bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of recombination current in CdTe/CdS solar cells
Authors: Oman D. M. , Dugan K. M. , Killian J. L. , Ceekala V. , Ferekides C. S. , Morel D. L.
Published: July 2002

A study of the current–voltage behavior of recombination current in CdTe/CdS solar cells has shown that the reverse saturation current, J0, and the diode quality factor, A, are correlated. Our better devices typically have low values of both A and J0. Spectral response data indicate that devices with a gradual decline in quantum efficiency beginning at about 600 nm show better performance than devices with a sharp drop at the CdS band gap of 510 nm, which is interpreted as an indication that mixing between CdS and CdTe during processing reduces the amount of recombination current at the interface.
A flexible data acquisition system for timing pulsars
Authors: Stinebring D. R. , Kaspi V. M. , Nice D. J. , Ryba M. F. , Taylor J. H. , Thorsett S. E. , Hankins T. H.
Published: July 2002

We describe a flexible, inexpensive data acquisition system built for high-precision timing observations of pulsars. The system is designed to interface with a wide variety of radio telescope receiver back ends; it permits standardized measurement techniques and data formats in work carried out at a number of different observatories. Copies of the basic ‘‘Mark III’’ system are now in regular use at the Arecibo Observatory, Green Bank, and the Very Large Array. We describe the specifications, hardware, and software implementation of the system, and briefly outline some of its current applications.
Raytracing facility for soft x-ray and vacuum ultraviolet monochromators at NSRL
Authors: Lijun Lu
Published: July 2002

A raytracing facility for evaluating soft x-ray and vacuum ultraviolet optics, especially synchrotron radiation monochromators and beamlines, has been reported. Such kinds of optics consist of any number of reflecting mirrors, gratings, and, if needed, stop apertures: in coplanar or orthogonal configuration; conventional, holographic, and varied line-space gratings are available dispersing elements in design of a monochromator. Both normal and grazing incidence optics can be handled well. Point or finite sources, necessary to be setup in the raytracing process, may be used of isotropic or of Gaussian distribution. The spot diagram or grey level image simulation will be produced. Finally, an example of its applications, raytracing of a Seya–Namioka monochromator beamline at NSRL, will be presented.
Time-dependent resistance relaxation in carbon and RuO2 based thermometers
Authors: Skrbek L. , Stehno J. , Šebek J.
Published: July 2002

The long-term time-dependent relaxation of the electrical resistance in several carbon and RuO2 based temperature sensors at helium temperatures was investigated. The relative change of the resistance at fixed low temperature, measured immediately after sufficiently rapid cooldown has been found to be always logarithmic with time. In the helium temperature range, the spurious temperature drift associated with this effect for Allen–Bradley and Matsushita carbon radio resistors and for Philips RuO2 based thick film sensors reaches about 1 mK per time decade, while for Rivac carbon film sensors it is an order of magnitude higher. The theoretical model explaining this relaxation based on the variable range hopping conductivity mechanism and the standard levels AHV theory of glasses at low temperatures was developed.
Reduced background light in visual low-energy electron diffraction using an optical bandpass filter
Authors: Phaneuf R. J. , Kan H.-C.
Published: July 2002

We describe the use of an interference-type optical bandpass filter matched to the output spectrum of the phosphor screen to selectively attenuate the light background coming from nearby radiant objects, such as evaporative sources or the (hot) sample under investigation itself in low-energy electron diffraction. We find a dramatic improvement in signal-to-background intensity resulting in an enhanced signal-to-noise ratio over merely subtracting away the measured radiant background.
Automatic system for the measurement of very low coercive fields
Authors: Tejedor M. , Rubio H. , Elbaile L. , Iglesias R.
Published: July 2002

A simple method for the determination of coercive fields is described. It is based in the comparison between two signals; one proportional to the applied field which excites the sample, and the other proportional to the internal field that acts directly on the magnetization. Coercive fields as low as 0.14 A/m can be reliably measured and the error using this system does not exceed 0.02 A/m.
Photoacoustic spectroscopy use in the analysis of ion-implanted CuInSe2 single crystals
Authors: Zegadi A. , Al-Saffar I. S. , Yakushev M. V. , Tomlinson R. D.
Published: July 2002

A high-resolution near-infrared photoacoustic spectrometer of the gas–microphone type is used for room-temperature analysis of the defect states in ion-implanted CuInSe2 single crystals. A wide range of ions differing in their masses as well as in their electrical activities in the host crystal (O+, Ne+, Cu+, Xe+, and Li+) have been implanted at various energies and doses to assess the technique sensitivity to detect changes affecting the compound subgap absorption spectrum, which is characteristic of impurities. The detected changes (either by the appearance of new peaks or by a change in the impurity or defect concentrations) are shown to differ from one ion species to another. The depth profiling capability of the technique in analyzing implanted samples is also discussed. The results obtained here are correlated to existing published data. It is shown that photoacoustic spectrometry can be very useful if used to appraise the complex defect structure of ion-implanted CuInSe2.
Instrumentation and key elements of the dispersive x-ray absorption spectrometer for accurate measurements (invited) (abstract)
Authors: Fontaine A. , Baudelet F. , Dartyge E. , Dubuisson J. M. , Giorgetti C. , Pizzini Stefania , Andrault D. , Farges F. , Fiquet G. , Itié J. P. , Polian A. , Miguel A. San , Tolentino H.
Published: July 2002

Measurement of very small differences of the total cross section is the current demand for the spectrometers dedicated to time-dependent experiments carried out under various time-ramped parameters. The dispersive optics and more precisely the full x-ray-absorption spectrometer is mechanically movement-free during data collection which can last over 12 h at LURE-DCI to be sensitive to relative change of the absorption of the order of 10−5. In this range, artefacts due to the drift of silicon lattice spacing under temperature change of the crystal, and drifts of the detector position because of liquid–nitrogen evaporation contained in the cryostat, are sources of errors which have been identified and cured or ... by-passed. The accuracy in difference measurements is now of the order of 10−5 for a total cross section measured equal to 1. In term of optics stability a difference signal of 10−4 out of 1 can be generated by an absorption edge shift caused by a 0.05 K drift of the temperature of the silicon crystal at 7 keV. These performances are essential for the measurement of XMCD in the hard-x-ray range. Water cooling of the dynamically bent crystal reduces dramatically the change of the Si temperature. Adequate geometry makes the spatial drift of the position of the photodiode array much less concerning. The focusing efficiency is also a key parameter to push high-pressure x-ray-absorption spectroscopy (55 GPa), and high-temperature XAS (2000 K), and the combination (15 GPa, 800 K). Simple devices, taking advantage of the focusing geometry, have been successfully tested these last two years.
Photon beam position monitor for SSRL Beamline 9
Authors: Cerino John A. , Rabedeau Thomas , Bowen William
Published: July 2002

We present here the concept of a simple one-dimensional photon beam position monitor for use with high-power synchrotron radiation beams. It has micron resolution and reasonable linearity in an inexpensive design. Most important, is its insensitivity to diffusely scattered low-energy radiation from components upstream of the monitor.
The Troika Beamline at ESRF (abstract)
Authors: Grübel G. , Als-Nielsen J. , Abernathy D.
Published: July 2002

The Troika Beamlime at ESRF is based on the concept of beam multiplexing by using x-ray transparent diamond and/or beryllium monochromators. The favorable thermal and crystallographic properties of perfect diamond are well matched to the characteristics of the new low emittance undulator sources. A series of such transmission monochromators can use the same white beam and supply several experimental stations simultaneously with monochromatic x-rays of slightly different energies. The first experimental station of the Troika beamline is operating and the multiplexing mode has been tested successfully. First experiments including protein crystallography, resonant magnetic scattering, liquid surface diffraction, and scattering with coherent x-rays were carried out during the commissioning period and the results demonstrate the wide potential of third-generation synchrotron sources.
Macromolecular crystallographic results obtained at CHESS using a detector incorporating a charge-coupled device
Authors: Thiel Daniel J. , Walter Richard L. , Ealick Steven E. , Bilderback Donald H. , Tate Mark W. , Gruner Sol M. , Eikenberry Eric F.
Published: July 2002

Results from various macromolecular crystallography experiments are presented showing the effectiveness of a recently installed detector incorporating a charge-coupled device (CCD). This detector uses a 1024×1024 CCD directly coupled to an x-ray sensitive phosphor by a fiber optic taper. The pixel size at the phosphor (50 μm) results in a point spread of 80 μm full width at half-maximum. Even with the relatively small active area, 51×51 mm2, about 150 orders of diffraction can be resolved across the detector face. With this detector format, well-resolved diffraction data have been collected from unit cells with edges as large as 360 Å. In an offset configuration, the detector has been used to collect extremely high-resolution data (1 Å). A number of data sets have been collected having Rsym values in the 4%–6% range; in the case of room-temperature lysozyme, an Rsym value as small as 2.1 was obtained for a 2.5 Å resolution data set. In addition to fixed wavelength studies, the detector has also been used to collect MAD data. In all cases, the use of this detector has proven to be more efficient than using standard image plates since less x-ray exposure time and no distinct scanning step are required. Furthermore, the data quality is as good and in some cases better than those from previous image plate measurements.
CO2 laser heating instrumentation at CHESS (abstract)a)
Authors: Brister Keith , Bassett William
Published: July 2002

A new instrument constructed at the high-pressure facility at CHESS provides a simple mechanism to group MCA data on the basis of a rapidly varying sample temperature. This system allows powder diffraction from samples at simultaneous high pressures and high temperatures in a diamond-anvil cell. The instrument consists of a laser beam delivery system and incandescent light collection optics to analyze the resulting graybody spectra. A portion of the incandescent light controls into which multichannel analyzer group the x-ray-diffraction pattern accumulates. We illustrate the performance of the system with recent experiments.
Construction of a system for novel low-temperature growth of II–VI compound semiconductors using synchrotron radiation
Authors: Ogata Toshihiro , Ikejiri Makoto , Gheyas Syed Irfan , Ogawa Hiroshi , Nishio Mitsuhiro
Published: July 2002

As a novel application of synchrotron radiation, we describe a growth technique for the II–VI compound semiconductors. A growth system suitable for synchrotron-radiation excited deposition has been designed and constructed in the beam line BL4A at the UVSOR facility. Characteristics of this growth system and experimental results with respect to ZnTe as an example are described. It has been confirmed by using the system constructed that this method is useful as a low-temperature growth technique for II–VI compounds.
A microscopic setup for combined, and time-coordinated electrophysiological and confocal fluorescence microscopic experiments on neurons in living brain slices
Authors: Helm P. J.
Published: July 2002

In this paper, a microscopic system for cell physiological research is presented. The setup which is to a large extent based on commercially available products was designed to establish a platform for time-coordinated electrophysiological and fluorescence optical compound experiments on living neurons in brain slices. Instruments for infrared differential interference contrast video microscopy (IRDICM), confocal scanning laser microscopy (CSLM), and for patch clamp studies have been assembled into one unit. Using the IRDICM equipment, a neuron can be patched somatically and dendritically. Loading the neuron with a Ca2+ indicating dye substance can be examined epifluorescence optically using the Hg lamp or Xe lamp of the microscope. A stimulus initiating the propagation of an action potential through a dendrite can be synchronized to the electronic control unit of the CSLM, and changes in the concentration of Ca2+ in the dendrite can be recorded in a time-coordinated way. The setup has been used successfully in order to study in vitro the dynamics of intracellular Ca2+ in the dendritic system of living neurons in brain slices.
Circulation pump for high purity gases at high pressures and a novel linear motor positioning system
Authors: Walker I. R.
Published: July 2002

A clearance-sealed piston pump has been developed which can be used to move high pressure gases in a closed loop for the purpose of purification, mixing, or phase equilibration. It has been designed primarily with the former role in mind, so that inert gases may be used in the preparation of high purity intermetallic compounds to suppress the evaporation of volatile constituents without introducing contamination. To this end, the device is made in such a way as to minimize outgassing, leakage, the formation of dead volumes, and the creation of debris. The pump is intended for use at pressures of up to 200 bar. Its structural materials are highly resistant to corrosion, and this should enable the device to be used with a wide variety of reactive gases. Flow rates of between 4.3 and 0.043 ℓ min−1 can be sustained without difficulty using realistic loads, although larger and smaller ones are possible. The pump is capable of producing a head of 0.23 bar. A novel system has been developed for sensing and controlling the position of the piston. This makes it possible to monitor and vary the instantaneous flow rate while minimizing wear and vibration. The arrangement does not require the presence of a transducer or any kind of feedthrough in the clean, high pressure environment. It may find applications in other areas where positioning is needed under hostile or demanding conditions, such as inside ultrahigh vacuum apparatus.
Use of a double-Wollaston prism laser differential interferometer in a plasma focus
Authors: Lu Ming Fang
Published: July 2002

A double-Wollaston prism laser differential interferometer (LDI) has been developed to observe, for the first time, the evolution of the imploding current sheath (CS) and the high temperature and high density plasma pinch in the plasma focus. The light source is a Q-switched and frequency-doubled YAG laser operated in a single-pulse mode: λ=532 nm, the pulse width (FWHM) about 10 nm (also the resolution time of the LDI). The LDI measures density gradients and has a line sensitivity of about ne′=(2.58±0.46)×1025 m−4 for a typical sheath thickness of 1.6 mm and a minimum distinguishable fringe shift of 5%, and a spatial resolution of 1.26 mm. The density gradient and equivalent density of the CS are measured to be ne′≈(2.58±0.46)×1026 m−4 and ne≈(3.25±0.59)×1023 m−3, respectively. More importantly in this article, the double-Wollaston prism LDI, with a simple optical arrangement, gives direct physical pictures of the high density gradient plasma configuration and structure which are of interest in studying the status of plasma motion.
Reflection time-of-flight mass spectrometer for charge-transfer cross section measurements
Authors: Wang Jiebing , Kwong Victor H. S.
Published: July 2002

A new method is described that combines the production of ions by laser ablation with a reflection time-of-flight mass spectrometer for charge-transfer cross section measurements. This method allows a specific charge-transfer channel of an ion-neutral pair to be measured at energies of about 0.1 keV/amu. The metastable state ion fraction in the laser ablation ion beam is shown to be negligible. The charge-transfer cross section is determined by measuring the intensity ratio of the product ions to the parent ions after the charge-transfer reactions occur in the reflection drift tube. Verification on the apparatus is demonstrated through investigation of a single electron charge transfer of ground state C2+ions and H2 with the incident energy of C2+at 3045.6(σ=12.4) eV. Our measured cross section of 6.90(±0.78)×10−16 cm−2is consistent with ground state measurements reported previously. Because of the versatility of the pulsed laser ablation ion source, this facility can be used to examine the cross sections of a variety of multiply charged ions from refractory or gaseous elements.
A large aperture laser triggered intensified charge coupled device using second-harmonic laser light triggering
Authors: Yamauchi Toshihiko , Dimock Dirck
Published: July 2002

For application to a ruby laser Thomson scattering system, we have developed a laser triggered intensified charge coupled device (CCD) with 80 mm aperture, two stages of intensification, and 80 ns gating. To improve the dynamic range, the CCD is cooled and read out slowly (1 s). To obtain a good extinction ratio (>1.1×107), the zoom electrode of the first intensifier is gated using a ∼10 kV laser triggered spark gap. The stability of this spark gap has been greatly improved by frequency doubling the laser trigger light.
Stabilization of thermal instability of multislit ion–optics system by longitudinal tension
Authors: Davydenko V. I. , Morozov I. I.
Published: July 2002

A thermal instability of electrodes of a large multislit ion–optics system is considered. The mechanism of this instability is that under certain conditions a random bending of the electrode increases due to the increase in heating of the convex side of the electrode. The thermoelastic model for the tension in the electrode is used. This instability is close to the Eiler instability of a longitudinally compressed bar. The instability threshold depends on the power gradient near the electrode edge. This gradient is sufficiently small in an optimal beam formation and sharply increases in nonoptimal regimes. The thermal instability analysis based on this model applied to the INAK proton source and its predictions are in a good agreement with experimental data. To eliminate this instability, it was suggested to use the longitudinal tension of the electrodes. This suggestion was realized in the IK-50 proton source ion–optics system. Molybdenum wires of 1 mm in diameter are loaded by a spring with 100 N force that is lower than the experimentally measured limit of fluidity. The IK-50 source operation in various regimes does not show any evidence of the thermal instability.
A bakeable in-line ultrahigh-vacuum valve
Authors: Budge J. , Hayes P. A. , Yu D. H. , Williams J. F. , Robins J. L.
Published: July 2002

A bakeable ultrahigh-vacuum valve, with a coarse screw thread and conical springs, eliminates slip common to differential thread valves and reduces the bakeout-induced compression and release of the valve disk. The straight-through valve isolates a polarized electron source from gas scattering regions and maintains precision electron optical paths using a right-angled insertable electron lens.
Fast wavelength switching of narrow-band excimer lasers
Authors: Grebner D. , Müller D. , Triebel W.
Published: July 2002

A novel system was developed, which allows one to switch the wavelength of a narrow-band excimer laser between two successive light pulses at a repetition rate of at least 250 Hz. This is realized by a periodically driven piezo actuator, which is attached to the diffraction grating of the narrow-band KrF excimer laser. The achieved position accuracy of the grating leads to a wavelength reproducibility of ±0.2 pm, which allows one to apply this system to laser spectroscopic investigations like LIF or LIPF of OH in flames. Using the fast wavelength switching system background reduced concentration and temperature fields in flames can be measured within one sequence. Some possible realized and planned applications like the measurement of gas temperature, the diagnostic of turbulent combustion processes, and the investigation of combustion processes under microgravity are discussed.
Use of thermal barriers in conceptual studies of high-temperature, high-intensity targets for producing radioactive ion beams
Authors: Talbert W. L. , Hodges T. A. , Hsu H.-H. , Fikani M. M.
Published: July 2002

Thermal analyses are presented of a cylindrical target concept for the production of radioactive beams by intense, high-energy proton production beams. The basic principle is to extract heat generated internally by the production beam interactions with the target material through appropriate thermal barriers. This approach allows the target material to be operated at an elevated temperature to enhance the release of radioactivities produced by the production beam bombardment, yet remove the heat generated initially. Three classes of targets are considered: high temperature and moderate heat generation; moderate temperature and low heat generation; and low temperature and high heat generation. Various thermal barriers approaches appropriate to the combined temperature and heat removal constraints are included, such as contact thermal resistance, refractory material interfaces, and porous metal interfaces. It is shown that suitable thermal barrier approaches exist to encompass the range of target conditions expected for the production of intense beams of radioactive ions.
Laser ion source via direct ionization at the outlet of a helium jet
Authors: Rencheng Shang , Sida Xu , Wei Zhang , Rong Yi , Shuming Zhang , Zipiao Ye , Zhizheng Zhao , Yixiao Luo
Published: July 2002

A laser ion source based on laser resonant ionization at the outlet of a helium jet was proposed for on-line isotope separator of the Heavy Ion Research Facility in Lanzhou, China a few years ago. An off-line test setup was built at Tsinghua University. The initial experimental results of the setup indicate that carrying neutral Na monoatoms to the outlet of a helium jet and directly ionizing the Na atoms in the helium jet beam by laser resonant ionization is very efficient. It provides an effective method for producing element selected ions with high efficiency, low background, and short transporting time. It is applicable for the separation of various elements, and is particularly useful for refractory elements.
Ion energy loss spectroscopic apparatus using cylindrical electrostatic energy analyzer equipped with the Matsuda plate
Authors: Iwamoto Kenichi , Matsumoto Akira
Published: July 2002

An ion energy loss spectrometer is designed and fabricated. The energy analyzer in our apparatus consists of 180°-cylindrical condenser electrodes equipped with the Matsuda plates. Its advantage is that focusing can be achieved by changing the electric potential applied to the Matsuda plates, which are placed at both ends of the cylindrical condenser. By this method, our energy analyzer becomes equivalent to the usual spherical condenser and its fringing field can be eliminated. The best energy resolution is 50 meV. Vibrational excitations of CO and CO2 by Li+ impact are measured with our spectrometer.
Installation of a high-sensitivity laser strainmeter in a tunnel in central Italy
Authors: Crescentini Luca , Amoruso Antonella , Fiocco Giorgio , Visconti Guido
Published: July 2002

A new laser interferometer for geophysical purposes is being operated in an underground laboratory in central Italy. A simple electro-optical technique has been used to limit the costs. The main characteristics of this instrument are: high sensitivity (Δl/l≈10−12), fast sampling rate (up to 6 kHz), large dynamic range (unbounded in principle), the capability of following strain rates as high as 7×10−5 s-1, and good reliability (two failures in nearly two years).
Pseudo-incommensurate two-stimulus generator
Authors: Mitschke F.
Published: July 2002

A signal generator is described that provides two oscillations of “almost” incommensurate frequencies, along with their sum and difference frequency. There is no phase drift between the outputs since all signals are generated from a single master clock. The concept is based on Fibonacci approximands to the golden mean. Technical implementation requires ordinary digital frequency dividers and a single phase-locked-loop frequency multiplier. Applications are measurements of weak nonlinearities in “almost linear” transfer functions.
Accelerometer adaptor for measurements of metal plate response from a near field explosive detonation
Authors: Yiannakopoulos George
Published: July 2002

An accelerometer adaptor, for near field shock wave measurements, is described for applications in which the mounting structure undergoes elasto-plastic deformation. It is of simple construction, light, easy to install and remains attached on the mounting surface during relatively large deformations. The design overcomes the possibility of the accelerometer being projected from the mounting plate, which results from mounting directly on a plate surface. It was successfully employed for measuring peak accelerations up to 100 000 g.
Interpretation of the connecting lines in the projectional xx′ emittance in view of Liouville’s theorem
Authors: Sarstedt M.
Published: July 2002

For the analytical and numerical description of the emittance of a particle beam in cylindrical symmetric transport and accelerator systems often the rr′ plane is used, yielding a sectional emittance ε (r, r′). In contrast, emittance measurements are mostly taken as the projectional emittance ε (x, x′). As could be shown earlier, the description of a cylindrical symmetric beam in the projectional xx′ plane of phase space results in the presence of lines for each ring of particles, connecting the two corresponding points, with which the same beam is described in the rr′ plane. There is a very special intensity distribution along these lines, both for straight as well as for skew trajectories. It is shown here that the theoretically obtained density distribution along such a line is a weight function for the intensity measured with a slit of width Δx. For one particle it can also be interpreted as a probability function for the particle being at a certain position x0. In view of Liouville’s theorem, the case of the two-dimensional emittance in cylindrical symmetric systems is discussed, where this law of conservation is, due to the coupling of the x and y planes, not generally applicable. It is shown here that for an emittance measurement performed in the xx′ plane, care has to be taken when choosing the slit width, since a small Δx yields a good spatial resolution, but increases the risk of missing information in the center of each connecting line.
A partial pressure monitor and controller for stable ozone flow from a silica gel trap
Authors: Stevens R. E. , Hsiao C.-W. , Le Linh , Curro N. J. , Monton B. J. , Chang B.-Y. , Kung C.-Y. , Kittrell C. , Kinsey J. L.
Published: July 2002

A new ozone trapping system designed for safe and consistent delivery to a reaction vessel is described. Silica gel is used to trap the ozone because of its known safety advantages over traps that store ozone in liquid form. The new design is free of any liquid baths, such as freon or flammable solvents. A circuit design for monitoring and controlling the ozone partial pressure of 6–25 Torr is also described.
A simple approach for design of coaxial reflection coefficient standards
Authors: Negi P. S. , Singh Ranjit , Yadava R. S.
Published: July 2002

A simple approach for design of coaxial reflection coefficient standards has been described. Coaxial transfer standards of voltage standing-wave ratios 1.30 and 1.50 have been designed at 4 GHz in the form of a step-up quarter-wave coaxial line terminated by a precision match termination. The uncertainties in the reflection coefficient magnitude of the coaxial standards due to the effect of discontinuity susceptances, dimensional tolerances, and reflection from the match termination have been presented.
The University of New Mexico/Sandia National Laboratories small-angle scattering laboratory
Authors: Rieker Thomas P. , Hubbard Paul F.
Published: July 2002

The University of New Mexico/Sandia National Laboratories small-angle scattering laboratory provides a wide q-range, 3×10−4 Å−1<q<0.7 Å−1, for the structural analysis of materials on length scales from a few angstrom to ∼0.1 μm. The wide q-range is accomplished by combining data from a Bonse-Hart spectrometer (3×10−4 Å−1<q<3×10−2 Å−1) and a 5 m pinhole (3×10−3 Å−1<q<0.7 Å−1) instrument. Automation of the data acquisition systems along with a variety of sample environments and sample changers yields flexible, high throughput instruments.
A novel spectrometer combining laser and electron excitation and deflection of atoms and molecules
Authors: Murray Andrew J. , Hammond Peter
Published: July 2002

A new spectrometer is described which combines electron impact excitation and deflection studies of atoms and molecules with laser spectroscopy. The spectrometer initially excites ground state atomic or molecular targets to a metastable state by employing an electron beam well defined in direction and energy. These metastable targets are then further excited to high Rydberg states (n⩾20) by employing resonant laser radiation derived from a frequency doubled pulsed dye laser. The high-n Rydberg targets are subsequently field ionized by a pulsed electric field and are detected as a function of both laser wavelength and electron impact energy, allowing state selected differential cross section measurements to be ascertained. The momentum transferred to the target by the electron impact can be exploited to provide additional information about the atomic or molecular state excited by electron impact.
Novel hydrogen sensors using evanescent microwave probes
Authors: Tabib-Azar M. , Sutapun B.
Published: July 2002

Gas sensing using local probes, such as atomic force and scanning tunneling microscopes, enables accurate measurement and detection of very small quantities of gas molecules and chemicals. Here, we report a unique application of the evanescent microwave probes (EMP) in detecting hydrogen. The EMP is extensively used to map resistivity and other nonuniformities in a variety of materials including metals, insulators, semiconductors (both organic and inorganic), composites, and biological specimens. The EMP detects the microwave resistivity of the sample and it has an exponential sensitivity to distance and thickness variations. Here, the EMP is used to detect deflections in a Pd-coated cantilever and to quantify the amount of stress and the resistivity change in the Pd film as a function of hydrogen concentration. The stress was in the range of 5.26–8.59×107 Pa for H2 concentrations of 0.5%–1.4% at room temperature, which is about three times larger than that found in the bulk Pd for the same range of H2 concentrations. The Pd film’s resistivity changed by 13.5% at 3.0%H2 concentration and it resulted in an 18% change in the EMP signal. The EMP with an appropriate frequency can also be used to resonantly detect various physi-absorbed molecules at the surface of an appropriate material as well. We discuss these possibilities along with some specific experimental data.
Third-order optical nonlinearity and all-optical switching in porous silicon
Authors: Henari Fryad Z. , Morgenstern Kai , Blau Werner J. , Karavanskii Vladimir A. , Dneprovskii Vladimir S.
Published: July 2002

The third-order optical nonlinearity χ(3) of porous silicon has been measured using the Z-scan technique. Intensity dependent absorption was observed and attributed to a resonant two photon absorption process. The real and imaginary parts of χ(3) have been measured at 665 nm and found to be 7.5×10−9 esu and −1.9×10−9 esu, respectively. This constitutes a significant enhancement over crystalline silicon. All optical switching based on nonlinear absorption is demonstrated.
Electric-field induced cylindrical lens, switching and deflection devices composed of the inverted domains in LiNbO3 crystals
Authors: Yamada M. , Saitoh M. , Ooki H.
Published: July 2002

Three kinds of electro-optic devices composed of the inverted domains in LiNbO3 substrates were fabricated. The devices are induced and controlled by applying an electric field. The three devices are: (i) a cylindrical lens with an aperture of 340 μm and length of 10 mm, which can tune the focusing length from 20 to 50 mm depending on an electric field ranging from 250 to 150 V/mm, (ii) an optical switching device composed of a periodically inverted domain structure, which can reflect the whole power of an incident light beam by applying an electric field of 700 V/mm, and (iii) a deflection device with a deflection angle of about 5°, depending on an electric field of 750 V/mm.
Sequential lateral solidification of thin silicon films on SiO2
Authors: Sposili Robert S. , Im James S.
Published: July 2002

We report on a low-temperature excimer-laser-crystallization process that produces a previously unattainable directionally solidified microstructure in thin Si films. The process involves (1) inducing complete melting of selected regions of the film via irradiation through a patterned mask, and (2) precisely controlled between-pulse microtranslation of the sample with respect to the mask over a distance shorter than the single-pulse lateral solidification distance, so that lateral growth can be extended over a number of iterative steps. Grains up to 200 μm in length were demonstrated; in principle, grains of unlimited length can be produced. We discuss how the technique can be extended to produce large single-crystal regions on glass substrates.
Use of the anisotropic magnetoresistance to measure exchange anisotropy in Co/CoO bilayers
Authors: Miller B. H. , Dahlberg E. Dan
Published: July 2002

Direct ferromagnetic antiferromagnetic exchange biasing energy is determined by small reversible rotations of the magnetization away from the unidirectional easy axis using an externally applied magnetic field. The angle the magnetization makes relative to the easy direction is determined by measuring the anisotropic magnetoresistance. This technique gives energies larger by a factor of 2 than the traditional measurements of the shift in the hysteresis loop (an irreversible process) of the ferromagnetic layer in bilayer samples of Co/CoO. An apparent Co thickness variation of the experimentally determined exchange biasing interface energy indicates the Co magnetization is not uniform but probably spirals through the thickness of the film.
Electron beam induced crystallization in Fe-doped SnO2 nanoparticles
Authors: Lu Bin , Wang Changsui , Zhang Yuheng
Published: July 2002

Nanoscale particles of Fe-doped SnO2 were intensively radiated in a high-energy electron beam observed in situ in a transmission electron microscope. Generation of small crystalline grains from agglomerated nanoparticles was observed. Electron diffraction patterns confirmed that the grains belonged to the orthorhombic phase of SnO2, which forms only under pressures higher than 140 kbar according to previous research. A possible process for the phase transition is discussed. The result suggests a novel method of producing orthorhombic SnO2 at low pressure.
Evolution of texture at growth of titanium nitride films prepared by photon and ion beam assisted deposition
Authors: Zeitler M. , Gerlach J. W. , Kraus T. , Rauschenbach B.
Published: July 2002

The effect of the film thickness on the evolution of texture of polycrystalline titanium nitride films grown by photon and ion beam assisted deposition has been investigated. The layers were deposited in high-vacuum on (111)Si with the N-ion energy constant at 2 keV and the incident ion/titanium flux ratio constant at 0.66 ions/atom. X-ray pole figure measurements show that the biaxial {001} texture is changed to the biaxial {111} texture with an increase of the film thickness. The texture evolution is explained by the existence of open channeling directions and the minimization of the elastic deformation energy.
Electric field measurement in the cathode fall region of a glow discharge in helium
Authors: Kuraica M. M. , Konjević N.
Published: July 2002

Spatial distribution of electric field strength in the cathode fall region of an analytical glow discharge in helium and helium-hydrogen mixture is determined from the Stark splitting and shifting of three visible helium lines and their forbidden components. For this diagnostic technique the basic theory is outlined. The results in gas mixture agree well with electric fields determined from the shape of Hβ line.
Thermal processing of strained InGaAs/GaAs quantum well heterostructures bonded to Si via an epitaxial lift-off technique
Authors: Rammohan K. , Rich D. H. , MacDougal M. H. , Dapkus P. D.
Published: July 2002

We have investigated the effects of thermal cycling on the optical properties of In0.2Ga0.8As/GaAs single quantum well films bonded to Si(001) via the epitaxial lift-off technique. The optical and structural quality of the bonded films were monitored using cathodoluminescence (CL) imaging and spectroscopy. The films were stable through the temperature range (500–700 °C) used in normal InxGa1−xAs device processing. However, annealing at temperatures greater than ∼700 °C resulted in layer intermixing accompanied by a blue-shift in the CL peak energy. The shifts in the CL peak energy were modeled by considering In–Ga interdiffusion at the interface and solving the Schrödinger equation using appropriate band profiles for this region.
Identification of the terminating structure of 6H–SiC(0001) by coaxial impact collision ion scattering spectroscopy
Authors: Ishiyama O. , Nishihara T. , Shinohara M. , Ohtani F. , Nishino S. , Saraie J.
Published: July 2002

The terminating structure of 6H–SiC(0001) substrates fabricated by the Acheson method was directly identified by means of coaxial impact collision ion scattering spectroscopy (CAICISS). The CAICISS spectra showed that the topmost surfaces of the samples were Si-terminated planes for both the front and rear faces. It was also shown that the (0001)Si face was composed of Si-terminated flat terraces and steps, the height of which corresponded to one-half the unit cell length along the 6H–SiC c axis.
Surface potential of thin perfluoropolyether films on carbon
Authors: Novotny V. J. , Karis T. E.
Published: July 2002

Perfluoropolyether (PFPE) films for lubrication of thin film magnetic recording media are made progressively thinner and their physical properties are increasingly dominated by molecular interactions with the carbon overcoat. Surface potential measurement is one of a few techniques to study the interaction of ultrathin films with surfaces. A scanning Kelvin probe apparatus with spatial resolution of 100 microns and potential sensitivity of 0.5 mV was employed to study the surface potentials of linear and branched PFPE films with methyl, hydroxyl, phenyl ester, and carboxylic acid end groups on amorphous hydrogenated carbon surfaces. The surface potential is dominated by polar groups rather than the PFPE monomers. Application of the scanning surface potential technique to measure the migration of PFPE films is also shown.
Novel application of a perturbed photonic crystal: High-quality filter
Authors: Lei Xin-Ya , Li Hua , Ding Feng , Zhang Weiyi , Ming Nai-Ben
Published: July 2002

The transmission of light waves through a perturbed photonic crystal has been investigated. The perturbed photonic crystal was constructed by randomly repeated stacking of a number of identical unit cells. Although most of the light waves are localized by the randomness, there still exist light waves with special wavelengths which are in extended states. This produces a high-quality resonant tunneling with a very narrow transmission coefficient peak.
Nanoscale imaging of domain dynamics and retention in ferroelectric thin films
Authors: Gruverman A. , Tokumoto H. , Prakash A. S. , Aggarwal S. , Yang B. , Wuttig M. , Ramesh R. , Auciello O. , Venkatesan T.
Published: July 2002

We report results on the direct observation of the microscopic origins of backswitching in ferroelectric thin films. The piezoelectric response generated in the film by a biased atomic force microscope tip was used to obtain static and dynamic piezoelectric images of individual grains in a polycrystalline material. We demonstrate that polarization reversal occurs under no external field (i.e., loss of remanent polarization) via a dispersive continuous-time random walk process, identified by a stretched exponential decay of the remanent polarization.
Low temperature formation of C54–TiSi2 using titanium alloys
Authors: Cabral C. , Clevenger L. A. , Harper J. M. E. , d’Heurle F. M. , Roy R. A. , Lavoie C. , Saenger K. L. , Miles G. L. , Mann R. W. , Nakos J. S.
Published: July 2002

We demonstrate that the temperature at which the C49 TiSi2 phase transforms to the C54 TiSi2 phase can be lowered more than 100 °C by alloying Ti with small amounts of Mo, Ta, or Nb. Titanium alloy blanket films, containing from 1 to 20 at. % Mo, Ta, or Nb were deposited onto undoped polycrystalline Si substrates. The temperature at which the C49–C54 transformation occurs during annealing at constant ramp rate was determined by in situ sheet resistance and x-ray diffraction measurements. Tantalum and niobium additions reduce the transformation temperature without causing a large increase in resistivity of the resulting C54 TiSi2 phase, while Mo additions lead to a large increase in resistivity. Titanium tantalum alloys were also used to form C54 TiSi2 on isolated regions of arsenic doped Si(100) and polycrystalline Si having linewidths ranging from 0.13 to 0.56 μm. The C54 phase transformation temperature was lowered by over 100 °C for both the blanket and fine line samples. As the concentration of Mo, Ta, or Nb in the Ti alloys increase, or as the linewidth decreases, an additional diffraction peak appears in in situ x-ray diffraction which is consistent with increasing amounts of the higher resistivity C40 silicide phase.
Intermixing induced changes in the radiative emission from III–V quantum dots
Authors: Lobo C. , Leon R. , Fafard S. , Piva P. G.
Published: July 2002

We have examined the effect of thermally induced interdiffusion on the luminescence emission from red and infrared emitting self-assembled III–V quantum dots. Three different combinations of dot/barrier materials have been investigated: InAlAs/AlGaAs, InGaAs/AlGaAs and InGaAs/GaAs. In all cases, thermal intermixing was found to result in significant blueshifts of the photoluminescence (PL) emission. In addition, narrowing of the linewidth of the inhomogeneously broadened PL peak was observed. Both effects were found to be strongly dependent on the material system and average dot size. InAlAs/AlGaAs quantum dots exhibited the greatest linewidth reduction after intermixing, indicating this to be a promising method of achieving narrower luminescence lines for devices such as red-emitting zero-dimensional lasers.
Crystallization and orientation of C60 from C60/polymethyl methacrylate films
Authors: Chen Guanghua , Ma Guobin
Published: July 2002

The crystallization and orientation behaviors of C60 for C60-doped polymethyl methacrylate films are reported. The results show a high tendency of crystallization of C60 with increasing its content, and a preferential (111) orientation for heavily doped films upon high-temperature annealing. The expansion of the lattice constant and the existence of hexagonal close-packed stacking faults are also investigated. The orientation phenomenon indicates an efficient method for the growth of (111)-oriented C60 on a variety of substrates, including those with strong surface bondings on which the orientation is difficult to form via conventional methods.
Polarity determination for GaN films grown on (0001) sapphire and high-pressure-grown GaN single crystals
Authors: Rouviere J. L. , Weyher J. L. , Seelmann-Eggebert M. , Porowski S.
Published: July 2002

In order to resolve any doubt in lattice polarity calibrations, a given undoped GaN layer deposited on (0001) sapphire by metalorganic chemical vapor deposition and a given high-pressure-grown GaN single crystal have been studied by three different techniques: Hemispherically scanned x-ray photoelectron diffraction, convergent beam electron diffraction, and chemical etching. We conclude that Ga-polar surfaces are resistant to a 200 °C molten NaOH+KOH etching whereas N-polar surfaces are chemically active. All the observed flat GaN films grown on (0001) sapphire have Ga polarity. On the contrary, the native flat faces of undoped GaN bulk crystals have N polarity.
Thin multiplication region InAlAs homojunction avalanche photodiodes
Authors: Lenox C. , Yuan P. , Nie H. , Baklenov O. , Hansing C. , Campbell J. C. , Holmes A. L. , Streetman B. G.
Published: July 2002

Low excess noise in avalanche photodetectors (APDs) is desired for improved sensitivity and high-frequency performance. Gain and noise characteristics are measured for InAlAs p-i-n homojunction APDs that were grown with varying i-region widths on InP by molecular beam epitaxy. The effective ionization ratio k (β/α) determined by noise measurements shows a dependence on multiplication region width, reducing from 0.31 to 0.18 for multiplication region thicknesses of 1600–200 nm. This trend follows previously shown results in AlGaAs-based APDs, which exhibit reduced excess noise due to nonlocal multiplication effects. These results show that this effect is a characteristic of thin avalanche regions and is not a material-specific phenomenon.
Raman study of BaFe12O19 thin films
Authors: Kreisel J. , Pignard S. , Vincent H. , Sénateur J. P. , Lucazeau G.
Published: July 2002

We report on Raman spectra of BaFe12O19 thin films. These thin films have been deposited by injection chemical vapor deposition on three different substrates: Al2O3 (001), Gd3Ga5O12 (111), and Si (100). The observed Raman-active vibrations of the films are compared with recently published Raman spectra from bulk compounds. Surprisingly, we observed nearly the same spectra for all the films, although x-ray diffraction indicates polycrystalline (Si), textured (Gd3Ga5O12), and epitaxial (Al2O3) structure. We interpret these results by supposing the coexistence of well oriented regions and randomly oriented microcrystallites, which are not detectable by x-ray diffraction. Furthermore, by Raman spectroscopy we identified an additional phase for the films deposited on Al2O3 which has not been observed by x-ray diffraction either.
Tailoring of electron energy distributions in low-pressure inductive discharges
Authors: Haas F. A. , Braithwaite N. St. J.
Published: July 2002

Assuming a background Maxwellian electron distribution, the effects of adding an energetic tail upon the electron temperature and density in an inductive low-pressure argon discharge are investigated theoretically. The principal effect of the tail is to modify the rate constants for ionization, excitation, and momentum transfer. Using particle and energy conservation, the possibility of suppressing the electron temperature and increasing the electron density is demonstrated. It is found that under typical conditions of operation the electron temperature can be decreased from 2.5 to 1.5 eV, and the electron density increased by at least a factor of 2.4.