bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective and epitaxial deposition of β-FeSi2 on silicon by rapid thermal processing-chemical vapor deposition using a solid iron source
Authors: Regolini J. L. , Trincat F. , Berbezier I. , Shapira Y.
Published: July 2002

Selective semiconducting iron disilicide has been epitaxially deposited by rapid thermal processing chemical vapor deposition onto patterned silicon wafers. Using a solid iron source, we obtained stoichiometric β-FeSi2. The extrinsic conductivity energy levels are about 0.1 eV from the valence band and we show that they are responsible for the observed ‘‘infrared quenching.’’
Indium tin oxide as transparent electrode material for ZnSe-based blue quantum well light emitters
Authors: Hagerott M. , Jeon H. , Nurmikko A. V. , Xie W. , Grillo D. C. , Kobayashi M. , Gunshor R. L.
Published: July 2002

Sputter deposited indium tin oxide layers have been used as the top contact for blue LEDs and diode lasers in (Zn,Cd)Se/Zn(S,Se) quantum well heterostructures. The contact resistance to n-Zn(S,Se) is comparable to that with indium or gold. The optically transparent contacts have been utilized, as an example, in the fabrication of a numeric display device and to show that LED emission is of excitonic origin in these type I quantum wells.
Vacuum ultraviolet fluorescence of (XeRb)+ produced in an electron-beam-pumped gas mixture
Authors: Bastiaens H. M. J. , Lankhorst F. T. J. L. , Peters P. J. M. , Witteman W. J.
Published: July 2002

With a pulsed electron beam a gas mixture of Ar, Xe, and Rb was excited producing (XeRb)+ ionic excimer molecules. To study the formation kinetics the (XeRb)+ fluorescence pulse was measured as a function of the gas composition and the pumping density. From the observed fluorescence signal decay a value of 6±1×10−30 cm6/s for the formation rate constant of (XeRb)+ from Xe+, Ar, and Rb was determined.
New insight into the structure and growth of CaF2/Si(111)
Authors: Lucas C. A. , Loretto D.
Published: July 2002

We have used transmission electron microscopy and x-ray crystal truncation rod measurements to investigate thin (<50 Å) CaF2 films grown on Si(111) substrates by molecular beam epitaxy. The results indicate that CaF2/Si can be structurally as perfect as NiSi2/Si and CoSi2/Si, and that a reconstructed layer is present at the CaF2/Si(111) interface.
Ballistic versus diffusive base transport in the high-frequency characteristics of bipolar transistors
Authors: Grinberg Anatoly A. , Luryi Serge
Published: July 2002

The time-dependent Boltzmann equation is used to calculate the small-signal complex base transport factor α(ω) for different ratios between the base width W and the scattering mean-free path lsc. It is shown that the phase trajectory (Re α, Im α) has a universal character both in the diffusion limit (W≫lsc) and the ballistic limit (lsc≫W). In the latter limit, the trajectory is completely determined by the distribution function of minority carriers injected into the base. The complex trajectories are plotted for several model distributions, including the usual thermal distribution and taking into account the injection energy appropriate for a heterojunction bipolar transistor with a wide-gap emitter.
Time-evolved numerical simulation of a two-dimensional electron wave packet through a quantum point contact
Authors: Endoh Akira , Sasa Shigehiko , Muto Shunichi
Published: July 2002

We performed time-evolved numerical simulation of a two-dimensional electron wave packet through a quantum point contact using the finite difference method to simulate the diffraction phenomenon of a single electron. We found that the transmitted wave packet has diffracted subpeaks which show the following properties: (1) The traces of diffracted subpeaks start from the center of the slit entrance. (2) Lateral wave number of diffracted subpeaks is quantized. (3) The diffraction angles are determined by slit width and the initial electron wave packet energy. (4) The number of allowed diffracted subpeaks is determined by potential barrier thickness. (5) There is a delay in the motion of diffracted subpeaks due to quantization inside the slit.
High valence-band offset of GaSbAs-InAlAs quantum wells grown by molecular beam epitaxy
Authors: Yu P. W. , Reynolds D. C. , Jogai B. , Loehr J. , Stutz C. E.
Published: July 2002

Photoluminescence measurements were made at 2–300 K on GaSbAs-InAlAs single quantum wells lattice matched to InP grown by molecular beam epitaxy. The experimental exciton transition energy from the first electron subband to the first heavy hole subband was analyzed with calculated values obtained from the envelope function method. The quantum well exciton transition energy for well widths of 10–300 Å is fitted to a large valence-band offset (ΔEv) of 0.93 ΔEg. The exciton linewidth increases with decreasing well width. The two dominant exciton line broadening mechanisms were found to be monolayer fluctuations of the well width and the band filling of electron.
Microgun-pumped semiconductor laser
Authors: Molva E. , Accomo R. , Labrunie G. , Cibert J. , Bodin C. , Dang Le Si , Feuillet G.
Published: July 2002

We demonstrate the feasibility of a novel microgun-pumped semiconductor laser. This is the most compact (a few cm3) and the lowest threshold electron-beam-pumped semiconductor laser ever reported. The electron source is provided by a 104–105/mm2 array of field emissive microtip cathodes each of 1.5 μm diam. The laser operates below 10 kV and below 1 A/cm2. Laser action in a quasi-cw mode with 5 μs pulses at 2 kHz has been obtained between 90 and 300 K with CdTe-CdMnTe graded index separate confinement quantum-well heterostructures, as well as with GaAs-GaAlAs structures. Since neither doping nor ohmic contacts are needed, the microgun laser can use all direct gap semiconductors. It appears as a viable solution for making compact II-VI lasers in the visible domain.
Nonlinear interdiffusion in semiconductor superlattices: Case of CdTe/HgTe
Authors: Tardot A. , Hamoudi A. , Magnea N. , Gentile P. , Pautrat J. L.
Published: July 2002

Experiments have been designed to measure the interdiffusion coefficients in CdTe/HgTe (001) superlattices grown by molecular beam epitaxy. The interdiffusion coefficients are deduced from double-crystal x-ray diffraction on samples annealed in the 200–240 °C range under a Hg saturated pressure. Our results indicate that the interdiffusion is strongly dependent on concentration with a coefficient given by D(CCd,T)=1.0 exp{[−1.45(±0.1) eV]/(kT)} exp {[−0.55 (±0.1) CCd eV]/(kT)} cm2/s. The activation energies ΔEHgTe≊1.45 eV and ΔECdTe≊2.0 eV are consistent with an interdiffusion process by a vacancy mechanism.
Observation of magnetic-domain states of barium ferrite particles by electron holography
Authors: Hirayama T. , Ru Q. , Tanji T. , Tonomura A.
Published: July 2002

Magnetic domain states of completely isolated particles of barium ferrite between 0.1 and 2 μm in size are investigated by electron holography. Phase distribution is reconstructed digitally by the Fourier transform method and converted to interference micrographs. In the interference micrographs single magnetic-domain particles are observed directly and clearly for the first time. Furthermore, it is found that single-domain and two-domain particles coexist down to sizes as small as about 0.1 μm.
Large third-order optical nonlinearity of tin microcrystallite-doped silica glass formed by ion implantation
Authors: Takeda Yasuhiko , Hioki Tatsumi , Motohiro Tomoyoshi , Noda Shoji
Published: July 2002

Sn+ ions were implanted into silica glass at an acceleration energy of 400 keV to a dose of 2×1017 ions/cm2. Metallic Sn microcrystallites of 4–20 nm in diameter were formed to attain the average volume fraction of 28%. The dielectric function, ε, and the absolute value of the third-order optical nonlinear susceptibility, ‖χ(3)‖, showed dispersions around a wavelength of 500 nm, owing to surface plasmon resonance. The difference in the peak width of ‖χ(3)‖ and the imaginary part of ε can be explained by an effective medium theory. The maximum of ‖χ(3)‖ was 3×10−6 esu, which is as large as those reported for semiconductor-doped glasses.
Triple crystal x-ray diffractometry of periodic arrays of semiconductor quantum wires
Authors: Holý V. , Tapfer L. , Koppensteiner E. , Bauer G. , Lage H. , Brandt O. , Ploog K.
Published: July 2002

Kinematical diffraction theory and the optical coherence formalism have been used for calculating the diffuse x-ray scattering from periodic quantum wires. The method calculates the distribution of the diffusely scattered intensity in the reciprocal lattice plane. The simulated distributions have been compared with those measured on a InAs/GaAs quantum wire by means of triple crystal x-ray diffractometry and a good agreement has been achieved. The method can be applied to studies of internal stress relaxation in quantum wires.
Scanning electro-optical and pyroelectrical microscopy for the investigation of polarization patterns in poled polymers
Authors: Yilmaz Ş. , Bauer S. , Wirges W. , Gerhard-Multhaupt R.
Published: July 2002

Compact and simple experimental setups for scanning pyroelectrical and electro-optical microscopy are introduced. Their feasibility is demonstrated with scans of periodically poled layers of a nonlinear optical side-chain polymer. While the scanning pyroelectrical microscope has a less complex design and is easier to use, the scanning electro-optical microscope exhibits better spatial resolution and higher contrast. Both tools will be essential for optimizing the patterned poling of nonlinear optical waveguides, modulators, and sensors.
Luminescence study on interdiffusion in strained Si1−xGex/Si single quantum wells grown by molecular beam epitaxy
Authors: Sunamura H. , Fukatsu S. , Usami N. , Shiraki Y.
Published: July 2002

Optical investigation of interdiffusion at Si1−xGex/Si heterointerfaces has been performed for the first time in strained Si1−xGex/Si single quantum wells (SQWs). Photoluminescence (PL) peak energy blue shift of up to 22 meV due to interdiffusion-induced potential profile modulation was observed after annealing in vacuum. The diffusion coefficients obtained were found to closely follow an Arrhenius behavior with an activation energy of 2.47±0.4 eV. Dramatic increase in the integrated PL intensity was observed in the annealed samples, as a result of the elimination of effective nonradiative centers. Strain relaxation was hardly observed even after 900 °C annealing, indicating the unprecedented structural stability of SQWs in contrast to rather vulnerable thick alloy layers. Anomalous peak red shift, probably due to surface oxidation, was observed by annealing in N2 ambient.
Nanometer-scale modification of biological membranes by field emission scanning tunneling microscopy
Authors: García Ricardo
Published: July 2002

Manipulation and modification at atomic and nanometer scales of some semiconductor and metallic samples has been made possible by scanning tunneling microscopy (STM). This has generated novel approaches for designing new devices at nanometer scale. The poor electronic conductivity of biological molecules has prevented the extension of those methods to them. Here, it is described how a low current STM operated in the field emission regime allows, reproducible imaging and selective modification of biological membranes. A method is presented (i) to visualize at high-resolution hydrated purple membrane sheets, (ii) to produce nanometer-scale marks on them, and (iii) to image the altered membranes.
Magnetic structure determination for Fe3O4/NiO superlattices
Authors: Borchers J. A. , Erwin R. W. , Berry S. D. , Lind D. M. , Lochner E. , Shaw K. A.
Published: July 2002

Neutron diffraction measurements reveal the nature of the magnetic structure in Fe3O4/NiO superlattices grown by molecular beam epitaxy. Taking advantage of differences between the Fe3O4 and NiO crystalline symmetries, we have determined independently the magnetic order parameters of the bilayer components. The NiO antiferromagnetic order propagates coherently through several superlattice bilayers, while the magnetic coherence of the ferrimagnetic Fe3O4 is restricted to a single interlayer due to the random stacking of the spinel unit cells at the interfaces. A model for the diffraction data, based upon a Hendricks–Teller description of the interfacial disorder, demonstrates that the observed broadening of selected reflections originates directly from these stacking faults.
Photothermal poling of nonlinear optical polymer films
Authors: Yilmaz Ş. , Bauer S. , Gerhard-Multhaupt R.
Published: July 2002

Photothermal heating of a nonlinear optical polymer film with a focused laser beam leads to local temperatures above the glass transition so that the molecular dipoles orient in the electric field applied to the electrodes. Periodic switching of the field direction during movement of the sample yields gratings with alternating polarity which were studied with scanning electro-optical microscopy. The width and the depth of the poled stripes were probed with electro-optical and pyroelectrical techniques, respectively. Photothermal poling may be combined with other poling techniques in order to produce various dipole-orientation patterns for device applications.
Two-dimensional arsenic precipitation by In delta doping during low temperature molecular beam epitaxy growth of GaAs or AlGaAs
Authors: Cheng T. M. , Chang C. Y. , Chin Albert , Huang M. F. , Huang J. H.
Published: July 2002

Low temperature (LT) GaAs delta doped with In and Al have been grown by molecular beam epitaxy and annealed at 600–900 °C for 10 min. As precipitates have been observed to form preferentially on In doping planes while depleting on the Al planes. Similar As precipitates in In-doped LT-Al0.25Ga0.75As are 50% more efficient than that of GaAs. The accumulation or depletion of As precipitates in two-dimensional planes in LT materials using isoelectronic impurities show that the phenomena is not directly related to the electronic properties of dopant impurities and therefore has many device applications.
Time-resolved emission spectra of plasma produced by excimer laser ablation of Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O superconductors in the air
Authors: Engst P. , Kubát P. , Boháček P. , Wild J.
Published: July 2002

Time-resolved emission spectroscopy was employed to detect excited species formed by the laser ablation of Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O targets at atmospheric pressure. The emission spectra at times of up to 100 ns are characterized by the broadband emission of high-density plasma; for longer times, sharp atomic and ionic lines were found (Bi, Sr+, Sr, Ca+, Ca, and Cu for the ablation of Bi-Sr-Ca-Cu-O and Y, Y+, Ba+, and Cu for the ablation of Y-Ba-Cu-O). At times greater than 30 μs (Bi-Sr-Ca-Cu-O) or 2 μs (Y-Ba-Cu-O) primarily excited metal oxides occurred in the plasma. Experiments in oxygen, nitrogen, argon, and helium atmosphere indicate that part of the excited metal oxides are formed by reaction of the excited species with molecular or atomic oxygen.
Diffusion-limited interaction of dislocation loops and interstitials during dry oxidation in silicon
Authors: Park Heemyong , Robinson Heyward , Jones Kevin S. , Law Mark E.
Published: July 2002

The interaction of implantation-induced dislocation loops and interstitials in silicon is studied. Experiments under dry oxidation conditions consistently show a significant reduction of OED (oxidation enhanced diffusion) of boron in a buried layer due to very efficient interstitial capturing action of dislocation loops, suggesting diffusion-limited dislocation loop growth. Simple analytic solution of interstitial supersaturation and analysis of the data in terms of time dependence of the OED suppression demonstrate that the interaction of dislocation loops and interstitials is not a reaction-limited but a diffusion-limited process. Simulations incorporating the model for the interaction mechanism agree with both secondary ion mass spectroscopy and transmission electron spectroscopy data.
Study on growth processes of particulates in helium-diluted silane rf plasmas using scanning electron microscopy
Authors: Shiratani M. , Kawasaki H. , Fukuzawa T. , Tsuruoka H. , Yoshioka T. , Watanabe Y.
Published: July 2002

Size, density, and morphology of particulates in helium-diluted silane rf plasmas are studied using a scanning electron microscopic method. The experimental results show that particulates grow through three phases of nucleation, rapid growth, and growth saturation. Particulates in two different size ranges coexist after the initiation of the rapid growth phase, the size distribution of particulates in each size group is found to be well expressed by both the lognormal and normal distributions with a narrow size dispersion, and coagulation of particulates plays a crucial role in the rapid growth phase. The dependencies of size and density of particulates in the large-size group on rf-power-on period are very similar to their temporal evolutions obtained by an in situ laser light scattering method.
Internal quantum efficiency of thin epitaxial silicon solar cells
Authors: Brendel Rolf , Hirsch Michèle , Stemmer Michael , Rau Uwe , Werner Jürgen H.
Published: July 2002

A new theoretical expression is derived for the internal quantum efficiency of solar cells homoepitaxially grown on highly doped monocrystalline substrates. This expression is used to characterize our thin-layer silicon cells grown by chemical vapor deposition. These cells reach a confirmed efficiency of 17.3% although the active layer thickness is only 48 μm. The internal quantum efficiency analysis demonstrates that the open circuit voltage is limited by carrier injection into the highly doped substrate. Carrier generation in the substrates accounts for 0.7% of the short circuit current.
Avalanche breakdown in A
l
x
G
a1−x
A
s alloys and A
l0.3G
a
0.7
A
s
/
G
a
A
s multilayers
Authors: David J. P. R. , Allam J. , Adams A. R. , Roberts J. S. , Grey R. , Rees G. J. , Robson P. N.
Published: July 2002

The avalanche breakdown voltage (Vb) has been measured in a range of bulk AlxGa1−xAs alloys and Al0.3Ga0.7As/GaAs multilayer structures. The bulk alloys show a linear dependence of Vb on x up to at least x=0.6. Multilayers with thin (≤100 Å) dimensions follow this trend, with Vb being determined by the average Al fraction of the multilayer ‘‘pseudoalloy’’. For thicker (≥500 Å) layers Vb tends to a mean of the bulk values of the layers. The transition from pseudoalloy to bulklike behavior is interpreted in terms of the momentum and energy relaxation lengths, estimated for bulk GaAs using a Monte Carlo solution of the semiclassical transport equation.
AlxGa1−xAs–GaAs metal–oxide semiconductor field effect transistors formed by lateral water vapor oxidation of AlAs
Authors: Chen E. I. , Holonyak N. , Maranowski S. A.
Published: July 2002

Data are presented demonstrating a GaAs-based metal–oxide semiconductor field effect transistor employing in the gate region a laterally formed native oxide of AlAs. The gate oxide, formed by a water vapor process, is similar to that used successfully in recently developed semiconductor laser devices. The transistors described here represent an extension of the ‘‘wet’’ oxidation Al-based III–V native oxide technology employed successfully in light-emitting and laser devices.
Resonant cavity light emitting diode with an AlxOy/GaAs reflector
Authors: Huffaker D. L. , Lin C. C. , Shin J. , Deppe D. G.
Published: July 2002

A resonant cavity light emitting diode is fabricated which makes use of a Ag mirror/contact and a buried AlxOy/GaAs Bragg reflector. The buried AlxOy is formed by the selective conversion of AlAs. The differential light output efficiency is measured and found to be ∼5.5% when the AlxOy/GaAs reflector is present versus ∼2.5% for a control device without the AlxOy/GaAs mirror. The measured efficiencies are compared with calculations.
Microwave Fourier-transform spectrometer for the entire K band for the investigation of rotational spectra of molecules in the gas phase
Authors: Stahl W. , Bestmann G. , Dreizler H. , Andresen U. , Schwarz R.
Published: July 2002

We present the experimental set up of a microwave Fourier-transform spectrometer for the entire K band from 18 to 26.4 GHz. It is hereby shown that this type of spectroscopy is achieved above 18 GHz. Advantages and disadvantages are discussed. The performance is illustrated by the recordings of rotational transitions of various molecules.
‘‘Video lock-in amplifier’’: Phase-sensitive detection of digital image sequences
Authors: Hartsough Neal , Kolodner Paul
Published: July 2002

A lock-in amplifier uses demodulation techniques to extract the component of an electronic signal which has the same phase and frequency as an oscillating reference signal. We have used a digital image processor to perform this demodulation simultaneously on all pixels in a sequence of video-taped images. To demonstate the use of this technique, we extract, from a recording of a hydrodynamic flow pattern exhibiting complicated spatial and temporal behavior, an image of a spatially localized mode which oscillates at a discrete temporal frequency. Demodulation at synthesized mixing frequencies can reveal the spatial dependence of the nonlinear interactions between different localized modes.
Amplitude measurement in acoustic emission
Authors: Cáceres Carlos H.
Published: July 2002

A circuit capable of measuring the amplitude of continuous emission and acoustic bursts is presented. The circuit shows linear behavior (+/−5%) over a dynamic range in excess of 65 dB, for frequencies up to 250 KHz. Possible applications are discussed.
Cylinder radioactive source for slow-positron beams
Authors: Brusa R. S. , Grisenti R. , Oss S. , Zecca A. , Dupasquier A.
Published: July 2002

The geometrical efficiency is calculated for a radioactive source-moderator assembly, which is often used for the production of slow-positron beams, and comparisons are made between a cylinder source, touching the circumference of the moderator, and a spot source, facing the center of the moderator. It is shown that higher beam intensity and brightness can be obtained with the cylinder source in most practical situations.
Microchannel-plate intensified crystal spectrometer for use in soft x-ray spectroscopy
Authors: Hailey C. J. , Rockett P. , Eckart M. , Burkhalter P. G.
Published: July 2002

A Bragg crystal spectrometer, utilizing a microchannel plate coupled to optical film as the detection medium, has been constructed for use in soft x-ray spectroscopy. The sensitivity of this intensified gated camera to x-rays has been compared directly with standard x-ray film using a calibrated x-ray source. In addition, this high gain, intensified crystal spectrograph (ICS) has been used in an experiment to precisely measure spectral coincidences between x-ray lines in laser-generated plasmas, thus identifying candidates for photoresonant x-ray lasing schemes in the 10–21-Å region. At long wavelengths the ICS was able to obtain useful data on faint lines in a single laser shot, rather than the multiple shots required by an adjacent spectrograph using x-ray film. It also allowed line coincidences to be verified by a new technique utilizing split disk targets. The design and construction of the ICS and results obtained with it are compared with those obtained with standard x-ray film.
Coaxial electrical pulse shaper for picosecond electronics
Authors: Margulis W. , Persson R.
Published: July 2002

A miniature coaxial passive picosecond electric pulse shaper (PEPS) is described. The component is small and rugged, has high-voltage capability, is compatible with 50-Ω microwave and high-speed electronics, and is of simple construction. Its performance has been tested in the shaping of pulses as short as <30 ps, and its uses include microwave pulse generation, high-speed modulation, and picosecond electronic differentiation.
Design for improved resolution in a time-of-flight mass spectrometer using a supersonic beam and laser ionization source
Authors: Lubman David M. , Jordan Russ M.
Published: July 2002

This article describes the design of a time-of-flight mass spectrometer (TOFMS) constructed for optimum use with resonance-enhanced multiphoton ionization spectroscopy in supersonic beams. The use of the supersonic beam results in a great improvement in resolution, i.e., at least 800 at mass 93. Ion packets on the order of 10 ns FWHM or less are observed at our flat dual channel plate detector and the resolution ultimately appears to be laser-pulse-width limited. The design of this TOFMS utilizes fast-pulsed molecular beam techniques to allow the use of reservoir pressures >1 atm with a large orifice (0.5 mm) in order to provide high on-axis intensity for maximizing the photoionization signal produced by our pulsed laser system with the use of only modest pumping capacity. It also uses a skimmed beam, differential pumping, and a liquid-N2 baffle in order to maintain the flight tube at pressures on the order of 5×10−7 Torr and to eliminate organic contamination from the ionization region.
Pseudostatistical light chopper for time-of-flight analysis of laser excited species
Authors: Düren R. , Gröger W. , Liedtke R.
Published: July 2002

Application of the cross correlation chopper technique to the measurement of a time-of-flight (TOF) spectrum of excited atoms by modulation of the exciting laser light is described. The principle and the practical aspects are discussed in a comparison with mechanical systems. Results are given for angular resolved scattering of excited sodium from potassium.
Inherent magnetic field error measurements in ELMO Bumpy Torus
Authors: Uckan Taner
Published: July 2002

The inherent magnetic field error and its radial distribution in the closed field line device of ELMO Bumpy Torus (EBT) have been measured with an electron beam probe. It is found that the field error is almost radially uniform and is about ΔB≤4 G at an average field of B≂7.2 kG. This yields ΔB/B≂5×10−4, which is large enough to open the confined drift surfaces of the toroidally circulating electrons as a result of field-error-dominated large radial shifts. By using two pairs of correction coils (loops) around the device, this inherent field error has been successfully reduced to a level of 10−4 or less.
Improved temperature control for samples in electron-paramagnetic-resonance spectroscopy
Authors: Morse Philip D. , Magin Richard L. , Swartz Harold M.
Published: July 2002

An improved method of temperature control for electron-paramagnetic-resonance (EPR) spectroscopy is described that reduces the large (1°–2 °C/cm) temperature gradients along the sample associated with gas flow EPR temperature controllers. Circulation of dimethylpolysiloxane through an EPR cavity Dewar using a temperature programmable bath reduces gradients to typically 0.01 °C/cm. Temperature changes within the cavity Dewar can be programmed at rates up to 5 °C/min. This technique provides more precise control of sample temperature and allows the sample to be reset to a specified temperature with an uncertainty of less than 0.1 °C.
Counting efficiency of systems having both paralyzable and nonparalyzable elements
Authors: Lampton M. , Bixler J.
Published: July 2002

Electronics for processing random event trains may contain some elements which are paralyzable in combination with others which are nonparalyzable. An expression is derived which gives the counting efficiency or live time of such a system when its input is a Poisson random arrival process.
Intensified photodiode array applied to one-dimensional auroral imaging
Authors: Steen Åke
Published: July 2002

An imaging instrument that can replace mechanically scanning photometers in ground based auroral photometry has been developed. The instrument utilizes a Reticon photodiode array, 1*1024 pixels, coupled with fiber optics to a second generation image intensifier. The optics are a telecentric design allowing for 170° field of view (FoV) with narrow-band interference filters. Peltier element cooling is found to be sufficient to neglect dark current noise for 1-s integration time. The whole system is controlled by a computer via the IEEE-488 bus. Initial results and instrument performance are reported.
Reversal ion source: A new source of negative ion beams
Authors: Orient O. J. , Chutjian A. , Alajajian S. H.
Published: July 2002

We demonstrate a new type of ion source for producing either pulsed or continuous negative ion beams. The source, dubbed the ‘‘reversal ion source,’’ utilizes an electrostatic ‘‘mirror’’ which reverses trajectories in an electron beam, producing electrons at their turning point having a distribution of velocities centered at zero velocity. A gas which attaches zero-velocity electrons is introduced at this turning point. Negative ions are produced by the attachment or dissociative attachment process. The cross section for this process is extremely large, varying as (electron energy)−1/2, or just the s-wave threshold law. The operation of the source is demonstrated for continuous and pulsed production of Cl− beams by dissociative attachment to CFCl3. Estimates of the current density of this source are given, and applications to the production of ions through higher energy resonances are discussed.
Novel Hall-effect measuring device for use in superconducting solenoids
Authors: Heinemann K. , Krokoszinski H. J. , Langohr K. , Bärner K.
Published: July 2002

A new device measuring Hall voltages down to 5 nV in fields up to 7 T is presented. The setup uses the double-ac method and works at temperatures ranging from 450 to 4.2 K. As a convenience, manual or automatic field sweeps can be chosen.
Effect of externally induced fluctuations on an ON–OFF temperature controller
Authors: Neelakantan K. , Seshadri V. R.
Published: July 2002

A simple scheme of improving the control characteristics of an ON–OFF controller by deliberately coupling external fluctuations is described. The principle of the technique is presented along with some experimental results.
Improvements in real-time data acquisition for gas electron diffraction
Authors: Ewbank John D. , Schäfer Lothar , Paul David W. , Monts David L. , Faust Walter L.
Published: July 2002

Several improvements are described of a recently reported prototype real-time data-acquisition system for gas electron diffraction (GED), in which the scattered intensity distribution is recorded by a photodiode array. The use of a computer-designed and photographically produced ‘‘butterfly’’ slit in the optical track of the instrument, which simulates the effects of the rotating sector of conventional GED, as well as a number of other modifications, now makes it possible to record, for the first time by this technique, scattered electron intensities in a region around s=300 nm−1. Modeling of several test molecules shows that structural parameters can be determined accurately by the novel procedure, but systematic inaccuracies still exist in the determination of mean amplitudes of vibration. Data evaluation is based on a novel ratiometric analysis procedure, whose essential features are briefly discussed.
Space- and time-resolving spectrograph for high-temperature plasma diagnostics
Authors: Content D. , Wróblewski D. , Perry M. , Moos H. W.
Published: July 2002

Construction of an EUV (60 –370 Å) space- and time-resolving, grazing incidence spectrograph (STRS) is described. The simultaneous spectral coverage of the instrument ranges from 40 to 75 Å, depending on the wavelength region. The spectral resolution is about 1 Å. The spatial resolution, accomplished by using the pinhole camera effect and the inherent astigmatism of a concave grating in grazing incidence, is about 2 cm, with a total field of view of 60 cm at a distance of 2 m from the plasma. The detector consists of a 75-mm MCP image intensifier optically coupled to three CCD area array detectors. Time resolution of up to 2 ms is achieved with high-speed readout electronics. A PDP 11/73 minicomputer controls the spectrograph and collects and reduces 3.0 Mbyte of data per shot.
Simple capacitive probe for high-voltage nanosecond pulses
Authors: Gratton Roberto , Mangioni Sergio , Niedbalski Jorge , Valent Roberto
Published: July 2002

We describe a capacitive probe for the observation of high-voltage fast pulses (1–100 kV, 1 to 10 ns) and we also show the results of some tests performed on a prototype. The probe is extremely simple and cheap, easy to build by small research groups. The attenuation factor can be adjusted through a simple operation which does not require substitution of components.
Variable Rowland radius laboratory EXAFS system
Authors: Yacoby Y. , Brettschneider M. , Bezalel M.
Published: July 2002

We report here on a new EXAFS laboratory facility. It features a variable Rowland radius with a source to bent crystal distance that can vary from 250 to 750 mm. It has a sample carrying table which is mechanically detached from the monochromator and can carry more than 50 lb with no effect on the monochromator. The system is completely computer controlled in such a way that the operator can control every part of the system separately as well as perform complete automatic runs. The data-analysis programs had been divided into a general package which performs the bookkeeping of files experimental parameters and program parameters and a specific package for the analysis of the EXAFS data. The monochromator is shown to have almost theoretical resolution. We present experimental results of EXAFS on copper. The Fourier transform of these spectra agree very well with the Fourier transform of EXAFS spectra measured on a synchrotron. It is shown that the resolution of 4.5 eV of these data does not present a limitation on the quality of the data. The signal-to-noise ratio is, on the other hand, quite critical.
Feasibility of a detector for nuclear radiation based on superconducting grains
Authors: Seidel W. , Oberauer L. , Feilitzsch F. v.
Published: July 2002

We studied the sensitivity of a radiation detector based on metastable superconducting grains. Radiation is detected by the phase transition from the superconducting to the normal-conducting state of a grain induced by energy absorption. Metastable states of tin and cadmium grains were tested. The phase boundary of a large sample of grains was found to be broadened due to variations of the phase diagrams of single grains. Therefore, the use of superconductors with a low critical temperature Tc and an operation temperature close to Tc seems advisable to increase the sensitivity of the detector. For Cd grains a sensitivity normalized to the grain volume of 12 eV/μm3 was achieved for the detection of γ rays. These grains showed an instability in the superconducting to normal-conducting phase transition for temperatures below 350 mK.
Molybdenum resistance heater
Authors: Lindemer Terrence B.
Published: July 2002

This note describes an inexpensive and expendable molybdenum heater that can be used as a direct replacement for much more expensive heaters in the smaller commercial resistance heated furnaces.
Stable electrical contacts to thin films at low temperatures
Authors: Guillon F. , Julien C. , Cheeke J. D. N.
Published: July 2002

We describe some techniques for making reliable and stable electrical contact to thin films using a gold wire bonding machine. Applications of these techniques to specific low-temperature experiments are given.
Differentiating measuring coils for pulsed currents in the MA/MHz range
Authors: Boggasch E. , Grüb R.
Published: July 2002

The design and construction of a high-performance differentiating pick-up coil for a 500-kA/ 4-μs pulsed current is described. Based on the Rogowski principle, the coil was made by using the printed-circuit technique. The coil is 1 mm thick; inclusive of electrostatic shielding and can be reproduced from one master print at nearly any size. Measurements up to 5 MHz showed no significant change of self-inductance. We believe that the coil is a versatile tool to measure and monitor current pulsed in the megampere/megahertz range.
Measurement of the local particle diffusion coefficient in a magnetized plasma
Authors: Levinton F. M. , Meyerhofer D. D.
Published: July 2002

Local impurity particle diffusion coefficients have been measured in a low temperature plasma by the injection of test particles at the center of the plasma. The injection is accomplished by a high-voltage discharge between two small graphite electrodes on a probe. The probe can be located anywhere in the plasma. The diffusion is observed spectroscopically. An analysis of the spatial and temporal evolution of the C ii radiation from the carbon discharge can determine the parallel and perpendicular diffusion of the impurity ions. Results with the diagnostic have been obtained in the Proto S-1/C spheromak. The measured value of the diffusion coefficient in the afterglow plasma is in good agreement with classical predictions.
Medium resolution atmospheric pressure ionization mass spectrometer
Authors: Grange Andrew H. , O’Brien Robert J. , Barofsky Douglas F.
Published: July 2002

An atmospheric pressure ionization (API) source for a VG 7070E-HF mass spectrometer has been built and successfully operated at an accelerating potential of 6 kV. Hydrated protons and hydrated organic ions formed in the API source can be either partially or completely disaggregated by collisionally induced dissociation before entering the mass analyzer. The protonated molecular ions of pinacolone and 2,4-pentanedione can be fully separated (R=2800, m/z 101, <1% valley) at one sixth of their maximum signal strengths, and the 13C-xylene radical ion and protonated benzaldehyde can be fully separated (R=3300, m/z 107, <1% valley) at one tenth of their maximum signal strengths. With 1% transmission, the resolving power of the VG 7070E-HF operating in the API mode is estimated to be 4800 (m/z 92, 10% valley). This resolution is more than sufficient to separate two oxidized hydrocarbons whose masses differ by 0.0364 daltons, the difference between a –CH2CH2– group and a 〉CO group, and to permit unambiguous assignment of their molecular formulas. No other form of API mass spectrometer, including the triple quadrupole version, has this capability.
On the fifth order aberration in a sextupole corrected probe forming system
Authors: Shao Zhifeng
Published: July 2002

The mechanisms of the generation of the fifth order aberrations in a sextupole corrected electron optical system are carefully analyzed, and a new principle is presented to compensate the rotationally symmetric part of the fifth order aberration. A numerical simulation shows that the probe radius can be reduced from 0.8 Å to about 0.4 Å for 200-keV electrons by using an additional round lens.
Low-temperature ultrahigh-vacuum scanning tunneling microscope
Authors: Lang C. A. , Dovek M. M. , Quate C. F.
Published: July 2002

We describe a multipurpose scanning tunneling microscope designed to operate in ultrahigh vacuum as well as in air, over a range extending from room temperature to liquid-nitrogen temperatures. It is a single-tube scanner design with a differential flexing approach mechanism mounted on a vibration isolation stack. The instrument features a novel in situ tip and sample exchange mechanism for extended operation under vacuum. A unique characteristic is that the vacuum chamber and all components with the exception of the gas-cooled sample holder are at room temperature. We present preliminary data taken with this instrument, demonstrating atomic resolution constant current, constant height, and multiple-bias imaging, gap-modulated current-voltage spectroscopy or simultaneous topography, and work function measurements, as well as lithography on the surfaces of graphite, Au(111) on mica, and GaAs(110).
Simple method for stabilizing frequency-modulated microwaves
Authors: Tanaka Takehiko , Kato Kinya , Okabayashi Toshiaki , Tanaka Keiichi
Published: July 2002

A simple method for stabilizing frequency-modulated microwaves based on a principle similar to that of a phase-locked loop (PLL) is described. This method is featured by the use of a sample/hold integrated circuit sampling a triangular wave as a phase detector. Applications of the method to stabilize klystrons for source-modulation microwave spectroscopy and infrared-laser-microwave double resonance (LMDR) are also described.
The BESSY wiggler/undulator-TGM-5 beamline (invited)
Authors: Peatman W. , Carbone C. , Gudat W. , Heinen W. , Kuske P. , Pflüger J. , Schäfers F. , Schroeter T.
Published: July 2002

In actual performance, the 35 pole wiggler/undulator (W/U) at BESSY has been shown to deliver 50 to 250 times more flux than a TGM with 10 mrad of dipole radiation under otherwise comparable conditions. The beamline, laid out for photon energies from 15 to 400 eV, has been calibrated and the resolution measured at several energies. Interactions of the W/U with the storage ring have been studied and, in part, corrected for: the working point does not change in either direction (<10%) as the gap is varied and the electron beam position in the ring remains constant to within 10 μm and the angle of emission of the SR from the ring to within 5 μrad for K≤2.7. The reduction of the lifetime of the electron beam in the ring and the change in the vertical size of the beam as a function of the gap are typical of the problems associated with the interaction of such a device on a high brightness ring. The beamline has been in normal user operation for over a year.
Efficient energy spectrometer for charged particle detection in surface studies
Authors: Mayer R. , Becker D. , Schwab A. , Weiss A.
Published: July 2002

We have recently built a spectrometer that efficiently collects the energy spectrum of charged particles that emerge from targets bombarded by low-flux (10−15 A) incident beams. The spectrometer is used to detect positron-induced secondary electrons and low-energy positron-stimulated Auger electron emission. Slow positrons and positron-induced secondary electrons are generated from a cold neon positron moderator deposited onto an encapsulated 22Na source. The moderated beam is magnetically transported to the target with two sets of E×B plates. The particles emerging from the target are energy dispersed by a third set of plates and are detected with a one-dimensional position-sensitive detector. The data-collection rate for the energy-distribution spectrum is ∼10–100 times faster for this experiment relative to the more common method of sweeping grids or the plates.
High-field ion sources
Authors: Bell A. E. , Jousten K. , Swanson L. W.
Published: July 2002

High electric fields may be used to create ions either by field evaporation, as in the case of liquid metal ion sources (LMISs) or by field ionization, as in the case of gas-phase field ionization sources (GFISs). LMISs have now reached a mature state of development and have found an increasing number of focused beam applications, ranging from submicron mask repair to maskless ion implantation. They may be fabricated from either pure elements, or from alloys, provided that the element or alloy vapor pressure is low enough to avoid excessive evaporation. In the case of alloys, it is necessary to employ a mass filter, typically a Wien filter, to remove unwanted ion species from the ion beam. Angular intensities, at the threshold of source operation, range from 1 μA/cm2 for alloy LMIS ion species to 20 μA/cm2 for elemental LMISs; under the same operating conditions, the ion energy spreads are ∼5 eV. Recent advances in the development of GFISs raise the possibility that GFISs may be nearing the stage when they also might be used in fine focus applications. By special shaping of the metal emitter in the apex region and by cooling the emitter to ∼20 K; it has been found possible to cause confinement of the ion emission to ∼0.5° half-angle, thereby increasing angular intensities of beams of He+ or H+2 to values similar to those obtained from LMISs.
High-frequency response of capacitors fabricated from fine grain BaTiO3 thin films
Authors: Singh P. K. , Cochrane S. , Liu W.-T. , Chen K. , Knorr D. B. , Borrego J. M. , Rymaszewski E. J. , Lu T.-M.
Published: July 2002

Fine grain BaTiO3 thin films with a grain size ranging between 100 and 1000 Å were deposited using the reactive partially ionized beam deposition technique at 550–600 °C. A metal/insulator/metal structure of these materials was fabricated and the dielectric response was measured up to 40 GHz using a network analyzer. It is shown that these films are not ferroelectric. However, these films show a dielectric relaxation in the frequency interval between several MHz and 1 GHz. We propose that this indicates a relaxation mechanism not related to the ferroelectric domain walls.
Pulsed valve for supersonic nozzle experiments at cryogenic temperatures
Authors: Hagena Otto F.
Published: July 2002

This note describes the design and operational experience of a solenoid valve used for pulsed supersonic beam experiments at cryogenic temperatures.
Multilayer optics for intense synchrotron x-ray beams: Recent results on their performance
Authors: Ziegler E. , Marot G. , Freund A. K. , Joksch St. , Kawata H. , Berman L. E. , Iarocci M.
Published: July 2002

Present-day synchrotron x-ray beams are very demanding in terms of thermal, mechanical, and radiation stability of any optical element to be inserted in the beam. A set of multilayers was recently exposed and could resist to an x-ray power density in excess of 7.5 W/mm2, which is comparable to the one expected for the multilayers to be used at ESRF. Such a power density was obtained by setting the multilayers at a grazing angle of about 2° in a focused wiggler beam of 4.6 keV critical energy. The specimen, W/B4C and W/Si multilayers, were cooled either at room temperature or down to liquid nitrogen temperature during an 8–16 h exposure time.
Enhanced electroabsorption in selectively doped (Ga,In)As/(Al,In)As asymmetric double quantum wells
Authors: Krol M. F. , Leavitt R. P. , Pham J. T. , McGinnis B. P. , Peyghambarian N.
Published: July 2002

We report enhanced electroabsorption in selectively doped (Ga,In)As/(Al,In)As asymmetric double quantum wells (ADQWs) by the use of real space electron transfer. The electron concentration in both the wide and narrow wells is investigated by field dependent absorption and photoluminescence spectroscopy. The results are compared to absorption changes in an undoped ADQW structure that utilizes the quantum confined stark effect. The doped modulator exhibits a significantly larger red shift with applied field than the undoped structure.
Long pulse operation of a cesium-seeded multicusp H− ion source
Authors: Okumura Y. , Hanada M. , Inoue T. , Mizuno M. , Ohara Y. , Suzuki Y. , Tanaka H. , Tanaka M. , Watanabe K.
Published: July 2002

It is demonstrated that a cesium-seeded volume H− ion source can be operated very stably for long pulse durations of up to 24 h. The source consists of a 20 cm cylindrical multicusp plasma generator and a 9 cm × 10 cm multiaperture extractor. By seeding a small amount of cesium, the source has produced 50 keV, 0.5 A, 1000 s H− ion beams with a current density of 14 mA/cm2. The cesium effect lasted for more than 24 h once 100 mg cesium was seeded before operation. Power flow measurement revealed that the heat loading of the ion source was low enough to operate the source in the dc mode.
High efficiency ion sources for on-line mass separators: A brief review (invited)
Authors: Duppen P. Van , Decrock P. , Huyse M. , Kirchner R.
Published: July 2002

A review on low-charge state high-efficiency ion sources used at on-line isotope separators (ISOL) is given. These sources for which the efficiency is optimized, can be distinguished from ion sources used at, e.g., accelerators where essentially the output current is optimized. Recent developments conducted to meet the special requirements necessary for on-line ion sources−high efficiency, selectivity, and short delay times−are presented and new ionization schemes like ECR sources or laser resonant photo ionization, implemented during recent years at ISOL systems, are discussed.