bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymerized complex synthesis and intergranular coupling of Bi-Pb-Sr-Ca-Cu-O superconductors characterized by complex magnetic susceptibility
Authors: Kakihana Masato , Yoshimura Masahiro , Mazaki Hiromasa , Yasuoka Hiroshi , Börjesson Lars
Published: July 2002

Superconducting Bi-Pb-Sr-Ca-Cu-O ceramics have been synthesized by the polymerized complex method at the Bi1.8Pb0.2Sr2Ca2Cu3Oy, Bi1.6Pb0.4Sr2Ca2Cu3Oy and Bi1.68Pb0.32Sr1.75Ca1.82Cu2.83Oy compositions. The polymerized complex method includes three important major steps: (1) formation of stable citrate complexes uniformly dispersed into ethyleneglycol and water, (2) fabrication of polymerized complexes which are formed through dehydration (or esterification) between ethyleneglycol and metal-citrate complexes, and (3) pyrolysis of the polymerized complex precursor and the subsequent heat treatments for producing the Bi-Pb-Sr-Ca-Cu-O superconductor. The present technique offers more convenient and easier fabrication of (Bi,Pb)2Sr2Ca2Cu3Oy superconductors compared with other more elaborate preparation procedures based on wet-chemical techniques, as it eliminates many steps such as ageing, filtration, washing, and pH control. ‘‘X-ray-clean’’ (Bi,Pb)-2223 superconductors have been obtained for all the three compositions after sintering at 850 °C in air for 94–235 h, depending upon the nominal composition of the starting batch. Noticeable is that a small deficiency of Sr, Ca, and Cu relative to the ideal stoichiometric composition of the (Bi,Pb)2Sr2Ca2Cu3Oy significantly accelerates the formation of the (Bi,Pb)-2223 phase.

Complex magnetic susceptibility measurements show that Tc(onset) of the bulk (Bi,Pb)-2223 phase remains almost constant at around 108 K, independent of the compositions. However, it is stressed that low-level and/or amorphous impurity phases possibly concentrated on grain boundaries can have dramatic effects on the overall magnetic properties even for materials which look like very ‘‘clean’’ by x-ray diffraction. The best superconducting properties were obtained with samples with a nominal composition of Bi1.6Pb0.4Sr2Ca2Cu3Oy after sintering in air at 850 °C for 180–280 h. The onset temperature of superconducting transition obtained by complex susceptibility was 108.0 K and the transition width (10%–90%) of full diamagnetism was 5.2 K for a measuring field of 100 mOe.
Modeling the self-sustained discharge-excited XeCl laser in two dimensions
Authors: Turner M. M.
Published: July 2002

A new two-dimensional model for transverse discharge-excited gas lasers is described. The model can compute accurate electric fields for complex geometries. This facility is exploited to investigate the effect of the discharge electrode profile on XeCl laser performance. It is found that any of the stock electrode designs is satisfactory for high-efficiency lasers with excitation pulses lasting for up to 200 ns. For longer-pulse lasers, the pulse length and energy output are sensitive to the choice of electrode and there are grounds for preferring the Stappaerts profile over the other available designs.
The influence of oxygen on the electrical and optical properties of GaN crystals grown by metalorganic vapor phase epitaxy
Authors: Chung B-C. , Gershenzon M.
Published: July 2002

Oxygen was observed to influence the electrical and optical properties of GaN layers grown by metalorganic vapor phase epitaxy. The carrier concentrations obtained from Van der Pauw–Hall measurements increased an order of magnitude when oxygen was incorporated into the grown layers. Additionally, the presence of oxygen in the GaN layers also changed the compensation behavior of Zn. Anomalous behavior of optical transitions in the oxygen-doped GaN layers was observed by optical absorption spectroscopy and low-temperature (4.2 K) photoluminescence measurements. These properties were studied as a function of growth parameters including growth temperature, amount of doping, etc. A model based on impurity band formation is proposed to explain these experimental results, and it is concluded that oxygen is a ‘‘shallow’’ deep donor in GaN.
Zero-dimensional states in submicron double-barrier heterostructures laterally constricted by hydrogen plasma isolation
Authors: Van Hove M. , Pereira R. , De Raedt W. , Borghs G. , Jonckheere R. , Sala C. , Magnus W. , Schoenmaker W. , Van Rossum M.
Published: July 2002

The lateral dimensions of resonant tunneling AlGaAs-GaAs double barrier heterostructures have been restricted by hydrogen plasma exposure. Ohmic contacts to the submicron diodes have been made by solid phase epitaxial growth of Ge on GaAs. The current-voltage characteristics show a fine structure splitting that is inversely proportional to the lateral size of the diode. The results are interpreted as resonant tunneling through zero-dimensional states in the quantum box confined by the AlGaAs barriers and a harmonic lateral confining potential.
Quantitative characterization of residual strains in gallium phosphide (100) wafers
Authors: Yamada Masayoshi
Published: July 2002

Residual strains in thin GaP (100) wafers, sliced from crystalline ingot grown by the liquid-encapsulated Czochralski method, have been first characterized by measuring strain-induced birefringence. The absolute values of the residual strain components ‖Sr−St ‖, ‖Syy−Szz ‖, and 2‖Syz ‖ are quantitatively characterized. It is found that their two-dimensional distribution maps exhibit fourfold symmetry and that most of wafers exhibit U- or M-shape distributions along diametric directions, but some wafers with a low level of strains exhibit distorted-shape distributions. The maximum strain value attains to the order of 10−4 and the corresponding stress is about 7.5×106 N/m2.
Deposition of copper films on silicon substrates: Film purity and silicide formation
Authors: Padiyath R. , Seth Jayshree , Babu S. V. , Matienzo L. J.
Published: July 2002

Deposition of copper films on silicon substrates by the radio-frequency plasma reduction of spin-coated copper formate films in hydrogen and oxygen plasma discharges has been investigated further. The atomic compositions of these films, determined by Auger electron and x-ray photoelectron spectroscopy, were found to be a strong function of the processing conditions, especially power density and temperature. Rutherford backscattering studies (RBS) of the silicon–copper interface revealed the formation of copper silicide at deposition temperatures that are nominally as low as 40 °C. The silicide formation was further investigated by depositing pure copper films on silicon substrates by thermal evaporation. The Cu/Si interface was analyzed before and after in situ annealing at 300 °C and 10−8 Torr and compared with the results for the plasma deposited films. RBS data show that diamondlike carbon films are excellent diffusion barriers between Si and Cu.
Orientational decay in poled second-order nonlinear optical guest-host polymers: Temperature dependence and effects of poling geometry
Authors: Stähelin M. , Walsh C. A. , Burland D. M. , Miller R. D. , Twieg R. J. , Volksen W.
Published: July 2002

The orientational decay of chemically and thermally stable high-temperature chromophores doped into thin films made from polyimides and a variety of other polymeric hosts has been investigated. The chromophores are aligned using electric field poling and second-harmonic generation (SHG) is used to probe the decay of the electric field poling induced alignment. The decay rate of the SHG signal from films poled using both a corona discharge and side-by-side in-plane electrodes was measured. When electrodes are chosen so that the effects of charge injection are minimized, little difference has been observed between the orientational decays from films poled using the two methods for either an amorphous preimidized polyimide host or a highly anisotropic film poled during imidization. The films imidized during poling showed significant orientational stability at 250 °C for over 15 h after a fast initial partial decay. In addition, the decay of the SHG signal was measured as a function of temperature below the glass transition in a wide variety of different polymer host systems. The temperature dependence of the decay was found to be non-Arrhenius, but could be strongly correlated with the glass transition temperature of the guest-host system using an empirical relationship similar to the Williams–Landel–Ferry or Vogel–Tamann–Fulcher equation.
K-shell x-ray yield scaling for aluminum x-pinch plasmas
Authors: Kalantar D. H. , Hammer D. A. , Mittal K. C. , Qi N. , Young F. C. , Stephanakis S. J. , Burkhalter P. G. , Mehlman G. , Newman D. A.
Published: July 2002

We report results from experiments performed to measure and characterize the intense K-shell radiation from aluminum x-pinch plasmas at peak driving currents ranging from 280 kA to 1.0 MA. Single pulse aluminum K-shell (predominantly line radiation at 1.6–2 keV) x-ray yields ranged from 7.6 J at 290 kA to 240 J at 1.0 MA. In the range from 280 to 470 kA, the yield scales with current to the power of 3.6, whereas nonoptimized K-shell yields at 800 kA and 1.0 MA indicate a power of about 3 or higher.
Photoluminescence and photoluminescence excitation spectroscopy of Al0.48In0.52As
Authors: Olsthoorn S. M. , Driessen F. A. J. M. , Eijkelenboom A. P. A. M. , Giling L. J.
Published: July 2002

A detailed study of the photoluminescence (PL) and photoluminescence excitation (PLE) properties of Al0.48In0.52As is presented. A PL linewidth of 13 meV and a Stokes shift of only 9 meV at 4.2 K both indicate that the effect of clustering is minimal in our samples. The Stokes shift is three times lower than the lowest reported in the literature. No shift was observed in the position of the PL peak with changing excitation intensity. Both the PL energy and intensity showed anomalous temperature behavior: The energy first decreased, then increased, and finally decreased again with increasing temperature (the so-called inverted S shape); the intensity showed a temperature dependence similar to that of amorphous semiconductors and disordered superlattices. These two phenomena suggest strong localization of carriers in Al0.48In0.52As, even when the effect of clustering is minimal. The PLE spectra showed excitonic enhancement only above 40 K. The first observation of phonons with PL is reported in Al0.48In0.52As. Energies of 29.6 and 45.9 meV were measured for the InAs-like and the AlAs-like LO phonons, respectively. These phonons could only be detected below 40 K, which, on the basis of selection rules for LO phonon scattering, confirms the localized nature of the luminescence.
The electromagnetic field of a horizontal electric dipole in the presence of a three-layered region: Supplement
Authors: King Ronold W. P.
Published: July 2002

The electromagnetic field generated by a horizontal electric dipole in the air over a dielectric-coated conducting or dielectric half-space is evaluated in an earlier paper subject to the conditions k20≪k21≪‖k22‖ on the wave numbers of the three regions and the condition k1l≤ 0.6 on the thickness l of the dielectric layer. Unintentionally, the severe condition ‖k2 l‖2≪1 was also imposed in the determination of the field in the dielectric layer and the half-space below it. That restriction is removed in this paper and new complete formulas are derived which have wide potential application.
Critical epitaxial thicknesses for low-temperature (20–100 °C) Ge(001)2×1 growth by molecular-beam epitaxy
Authors: Xue G. , Xiao H. Z. , Hasan M.-A. , Greene J. E. , Birnbaum H. K.
Published: July 2002

The growth of Ge(001) by molecular-beam epitaxy at temperatures Ts between 20 and 100 °C, and deposition rates of 0.5 and 1 Å s−1, was investigated using a combination of in situ reflection high-energy electron diffraction and post-deposition cross-sectional transmission electron microscopy. All films consisted of three zones beginning with a defect-free epitaxial layer of thickness t1 in which ln(t1)∝(1/Ts). The second zone was a narrower intermediate layer containing {111} stacking faults and microtwins, while the third zone was amorphous. An atomistic growth model is proposed to explain the observed morphological breakdown during low-temperature growth.
Epitaxial tetragonal PtCo (001) thin films with perpendicular magnetic anisotropy
Authors: Lairson B. M. , Visokay M. R. , Marinero E. E. , Sinclair R. , Clemens B. M.
Published: July 2002

The ordered PtCo tetragonal intermetallic compound with perpendicular magnetic anisotropy and a preferred c-axis orientation perpendicular to the film plane has been produced by annealing epitaxial multilayers of Pt and Co. These films demonstrate large magnetic anisotropy, magneto-optic Kerr rotations, and magnetization, suggesting them as candidates for magneto-optic and perpendicular magnetic recording.
Deep level transient spectroscopy of high-energy heavy ion irradiation-induced defects in n-type germanium
Authors: Marie P. , Levalois M. , Bogdanski P.
Published: July 2002

Swift heavy ion irradiation-induced defects have been studied in n-type germanium at room temperature using deep level transient spectroscopy. Several electron traps have been observed after irradiation. The corresponding energies have been determined to be at Ec−0.22, Ec−0.275, Ec−0.29, Ec−0.32, and Ec−0.465 eV. The isochronal annealing behavior of these traps has been studied in detail between room temperature and 200 °C. Comparison of our results with previously published ones allowed an identification of these defects with complexes like divacancies or associations of vacancies with impurities.
Enhanced fatigue and retention in ferroelectric thin-film memory capacitors by post-top-electrode anneal treatment
Authors: Thakoor Sarita
Published: July 2002

Remanent polarization in thin ferroelectric films of lead zirconate titanate (PZT) is of considerable interest for rad-hard, nonvolatile memory applications. The fatigue and retention characteristics of PZT films, however, are influenced markedly by the processing and patterning techniques for the capacitor. A post-top-electrode anneal treatment of thin-film ferroelectric capacitor device structures, with the top electrode defined by conventional lift-off patterning, that clearly shows a significant enhancement in the retention and fatigue characteristics of ferroelectric memories is described. In addition to the remanent polarization characteristics of Ti-Pt/PZT/Pt sandwich structure, studied using conventional electronic probe techniques, an optical probe is employed to probe the probable influence of Schottky junction(s) and/or stress at the electrode/PZT interfaces in the device. The significant improvement in the fatigue/retention performance of the devices by the post-top-electrode anneal treatment is attributed primarily to the formation of stable interfaces, as shown by the voltage cycling studies. The effects of operational history on retention performance provide further insight into the role of time-dependent depolarization/polarization components in the functioning of the memory.
Magnetic properties of Ba2(ZnxFe1−x)2Fe28O46 X-type hexaferrites
Authors: Gu B. X.
Published: July 2002

Polycrystalline samples of Ba2(ZnxFe1−x)2Fe28O46 [(ZnxFe1−x)2−X, 0≤×≤1] X-type hexaferrites were prepared by the ceramic method. Magnetization, magnetic moment, and Curie temperature were investigated. With increasing Zn content the magnetization and magnetic moment increase linearly, but the Curie temperature decreases. A discrepancy between experimental and theoretical values of the magnetic moment, which increases with increasing Zn content, was observed. The effect may be due to the partial occupation of the octahedral sites by the Zn2+ ions and resulting in random spin canting.
Fabry–Pérot line shape analysis on an expanding cascaded arc plasma in argon
Authors: Meulenbroeks R. F. G. , van der Heijden P. A. A. , van de Sanden M. C. M. , Schram D. C.
Published: July 2002

Fabry–Pérot line profile measurements have been used to obtain heavy particle temperatures and electron densities for an expanding cascaded arc plasma in argon. This was done for the argon 415.9 and 696.5 nm neutral lines as a function of the distance from the onset of the expansion. Temperatures in the range of 2000–12 000 K were obtained. The electron density in the beginning of the expansion appeared to be 5.6×1021 m−3. The 696.5 nm line profiles appeared to be asymmetric because of self-absorption by cool metastables around the plasma. The density and temperature of these metastables could be determined by fitting the measurements to a theoretical model, and appeared to be around 1017 m−3 and around 3000 K, respectively.
Annealing behavior of deep-level defects in 1 MeV electron irradiated GaAs
Authors: Lai S. T. , Nener B. D.
Published: July 2002

Isochronal annealing behavior of deep-level defects in 1 MeV electron irradiated vapor phase epitaxy GaAs was studied through deep level transient spectroscopy measurements. As the annealing temperature was increased, the activation energy of the EL2-A trap remained at Ec−0.823 eV, whereas the EL2-B trap (Ec−0.843 eV) transformed into a new trap, ELN-1 (Ec−0.870 eV), and finally into another new trap, ELN-2 (Ec−0.891 eV) before returning to the single EL2-A level at a 270 °C annealing temperature. The EL6 trap (Ec−0.335 eV) varied similarly, transforming into Ec−0.357 eV (P1) before staying constant at Ec−0.396 eV (ELN-3) after a 270 °C annealing temperature. The capture cross sections of EL2-B and EL6 increased by an order of magnitude during the annealing. These results suggest that the EL2-B trap which was split from the EL2 center by the 1 MeV electrons could be related to EL6. Traps E1 and E2 remain at Ec−0.032 eV and Ec−0.129 eV, respectively, throughout the annealing, before annihilation at a 290 °C annealing temperature. This result indicates that the atomic structures of E1 and E2 defects could be related. The EL3 (Ec−0.420 eV) is transformed into a new trap, ELN-4 (Ec−0.456 eV), and then into Ec−0.50 eV (P2) during annealing. The free carrier concentration of the irradiated sample increases rapidly with annealing temperature and returns back to the starting free carrier concentration due to the rapid annealing rates of the electron induced defects.
Strong stripes as a paradigm of quasi-topological hysteresis
Authors: Labrune Michel , Miltat Jacques
Published: July 2002

Micromagnetic numerical computations are used to simulate the equilibrium magnetization distribution within (periodic) stripe patterns in thin films with a canted easy axis and intermediate quality factor. Two thicknesses are considered, either close to the critical thickness for domain nucleation in zero field or in fair excess of this last quantity. Several micromagnetic structural transitions are observed to take place under the action of an external field applied along the stripe’s elongation direction. The computed intrinsic hysteresis curves prove to be in excellent agreement with experimental data, provided some degree of heterogeneous nucleation is accounted for. Although all computed equilibrium structures are homotopic to a point, transient magnetization distributions are shown to be just filling the order parameter space. For this reason, the transitions and the intrinsic hysteresis phenomena are termed quasi-topological.
Effects of active hydrogen on the stress relaxation of amorphous SiNx:H films
Authors: Hasegawa S. , Amano Y. , Inokuma T. , Kurata Y.
Published: July 2002

Amorphous SiNx:H (a-SiNx:H) films were deposited at 300 °C by plasma-enhanced chemical vapor deposition using SiH4–NH3–H2 mixtures. The stress, vibrational absorption, buffered HF (BHF) etch rate, and breakdown strength were investigated as a function of the gas volume ratio [H2]/[SiH4](=RH) and rf power. The [NH3]/[SiH4] ratio was maintained at 10, in which nitride films having a near-stoichiometric composition can be obtained. The measured stress for these films was intrinsic stress. It was suggested that the stress is relaxed by forming Si—NH—Si bonds instead of N—Si3 bonds. An increase in both RH and rf power values was found to decrease the stress and BHF etch rate and increase the breakdown strength. A change in the bonding structure with increasing RH and rf power is examined in terms of a thermodynamic equilibrium reaction, and it was suggested that increased H* radicals and/or H+ ions play an active role in relaxing the stress through the structural change.
Spatial distribution of charges in ultrathin polyimide Langmuir–Blodgett films
Authors: Iwamoto Mitsumasa , Fukuda Atsushi , Itoh Eiji
Published: July 2002

The spatial distribution of charges in ultrathin polyimide (PI) Langmuir–Blodgett (LB) films, with a monolayer thickness of 0.4 nm, deposited onto metals was determined by measuring the surface potential of the PI LB films as a function of the number of deposited layers. The depth of penetration of the excess charges displaced from metal electrodes into the PI LB films was about 3 nm. The saturated surface potential was an accurately linear function of the work function of the metal. We concluded that excess charges (mainly electrons) were transferred from metals into as-deposited PI LB films until thermodynamic equilibrium was established at the metal/PI interface by electron tunneling.
Growth and properties of ion beam synthesized Si/CoxNi1−xSi2/Si(111) structures
Authors: Wu M. F. , Wachter J. De , Van Bavel A.-M. , Pattyn H. , Langouche G. , Vanhellemont J. , Bender H. , Temst K. , Wuyts B. , Bruynseraede Y.
Published: July 2002

Heteroepitaxial CoxNi1−xSi2 layers with good crystalline quality (χmin=3.5%) have been formed by ion beam synthesis. For a sample with x=0.66, we found that this ternary silicide layer contains 11% type B and 89% type A orientation. The transmission electron microscopy investigation reveals that the type B component is mainly located at the interfaces and with a thickness of only a few monolayers. X-ray diffraction studies of the sample show that the strain of the type B component is smaller than that of the type A and is probably the reason for such a unique distribution of the type B component in the epilayer. Rutherford backscattering-channeling, Auger electron spectroscopy, transmission electron microscopy, and x-ray diffraction have been used in this study.
Comparison of the improvement of thermal stability of NdFeB sintered magnets: Intrinsic and/or microstructural
Authors: Ma B. M. , Liu W. L. , Liang Y. L. , Scott D. W. , Bounds C. O.
Published: July 2002

Temperature-dependent magnetic properties of nine NdFeB sintered magnets with various Co-Nb, Co-V, or Co-Mo additions have been measured up to 175 °C using both closed-loop and open-circuit methods. The irreversible loss of induction, reversible temperature coefficient of induction (α), and temperature coefficient of intrinsic coercivity β have been related to the Tc, the Br, and the Hci at 25 and 175 °C. The irreversible loss of induction is strongly affected by the Hci at 25 °C and the α has been found to be strongly dependent upon the Tc. Intrinsic coercivity of more than 25 and 7.5 kOe at 25 and 175 °C, respectively, are essential to bring the β to better than −0.5%/ °C. A magnet with a composition of Nd12Dy3Fe70Co5Nb2B8 has been found to exhibit an outstanding thermal stability: a Br of 8.5 kG (comparable to that of SmCo5 sintered magnet) and a Hci of 12.9 kOe when measured at 175 °C. An α of −0.10%/ °C and a β of −0.4%/ °C have been obtained.
Optical and electrical properties of radio frequency sputtered tin oxide films doped with oxygen vacancies, F, Sb, or Mo
Authors: Stjerna B. , Olsson E. , Granqvist C. G.
Published: July 2002

Tin oxide films doped with oxygen vacancies, F, Sb, or Mo were made by reactive rf magnetron sputtering of Sn, Sn-Sb, or Sn-Mo in Ar+O2(+CF4) onto glass heated to a temperature up to 530 °C. Electrical dc resistivity, mobility, free-electron density, spectral optical properties, and microstructure were investigated as a function of sputtering parameters. Optimized deposition parameters gave SnOx:(Sb,F) films with high luminous transmittance, low luminous absorptance, high infrared reflectance, and dc resistivity down to 9.1×10−4 Ω cm. Refractive index n and extinction coefficient k were evaluated from spectrophotometric transmittance. In the luminous range, the films had 1.90<n<2.0 and k of the order of 10−2. Hall-effect measurements showed n-type conduction with electron densities in the 1020–1021 cm−3 range. Band-gap broadening from 4.06 to 4.45 eV was observed with increasing electron density. X-ray diffractometry and transmission electron microscopy showed that the structure factor of the films depended on the oxygen content as well as on the specific doping species. A preferred direction of film growth was probably also present. Transmission electron microscopy indicated different grain sizes, between 6 and 30 nm, depending on oxygen content, substrate temperature, and doping species. Optical and electrical properties were compared with results from a quantitative model for wide band-gap semiconductors. The theory is based on heavy n doping by oxygen vacancies or by Sb or/and F and encompasses ionized impurity scattering of the free electrons. It was found that ionized impurity scattering, as well as an additional scattering mechanism tentatively ascribed to grain boundaries, prevailed in the films.
Evolution of the In oxide/Si(111) interface: Analysis by electron spectroscopies
Authors: Öfner H. , Shapira Y. , Netzer F. P.
Published: July 2002

The growth of thin In oxide layers on Si(111) substrate surfaces by reactive evaporation of In in oxygen atmosphere and the formation of the In oxide–Si interface under ultrahigh-vacuum conditions has been studied by Auger electron spectroscopy, electron-energy-loss spectroscopy, photoemission with use of synchrotron radiation, and inverse photoemission. Oxygen pressure and substrate temperature were varied as the parameters of the reactive evaporation. The combined electron spectroscopic results indicate that for In deposition onto room-temperature substrate surfaces and PO2<5×10−5 mbar the interfacial layer contains metallic In and oxidized Si, but that for higher PO2 the metallic In concentration at the interface is reduced. The oxidation of In appears to be enhanced away from the In-Si interface, and for PO2≳5×10−5 mbar the oxide stoichiometry approaches that of In2O3. At elevated substrate temperature (250 °C) the growth rate of In oxide layers is reduced as compared to room temperature, but the oxidation yield at the interface is enhanced. For PO2=2×10−4 mbar and 250 °C substrate temperature the growth of a uniform near-stoichiometric In oxide layer is indicated.
Power flow between a plasma-opening switch and a load separated by a high-inductance magnetically insulated transmission line
Authors: Swanekamp S. B. , Grossmann J. M. , Ottinger P. F. , Commisso R. J. , Goyer J. R.
Published: July 2002

Results are presented from particle-in-cell simulations of the electron flow launched from a plasma opening switch (POS) into a magnetically insulated transmission line (MITL) as the POS opens. The opening process of the POS is treated by removing plasma from a fixed anode-cathode gap with an opening time of τrise. To be similar to opening switch experiments at Physics International, the simulations were performed with the same inductance LMITL between the POS and load. When LMITL/τrise is large compared to the POS flow impedance, this inductance effectively isolates the POS from the load during the opening process and the POS voltage is insensitive to changes in the load impedance. Analysis and simulations show that the peak load power is maximized when the load impedance is equal to the POS flow impedance. In contrast to previous theories and simulations of magnetically insulated flows, a large amount of electron flow in the MITL is concentrated near the anode. This is a result of the high effective impedance imposed on the POS by the inductive load which causes a significant electron current loss in the POS. As a result, many electrons lose insulation on the load side of the POS gap and those that do flow into the MITL have been accelerated to nearly the full POS potential. Electrons then E×B drift on equipotential lines close to the anode as they enter the MITL and flow toward the load. Current losses in the MITL are observed due to the proximity of the electron flow to the anode. Some electrons flow from the MITL directly into the load and are registered as load current while others E×B drift back toward the POS along the cathode surface. This is possible because the electron flow launched into the MITL from the POS is large enough to cause sufficient positive image charges on the cathode so that the electric field points out of the cathode surface.
Correlation of substitutional hydrogen to refractive index profiles in annealed proton-exchanged Z- and X-cut LiNbO3
Authors: Zavada J. M. , Casey H. C. , States R. J. , Novak S. W. , Loni A.
Published: July 2002

Previous disagreements concerning a linear correlation between the hydrogen (H) concentration and the extraordinary refractive index ne in proton-exchanged lithium niobate (LiNbO3) have been resolved by partitioning the total H into optically active substitutional H and optically inactive interstitial H. The H and Li spatial variations in both Z- and X-cut crystals were determined by secondary-ion-mass spectrometry (SIMS) with a quantitative evaluation in atoms/cm3. These samples were proton exchanged in neat benzoic acid at 185 °C and then were annealed at 400 °C for times t from 6 to 240 min in wet flowing oxygen. For the Z-cut crystals, fit of the SIMS measured H profiles by expressions obtained from the diffusion equation for diffusion from a finite layer gave a substitutional H diffusivity of DZs=5.0±0.3×10−12 cm2/s and an interstitial H diffusivity of DZi=1.4±0.1×10−11 cm2/s. The wet flowing oxygen acts as a constant source of interstitial H at the surface with the diffusivity DZi and gives an integrated H concentration due to the flowing wet oxygen which increases as √t. The Li diffusivity was DLiZ=4.8±0.2×10−12 cm2/s which is nearly equal to DZs. For X-cut crystals, the substitutional H diffusivity was DXs=3.4±0.2×10−12 cm2/s and the interstitial diffusivity was DXi=1.3±0.2×10−11 cm2/s. The ne profiles were evaluated by means of optical prism-coupling measurements and numerical simulations. In both cases of crystal orientation, the effective index diffusivity is nearly equal to the diffusivity of substitutional H. Furthermore, there is an excellent linear relationship between the ne profile and the corresponding substitutional H distribution.
Phosphorus-vacancy-related deep levels in GaInP layers
Authors: Huang Z. C. , Wie C. R. , Varriano J. A. , Koch M. W. , Wicks G. W.
Published: July 2002

Deep levels in lattice-matched Ga0.51In0.49P/GaAs heterostructure have been investigated by thermal-electric effect spectroscopy (TEES) and temperature-dependent conductivity measurements. Four samples were grown by molecular-beam epitaxy with various phosphorus (P2) beam-equivalent pressures (BEP) of 0.125, 0.5, 2, and 4×10−4 Torr. A phosphorus vacancy (VP) -related deep level, an electron trap, was observed located at EC−0.28±0.02 eV. This trap dominated the conduction-band conduction at T≳220 K and was responsible for the variable-range hopping conduction when T<220 K. Its concentration decreased with the increasing phosphorous BEP. Successive rapid thermal annealing showed that its concentration increased with the increasing annealing temperature. Another electron trap at EC−0.51 eV was also observed only in samples with P2 BEP less than 2×10−4 Torr. Its capture cross section was 4.5×10−15 cm2. This trap is attributed to VP-related complexes.
Impact of oxygen related extended defects on silicon diode characteristics
Authors: Vanhellemont J. , Simoen E. , Kaniava A. , Libezny M. , Claeys C.
Published: July 2002

The electrical activity of extended lattice defects formed by interstitial oxygen precipitation in silicon is studied. Their impact on diode characteristics and on minority carrier lifetime is addressed for different initial oxygen contents and pretreatments. The carrier traps present in the substrate are studied with deep level transient spectroscopy and with photoluminescence spectroscopy. The obtained electrical results are correlated with those of structural and chemical characterization using cross-section transmission electron microscopy and Fourier transform infrared spectroscopy.
The dielectric dispersion of insulating films with long-range movements of charge carriers
Authors: Iwamoto Mitsumasa
Published: July 2002

Based on the ion hopping model, the dielectric dispersion of insulating films with long-range movements of charge carriers has been analyzed without neglecting space-charge field and diffusion. The complex dielectric constant of films with long-range movements of charge carriers (impurity ions) which are blocked at the electrodes was analyzed. The anomalous increase in the complex dielectric permittivity in the region of low frequency was explained. Finally it was concluded that the analysis developed here is very helpful for a better understanding of the dielectric dispersion of insulating films with long-range movements of charge carriers.
Photoemission study of CdS heterojunction formation with binary selenide semiconductors
Authors: Nelson Art J.
Published: July 2002

Synchrotron radiation soft x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS/Cu2−xSe and CdS/In6Se7 heterojunction interfaces. Cu2−xSe and In6Se7 layers were deposited on GaAs (100) by physical vapor deposition from Cu2Se and In2Se3 sources. CdS overlayers were then deposited in situ, at room temperature, in steps on these layers. Photoemission measurements were acquired after each growth to observe changes in the valence-band electronic structure and changes in the In4d and Cd4d core lines. The results were used to correlate the interfacial chemistry with the electronic structure and to directly determine the CdS/Cu2−xSe and CdS/In6Se7 heterojunction valence-band discontinuities and the consequent heterojunction band diagrams. These results are compared to the valence-band offset (ΔEv) for the CdS/CuInSe2 heterojunction interface.
Modeling space charge in alternating-current thin-film electroluminescent devices using a single-sheet charge model
Authors: Keir P. D. , Ang W. M. , Wager J. F.
Published: July 2002

A simulation of alternating-current thin-film electroluminescent device operation with positive space charge present in the phosphor layer of the device is presented. The simulation is based on modeling the space-charge distribution using a single-sheet charge model. The simulation is performed for two cases of space-charge creation: by impact ionization of deep levels in the phosphor or by field emission from traps in the phosphor. Results of the simulation show that space-charge creation by either mechanism is capable of causing overshoot in both capacitance-voltage and internal charge-phosphor field (Q-Fp) plots.
Chromium diffusion in lithium niobate for active optical waveguides
Authors: Almeida José M. , Boyle Gerard , Leite António P. , De La Rue Richard M. , Ironside Charles N. , Caccavale Federico , Chakraborty P. , Mansour I.
Published: July 2002

A method to fabricate chromium-doped lithium niobate substrates in which the active ions are introduced by thermal diffusion from a film is reported. Chromium concentration depth profiles have been obtained by secondary-ion-mass spectrometry and the relevant diffusion parameters have been derived. Fluorescence spectrum and upper laser level lifetime of chromium diffused proton-exchanged and chromium/titanium-diffused lithium niobate waveguides have been measured. A simple model has been used to estimate the performance of such structures as waveguide optical amplifiers and lasers.
Si–C–H bonding in amorphous Si1−xCx:H film/substrate interfaces determined by real time infrared absorption during reactive magnetron sputter deposition
Authors: Katiyar M. , Yang Y. H. , Abelson J. R.
Published: July 2002

We determine the evolution of Si–H and C–H bonding during the growth of hydrogenated amorphous silicon carbide films by reactive magnetron sputtering of a Si target in (Ar+H2+CH4). Si–H and C–H modes are observed by infrared reflectance spectroscopy. An optical cavity substrate is used to enhance the sensitivity. We identify Si–H stretching modes at 2110 and 2145 cm−1 due to Si–H clusters in microvoids and Si–H back-bonded to carbon, respectively. C–H stretching modes are identified at 2870, 2900, and 2950 cm−1. These indicate dominant sp3 bonding configuration for C. During initial growth, a transition layer rich in H and C is observed. Steady state growth is not achieved until ≳250 Å on SiO2 substrates, and ∼70 Å on a-Si:H substrates.
Characterization and optimization of Ti-diffused LiNbO3 optical waveguides by second diffusion of magnesium
Authors: Caccavale F. , Chakraborty P. , Capobianco A. , Gianello G. , Mansour I.
Published: July 2002

Mg diffusion in Ti-diffused LiNbO3 (Ti/Mg:LiNbO3) optical waveguides has been studied. Secondary ion mass spectrometry has been used to obtain Ti/Mg dopant concentration profiles. Comparison of the diffusion behavior of Mg in pure LiNbO3 and titanium-diffused LiNbO3 (Ti:LiNbO3) has been made. A numerical study, based on semivectorial finite difference method to determine the coupling loss between single-mode fibers and Ti/Mg:LiNbO3 optical waveguides has been performed. It has been demonstrated that the use of Mg can reduce the asymmetry-induced coupling loss to almost zero. A method that predicts the best relative position of the fiber axis with respect to the surface of Ti/Mg:LiNbO3 waveguides has been presented.
Properties of a vacuum ultraviolet laser created plasma sheet for a microwave reflector
Authors: Shen W. , Scharer J. E. , Lam N. T. , Porter B. G. , Kelly K. L.
Published: July 2002

A 193 nm excimer laser and a custom fabricated cylindrical lens system is used to produce a plasma sheet of 8 cm×30 cm×0.4 cm in tetrakis(dimethylamino)ethylene (TMAE), a low ionization energy organic gas. Plasma density variation due to photon absorption is studied by scanning the filling pressure of TMAE between 12 and 150 mTorr. A high density (n≥2.0×1013 cm−3), low temperature (Te≊0.8 eV) plasma sheet of 4 mm thickness is obtained with less than 50% spatial density variation over the 30 cm axial length. Charge recombination is found to be the dominant process for t≤1.2 μs with the plasma diffusion playing a perturbational role. A one-dimensional plasma model is utilized to model the experimental plasma data by treating the diffusion as a perturbation. This study shows that the recombination coefficient is 1.8±0.1×10−7 cm3 s−1 and the diffusion coefficient is 2.8±0.4×104 cm2 s−1. The plasma sheet has attractive properties for a microwave agile mirror.
Near-infrared electroabsorption in p+/n−/n+ GaSb diodes
Authors: Gouskov L. , Pérotin M. , Almuneau G. , Luquet H.
Published: July 2002

Liquid phase epitaxial growth of Te-compensated GaSb results in a very low doped n− GaSb epilayer (n≊1015 cm−3). Be+-implanted photodiodes produced from this material exhibit voltage breakdown values reaching 70 V. Generation-recombination lifetimes in the space charge region around 10−8 s have been deduced from these diode photoelectrical properties. The high value of the space charge width leads to an efficient redshift due to the electroabsorption. The variation of the absorption coefficient value is 1350 cm−1 at 1.72 μm for a variation of the electric field maximum of 1.2×105 V/cm.
Linear and nonlinear optical properties of simple oxides. II
Authors: Dimitrov Vesselin , Sakka Sumio
Published: July 2002

A suitable relationship between the linear refractive index n0, the energy gap Eg, and the nonlinear refractive index n2 has been looked for on the basis of experimental and theoretical data reported in the literature for numerous simple oxides. It has been established that the nonlinear refractive index increases with increasing linear refractive index and decreasing energy gap of the oxides. This is related to the increasing metallicity of the oxides. Oxides with a high nonlinear refractive index posses a metallization criterion of approximately 0.30–0.45.
Oxide, interface, and border traps in thermal, N2O, and N2O-nitrided oxides
Authors: Fleetwood D. M. , Saks N. S.
Published: July 2002

We have combined thermally stimulated-current (TSC) and capacitance–voltage (C–V) measurements to estimate oxide, interface, and effective border trap densities in 6–23 nm thermal, N2O, and N2O-nitrided oxides exposed to ionizing radiation or high-field electron injection. Defect densities depend strongly on oxide processing, but radiation exposure and moderate high-field stress lead to similar trapped hole peak thermal energy distributions (between ∼1.7 and ∼2.0 eV) for all processes. This suggests that similar defects dominate the oxide charge trapping properties in these devices. Radiation-induced hole and interface trap generation efficiencies (0.1%–1%) in the best N2O and N2O-nitrided oxides are comparable to the best radiation hardened oxides in the literature. After ∼10 Mrad(SiO2) x-ray irradiation or ∼10 mC/cm2 constant current Fowler–Nordheim injection, effective border trap densities as high as ∼5×1011 cm−2 are inferred from C–V hysteresis. These measurements suggest irradiation and high-field stress cause similar border trap energy distributions. In each case, even higher densities of compensating trapped electrons in the oxides (up to 2×1012 cm−2) are inferred from combined TSC and C–V measurements. These trapped electrons prevent conventional C–V methods from providing accurate estimates of the total oxide trap charge density in many irradiation or high-field stress studies. Fewer compensating electrons per trapped hole (∼26%±5%) are found for irradiation of N2O and N2O-nitrided oxides than for thermal oxides (∼46%±7%). More compensating electrons are also found for high-field electron injection than radiation exposure, emphasizing the significance of border traps to metal-oxide-semiconductor long term reliability. The primary effect of nitrogen on charge trapping in these oxides appears to be improvement of the near interfacial oxide in which border traps are found.
Interface traps creation by sub-band gap irradiation in silicon dioxide on silicon without applied electric field
Authors: Zhong Lei , Shimura Fumio
Published: July 2002

The effective recombination lifetime of thermally oxidized silicon wafers is found to vary little following 4.2 eV ultraviolet irradiation but decrease dramatically when the photon energy is elevated up to 4.9 eV, indicating generation of the interface traps. This finding is discussed with the model of the hot-electrons induced hydrogen redistribution in which about 2 eV energy is necessary for the electrons in the oxide conduction band to liberate a trapped hydrogen atom and generate in turn interface traps. It is stressed, however, that if the model is true the release of hydrogen atoms trapped inside the oxide should be, at least partly, responsible for the generation of interface traps because the samples used in this article are gate-free.
M
3,2-edge x-ray absorption near-edge structure spectroscopy: An alternative probe to the L3,2-edge near-edge structure for the unoccupied densities of d states of 5d metals
Authors: Sham T. K. , Naftel S. J. , Coulthard I.
Published: July 2002

We report M3,2-edge x-ray absorption near-edge structure (XANES) measurements for a series of 5d metals, Ta, W, Pt, and Au using a total electron yield technique. It is found that the M3,2 XANES absorption features and their systematics are comparable to their L3,2 counterparts. These results clearly indicate that M3,2-edge XANES can be used as an alternative probe for the unoccupied densities of d states of the 5d metals and their compounds. The implication of these results is discussed.
Nature of the interlayer coupling in annealed Ni80Fe20/Ag multilayers
Authors: Borchers J. A. , Gehring P. M. , Erwin R. W. , Majkrzak C. F. , Ankner J. F. , Hylton T. L. , Coffey K. R. , Parker M. A. , Howard J. K.
Published: July 2002

Using x-ray and polarized neutron (PNR) reflectivity, we have measured the structural and magnetic depth profiles of annealed Ni80Fe20 (20 Å)/Ag (40 Å) multilayers. The x-ray data indicate that the interfaces are highly mixed. PNR measurements of the 335 °C annealed multilayer in small magnetic fields reveal a broad feature in the off-specular spin-flip scattering that is not present for the unannealed sample. The giant magnetoresistance is thus associated with antiferromagnetic correlations between micrometer-sized magnetic domains within the Ni80Fe20 layers. This spin ordering is consistent with a model in which weak dipolar forces lead to an antiparallel alignment of the domains across the Ag layers.
Manifestation of Nb dynamics in Raman, microwave, and infrared spectra of the AgTaO3-AgNbO3 mixed system
Authors: Fortin W. , Kugel G. E. , Grigas J. , Kania A.
Published: July 2002

The results of an extended investigation of the monoclinic (M2)–monoclinic (M3) phase transition in the mixed AgNbxTa1−xO3 system (ATN) with high concentration of niobium (Nb) are presented in this paper. ATN’s dielectric properties make it promising for microwave technologies and stimulate investigations of the niobium contribution to the dielectric response. The strong quasielastic diffusion and a significant softening of a low-frequency phonon mode, both observed by light scattering measurements on single crystals, are analyzed in the vicinity of this nonferroelectric phase transition. The quasielastic diffusion is confirmed to be caused by the relaxation mode related with Nb dynamics, the parameters of which are determined. The origin of the relaxational mode and possible mechanisms of the phase transition are discussed in connection with the dielectric dispersion and the infrared reflectivity.
Enhanced magnetoresistance in annealed and Cr doped Fe/Cr multilayers
Authors: Rensing N. M. , Clemens B. M. , Williamson D. L.
Published: July 2002

In previous work we reported that the magnetoresistance of Fe/Cr multilayers can be increased by annealing the films at moderate temperatures, which increases the spin-dependent scattering of the conduction electrons. Here we present Mössbauer data that demonstrate that the structural effect of annealing is to promote Cr interdiffusion into the bulk of the iron layers rather than short scale intermixing at the interfaces. We have also investigated the effect of increasing the asymmetric scattering by adding chromium to the iron in Fe/Cr multilayers. The additional Cr was either alloyed with the Fe in compositions ranging from 1.5% to 50% Cr in Fe, or concentrated into 1 or 2 Å layers embedded at various positions in the Fe. We report enhanced room-temperature magnetoresistance of up to 11.4% in sputter-deposited Fe/Cr multilayers when the Fe layers are doped with 20% Cr. The maximum magnetoresistance observed for samples with embedded Cr layers was 10.5%. In comparison, the magnetoresistance was 7.5% in a similar, undoped sample.
Interface properties of metal-oxide-semiconductor structures on n-type 6H and 4H-SiC
Authors: Friedrichs P. , Burte E. P. , Schörner R.
Published: July 2002

This work reports on the interface properties of metal-oxide-semiconductor (MOS) structures formed by thermal oxidation of n-type silicon carbide (SiC). The SiC layers, grown homoepitaxially on the silicon-face of 6H-SiC and 4H-SiC substrates, were oxidized at 1100 °C in dry or wet atmosphere. The interface properties of the MOS structures were investigated using both, the Terman and the high-low frequency method. The validity of these methods for wide band-gap semiconductors is clarified in a short theoretical analysis. The experimental results reveal moderate densities of interface states for MOS devices on 6H-SiC as well as on 4H-SiC. Only minor differences were observed between both polytypes. Current-voltage measurements prove earlier results and show good quality independent of the polytype used as substrate material.