bluuebunny/crossref_metadata_2025 huggingface dataset:
Axial Dispersion Model for Upflow Anaerobic Sludge Blanket Reactors
Authors: Singhal Ashish , Gomes James , Praveen V. V. , Ramachandran K. B.
Published: July 2002

Fluid flow in UASB reactors is usually described by multicompartment models consisting of separate ideally mixed zones, plug flow zones, and stagnant zones linked with bypassing flows and back‐mixing flows. A closer look at UASB reactor behavior indicates that this complexity is unnecessary. Our study on the startup and steady‐state operation of a UASB reactor shows that its fluid flow can be explained just as well with a simple axial dispersion model. The physical transitions, which occur in different zones of the UASB reactor as the microorganisms acclimate to the wastewater, are adequately described by the model. Further, the number of parameters, which is six in standard UASB reactor models, is reduced to four in the case of the axial dispersion model.
3‐(3′‐Fluorenyl‐9′‐oxo)‐l‐alanine: a novel photoreactive conformationally constrained amino acid
Authors: Han Y. , Bisello A. , Nakamoto C. , Rosenblatt M. , Chorev M.
Published: July 2002

Abstract: Photoaffinity scanning of the ligand–G‐protein‐coupled receptor bimolecular interface is a direct approach to mapping the interactions of ligands and receptors. Such studies are an important first step toward generating an experimentally based model of the ligand–receptor complex. The synthesis and spectroscopic characterization of Boc‐3‐(3′‐fluorenyl‐9′‐oxo)‐l‐alanine and 9‐fluorenone‐3‐carboxylic acid are described. Incorporation of these two photophores into the parathyroid hormone (PTH) molecule yields potent agonists. These photoreactive analogs cross‐link specifically with the recombinant human PTH1 receptor stably expressed in human embryonic kidney cells. The availability of the 9‐fluorenone (a conformationally constrained derivative of benzophenone, the abundantly used photophore) for photoaffinity scanning provides an important tool to probe the effect of conformational flexibility of the photophore on the selection of the cross‐linking site in the macromolecular acceptor.
The nutritional value of indigenous fruits and vegetables in Sarawak
Authors: Voon Boon Hoe  , Kueh Hong Siong
Published: July 2002

The proximate composition including mineral and vitamin contents of 16 fruits and 46 vegetables (leaves, fruits, palm hearts and shoots) of indigenous origin in Sarawak are provided. Fruits like dabai (Canarium odontophyllum), kembayau (Dacryodes rostrata f. cuspidata), durian nyekak (Durio kutejensis) and durian kuning (Durio graveolens) are very nutritious with high values for energy, protein and potassium. Among the vegetables, the protein content of letup (Passiflora foetida), kepayang (Pangium edule) and tubu (Pycnarrhena tumetacta) is high, ranging from 6 to 7%. The range of nutrients among foods of indigenous origin are generally comparable with those of many cultivated species except for vitamin C, which is lower. Teh Kampung (Leucosyke capitellata) leaves are particularly high in magnesium (626 mg/100 g). Some of the indigenous vegetables contain antinutritional factors. Kepayang has very high levels of hydrogen cyanide (1834 μg/g on dry basis) but this poison can be completely evaporated by boiling. Indigenous fruits and vegetables which are pesticide residue free are important food sources for rural populations. Nutritious indigenous fruits and vegetables have the potential to be promoted for wider use, domestication and commercialization.
Baseline studies and preliminary resistance survey of Australian populations of cotton aphid Aphis gossypii Glover (Hemiptera: Aphididae)
Authors: Herron Grant , Powis Kevin , Rophail Jeanette
Published: July 2002

Cotton aphids, Aphis gossypii, may be more troublesome in transgenic (Ingard®) cotton, because an overall reduction in pesticide use in transgenic cotton for the control of pests such as Helicoverpa spp., gives reduced control of concurrent aphids. Additionally, coincidental cotton aphid in conventional cotton is being exposed to an increasing number of organophosphate insecticides targeted against Helicoverpa spp. Resultant insecticide sprays targeted specifically at cotton aphid, are likely to increase and must be managed to maintain insecticide susceptibility. As a first step to studying resistance in cotton aphid, two strains were collected from unsprayed sources and tested against 21 registered or experimental insecticides by laboratory bioassay, to establish baseline data for resistance monitoring. The LC99.9 of the more susceptible strain was used arbitrarily as a discriminating concentration to detect resistance in three populations of cotton aphid collected in cotton growing districts of New South Wales. In contrast to overseas studies, our results suggest that Australian cotton aphid was resistant to endosulfan and pyrethroids but not to carbamates or organophosphates.
Demonstration of high-performance silicon microchannel heat exchangers for laser diode array cooling
Authors: Mundinger D. , Beach R. , Benett W. , Solarz R. , Krupke W. , Staver R. , Tuckerman D.
Published: July 2002

A heat exchanger package has been demonstrated for semiconductor laser arrays using silicon microstructures with water as the coolant. A thermal impedance of 0.04 °C cm2/W has been achieved for a single linear bar. This design makes use of efficient, edge-emitting laser diode arrays in a rack and stack architecture combined with a high-performance silicon microchannel structure to allow cw operation. The architecture can be scaled to large areas and we project a thermal impedance of 0.09 °C cm2/W for close-packed two-dimensional arrays on this device.
Photodetachment effect in a radio frequency plasma in CF4
Authors: Jauberteau J. L. , Meeusen G. J. , Haverlag M. , Kroesen G. M. W. , de Hoog F. J.
Published: July 2002

Experiments to study negative ion densities have been carried out using the photodetachment effect in a rf plasma in CF4. Electrons are detached from the negative ions under the influence of the pulse of a Nd:YAG laser. The induced increase of the electron density is measured as a function of time using the shift of the resonance frequency of a microwave cavity containing the plasma. The negative ion density [F−] is found to be about (4±1)×1015 m−3, a factor 4±1 higher than the electron density.
Ideal hydrogen termination of the Si (111) surface
Authors: Higashi G. S. , Chabal Y. J. , Trucks G. W. , Raghavachari Krishnan
Published: July 2002

Aqueous HF etching of silicon surfaces results in the removal of the surface oxide and leaves behind silicon surfaces terminated by atomic hydrogen. The effect of varying the solution pH on the surface structure is studied by measuring the SiH stretch vibrations with infrared absorption spectroscopy. Basic solutions ( pH=9–10) produce ideally terminated Si(111) surfaces with silicon monohydride ( 3/4 SiH) oriented normal to the surface. The surface is found to be very homogeneous with low defect density (<0.5%) and narrow vibrational linewidth (0.95 cm−1 ).
Dynamic measurements of film thickness over local topography in spin coating
Authors: Manske L. M. , Graves D. B. , Oldham W. G.
Published: July 2002

A technique is presented for making real-time, in situ measurements of film thickness profiles over local topography during spin coating. A laser is pulsed synchronously with the rotation of a spinning wafer to illuminate a microscope focused on a local feature being coated on the wafer. Interference fringes are captured photographically to allow observation of film thickness contours from initial spin-up to the final dried film. With this method we can observe the influcence of flow direction and microscopic feature shape and orientation on film profiles during the spinning and drying processes in spin coating.
Fluorinated thin SiO2 grown by rapid thermal processing
Authors: Ting W. , Lo G. Q. , Hsieh T. Y. , Kwong D. L. , Kuehne John , Magee Charles W.
Published: July 2002

High quality ultrathin fluorinated gate oxides have been grown for the first time by rapid thermal processing in diluted NF3 and O2. The chemical and electrical properties of fluorinated oxides have been studied as a function of growth conditions.
Unusually low resistivity of copper germanide thin films formed at low temperatures
Authors: Krusin-Elbaum L. , Aboelfotoh M. O.
Published: July 2002

We report a first observation of the remarkably low electrical resistivity of copper germanide thin films formed at temperatures below 200 °C. At these low temperatures, the ε-Cu3Ge phase with a monoclinic crystal structure is formed, with room-temperature resistivity which can be as low as 5.5 μΩ cm. The films are electrically stable up to at least 600 °C, and, unlike pure copper, are also stable against oxygen and air exposure.
Surface-emitting laser operation in vertical-to-surface transmission electrophotonic devices with a vertical cavity
Authors: Numai T. , Sugimoto M. , Ogura I. , Kosaka H. , Kasahara K.
Published: July 2002

We demonstrate the first surface-emitting laser operation in a vertical-to-surface transmission electrophotonic device with a vertical cavity. The thyristor-like current-voltage characteristics, which are required for optical and electrical switching, are achieved. Threshold current during the on state is as low as 1.2 mA. All 100 devices, which were randomly extracted from a grown wafer, emit laser light.
In situ growth of Y1Ba2Cu3O7−x superconducting thin films using a pulsed neodymium:yttrium aluminum garnet laser with CO2 laser heated substrates
Authors: Wu K. H. , Lee C. L. , Juang J. Y. , Uen T. M. , Gou Y. S.
Published: July 2002

By replacing the resistive heater with a CO2 laser to heat the substrates together with concentered oxygen stream blowing onto the substrate during deposition, high quality Y1Ba2Cu3O7−x thin films with nearly perfect c-axis orientation and Tc0=87 K were grown in situ without subsequent slow cooling in oxygen atmosphere or any further heat treatment. The rapid quenching, from typically 600 °C to room temperature in less than 50 s of the as-deposited films, excludes the possibility of further oxygen incorporation during the cooling process and indicates that the in situ growth may have completed during deposition under proper deposition conditions.
Interface morphology in molecular beam epitaxy grown In0.5Ga0.5As/GaAs strained heterostructures
Authors: Wang S. M. , Andersson T. G. , Ekenstedt M. J.
Published: July 2002

Interface morphology of strained In0.5Ga0.5As/GaAs wells grown by molecular beam epitaxy from 470 to 570 °C has been examined by photoluminescence at 77 K. Transition from the two-dimensional to three-dimensional (3D) growth was observed after a critical layer thickness, which largely depended on the growth temperature and was far ahead of the formation of misfit dislocations. Luminescence from the layer after the start of 3D growth had a high quantum efficiency but was rather broad or even split. The 3D growth started at nine monolayers for 470 °C and four monolayers for 540 °C. The reason for the onset of 3D growth is discussed in terms of In segregation.
Pressure-assisted zinc bonding of microcrystalline Sm2Fe17Nx powders
Authors: Kuhrt C. , O’Donnell K. , Katter M. , Wecker J. , Schnitzke K. , Schultz L.
Published: July 2002

Highly coercive isotropic magnets were prepared by pressure-assisted Zn bonding of microcrystalline Sm2Fe17Nx powders. Mechanically alloyed and two-step heat treated powder was mixed with elemental Zn powder and compacted by uniaxial pressing at elevated temperatures. The maximum room-temperature coercivity of such magnets was 34.7 kA/cm (43.6 kOe), which represents an increase by about 50% relative to that of the starting powder. The density was about 80% of the theoretical value resulting in a relatively low remanence of 0.4 T. This was achieved after compaction using parameters optimized with respect to coercivity, i.e., a Zn content of 20 wt. % (referred to the 2:17:N weight), a temperature of 425 °C and a pressure of 270 MPa. The coercivity increase induced by compaction with Zn presumably originates from improved magnetic decoupling of the 2:17:N grains which is caused by the paramagnetic Fe3Zn7 phase formed at the grain boundaries within the powder particles.
Piezoresistivity in vapor-deposited diamond films
Authors: Aslam M. , Taher I. , Masood A. , Tamor M. A. , Potter T. J.
Published: July 2002

We report the observation of a very large piezoresistive effect in both polycrystalline and homoepitaxial chemical-vapor-deposited diamond films. The gauge factor for polycrystalline p-type diamond at 500 microstrains was found to be only 6 at room ambient, but increased rapidly with temperature, exceeding that of polycrystalline silicon (30) at 35 °C, and that of single-crystal Si (120) at 50 °C. For strain and current flow in the [100] direction, the gauge factor of a (100)-oriented homoepitaxial diamond film was found to be at least 550 at room temperature. Although the origins and unexpected temperature dependence of piezoresistive effect in diamond are not yet understood, these findings may suggest diamond-based sensors with performance significantly superior to that of their Si counterparts.
Annealing effects on heavily carbon-doped GaAs
Authors: Han W. Y. , Lu Y. , Lee H. S. , Cole M. W. , Schauer S. N. , Moerkirk R. P. , Jones K. A. , Yang L. W.
Published: July 2002

The hole concentrations and lattice mismatch with the GaAs substrate of heavily carbon-doped epilayers (4.7×1019 and 9.8×1019 cm−3) were increased and the mobilities were decreased as compared with the as-grown samples by rapid thermal annealing silicon nitride capped samples at temperatures from 500 to 900 °C. However, for the more heavily doped sample, the hole concentration, mobility, and lattice mismatch decreased with increasing annealing temperature for annealing temperatures higher than 700 °C, but the hole concentration and lattice mismatch were still larger than those of the as-grown samples. Secondary ion mass spectroscopy results showed that annealing produced no change in the C concentration or distribution, but the hydrogen concentration decreased. Cross-sectional transmission electron microscopy indicated that no mismatch dislocations formed at the interface.
High-power strained-layer InGaAs/AlGaAs tapered traveling wave amplifier
Authors: Walpole J. N. , Kintzer E. S. , Chinn S. R. , Wang C. A. , Missaggia L. J.
Published: July 2002

High power, nearly diffraction-limited cw performance has been obtained from a traveling wave amplifier, fabricated in a strained-layer InGaAs/AlGaAs laser structure, with a laterally tapered gain region and with a cavity-spoiling feature to prevent laser oscillation. The input beam diffracts as it propagates, efficiently filling the tapered active region. For input optical power of 85 mW from a Ti:sapphire laser, total cw output of 1.44 W has been achieved with 1.28 W in a central lobe with width less than 1.2 times the diffraction limit at 977 nm wavelength. Only 15 mW of power incident on the amplifier was sufficient to provide 1 W output into the central lobe.
Nonlinearity in the excitation yield of ZnS:Mn electroluminescent devices
Authors: Geoffroy A. , Bringuier E.
Published: July 2002

Measurements of the excitation yield of ZnS:Mn electroluminescent devices are reported over a Mn concentration range of 0.2,...,1.1 mol %. They show a continuous increase in nonlinearity as the concentration is increased. This is attributed to the field dependence of the hot-electron impact efficiency and to the dependence of the nonuniform field profile on Mn content. This is directly relevant to the light-emitting performance of the devices.
Deposition of polytetrafluoroethylene films by laser ablation
Authors: Blanchet Graciela B. , Shah S. Ismat
Published: July 2002

Films of polytetrafluoroethylene (PTFE) were deposited by laser ablation using the fourth harmonic, at 266 nm, of a Nd-YAG laser. The films are found to be stoichiometric with the correct optical properties. We suggest that UV absorption onsets the pyrolitic decomposition of PTFE leading to a monomer that subsequently repolymerizes onto a substrate.
Extremely smooth YBa2Cu3Oy thin films grown using the reactive coevaporation technique in radical oxygen at an ultralow growth rate
Authors: Tazoh Yasuo , Miyazawa Shintaro
Published: July 2002

The effect of using drastically reduced growth rates on the surface morphology of YBa2Cu3Oy (YBCO) thin films grown on lattice-matched (110) NdGaO3 substrates using the reactive coevaporation technique in a radical oxygen atmosphere is reported. The surface of films grown at an ultralow growth rate (∼0.0065 nm/s) appears to be very smooth without any precipitates, holes, crevasses, or pits. The film surface roughness is on the order of the unit-cell constant of superconducting YBCO, about 1.2 nm. This shows that decreasing the growth rate enhances the lateral spreading of nucleated islands, with a height of one unit cell, in the Stranski–Krastanov growth mode [Ber. Akad. Wiss, Wien 146, 797 (1938)].
Effect of band structure on etch-stop layers in the photoelectrochemical etching of GaAs/AlGaAs semiconductor structures
Authors: Khare R. , Young D. B. , Snider G. L. , Hu E. L.
Published: July 2002

We have examined the limitations on selectivity of thin dopant-selective and band-gap-selective etch-stop layers in the photoelectrochemical (PEC) etch process. The ultimate selectivity of one layer from an underlying layer is affected not only by differences in material composition, but also by the sequencing of the layers within the structure which will determine the distribution of the photogenerated carriers. Three semiconductor structures with variations in both doping and band gap were etched to demonstrate this effect. A He-Ne laser (633 nm) and a tunable Ti/sapphire laser (690–830 nm) were used as light sources and a (1:20) HCl:H2O solution was the electrolyte.
Low resistance ohmic contacts on wide band-gap GaN
Authors: Lin M. E. , Ma Z. , Huang F. Y. , Fan Z. F. , Allen L. H. , Morkoç H.
Published: July 2002

We report a new metallization process for achieving low resistance ohmic contacts to molecular beam epitaxy grown n-GaN (∼1017 cm−3) using an Al/Ti bilayer metallization scheme. Four different thin-film contact metallizations were compared during the investigation, including Au, Al, Ti/Au, and Ti/Al layers. The metals were first deposited via conventional electron-beam evaporation onto the GaN substrate, and then thermally annealed in a temperature range from 500 to 900 °C in a N2 ambient using rapid thermal annealing techniques. The lowest value for the specific contact resistivity of 8×10−6 Ω cm2, was obtained using Ti/Al metallization with anneals of 900 °C for 30 s. X-ray diffraction and Auger electron spectroscopy depth profile were employed to investigate the metallurgy of contact formation.
Incommensuration in La-modified antiferroelectric lead zirconate titanate ceramics
Authors: Xu Z. , Dai Xunhu , Viehland Dwight
Published: July 2002

Lanthanum-modified lead zirconate titanate (PLZT) specimens with a La content of 2 at. % and a Zr/Ti ratio of 95/5 (PLZT 2/95/5) have been investigated by dielectric spectroscopy, Sawyer–Tower polarization (P-E) measurements, and hot-stage transmission electron microscopy (TEM). La ‘‘impurities’’ have been found to induce a 1/x〈110〉 incommensurate antiferroelectric structure at about 210 °C from a ferroelectric structure when cooled from above. The incommensurate structure was found to be stable below this temperature of the dielectric maximum, evolving slowly with decreasing temperature towards the commensurate antiferroelectric orthorhombic PZ structure. The incommensuration is believed to arise due to a competition between ‘‘broken’’ dipolar (ferroelectric) and sublattice (antiferroelectric) interactions. The ‘‘dirty’’ antiferroelectric Pb-based system may be the first example of a proper incommensurately displacively modulated ferroelectric-type material.
Construction and performance of the Princeton precision solenoid
Authors: Dewey M. S. , Dunford R. W.
Published: July 2002

We have assembled a water-cooled iron-free copper solenoid whose central magnetic field is constant to within one part in 105 over a region 1 cm in diameter extending 12 cm along the axis of the magnet. The solenoid operates without the use of shim coils or current shunts. It achieves a central field of 15.7 kG for a current of 1150 A. In this article, we report on features incorporated in the design of the solenoid and the methods of field shaping used to obtain a very uniform central field region. The use in our design of multiple current elements has the advantage that it allows for great flexibility in obtaining a desired field shape. We describe in detail the method used to arrive at an initial guess for the optimal positioning of the coils as well as an iterative corrective procedure involving sequences of measurement, calculation, and adjustment that can be used subsequently to zero errors in the field shape. These general methods are easy to implement on a computer, yet they are powerful and appear to converge rapidly.
Improved method for measuring the electric fields in microwave cavity resonators
Authors: Amato J. C. , Herrmann H.
Published: July 2002

The electric field distribution in microwave cavities is commonly measured by frequency perturbation techniques. For many cavity modes which are important in accelerator applications, the standard bead-pulling technique cannot provide adequate discrimination between fields parallel and perpendicular to the particle trajectory, leading to inaccurate and ambiguous results. A method is described which substantially increases the directivity of the measurements. The method has been successfully used to determine the accelerator-related cavity parameters at frequencies up to three times the fundamental resonant frequency.
New method for measuring ion temperatures in hot D–T plasma
Authors: Smither Robert K. , Greenwood Lawrence R. , Hendel Hans
Published: July 2002

A new method has been found to measure the ion temperature of a hot D–T plasma. The new method makes use of two new neutron dosimetry reactions, 54Fe(n,2n)53Fe and 27Al(n,2n)26Al. What makes these reactions special is that their threshold energies are quite close to the centroid of the energy distribution of the neutrons emitted from a D–T plasma. This makes their reaction yields sensitive to only the upper half of the neutron energy distribution and therefore sensitive to both changes in the centroid and the width of the neutron energy distribution. The sensitivity to the width of the neutron energy distribution allows one to measure the ion temperature. If the plasma is in thermal equilibrium the ion temperature can be calculated from the ratio of the yields of the 54Fe(n,2n)53Fe reaction to the 27Al(n, p)27Mg reaction or a similar nonsensitive reaction. No absolute measurements are needed. Using both of the new dosimetry reactions the asymmetry of the neutron energy distribution for nonequilibrium conditions (neutral beams) can be measured. The 54Fe(n,2n)53Fe reaction is sensitive enough to monitor a single shot in TFTR.
Scanning tunneling microscope combined with a scanning electron microscope
Authors: Gerber Ch. , Binnig G. , Fuchs H. , Marti O. , Rohrer H.
Published: July 2002

We have developed a small scanning tunneling microscope (STM) to be incorporated into a scanning electron microscope (SEM). Vibration isolation and damping is achieved solely with Viton dampers. As a stand-alone unit, a tunnel-gap stability of about 1 Å is reached at atmospheric air pressure without additional sound protection. Stability improves by at least an order of magnitude when incorporated into a SEM.
Carbon nanotubes synthesized in a hydrogen arc discharge
Authors: Wang X. K. , Lin X. W. , Dravid V. P. , Ketterson J. B. , Chang R. P. H.
Published: July 2002

We have developed a novel method to synthesize ‘‘clean’’ carbon nanotubes with relatively higher yield using a hydrogen arc discharge. The quality and yield of the tubes depend sensitively on the gas pressure in the arc discharge. We have observed sharp, open-ended nanotubes with clear lattice fringes at the edges and empty interiors. The existence of these frozen-open-ended tubes in the buckybundles provides evidence for an open-ended growth model for nanotubes.
Broadband cryogenic preamplifiers incorporating GaAs MESFETs for use with low-temperature particle detectors
Authors: Lee Adrian T.
Published: July 2002

Two voltage-sensitive preamplifier designs are presented for operation at 1.6 K. Both designs incorporate GaAs MESFETs (Plessy P35-1101). The first design has two stages including a common-source gain stage and a source follower stage. The noise performance, particularly with the low-frequency noise, was found to improve with cooling. The white-noise level at low temperature is 1 nV/Hz1/2, and the low-frequency noise corner occurs at approximately 1 MHz. The voltage gain into 50 Ω is 7.0 dB, with the −3-dB point occuring at 10 MHz. The noise of the first stage was found to dominate the total noise at the output of a low-noise room-temperature post amplifier. The output impedance of the preamplifier is 50 Ω. The second design incorporates one cold FET, dissipating 1 mW, in cascode with a room-temperature bipolar transistor. The noise of this design was found to be approximately equal to that of the two-cold-stage design except for a bulge in the voltage noise centered at 13 MHz due to impedance mismatching of the line to room temperature. The gain of this design is 21 dB, with the −3-dB point at 2 MHz. Cryogenic semiconductor operation is discussed, design parameters of the two preamplifiers are discussed in detail, noise measurements are presented along with a discussion of the different temperature- and bias-dependent noise sources, and an analysis of the signal-to-noise ratio and rise time for the present detection scheme is made.
A differential interferometer for force microscopy
Authors: Schönenberger C. , Alvarado S. F.
Published: July 2002

We present a polarizing optical interferometer especially developed for force microscopy. The deflections of the force-sensing cantilever are measured by means of the phase shift of two orthogonally polarized light beams, both reflected off the cantilever. This arrangement minimizes perturbations arising from fluctuations of the optical path length. Since the measured quantity is normalized versus the reflected intensity, the system is less sensitive to intensity fluctuations of the light source. The device is especially well suited to static force measurements. The total rms noise measured is ≲0.01 Å in a frequency range from 1 Hz to 20 kHz.
Organic electroluminescent devices fabricated using a diamine doped MgF2 thin film as a hole-transporting layer
Authors: Tokito Shizuo , Taga Yasunori
Published: July 2002

Organic electroluminescent (EL) devices have been fabricated which have a MgF2 layer doped with N, N′-diphenyl-N, N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4, 4′-diamine (TPD) as the hole- transporting layer, and the emitting layer of tris-(8-hydroxyquinoline) aluminum (Alq). For the organic EL devices, bright green emission with 2600 cd/m2 is observed at a voltage of 15 V. The luminous efficiency is about 0.3 lm/W at a current density of 100 mA/cm2. This high efficiency indicates that the diamine doped MgF2 layer plays the role of hole transport and confinement of electrons in the emitting layer. It is also found that the thermal stability of the organic EL device is higher than that of the conventional organic EL device.
Simple, safe, and economical microwave plasma-assisted chemical vapor deposition facility
Authors: Brewer M. A. , Brown I. G. , Dickinson M. R. , Galvin J. E. , MacGill R. A. , Salvadori M. C.
Published: July 2002

A simple and economical microwave plasma-assisted chemical vapor deposition facility has been developed and used for synthesis of diamond thin films. The system is similar to those developed by others but includes several unique features that make it particularly economical and safe, yet capable of producing high quality diamond films. A 2.45-GHz magnetron from a commercial microwave oven is used as the microwave power source. A conventional mixture of 0.2% methane in hydrogen is ionized in a bell jar reaction chamber located within a simple microwave cavity. By using a small hydrogen reservoir adjacent to the gas supply, an empty hydrogen tank can be replaced without interrupting film synthesis or causing any drift in plasma characteristics. Hence films can be deposited continuously for arbitrarily long periods while storing only a 24-h supply of explosive gases. System interlocks provide safe start-up and shut-down and allow unsupervised operation. Here we describe the electrical, microwave, and mechanical aspects of the system, and summarize the performance of the facility as used to reproducibly synthesize high quality diamond thin films.
Green luminescence from copper doped zinc sulphide quantum particles
Authors: Khosravi Ali Azam , Kundu Manisha , Jatwa Lalita , Deshpande S. K. , Bhagwat U. A. , Sastry Murali , Kulkarni S. K.
Published: July 2002

Free-standing powder of zinc sulphide quantum particles has been synthesized using a chemical route. X-ray diffraction analysis shows that the diameter of the particles is ∼21±2 Å which is smaller than the Bohr exciton diameter for zinc sulphide. UV absorption shows an excitonic peak centered at ∼300 nm corresponding to an energy gap of 4.1±0.1 eV. These particles show a luminescence band at ∼424 nm. The quantum particles could be doped with copper during synthesis without altering the UV absorption or x-ray diffraction pattern. However, doping shifted the luminescence to 480 nm, green wavelength in the visible region.
Oscillatory deep channel interfacial rheometer
Authors: Nagarajan R. , Wasan D. T.
Published: July 2002

An interfacial rheometer to measure the dynamic response of a liquid–liquid interface subjected to a small amplitude oscillatory shear stress is described. Experiments are conducted in a deep channel rheometer fitted with an oscillatory floor. This instrument is used to examine the rheological behavior of interfaces in the presence of surfactants. Rheological parameters are calculated from a hydrodynamic analysis incorporating interfacial rheological models. It is demonstrated here that an adsorbed layer of macromolecular surfactants at an oil–water interface is viscoelastic even though the adjacent phases are Newtonian.
Design review of an instrument for spectroscopic total integrated light scattering measurements in the visible wavelength region
Authors: Rönnow Daniel , Veszelei Eugen
Published: July 2002

A spectroscopic total integrated scattering instrument, which uses a focusing sphere and a broadband light source, has been constructed. It records total reflectance and transmittance spectroscopically, in the wavelength region 400–1000 nm. Diffuse reflectance and transmittance values below 10−4 can be registered. These measurements require low scattering optical components and low noise electronics. Design details are given about the detection system, particularly the low noise preamplifier. The purpose of the instrument is to measure diffuse reflectance and transmittance spectra of interference coatings. Such spectra can give information about the amplitude of the roughness of the interfaces and reveal if the interfaces are topographically correlated or uncorrelated. Examples of spectra in both reflectance and transmittance mode are given.
Characterization of piezoceramic crosses with large range scanning capability and applications for low temperature scanning tunneling microscopy
Authors: Helfrich J. A. , Adenwalla S. , Ketterson J. B. , Zhitomirsky G. A.
Published: July 2002

We have developed a large amplitude piezoceramic scanner which should have numerous applications. Scanning tunneling microscopy (STM) and other scanning probe microscopies predominantly use piezoceramics for the scanning elements. Similarly adaptive optics, high resolution lithography, and micromanipulators are other examples of research which regularly utilize piezoceramic scanners. We present a new geometry for a piezoceramic scanner which allows for both high resolution (∼nanometers) and large amplitude (∼400 μm) displacements. The cross-shaped geometry makes it possible to produce extremely long pieces with very high tolerances. We have shown its effectiveness by using it as the major component of a low temperature STM (LTSTM). This LTSTM is unique in two distinct ways: the scan range at low temperature is a factor of 10 larger than those reported and the coarse, approach mechanism is a single component piezoceramic—making coarse approach in situ much quieter and easier than in other designs.
High throughput screening by multichannel glass fiber fluorimetry
Authors: Schober Andreas , Günther Rolf , Tangen Uwe , Goldmann Gaby , Ederhof Tobias , Koltermann Andre , Wienecke Anja , Schwienhorst Andreas , Eigen Manfred
Published: July 2002

As a tool for screening large numbers of biological samples by means of amplification (e.g., Qβ or PCR) we have constructed a thermocycler that includes optionally a 96-channel or 960-channel glass fiber fluorimeter (combined with a cooled charge-coupled-device camera). We briefly describe the system integration of all components like liquid handling, thermostats, an x,y,z robot arm, and the glass fiber fluorimeter. The integrated glass fiber fluorimeter allows sensitive on-line measurements in 960 channels within 5 s. Two different screening procedures were carried out. In a first experiment PCR reactions were done in the presence of the known PCR inhibitor hematin and its suppressor transferrin. The system was used to titrate the suppressor with the inhibitor hematin in order to determine the maximum inhibitor concentration tolerated at a given suppressor concentration. We processed 96 PCR samples in parallel with 11 different concentration steps. In a second experiment the 960-channel glass fiber fluorimeter was used to monitor on line the amplification of the Qβ system in the presence or absence of an inhibitor (heparin). Since the doubling time of Qβ RNA variants is about 20 s, on-line detection is crucial for the experimental setup. The evolution of new RNA species adapted to high inhibitor concentrations could be proved by comparison of the fluorimetric signal and electrophoresis.
Reflectometry on ITER
Authors: Vayakis G. , Bretz N. , Doyle E. , Vershkov V. A. , Donné A. J. H. , Irby J. , Manso M. E. , Mase A. , Sanchez J. , Shevchenko V. F. , Walker C. I. ,   ITER Joint Central Team and Home Teams
Published: July 2002

Reflectometry will be used on ITER to measure the density profile in the main plasma and divertor regions, and to measure the plasma position and shape in order to provide a standby reference for the magnetic diagnostics in long pulse discharges. The high temperatures of the ITER core and the resultant significant relativistic downshift of the second-harmonic electron cyclotron absorption imply that both low-field side O-mode and high-field side lower cut-off (X−l mode) systems are required to access the full plasma profile. A low-field side upper cut-off (X−u mode) system will also be required for measurements of the scrape-off layer. For measurements of the plasma position and shape, an O-mode system is optimum due to the large range of magnetic field along the plasma periphery and the wide range of possible plasma configurations achievable on ITER. A robust real-time calibration technique of the whole transmission line is required. It is likely that an accurate estimate of the position of the plasma will require the simultaneous use of signals from the profile reflectometer. For the divertor, profiles with peak densities in the range 1019–1022/m3 are to be measured with a target resolution of 3 mm. The large density range will necessitate the use of more than one system. Installing these reflectometers on ITER incurs additional difficulties such as the routing of the millimetre wave radiation around the complicated first wall and divertor structures and design of antennas able to operate through the first wall and blanket.
Computational studies on primary electron orbits in an ion source
Authors: Kashiwagi Mieko , Ido Shunji
Published: July 2002

The three-dimensional particle orbit simulation is carried out to analyze the plasma generation in a bucket-type ion source. The characteristics of ion source plasma is analyzed when the filament current is changed. When the filament current is increased, the electron is trapped by the magnetic field made by a filament current, and makes less contribution to the plasma discharge. In this study, the filament configurations are studied in viewpoints of efficiency of discharge, where electron emission is examined by tracing electron orbits from and near the filaments. The uniformity of plasma distribution is also studied due to the filament configuration and current.
Ion sources for medical accelerators
Authors: Barletta W. A. , Chu W. T. , Leung K. N.
Published: July 2002

Advanced injector systems for proton synchrotrons and accelerator-based boron neutron capture therapy systems are being developed at the Lawrence Berkeley National Laboratory. Multicusp ion sources, particularly those driven by radio frequency, have been tested for these applications. The use of a radio frequency induction discharge provides clean, reliable, and long-life source operation. It has been demonstrated that the multicusp ion source can provide good-quality positive hydrogen ion beams with a monatomic ion fraction higher than 90%. The extractable ion current densities from this type of source can meet the injector requirements for both proton synchrotron and accelerator-based boron neutron capture therapy projects.
Comparison of one-photon and two-photon effects in the photosensitivity of germanium-doped silica optical fibers exposed to intense ArF excimer laser pulses
Authors: Albert J. , Malo B. , Hill K. O. , Bilodeau F. , Johnson D. C. , Thériault S.
Published: July 2002

The growth rate of fiber Bragg gratings written using 193 nm light from an ArF excimer laser is linearly proportional to the laser pulse energy density for fibers with high germanium doping but proportional to the square of the pulse energy density for standard telecommunications fibers with low germanium concentration. The two-photon process in standard fibers yields refractive index increases that saturate around 10−3, an order of magnitude improvement over previous results in this type of fiber without sensitization treatment. The two types of photoinduced refractive index gratings have comparable thermal stability and preserve about 50% of their initial magnitude after 30 min at 600 °C.
Radio-frequency impedance measurements using a tunnel-diode oscillator technique
Authors: Srikanth H. , Wiggins J. , Rees H.
Published: July 2002

A resonant method based on a tunnel-diode oscillator for precision measurements of relative impedance changes in materials is described. The system consists of an effective self-resonant LC tank circuit driven by a forward-biased tunnel diode operating in its negative resistance region. Samples under investigation are placed in the core of an inductive coil and impedance changes are determined directly from the measured shift in resonance frequency. A customized low temperature insert is used to integrate this experiment with a commercial Model 6000 Physical Property Measurement System (Quantum Design). Test measurements on a manganese-based perovskite sample exhibiting colossal magnetoresistance indicate that this method is well suited to study the magnetoimpedance in these materials.
A low temperature ultrahigh vaccum scanning force microscope
Authors: Hug Hans J. , Stiefel B. , van Schendel P. J. A. , Moser A. , Martin S. , Güntherodt H.-J.
Published: July 2002

This article describes the design of a versatile ultrahigh vaccum (UHV) low temperature scanning force microscope system. The system allows scanning probe microscopy measurements at temperatures between 6 and 400 K and in magnetic fields up to 7 T. Cantilevers and samples can be prepared in UHV and transferred to the microscope. We describe some technical details of our system and present first measurements performed at different temperatures and in various scanning force microscopy operation modes. We demonstrate distortion free and calibrated images at temperatures ranging from 8 to 300 K, atomic resolution on NaCl at 7.6 K and various magnetic force microscopy images of vortices in high transition temperature superconductors. It is demonstrated that our instrumentation reaches the thermodynamically determined sensitivity limit. Using standard cantilevers force gradients in the 10−6N/m range, corresponding forces of about 10−15N can be measured.
Ultrafast electro-optic field sensors
Authors: Wu Q. , Zhang X.-C.
Published: July 2002

We report our recent study of ultrafast electro-optic field sensors for the coherent measurement of freely propagating subpicosecond pulsed electromagnetic waves (THz beams). The sensitivity and bandwidth of these electro-optic sensors are comparable with the conventional ultrafast photoconductive dipole antennas. The simplicity of the detection geometry and capability of optical parallel processing make these sensors suitable for real-time 2D subpicosecond far-infrared imaging.
Surface enhanced Raman imaging of a patterned self-assembled monolayer formed by microcontact printing on a silver film
Authors: Yang X. M. , Tryk D. A. , Hasimoto K. , Fujishima A.
Published: July 2002

The surface enhanced Raman scattering effect was used in conjunction with a micro-Raman system to produce an image of a pattern, on an evaporated silver surface, formed by microcontact printing of p-nitrothiophenol (PNTP). This surface is characterized by roughness on the scale of 50–100 nm. It was confirmed that this type of printing technique forms a self-assembled monolayer with PNTP. Even without roughening of the silver surface, the surface enhancement provided a high contrast image. The resolution of the resulting image was approximately 1 μm.
Field emission from nanotube bundle emitters at low fields
Authors: Wang Q. H. , Corrigan T. D. , Dai J. Y. , Chang R. P. H. , Krauss A. R.
Published: July 2002

The fabrication of nanotube field emitters with an onset field as low as 0.8 V/μm is described and the low-field electron emission mechanism is discussed. These emitters are made using nanotube cathode deposit with the addition of epoxy resin. The preferred orientation of nanotubes in nanotube bundles of the deposit is preserved. The nanotube tips are sharpened by exposing the nanotube bundle surface to a microwave oxygen plasma. The local-field enhancement factor is estimated to be 8000 by using the Fowler–Nordheim equation. The low onset field is attributed to the well-distributed, highly orientated sharp tips at the sample surface.
Optical modes within III-nitride multiple quantum well microdisk cavities
Authors: Mair R. A. , Zeng K. C. , Lin J. Y. , Jiang H. X. , Zhang B. , Dai L. , Botchkarev A. , Kim W. , Morkoç H. , Khan M. A.
Published: July 2002

Optical resonance modes have been observed in optically pumped microdisk cavities fabricated from 50 Å/50 Å GaN/AlxGa1−xN(x∼0.07) and 45 Å/45 Å InxGa1−xN/GaN(x∼0.15) multiple quantum well structures. Microdisks, approximately 9 μm in diameter and regularly spaced every 50 μm, were formed by an ion beam etch process. Individual disks were pumped at 300 and 10 K with 290 nm laser pulses focused to a spot size much smaller than the disk diameter. Optical modes corresponding to (i) the radial mode type with a spacing of 49–51 meV (both TE and TM) and (ii) the Whispering Gallery mode with a spacing of 15–16 meV were observed in the GaN microdisk cavities. The spacings of these modes are consistent with those expected for modes within a resonant cavity of cylindrical symmetry, refractive index, and dimensions of the microdisks under investigation. The GaN-based microdisk cavity is compared with its GaAs counterpart and implications regarding future GaN-based microdisk lasers are discussed.
Characterization of piezoelectric (111)B InGaAs/GaAs p-i-n quantum well structures using photoreflectance spectroscopy
Authors: Chan C. H. , Chen M. C. , Lin H. H. , Chen Y. F. , Jan G. J. , Chen Y. H.
Published: July 2002

Strained-layer (111)B In0.2Ga0.8As/GaAs p-i-n quantum well structures grown with exciton transitions well resolved at room temperature have been studied by photoreflectance spectroscopy. Using the reduced mass deduced from experiments, the built-in electric field in the barrier region is obtained from the above band-gap Franz–Keldysh oscillations. The strain-induced piezoelectric field is then determined directly from a comparison of the periods of Franz–Keldysh oscillations in different samples. Numerical solutions for the exciton transitions from the derived potential profiles are in good agreement with the experimental results. The piezoelectric constant is also determined using the piezoelectric field.
Thermoelectric figure of merit of metal–semiconductor barrier structure based on energy relaxation length
Authors: Moyzhes B. , Nemchinsky V.
Published: July 2002

The thermoelectric figure of merit is calculated for a compound material comprising thin semiconductor and wider metallic layers. The layers are perpendicular to the direction of current. The semiconductor barriers exclude electrons with energies ε<μ from the current. This exclusion increases thermopower. One may obtain a material with a very high ZT if the distance between the barriers is on the order of the energy relaxation length. This material should have the resistivity characteristic of a metal and the thermopower characteristic of a semiconductor. An additional significant rise in ZT can be achieved by increasing the contact area at the metal–semiconductor interface.
The thickness dependence of the flow stress of capped and uncapped polycrystalline Ag thin films
Authors: Kobrinsky Mauro J. , Thompson Carl V.
Published: July 2002

The flow stress of capped and uncapped polycrystalline silver films on oxidized silicon wafers is reported as a function of Ag film thickness (in the range of 0.2–1.2 μm) and temperature (in the range of −50–500 °C). While the flow stress in capped films increases with decreasing film thickness, the flow stress in uncapped films increases when film thickness is decreased from 1.2 to 0.5 μm, but then decreases with further decreases in film thickness. A high temperature regime of purely plastic strain accommodation extends to lower temperatures in thinner uncapped films than in capped films, with a transition temperature to elastoplastic behavior characterized by an apparent activation energy consistent with diffusive mechanisms of strain relief. These results suggest that surface diffusion to, and down, grain boundaries (whose spacing scale with film thickness) mediates strain accommodation in uncapped films.
Growth of highly oriented Pb(Zr, Ti)O3 films on MgO-buffered oxidized Si substrates and its application to ferroelectric nonvolatile memory field-effect transistors
Authors: Basit Nasir Abdul , Kim Hong Koo , Blachere Jean
Published: July 2002

We have grown highly oriented lead zirconate titanate [Pb(Zr, Ti)O3 or PZT] films on oxidized silicon substrates using a thin MgO buffer layer (7–70 nm thick). Ferroelectric nonvolatile memory field-effect transistors (FETs) were successfully fabricated using the metal/PZT/MgO/SiO2/Si structure in conjunction with radio-frequency sputter deposition of PZT and MgO films. The fabricated devices show excellent performance in ferroelectric polarization switching and memory retention. The results indicate that a thin MgO buffer serves well not only as a template layer for the growth of oriented PZT films on amorphous substrates, but also as a diffusion barrier between a ferroelectric and a substrate during device fabrication, protecting the SiO2/Si interface and the FET channel region.