J CO2 laser and the resultant vacuum ultraviolet spectrum (300–700 Å) has been studied. Combinations of focal spot size, target depth, and target geometries are compared. Simple attenuation of energy is shown not to vary ionization stage composition significantly. Experiments conducted with grazing incidence targets result only in a hot plasma. Modular targets with cooling cylinders of various radii demonstrated good selectivity of the ionization states, but with low absolute signals. Finally, results from combinations of focal spot adjustment and radiative cooling illustrate increased control over desired plasma temperature and density for spectroscopic studies of molybdenum.
Predicted band gap of the new semiconductor SiGeSn
Authors: Soref Richard A. , Perry Clive H.
Published: July 2002

The direct and indirect band gaps of Si1−x−yGexSny are inferred from the calculated energy-band structure of α-Sn and from the known structures of Ge and Si. Our assumptions are: that the energy-band shapes of the binaries Sn1−xGex, Ge1−ySiy and Si1−ySny change smoothly with x and y, and that the energy gap of SiGeSn can be estimated by interpolation from the gaps of SnGe, GeSi, and SiSn. The optical indices of refraction of SiGeSn are also estimated.
Magnetic force microscope study of the micromagnetics of submicrometer magnetic particles
Authors: Gibson G. A. , Schultz S.
Published: July 2002

A high-resolution, high-sensitivity magnetic force microscope (MFM) with the ability to image in an in situ magnetic field is described. This MFM has been used to investigate the micromagnetics of nanolithographically produced magnetic particles. It is shown that the particles’ switching fields can be determined without being perturbed by the stray fields from the sensing tip. This allows the study of the evolution of the particles’ magnetic states as a function of applied field and the direct observation of cooperative switching among interacting particles. The switching fields of individual particles are compared with remanent magnetization data, taken with an alternating gradient magnetometer, on both isolated and interactive arrays of particles. A method is described for estimating the strength of the interaction between particles by comparing the switching fields of different configurations of particle moments created by using the MFM tip as a local field source. Finally, a novel remanent magnetization state has been observed which provides a check on the validity of micromagnetic numerical simulations.
Temperature dependence of Schottky barrier heights on silicon
Authors: Werner Jürgen H. , Güttler Herbert H.
Published: July 2002

We investigate the temperature dependence of Schottky barrier heights on silicon. The analysis of a large variety of polycrystalline diodes shows that the temperature coefficient of the barrier height depends on the chemical nature of the metal. This observation is in contradiction with models suggesting Fermi-level pinning at the center of the semiconductor’s indirect band gap. From the analysis of epitaxial NiSi2/Si Schottky contacts, we conclude that there is a direct influence of interface crystallography on both the barrier height and its temperature dependence. Finally, we present some new results on the pressure coefficient of barrier heights. Pressure and temperature coefficients of polycrystalline Schottky contacts are correlated similarly to the pressure and temperature coefficients of the band gap.
Spectrometry of very long-current transients in almost ideal silicon p-n junctions
Authors: Basso G. , Pellegrini B. , Polignano M. L.
Published: July 2002

Proper gettering and annealing processes allow construction of silicon p-n junctions whose current-voltage characteristic either completely obeys the Shockley equation (ideal junctions) or, for reverse bias, has three components (almost ideal junctions): a voltage-independent term, which may be much smaller than the diffusion saturation current, a generation-recombination contribution, and an ohmic component. The last two currents are due to defect centers that have the same activation energy and which are electrically neutral. In preceding works it has been shown that such an experimental finding may be ascribed to four-state traps, i.e., to defect centers that may be empty of carriers, or filled by an electron or a hole, or both, and which are created by localized states, with different positions and energy levels, due to the oxygen. In the present work an experimental system for measuring, at 0±0.05 °C, the current transients produced in almost ideal junctions by changes of the reverse-bias voltage, and an analysis method for performing the spectrometry of such transients are described. It is found that these last a few hours and that they are composed of four exponential terms whose relaxation times range from tens to a few thousands of seconds. Finally, it is shown that such experimental results also can be ascribed to the preceding defect centers generated by SiyOx clusters of a few hundred atoms of oxygen put near the junction interface, which emit carriers through a tunnel-assisted thermal emission.
Performance characteristics of endoreversible chemical engines
Authors: Gordon J. M. , Orlov Vladimir N.
Published: July 2002

Chemical engines process mass flows to convert differences in chemical potential into work—the analog of heat engines processing heat flows to generate work from temperature differences. For isothermal endoreversible chemical engines constrained to finite-time operation—examples of which include mass exchangers, electrochemical, photochemical, and solid-state devices: (i) optimal cycle types for maximizing average power output, (ii) upper bounds on power production, and (iii) sensitivity of these results to mass-transfer law, illustrated for linear and diffusive behavior, are derived.
Evidence of a nonthermal mechanism for ejection of ions and neutrals during excimer laser ablation of Ge
Authors: Solis J. , Vega F. , Afonso C. N. , Georgiou E. , Charalambidis D. , Fotakis C.
Published: July 2002

Resonance ionization spectroscopy combined with time of flight mass spectrometry is used to analyze the ejection of ions and neutrals from the surface of a Ge target irradiated with ultraviolet XeCl excimer laser pulses. The ejection of ions and neutrals has been observed to occur at temperatures well below the melting point of the target and, therefore, through a nonthermal mechanism that may be dominant for fluences below the threshold for visible plasma formation. Within this regime, the velocities of the ejected neutrals in the ground state are in the order of 3×104 cm/s.
Minority carrier diffusion length and edge surface-recombination velocity in InP
Authors: Hakimzadeh Roshanak , Bailey Sheila G.
Published: July 2002

A scanning electron microscope was used to obtain the electron-beam-induced current (EBIC) profiles in InP specimens containing a Schottky barrier perpendicular to the scanned (edge) surface. An independent technique was used to measure the edge surface-recombination velocity (Vs). These values were used in a fit of the experimental EBIC data with a theoretical expression for normalized EBIC [C. Donolato, Solid State Electron. 25, 1077 (1982)] to obtain the electron (minority carrier) diffusion length (Ln).
Determination of cubic-tetragonal phase boundary in Zr1−XYXO2−X/2 solid solutions by Raman spectroscopy
Authors: Yashima Masatomo , Ohtake Katsuya , Arashi Haruo , Kakihana Masato , Yoshimura Masahiro
Published: July 2002

Raman spectroscopy is found to be a powerful tool to determine the structural phase boundary between cubic (Fm3m) and tetragonal (P42/nmc) phase in arc-melted Zr1−XYXO2−X/2 (0.08≤X≤0.24) solid solution. The Raman peak intensity characteristic of the tetragonal phase at about 470 cm−1 decreases with the YO1.5 content X and becomes 0 around X=0.18.
Orientational and structural dependence of magnetic anisotropy of Cu/Ni/Cu sandwiches: Misfit interface anisotropy
Authors: Jungblut R. , Johnson M. T. , aan de Stegge J. , Reinders A. , den Broeder F. J. A.
Published: July 2002

Magnetic anisotropies and misfit strain relaxations have been investigated in Cu/Ni-wedge/Cu (100) and (111) sandwiches deposited by molecular beam epitaxy on single-crystal Cu substrates. Our results reveal a clear distinction in the nature of the measured anisotropy at Ni thicknesses below and above the critical value tc, where the growth becomes incoherent. Below tc, coherent lattice strain modifies only the volume anisotropy, while interface anisotropy is Néel type; above tc, magnetoelastic effects are found to contribute to the interface anisotropy.
Temperature dependence of the band-gap energy of disordered GaInP
Authors: Ishitani Yoshihiro , Minagawa Shigekazu , Tanaka Toshiaki
Published: July 2002

The temperature variation of the photoluminescence peak energy of GaxIn1−xP shows a complex dependence on the structural order; however, such effects are not well explained even for the fully disordered material. The band-gap energy of disordered GaxIn1−xP was measured at temperatures from 10 to 300 K and the measured values were used to find the best parameters in a theoretical equation. Since a simpler expression does not fit the experimental data accurately (especially below 30 K), an expression consisting of three terms which represent the effect of thermal expansion, electron–optical-phonon coupling, and electron–acoustic-phonon coupling was adopted. Dividing an electron-phonon coupling term into two terms results in a better expression for InP over the entire range of measuring temperatures. This function was applied to disordered GaxIn1−xP (x=0.5, 0.7). It is found that in InP the electron–acoustic-phonon coupling is stronger than electron- optical-phonon coupling, while in GaxIn1−xP the opposite is true.
A quantitative analysis of the polarization reversal in the 73 mol % vinylidene fluoride–27 mol % trifluorethylene copolymer
Authors: Leal Ferreira G. F. , Moreno R. A.
Published: July 2002

We show that a time-dependent, effective-medium approximation essentially explains the time behavior of the polarization reversals obtained in doped copolymers of vinylidene fluoride and trifluorethylene at 60 °C by Ieda, Fukada, and Wada [J. Appl. Phys. 64, 2026 (1988)], who attributed the observed effects to charge accumulation at the boundaries of the permanently polarized crystallites. Moreover, the results seem to indicate that some hindrance (perhaps of mechanical origin) opposes the action of the switching electric field.
Methods of determining magnetization and uniaxial anisotropy of multilayers by means of torque magnetometry
Authors: Poulopoulos P. , Flevaris N. K. , Krishnan R. , Porte M.
Published: July 2002

Torque data for Pd-Ni and Pt-Co multilayers are analyzed within simple models in order to obtain, analytically or by numerical analysis, the anisotropy constant(s) and the magnetization. The analysis of such data can be performed in two ways: first, by considering second-order anisotropy or, second, two uncoupled magnetic regions. Finally, a generalization of the well-known treatment of (L/H)2 vs L plots is proposed in order to determine the first- and second-order uniaxial anisotropy constant together with the magnetization.
The effect of the InAs layer thickness on the peak current density and subband properties of the GaSb/InAs/GaSb/AlSb/InAs structures
Authors: Liu M. H. , Wang Y. H. , Houng M. P.
Published: July 2002

The incorporation of the InAs layer as the blocking layer into the GaSb side of the GaSb/AlSb/InAs single-barrier interband tunneling structure resulting in a GaSb/InAs/GaSb/AlSb/InAs resonant interband tunneling structure has been proven to greatly enhance negative differential resistance peak-to-valley current ratios and peak current density. The role of the InAs layer induced electron and light hole coupling related to the device performance is then investigated. A three-band model, incorporating the coupling effect of the spin-orbit split-off hole band, is employed to probe the effect of the InAs layer thickness on the peak current densities and the subband properties of the GaSb/InAs/GaSb/AlSb/InAs resonant interband tunneling structures. The calculated peak current densities are in reasonable agreement with the experimental data reported previously. The transmission coefficients based on the three-band calculation can be used to interpret the variations of the peak current densities well. In addition, the ‘‘repulsion’’ of the conduction subbands in the InAs well and light-hole subbands in the GaSb well is observed for larger InAs layer thickness. A ‘‘transition energy region’’ resulting from the crossing of the respective subbands in the InAs and GaSb wells is also observed. The effect of the InAs layer induced subband properties related to the carrier transport in the peak current of the GaSb/InAs/GaSb/AlSb/InAs structure is also discussed.
Modeling of mixing in chemical oxygen-iodine lasers: Analytic and numerical solutions and comparison with experiments
Authors: Barmashenko B. D. , Elior A. , Lebiush E. , Rosenwaks S.
Published: July 2002

The processes of iodine dissociation, population inversion, and lasing in the chemical oxygen-iodine laser (COIL) are affected by the mixing between the flows of oxygen and injected iodine. The effect of mixing on the operation of the COIL is studied theoretically applying a simple one-dimensional leaky stream tube model and the results are compared to available experimental data. The model enables the calculation of the iodine dissociation and the gain along the flow and of the lasing power, as a function of the iodine flow rate (nI2), the yield of singlet oxygen [O2(1Δ)] and the pressure in the cavity. Both the fraction of the dissociated iodine and the maximum gain are shown to be nonmonotonous functions of nI2. There is an optimal value of nI2, depending on the O2(1Δ) yield, the gas velocity, and the temperature in the cavity, for which the gain achieves its maximum and the iodine dissociation length its minimum. The model shows that the maximum nI2 for which lasing is possible is less than 5% of the oxygen flow rate. This result is in agreement with experimental data and cannot be explained by models based on the assumption of a premixed flow. Simple analytic expressions are derived for the optimal nI2, the characteristic length of iodine dissociation, the gain, and the lasing power. The calculated gain and lasing power are compared with available experimental results for both subsonic and supersonic COILs.
Melt texturing of preferentially aligned YBa2Cu3Ox superconductor by a seeded directional solidification method
Authors: Lee D. F. , Partsinevelos C. S. , Presswood R. G. , Salama K.
Published: July 2002

Directional solidification has been shown to be capable of producing long lengths of melt-textured YBa2Cu3Ox. In order to maximize the current carrying capability of these superconductors, grain alignment needs to be directed along the sample axis. So far, this preferential grain alignment can only be achieved in samples of small cross-sectional areas. We have developed a seeded directional solidification method which allows the fabrication of long lengths of single-domained YBa2Cu3Ox with large cross-sectional areas and predetermined grain alignment. The current carrying capability of these superconductors is superior to that of the misaligned ones, and the Ic is estimated to be a few thousand amperes for samples of 4×8 mm2 cross-sectional area.
Simultaneous bolometric and nonbolometric microwave response in biepitaxial Y-Ba-Cu-O thin films
Authors: Grabow B. E. , Boone B. G.
Published: July 2002

Measurements and the modeling of the microwave (9 GHz) response of a biepitaxial thin film showing the simultaneous presence of bolometric and nonbolometric response peaks in the same sample are reported. The nonbolometric response in this Y-Ba-Cu-O thin film gives further evidence of microwave detection in the networks of inherent Josephson junctions present at the grain boundaries between two epitaxial layers. By modeling the film as a distribution of granular connections with varying critical currents and temperatures we achieve results similar to those observed in microwave response measurements in granular Bi-Sr-Ca-Cu-O thin films.