bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of vacuum seals for diagnostic windows of the International Thermonuclear Experimental Reactor
Authors: Nagashima A. , Nishitani T. , Fujisawa T. , Sugie T. , Kasai S.
Published: July 2002

For International Thermonuclear Experiment Reactor (ITER) diagnostic windows a new sealing method based on a V-shaped elastic ring has been developed. The ring, compressed by two valves, makes vacuum tight contact on the polished edge of the window material. Two types of V-shaped rings have been tested (one of silver coated copper and one in polyimide vespel SP-1) with three different window materials (fused quartz, sapphire, and ZnSe). The wavelength range of interest is from ∼0.4 to ∼10 μm. The performance of the seals to inner pressure rise resistance, the heat cycle, and acceleration at the level expected in the ITER environment has been examined. The tests have been carried out successfully for 120 mm diameter windows.
Far ultraviolet polychromator for spectroscopic characterization of the tokamak divertor and plasma scrape-off layer
Authors: Soukhanovskii V. A. , Stutman D. , May M. J. , Finkenthal M. , Moos H. W. , Terry J. L. , Goetz J. A. , Lipschultz B.
Published: July 2002

The Plasma Spectroscopy Group of The Johns Hopkins University is developing diagnostics for spectroscopic characterization of the tokamak plasma scrape-off layer and divertor regions. A far ultraviolet polychromator has been designed for radiative divertor studies at the Alcator C-Mod and D-IIID tokamaks. Local measurements of resonant transitions of lithium- to boron-like ions of intrinsic or seeded low Z impurity elements will be performed along multiple chords around the X point. Planar diffraction gratings and stacked grids will be used for dispersion and angular collimation of radiation. Phosphor wavelength converters coupled to a photomultiplier tube by an optical fiber will be used as detectors. The design provides a wavelength resolution of ≃10 Å, a spatial resolution of ⩽2 cm, and an adequate photometric sensitivity. The in-vessel instrument, proposed for the Alcator C-Mod tokamak, will measure intensities of the lines at 1240 (N V), 765, 923 (N IV), and 990 Å (N III). The port-mounted polychromator at DIII-D will be able to monitor intensities of 1550 (C IV), 977, 1176 (C III), and 1335 Å (C II) lines. This, together with visible and bolometric diagnostics, should enable estimates of power losses, charge state distribution and local transport of the impurity ions in the divertor. A one-channel prototype of the C-Mod and D-IIID instruments is being built for the CDX-U spherical tokamak. Line-integrated brightnesses of the 2s–2p transition at 1550 Å will be measured and inverted to obtain C IV emissivity distribution.
Modulated optical solid-state spectrometer applications in plasma diagnostics
Authors: Howard John
Published: July 2002

A new electro-optically modulated optical solid-state (MOSS) interferometer has been constructed for the measurement of the low order spectral moments of line emission from optically thin radiant media. The instrument, which is based on the principle of the Fourier transform spectrometer, is rugged, compact, and inexpensive and offers a number of advantages over conventional grating based spectrometers. Most importantly, by employing electro-optical path-length modulation techniques, the spectral information is obtained using a single photomultiplier tube. Specifically, the zeroth moment (brightness) is given by the average signal level, the first moment (shift) by the modulation phase and the second moment (line width) by the modulation amplitude. In applications such as Zeeman spectroscopy and motional Stark effect (MSE), polarization modulation can be used to effect a modulation of the center frequency and/or coherence of the light which is then measured by the MOSS spectrometer. This article describes a number of applications, including Doppler and charge exchange recombination spectroscopy and polarization spectroscopy (Zeeman and MSE) for which the MOSS spectrometer is an inexpensive and powerful alternative to multichannel grating spectrometers.
Experimental configuration of direct drive cylindrical implosions on the OMEGA laser
Authors: Barnes Cris W. , Tubbs David L. , Beck J. B. , Hoffman N. M. , Klare K. A. , Oertel J. A. , Watt R. G. , Boehly T. R. , Bradley D. K. , Knauer J. P.
Published: July 2002

Details about the cylindrical implosions using direct-drive irradiation on the OMEGA Laser facility are provided. The experimental configuration, including orientation, construction, and mounting of the targets is described. An attempt to characterize the modulation transfer function of the primary x-ray framing camera diagnostic results in insufficient exposure contrast but relative agreement with other determinations. The x-ray intensity of the titanium backlighter driven by the 2.5-ns-linear ramp of the laser beams is described, and the relative intensity on film is compared to similar Nova experiments. The parallax effects of different length marker layers of high-opacity dichloropolystyrene are measured, resulting in the conclusion that the marker layer length should be matched to the laser drive illumination profile.
Overview of probe diagnostics on the H-1 heliac
Authors: Rudakov D. L. , Shats M. G. , Boswell R. W. , Charles C. , Howard J.
Published: July 2002

A complex of probe diagnostics allows extensive characterization of the plasma parameters in the H-1 heliac. The probes used on H-1 include quadruple probes, poloidal and radial “fork” probes, a Mach probe, a 24-channel probe array, and a retarding field energy analyzer. This article provides details of the probe design and a brief description of the experimental techniques involved. Different techniques are compared. Sample results in two different modes of confinement in H-1 are presented. The capabilities of the probe diagnostics used in different combinations are discussed.
A sublimation probe for the injection of high-Z impurities into fusion devices
Authors: Geier A. , Asmussen K. , Bard A. , Neu R. , Krieger K.
Published: July 2002

For the investigation of high-Z impurities in the ASDEX Upgrade tokamak a sublimation probe was developed and tested. With this probe it is possible to inject materials, that sublimate at temperatures from about 50 to 150 °C into the plasma through a controllable valve. For the investigation of the tungsten transport in ASDEX Upgrade the probe was operated with tungsten carbonyl. The flux of tungsten, which is difficult to determine directly because of the uncertain atomic data, can be determined using the fluxes of oxygen and carbon, the atomic data of which are better known. In this article the setup of the probe and first experiments are described. Here the layer of deposited tungsten was investigated and the number of emitted photons per ionization (the S/XB ratio) for the 400.8 nm line of W I was estimated.
Picosecond time-resolved electronic spectroscopy in plate impact shock experiments: Experimental development
Authors: Knudson M. D. , Zimmerman K. A. , Gupta Y. M.
Published: July 2002

An experimental method was developed to perform picosecond time-resolved electronic spectroscopy in single-event, plate impact, shock wave experiments. Several experimental difficulties had to be addressed due to the fast time resolution (100 ps) and short time duration (12.7 ns) of such experiments. Procedures are described to address the following experimental issues: (i) synchronization of the light source, detection equipment, and the shock event within the experimental duration, (ii) incorporation of a Nd:YAG laser (operative in a repetitive mode) into the experimental configuration, and (iii) sources of temporal dispersion. Representative results are shown from experiments performed on single crystal CdS. The developments described here are also expected to be useful for shock wave experiments involving Raman, fluorescence, or other types of spectroscopy which require the use of a laser.
A new method for nondestructively monitoring the position of a charged particle beam in real time
Authors: Asada J. , Currell F. J. , Fukami T. , Nakamura N. , Nojikawa E. , Ohtani S. , Watanabe H.
Published: July 2002

The design and construction of a simple new device for nondestructively monitoring the position of an electron beam is described. By modulating a small portion of the electron-beam current, changes in the amounts of charge induced on the monitor electrodes are detected as currents. These currents are related to the location of the “center of charge” of the electron beam. Calculations and experimental results which illustrate the performance of the device are reported. This device is primarily intended for use in electron-beam ion sources and traps, although it could be applied to other situations where the beam current can be modulated.
Single-beam integrating sphere spectrophotometer for reflectance and transmittance measurements versus angle of incidence in the solar wavelength range on diffuse and specular samples
Authors: Nostell Per , Roos Arne , Rönnow Daniel
Published: July 2002

A multipurpose instrument for the measurement of reflectance and transmittance versus angle of incidence for both specular and diffuse samples in the solar wavelength range has been constructed and evaluated. The instrument operates in the single-beam mode and uses a common light source for three experimental setups. Two integrating spheres, 20 cm in diameter, are used for diffuse transmittance and reflectance measurements. The transmittance sphere can be turned around an axis through the sample to vary the angle of incidence. The reflectance sphere uses a center mounted sample and a special feature is the position of the detector, which is mounted on the sample holder at the center of the sphere. This way the detector always sees the same part of the sphere wall and no light can reach the detector directly from the sample. The third setup is an absolute instrument for specular samples. It uses a small averaging sphere as a detector. The detector is mounted on an arm which rotates around the center of the sample, and it can thus pick up both the reflected and transmitted beams including all multiply reflected components. The averaging sphere detector is insensitive to small side shifts of the detected beams and no multiple reflections between detector and optical system occur. In this report a number of calibration procedures are presented for the three experimental setups and models for the calculation of correct transmittance and reflectance values from measured data are presented. It is shown that for integrating sphere measurements, the geometry of the sphere and the diffusivity of the sample as well as the sphere wall reflectance and port losses are important factors that influence the result. For the center mounted configuration these factors are particularly important and special emphasis is given to the evaluation of the reflectance sphere model. All three instrument setups are calibrated using certified reference materials and nonscattering mirrors and substrates. The results are also compared to the results of a double-beam Beckman integrating sphere for near normal angles of incidence and Fresnel calculations. The results in this article show that good agreement is obtained between results from the different instruments if, and only if, proper evaluation procedures are applied to the measured signals.
Low-noise front-end electronics for solid-state fluorometers
Authors: Rovati Luigi , Docchio Franco
Published: July 2002

New steady-state fluorometric systems are based on solid state-optoelectronic components such as blue light-emitting diodes, avalanche photodiodes, and standard photodiodes. In the latter case, the noise performance of the front-end electronics limits the sensitivity of the instrumentation. However, signal detection performed by standard photodiode is appealing in low-cost applications. In this article, a low-noise electronic setup which processes the signal from photodetectors without internal amplification is presented. Low-noise preamplification and optimal signals shaping allow to minimize the fluorometric measurement uncertainty. The circuit has been accordingly developed and tested in operation. Using a low-cost silicon photodiode, a minimum equivalent noise power less than 1 pW/Hz has been obtained at a shaping time of 200 μs. The circuit exhibits excellent rejection to continuous ambient light and partially suppresses the alternating components.
High-efficiency Bragg–Fresnel lenses with 100 nm outermost zone width
Authors: David C. , Souvorov A.
Published: July 2002

In this article, we describe the manufacture and characterization of linear silicon Bragg–Fresnel lenses (BFLs) with outermost zone widths of 100 nm. This is, to our knowledge, a factor of 3 smaller than any other device of this kind reported so far. Furthermore, we give the first detailed description of an accurate and robust method to measure the diffraction efficiency of BFLs. The first-order diffraction efficiency of our lenses at 13.25 keV photon energy was 26%±0.5%. The combination of wide aperture angle, high efficiency, and large size of our devices results in a significant gain in achievable x-ray flux.
A novel pulling device for crystal growth
Authors: He Yizong , Zhou Fang
Published: July 2002

A novel pulling mechanism for crystal growth based on a metal rod’s thermal expansion is proposed. The pulling rate of this apparatus can be controlled continuously and smoothly by a temperature controller. A NaCl single crystal 20 mm in diameter and 4.17 mm in thickness has been successfully grown, proving the feasibility of this new device. Further improvements and potential applications are discussed briefly.
Sputtering efficiency of LiF surfaces on impact of low energy neutral helium (20–80 eV): Calibration of the interstellar neutral helium instrument on ULYSSES
Authors: Witte M. , Bleszyński S. , Banaszkiewicz M. , Rosenbauer H.
Published: July 2002

For the detection of interstellar neutral helium particles entering the inner solar system, a novel detection technique has been developed using sputtering of secondary ions from lithium-fluoride (LiF) surfaces on the impact of He particles. In order to be able to determine the interstellar He fluxes, the detection efficiency had to be determined in an energy range Ekin≈20 to 200 eV, an energy range for which data were not available in literature. Therefore, a calibration had to be performed in a dedicated accelerator system providing a neutral beam in the required energy range. While precise values could be obtained for energies above about 50 eV, significant uncertainties in the efficiency remained for lower energies, due to the difficulty in determining the absolute flux of the primary beam after acceleration, as elastic scattering of particles out of the beam geometry during the charge exchange process becomes more important. Corrections have been applied using a theoretical simulation of this process. These uncertainties have subsequently been eliminated, using the inflight measurements of neutral He during the ULYSSES mission. Due to the orbital parameters of this spacecraft, the relative energy of the interstellar He particles in the instrument’s reference system varies in the range 20–80 eV. Assuming that the interstellar He flow is stationary, i.e., it shows only negligible time variations, constant count rates would be expected over this energy range. The energy dependence in the actually observed count rates has been used to refine the efficiency calibration at low energies (⩽40 eV).
A compact x-ray beam intensity monitor using gas amplified sample current measurement
Authors: Hayakawa Shinjiro , Kobayashi Kazuo , Gohshi Yohichi
Published: July 2002

Development of a compact beam intensity monitor using gas amplified sample current measurement is described. The monitor can be a powerful tool for x-ray spectroscopy and microscopy when the beam is defined by a small pinhole or slits and when the workspace around the sample is limited. The thickness of the monitor is as small as approximately 3 mm, and the dimension is 10 mm square. The photon flux is monitored by measuring x-ray excited current from an Al foil under atmospheric conditions. Emitted electrons from the Al foil can ionize surrounding air molecules, and the gas amplified current can be measured with the use of a biased grid that prevents created ion pairs from recombination.
A thermoelastic method for the measurement of thermal expansion coefficient of solids
Authors: Beghi Marco G. , Luzzi Lelio
Published: July 2002

A measurement method for the thermal expansion coefficient of elastic solids has been developed. The method exploits the thermoelastic effect, the dual effect of thermal expansion: it is based on elastic compression of a small cylindrical specimen by a simple accessory for a conventional material testing machine whose applications are extended to the measurement of thermophysical properties. Compression induces a temperature variation proportional to the ratio of thermal expansion coefficient to specific heat; the expansion coefficient is then derived by an independent measurement of specific heat. Temperature can be measured in both quasiadiabatic and nonadiabatic conditions, and also allows in situ characterization of the temperature sensor promptness. Precision and accuracy of the measured ratio have been assessed by Certified Reference Materials: they are comparable to those of other methods.
Electrothermography apparatus for kinetics of rapid high-temperature reactions
Authors: Pelekh Aleksey , Mukasyan Alexander , Varma Arvind
Published: July 2002

A computer-assisted electrothermography setup has been developed to determine the intrinsic kinetics of rapid heterogeneous reactions under conditions of high heating rate. In this method, metal wires are heated in a reactive gas atmosphere to desired temperature in a controlled manner by passing electric current, and then by measuring time-dependence characteristics of electric power applied to the wire, the reaction kinetics is extracted. The described setup allows heating rates up to 3×105 K/s and permits investigation of reaction kinetics over time scale of few milliseconds to seconds. Other applications are also possible that require fast heating and temperature control.
Absolute and differential measurement of water vapor supersaturation using a commercial thin-film sensor
Authors: Chng C. K. , Yu H. , Libbrecht K. G.
Published: July 2002

We describe a technique for measuring the water vapor supersaturation of normal air over a temperature range of −40≲T≲0 °C. The measurements use an inexpensive commercial hygrometer which is based on a thin-film capacitive sensor. The time required for the sensor to reach equilibrium was found to increase exponentially with decreasing sensor temperature, exceeding 2 min for T=−30 °C; however, the water vapor sensitivity of the device remained high down to this temperature. After calibrating our measurement procedure, we found residual scatter in the data corresponding to an uncertainty in the absolute water vapor pressure of about ±15%. This scatter was due mainly to long-term drift, which appeared to be intrinsic to the capacitive thin-film sensor. The origin of this drift is not clear, but it effectively limits the applicability of this instrument for absolute measurements. We also found, however, that the high sensitivity of the thin-film sensor makes it rather well suited for differential measurements. By comparing supersaturated and saturated air at the same temperature we obtained a relative measurement uncertainty of about ±1.5%, an order of magnitude better than the absolute measurements.
On-ground investigation of space accelerometers noise with an electrostatic torsion pendulum
Authors: Willemenot E. , Touboul P.
Published: July 2002

A torsion pendulum has been used to measure very weak forces that limit the resolution of highly sensitive space accelerometers. A new method is described to measure damping with a feedback loop. The main results are (i) an upper limit to time evolution of contact potential differences inside electrostatic space accelerometers, (ii) the stiffness and damping from a very thin conducting wire, and (iii) an additional damping from unknown source. Consequences for space accelerometers design are derived.
Electrostatically suspended torsion pendulum
Authors: Willemenot E. , Touboul P.
Published: July 2002

A torsion pendulum without a torsion wire has been designed and realized, in order to measure very weak forces. The arm of this torsion pendulum (5.40 g, 1.32×10−6 kg m2 of inertia) is electrostatically suspended. Its 6 degrees of freedom are controlled thanks to electrostatic forces, and capacitive position sensing with a noise spectral density between 10−10 and 10−13 m/Hz. The torque noise spectral density is 1.3×10−14 Nm/Hz around 0.05 Hz with a 1/f increase at lower frequency, corresponding to 10−8 rad/s2/Hz, and 2×10−10 ms−2/Hz with a lever arm of 2 cm. The residual seismic noise limit the performances above 0.1 Hz. The free oscillating mode has a torsion stiffness of 5.14×10−8 Nm/rad and a Q of 217. This new instrument allows on ground experiments on very weak parasitic forces inside space accelerometers developed in ONERA, with a good representativeness. For example, it is possible to measure electrostatic stiffnesses with high resolution thanks to the low torque noise spectral density; the electrostatic damping phenomenon is also well seen as illustrated by the rather low Q. The instrument design and operation are described, the main performances are given, and the possibilities offered are discussed.
A time delay system with high threshold immunity
Authors: Wang Xin Xin , Chen Jianhui
Published: July 2002

A time delay system of high threshold immunity was constructed with specially designed NAND gates in which the transistors were biased off with a considerably high biasing voltage. Such a system was reliably used in the pulsed power experiment where strong electromagnetic noise was produced and proved itself to be superior to the conventional time delay system consisting of integrated circuit chips in noise immunity.
A task-switching system for digital signal processor-based scanning probe microscopes
Authors: Hall B. D. , Klank H. , Eccles C. D.
Published: July 2002

A simple software framework to manage the concurrent execution of small, programmable, tasks is described. The system is intended for use with a digital signal processor-based scanning probe microscope and is written in ANSI C. The design provides independent memory management, message passing, and structured programming of tasks.
Servomechanism for locking scanning tunneling microscope tip over surface nanostructures
Authors: Ito K. J. , Uehara Y. , Ushioda S. , Ito K.
Published: July 2002

Measurement of the light emission spectrum from a scanning tunneling microscope (STM) requires a long exposure time due to its extremely low intensity, and thermal drift of the tip during the exposure time limits the spatial resolution. To improve the resolution, a computer controlled servomechanism that locks the STM tip over a target position has been developed. We have measured the light emission spectra from individual nanometer scale structures on an evaporated Au film with and without this mechanism, and demonstrated the effectiveness of the servomechanism.
Diamond polytypes in the chemical vapor deposited diamond films
Authors: Bhargava Sanjay , Bist H. D. , Sahli S. , Aslam M. , Tripathi H. B.
Published: July 2002

Micro-Raman spectroscopy and x-ray diffraction measurements have been used to identify the presence of hexagonal diamond polytypes in chemical vapor deposited diamond films. The presence of additional reflections, in addition to the normal cubic diamond reflections in the diffraction spectra and bands at 1306 and 1193 cm−1 in the Raman spectra, are attributed to the presence of diamond 6H polytype. The presence of the 1324 cm−1 band in addition to the main diamond peak in the expanded spectra is attributed to regions with hexagonal symmetry, thus supporting the presence of hexagonal diamond polytypes. The compressive strain in diamond layers on the Si substrate is believed to create regions of hexagonal symmetry and vice versa.
Electron beam ion sources in the reflex mode of operation (review and progress report) (invited)
Authors: Donets E. D.
Published: July 2002

The reflex mode of electron beam ion source (EBIS) operation can provide repeated use of electrons, emitted by the gun cathode both for sequential ionization of positive ions and for creation of negative space charge to keep ions in an electrostatic ion trap of the source. This mode of operation provides as well a corresponding decrease of a consumed electric power compared to the electron beam power in the normal mode of EBIS operation. The studies of the reflex mode resulted in an observation of a transition to the so-called electron string state. Electron energy distributions in the strings differ from those in electron beams. Electron strings are used for production of highly charged ions. The sequence of the ion production in a string is the same as in an electron beam. The first review of experimental methods and experimental results, including the latest ones and of the first attempts to give a theoretical description of the reflex mode, is presented.
Full-field x-ray fluorescence imaging microscope with a Wolter mirror
Authors: Takeuchi Akihisa , Aoki Sadao , Yamamoto Kimitake , Takano Hidekazu , Watanabe Norio , Ando Masami
Published: July 2002

Full-field x-ray fluorescence (XRF) and transmission x-ray microscopic images were obtained with a Wolter-type mirror (10× magnification). A synchrotron radiation white beam (4–20 keV) from a bending magnet beamline at the Photon Factory was used to obtain XRF images and a conventional laboratory x-ray source (8.04 keV) was used to obtain transmission x-ray images. The effects of the coherent and the incoherent scattering x rays on the contrast of an XRF image were estimated. The scattering angle between the incidence x ray and the optical axis of the XRF microscope should be 90° to obtain the highest contrast image when the incidence x ray is horizontally polarized. Observation of small metallic inclusions in the synthesized diamond showed that the contrast of the XRF image was better than that of the transmission x-ray image.
Transport mechanisms in infinite layer phase compounds grown by molecular beam epitaxy
Authors: Xie X. M. , Hatterer C. , Mairet V. , Beuran C. F. , Coussot C. , Cavellin C. Deville , Eustache B. , Laffez P. , Xu X. Z. , Laguës M.
Published: July 2002

Thin films of infinite layer compounds were prepared by molecular beam epitaxy. Defect layers were incorporated into the structure in order to dope the infinite layer phase. Hole type doping is usually observed. Resistivity measurements show that the conduction mechanisms change gradually with increasing doping level, from activational type to variable range hopping (or a mechanism governed by the Coulomb interaction between localized electrons) and then further to a mechanism related to weak localization which can be described by Δρ=T−S, where the exponent S ranges from 0.5 to 1.5.
Simultaneous measurements of small angle x-ray scattering, wide angle x-ray scattering, and dielectric spectroscopy during crystallization of polymers
Authors: Šics I. , Nogales A. , Ezquerra T. A. , Denchev Z. , Baltá-Calleja F. J. , Meyer A. , Döhrmann R.
Published: July 2002

A novel experimental setup is described which allows one to obtain detailed information on structural and dynamical changes in polymers during crystallization. This technique includes simultaneous measurements of small angle-wide angle x-ray scattering and dielectric spectroscopy (SWD). The capabilities of the technique have been probed by following in real time the crystallization process of a model crystallizable polymer: poly(ethylene terephthalate). By performing these experiments, simultaneous information from both, the amorphous and the crystalline phase is obtained providing a complete description of changes occurring during a crystallization process. The SWD technique opens up new promising perspectives for the experimental study of the relation between structure and dynamics in materials science.
Highly charged ion based time-of-flight emission microscope
Authors: Hamza Alex V. , Barnes Alan V. , Magee Ed , Newman Mike , Schenkel Thomas , McDonald Joseph W. , Schneider Dieter H.
Published: July 2002

An emission microscope using highly charged ions as the excitation source has been designed, constructed, and operated. A novel “acorn” objective lens has been used to simultaneously image electron and secondary ion emission. A resistive anode-position sensitive detector is used to determine the x–y position and time of arrival of the secondary events at the microscope image plane. Contrast in the image can be based on the intensity of the electron emission and/or the presence of particular secondary ions. Spatial resolution of better than 1 μm and mass resolution m/Δm of better than 400 were demonstrated. Background rejection from uncorrelated events of greater than an order of magnitude is also achieved.
Ion dynamics in the sheath in multicomponent plasma with negative ions
Authors: Prakash Ram , Sarma A. , Chutia Joyanti
Published: July 2002

Observations on steady state ion-rich sheath around a negatively biased grid in a double plasma device have been made in multicomponent plasma with negative ions. A hump in the potential profile is found to occur at the sheath edge. The characteristics of the hump depend on the grid voltage, source biasing voltage, density difference in the two chambers, and the negative to positive ion concentration ratio. It is argued that resonance which is coupled with the beam ions and background ions is associated in the excitation mechanism to create the nonsymmetrical structures in the plasma potential profile. Below the critical concentration ratio, the hump grows in height and above the critical ratio, the width of the hump increases but the height decreases and ultimately it vanishes. The variation in the hump potential profile due to the injection of negative ions can be explained by the ion momentum exchange and by their dynamics.
Molecular light-emitting diodes using quinquethiophene Langmuir–Blodgett films
Authors: Pal A. J. , Paloheimo J. , Stubb H.
Published: July 2002

We report extended studies on electroluminescence from molecularly thin semiconducting Langmuir–Blodgett films of quinquethiophene. The effect of the thickness of active layer and cathode electrode material has been investigated. From all these devices, greenish electroluminescence (visible in a dark room) has been observed with quantum efficiencies of the order of 10−3%. Even five or nine layers of Langmuir–Blodgett films yield the same luminance as thicker films. The electroluminescence spectrum showed a profile identical to the photo- luminescence spectrum.
Local electrochemical oxidation/reduction: First step towards a new lithography?
Authors: Locquet Jean-Pierre , Arrouy Frédéric , Mächler Erich , Despont Michel , Bauer Peter , Williams Erica J.
Published: July 2002

Using c-axis La2CuO4 thin films, we first demonstrate that the electrochemical oxidation mainly occurs along the c axis. Then we induce oxygen-rich regions electrochemically into an otherwise oxygen-deficient matrix. On a microscopic scale the extra oxygen introduced creates metallic and/or superconducting regions in the insulating matrix. Contrary to other lithographic techniques in which large amounts of material are either removed or deposited, this technique does not induce significant height differences.
Kinetic modeling of microscopic processes during electron cyclotron resonance microwave plasma-assisted molecular beam epitaxial growth of GaN/GaAs-based heterostructures
Authors: Bandić Z. Z. , Hauenstein R. J. , O’Steen M. L. , McGill T. C.
Published: July 2002

Microscopic growth processes associated with GaN/GaAs molecular beam epitaxy (MBE) are examined through the introduction of a first-order kinetic model. The model is applied to the electron cyclotron resonance microwave plasma-assisted MBE (ECR-MBE) growth of a set of δ-GaNyAs1−y/GaAs strained-layer superlattices that consist of nitrided GaAs monolayers separated by GaAs spacers, and that exhibit a strong decrease of y with increasing T over the range 540–580 °C. This y(T) dependence is quantitatively explained in terms of microscopic anion exchange, and thermally activated N surface-desorption and surface-segregation processes. N surface segregation is found to be significant during GaAs overgrowth of GaNyAs1−y layers at typical GaN ECR-MBE growth temperatures, with an estimated activation energy Es∼0.9 eV. The observed y(T) dependence is shown to result from a combination of N surface segregation/desorption processes.
Simulation of scanning tunneling microscope interaction with resists
Authors: Dobisz E. A. , Koops H. W. P. , Perkins F. K.
Published: July 2002

Three-dimensional electron optical simulations were used to model scanning tunneling microscope (STM) lithography in resists under field emission conditions. This work focuses on the effect of resists, as dielectric layers, between the tip and conducting substrate on the operation of the STM. Simulations were performed for resist thicknesses of 1–50 nm and tip-resist separations of 1–20 nm. For a fixed 10 nm tip-resist separation, the axial electric field at the tip decreases by a factor of 2.3 over the resist thickness range. The results show that the tip-resist separation must decrease with increasing resist thickness, to achieve the operating conditions and the energy of electrons entering the resist can be significantly less than the applied tip-substrate bias.
Interface structures of InGaAs/InGaAsP/InGaP quantum well laser diodes grown by metalorganic chemical vapor deposition on GaAs substrates
Authors: Bhattacharya A. , Mawst L. J. , Nayak S. , Li J. , Kuech T. F.
Published: July 2002

We have studied the effects of substrate misorientation on the growth of strained-layer In0.18Ga0.82As quantum well laser structures with InGaAsP confinement layers and In0.5Ga0.5P cladding layers lattice matched to a GaAs substrate. Low-temperature photoluminescence (PL) and atomic force microscopy (AFM) provide evidence of a strong substrate-orientation dependence of the interface structure. The surface morphology of the InGaAs quantum well is found to be determined primarily by the underlying InGaAsP confinement layer. Structures grown on exact-(100) oriented substrates exhibit three-dimensional island surface morphology, whereas growths on (100) substrates oriented 2° towards [110] exhibit high surface roughness, possibly due to step bunching. These observations correlate well with previously reported device performance from strained quantum well laser diodes in the InGaAs/InGaAsP/InGaP material system, and can serve as a tool to optimize device performance.
Strain-compensated InAsP/GaInP multiple quantum wells for 1.3 μm waveguide modulators
Authors: Mei X. B. , Loi K. K. , Wieder H. H. , Chang W. S. C. , Tu C. W.
Published: July 2002

We show that high-quality strain-compensated InAsxP1−x/GayIn1−yP multiple quantum wells (MQWs) can be grown by gas-source molecular beam epitaxy (GSMBE) on InP substrates. Very sharp satellite peaks in double-crystal x-ray diffraction are obtained from a p-i-n waveguide structure consisting of 21 periods of 93 Å/135 Å InAs0.4P0.6/Ga0.13In0.87P MQWs. The surface-normal electroabsorption exhibits a significant quantum-confined Stark effect (QCSE) near 1.3 μm wavelength with a field-dependent absorption coefficient change of 6000 cm−1 and a very small zero-bias residual absorption. Electroabsorption waveguide modulators fabricated using similar material exhibit a large optical saturation threshold in excess of 10 mW incident optical power at 32 meV detuning energy.
Single transducer generation of unipolar pressure waves
Authors: Holé Stéphane , Lewiner Jacques
Published: July 2002

In this letter, we present a method to generate short unipolar pressure pulses using a single piezoelectric transducer. Such systems are of great interest in many fields, for instance, nondestructive testing. The system is composed of a thin piezoelectric material coupled with a waveguide and a backing medium. It is shown that by applying a step voltage, the system acts as a high amplitude short duration unipolar pulse/generator. A particular experimental procedure has been used to compare the emitted pressure pulse with the predicted one, without using a piezoelectric detector. Pulses of 90 ns width and 0.5 MPa amplitude are shown.
Optical gain and carrier lifetime of InGaN multi-quantum well structure laser diodes
Authors: Nakamura Shuji , Senoh Masayuki , Nagahama Shin-ichi , Iwasa Naruhito , Yamada Takao , Matsushita Toshio , Sugimoto Yasunobu , Kiyoku Hiroyuki
Published: July 2002

InGaN multi-quantum well (MQW) structure laser diodes (LDs) with various different cavity lengths were fabricated on sapphire substrates with (112̄0) orientation (A face). The external differential quantum efficiency was obtained as a function of the cavity length. An internal quantum efficiency of 86%, an intrinsic loss of 54 cm−1 and a threshold gain of 110 cm−1 were obtained. Measuring the pulse response of the LDs, a carrier lifetime of 2.5 ns was obtained. A threshold carrier density was calculated as 1.3×1019/cm3. The emission wavelength of the LDs was around 406 nm.
Electron and hole g-factors in CdTe/CdMgTe quantum wells
Authors: Zhao Q. X. , Oestreich M. , Magnea N.
Published: July 2002

Single CdTe/CdMgTe quantum well (QW) structures are investigated by stationary and time-resolved photoluminescence in the presence of an applied magnetic field. We study the dependence of the electron and the hole g factors on the well width by combining Zeeman measurements and the recently developed spin quantum beats technique. The experimental results show that both the electron and the hole g factors have the same sign in wide QWs and increase with decreasing well width. The electron spin phase relaxation time is about 250 ps in our QW structures.
PdIn contacts to n-type and p-type GaP
Authors: Lin C. -F. , Ingerly D. B. , Chang Y. A.
Published: July 2002

PdIn was used as a contact material to n-type and p-type GaP. On n-type GaP it forms a low resistance ohmic contact upon rapid thermal annealing. PdIn/n-GaP (S doped at 2–3 ×1018 cm−3) contacts annealed at 600 °C for 1 min had specific contact resistance’s lower than 1×10−4 Ω cm2. Unlike the contacts to n-GaP, PdIn contacts to p-GaP (Zn doped 1–2×1018 cm−3) show rectifying behavior at all annealing conditions. However, the effective Schottky barrier height seems to decrease significantly with thermal annealing. In addition to the electrical measurements, glancing angle x-ray diffraction was used to characterize the contacts. The glancing angle x-ray diffusion pattern of PdIn/n-GaP, annealed at 600 °C for 1 min, is consistent with the formation of an (InyGa1−y)P phase due to the thermal annealing. The ohmic behavior of the PdIn contacts to n-type GaP and the decrease in the contact’s Schottky barrier height on p-type GaP is attributed to the formation of this (InyGa1−y)P phase at the contact’s interface.
Dislocation velocity in GeSi alloy
Authors: Yonenaga I. , Sumino Koji
Published: July 2002

Velocities of dislocations in single crystal Ge1−xSix alloy semiconductors with x=0.004–0.022 grown by the Czochralski method were investigated by means of etch pit technique in the temperature range 450–700 °C and the stress range 3–20 MPa. The dislocation velocity in the GeSi decreases monotonically with an increase in the Si content, reaching about a half of that in Ge at x=0.022. The dependencies of the dislocation velocity on stress and temperature in the alloys are expressed by the same type of empirical equation as those in other elemental and compound semiconductors.
Inhibition of thickness variations during growth of InAsP/InGaP and InAsP/InGaAsP multiquantum wells with high compensated strains
Authors: Patriarche G. , Ougazzaden A. , Glas F.
Published: July 2002

We demonstrate by using transmission electron microscopy that the insertion of small amounts of a well-chosen material lattice matched to the substrate at the interfaces between the highly strained layers of a strain-compensated multiquantum well (MQW) may prevent the catastrophic morphological degradation of the epitaxial structure as growth proceeds. For InAsP/InGaP and InAsP/InGaAsP MQWs grown on an InP substrate, we find that InP itself is an efficient interfacial material, whereas for the same InAsP/InGaAsP MQWs, an InGaAsP alloy is less effective. We show that the interfacial InP restores the planarity of the growth surface by filling the depressions of the underlying undulating strained layer.
Electron beam induced current measurements of minority carrier diffusion length in gallium nitride
Authors: Chernyak Leonid , Osinsky Andrei , Temkin Henryk , Yang J. W. , Chen Q. , Asif Khan M.
Published: July 2002

Minority carrier diffusion length in epitaxial GaN layers was measured as a function of majority carrier concentration and temperature. The diffusion length of holes in n-type GaN is found to decrease from 3.4 to 1.2 μm in the doping range of 5×1015–2×1018 cm−3. The experimental results can be fitted by assuming the Einstein relation and by the experimental dependence of hole mobilities on carrier concentration. The low injection carrier lifetime of ∼15 ns, used in the fit, is largely independent of the doping level. The diffusion length, measured for ∼5×1015 and 2×1018 cm−3 dopant concentrations, shows an increase with increasing temperature, characterized by an activation energy Ea of ∼90 meV, independent of the impurity concentration.
Remote infrared radiation detection using piezoresistive microcantilevers
Authors: Datskos P. G. , Oden P. I. , Thundat T. , Wachter E. A. , Warmack R. J. , Hunter S. R.
Published: July 2002

A novel micromechanical infrared (IR) radiation sensor has been developed using commercially available piezoresistive microcantilevers. Microcantilevers coated with a heat absorbing layer undergo bending due to the differential stress between the top layer (coating) and the substrate. The bending causes a change in the piezoresistance and is proportional to the amount of heat absorbed. The microcantilever IR sensor exhibits two distinct thermal responses: a fast one (<ms) and a slower one (∼10 ms). A noise equivalent power (at a modulation frequency of 30 Hz) was estimated to be ∼70 nW/Hz1/2. This value can be further reduced by designing microcantilevers with better thermal isolation that can allow microcantilevers to be used as uncooled IR radiation detectors.
Microdroplet dye laser enhancing effects in dye-highly scattering intralipid mixture
Authors: Tanosaki Shinji , Taniguchi Hiroshi , Tsujita Kazuhiro , Inaba Humio
Published: July 2002

The significant effect of fat emulsion intralipid-10% mixing on lasing behaviors of liquid microdroplets was studied using rhodamine 6G dye. This highly scattering medium allows one to make the high-gain laser dye-soft scatterers microsystems that can provide well-defined lasing threshold and one-order or more magnitude enhancement of emission intensity with suitable (optimum) conditions of the mixing ratio, in comparison with original neat-dye lasing microdroplets. We also present and discuss the measured results of input–output intensities for different dye concentrations and dye-intralipid mixing ratios, and microscope images of spatial distribution of emission from both the microdroplets containing neat-dye and dye-intralipid mixture.
A novel yellow-emitting material, 5,5′′-bis{4-[bis(4-methylphenyl)amino] phenyl}-2,2′:5′,2′′-terthiophene, for organic electroluminescent devices
Authors: Noda Tetsuya , Ogawa Hiromitsu , Noma Naoki , Shirota Yasuhiko
Published: July 2002

A novel amorphous molecular material, 5,5′′-bis{4-[bis(4-methylphenyl)amino]phenyl}2,2′:5′,2′′-terthiophene (BMA-3T), has been found to function as a yellow-emitting material in organic electroluminescent (EL) devices. Both the single layer EL device using BMA-3T alone and the double layer EL device consisting of an emitting layer of BMA-3T and an electron-transport layer of tris(8-quinolinolato)aluminum sandwiched between indium-tin-oxide (ITO) and an alloy of magnesium and silver (∼10:1) electrodes emitted a bright yellow light resulting from BMA-3T. The double layer EL device showed much better performances than the single layer EL device, exhibiting a maximum luminance of ∼13 000 cd m−2 at a driving voltage of 18 V, and a luminous efficiency of 1.1 lm W−1 at a luminance of 300 cd m−2.
Ultrathin crystalline silicon solar cells on glass substrates
Authors: Brendel Rolf , Bergmann Ralf B. , Lölgen Peter , Wolf Michael , Werner Jürgen H.
Published: July 2002

We fabricate thin crystalline silicon solar cells with a minority carrier diffusion length of 0.6±0.2 μm by direct high-temperature chemical vapor deposition on glass substrates. This small diffusion length does not allow high cell efficiencies with conventional cell designs. We propose a new cell design that utilizes submicron thin silicon layers to compensate for low minority carrier diffusion lengths. According to theoretical modeling, our design exhibits excellent light trapping properties and allows for 10% efficiency at an optimum cell thickness of 0.4 μm only. This submicron range of cell thicknesses was formerly thought to require direct band gap semiconductors.
Magnetoresistance behavior of submicron Ni80Fe20 wires
Authors: Adeyeye A. O. , Lauhoff G. , Bland J. A. C. , Daboo C. , Hasko D. G. , Ahmed H.
Published: July 2002

We report the evolution of the magnetoresistance (MR) and magnetization behavior of Ni80Fe20 wire arrays as the width (w) is reduced from 200 to 0.3 μm. At around 1.5 μm width, the hysteretic behavior seen in continuous films shows the near reversible behavior characteristic of spin rotation processes. At low field (HMs), the linear MR response to the in-plane perpendicular hard axis field suggests a bulklike transverse MR effect.
On the presence of molecular nitrogen in nitrogen-implanted amorphous carbon
Authors: Grigull S. , Jacob W. , Henke D. , Mücklich A. , Spaeth C. , Sümmchen L.
Published: July 2002

Hard amorphous carbon (ta-C) films were implanted with 20 keV N+ ions into saturation at two different temperatures. Monitoring the composition ratio [N]/[C] using in situ elastic recoil detection analysis, saturation levels [N]/[C] of 0.35 and 0.16 have been found for implantations at room temperature and 400 °C, respectively. Raman and x-ray photoelectron spectroscopy analyses of the implanted films indicate the presence of N2 molecules inside room-temperature implanted samples, but not for the case of implantation at 400 °C. Cross-section transmission electron microscopy images show the presence of near-surface voids, interpreted as remnants of N2-filled bubbles, in the former case. Annealing experiments show that about 50% of the total N inventory consists of nitrogen only weakly trapped inside the carbon matrix in room-temperature implanted films, this fraction being significantly reduced in samples held at 400 °C during implantation.
Synthesis of nanosized silver particles in ion-exchanged glass by electron beam irradiation
Authors: Hofmeister H. , Thiel S. , Dubiel M. , Schurig E.
Published: July 2002

Ag particles of 4.2 nm mean diameter have been formed inside a glass matrix, doped with silver by ion exchange, by electron beam irradiation of the glass cut into thin slices by ultramicrotomy. By this treatment, a high concentration of particles which are homogeneously arranged throughout the glass and exhibit a narrow size distribution is achieved (volume fraction of particulate silver: 3.5×10−2). The interface stress reflecting the particle/matrix interaction is comparable to that of isolated Ag particles. This new route of synthesis will allow to generate materials with strong third order nonlinear susceptibility.