bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultraviolet light-emitting diode of a cubic boron nitride p
n junction made at high pressure
Authors: Mishima Osamu , Era Koh , Tanaka Junzo , Yamaoka Shinobu
Published: July 2002

Injection luminescence in the ultraviolet is observed from a cubic boron nitride pn junction diode made at high pressure. Microscopic observation and spectroscopic studies show that the light emission occurs near the junction region only in the forward-bias condition. The spectra extend from ∼215 nm to the red, having a few peaks mainly in the ultraviolet.
Electron-induced chemical vapor deposition by reactions induced in adsorbed molecular layers
Authors: Bozso F. , Avouris Ph.
Published: July 2002

We demonstrate the feasibility of electron-induced chemical vapor deposition of thin films using low-energy electrons to induce reactions in adsorbed molecular layers. Amorphous hydrogenated silicon, silicon dioxide, silicon oxynitride, and silicon nitride films have been deposited by establishing adsorbed Si2H6, Si2H6-O2, Si2H6-NO, and Si2H6-NH3 layers at 100 K and using 300–1000 eV electron beams.
On the possibility of transistor action based on quantum interference phenomena
Authors: Sols Fernando , Macucci M. , Ravaioli U. , Hess Karl
Published: July 2002

A theoretical study of quantum interference phenomena in a T-shaped semiconductor structure is presented. Transmission and reflection coefficients are computed by use of a tight-binding Green function technique. As expected, the results resemble the well-known solutions for the electromagnetic field in waveguides with the main difference that the penetration of the wave function of the electrons can be controlled by external voltages. We conclude that transistor action based on quantum interference should be observable in such structures, and we present general results for the functional dependences of the transmission coefficient which corresponds to a transconductance.
Dual wavelength visible upconversion laser
Authors: McFarlane R. A.
Published: July 2002

Laser operation has been obtained at 551 and 671 nm by pumping 5% Er:YLiF4 at 791 nm. Time dependence studies of the emission show that the excitation process has a component related to cooperative energy transfer, and a component related to stepwise multiple photon absorption. Self-Q-switched operation at 551 nm is seen to impart a time dependence to an otherwise cw output at 671 nm.
High-efficiency and narrow-linewidth operation of a two-crystal β-BaB2O4 optical parametric oscillator
Authors: Bosenberg W. R. , Pelouch W. S. , Tang C. L.
Published: July 2002

We report a novel, two-crystal, walkoff-compensated optical parametric oscillator design using β-BaB2O4, which significantly improves the performance of the device. The oscillator is pumped at 354.7 nm and is tunable throughout 0.42–2.3 μm with overall conversion efficiencies as high as 32%. We also report on demonstration of linewidth narrowing in the same β-BaB2O4 oscillator, obtaining linewidths as narrow as 0.3 Å.
Nonlinear optical properties of p-substituted benzalbarbituric acids
Authors: Kondo K. , Ochiai S. , Takemoto K. , Irie M.
Published: July 2002

A number of p-substituted benzalbarbituric acid derivatives were synthesized by the reaction of p-substituted benzaldehyde with barbituric acid, and their nonlinear optical properties were investigated by using the Kurtz powder test. p-acetamidobenzalbarbituric acid derivatives were found to exhibit the relatively high second-harmonic intensity and have the higher thermal stability.
Low-noise high-speed dc superconducting quantum interference device magnetometer with simplified feedback electronics
Authors: Drung D. , Cantor R. , Peters M. , Scheer H. J. , Koch H.
Published: July 2002

A dc superconducting quantum interference device (SQUID) magnetometer has been integrated on a 9×9 mm2 chip with eight pick-up loops in parallel to directly form a SQUID inductance of about 0.5 nH. Very simple feedback electronics have been developed which do not require liquid-helium temperature impedance matching circuits or flux modulation techniques. The magnetometer has a typical white noise of 8 fT/(Hz)1/2 and a 1/f  corner frequency below 3.5 Hz. With an additional positive feedback circuit at 4.2 K the white noise level has been further reduced to 4.5 fT/(Hz)1/2. Using a two-pole integrator, a 3 dB bandwidth around 0.5 MHz and a maximum slew rate of 3 mT/s at 1.3 kHz have been attained with a ±0.4 μT feedback range.
Reactive ion etching of monocrystalline, polycrystalline, and amorphous silicon carbide in CF4/O2 mixtures
Authors: Padiyath R. , Wright Robert L. , Chaudhry M. I. , Babu S. V.
Published: July 2002

Reactive ion etching of monocrystalline and polycrystalline β-SiC and hydrogenated amorphous a-SiC:H in CF4/O2 mixtures was investigated. The a-SiC:H films, deposited by plasma-enhanced chemical vapor deposition, had the highest etch rate while monocrystalline β-SiC had the lowest etch rate at all compositions of the CF4/O2 mixture. The etch rates for the three materials increased with the addition of oxygen to CF4 and reached a maximum, but the maxima occurred at different compositions due to different rates of oxide formation.
Effects of oxygen in TiNx on the diffusion of Cu in Cu/TiN/Al and Cu/TiNx/Si structures
Authors: Olowolafe J. O. , Li Jian , Mayer J. W. , Colgan E. G.
Published: July 2002

The role of oxygen has been found to be very significant in the diffusion of Cu in Cu/TiNx/Al and Cu/TiNxOy/Al thin film structures. While no interdiffusion takes place in the Cu/TiNxOy/Al structure up to 575 °C, a substantial interdiffusion, with Cu and Al moving in opposite directions, has been found in the Cu/TiNx/Al structure below 425 °C. Both Cu/TiNx/Si and Cu/TiNxOy/Si systems have been found to be stable for temperatures below 600 °C, with TiNx degrading before TiNxOy above this temperatures. Nuclear resonances, 16O(α,α)16O (3.052 MeV) and 14N(α,α)14N (3.593 MeV), for oxygen and nitrogen respectively, were used to determine the concentration of oxygen and the stoichiometry of the titanium nitride films.
Two-wave mixing in photorefractive AlGaAs/GaAs quantum wells
Authors: Wang Q. N. , Nolte D. D. , Melloch M. R.
Published: July 2002

We have observed two-wave mixing in semi-insulating AlGaAs/GaAs multiple quantum well structures at wavelengths near the exciton absorption. The photorefractive index changes are caused by the Franz–Keldysh effect on quantum-confined excitons. Photorefractive gains larger than 200 cm−1 are obtained for the first time at wavelengths near 836 nm using stationary fringes and dc applied fields up to 5 kV/cm. The direction of energy transfer between the two beams is determined by the direction of applied electric field.
Direct observation of the pressure developed in a liquid during cavitation-bubble collapse
Authors: Ward B. , Emmony D. C.
Published: July 2002

A Mach–Zehnder interferometer with a pulsed dye-laser light source is used to observe the collapse of laser-produced cavitation bubbles in water near a rigid transparent polymeric boundary. Vapor bubbles with a maximum radius of about a millimeter are formed using a Q-switched Nd:YAG laser operating at 1.06 μm with a pulse energy of 4.6 mJ and a pulse duration of 8 ns. The pressure in the liquid around the bubbles is determined directly from the resulting interferograms using a fringe tracing method. Prior to bubble rebound, a region of compressed water develops adjacent to the cavity and a weak acoustic wave is directed towards the rigid boundary.
High intensity generation of 9–13 Å x-rays from BaF2 targets
Authors: Zigler A. , Burkhalter P. G. , Nagel D. J. , Boyer K. , Luk T. S. , McPherson A. , Solem J. C. , Rhodes C. K.
Published: July 2002

Studies of the interaction of condensed matter with short pulse (∼ 600 fs) high intensity (∼1017 W/cm2) ultraviolet (248 nm) radiation show that intense spatially compact sources for x-ray emission in the kilovolt range (0.5–1.0×1015 W/cm2) can be generated from solid targets at close to the maximum volume specific rate allowed.
Gallium arsenide: A new material to accomplish passively mode-locked Nd:YAG laser
Authors: Zhang Zhuhong , Qian Liejia , Fan Dianyuan , Deng Ximing
Published: July 2002

A passively mode-locked Nd:YAG laser using a semi-insulating GaAs is accomplished. Ultrashort pulses, shorter than 10 ps, with an energy of 10 μJ per pulse are obtained. The dynamics of the pulse formation is described.
Stable cw operation at room temperature of a 1.5-μm wavelength multiple quantum well laser on a Si substrate
Authors: Sugo M. , Mori H. , Sakai Y. , Itoh Y.
Published: July 2002

Room-temperature cw operation of an InGaAs/InGaAsP multiple quantum well (MQW) laser diode on a Si substrate is reported. The MQW laser emits at a 1.54 μm wavelength and exhibits no degradation after over 2000 h of operation. Employing a hybrid organometallic vapor phase epitaxy/vapor mixing epitaxy method and a layer structure for improving crystalline quality, high-quality MQW layers are obtained. A stable longitudinal mode spectrum demonstrates the effectiveness of the MQW active layer.
Admittance spectroscopy measurements of band offsets in Si/Si1−xGex/Si heterostructures
Authors: Nauka K. , Kamins T. I. , Turner J. E. , King C. A. , Hoyt J. L. , Gibbons J. F.
Published: July 2002

Admittance spectroscopy has been used to measure conduction- and valence-band discontinuities in Si/Si1−xGex heterojunctions (0<x<0.45). Most of the band-gap discontinuity was in the valence band. The measured valence-band offset increased with increasing Ge concentration in the strained Si1−xGex films, and it decreased when the Si1−xGex layers started to relax. These results indicate that admittance spectroscopy can be used to monitor the electronic properties of transistorlike Si/Si1−xGex/Si heterostructures.
Scanning probe microscopy of thermal conductivity and subsurface properties
Authors: Nonnenmacher M. , Wickramasinghe H. K.
Published: July 2002

The past six years has seen a tremendous growth in scanned probe microscopies of various sorts. In this letter, we add a new capability to this family−mapping of thermal conductivity variations on a nanometer scale. We show how our new probe technique can be used to measure thermal conductivity of conductors and thin insulating films deposited on top of conductors. Our results also demonstrate for the first time, the capability of the technique to image subsurface details of samples. As the thermal conductivities of different materials can vary by over three orders of magnitude, we suggest this as an important new contrast mechanism for studying materials on the nanometer scale.
On the characteristics of narrow-band resonant modulation of semiconductor lasers beyond relaxation oscillation frequency
Authors: Lau K. Y. , Georges J. B.
Published: July 2002

We consider practical issues related to narrow-band resonant modulation of laser diodes at frequencies above relaxation oscillation. We established the limits to the performance of this approach based on bandwidth, noise, and intermodulation distortion considerations, as well as the proper trade-offs between these three quantities.
On the growth of nanocrystalline grains in an aluminum-based amorphous alloy
Authors: Nakazato Kazuki , Kawamura Yoshihito , Tsai An Pang , Inoue Akihisa , Masumoto Tsuyoshi
Published: July 2002

We have identified a growth process of nanocrystalline grains in amorphous Al87Ni10Ce3 by means of differential scanning calorimetry and transmission electron microscopy. The grain size of the final grown Al was estimated to be ∼15 nm. A typical nucleation-growth process was observed during the transformation in an amorphous Al85Ni10Ce5. The grain growth process was only observed in Al-enriched alloys (Al ≳ 87 at. %), indicating that the nuclei pre-existed in an Al-enriched area in the original amorphous state.
Enhanced photoluminescence by resonant absorption in Er-doped SiO2/Si microcavities
Authors: Schubert E. F. , Hunt N. E. J. , Vredenberg A. M. , Harris T. D. , Poate J. M. , Jacobson D. C. , Wong Y. H. , Zydzik G. J.
Published: July 2002

Si/SiO2 Fabry–Perot microcavities with an Er-implanted SiO2 active region resonant at the Er excitation wavelength of 980 nm have been realized. Room-temperature photoluminescence measurements reveal that the Er luminescence intensity increases by a factor of 28 as compared to a structure without cavity enhancement. We show that the experimental enhancement of the luminescence intensity agrees with theory if optical absorption of the 980 nm light in the Si layers of the cavity and reduced mirror reflectivities are taken into account.
Spatial hole burning and self-focusing in vertical-cavity surface-emitting laser diodes
Authors: Wilson G. C. , Kuchta D. M. , Walker J. D. , Smith J. S.
Published: July 2002

We measure spatial hole burning in weakly index guided vertical-cavity surface-emitting laser diodes (VCSELs) by spatially and spectrally resolving the spontaneous emission near field above threshold and show that spatial holes produce a significant lensing effect. We demonstrate experimentally, and with a simple model, that in weakly index guided VCSELs, self-focusing causes the fundamental mode width to decrease with increasing output power, exacerbating the spatial hole burning problem and inducing a transition to multimode operation at relatively low powers.
High photon conversion in a light transducer combining organic electroluminescent diode with photoresponsive organic pigment film
Authors: Katsume Tadashi , Hiramoto Masahiro , Yokoyama Masaaki
Published: July 2002

An all-organic light transducer based on a hybridization of an organic electroluminescent diode and a perylene pigment film as an electron photoinjecting electrode has been successfully designed. The quantum efficiency of photon conversion from red to red light reached 40% with the assistance of effective electron photoinjection due to large photocurrent multiplication in a photoresponsive perylene film.
Optically induced rotation of anisotropic micro-objects fabricated by surface micromachining
Authors: Higurashi E. , Ukita H. , Tanaka H. , Ohguchi O.
Published: July 2002

Optical trapping and directional high-speed rotation by radiation pressure are demonstrated for anisotropic micro-objects fabricated by reactive ion-beam etching. These micro-objects, which have shape dissymmetry (not bilateral symmetry but rotational symmetry) in the horizontal cross section, rotate about the laser beam axis in the designed direction in a liquid medium (e.g., water or alcohol). The rotation speed is almost proportional to the input laser power.
Simultaneous scanning tunneling microscope and collection mode scanning near-field optical microscope using gold coated optical fiber probes
Authors: Garcia-Parajo M. , Cambril E. , Chen Y.
Published: July 2002

Simultaneous scanning tunneling microscope (STM) and collection mode scanning near-field optical microscope (SNOM) images using tunneling regulation are presented. The images were obtained using a gold coated single optical fiber as both a tunneling and near-field optical probe. The method counts on the reliable STM distance regulation and the short separation between tip and sample (<1 nm). Using optimized fiber probes, both STM and SNOM images show good resolution and image contrast. We describe the STM/SNOM system and present the first images obtained in the collection mode with calibration samples of gratings of period down to 200 nm.
Low-temperature plasma enhanced chemical vapor deposition of SiO2
Authors: Deshmukh Shashank C. , Aydil Eray S.
Published: July 2002

Silicon dioxide (SiO2) films, with qualities approaching to those of thermal oxide, were deposited at 40 °C in a helical resonator plasma reactor from tetraethylorthosilicate (TEOS) and oxygen discharge. The films were characterized using transmission infrared spectroscopy, variable angle spectroscopic ellisometry, and wet etch rate measurements. It was found that the TEOS/O2 ratio, ℜ, in plasma enhanced chemical vapor deposition of SiO2 is as important a parameter as the substrate temperature. Using low TEOS/O2 ratio (ℜ<1:20), high quality SiO2 films could be deposited by PECVD at room temperature. At high TEOS/O2 ratio, particularly at low temperature, ethoxy ligands of the TEOS molecule are incorporated into the film disrupting the connectedness of the SiO4 tetrahedra resulting in porous, low density films with high OH content.
Characteristics of high quality ZnO thin films deposited by pulsed laser deposition
Authors: Craciun V. , Elders J. , Gardeniers J. G. E. , Boyd Ian W.
Published: July 2002

Thin films of ZnO have been deposited on glass and silicon substrates by the pulsed laser deposition technique employing a KrF laser (λ=248 nm). The influence of the deposition parameters, such as substrate temperature, oxygen pressure, and laser fluence on the properties of the grown films, has been studied. All the films grown over a rather wide range of deposition conditions were found to be optically transparent, electrically conductive, and c-axis oriented, with the full width at half-maximum (FWHM) of the (002) x-ray reflection line being very often less than 0.25°. Under optimized laser fluence and oxygen pressure conditions, highly c-axis oriented films having a FWHM value less than 0.15° and optical transmittance around 85% in the visible region of the spectrum have been grown at a substrate temperature of only 350 °C. These are among the best properties yet reported for ZnO films grown by any technique at such a low temperature.
Second harmonic generation in hexagonal silicon carbide
Authors: Lundquist P. M. , Lin W. P. , Wong G. K. , Razeghi M. , Ketterson J. B.
Published: July 2002

We report optical second harmonic generation measurements in single crystal α-SiC of polytype 6H. The angular dependence of second harmonic intensity was consistent with two independent nonvanishing second order susceptibility components, as expected for a crystal with hexagonal symmetry. For the fundamental wavelength of 1.064 μm the magnitudes of the two components were determined to be χzzz(2)=±1.2×10−7 and χzxx(2)=∓1.2×10−8 esu. The corresponding linear electro-optic coefficient computed from this value is rzzz=±100 pm/V. The wavelength dependence of the nonlinear susceptibility was examined for second harmonic wavelengths between the bandgap (400 nm) and the red (700 nm), and was found to be relatively uniform over this region. The refractory nature of this compound and its large nonlinear optical coefficients make it an attractive candidate for high power nonlinear optical waveguide applications.
Kink power in weakly index guided semiconductor lasers
Authors: Schemmann M. F. C. , van der Poel C. J. , van Bakel B. A. H. , Ambrosius H. P. M. M. , Valster A. , van den Heijkant J. A. M. , Acket G. A.
Published: July 2002

A periodic dependence of kink power on laser length is observed and explained. Weakly index guided high power stripe lasers in the AlGaAs, InGaAlP, and InGaAs–AlGaAs material systems are studied and oscillation periods of 100–350 μm are found. Relative kink power differences exceeding a factor of 4 are observed. Facet coatings lead to differences in the oscillation amplitude but not in the oscillation period. The observations indicate that phase-locked fundamental and first-order modes exist at certain preferred laser lengths. This general model fully explains the oscillatory behavior of the kink power and the correlated changes in lateral far field distributions at the front and rear mirrors. It is concluded that the optimum diffraction limited power output can be obtained by choosing the proper laser length.
Low-field magnetic sensors based on the planar Hall effect
Authors: Schuhl A. , Van Dau F. Nguyen , Childress J. R.
Published: July 2002

Sensitive magnetic field detection devices have been fabricated based on the planar Hall effect. The active material consists of permalloy ultrathin films (6 nm thick) epitaxially grown by molecular beam epitaxy. Uniaxial magnetic anisotropy is induced in the film through ferromagnetic coupling with a Fe/Pd bilayer epitaxially grown on MgO(001). The active layer shows a magnetoresistive ratio ΔR/R=2%. The device gives a sensitivity of 100 V/TA and a minimum detectable field below 10 nT. The detector response is linear over at least four decades. The transverse resistivity is sensitive only to the anisotropic resistivity, and not to the isotropic resistivity term which is highly temperature sensitive. Consequently, the thermal noise at 1 Hz is reduced by four orders of magnitude compared to a similar longitudinal magnetoresistive detector.
Simple electrostatic quadrupole ion beam deflector
Authors: Farley John W.
Published: July 2002

An electrostatic quadrupole device capable of deflecting an ion beam at right angles is described. It is useful for overlapping an ion beam and a laser beam. Its aberrations are negligible in many applications where fine focusing is not required. The construction is simpler and less expensive than other similar devices.
Optical determination of chain orientation in electroluminescent polymer films
Authors: McBranch D. , Campbell I. H. , Smith D. L. , Ferraris J. P.
Published: July 2002

We report polarized optical transmission and reflection measurements which are used to determine the orientation of polymer chains in spin-cast thin films of soluble, electroluminescent polymers. We find that the polymer chains lie primarily in the plane of the film. This result has three important implications for polymer light emitting diodes: the electroluminescence is preferentially emitted propagating perpendicular to the polymer film; the relevant dielectric and electrical transport properties are those perpendicular to the polymer chains; and large area, uniform devices can be produced by spin casting.
Nova experimental facility (invited)
Authors: Campbell E. M. , Hunt J. T. , Bliss E. S. , Speck D. R. , Drake R. P.
Published: July 2002

The goals of the recently activated Nova laser facility are to address critical issues for evaluating the feasibility of inertial confinement fusion, to implode DT to densities exceeding 200 g/cm3 and pressures greater than 1011 atm, and to perform a wide range of high energy density plasma physics experiments in the areas of XUV/x-ray lasers, hydrodynamics, and radiation generation and transport. An extremely flexible and sophisticated facility is required to successfully perform such a variety of tasks. The ten-arm Nova laser is capable of irradiating complex targets with laser wavelengths of 0.53 and 0.35 μm and pulse widths that range from 0.09 to >5 ns, and peak powers greater than several terrawatts per beam line. A sophisticated, variable impedance, transmission line driven Pockels cell allows for complex temporal shaping of the laser pulse. Synchronized oscillators allow for different pulses to be propagated down the beam lines for experiments that require long-pulse or short-pulse x-ray backlighting. The output of the laser can be directed into two independent target areas: a 4.4-m-diam vacuum vessel for experiments which require 10 beams, and a 1.8-m-diam chamber for two Nova arms. The facility has been designed to allow nearly simultaneous, independent experiments to be conducted in both target areas. A number of sophisticated optical, XUV, x-ray, and particle diagnostics measure target performance. An optical fiducial system allows cross correlation of all of the diagnostic systems to better than 50 ps. An overview of the facility, diagnostics, and data-acquisition system will be discussed.
One Tesla rare-earth permanent quadrupole magnet for spin separation of metal clusters
Authors: Ziock Klaus-Peter , Little W. A.
Published: July 2002

We have constructed a 1.20-T pole tip field quadrupole magnet which is used to separate electrically neutral metal clusters by their spin magnetic moment. The device is magnetically energized with rare-earth samarium cobalt magnets. The use of this material allows for both the low cost and the small size of the device.
High-count-rate proportional counter for soft x-ray position detection
Authors: Källne E. , Källne J. , Atencio L. G. , Chmielewski J. , Idzorek G. , Morris C. L.
Published: July 2002

The design of a multiwire gas proportional counter for soft x-ray detection is described. Position information is obtained over a length of 110 mm from the signal induced in the cathode plane consisting of a delay line. A position resolution of better than 80 μm is demonstrated in tests performed with fluorescent x rays of well-defined energies in the range 1.6–6 keV. Count-rate capabilities reaching 1 MHz are demonstrated in crystal spectrometer measurements of the x-ray emission from tokamak plasmas. The use of this type of detector in other applications is also discussed, especially in view of the potential of measuring the xy position over areas up to 110×160 mm2.
Effects of strain on boron diffusion in Si and Si1−xGex
Authors: Kuo P. , Hoyt J. L. , Gibbons J. F. , Turner J. E. , Lefforge D.
Published: July 2002

Boron diffusion in in situ doped Si1−xGex and Si, subjected to inert-ambient furnace annealing at 800 °C, was investigated. For Si1−xGex, the effect of biaxial compressive and tensile strain on boron diffusion was studied using Si1−xGex layers with a constant Ge content (x≊0.10 and x≊0.20) grown epitaxially on various relaxed Si1−yGey (0≤y≤0.20) substrates. Boron diffusion is primarily a function of Ge content, x in the Si1−xGex layers, and does not show a strong dependence on macroscopic biaxial strain. For Si, the effect of biaxial tension was investigated using relaxed Si1−yGey layers as substrate templates for epitaxial Si layers. As in Si1−xGex, boron diffusion in Si does not depend strongly on biaxial strain.
Electric probe diagnostics in thermal plasmas: Double probe theory and experimental results
Authors: Leveroni E. , Pfender E.
Published: July 2002

Electric probes can be advantageously applied to the study of nonequilibrium induced in thermal plasmas by the presence of cold boundaries, since the interpretation of experimental data does not require any assumption about the thermodynamic state of the plasma. An experimental setup and procedure are described which allow accurate measurements of the electron temperature profiles in the near-wall region of wall stabilized, atmospheric pressure, argon dc arcs. An extension of the classical double floating probe theory was developed to include asymmetries in collecting areas and nonuniformities in the plasma. Excellent agreement between the measured probe characteristics and the analytical relationship was obtained.
JUSIFA—A new user-dedicated ASAXS beamline for materials science
Authors: Haubold H.-G. , Gruenhagen K. , Wagener M. , Jungbluth H. , Heer H. , Pfeil A. , Rongen H. , Brandenberg G. , Moeller R. , Matzerath J. , Hiller P. , Halling H.
Published: July 2002

The fully computer-controlled user-dedicated small-angle scattering facility JUSIFA was set up for general use at the DORIS Synchrotron Radiation Source in DESY (Hamburg). This beamline is especially designed for anomalous scattering studies of anisotropic samples in materials science and enables ASAXS studies to be undertaken on the length scale 0.5 to 100 nm in an energy range of 4.5 to 35 keV.
Gabor lens focusing of a proton beam
Authors: Palkovic J. A. , Mills F. E. , Schmidt C. , Young D. E.
Published: July 2002

Gabor or plasma lenses have previously been used to focus intense beams of positive ions at energies from 10 keV to 5 MeV. Such lenses are a possible candidate for matching an intense low-energy proton beam into a radio frequency quadrupole accelerator (RFQ). The conventional solution has been to match an intense beam with two solenoid lenses. This leads to a time-dependent emittance at the RFQ entrance due to neutralization effects. The neutralization time of a space-charge dominated 30–50 mA proton beam in the Gabor lens is <1 μs. A non-neutral electron plasma is contained in the Gabor lens by a 200 G solenoid magnet. The equivalent thin lens focal length of a Gabor lens operated at Fermilab has been determined to be 10 cm. This focusing strength is adequate for matching a proton beam into an RFQ.
Highly charged ECR ion sources: Summary and comments (invited)
Authors: Geller R.
Published: July 2002

A review is presented of the historical evolution of the ECR ion source and its application for the production of very highly charged ions. The status of our present understanding of the scaling laws for ion charge state and ion beam current as a function of ion mass, magnetic field strength, and the microwave frequency and power is summarized.
Recent diagnostic developments at Nova (invited)
Authors: Kilkenny J. D.
Published: July 2002

The Nova laser at Lawrence Livermore National Laboratory has about 60 diagnostics in use on its two target chambers. The broad rationale for the diagnostics is explained. Recent developments in diagnostic techniques on Nova for implosions, soft x-ray studies, and x-ray laser applications are described.
Nondispersive Bragg diffraction in the general case of two cylindrically bent crystals
Authors: Chukhovskii F. N. , Krisch M. , Freund A. K.
Published: July 2002

The conventional double crystal setup, employing two flat crystals with equivalent reciprocal lattice vectors generalizes for two crystals with different lattice vectors if the crystals are bent to their appropriate radii. The conditions for nondispersivity are derived in the most general case for two cylindrically bent crystals in reflection geometry with asymmetric cuts using different reflections. The theoretical predictions are verified by experiments.
Efficient luminescence from AlP/GaP neighboring confinement structure with AlGaP barrier layers
Authors: Issiki F. , Fukatsu S. , Shiraki Y.
Published: July 2002

Highly efficient photoluminescence (PL) was observed from a new class of AlP/GaP quantum-confined geometry, neighboring confinement structure (NCS). The PL intensity of AlP/GaP NCSs was even higher than that of a 300-period AlP/GaP superlattice (SL), and the PL of the NCS exhibited much improved immunity against thermal quenching compared to SLs. The luminescence origin of the NCS was confirmed from the well width dependence of the PL peak shift. The peak shifts were compared with the calculation within the effective mass approximation using the previously reported band parameters for AlP and GaP.
Pulsed Laval nozzle with a large optical path length of 50 cm
Authors: Okada Yoshiki , Isomura Shohei , Satooka Sakae , Takeuchi Kazuo
Published: July 2002

This note describes the design and performance of a pulsed valve developed as a gas source for a 500 mm long supersonic Laval nozzle with a 3 mm wide throat. The valve consists of a rotating drum with a slit, which allows an opening duration of approximately 14 ms. The duration of quasi-steady-state expansion is measured to be 10 ms at the nozzle throat when the pulsed valve is filled with 200 Torr of Ar gas.
Drive characterization of indirect drive targets on the Nova laser (invited)
Authors: Kauffman Robert L. , Kornblum H. N. , Phillion D. W. , Darrow C. B. , Lasinski B. F. , Suter L. J. , Theissen A. R. , Wallace R. J. , Ze F.
Published: July 2002

The indirect drive method of inertial confinement fusion uses a high-Z radiation case to convert energy from high-powered laser beams to x rays which implode fusion capsules. Experiments have been performed on the Nova laser to characterize the x-ray production in high-Z cavities for studying the efficiency for x-ray production using two methods for characterization. One method measures the shock velocity produced in low-Z materials by the radiation. The shock velocity is measured by observing the optical signal from the rear of a stepped or continuously varying thickness of Al placed over a hole in the cavity wall. The other method measures the reradiated x-ray flux from the cavity wall viewing through a hole in the cavity. Both methods have been shown to provide a consistent characterization of the x-ray drive in the cavity target.
Nitrogen diffusion mechanism in the R2Fe17 lattice
Authors: Zhang Y. D. , Budnick J. I. , Hines W. A. , Yang D. P.
Published: July 2002

In this report, a diffusion analysis has been extended to a lattice containing two interstitial sites, and the results obtained are used to understand: (1) the formation of a nitrided/unnitrided N configuration for intermediate N content and (2) the abnormally small (apparent) diffusion frequency factor, both of which characterize the newly developed R2Fe17 nitrides. It turns out that the diffusion mechanism for N atoms in the R2Fe17 lattice is a chemical reaction diffusion rather than a free-diffusion process.
A closed loop controller for electron-beam evaporators
Authors: Band Alan , Stroscio Joseph A.
Published: July 2002

A simple instrument for automatically controlling the deposition rate of an electron-beam evaporator is described. The design incorporates a commercially available, microprocessor based, proportional-integral-differential process controller that provides loop control and automatic determination of optimal proportional, integral, and differential loop constants. A logarithmic amplifier is used to linearize the overall loop response. The controller is used in conjunction with a compact electron-beam heated evaporator.
Spatially and temporally resolved crystal spectrometer for diagnosing high-temperature pinch plasmas on Z
Authors: Nash T. , Derzon M. , Leeper R. , Jobe D. , Hurst M. , Seamen J.
Published: July 2002

We have developed a spatially and temporally resolved crystal spectrometer for analyzing a variety of pinch experiments on Z. The spectrometer uses a convex curved crystal to disperse spectra onto a flat microchannel plate (MCP) framing camera detector. A single wide, 1 cm, strip on the MCP is gated to provide temporal resolution. The spectral range governed by the 4 cm length of the MCP strip varies with the central Bragg angle and crystal. For a KAP crystal a typical range is 1500–2000 eV. This range can be shifted by translating the crystal along the optical axis to access different Bragg angles. The spectrometer can therefore measure K shell spectra of a wide variety of elements such as Al, Ti, and Fe. The short 1 cm width of the strip is spatially resolved with an imaging cross slit. With a 500 μm cross slit and magnification 1 the spatial resolution at the pinch is 1 mm. The instrument may also be fielded with seven time frames using a seven strip-line microchannel plate as the detector by sacrificing the spatial resolution. We will present data obtained from an aluminum pinch on Z.
Pulse-stacked cavity ring-down spectroscopy
Authors: Crosson E. R. , Haar P. , Marcus G. A. , Schwettman H. A. , Paldus B. A. , Spence T. G. , Zare R. N.
Published: July 2002

Pulse stacking, or synchronous pumping, is a novel approach that offers important advantages in cavity ring-down spectroscopy. Using an ultrashort pulse, high repetition rate laser source we have shown that it is possible to resonantly stack pulses in a high finesse cavity, significantly enhancing the decay wave forms obtained when the laser source is abruptly terminated. We have achieved signal-to-noise ratio improvements of several orders of magnitude compared to single pulse injection systems, demonstrating a sensitivity of 2×10−9 cm−1 at 5.38 μm.
Low-cost device for ratiometric fluorescence measurements
Authors: Kostov Yordan , Rao Govind
Published: July 2002

An all-solid-state, low-cost device for fluorescent wavelength-ratiometric detection is described. Ultrabright light-emitting diodes were used as light sources. This allowed electronic modulation of the light, simple optical configuration, and miniaturization of the instrument. Narrow-bandpass interference filters were used for wavelength separation. Detection was accomplished by high-sensitivity, large-surface PIN photodiodes. An integrating double-ramp technique with fixed upper and lower thresholds was employed for conversion of the light intensities into time intervals. The duty ratio of the output signal was a function of the fluorescence intensity ratio. Additionally, the concentration of the fluorophore could be measured. The device could be easily designed as a battery-operated version. It could be used for a variety of ratiometric fluorescence measurements.
Production of bimetallic clusters by a dual-target dual-laser vaporization source
Authors: Bouwen Wim , Thoen Peter , Vanhoutte Frederik , Bouckaert Steven , Despa Florin , Weidele Horst , Silverans Roger E. , Lievens Peter
Published: July 2002

A new dual-target dual-laser vaporization source for the production of binary metallic clusters is presented. Clusters of the type AunXm (X=Al, Fe, Co, Ni) were produced. Excellent control over the mixing process was achieved by varying the delay time between the firing of the two lasers and their energy densities. Having identified these critical parameters, their influence over the production process is shown in detail for the AunAlm system. The production of bimetallic clusters in this source is due to the spatial and temporal overlap of the two laser vaporized materials in the source.
A probe for measurements of electrostatic fluctuations in a low-temperature magnetized plasma
Authors: Ratynskaia S. V. , Demidov V. I. , Rypdal K.
Published: July 2002

A cylindrical probe with insulating end plugs for investigations of fluctuations of electron temperature and plasma potential is proposed. The radii of the metallic rod and plugs are chosen to optimize the ratio of ion saturation current to electron saturation current (>1) for the probe oriented parallel to the magnetic field. This probe is applicable when the electron temperature is much larger than the ion temperature.
Nonlinear optical polymers with dipole moment aligned transverse to main chain
Authors: Tsutsumi Naoto , Matsumoto Osamu , Sakai Wataru , Kiyotsukuri Tsuyoshi
Published: July 2002

A new type of nonlinear optical (NLO) polymer for second harmonic generation is presented. This type of NLO polymer has a large dipole moment which is aligned transverse to the main chain. Poled polymer shows a large second order nonlinearity of 1.6×10−7 esu (67 pm/V). Good thermal stability of nonlinearity was observed in ambient condition.
Deposition of continuous and well adhering diamond films on steel
Authors: Fayer A. , Glozman O. , Hoffman A.
Published: July 2002

The present work reports a successful solution to the problem of diamond deposition onto steel. This was achieved through the use of an intermediate layer between the substrate and the deposited film. The intermediate layer consisted of a 10 μm thick nitridized chromium film. The chromium film was produced by electrochemical deposition and the nitridation was performed in an ammonia flow. This nitridation process results in the formation of mixed CrN and Cr2N crystalline phases, with the latter in contact with the steel substrate. During diamond deposition, partial carbidization of the chromium nitride interlayer took place resulting in the formation of a layer composed mainly of carbides and carbon phases onto which continuous diamond films were deposited. Beneath the carburized region a chromium nitride-rich phase, consisting predominantly of Cr2N, was observed. The diamond films were deposited using a hot filament system at a rate of 1 μm per hour and a substrate temperature of 800 °C. The toughness of the diamond films was evaluated by measuring the minimum load necessary to induce delamination with a cone-shaped diamond indenter. No delamination events occurred during indentation up to loads of 1000 N. The samples were examined by Auger electron spectroscopy, x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. It is suggested that chromium nitride interlayers could be employed in the deposition of diamond films on iron based alloys for industrial purposes.
Terahertz photomixing with diode lasers in low-temperature-grown GaAs
Authors: McIntosh K. A. , Brown E. R. , Nichols K. B. , McMahon O. B. , DiNatale W. F. , Lyszczarz T. M.
Published: July 2002

Recent optical heterodyne measurements with distributed-Bragg-reflector diode-laser pumps demonstrate that low-temperature-grown (LTG) GaAs photomixers will be useful in a compact all-solid-state terahertz source. Electrical 3 dB bandwidths as large as 650 GHz are measured in mixers with low electrode capacitance. These bandwidths appear to be independent of pump-laser wavelength over the range 780–850 nm. Shorter wavelength pumping results in a significant reduction of the bandwidth. The best LTG-GaAs photomixers are used to generate coherent continuous-wave output radiation at frequencies up to 5 THz.
High power continuous wave atomic Xe laser with radio frequency excitation
Authors: Vitruk P. P. , Morley R. J. , Baker H. J. , Hall D. R.
Published: July 2002

Radio frequency discharges in Ar/He/Xe gas mixtures have been studied in the range 5–150 MHz, and the importance of the ion sheaths in Xe laser excitation has been recognized. The discharge data have been used to improve the cw Xe laser performance, and efficiencies up to 0.8% observed. Area scaling in the slab geometry has been studied for α discharge excitation at 49 MHz, and multimode cw laser power up to 5.5 W has been observed. High quality beams have been produced at 4.9 W using a hybrid waveguide/unstable resonator.
Transmission electron microscopy study of interface and internal defect structures of homoepitaxial diamond
Authors: Tarutani M. , Takai Y. , Shimizu R. , Ando T. , Kamo M. , Bando Y.
Published: July 2002

Defect structures in a homoepitaxial diamond film grown by chemical vapor deposition have been studied by cross-sectional transmission electron microscopy. Many interstitial dislocation loops are discerned in the (001) interface. The internal region grown on the (11̄1) facet comprises stacking faults and twins, while that on the (001) face contains mainly interstitial dislocation loops aligned in rows along ∼〈112〉 directions. Fe and Si impurities were detected only at the interface by analytical electron microscopy. The origin of the defects is briefly discussed.
Magnetoelastic properties of nickel thin films
Authors: Betz J. , du Trémolet de Lacheisserie E. , Baczewski L. T.
Published: July 2002

The deflection of bimorphs consisting of thin films of nickel on silicon substrates has been accurately measured as a function of applied in-plane magnetic field, using an optical method. Striking differences in the magnetoelastic behavior are observed for these systems compared with bulk nickel, mainly due to the anisotropic behavior of silicon substrates and to large in plane tensile stresses in nickel films, which favor an easy magnetization axis perpendicular to the film plane: Deflections measured with the magnetic field parallel and perpendicular to the length of the bimorph exhibit the same sign, and the ‘‘parallel deflection’’ is enhanced by a factor 1.3. These are the first experiments demonstrating the validity of a formula recently derived for predicting the deflection of magnetostrictive bimorphs.
Electron spin resonance of polyparaphenylene-based carbons
Authors: Matthews M. J. , Dresselhaus M. S. , Kobayashi N. , Enoki T. , Endo M. , Takahashi T.
Published: July 2002

We report electron spin resonance (ESR) results on heat-treated polyparaphenylene (PPP) over the heat-treatment temperature (THT) range of 650–2900 °C. Two distinct spin centers are identified corresponding to a broad (∼5 G) ESR peak below THT=750 °C and a narrow (∼0.5 G) ESR peak above THT=650 °C. ESR peaks from both spin centers are observable for THT=700 °C, a material of particular interest for device applications. T1 and T2, the spin-lattice and spin-spin relaxation times, respectively, are estimated for both spin centers, and these results are discussed in relation to previously reported Raman spectroscopy and magnetic susceptibility measurements.
Picosecond acoustic measurements of longitudinal wave velocity of submicron polymer films
Authors: Lee Yung-Chun , Bretz Kathleen C. , Wise Frank W. , Sachse Wolfgang
Published: July 2002

We apply picosecond acoustic techniques to determine the longitudinal wave speed of submicron polymer films in the through-thickness dimension. The time-of-flight of an elastic wave propagating through the polymer film is measured using an optical pump/probe technique. The longitudinal wave speed in poly(methyl methacrylate) films of thickness ranging from 20 to 130 nm has been determined. A pronounced increase in longitudinal wave speed is observed for films of thickness less than 40 nm.
Enhancement of the light-to-current conversion efficiency in an n-SiC/solution diode by porous etching
Authors: van de Lagemaat J. , Plakman M. , Vanmaekelbergh D. , Kelly J. J.
Published: July 2002

Scanning electron microscopy micrographs of n-type silicon carbide (SiC) anodized in HF solution showed a highly porous layer having structures with dimensions of about 50 nm. The capacitance of the porous electrodes revealed a huge surface area. The photocurrent quantum yield of a porous SiC/electrolyte diode is spectacularly enhanced with respect to that of a flat diode for light absorbed in the indirect-bandgap and for sub-bandgap light.
Shape-anisotropy-controlled magnetoresistive response in magnetic tunnel junctions
Authors: Lu Yu , Altman R. A. , Marley A. , Rishton S. A. , Trouilloud P. L. , Xiao Gang , Gallagher W. J. , Parkin S. S. P.
Published: July 2002

We show that shape anisotropy can be used to control the response characteristics of magnetic tunnel junctions. By varying the junction shape, the resistance versus field curve was made to vary from a nonhysteretic linear curve with a high-field sensitivity (0.3%/Oe) to a hysteretic response curve with high squareness.
Electrical and structural analysis of high-dose Si implantation in GaN
Authors: Zolper J. C. , Tan H. H. , Williams J. S. , Zou J. , Cockayne D. J. H. , Pearton S. J. , Crawford M. Hagerott , Karlicek R. F.
Published: July 2002

For the development of ion implantation processes for GaN to advanced devices, it is important to understand the dose dependence of impurity activation along with implantation-induced damage generation and removal. We find that Si implantation in GaN can achieve 50% activation at a dose of 1×1016 cm−2, despite significant residual damage after the 1100 °C activation anneal. The possibility that the generated free carriers are due to implantation damage alone and not Si-donor activation is ruled out by comparing the Si results to those for implantation of the neutral species Ar. Ion channeling and cross-sectional transmission electron microscopy are used to characterize the implantation-induced damage both as implanted and after a 1100 °C anneal. Both techniques confirm that significant damage remains after the anneal, which suggests that activation of implanted Si donors in GaN doses not require complete damage removal. However, an improved annealing process may be needed to further optimize the transport properties of implanted regions in GaN.
Picosecond ultrasonics study of the modification of interfacial bonding by ion implantation
Authors: Tas G. , Loomis J. J. , Maris H. J. , Bailes A. A. , Seiberling L. E.
Published: July 2002

We report on experiments in which picosecond ultrasonic techniques are used to investigate the modification of interfacial bonding that results from ion implantation. The bonding is studied through measurements of the acoustic reflection coefficient at the interface. This method is nondestructive and can be used to create a map of the variation of the bonding over the area of the interface.