bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of radio frequency microcoils as nuclear magnetic resonance detectors in low-homogeneity high-field superconducting magnets
Authors: Wright A. C. , Neideen T. A. , Magin R. L. , Norcross J. A.
Published: July 2002

We describe here experiments evaluating the performance of solenoidal radio frequency probes having submillimeter dimensions (microcoils) as detectors for liquid nuclear magnetic resonance (NMR) in very low-homogeneity (100 ppm/cm) magnetic fields. Performance is based on the measured H2O linewidth. A series of solenoidal microcoils having sample volumes 8, 53, and 593 nl were filled with distilled H2O and evaluated for smallest obtainable unshimmed NMR spectral linewidths in a vertical bore superconducting magnet, stabilized at 5.9 T (1H frequency=250 MHz). The smallest microcoil (472 μm diameter) gave a smallest H2O linewidth of 525 Hz, 25 times smaller than that from a standard 5.7 mm probe. Linewidth increased approximately as the square root of sample volume. For comparison, shimmed H2O linewidths using the same microcoils in a high-homogeneity (0.1 ppm/cm) NMR magnet were also measured. Shimmed linewidths in the high-homogeneity magnet were two orders of magnitude smaller and exhibited a similar dependence on volume. The results demonstrate that by using microcoils the volume over which the polarizing magnetic field must meet a specified homogeneity can be significantly reduced, which would be advantageous for smaller, less expensive NMR systems.
A new linear amplifier for the RFX electron energy analyzer
Authors: Desideri D. , Bagatin M.
Published: July 2002

A simple low cost novel linear amplifier has been developed for the electron energy analyzer employed on the reversed field pinch experiment RFX. The amplifier is designed to provide a 1 kV output voltage from a 10 V input. The current rating is ±50 mA. It utilizes a configuration of four blocks in series, each of them with an output totem-pole configuration. The rise and fall times are of a few milliseconds. A fast protection against output short circuit has been implemented. The amplifier has been used in various experimental campaigns on RFX and multiple time resolved measurements of the edge electron energy distribution in a single plasma discharge have been obtained.
Measurement of the photon field, E>150 eV on Sandia’s Z Facility
Authors: Rochau G. E. , Derzon M. , Fehl D. , Rochau G. A. , Sweeney M. A. , Tabor D. , Lazier S. E. , Droemer D. , Helvin T. , Starbird R.
Published: July 2002

The Z Facility at Sandia National Laboratories utilizes z-pinch implosions to produce up to 2 MJ of x rays. On Z, bremsstrahlung radiation is produced in various parts of the machine as a product of both power flow electrons and those accelerated in the pinch region. An understanding of the energy spectra and intensity of this radiation is important to both the explanation of the z-pinch physics and the design of new diagnostics. A technique has been developed using a differential absorption spectrometer to measure the photon field for energies greater that 150 eV for bremsstrahlung from the z-pinch or the vacuum transmission lines. This article describes the techniques and results used to date.
Far infrared tangential interferometry/polarimetry on the National Spherical Tokamak Experiment
Authors: Park H. K. , Domier C. W. , Geck W. R. , Luhmann N. C.
Published: July 2002

Measurement of the core BT(r,t) value is essential in the National Spherical Tokamak Experiment (NSTX), since the effects of paramagnetism and diamagnetism in the NSTX are expected to be considerably greater than that in higher aspect ratio tokamaks. Therefore, without independent BT(r,t) measurement, plasma parameters dependent upon BT such as the q profile and local β value cannot be evaluated. Tangential interferometer/polarimeter systems (eight channels) [H. Park, L. Guttadora, C. Domier, W. R. Geck, and N. C. Luhman, Jr., First and Second NSTX Research Forums, Princeton, NJ, 1997 (unpublished)] for the NSTX will provide temporally and radially resolved toroidal field profile [BT(r,t)] and two-dimensional electron density profile [ne(r,t)] data. The outcome of the proposed system is extremely important to the study of confinement, heating, and stability of the NSTX plasmas. The research task is largely based on utilizing existing hardware from the TFTR multichannel infrared interferometer system [D. K. Mansfield, H. K. Park, L. C. Johnson, H. Anderson, S. Foote, B. Clifton, and C. H. Ma, Appl. Opt. 26, 4469 (1987) and H. K. Park, D. K. Mansfield, and C. L. Johnson, Proceedings of the 3rd International Symposium on Laser-Aided Plasma Diagnostic, Los Angeles, CA, 28–30 Oct. 1987 (unpublished), pp. 96–104] which will be reconfigured into a tangential system for NSTX, and to develop the additional hardware required to complete the system.
Infrared surface temperature measurement for long pulse real time feed-back control in an actively cooled machine
Authors: Guilhem D. , Martin G. , Reichle R. , Roche H. , Jouve M. , Ducobu L. , Messina P.
Published: July 2002

Tore-Supra is an actively cooled machine aiming at long pulse operation. Surface temperature measurements are necessary in this context to achieve a real time feed-back control on plasma parameters, as well as auxiliary heating systems. Safety interlock is also mandatory when using such actively cooled elements to prevent any damage due to overheating by the plasma, or a loss of active cooling. As an example, it will be shown how the actively cooled pump limiters test campaign has been conducted. The CIEL project for Tore-Supra is aimed at replacing the old generation of plasma facing components designed in 1984, by new ones with a full coverage of the inside vessel. A set of dedicated infrared systems will be used to measure the surface temperatures. They will be included in the real time feed-back loop control and the safety system.
Sweep system design for a heavy ion beam probe on Madison Symmetric Torus
Authors: Lei J. , Crowley T. P. , Shah U. , Schoch P. M. , Connor K. A. , Schatz J.
Published: July 2002

The sweep system for the heavy ion beam probe on the Madison Symmetric Torus (MST) is described. The two components of the system are the primary sweep optics and secondary collimation plates. Key issues in the sweep system design are the small entrance and exit ports available on MST, the significant toroidal beam motion induced by the strong poloidal magnetic field, and the excessive current loading due to plasma and ultraviolet (UV). The design accommodates these issues using a crossover sweep plate design in two dimensions for the primary beam as well as two dimensional sweeping on the secondary beam. The primary beam sweep design results in a sweep range of ±20° in one direction and ±5° in the perpendicular direction. The secondary beam sweep design results in entrance angles to the energy analyzer of <3° in radial and ∼0° in toroidal directions. The procedure for calculating sweep performance including fringe fields, a system for active trajectory control, and initial experiments on plasma and UV loading are also discussed.
Multiprocessor architecture to handle TJ-II VXI-based digitization channels
Authors: Crémy C. , Vega J. , Sánchez E. , Dulya C. M. , Portas A.
Published: July 2002

The data acquisition System (DAS) of the TJ-II stellerator provides up to 300 digitization channels integrated in register-based VXI modules designed in CIEMAT Laboratories. The modules are embedded into six 13-slot VXI chassis connected to the TJ-II DAS central computer by means of a dual LAN topology. During normal operation, remote control of the VXI systems and channel setup are accomplished through an Ethernet LAN, while two FDDI rings are dedicated to postdischarge fast data transfer. The former network link is performed by the bus controller whereas the latter one is provided through a FDDI node controller installed in the mainframe, thus creating a multiprocessor architecture. Dedicated software, running on the VxWorks operating system, has been developed to provide handling of the VXI systems including the following facilities: mainframe information readout, channel setup, real time digitization handling, and data transfer. This software, implemented in C++, is distributed over the two CPUs. Interprocessor communication for synchronization purposes is based on a backplane shared memory pool.
New tokamak physics and next step devices versus present limits of diagnostics (invited)
Authors: Orsitto F.
Published: July 2002

In recent years the necessity of understanding the physics concerning new tokamak results has clearly shown the limits of the actual diagnostic capability of existing devices, in terms of reliability, precision, spatial localization, and temporal resolution of measurements. This appears even more evident when next-step tokamak devices are considered. For example, the formation and evolution of the plasma internal transport barriers and the regulation of its positions by a detailed tailoring of the current spatial profile and plasma heating gives demanding requests to a complex set of diagnostics including motional Stark effect as well as incoherent Thomson scattering (ITS). The measurement of detachment of plasma in a divertor puts some requirements on a dedicated ITS. The rotational stabilization of ideal magnetohydrodynamic modes puts some important accent to the plasma rotation measurements. The coherent (or collective) Thomson scattering giving ion temperature can be useful in a prototype fusion reactor to monitor the ignition process. A state-of-the-art review for these diagnostics is carried out trying to outline the perspectives that are seen from the point of view of physics studies. A discussion of the present limits is presented and new directions of development identified, since a step foreward in the physics studies implies a parallel refinement and/or new conception of diagnostic equipment.
Response function measurement of a synthetic diamond radiation detector for 14 MeV neutrons
Authors: Kaneko Junichi , Ikeda Yujiro , Nishitani Takeo , Katagiri Masaki
Published: July 2002

The response function of a diamond radiation detector using a synthetic type IIa single diamond crystal for 14 MeV neutrons was measured. There was severe trapping of electrons in the synthetic diamond crystals used in this study. Accordingly, a prototype diamond radiation detector using the synthetic type IIa single diamond whose thickness was 0.1 mm was used with high bias voltage up to 1000 V, i.e., electric field of 100 kV/cm. The measurement resulted in the first observation of a 14 MeV neutron peak corresponding to C12(n,α)9Be reactions by a synthetic diamond radiation detector. Energy resolution of the prototype detector for 14 MeV neutrons was 9%. Experimental detection efficiency of the detector was consistent with calculated detection efficiency. Synthetic diamond crystals which do not have trapping of charge carriers are indispensable in order to improve energy resolution for 14 MeV neutrons.
Sensitivity measurements of a microchannel plate intensified x-ray detector in the 100–1500 eV photon energy range (abstract)
Authors: Ruggles L. E. , Porter J. L. , Simpson W. W. , Vargas M. F.
Published: July 2002

Microchannel plate intensified (MPI) x-ray detectors are commonly used for imaging and spectral measurements in the 100–1500 eV photon energy range. Using a laser-produced plasma x-ray source, we measured the integrated detector response versus incident x-ray intensity and the relative efficiency versus photon energy of a MPI x-ray detector. Two identical 2000 lines/mm transmission grating spectrometers simultaneously record broadband plasma source emission from a tantalum target. The relative efficiency was determined by comparing the spectrum recorded with an absolutely calibrated x-ray CCD reference detector on one spectrometer to the spectrum recorded with a MPI x-ray detector on the other spectrometer. The integrated detector response versus incident x-ray intensity was measured by simultaneously illuminating the CCD reference detector and the MPI detector with step-wedge-filtered magnesium plasma emission. The aluminum step wedge x-ray filters pass the 1s–2p emission lines of H-like Mg at 1470 eV and the 1s2–1s2p emission lines of He-like Mg at 1350 eV, and provide a four order of magnitude range in incident intensity on the detectors.
Microwave diagnostics in electron cyclotron resonance plasma sources
Authors: Larousse B. , Louvet P.
Published: July 2002

The plasma source, which is of high importance in the optimization of the separation of the gadolinium isotopes by the plasma separation process, requires a precise knowledge of its physical characteristics. Thus, a diagnostic has been developed to estimate the microwave power inside the source. A microstrip antenna has been designed and developed in order to characterize the microwave field at 36 GHz frequency in the plasma source. The experimental results for different plasma regimes are presented. The measurements inside the plasma source show a maximum of microwave absorption for an argon pressure of 10−4 mbar with 93% absorption of the incident wave in the conditions of isotope separation.
Real-time and multipoint monitoring the dissolution rate of photoresist film by using a novel plastic optical fiber bundle
Authors: Horng Jing Shyang , Lin Gong-Ru , Chen C. W.
Published: July 2002

A novel multipoint monitoring system with a plastic-optical-fiber-bundle (POFB) based feature is presented for measuring photoresist dissolution rate. The POFB that consists of different structures at probing and receiving ends excludes the needs of beam splitters and mirrors. The mean value and the standard deviation on thickness of AZ-1350 photoresist film coated on silicon wafer were measured to be 1850 and 26 nm, respectively. A measuring error of less than 1.5% is reported by using this system. The thickness data of photoresist films on Si wafer measured by this system are in good agreement with those measured by ellipsometry. This system exhibits superiorities of more flexible structures, easier operating procedures, and lower cost in comparison with conventional ones.
Final isolation stage for a spherical gravitational wave antenna
Authors: Merkowitz Stephen M. , Coccia Eugenio , Fafone Viviana , Raffone Guido , Schipilliti Maria , Visco Massimo
Published: July 2002

In order to measure the very weak interaction between a gravitational wave and a resonant-mass detector the antenna must be vibrationally isolated from all external excitations. In this article we describe an analytical and experimental study of the final support to a spherical antenna. We derive an analytical procedure for optimizing the dimensions of the support for maximum attenuation. The results of a finite element analysis are also presented that takes into account the elasticity of the sphere. The described techniques were used for designing the final support of a room-temperature prototype antenna. We found the measurements on this system to be in good agreement with the expected transfer functions.
Two-dimensional low-frequency vibration attenuator using X pendulums
Authors: Tatsumi D. , Barton Mark A. , Uchiyama T. , Kuroda K.
Published: July 2002

We have designed and constructed an improved two-dimensional X pendulum vibration–isolation table. It achieved a lower resonant frequency (7 s) than previous prototypes, and the effects of many parasitic elastic resonances have been reduced by careful balancing, leading to much improved vibration isolation around a few hertz.
Measurement of partial pressures in extremely high vacuum region using a modified residual gas analyzer
Authors: Watanabe Shu , Oyama Hitoshi , Kato Shigeki , Aono Masakazu
Published: July 2002

The measurement of partial pressures using a residual gas analyzer (RGA) in an extremely high vacuum (XHV) region has several problems, including the influence of electron stimulated desorption ions and the outgassing rate from the ion source of the RGA. In order to measure partial pressures in the XHV, a commercial RGA was modified as follows: an electrostatic analyzer was used to only measure gas phase ions; a low work function material, thoria, was used as a filament of the ion source to lower temperature of the filament and Cu wires connected the filament and releasing the heat around the ion source to atmosphere. After these modifications, the RGA could measure only gas phase ions and, at the same time the outgassing rate from the RGA was reduced. Partial pressures and total pressure in the XHV could be measured by the RGA.
Hermetic sample enclosure for simultaneous differential scanning calorimetry/synchrotron powder x-ray diffraction
Authors: Lexa Dusan
Published: July 2002

A hermetic sample enclosure for performing simultaneous differential scanning calorimetry/synchrotron powder x-ray diffraction was designed, and a prototype was fabricated. The enclosure design is based upon a Perkin–Elmer DSC-2C measuring head with modifications allowing an unobstructed x-ray beam access to the sample in a controlled-atmosphere environment. The modifications to the measuring head base are limited to exposing the sample and reference platinum cups and providing a mating surface for the head cover. A completely new head cover, featuring semicylindrical beryllium x-ray windows, is hermetically attached to the base. A new graphite sample pan, addressing the conflicting requirements of differential scanning calorimetry and powder x-ray diffraction, was designed, and multiple pans were fabricated. An alternative temperature measurement and control system was developed and assembled. The complete system was tested in three experiments. No problems were encountered with diffraction data acquisition and temperature control, however, calorimetric resolution was mediocre. The alternative temperature measurement and control system will have to be optimized.
A segmented ion chamber to measure the intensities and energies of synchrotron radiation x rays
Authors: Lee Chih-Hao , Yu Kuan-Li , Tseng Huan-Chi , Wang Tse-Min
Published: July 2002

A segmented cascade ion chamber was built to measure the intensities and energies of synchrotron radiation x rays at the same time. The ion chamber consists of 20 cathode cells. By measuring the ionized current collected in each cell and fitting the result, the energies and intensities of fundamental and high harmonic x-ray photons can be extracted.
Trim coil system design of a superconducting ring cyclotron
Authors: Kim J.-W. , Goto A. , Yano Y.
Published: July 2002

The trim coil system of a superconducting ring cyclotron currently under design at RIKEN is composed of five sets of superconducting and twenty sets of normal-conducting coils. A major correction for isochronization of the magnetic field is accomplished by the superconducting coils, and a fine correction by the normal-conducting coils. For an optimal design of the system, a numerical procedure was developed to generate isochronous fields for design nuclei and consequently current settings on the main and trim coils, employing an iteration of a least-squares fitting to minimize orbital frequency errors. The main and normal-conducting coils can also be used to correct unwanted harmonic fields with sector dependent and/or radially localized excitations. The correction schemes were conceived for presumed error fields, alignment tolerances being estimated based upon beam optics requirements. On the other hand, a new trim coil design was envisaged, which comprises only superconducting trim coils. The subcoils in the present five-set design can be independently excited to replace the normal-conducting coils. This option may be more economical, but complications on the superconducting coil system raise a reliability concern.
A precision capacitance cell for measurement of thin film out-of-plane expansion. II. Hygrothermal expansion
Authors: Snyder Chad R. , Mopsik Frederick I.
Published: July 2002

The data reduction techniques necessary for utilizing the capacitance cell described previously by us for thickness measurements [C. R. Snyder and F. I. Mopsik, Rev. Sci. Instrum. 69, 3889 (1998)] in a humid environment are presented. It is demonstrated that our data reduction techniques provide thicknesses that are equivalent to those measured under dry conditions within the expected experimental uncertainty. The utility of this technique is demonstrated by the measurement of the hygrothermal expansion (swelling) of a bisphenol-A based epoxy with novolac hardener and fused silica filler. Our technique is shown to have a higher sensitivity than most current thermomechanical analysis techniques and is readily amenable to humid conditions.
Compact simplified design of optical cell for single-molecule spectroscopy
Authors: Palm V.
Published: July 2002

A simplified modification of an optical assembly for single-molecule spectroscopy with the sample located at the joint focus of a parabolic mirror and a focusing lens is described. The optical cell fits a small helium cryostat with a 33 mm diam neck and can be used for experiments with thin films of frozen solutions as well as with other types of thin films. Described is the procedure of preadjustment of the position of a fixed focusing lens for work in different environments with the known index of refraction, such as superfluid liquid helium, helium gas, or vacuum; no adjustment of the lens during the experiment is required. A similar design of an optical cell could be used in a high-pressure cryostat with solid helium where the position of the lens cannot be adjusted. A signal-to-noise ratio of 15:1 was achieved for single-molecule spectra of terrylene in the Shpol’skii matrix n-decane.
A high pressure fiber-optic reactor with charge-coupled device array ultraviolet-visible spectrometer for monitoring chemical processes in supercritical fluids
Authors: Hunt Fred , Ohde Hiroyuki , Wai C.M.
Published: July 2002

A versatile spectroscopic reaction monitoring system for high-pressure liquids and supercritical fluids is described. The cell is designed to be attached to a charge-coupled device array ultraviolet-visible spectrometer via fiber optics, and has been shown to be capable of monitoring high speed reactions and rate of dissolution of a variety of compounds. The design is simple, inexpensive, rugged, and self-aligning. The cell has been tested up to 300 atm and 100 °C without failure.
A comparative study of emittance measurements using different techniques
Authors: Hamabe M. , Kuroda T. , Sasao M. , Nishiura M. , Wada M. , Guharay S. K.
Published: July 2002

The pepper-pot method and two slit-and-collector type techniques are tested for their applicability to measure the emittance of low energy ion beams. The exposure of Kapton foil, used here as the detector in the pepper-pot method, has been found to show a nonlinear behavior of the image contrast with the local power density of He+ beam for energy less than 10 keV. Therefore, the emittance measurement with the pepper-pot method must be made with the calibration of the contrast of the Kapton film in advance. The measured values of emittance, obtained by the different diagnostic schemes, are similar. From the view point of the negative ion beam measurement, the pepper-pot type system using Kapton film and the multislit-and-Faraday-cup system are proved to be promising.
Thomson scattering using an atomic notch filter
Authors: Bakker L. P. , Freriks J. M. , de Hoog F. J. , Kroesen G. M. W.
Published: July 2002

One of the biggest problems in performing Thomson scattering experiments in low-density plasmas is the very high stray light intensity in comparison with the Thomson scattering intensity. This problem is especially present in fluorescent lamps because of the proximity of the glass tube. We propose an atomic notch filter in combination with a dye laser and an amplified spontaneous emission (ASE) filter as a way of reducing this stray light level. The dye laser produces 589 nm radiation which is guided through the ASE filter that increases the spectral purity. The beam is then guided in the fluorescent lamp, where the Thomson scattering process takes place. The scattered light is collected and guided through a sodium vapor absorption cell, where the stray light is absorbed because it is resonant to the D2 transition of sodium. The spectral width of the Thomson scattering light is large enough to be transmitted through the absorption cell. In this way we only measure the Thomson scattering light.
Fast reciprocating probe assembly for the Hanbit magnetic mirror device
Authors: Bak J. G. , Lee S. G. , Hwang S. M. , Choi Y. S. , Chung K. S.
Published: July 2002

A fast reciprocating probe assembly (RPA), which can scan a long length up to 100 cm (with maximum velocity of 136 cm/s), is fabricated to measure basic plasma parameters during a plasma discharge time (∼500 ms) in the Hanbit magnetic mirror device. The probe driving mechanism consists of two steps of movements; first a slow movement to set the probe at a standby position, and then a fast one to measure plasma parameters within an adjustable time interval. Both movements are driven by only a pneumatic system. This is a distinctive feature of the probe drive system that has advantages of a simple driving mechanism and an easy adjustment of the fast stroke length for the wide range. The probe head is fabricated as a modular type for easy replacement. Performance test results and initial measurements from the fabricated RPA will be discussed.
Surface structure of homoepitaxial diamond (001) films, a scanning tunneling microscopy study
Authors: Kuang Yalei , Wang Yafei , Lee Naeson , Badzian Andrzej , Badzian Teresa , Tsong Tien T.
Published: July 2002

The surface structures of homoepitaxial diamond (001) films have been studied by using scanning tunneling microscopy. Boron-doped films were grown on natural diamond substrates. Images showed a dimer-type 2×1 reconstruction with well-resolved dimers. The surface consists of alternating terraces of 2×1 and 1×2 dimerization which are separated by single-layer steps with inequivalent step edges along 〈110〉 directions. Double-layer steps running parallel to dimer rows of the upper terraces were observed locally. We have also observed local 3×1 configurations, antiphase boundaries, and dimer vacancies, etc.
Enhancement of the response rate of internal reflection self-pumped phase conjugators with Ce- and Mn-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 crystals using intermittent light
Authors: Zhang Jingwen , Zhang Liangmin , Mu Xiaodong , Shao Zongshu , Chen Huanchu , Jiang Minhua
Published: July 2002

Dramatic enhancement of the response rate of internal reflection self-pumped phase conjugators with Ce- and Mn-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 crystals is observed with an intermittent laser beam as the pumping beam. Analysis that involves charge carrier migration driven by a photoinduced electric field is given.
Evaluation of the effective hole masses in pseudomorphic compressively strained GaxIn1−xAs/InP quantum wells
Authors: Rapp S. , Härle V. , Bolay H. , Hangleiter A. , Scholz F. , Limmer W. , Vasiliadou E. , Grambow P. , Weiss D.
Published: July 2002

The valance band structure of metalorganic vapor phase epitaxy (MOVPE) grown strained GaxIn1−xAs/InP single quantum well structures is experimentally verified by the determination of the effective in-plane hole masses. The masses are obtained by performing magnetotransport experiments. Mobilities up to 8700 cm2/V s for gallium content of x=0.3 were reached. The effective heavy hole masses of compressively strained GaInAs are drastically reduced compared to bulk material in excellent agreement to calculations using the k⋅p-perturbation theory, whereas the masses of the uppermost valence band of tensile strained material appear to be rather high. Consequently, no experimental determination was possible in the latter case. A precise analysis of the Shubnikov–de Haas oscillation patterns of compressively strained quantum wells shows a spin splitting of the uppermost heavy hole band, containing two different effective masses.
The bistability of the thermal donors in silicon
Authors: Hallberg T. , Lindström J. L.
Published: July 2002

The bistability of the two first thermal donors (TDs) in silicon has been studied by means of infrared (IR) spectroscopy. The two IR vibrational bands positioned at about 975 and 988 cm−1 which are due to TD1 and TD2, respectively, have been found to show bistable properties. It is shown that the low energy configurations of both TD1 and TD2 give rise to IR absorption, with a common vibrational band at about 1020 cm−1.
II–VI quantum confined Stark effect waveguide modulators
Authors: Thompson P. J. , Wang S. Y. , Horsburgh G. , Steele T. A. , Prior K. A. , Cavenett B. C.
Published: July 2002

Quantum confined Stark effect p-i-n waveguide modulators, grown on GaAs substrates by molecular beam epitaxy and using an undoped ZnSe/ZnCdSe multiquantum well structure as the guiding layer, have exhibited intensity modulation at wavelengths of 496 and 501 nm with extinction ratios of 6 and 4, respectively. These same devices have also demonstrated a transverse linear electro-optic effect observed as a superimposed secondary effect on the lateral intensity modulation at 514 nm in the form of phase modulation in the output of the same device. Intensity modulation has also been observed in quaternary laser waveguide structures, indicating that this is a device structure which is suitable for monolithic integration.
Resistivity reduction and chemical stabilization of organometallic chemical vapor deposited titanium nitride by nitrogen rf plasma
Authors: Danek M. , Liao M. , Tseng J. , Littau K. , Saigal D. , Zhang H. , Mosely R. , Eizenberg M.
Published: July 2002

In situ, nitrogen rf plasma treatment of organometallic chemical vapor deposited (OMCVD) TiN, synthesized by thermal decomposition of tetrakis(dimethylamido) titanium, yielded films with low resistivity and enhanced chemical stability. A sequential OMCVD-plasma treatment process allowed deposition of films with bulk resistivity as low as 400 μΩ cm. The nitridation resulted in reduction of the carbon concentration in the films, and crystallization of TiN. The composition and electrical properties of the nitridized films were found to be stable upon air exposure. The films possess excellent step coverage (≳70% in 0.35 μm device structures with aspect ratio ∼3) and low defect density (∼0.06 cm−2 for defect size ≥0.2 μm).
Selective deposition of polycrystalline silicon thin films at low temperature by hot-wire chemical vapor deposition
Authors: Yu S. , Gulari E. , Kanicki J.
Published: July 2002

Polycrystalline silicon thin films have been selectively deposited at a substrate temperature of 300 °C on molybdenum or silicon over silicon dioxide, silicon nitride or Corning 7059 glass substrates in a continuous hot-wire chemical vapor deposition (HWCVD) process involving hydrogen and disilane. Excellent selectivity is achieved on features as small as 1 μm spaced molybdenum lines. The deposition rate on molybdenum is 60–100 Å/min which is higher than that obtained by a pulsed gas plasma-enhanced chemical vapor deposition (PECVD) or a very high-frequency PECVD (VHF-PECVD). The selective deposition rate obtained in our system is attributed to the high concentration of atomic hydrogen generated when molecular hydrogen passes over a heated tungsten filament.
Time-resolved D-band luminescence in strain-relieved SiGe/Si
Authors: Fukatsu S. , Mera Y. , Inoue M. , Maeda K. , Akiyama H. , Sakaki H.
Published: July 2002

Temporal decay characteristics of dislocation-related luminescence bands (D1–D4) were explored in strain-relieved epitaxial SiGe/Si(100). Close similarity of the decay profiles was observed not only between D1 and D2 bands but also between D3 and D4 bands. The decay transients of the D1 and D2 bands at low temperatures are characterized by long decay times, τ≳200 ns, whereas the D3 and D4 bands exhibit even sharper transients with τ<60 ns. Temperature dependence of ‘‘radiative’’ lifetimes implies a free-to-bound nature of the D1 and D2 bands, while a bound-to-bound character of the luminescence origins for the D3, D4 bands.
All optical switching based on intensity induced absorption in C60
Authors: Henari Fryad Z. , Cazzini Karl H. , Weldon Declan N. , Blau Werner J.
Published: July 2002

In this letter, we demonstrate that the strong reverse saturation which has been observed at high intensity in a C60 solution, is also manifest at a low intensity. The behavior fits well to a rate equation model based on a six level system with known photophysical parameters. Furthermore, we demonstrate that it can be utilized to generate optical switching and bistability.
Bimolecular reactions of singlet excitons in tris(8-hydroxyquinoline) aluminum
Authors: Sokolik I. , Priestley R. , Walser A. D. , Dorsinville R. , Tang C. W.
Published: July 2002

We have studied singlet excited state dynamics in thin films of tris(8-hydroxyquinoline) aluminum (Alq3), a well known emitter for organic electroluminescent devices. Our experimental results show that bimolecular recombination dominates the singlet exciton decay in pristine films at high intensities, thus decreasing the photoluminescence quantum efficiency and the singlet lifetime. Because of the relatively low carrier concentration at which light emitting diodes operate the electroluminescence efficiency is not affected. The measured rate constant of singlet–singlet annihilation in Alq3 films is γss=(3.5±2.5)×10−11 cm3 s−1. The diffusion coefficient and the diffusion length of singlet excitons estimated from γss are Ds=(1.2±0.8)×10−5 cm2 s−1 and L=98±40 Å, respectively.
Target atomic number effect on the duration and conversion efficiency of ultrashort x-ray pulses
Authors: Pelletier J. F. , Chaker M. , Kieffer J. C.
Published: July 2002

High-density plasmas produced by 400 fs, 1018 W/cm2 laser pulses are characterized with a transmission grating spectrometer coupled to an x-ray streak camera. Conversion efficiencies and durations of the soft x-ray emission in the 0.1–1.2 keV energy range are analyzed for different target materials (Fe, Cu, Mo, Ta, and Pb). Our results show that the x-ray emission duration is constant for the different materials, with an average value of 4 and 5.7 ps in the 0.8–1.2 keV and 0.2–0.3 keV ranges, respectively. The converstion efficiency is optimal for a Ta target and is about 0.3% for both energy ranges.
Enhanced magnetoresistance in YBa2Cu3O7/Nd0.7Sr0.3MnO3 heterostructures using magnetic flux focusing
Authors: Dong Z. W. , Boettcher T. , Chen C-H. , Takeuchi I. , Rajeswari M. , Sharma R. P. , Venkatesan T.
Published: July 2002

Enhanced low field magnetoresistance (MR) in Nd0.7Sr0.3MnO3 (NSMO) has been achieved by using high-Tc superconducting flux focusing devices made of YBa2Cu3O7(YBCO)/NSMO heterostructures. Two kinds of flux focusing schemes, gap, and washer devices, have been used where an applied magnetic field is expelled from patterned YBCO pads and focused onto a bridge of NSMO film. Using such a magnetic lens, at temperatures below 77 K ∼800% enhancement in MR=−(RH−R0)/R0 was observed for different samples. This corresponds to more than 10% change in the MR of NSMO in the presence of 200 G. For the maximum MR response in NSMO, the YBCO/NSMO heterostructures were deposited on (100) LaAlO3 substrate by pulsed laser deposition in situ so that the peak resistance temperature (Tp) of NSMO was below the superconducting transition temperature (Tc) of YBCO.
Holographic storage and high background imaging using photorefractive multiple quantum wells
Authors: Jones R. , Hyde S. C. W. , Lynn M. J. , Barry N. P. , Dainty J. C. , French P. M. W. , Kwolek K. M. , Nolte D. D. , Melloch M. R.
Published: July 2002

We report holographic, real time, depth-resolved image acquisition, storage, and reconstruction in photorefractive GaAs/AlGaAs multiple quantum wells under high background radiation conditions. Reconstructed images of 50 μm transverse and depth resolution have been achieved using this device as a coherence gate to image through 9 mean free paths of turbid scattering medial
Electron field emission from diamond tips prepared by ion sputtering
Authors: Nützenadel Christoph , Küttel Olivier M. , Gröning Oliver , Schlapbach Louis
Published: July 2002

In this letter we report the field emission from cones etched into a synthetic-type IIb (100) oriented boron-doped diamond crystal. The cones were produced with an ion sputtering process. With a high-resolution scanning electron microscope we found the curvature radius at the end of the cones to be less than 10 nm. The length of these cones is in the range of 10 μm giving a field enhancement of approx. 1000. Field emission started at field strength of 2 V/μm, and at 3.8 V/μm 10 nA were measured using a spherical anode of 4 mm diam. From a Fowler-Nordheim fit the work function could be deduced to be 3–4 eV. Hence, electrons are emitted from the valence band.
Epitaxy-ready Si/SiO2 Bragg reflectors by multiple separation-by-implanted-oxygen
Authors: Ishikawa Yukari , Shibata N. , Fukatsu S.
Published: July 2002

A Si substrate purposely grown for Si-based optoelectronic applications is described in this letter. The structure contains a built-in Si/SiO2 Bragg reflector which is prepared by multiple separation-by-implanted-oxygen technique, where in situ low energy oxygen ion implantation is performed on molecular beam deposited Si to create alternating Si/SiO2 epitaxial bilayers. The quality of the top Si layer was confirmed to be epitaxy-ready after cross-sectional transmission electron microscopy. Maximum reflectance at near normal incidence was over 90% for bilayer periods of 4 to 5.
Resistance-expansion-temperature behavior of a disordered conductor–insulator composite
Authors: Heaney Michael B.
Published: July 2002

I have measured the resistance and linear expansion of a disordered carbon-black–polymer composite as a function of temperature from 25 to 180 °C. The sample resistance and thickness both increases monotonically as a function of temperature, with precipitous increases at the polymer melt temperature. The resistance versus thickness data show a monotonic increase with no precipitous changes at any point. These results suggest the electrical conduction mechanism is the same below, during, and above the polymer melt temperature. This casts doubt on some earlier models proposed to explain the resistance versus temperature behavior of these systems. These results also suggest a new approach to understanding the resistance versus temperature behavior by first developing a quantitative understanding of the resistance versus thickness behavior.
Solid-phase epitaxial growth of amorphized GaAs: The influence of macroscopic nonstoichiometry
Authors: Belay K. B. , Llewellyn D. J. , Ridgway M. C.
Published: July 2002

Defective recrystallization in the form of twins and stacking faults is characteristic of the solid-phase epitaxial growth (SPEG) of amorphized GaAs at temperatures ∼<400 °C. For the present report, the influence of macroscopic nonstoichiometry on defect formation has been investigated by comparing the SPEG of Ga- and/or As-implanted samples. The onset of twinning was independent of the chemical concentration of the implanted atom at the amorphous/crystalline interface, indicating that defective recrystallization was not the result of a limited availability of a given lattice constituent. Thereafter, a rapid amorphous-to-crystalline transformation was observed in the presence of excess Ga. In contrast, excess As had no significant effect on the recrystallization kinetics. Measurements derived from in situ transmission electron microscopy showed that the velocity of the amorphous/twinned interface was well correlated with the excess Ga concentration, the latter potentially in the form of molten precipitates. The rapid amorphous-to-crystalline transformation may thus be melt mediated although in addition nonstoichiometry could also result in a local increase in defect concentration particular to an enhanced twinned regrowth velocity.
Temporal evolution of soft x-ray pulse emitted from aluminum plasma produced by a pair of Ti:sapphire laser pulses
Authors: Nakano H. , Nishikawa T. , Ahn H. , Uesugi N.
Published: July 2002

The temporal and spectral evolution of soft x-ray pulses (40–100 Å) emitted from Al plasma produced by a pair of femtosecond Ti:sapphire laser pulses at normal incidence was studied. Both the soft x-ray emission and the pulse duration increased with increase in the scale length of the preformed plasma. Prepulse enhanced soft x-ray emission about 100 times with a pulse duration of 100–130 ps. A spectrally resolved time history revealed that the emission at shorter wavelengths started and decayed relatively more quickly, and emissions at longer wavelengths built up and decayed more slowly.
Geometrically enhanced magnetoresistance in ferromagnet–insulator–ferromagnet tunnel junctions
Authors: Moodera J. S. , Kinder L. R. , Nowak J. , LeClair P. , Meservey R.
Published: July 2002

Ferromagnetic–insulator–ferromagnetic trilayer tunnel junctions show magnetoresistance (JMR) effects of about 14% or greater at room temperature. Much larger values of the JMR (100% or more) are observed when the actual tunneling resistance (RT) is comparable to electrode film resistance (RL) over the junction area. This latter apparent JMR is an artifact of the nonuniform current flow over the junction in the cross geometry of the electrodes. The ferromagnetic films were CoFe and Co or Ni0.8Fe0.2, and the tunnel barrier was AlN or Al2O3. These junctions show nonvolatile memory effects. The geometrically enhanced large JMR in junctions can be effectively used as magnetic sensors and memory elements.
Electronic and structural properties of GaN grown by hydride vapor phase epitaxy
Authors: Götz W. , Romano L. T. , Krusor B. S. , Johnson N. M. , Molnar R. J.
Published: July 2002

The electronic and structural properties of GaN were investigated for heteroepitaxial layers grown by hydride vapor phase epitaxy. Uniform film nucleation on the sapphire substrates was facilitated by a GaCl pretreatment. The films were all unintentionally doped n type. Variable temperature Hall effect measurements reveal electron concentrations as low as 2×1017 cm−3 and electron mobilities as high as 460 cm2/V s at 300 K. The films exhibit bound exciton photoluminescence lines with a full width at half-maximum (FWHM) of 2.42 meV at 2 K. Transmission electron microscopy studies of the GaN/sapphire interface reveal a ∼200 nm thick, highly defective GaN layer consisting predominantly of stacking faults. The excellent quality of these GaN films is attributed to this ‘‘auto-buffer’’ layer which enables growth of GaN cells with a dislocation density of ∼3×108 cm−2 after ∼12 μm of film growth.
Molybdenum contamination in low-temperature epitaxial silicon films grown by remote plasma chemical vapor deposition
Authors: Sharma R. , Fretwell J. , Doris B. , Banerjee S.
Published: July 2002

Molybdenum is a material commonly used in ultrahigh vacuum silicon processing systems. This letter shows that even at temperatures as low as 500 °C, the presence of Mo in contact with silicon during processing can, under certain circumstances, lead to Mo contamination of the silicon. MOS capacitors were fabricated on epitaxial silicon films grown at ∼500 °C by remote plasma chemical vapor deposition. The wafers were mounted on metal pucks made of either molybdenum or steel during the epitaxial growth process. Capacitor results of the Mo puck-mounted wafers showed low minority carrier lifetimes and trapping ledges in the I–V plots, problems which were absent when steel pucks were used. Structural defects and plasma-induced sputtering were ruled out and secondary ion mass spectroscopy (SIMS) analysis verified the presence of Mo in the wafers, confirming that Mo contamination from the puck during epitaxial growth was responsible for the poor electrical results.
Formation and characteristics of Pb(Zr,Ti)O3 field-effect transistor with a SiO2 buffer layer
Authors: Yu Jun , Hong ZhaoJian , Zhou Wenli , Cao Guangjun , Xie Jifan , Li Xingjiao , Li Shaoping , Li Zhuang
Published: July 2002

Ferroelectric heterostructures of Au/Pb(Zr0.52Ti0.48)O3/SiO2/Si and Au/Pb(Zr0.52Ti0.48)O3/Si have been fabricated by using laser ablation technique. Electrical properties of these ferroelectric field-effect transistors have been characterized through both the current vs voltage and capacitance vs voltage (C–V) measurements. The C–V characteristics of Au/Pb(Zr0.52Ti0.48)O3/SiO2/Si heterostructures demonstrate a polarization switching behavior, showing a memory window as much as 1 V at 1 kHz. In addition, the experimental results reveal that a SiO2 buffer layer is essential for memory properties in the Au/Pb(Zr0.52Ti0.48)O3/SiO2/Si gate structure.
Energy distribution of field emitted electrons from diamond coated molybdenum tips
Authors: Schlesser R. , McClure M. T. , Choi W. B. , Hren J. J. , Sitar Z.
Published: July 2002

Field emission energy distribution (FEED) measurements were performed on Mo and diamond coated Mo tips under ultrahigh vacuum conditions to investigate the origin of field emitted electrons. Mo emitters were prepared by electrochemical etching and were subsequently coated with diamond powder by a dielectrophoretic procedure. Field emission energy spectra were taken on the same samples before and after diamond coating. In vacuo thermal annealing of coated samples was essential to obtain stable field emission. FEED data indicated that the field emission current originated from the diamond/vacuum interface, and that electrons were emitted from the conduction band minimum of diamond.
Compensating defects in heavily nitrogen-doped zinc selenide: A photoluminescence study
Authors: Moldovan M. , Setzler S. D. , Myers T. H. , Halliburton L. E. , Giles N. C.
Published: July 2002

Photoluminescence (PL) from a heavily nitrogen-doped ZnSe epilayer grown by molecular beam epitaxy was studied as a function of excitation wavelength, power density, and temperature. Also, the time decay of the PL emission was measured. Detailed analysis of the PL data indicates that the deep broad emission is composed of three distinct recombination processes, two are dominant at low power and a third can be detected at higher excitation power. These three bands are labeled NI, NII, and NIII with corresponding peak energies at 2.54, ∼2.58, and 2.65 eV. The NI band is accompanied by phonon replicas of energy 69±3 meV. The behaviors of the NI, NII, and NIII bands are consistent with intracenter recombination, donor–acceptor pair recombination, and electron–acceptor recombination, respectively.
Hole injection and transport in tris-(8-hydroxyquinolinato) aluminum
Authors: Lin L.-B. , Jenekhe S. A. , Young R. H. , Borsenberger P. M.
Published: July 2002

Time-resolved measurements of the passage of holes through thin layers of tris-(8-hydroxyquinolinato) aluminum (Alq) sandwiched between two hole-transporting layers give an effective mobility of order 10−6–10−5 cm2/V s, hole range of 10–30 Å, and effective activation energy of 0.12 eV. Phenomenological mobilities, hole ranges, and overall transmission probabilities through the Alq depend strongly on electric field strength and temperature. These hole injection and transport characteristics of Alq affect the behavior of electroluminescent devices based on these materials and, in particular, the location of the recombination zone.
Alternative approach to electroless Cu metallization of AlN by a nonaqueous polyol process
Authors: Chow G. M. , Kurihara L. K. , Ma D. , Feng C. R. , Schoen P. E. , Martinez-Miranda L. J.
Published: July 2002

Cu metallization of AlN substrates was performed using a nonaqueous, electroless, alcohol based approach known as the polyol method. The concentration of Cu2O in the film depended on the orientation of the substrates during deposition. This approach is very attractive for metallizing electronic substrates which are susceptible to hydrolytic degradation.