bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotational and magnetic shear stabilization of magnetohydrodynamic modes and turbulence in DIII-D high performance discharges
Authors: Lao L. L. , Burrell K. H. , Casper T. S. , Chan V. S. , Chu M. S. , DeBoo J. C. , Doyle E. J. , Durst R. D. , Forest C. B. , Greenfield C. M. , Groebner R. J. , Hinton F. L. , Kawano Y. , Lazarus E. A. , Lin-Liu Y. R. , Mauel M. E. , Meyer W. H. , Miller R. L. , Navratil G. A. , Osborne T. H. , Peng Q. , Rettig C. L. , Rewoldt G. , Rhodes T. L. , Rice B. W. , Schissel D. P. , Stallard B. W. , Strait E. J. , Tang W. M. , Taylor T. S. , Turnbull A. D. , Waltz R. E. ,   the DIII-D Team
Published: July 2002

The confinement and the stability properties of the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high-performance discharges are evaluated in terms of rotational and magnetic shear, with an emphasis on the recent experimental results obtained from the negative central magnetic shear (NCS) experiments. In NCS discharges, a core transport barrier is often observed to form inside the NCS region accompanied by a reduction in core fluctuation amplitudes. Increasing negative magnetic shear contributes to the formation of this core transport barrier, but by itself is not sufficient to fully stabilize the toroidal drift mode (trapped-electron-ηi mode) to explain this formation. Comparison of the Doppler shift shear rate to the growth rate of the ηi mode suggests that the large core E×B flow shear can stabilize this mode and broaden the region of reduced core transport. Ideal and resistive stability analysis indicates the performance of NCS discharges with strongly peaked pressure profiles is limited by the resistive interchange mode to low βN≤2.3. This mode is insensitive to the details of the rotational and the magnetic shear profiles. A new class of discharges, which has a broad region of weak or slightly negative magnetic shear (WNS), is described. The WNS discharges have broader pressure profiles and higher β values than the NCS discharges, together with high confinement and high fusion reactivity.
Scaling of anisotropic spectra due to the weak interaction of shear-Alfvén wave packets
Authors: Ng C. S. , Bhattacharjee A.
Published: July 2002

Weak magnetohydrodynamic turbulence in the presence of a uniform magnetic field is dominated by three-wave interactions that mediate the collisions of shear-Alfvén wave packets propagating in opposite directions parallel to the magnetic field. The scaling of three-wave couplings is calculated by asymptotic analysis and a direct numerical evaluation of the nonlinear interaction based on the reduced magnetohydrodynamic equations. A new relation is derived between the spectral index of three-wave coupling and the spectral indices of two random-amplitude wave packets. This relation has significant implications for the anisotropic energy spectrum.
Inertial confinement fusion using hohlraum radiation generated by heavy-ion clusters
Authors: Tahir N. A. , Lutz K.-J , Geb O. , Maruhn J. A. , Deutsch C. , Hoffmann D. H. H.
Published: July 2002

This paper discusses the feasibility of employing heavy-ion cluster beams to generate thermal radiation that can be used to drive inertial fusion capsules. The low charge-to-mass ratio of a cluster may allow the driver beam to be focused to a very small spot size with a radius of the order of 100 μm, while the low energy per nucleon (of the order of 10 keV) may lead to a very short range of the driver particles in the converter material. This would result in high specific power deposition that may lead to a very high conversion efficiency. The problem of cluster stopping in cold matter, as well as in hot dense plasmas has been thoroughly investigated. The conversion efficiency of cluster ions using a low-density gold converter has also been calculated over a wide range of parameters including converter density, converter geometry, and specific power deposition. These calculations have been carried out using a one-dimensional hydrodynamic computer code that includes a multigroup radiation transport scheme [Ramis et al., Comput. Phys. Commun. 49, 475 (1988)]. The problem of symmetrization of this radiation field in a hohlraum with solid gold walls has also been thoroughly investigated using a three-dimensional view factor code. The characteristics of the radiation field obtained by this study are used as input to capsule implosion calculations that are done with a three-temperature radiation-hydrodynamic computer code MEDUSA-KAT [Tahir et al., J. Appl. Phys. 60, 898 (1986)]. A reactor-size capsule which contains 5 mg deuterium–tritium (DT) fuel is used in these calculations. The problem of using a fuel mixture with a substantially reduced tritium content has also been discussed.
High performance Joint European Torus (JET) plasmas for deuterium–tritium operation with the MkII divertor
Authors: Jones T. T. C. ,   Jet Team
Published: July 2002

Planned experiments in the Joint European Torus [Plasma Physics and Controlled Fusion Research, Proceedings, 13th International Conference, Washington, D.C., 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 1, p. 27] (JET) with deuterium–tritium (D–T) plasmas require high fusion performance for α-particle heating studies and for investigation of isotope dependence in conditions relevant to the International Thermonuclear Experimental Reactor [Plasma Phys. Controlled Fusion 37, A19 (1995)]. In deuterium plasmas, the highest neutron rates have been obtained in the hot-ion high-confinement mode (H mode) which is ultimately limited by magnetohydrodynamic (MHD) phenomena when the pressure gradient approaches ideal ballooning and kink stability limits in the vicinity of the edge transport barrier. Results are reported confirming the MkII divertor’s increased closure and pumping in this regime, progress in understanding the MHD-related termination is discussed, and the use of ion cyclotron resonance heating (ICRH) in combination with high-power neutral beams to increase the neutron yield is described. In separate experiments internal transport barriers have been established through careful programming of the current ramp and heating waveforms, and neutron emission comparable with the best hot-ion H-modes achieved. Steady-state H-mode discharges exhibiting edge localized modes (ELMs) in reactor-like configurations and conditions have been demonstrated, including cases in which relevant dimensionless parameter values are preserved, ready also for testing in D–T.
Two-dimensional coherent structures of drift waves exhibiting non-Boltzmann relationships in toroidal plasmas
Authors: Katou K.
Published: July 2002

The two-dimensional mode equation describing drift waves that exhibit a non-Boltzmann relationship in a toroidal plasma is derived. Three types of solutions are obtained: (1) propagating cell patterns, in particular, triangular and hexagonal cell patterns, (2) a purely growing harmonic function, and (3), an isolated vortex propagating in the ion diamagnetic direction.
Recent experimental and analytic progress in the Japan Atomic Energy Research Institute Tokamak-60 Upgrade with W-shaped divertor configuration
Authors: Shirai H. ,   JT-60 Team
Published: July 2002

The Japan Atomic Energy Research Institute (JAERI) completed the divertor modification of the JAERI Tokamak-60 Upgrade (JT-60U) [Y. Koide and the JT-60 Team, Phys. Plasmas 4, 1623 (1997)] in June, 1997, and experiments with the W-shaped pumped divertor have been carried out. The helium exhaust was demonstrated in the steady state by using helium neutral beam injection (NBI). The ratio of the effective particle confinement time of helium to the energy confinement time, τHe*/τE, became about 4 and the obtained enrichment factor of helium in the divertor was about 1. The high confinement mode (H-mode) plasma with edge localized mode (ELM) was sustained for 9 s with a confinement–enhancement factor (H factor) of ∼1.7. No increase of recycling and carbon impurity density was observed with the integrated NBI input energy of 203 MJ. In the reversed shear (RS) experiments, a quasi-steady-state ELMy H mode was achieved with an H factor ∼2.4. The stability of high-n toroidal drift modes was analyzed in the RS plasma. The E×B shearing rate became of the same order of magnitude as the linear growth of the dominant mode around the internal transport barrier. The semiglobal structure of radial transport was analyzed by the toroidal geometry particle simulation code. The discontinuity in the electrostatic potential occurred at the qmin region and radial transport was reduced.
The development and advantages of beryllium capsules for the National Ignition Facility
Authors: Wilson Douglas C. , Bradley Paul A. , Hoffman Nelson M. , Swenson Fritz J. , Smitherman David P. , Chrien Robert E. , Margevicius Robert W. , Thoma D. J. , Foreman Larry R. , Hoffer James K. , Goldman S. Robert , Caldwell Stephen E. , Dittrich Thomas R. , Haan Steven W. , Marinak Michael M. , Pollaine Stephen M. , Sanchez Jorge J.
Published: July 2002

Capsules with beryllium ablators have long been considered as alternatives to plastic for the National Ignition Facility laser [J. A. Paisner et al., Laser Focus World 30, 75 (1994)]; now the superior performance of beryllium is becoming well substantiated. Beryllium capsules have the advantages of high density, low opacity, high tensile strength, and high thermal conductivity. Three-dimensional (3-D) calculations with the HYDRA code [NTIS Document No. DE-96004569 (M. M. Marinak et al. in UCRL-LR-105821-95-3)] confirm two-dimensional (2-D) LASNEX [G. B. Zimmerman and W. L. Kruer, Comments Plasmas Phys. Controlled Thermonucl. Fusion 2, 51 (1975)] results that particular beryllium capsule designs are several times less sensitive than the CH point design to instability growth from deuterium-tritium (DT) ice roughness. These capsule designs contain more ablator mass and leave some beryllium unablated at ignition. By adjusting the level of copper dopant, the unablated mass can increase or decrease, with a corresponding decrease or increase in sensitivity to perturbations. A plastic capsule with the same ablator mass as the beryllium and leaving the same unablated mass also shows this reduced perturbation sensitivity. Beryllium’s low opacity permits the creation of 250 eV capsule designs. Its high tensile strength allows it to contain DT fuel at room temperature. Its high thermal conductivity simplifies cryogenic fielding.
Complete integral suppression of Pfirsch–Schlüter current in a stellarator plasma in Heliotron E
Authors: Besshou S. , Pustovitov V. D. , Fujita N. , Kondo K. , Mizuuchi T. , Nagasaki K. , Nakasuga M. , Obiki T. , Okada H. , Sano F. , Zushi H.
Published: July 2002

The poloidal magnetic field was measured to detect the plasma boundary position. It was found that the pressure-induced plasma shift, an observable characteristic of the Pfirsch–Schlüter current, depends strongly on the initial position of the magnetic axis. When the axis was moved by the vertical field inside the torus, the finite-β shift became smaller. Complete suppression of the finite-β plasma shift was achieved in a deeply inward shifted configuration: 7 cm from the standard position Raxis=2.20 m. This effect is explained by magnetohydrodynamic (MHD) equilibrium theory for stellarator toroidal plasmas with a large magnetic hill and deep inward shift.
Carbon flows in attached divertor plasmas
Authors: Isler R. C. , Brooks N. H. , West W. P. , Porter G. D. ,   The DIII-D Divertor Team
Published: July 2002

Parallel flow velocities of carbon ions in the DIII-D divertor [J. Luxon et al., Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; S. L. Allen et al., Controlled Fusion and Plasma Physics, 1987 (Proc. 24th European Conf. Berchtesgaden, 1997), Vol. 21 A, Part III, p. 1129] have been studied under various operating conditions: L-mode (low-confinement mode), H-mode (high-confinement mode) with low-frequency ELMs (edge-localized modes), and H-mode with high-frequency ELMs. Both normal and reversed flows (toward the target plate and away from the target plate, respectively) are observed under all conditions, with the reversed speeds being as much as a factor of four greater than normal speeds. Magnitudes are approximately the same for L-mode and H-mode operation with high-frequency ELMs. In H-mode conditions with low-frequency ELMs, normal velocities are frequently observed to decline while reversed velocities increase in comparison to the other two conditions.
Effect of isotope mass on transport simulations of Joint European Torus high-mode plasmas with Edge Localized Modes
Authors: Bateman Glenn , Kritz Arnold H. , Parail Vassili V. , Cordey J. G. ,   the JET Team
Published: July 2002

The effect of isotopic mass on heat and particle transport in Joint European Torus (JET) [P.-H. Rebut et al., Nucl. Fusion 25, 1011 (1985)] plasma discharges is studied using the Multi-Mode model in the BALDUR predictive transport code [Bateman et al., Phys. Plasmas 5, 1793 (1998)]. Temperature and density profiles from these simulations generally agree with the experimentally measured profiles for high-mode JET discharges with Edge Localized Modes in hydrogen, deuterium, and tritium discharges. It is surprising that a purely gyro-Bohm transport model, used in these simulations, correctly predicts the experimentally observed improvement in confinement as the isotope mass is increased—given the fact that gyro-Bohm diffusion coefficients increase with isotope mass when the shapes of all the plasma profiles are held fixed. However, in the JET experiment, it was found that the electron and ion temperature at the top of the edge pedestal increases systematically as the isotope mass in increased (J. G. Cordey et al., Report No. JET-P (98)53, 1998). The numerical simulations reported here show that this increase in the edge temperatures and subsequent broadening of the temperature profiles account for the improvement in confinement as the isotope mass is increased.
Photodisplacement imaging—A static regime
Authors: Tankovsky N. S. , Ivanov D. V.
Published: July 2002

An optical interferometric method has been used to measure the static surface deformations caused by a point-focused cw laser. Experiments carried out in Plexiglass show that one can guess for defects or inhomogeneities under the surface through the topography of these deformations.
Si liquid-amorphous transition and impurity segregation
Authors: Campisano S. U. , Jacobson D. C. , Poate J. M. , Cullis A. G. , Chew N. G.
Published: July 2002

Pulsed laser irradiation of amorphous Si has been used to produce undercooled liquid Si from which the amorphous phase can directly form. Implanted In, Bi, and As impurities are observed to diffuse and be segregated in a novel fashion by liquid-amorphous interfaces moving from the bulk and surface. Ultrathin impurity segregation layers can be formed within amorphous Si by this process. The first measurements of interfacial segregation coefficients during a liquid-amorphous transition are found to be similar to liquid-crystal values at the same velocity.
Laser-controlled collective ion accelerator
Authors: O’Shea P. G. , Destler W. W. , Rodgers J. , Segalov Z.
Published: July 2002

We report first results from a new collective accelerator experiment in which a laser-controlled channel of ionization is used to control the propagation of the potential well at the front of an intense relativistic electron beam injected at currents above the space-charge limit. The controlled acceleration of protons at the rate of 40 MeV/m over a distance of 45 cm is reported, in good agreement with experimental design values.
Statistical equilibrium in particle channeling
Authors: Davidson B. A. , Feldman L. C. , Bevk J. , Mannaerts J. P.
Published: July 2002

We have used a unique sample configuration consisting of thin, epitaxial films of Ge sandwiched within a Si(100) lattice to explore the conditions for statistical equilibrium in particle channeling. Indications of nonequilibrium came about from a strong asymmetry in the off-normal angular scans. We find the depth necessary to achieve statistical equilibrium to be ∼2200 Å for 1.8 MeV He particle channeling along the Si〈110〉 direction. This measurement provides a useful guide for the interpretation of channeling experiments in a variety of near-surface applications.
Pulse-laser-irradiated high-brightness photoelectron source
Authors: Oettinger P. E. , Bursuc I. , Shefer R. E. , Pugh E.
Published: July 2002

Linac-driven free-electron lasers, new powerful synchrotron radiation sources, and advanced high-power microwave devices will require very bright emitters of electrons to operate efficiently. By irradiating a Cs3Sb photocathode with a frequency-doubled, Nd:glass laser, we have obtained a very high normalized electron beam brightness of over 1011 A/m2/rad2. Peak currents emitted from the 1 cm2 surface in 50 ns pulses ranged up to 80 A. Measured normalized emittances were between 5 and 9 π mm mrad.
Optical switching by saturation-induced phase changes in an active directional coupler
Authors: Liu J. M. , Yeh C.
Published: July 2002

The refractive index in a traveling-wave semiconductor waveguide amplifier changes with light injection at intensities close to the saturation intensity due to light-induced changes in the carrier density. The saturation-induced optical switching in an active directional coupler switch based on this effect is investigated. The system can switch from a cross state at a low input power to a bar state at a high input power. This device may be used as a power-limiting directional coupler switch with gain in a local area network.
Fluorine in low-pressure chemical vapor deposited W/Si contact structures: Inclusion and thermal stability
Authors: Whitlow H. J. , Eriksson Th. , Östling M. , Petersson C. S. , Keinonen J. , Anttila A.
Published: July 2002

Concentration distributions of fluorine in low-pressure chemical vapor deposited W/(100)Si structures have been studied by the nuclear resonance broadening technique through the reaction 19F( p,αγ)16O. In unannealed structures the total fluorine content (4.8×1015 at. cm−2) was chiefly concentrated around the W/Si interface. No loss or redistribution of fluorine was observed on annealing at a temperature of 600 °C or below where no silicide formation took place. About 20% reduction of the fluorine content was observed after annealing at 700 °C and above where WSi2 formation occurred. No evidence of fluorine diffusion into the silicon substrate was seen for annealing up to 900 °C for 1 h.
Pulse shortening of actively mode-locked diode lasers by wavelength tuning
Authors: Serenyi M. , Kuhl J. , Göbel E. O.
Published: July 2002

The pulse width of an actively mode-locked GaAs/AlGaAs laser diode in an external cavity configuration is continuously decreased from 22 to 7 ps by tuning the laser wavelength from the gain maximum close to the high-energy cutoff of the gain profile. This wavelength-dependent pulse shortening can be explained by the dynamics of the excited electron-hole plasma.
Activation characteristics and defect structure in Si-implanted GaAs-on-Si
Authors: Vernon S. M. , Pearton S. J. , Gibson J. M. , Short K. T. , Haven V. E.
Published: July 2002

Undoped metalorganic chemical vapor deposited GaAs layers on Si substrates were implanted with 29Si ions (5×1012 cm−2 dose at 100 keV energy) to form a shallow n-type region. The net donor activation (74%) and electron mobility (3014 cm2 V−1 s−1) after rapid thermal annealing (900 °C, 10 s) were compared to those obtained for similar implants into bulk GaAs. There was a slight improvement in the proton backscattering yield from the GaAs-Si interface region after the annealing cycle, consistent with cross-sectional transmission electron microscopy data showing an alignment of defects in annealed samples.
Ultraviolet-excited photoluminescence and Raman scattering in Cd1−xMnxTe-CdTe microstructures
Authors: Perkowitz S. , Yom S. S. , Bicknell R. N. , Schetzina J. F.
Published: July 2002

Photoluminescence (PL) and Raman scattering from Cd1−xMnxTe-CdTe superlattices (x=0.06, 0.23, and 0.45) have been excited for the first time by ultraviolet light of energy 3.4–3.7 eV. The PL spectra show the known confinement-enhanced E0(Γ6,c−Γ8,v) transition and a new peak near the E0+Δ0(Γ6,c−Γ7,v) transition. Raman spectra resemble those from bulk Cd1−xMnxTe. Resonant or nearly resonant Raman scattering, manifested through phonon overtones, occurs near the E0+Δ0 and E1(Λ6,c−Λ4,5,v) transitions. A superlattice with extremely thin layers (16 Å/21 Å) shows good Raman spectral quality.
Coherent coupling of pulsed dye oscillators using nonlinear phase conjugation
Authors: White Jeffrey O. , Valley George C. , McFarlane Ross A.
Published: July 2002

We have obtained coherent operation of multiple pulsed dye oscillators by using a single phase conjugate mirror as a common end mirror for up to three physically distinct cavities. The phase conjugate mirror operates via the photorefractive effect in a crystal of BaTiO3, through a four-wave mixing process that requires no external pumping beams. The system has been operated in both a narrow-band (0.05 nm) and a broadband (0.25 nm) configuration.
Novel laser diagnostic for mercury rare gas low pressure discharges
Authors: Moskowitz Philip E.
Published: July 2002

Knowledge of the Hg(3P1) spatial distribution in Hg rare gas low pressure discharges is important for understanding radiation transport, and aids in the formulation of discharge models for fluorescent lamps. We report on a novel single laser, two intersecting beams technique, which, for the first time, yields pinpoint information on the radial density profile of excited state mercury in the discharge positive column. Advantages over conventional single beam absorption are discussed, and preliminary data for a discharge containing one isotope (198Hg) of mercury and 2.5 Torr argon are presented.
Oxidation behavior of Au-Si films
Authors: Hewett C. A. , Lau S. S.
Published: July 2002

We have investigated the oxidation behavior of co-deposited Au-Si films at low temperatures (∼200 °C). Alloys spanning the Au-Si phase diagram have been examined. Films with greater than 40 at. % Au were found to oxidize forming SiO2, while films with less than 40 at. % Au were found to be relatively stable in an oxidizing ambient. This phenomenon was used to form Au lines with a self-passivating SiO2 coating. The resistivity of these lines is estimated to be 6–10 μΩ cm.
Coupled stripe AlxGa1−xAs-GaAs quantum well lasers defined by impurity-induced (Si) layer disordering
Authors: Deppe D. G. , Jackson G. S. , Holonyak N. , Burnham R. D. , Thornton R. L.
Published: July 2002

A high-performance index-guided ten-stripe AlxGa1−xAs-GaAs quantum well heterostructure laser array fabricated using Si diffusion to effect impurity-induced layer disordering between the active region stripes is described. The fine spacing (1 μm) between (3 μm) emitters allows coupled mode laser operation at thresholds (Ith) as low as 3–4 mA per stripe and with stable near- and far-field patterns in spite of band filling (single quantum well). This form of coupled stripe laser is capable of high efficiency and high power output (250 mW at 300 mA) as well as a large excitation range extending from Ith to 9Ith.
Interaction of hydrogen and thermal donor defects in silicon
Authors: Chantre A. , Pearton S. J. , Kimerling L. C. , Cummings K. D. , Dautremont-Smith W. C.
Published: July 2002

We have studied the interaction of hydrogen with thermal donors in silicon using transient capacitance and current spectroscopy. We find that a large degree of thermal donor passivation (a factor of 40) can be achieved by hydrogen plasma exposure at 120 °C. The residual electrical activity is shown to arise from perturbed E(0.07) and E(0.15) donor states. Annealing at 200 °C almost completely reactivates the low concentration of thermal donors present in these samples. A model involving different incorporation sites for hydrogen is proposed to explain the results.
Large monolithic two-dimensional arrays of GaInAsP/InP surface-emitting lasers
Authors: Liau Z. L. , Walpole J. N.
Published: July 2002

A 1 mm×3 mm monolithic two-dimensional array (incoherent) of 112 mass-transported buried-heterostructure lasers with integrated beam deflectors has been fabricated with good uniformity. An average cw output of 14 mW per laser and an average optical flux of 57 W/cm2 have been obtained when the array is operated one section (approximately 14% of the total area) at a time. The total cw output of the entire array is thermally limited to 0.7 W.
Thin-film reaction between Ti and Si3N4
Authors: Barbour J. C. , Kuiper A. E. T. , Willemsen M. F. C. , Reader A. H.
Published: July 2002

The thermal reaction of Ti with Si3N4 was studied over the temperature range from 500 to 800 °C with Auger electron spectroscopy, Rutherford backscattering spectrometry, and transmission electron microscopy. The initial reaction consumes part of the silicon nitride and yields a two-layer morphology of Ti(N) on top of Ti5Si3. As the reaction proceeds, the Ti5Si3 layer is converted to TiSi2. At 800 °C, a multilayer morphology is observed containing primarily TiN and TiSi2.
Modulated laser beam relaxation spectrometry of laser-induced chemical vapor deposition
Authors: Comita Paul B. , Kodas Toivo T.
Published: July 2002

The surface chemical reactions occurring during the laser-assisted deposition of gold from dimethyl gold hexafluoroacetylacetonate were studied using a photothermal modulation technique. A modulated argon ion laser was used to heat an area roughly 1 mm in diameter on an alumina substrate. Products of the photothermal reaction along with reactants were sampled through a 150×150 μm orifice located at the center of the deposit and were then introduced directly into a quadrupole mass filter. An inert buffer gas was required to confine changes in the reactant and product concentrations to the region surrounding the sampling orifice. Since the reactant concentration at the surface decreased when the laser was turned on while the product concentration at the surface increased when the laser was turned on, modulating the surface reaction rate by modulating the argon ion laser beam and employing phase-sensitive detection allowed the identification of reaction products. The behavior of the system was described qualitatively using a theory for coupled reactant transport to the deposit surface and surface chemical reaction.
X-ray photoemission study of the Te-precursor surfaces and the initial stages of growth of ZnTe on GaAs (100)
Authors: Tatarenko S. , Saminadayar K. , Cibert J.
Published: July 2002

The initial stages of epitaxial growth of ZnTe on GaAs (100) have been studied by x-ray photoemission spectroscopy. The two surface structures (6×1 and (3)1/2×3 ) resulting from the adsorption of Te on GaAs (100) were used as precursor for ZnTe growth. Each of these structures is characterized by two different adsorbed Te states. For the 6×1 structure, the two states are assigned to As–Te–As and tentatively to Te–Te–Te bonds; and for the (3)1/2×3 structure, the assigned bonds are As–Te–As and GaGa Te–As. Growth of ZnTe (100) does not induce any change in the bonds associated with the 6×1 structure but modifies that associated with the (3)1/2×3 surface.
Ballistic peaks in the distribution function from intervalley transfer in a submicron structure
Authors: Baranger Harold U. , Pelouard Jean-Luc , Pône Jean-François , Castagné René
Published: July 2002

Using Monte Carlo simulation, we show that ballistic electrons coupled with intervalley scattering produce peaks in the distribution function of electrons in submicron structures. The distribution functions f(v,x) and f(ε,x) for a submicron N+-N−-N+ GaAs structure indicate that ballistic electrons cause both the dominant peak in f(v,x) throughout the N− region and additional peaks in f(ε,x) following transfer from the L valley to the Γ valley. For low densities and low temperatures (T=77), both ballistic peaks in f(ε,x) split into several sharp peaks separated in energy by the optic-phonon energy.
Localized large superconducting critical currents in Ba2Y1Cu3O9−y
Authors: Kumakura H. , Uehara M. , Togano K.
Published: July 2002

Magnetization measurements of powder and sintered samples of Ba2Y1Cu3O9−y have been made at 77 K. Excellent critical current densities Jc’s of about 3×104 A/cm2 at 10 kOe were estimated for the powder samples, which consisted of single-crystal particles of ∼3 μm in dimension. These Jc’s were about two orders of magnitdue larger than those of the sintered sample.
Hot-electron transport in GaAs in the presence of a magnetic field
Authors: Beton P. H. , Long A. P. , Kelly M. J.
Published: July 2002

We describe the results of the incorporation of magnetic field effects into the Monte Carlo simulation of hot electrons traversing narrow regions of heavily doped GaAs. In addition to accounting for the experimentally observed suppression of the ballistic contribution to the hot-electron spectrum, a further analysis allows us to infer the spread in transverse energy of the injected hot electrons.We attribute this loss of collimation to scattering by unscreened ionized impurities in the depletion region which is set up when a hot-electron injector is forward biased.
Spectroscopic evidence for passivation of the La1.85Sr0.15CuO4 surface with gold
Authors: Meyer H. M. , Wagener T. J. , Hill D. M. , Gao Y. , Anderson S. G. , Krahn S. D. , Weaver J. H. , Flandermeyer B. , Capone D. W.
Published: July 2002

High-resolution x-ray photoemission and inverse photoemission have been used to study the microscopic formation of Au overlayers on the high Tc superconductor La1.85Sr0.15CuO4. Our results indicate that Au does not induce disruption or surface reaction, unlike the reactive transition metals. The electronic states of the superconductor are attenuated as the Au overlayer covers the surface. We conclude that Au is a promising material for metallization and for passivation.
Reaction and intermixing at metal-superconductor interfaces: Fe/YBa2Cu3O6.9
Authors: Gao Y. , Wagener T. J. , Weaver J. H. , Flandermeyer B. , Capone D. W.
Published: July 2002

Inverse photoemission studies of the interface formed when Fe is deposited onto the high-temperature superconductor YBa2Cu3O6.9 show that Fe leaches oxygen from the near surface region to nucleate an insulating form of Fe-O. Ultimately, a metallic Fe layer grows but it has surface segregated Ba, even after 250 Å of coverage. These results demonstrate that reactive metal overlayers drastically alter the chemical and physical properties of the superconductor.
Photoconductivity in CuInSe2 thin films
Authors: Ramanathan V. , Datta T. , Noufi R.
Published: July 2002

We report the photoconductivity spectra of CuInSe2 thin films of precisely defined compositions that are required to fabricate high-efficiency CdS/CuInSe2 thin-film solar cells. The Cu-deficient, high-resistivity CuInSe2 layer is found to be much more photoconducting than the stoichiometric, low-resistivity CuInSe2. We show that the spectral dependence of the photoconductivity of the composite CuInSe2 layer is intimately related to the spectral response of the solar cells.
Laser beam scanning using a local deflector integrated with an effective mode filter
Authors: Mukai S. , Kaneko Y. , Watanabe M. , Itoh H. , Yajima H.
Published: July 2002

Deflection of a diode laser beam using an injection-type deflector monolithically integrated with a very long waveguide is demonstrated. The deflector and the waveguide constitute a laser cavity. The waveguide filters out higher order modes, and only the fundamental-mode light is incident on the deflector. Because the incident light is of a fixed single mode, the deflection of the output beam is very smooth. The deflection mechanism is primarily due to interference between constituent modes for short deflectors, and phase-front tilting of each mode for long deflectors.
Donor binding energies determined from temperature dependence of photoluminescence spectra in undoped and aluminum-doped beta SiC films
Authors: Freitas J. A. , Bishop S. G. , Nordquist P. E. R. , Gipe M. L.
Published: July 2002

Measurements of the temperature dependence of N-Al donor-acceptor pair photoluminescence spectra in cubic SiC films demonstrate that the thermal activation energy for the nitrogen donors is equivalent to the 54 meV binding energy for nitrogen determined from the spectral energies of the sharp-line close pair spectra. It follows that the 15–20 meV donor which dominates the electrical properties of n-type films is not isolated, substitutional nitrogen. Spatial variations observed in the intensity of a new 2.368 eV luminescence band demonstrate that the radiative recombination centers are inhomogeneously distributed in the films.
Initial stages of epitaxial growth: Gallium arsenide on silicon
Authors: Zinke-Allmang M. , Feldman L. C. , Nakahara S.
Published: July 2002

A model for the morphology of the first layers of GaAs on Si(111) is proposed based on observations of gallium cluster formation on As-terminated Si(111). In this model Ga is mobile and tends to form clusters, but is immobilized by arriving As atoms. Substrate-temperature-dependent ion scattering and transmission electron microscopy investigations are in agreement with this model and allow the extraction of a clustering related activation energy. These results establish conditions necessary for uniform film growth of GaAs/Si at the important film/substrate interface.
Composition dependence of viscosity for molten Ga1−xAsx (0.0≤x≤0.53)
Authors: Kakimoto Koichi , Hibiya Taketoshi
Published: July 2002

Viscosity of molten Ga1−xAsx was directly measured by an oscillating cup method. The composition dependence of the synergism viscosity remarkably increases in the vicinity of stoichiometric composition; strong temperature dependence of viscosity was also observed at that composition. Activation energy for viscous flow at the stoichiometric Ga1−xAsx (x=0.5) melt ranges from 250 to 600 meV, which was larger than those of metals such as gallium and indium whose activation energies were about 60–100 meV. We estimate, therefore, that the melt of stoichiometric composition has middle-range ordering like an aggregation whose range is larger than that of short-range ordering in metals such as gallium and indium.
High-efficiency superlattice graded-index separate confining heterostructure lasers with AlGaAs single quantum wells
Authors: Shealy J. R.
Published: July 2002

Superlattice graded-index separate confining heterostructure lasers, with AlGaAs single quantum wells operating in the wavelength range from 700 to 845 nm, are reported. These structures have external power efficiency above 40%, which is the highest reported to date over this entire wavelength range. By examining the performance of these structures as the thin quantum well active region is alloyed with aluminum, a better understanding of the dominant loss mechanism in thin single quantum well lasers results: it is concluded from this study that the carrier population of the higher energy states in the quantum well, and of states associated with the graded-index regions, is the dominant carrier loss mechanism which limits the device performance. The energies of these states involving direct transitions are readily observed with room-temperature photoluminescence. They include the n=2 states of the quantum well and the confined states (n=3, 4,...) extending into graded-index regions. Additional states resulting from the X conduction band in the graded-index regions appear at energies near the top of the well (∼ 2 eV at room temperature) for the structures evaluated in this study. The growth of these structures and the limitations of the devices’ performance under continuous wave conditions at the shorter wavelengths are reviewed.
Ultrathin semiconductor layer masks for high vacuum focused Ga ion beam lithography
Authors: Temkin H. , Harriott L. R. , Panish M. B.
Published: July 2002

The application of thin semiconductor layers as etch masks for high vacuum lithography is described. Heteroepitaxial layers of In0.53Ga0.47As or InP, as thin as 30 Å, were grown by molecular beam epitaxy and patterned using a focused beam of Ga ions. The Ga ion beam exposure is very rapid, since only a small amount of the mask material needs to be removed, and readily produces features with submicron sizes. The patterned thin layer can then be used as a mask for deep, material selective etching. The feasibility of selective dry etching of InP based compounds is discussed. This combination of molecular beam epitaxy and efficient precision patterning techniques is expected to result in a new flexibility in design and fabrication of semiconductor devices.
Experimental measurement of the conditions for the planarity of laser-driven shock waves
Authors: Salzmann David , Gilath Irith , Arad Benyamin
Published: July 2002

Laser-driven shock wave experiments have been conducted in the regime of 1011 W/cm2 in which incipient spall in a 300-μm-thick aluminum foil was used as an indicator of a constant shock state. Laser input energy and deposition spot size were varied to obtain a condition of incipient spall. The results agree with previous models in that a constant laser irradiance produces a constant shock state. The effective diameter of the laser is indicated to be about 0.44 mm larger than the laser spot diameter due to lateral effects during the shock generation or propagation phases.
Experimental and theoretical mobility of electrons in δ-doped GaAs
Authors: Gillman G. , Vinter B. , Barbier E. , Tardella A.
Published: July 2002

We have prepared and measured the mobility of several samples of planar-doped GaAs. A maximum electron density of 2.7×1013 cm−2 has been obtained. Calculations of the mobility in a complete quasi-two-dimensional description are presented and compared with the measured results. Qualitatively, all features in the mobility are reproduced; the quantitative comparison may indicate that compensation effects play a role.
CoSi2 and Si epitaxial growth in 〈111〉 Si submicron lines with application to a permeable base transistor
Authors: Glastre G. , Rosencher E. , d’Avitaya F. Arnaud , Puissant C. , Pons M. , Vincent G. , Pfister J. C.
Published: July 2002

We report for the first time the epitaxy of CoSi2 on 〈111〉 Si submicron lines together with the overgrowth of Si on top of the resulting grating. Results indicate that strain fields and huge mass transport control the morphology of the resulting structures. Silicon is shown to grow two dimensionally when the grating period is in the submicrometer range. Preliminary results on the electrical performance of those Si/CoSi2 /Si permeable base transistors are presented.
Resonant, dispersive optical tuning in an epitaxial (Al,Ga)As Fabry–Perot étalon
Authors: Gourley P. L. , Drummond T. J.
Published: July 2002

We report optical tuning (an optically induced shift of the transmittance peak) of an epitaxial Fabry–Perot étalon comprising AlAs/AlGaAs quarter-wave high reflectors surrounding a GaAs/AlGaAs multiple quantum well spacer layer. The reflectors and spacer were produced in a single growth process by using molecular beam epitaxy. Low-power cw reflection and trasmittance spectra as well as higher power pulsed trasmittance spectra were measured at room temperature. A very sharp (∼20 Å full width at half-maximum) Fabry–Perot transmittance peak was observed near the resonant exciton wavelength (8500 Å) at room temperature. The tuning of this transmittance mode under pulsed optical excitation is as large as 27 Å. These results indicate that very large on/off switching ratios (∼10:1) can be achieved with these structures.
Y-Ba-Cu-O thin films prepared by a multilayer vacuum method
Authors: Qiu C. X. , Shih I.
Published: July 2002

Polycrystalline Y-Ba-Cu-O thin films with a thickness of about 1 μm have been deposited on alumina substrates. The deposition was made by first sequentially evaporating Y/Ba/Cu layers followed by a heat treatment in an environment containing oxygen. The treated films were polycrystalline, and the electrical results showed an onset temperature of about 100 K and a zero-resistance temperature of 78 K for the films treated at 850 °C for 2 h in oxygen.
Observation of luminescence quenching dislocations in mercuric iodide by cathodoluminescence in a scanning electron microscope
Authors: James T. W. , Milstein Frederick
Published: July 2002

Cathodoluminescence images of ingrown and deformation-induced dislocations were observed in single crystals of mercuric iodide that were vapor grown for the fabrication of radiation detectors. The imaging was done at 80 K in a scanning electron microscope.
Slope resistance characteristics of GaAs-(Al,Ga)As-GaAs single barrier structures
Authors: Lacklison D. E. , Duggan G. , Harris J. J. , Foxon C. T. B. , Hilton D. , Roberts C. , Hellon C. M.
Published: July 2002

Measurements of the incremental slope resistance of a GaAs-(Al,Ga)As-GaAs single barrier structure have been made at temperatures between 70 and 230 K. In contrast with other work we deliberately concentrate on the region close to zero applied bias. The deficiencies in the often-used Wentzel–Kramers–Brillouin analysis of the electrical characteristics are exposed in this regime, and an exact, Airy function approach is found to be essential to describe our observations.
Electron densities in xenon chloride laser mixtures
Authors: Johnson T. H. , Cartland H. E.
Published: July 2002

A new, comprehensive kinetic model has been used to calculate the time-dependent behavior of electron number density in electron-beam-pumped XeCl excimer laser gas mixtures. Predictions of the model are compared to recently published experimental results and are shown to be in good agreement for moderate and high HCl concentrations (≥0.12%). At low HCl concentration a clear discrepancy is apparent, one which cannot be explained by assuming any reasonable electron energy distribution.
Graded-thickness samples for molecular beam epitaxial growth studies of GaAs/Si heteroepitaxy
Authors: Biegelsen D. K. , Ponce F. A. , Krusor B. S. , Tramontana J. C. , Yingling R. D.
Published: July 2002

In this letter we discuss the technique of graded-thickness sample deposition for studying the growth mechanisms of GaAs heteroepitaxy on Si. We can observe the continuous evolution from the initial clean surface, through nucleation, growth, and coalescence of the deposited material. We describe results for a sample typical of buffer layer growth in the two-step molecular beam epitaxial deposition of GaAs directly on Si. We are led to a specific model for the three-dimensional nucleation and growth mechanisms in which Ga atom diffiusion dominates the stable cluster formation, As capture from the vapor by the islands immobilizes the Ga, and island growth is limited by the binding of diffusing Ga.
Dark-line observations in failed quantum well lasers
Authors: Waters R. G. , Bertaska R. K.
Published: July 2002

The electron-beam-induced current technique has been used to disclose dark-line patterns in degraded AlxGa1−xAs quantum well lasers. At least four distinct types of pattern exist, each being characteristic of a particular device structure.
Reaction kinetics of nickel/silicon multilayer films
Authors: Clevenger L. A. , Thompson C. V. , Cammarata R. C. , Tu K. N.
Published: July 2002

We report on the use of differential scanning calorimetry to study the temperatures and kinetics of nickel silicide formation from nickel/amorphous silicon multilayer films. When the layer thickness ratio of a multilayer film is 1:1, Ni2 Si is the only phase to form. The activation energy for this reaction is 1.5 eV and the interdiffusivity pre-exponential is found to be 6 cm−2s−1. These values are in excellent agreement with values obtained using different techniques. The temperature at which Ni2 Si formation is observed a function of layer thickness, with the thinner layers reacting at lower temperatures. This layer thickness dependence can be explained by the lower reaction times for thinner layers. Upon mechanical impact, films composed of very thin layers (<125 Å) reacted explosively at room temperature to form Ni2 Si. Explosive silicidation is presumed to occur when the rate of heat generation at the many reacting interfaces exceeds the rate of heat dissipation.
Raman spectroscopic investigation of superconducting YBa2Cu3O7−x, semiconducting YBa2Cu3O6+x, and possible impurity phases
Authors: Mascarenhas A. , Geller S. , Xu L. C. , Katayama-Yoshida H. , Pankove J. I. , Deb S. K.
Published: July 2002

A Raman spectroscopic investigation of specimens of superconducting YBa2Cu3O7−x and of the possible impurity phases YBa2Cu3O6+x (semiconductor), Y2BaCuO5, Y2Cu2O5, BaCuO2, CuO, Y2O3, and BaCO3 indicates that in the range 100–700 cm−1, there are six characteristic lines belonging to the superconductor. At 13 K, these lines are at 150, 338, 441, 507, 590, and 644 cm−1. Comparison of the Raman spectra of the superconductor and the semiconductor indicates a mode stiffening of the pair at 338 and 441 cm−1, but a mode softening of the pair at 507 and 590 cm−1. A factor group analysis leads to a tentative assignment of the Raman and infrared allowed modes.
Rapid thermal anneal of sprayed Y1Ba2Cu3O7−x slurry
Authors: Cody N. W. , Sudarsan U. , Solanki R.
Published: July 2002

Thick (∼ 20 μm) superconducting films of Y1 Ba2 Cu3 O7−x have been produced on 3 in. wafers of silicon, SiO2 -coated silicon, and sapphire. The process involves spraying of a slurry of finely ground powder of Y1 Ba2 Cu3 O7−x and methyl alcohol, followed by rapid thermal anneal for sintering. The Tc for Si, SiO2 , and sapphire are 70, 81, and 62 K, respectively. Post-sinter anneal in oxygen at 400 °C further increases Tc . The adhesion of the films sintered above 980 °C is excellent.
High-efficiency fast response in photorefractive BaTiO3 at 120 °C
Authors: Rytz D. , Klein M. B. , Mullen R. A. , Schwartz R. N. , Valley G. C. , Wechsler B. A.
Published: July 2002

Measurements of beam coupling gain and response time in BaTiO3 show a decrease by two orders of magnitude in response time and an unchanged gain coefficient as the temperature is increased from 20 to 120 °C.
Preparation of high T
c and J
c films of Ba2YCu3O7 using laser evaporation of a composite target containing BaF2
Authors: DeSantolo A. M. , Mandich M. L. , Sunshine S. , Davidson B. A. , Fleming R. M. , Marsh P. , Kometani T. Y.
Published: July 2002

High Tc and Jc superconducting films of Ba2YCu3O7 are prepared on SrTiO3 〈100〉 substrates using pulsed excimer laser evaporation of a composite target containing BaF2, Y2O3, and CuO, followed by annealing in wet oxygen. High transition temperatures (R=0 from 89.5 to 91 K) and high critical current densities (Jc≥7×105 A cm−2) are obtained. The electrical transport properties of these films are significantly better than films previously grown via laser ablation of Ba-Y-Cu-O targets.
Optical measurement of surface recombination in InGaAs quantum well mesa structures
Authors: Tai K. , Hayes T. R. , McCall S. L. , Tsang W. T.
Published: July 2002

Surface recombination of optically created electron-hole plasma in InGaAs/InP quantum well mesa structures formed by chemical beam epitaxy followed by anisotropic plasma etching is observed optically by a picosecond pump-probe method. The exponential carrier lifetime in 3.3-μm-diam structures is reduced from 31 ns as measured for large diameters to 5.5 ns. We ascribe this reduction to a surface recombination velocity of 1.2×104 cm/s. The surface recombination velocity is about two orders of magnitude smaller than those reported for bulk GaAs layers exposed to air.