bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonstationary signal analysis of magnetic islands in plasmas
Authors: Taylor E. D. , Cates C. , Mauel M. E. , Maurer D. A. , Nadle D. , Navratil G. A. , Shilov M.
Published: July 2002

Rotating magnetic islands produce fluctuations on a variety of diagnostics in magnetic fusion energy plasmas. The analysis of these fluctuations requires the calculation of the amplitude, phase, and frequency of the oscillations. These three spectral quantities generally evolve in time, necessitating nonstationary signal analysis techniques. The Hilbert transform offers an efficient and accurate method of calculating these three quantities from one diagnostic signal. This feature allows the Hilbert transform to determine the success of the active rotation control of magnetic islands, and to calculate the profile of the diagnostic measurements in a frame of reference co-rotating with the magnetic island. Comparisons to quadrature and spectrogram techniques demonstrate the accuracy of the Hilbert transform method.
Direct scanning tunneling microscope detection of laser induced ultrasonic pulses with nanometer resolution
Authors: Jersch J. , Demming F. , Fedotov I. , Dickmann K.
Published: July 2002

We show the use of scanning tunneling microscope (STM) with a self-designed wide-bandwidth current preamplifier (50 MHz) for direct registration of ultrasonic pulses induced by nanosecond laser pulses in substrate. The changes in tip–sample separation caused by ultrasonic vibrations are seen as perturbations in tunneling current. At moderate incident laser pulse energy of 1–2 mJ ultrasonic waves in glass rod and silica wafer were observed. This wide-band signal, low noise registration in addition with nanometer spatial resolution of a STM opens new possibilities in investigations of ultrasonic near-field distribution, elastic material properties on a nanometer scale, and measurements of the ultrasound velocity in laser ultrasonics.
A novel quartz dendritic growth chamber for low temperature microgravity experimentation
Authors: Schrage Dean S. , Malarik Diane C.
Published: July 2002

The material science community has demonstrated keen interest in performing a range of thermodiffusional dendritic growth studies in microgravity. While each of these experiments differ in the thermal-physical properties of the test fluid, the initial dendrite seeding configuration, and the resultant dendrite morphology, they are similar as each must be conducted within a growth chamber. Clearly, the growth chamber is the single most crucial experimental component because the ambience delivered by the chamber intrinsically effects the resultant dendritic growth. A unique sample chamber, comprised nearly entirely of precision machined quartz components, was developed for use in the microgravity experiment Isothermal Dendritic Growth Experiment (IDGE), which was conducted in the cargo bay of the Space Shuttle Columbia, as part of the Fourth United States Microgravity Payload (USMP-4), in November 1997. The growth chamber discussed is conventional in the selection of the construction materials, but is unique and unconventional from the standpoint of the quartz fabrication and microgravity operation. First, the selection of a fused quartz material was design enabling because the test fluid, pivalic acid, an organic material which melts at 35.975 °C, could be maintained ultrapure over the three-year duration of the complete experiment (assembling, ground test, shuttle integration, flight). Second, the quartz chamber has demonstrated large-scale fabrication of complicated fused quartz pieces, into a final monolithic structure. Third, the quartz chamber was successfully interfaced with ancillary hardware and was not damaged or operationally compromised through ground testing, shuttle launch, microgravity experimentation and shuttle return. Fourth and finally, the chamber has demonstrated a novel means to control, in a microgravity environment, a vapor bubble, which was included in the chamber to provide a volume dedicated to the expansion of the sample fluid during heating. The bubble was controlled by applying a Couette flow device to generate a transient, controlled cavitation of the test fluid. Overall, the critical technologies derived in the present study should lend themselves directly to the development of future microgravity dendritic growth experiments, thereby minimizing program risk and cost.
A versatile computer-controlled pulsed nuclear quadrupole resonance spectrometer
Authors: Fisher Gregory , MacNamara Ernesto , Santini Robert E. , Raftery Daniel
Published: July 2002

A new, pulsed nuclear quadrupole resonance (NQR) spectrometer capable of performing a variety of pulsed and swept experiments is described. The spectrometer features phase locked, superheterodyne detection using a commercial spectrum analyzer and a fully automatic, computer-controlled tuning and matching network. The tuning and matching network employs stepper motors which turn high power air gap capacitors in a “moving grid” optimization strategy to minimize the reflected power from a directional coupler. In the duplexer circuit, digitally controlled relays are used to switch different lengths of coax cable appropriate for the different radio frequencies. A home-built pulse programmer card controls the timing of radio frequency pulses sent to the probe, while data acquisition and control software is written in Microsoft Quick Basic. Spin-echo acquisition experiments are typically used to acquire the data, although a variety of pulse sequences can be employed. Scan times range from one to several hours depending upon the step resolution and the spectral range required for each experiment. Pure NQR spectra of NaNO2 and 3-aminopyridine are discussed.
A vector fetal magnetocardiogram system with high sensitivity
Authors: Kandori Akihiko , Miyashita Tsuyoshi , Tsukada Keiji , Horigome Hitoshi , Asaka Mitsuhiro , Shigemitsu Sadahiko , Takahashi Miho , Terada Yasushi , Mitsui Toshio , Chiba Yoshihide
Published: July 2002

The vector fetal magnetocardiogram (V-FMCG) system that measures the three orthogonal components of the magnetic field from a fetal heart has been developed to clearly observe fetal cardiac activity during pregnancy by using the superconducting quantum interference device. To detect a clear V-FMCG signal, the bottom of the cryostat was made of thin glass–fiber-reinforced plastic and the total length between the pickup coil to the outer surface is 12 mm. Because the cryostat bottom was made thinner, the area of the cryostat’s top and bottom could be made smaller, thus a low evaporation loss (<1.2 l per day) and a long refilling interval (>10 days) were obtained. The gantry was able to tilt the cryostat and the bed could move in three axis directions, which made it possible to easily locate the vector pickup coil at an optimum position to obtain the maximum magnetic field from a fetal heart. We obtained V-FMCGs from 21 normal fetuses with gestation periods of 27–38 weeks. Using these vector signals, the dipoles were estimated and the relationship between the strength of the dipole moments and the number of gestation weeks could be obtained. Thus, V-FMCG seems to represent a new noninvasive tool for clearly detecting the electrophysiological activity of a fetal heart.
Production of radioactive ion beams using the in-flight technique
Authors: Harss B. , Pardo R. C. , Rehm K. E. , Borasi F. , Greene J. P. , Janssens R. V. F. , Jiang C. L. , Nolen J. , Paul M. , Schiffer J. P. , Segel R. E. , Specht J. , Wang T. F. , Wilt P. , Zabransky B.
Published: July 2002

Reactions with a heavy projectile incident on a light target can be used for the efficient in-flight production of secondary radioactive beams. An overview of this technique is given using data on F17 beams produced via the p(17O, 17F)n and d(16O, 17F)n reactions. With primary O16,17 beam currents of 100 pnA, intensities of up to 2×106 17F/s on target were achieved. Using this beam, the p(17F,α)14O reaction was measured.
Real time imaging of two-dimensional charge on dielectric surfaces
Authors: Budakian R. , Putterman S. J.
Published: July 2002

A technique has been developed to measure two-dimensional (2D) charge distributions on dielectric surfaces in real time. A thin layer of polymer-dispersed liquid crystal (PDLC) placed between a dielectric substrate and a conducting plane undergoes a transition from an opaque to a transparent state due to the electric field of the surface charge. The cell is uniformly illuminated from the front and the transmitted light, which is proportional to the local charge density, is imaged using a charge coupled device camera. Due to the finite resistivity of the liquid crystal, however, the static field from the charges must be modulated in time in order to produce a sustained transition inside the PDLC. The modulation is produced by placing a rotating metal chopper near the surface. The magnitude and sign of the charge are measured by calibrating the response of the PDLC to a series of bias voltages. The technique has been used to image surfaces as large as 3 mm×5 mm with 30 μm spatial resolution in 333 ms.
Comparison of dc and ac excitation of a sealed CO2 laser
Authors: Lee Dong-Hoon , Chung Hyun-Ju , Kim Hee-Je
Published: July 2002

We demonstrate a sealed CO2 laser excited by 60 Hz ac discharges using a high-leakage transformer typical of neon signs. The transformer is employed to limit a short circuit current into an energy-storage capacitor. The laser performance characteristics versus pressure and discharge current for pumping with a dc and 60 Hz ac discharge, are investigated. It is found that there is no difference in laser output power and system efficiency as functions of total input power between them. The maximum laser power of about 40 W is obtained at the condition of 18 Torr and 35 mA.
Pulse stretching due to partial temporal overlap of two modes in a TEA CO2 laser
Authors: Nilaya J. Padma , Biswas Dhruba J.
Published: July 2002

Pulse duration as long as 14 μs has been obtained from a single longitudinal mode TEA CO2 laser. Such stretching occurred under conditions for which oscillation on a higher order transverse mode followed that on the TEM00 mode with partial temporal overlap between the two. Control of the intracavity aperture size in conjunction with cavity length tuning helped realize such an oscillation condition.
Versatile sample viewing system with large magnification range
Authors: Ocker K. D. , Thonnard N. , Joyner C. F.
Published: July 2002

A sample viewing system has been designed and constructed to assist in the in situ analysis of terrestrial and extraterrestrial samples by laser microprobe gas extraction. The system provides sample viewing fields of 36 mm, 3.3 mm, and 370 μm, and combines and focuses the microprobing ultraviolet laser beam onto the sample being studied.
The National Institute of Standards and Technology glow discharge resonance ionization mass spectrometry system
Authors: Pibida L. , Hutchinson J. M. R. , Wen Jesse , Karam L.
Published: July 2002

A new resonance ionization mass spectrometry system at the National Institute of Standards and Technology using glow discharge atomization and continuous-wave lasers has been developed. Low concentrations of Cs133 in a silver matrix have been measured using this new system. In addition a detailed characterization of the glow discharge source and laser ionization processes are made.
Characteristics of the beam line at the Tokyo electron beam ion trap
Authors: Shimizu Hiroshi , Currell Frederick J. , Ohtani Shunsuke , Sokell Emma J. , Yamada Chikashi , Hirayama Takato , Sakurai Makoto
Published: July 2002

A new beam line has been constructed to make various experiments with highly charged ions produced in an electron beam ion trap. The characteristics of the beam line are reported. Ions are extracted upward into the beam line and are deflected horizontally and analyzed for the charge states by a double-focusing magnet. To obtain sufficient intensity, several electrostatic lenses are located. A quadrupole lens is used to correct the distorted beam shape before an entrance slit of the magnet. Ions are accelerated during the passing of the analyzing magnet to obtain the higher mass resolution. Trajectories were calculated by a ray-tracing program and matrix multiplication for lens actions. Preliminary results are shown here for investigation of characteristics of extracted ions.
A new scheme of direct beam chopping in a negative hydrogen ion source
Authors: Shinto K. , Takagi A. , Ikegami K. , Mori Y.
Published: July 2002

Direct fast H− beam chopping in a surface-plasma-type negative hydrogen ion source has been studied at KEK. The H− beam is chopped at several MHz by modulating the converter bias voltage of the ion source. However, in this case, a slow rise time of the chopped H− beam is one of the most serious problems for synchrotron injection. In order to make the rise time faster, a negative voltage was applied to the anode electrode. In the new scheme, mesh inserts were installed inside the ion extraction hole of the anode. Applying a retarding voltage on the meshes, the fast beam chopping was tested and the results are reported and discussed in the article.
Broad-beam modeling and experiments for electric spacecraft propulsion
Authors: Tartz M. , Hartmann E. , Deltschew R. , Neumann H.
Published: July 2002

At IOM Leipzig, we developed an efficient grid erosion simulation code. In our approach to ion beam extraction and grid erosion occurring in a multi-grid multi-aperture ion thruster we break down the complex interplay of pertinent elementary processes into consecutive steps. On the basis of ion optical and short-time grid-erosion measurements on a small broad-beam ion source, a comprehensive experimental validation of this code has been done. The good agreement between measured and simulated data furnishes confidence in the methodology.
Computational studies on ion source plasmas of the neutral beam injection system
Authors: Kashiwagi M. , Ido S. , Okumura Y.
Published: July 2002

A three-dimensional particle code taking into account the collision terms between fast electrons and hydrogen molecules is developed, where the elastic, ionization, excitation, and vibrational excitation collisions are calculated. This code is applied to investigate plasma generation and behavior in an ion source of the neutral beam injection system. It is found that the distribution of collision points is affected by grad-B drift when the gas pressure becomes lower. The sheath region around the filament is also taken into account, making it possible to optimize the filament shape and position in a plasma generator.
Alice ion source and its high voltage platform
Authors: Cavenago M. , Kulevoy T.
Published: July 2002

The electron cyclotron resonance ion source Alice is a small 14.4 GHz ion source intended to be a general purpose ion source for the ALPI ion linac. To increase the speed of emitted ions to more than 0.009 c it was installed on a high voltage platform. Noteworthy details of the platform complex such as the 400 kV insulation transformer with the power line connecting it to the platform and the acceleration tube are reviewed. The whole complex can operate up to 350 kV and up to 36 μA of extracted current, the current dispersed is small and upgrading to 400 kV looks possible. Details of the beam current, ion source optimization, source emittance and beam transport are discussed and show good agreement between experiments and calculated beam sizes.
Specific modification of polysulfone with cluster bombardment with assistance of Ar ion irradiation
Authors: Xu Guochun , Hibino Y. , Awazu K. , Tanihara M. , Imanishi Y.
Published: July 2002

Objective: To develop a rapid method for the modification of polysulfone with ammonium sulfamate with the assistance of Ar ion irradiation with a multi-source cluster deposition apparatus. These surfaces mimicking the structure of heparin, a bioactive molecule, have a high anti-thrombosis property. Experimental Design: Polysulfone film, setting on a turning holder, was irradiated by Ar ions during bombardment with ammonium sulfamate clusters. The Ar ion source serves for the activation of a polymer surface and a cluster ion source supplies ammonium sulfamate molecules to react with the activated surface. After thorough washing with de-ionized sterile water, the modified surfaces were evaluated in terms of the contact angle of water, elemental composition, and binding state on electron spectroscopy for chemical analysis and platelet adhesion with platelet rich plasma. Results: The modification of polysulfone decreased the contact angle of water on surfaces from 82.6 ° down to 34.5 °. Ammonium, amine, sulfate, and thiophene combinations were formed on the modified surfaces. The adhesion numbers of the platelet were decreased to one tenth compared to the original surface. The same process was also applied to other polymers such as polyethylene, polypropylene, and polystyrene and similar outcomes were also observed. Conclusion: The primary studies showed successful modification of polysulfone with ammonium sulfamate with the assistance of Ar ion irradiation. Since the same concept can also be applied to other materials with various substrates, combined with the features of no solvent and no topographic changes, this method might be developed into a promising way for modification of polymeric materials.
Selective minority-ion heating in the afterglow of an electron cyclotron resonance ion source
Authors: Nadzeyka A. , Meyer D. , Barzangy F. , Drentje A. G. , Wiesemann K.
Published: July 2002

We report first experimental results on selective minority-ion heating in the afterglow mode of electron cyclotron resonance ion sources in Bochum and at the KVI (Groningen) in mixtures of Ar/O/He and in pure nitrogen. In addition we measured time resolved vacuum ultraviolet-line intensities of different ion species and compared them to the extracted ion currents in the afterglow. In contrast to our model calculations, selective ion heating of medium and high charge states of, e.g., oxygen results in an instantaneous destruction of the respective afterglow peak. Our observations show that the physics of the afterglow peak is not yet fully understood. It remains questionable whether the afterglow peaks can be solely explained by a destruction of electrostatic confinement in the afterglow.
Radio frequency linear ion beam source with 6 cm×66 cm beam
Authors: Siegfried D. , Buchholtz B. , Burtner D. , Foster W.
Published: July 2002

An inductively coupled radio frequency (rf) linear ion beam source with a 6×66 cm rectangular cross-section beam has been developed and tested. This source was designed to provide filamentless, low maintenance operation, and large area coverage for materials processing applications, typically involving translation of substrates across the narrow beam dimension. The source has been operated on argon, oxygen, and argon/oxygen mixtures at beam energies from 100–1500 eV. Beam currents up to 1.0 A have been obtained with argon at a rf discharge power of approximately 1 kW. Longitudinal beam current uniformity of better than ±10% has been obtained over a 50 cm length at a distance 25 cm from the ion source over a wide range of operating conditions. Source operating characteristics and performance data are presented including lateral and longitudinal beam current density profiles.
Performance of the NANOGUN™ electron cyclotron resonance ion source applied for nuclear astrophysics
Authors: Itahashi T. , Kudomi K. , Kume K. , Takahisa K. , Yoshida S. , Ejiri H. , Toki H. , Nagai Y. , Ohsumi H. , Komori M. , Yamasaki K.
Published: July 2002

A compact low-energy, high current accelerator has been constructed for the study of fusion reactions relevant to the field of nuclear astrophysics. It consists of a modified NANOGUN™, a low-energy beam transport, a windowless gas target, a beam calorimeter, and a detector system. The accelerator and the NANOGUN ion source with a single extraction electrode provides 930 μA He1+3 of 20 keV at a gas target chamber. A two-electrode extraction has been tested for a few source voltages. The obtained target current is 75, 140, 110, 110, 105, 78, and 80 μA for 20, 25, 30, 35, 38, 40, and 45 kV potential, respectively. The transport efficiency from the source to the target is 5.7%.
Development and properties of a Freeman-type hybrid ion source
Authors: Matsumoto T. , Mimoto K. , Goto S. , Ohba M. , Agawa Y. , Kiuchi M.
Published: July 2002

In order to investigate the fundamentals of the deposition of ions with energies in the range of 10–100 eV, we developed Freeman-type hybrid ion source and a low-energy mass-analyzed ion beam deposition system. Analyzing the energy distributions of ions generated, we estimated the properties of the ion source. Energy distributions of noble gas ions (Ne+, Ar+, Kr+, Xe+), and metal ions (Ti+, Fe+, W+, C+) were measured by a PPM421 plasma process monitor with a cylindrical mirror analyzer and a quadrupole mass spectrometer. For instance, Ar+ ions transported at 25 keV were decelerated to 103 eV with an energy spread of ±3 eV, and Ti+ ions generated by sputtering of a titanium target had an energy distribution of 107±3 eV. The energy of ions generated by this apparatus was well defined, and so it is possible to investigate film formation processes by low-energy ions.
Production of multiply charged ion target for photoionization studies using synchrotron radiation
Authors: Oura Masaki , Yamaoka Hitoshi , Kawatsura Kiyoshi , Hayaishi Tatsuji , Kimata Junichi , Kojima Takao M. , Kimura Masahiro , Sekioka Tsuguhisa , Terasawa Mititaka
Published: July 2002

Multiply charged ions for some gaseous and metallic elements have been produced as the target for photoionization studies using synchrotron radiation. The target densities have been measured to be typically of the order of 106 ions/cm3. Characteristics of the beam transport system is described and the feasibility of photoionization experiments along the isonuclear and the isoelectronic sequences is also discussed.
Development of a high-current laser ion source for induction accelerators
Authors: Yoshida M. , Hasegawa J. , Fukata S. , Oguri Y. , Ogawa M. , Nakajima M. , Horioka K. , Shiho M.
Published: July 2002

We have developed a high-current laser ion source that can provide low-charge-state ions for induction accelerators. A frequency-doubled Nd:YAG laser (λ=532 nm) irradiated a copper target with relatively low intensities of 108–109 W/cm2. The laser-produced plasma supplied a large number of Cu+ and Cu2+ ions over 1014 ions/cm2 at a distance of 10 cm from the target. We have successfully extracted high-current copper beams over 0.1 A/cm2 using an inductive acceleration module. The beam emittance measured by a pepper-pot method was about 40 πmm mrad. © 2000 American Institute of Physics.
A fast readout and processing electronics for photon counting intensified charge-coupled device
Authors: Bergamini P. , Bonelli G. , Tanzi E. G. , Uslenghi M. , Poletto L. , Tondello G.
Published: July 2002

The design features and the performances of a prototype photon counting imaging detector, being developed for the international ultraviolet (UV) space mission Spectrum UV, are presented. The photon counter is an intensified charge coupled device (ICCD) in which photon events, generating an electron cascade through a high gain microchannel plate (MCP) stack, are transduced, via a phosphor screen and a fiber optics reducer, into a 3×3 pixel2, quasi-Gaussian charge distributions on a 15×15 μm2,512×512 pixel2 format CCD matrix. The CCD is read out in the frame-transfer mode at a pixel rate of 19.75 MHz, and its output data flow is acquired serially as to generate a 3×3 pixel2 event sash that sweeps dynamically the CCD matrix at the 50.6 ns rate of the readout clock. Each and every event sash is searched for the presence of events whose charge content lie within proper limits and satisfy a given set of morphological rules, i.e., a single peak charge profile. The centroid coordinates of identified events are determined with subpixel accuracy (up to a 210 bin/pixel) and subsequently stored as photon list coordinate pairs. The data acquisition and processing system is based on field programmable gate array technology and is capable of satisfying the requirements of real-time operation. The modular construction of the data acquisition and processing electronics provides a great deal of flexibility for supporting advancements in CCD readout techniques (multiple output and higher clocking speed) and of MCPs (larger formats, smaller pore, and higher dynamic range). The results of the performance verification of the data acquisition and processing system integrated with a laboratory ICCD prototype are presented and discussed.
A new concept for the design and realization of metal based single electron devices: Step edge cut-off
Authors: Altmeyer S. , Spangenberg B. , Kurz H.
Published: July 2002

To increase the operating temperature of a single electron circuit, it is necessary to reduce the capacitance of the tunnel junction. Usually this is done by reducing the linewidth of the capacitor forming metal stripes, which are sandwiched with an intermediate insulator. The use of alternative materials, however, allows capacitance reduction by means of thicker isolation layers or by a capacitor geometry different from a sandwich. The new SECO (step edge cut off) method, for the fabrication of single electron devices will be presented.
PdAl Schottky contact to In0.52Al0.48As grown by metalorganic chemical vapor deposition
Authors: Lin C.-F. , Chang Y. A. , Pan N. , Huang J.-W. , Kuech T. F.
Published: July 2002

β-PdAl was studied as a Schottky contact to metalorganic chemical vapor deposition grown In0.52Al0.48As. Intermetallic alloy β-PdAl was chosen in order to utilize the Al–In exchange reaction which may occur between PdAl and In0.52Al0.48As, which would result in an enhanced Schottky barrier height. I–V, C–V, and deep level transient spectroscopy (DLTS) were used to determine the contact characteristics. The contact barrier height (φb) was measured by I–V and C–V methods after different annealing conditions, and good agreement between I–V and C–V results were obtained. The largest φb value is 0.67 eV from I–V measurement (0.69 eV from C–V) after the diode was annealed at 450 °C for 1 min. DLTS measurements were carried out to examine the effect of deep traps in the In0.52Al0.48As layer. Two deep levels were found, but the concentrations are lower than the intrinsic donor concentration obtained from the Hall method. The activation energies for these two deep levels obtained from an Arrhenius plot are 0.38 and 0.65 eV, respectively.
Magneto-mechanical instability in Terfenol-D films
Authors: Wuttig Manfred , Su Quanmin , Zheng Y. , Wen Yiting
Published: July 2002

Tensioned 1 μm nanocrystalline Terfenol-D films on 50 μm Si substrates display a pronounced damping maximum at a magnetic field of about 1.5 kOe oriented perpendicular to the plane of the film. The phenomenon is critically dependent on the orientation of the magnetic field and is the result of a magnetomechanical instability in the Terfenol film.
Applicability of one-dimensional diffusion model for step coverage analysis—Comparison with a simple Monte Carlo method
Authors: Akiyama Y. , Imaishi N.
Published: July 2002

Applicability of a one-dimensional reaction-diffusion model (ORDM) as a tool for analyzing the gas–solid phase transition rate process during chemical vapor deposition is tested by comparing its results with those predicted by a simple Monte Carlo method. The results reveal that the ORDM is applicable when the conditions of Knudsen number (Kn)<0.03, aspect ratio (As)≳1.0, and reactive sticking coefficient (η)<0.1 are fulfilled. At large Kn and large η, the ORDM gives quite an erroneous result. The ORDM is also applicable to predict the grown film shape when η<0.1, Kn ≫1.0, and As≳2.0.
First order distributed feedback operation in ZnSe based laser structures
Authors: Illing M. , Bacher G. , Forchel A. , Hommel D. , Jobst B. , Landwehr G.
Published: July 2002

First order distributed feedback laser with periods down to 94 nm based on ZnSe have been realized by electron beam lithography and wet chemical etching. Distributed feedback operation was demonstrated by optical excitation using a pulsed N2 laser. A threshold density of 80 kW/cm2 was found at room temperature for a resonator length of 225 μm. From the stop band width, a coupling coefficient of 120 cm−1 can be estimated. By varying the grating period the emission wavelength can be tuned over a wide spectral range of more than 130 meV. Measurements in the range between 20 and 300 K show that the shift of the emission wavelength with temperature is reduced by more than a factor of four as compared to the temperature shift of the spontaneous emission.
Heat diffusivity of La1−xCaxMnO3 epitaxial layers
Authors: Liebe J. , Kraus E. , Haupt L. , Mandal P. , Bärner K. , Helmolt R. v.
Published: July 2002

The Seebeck effect and the thermal diffusivity of La0.67Ca0.33MnO3−δ were investigated in the temperature range 35<T<300 K and in particular in the regime of the high magnetoresistance and maximum resistivity ρmax. We find a sign change of the thermoelectric power S(T) and a step in heat conductivity near ρmax which we attribute to a temperature-induced metal–insulator transition at about 80 K, suggesting that the large giant magnetoresistance found in these substances is due to a field-induced metal–insulator transition.
Low energy electron-enhanced etching of GaAs(100) in a chlorine/hydrogen dc plasma
Authors: Gillis H. P. , Choutov D. A. , Martin K. P. , Song Li
Published: July 2002

Low energy electron-enhanced etching of GaAs(100) has been achieved by placing the sample on the anode of a low-pressure hydrogen/chlorine dc discharge. Samples etched at room temperature reveal good anisotropy (≳20), good selectivity (≳200 against SiO2 masks at room temperature), and smooth surfaces at etch rates of 250 Å/min; etch rates up to 4.5 μm/min were achieved at 150 °C. The dependence of the etch characteristics on gas composition, pressure, and temperature is described.
Low-noise 1 THz niobium superconducting tunnel junction mixer with a normal metal tuning circuit
Authors: Bin M. , Gaidis M. C. , Zmuidzinas J. , Phillips T. G. , LeDuc H. G.
Published: July 2002

We describe a 1 THz quasioptical SIS mixer which uses a twin-slot antenna, an antireflection-coated silicon hyperhemispherical lens, Nb/Al-oxide/Nb tunnel junctions, and an aluminum normal-metal tuning circuit in a two-junction configuration. Since the mixer operates substantially above the gap frequency of niobium (ν≳2Δ/h∼700 GHz), a normal metal is used in the tuning circuit in place of niobium to reduce the Ohmic loss. The frequency response of the device was measured using a Fourier transform spectrometer and agrees reasonably well with the theoretical prediction. At 1042 GHz, the uncorrected double-sideband receiver noise temperature is 840 K when the physical temperature of the mixer is 2.5 K. This is the first SIS mixer which outperforms GaAs Schottky diode mixers by a large margin at 1 THz.
Large-area diamond deposition in an atmospheric pressure stagnation-flow reactor
Authors: Hahn D. W. , Edwards C. F. , McCarty K. F. , Kee R. J.
Published: July 2002

We present the results of large-area (20 cm2) diamond deposition from a scaled-up stagnation-flow reactor. The reactor uses a unique nozzle geometry that optimizes reagent gas usage. The premixed acetylene–oxygen–hydrogen flames were operated in a highly strained configuration, allowing uniform deposition of diamond with growth rates exceeding 25 μm/h. Substrate temperature control and flame stability of the chemical vapor deposition reactor are described. Diamond films were deposited on a molybdenum substrate with a surface temperature of approximately 1200 K and C/O ratio of 1.03. Diamond film growth results are presented, and film uniformity is assessed using micro-Raman spectroscopy.
Room-temperature stimulated emission in GaN/AlGaN separate confinement heterostructures grown by molecular beam epitaxy
Authors: Schmidt T. J. , Yang X. H. , Shan W. , Song J. J. , Salvador A. , Kim W. , Aktas Ö. , Botchkarev A. , Morkoç H.
Published: July 2002

Strong near-ultraviolet stimulated emission was observed at room temperature in GaN/AlGaN separate confinement heterostructures (SCH) grown by molecular beam epitaxy (MBE) on sapphire substrates. The MBE grown GaN/AlGaN SCH samples exhibited stimulated emission threshold pumping powers as low as 90 kW/cm2 at room temperature under the excitation of a frequency-tunable nanosecond laser system with a side-pumping configuration. This represents an order of magnitude reduction over bulklike GaN. Our results suggest that the carrier confinement and waveguiding effects of the SCH samples result in a substantial decrease in the stimulated emission threshold.
Integrated YBa2Cu3O7−x magnetometer for biomagnetic measurements
Authors: Drung D. , Ludwig F. , Müller W. , Steinhoff U. , Trahms L. , Koch H. , Shen Y. Q. , Jensen M. B. , Vase P. , Holst T. , Freltoft T. , Curio G.
Published: July 2002

An integrated dc superconducting quantum interference device (SQUID) magnetometer has been fabricated using a YBa2Cu3O7−x–SrTiO3–YBa2Cu3O7−x multilayer process. The magnetometer consists of a 8.3 mm×8.6 mm pickup coil coupled inductively to a small washer-type SQUID with 9 Ω bicrystal junctions via an integrated 101/2-turn input coil. Using simple direct-coupled read-out electronics with additional positive feedback, a noise level of 9.7 fT/√Hz at 1 kHz and 53 fT/√Hz at 1 Hz was measured inside a magnetically shielded room. Due to the low noise level biomagnetic heart and brain signals with high quality and the very weak signals of the peripheral nerve system were recorded.
Reduced-temperature crystallization of thin amorphous Fe80B20 films studied via empirical modeling of extended x-ray absorption fine structure
Authors: Harris V. G. , Oliver S. A. , Ayers J. D. , Das B. N. , Koon N. C.
Published: July 2002

The evolution of the local atomic environment around Fe atoms in very thin (15 nm), amorphous, partially crystallized and fully crystallized films of Fe80B20 was studied using extended x-ray absorption fine structure (EXAFS) measurements. The relative atomic fraction of each crystalline phase present in the annealed samples was extracted from the Fe EXAFS data by a least-squares fitting procedure, using data collected from t-Fe3B, t-Fe2B, and α-Fe standards. The type and relative fraction of the crystallization products follows the trends previously measured in Fe80B20 melt-spun ribbons, except for the fact that crystallization temperatures are ≊200 K lower than those measured in bulk equivalents. This greatly reduced crystallization temperature may arise from the dominant role of surface nucleation sites in the crystallization of very thin amorphous films.
Origin of large-amplitude random telegraph signal in silicon bipolar junction transistors after hot carrier degradation
Authors: Pogany D. , Chantre A. , Chroboczek J. A. , Ghibaudo G.
Published: July 2002

The random telegraph signal (RTS) with a relative amplitude of up to 100% has been observed in the forward and reverse base current in polycrystalline emitter bipolar junction transistors after hot carrier degradation. The RTS is explained by modulations in the surface generation-recombination rate due to fluctuations in the capture cross section of two-state interface centers. Carrier trapping/emission on slow oxide traps and/or defect reconfiguration are assumed to be responsible for the cross-section fluctuations
Variation of surface morphology with substrate temperature for molecular beam epitaxially grown GaSb(100) on GaAs(100)
Authors: Brown S. J. , Grimshaw M. P. , Ritchie D. A. , Jones G. A. C.
Published: July 2002

Using molecular beam epitaxy (MBE) several layers of GaSb were grown on GaAs at substrate temperatures of 400, 475, and 550 °C, and the surface morphology was studied with an in situ ultra high vacuum scanning tunneling microscope (STM). We have observed spiral mound growth of different morphology originating from surface dislocations for the samples grown at 400 and 475 °C, however at 550 °C there is no spiral mound growth and neighboring dislocations are joined by a single step. The surfaces have different rms surface roughness and dislocation density which has important consequences with regard to heterointerface quality.
Evidence of enhanced pinning properties in optimally doped Bi2Sr2Ca1−xYxCu2O8+δ  single crystals
Authors: Villard G. , Pelloquin D. , Maignan A. , Wahl A.
Published: July 2002

A comparative study of the magnetic properties of Bi2Sr2Ca1−xYxCu2O8+δ single crystals with different yttrium contents is presented. An optimum in the doping can be reached that corresponds to a high Tc (onset) value (91.5 K) and a high position of the irreversibility line. Moreover, the fishtail feature disappears for this optimally Y doped Bi-2212 crystal due to the increase of the magnetic field dependence of the critical current density. This demonstrates the better pinning efficiency of the crystals with the highest Tc.
Activation volume for arsenic diffusion in germanium
Authors: Mitha Salman , Aziz Michael J. , Schiferl David , Poker David B.
Published: July 2002

We have measured the effect of pressure on As diffusion in Ge. Diffusion anneals on ion-implanted samples were carried out in a high-temperature diamond anvil cell using fluid argon as a clean, hydrostatic pressure medium. At 575 °C over the pressure range 0.1–4 GPa, pressure slightly enhances the diffusivity, characterized by an activation volume of −1.7±1.4 cm3/mole or −0.12±0.10 times the atomic volume. The results call into question the prevailing view that diffusion of groups III, IV, and V elements are mediated entirely by vacancies. If diffusion of As is mediated entirely by vacancies then either the vacancy formation volume must be unexpectedly low or the energy of vacancy migration must be unexpectedly high.
Dislocations and related traps in p-InGaAs/GaAs lattice-mismatched heterostructures
Authors: Du A. Y. , Li M. F. , Chong T. C. , Teo K. L. , Lau W. S. , Zhang Z.
Published: July 2002

Dislocations and traps in p-InGaAs/GaAs lattice-mismatched heterostructures are investigated by cross-section transmission electron microscopy (XTEM) and deep level transient spectroscopy (DLTS). The misfit dislocations and threading dislocations observed by XTEM in different samples with different In mole fractions and different InGaAs layer thicknesses over all satisfy the Dodson–Tsao plastic flow critical layer thickness curve. By comparing the XTEM and DLTS results, we identify that the threading dislocations in bulk layers introduce three hole trap levels H1, H2, and H5 with DLTS activation energies of 0.32, 0.40, and 0.88 eV, respectively, and one electron trap level E1 with a DLTS activation energy of 0.54 eV. The misfit dislocations in the relaxed InGaAs/GaAs interface induce a hole trap level H4 with a DLTS activation energy of 0.67–0.73 eV.
Single charge and confinement effects in nano-crystal memories
Authors: Tiwari Sandip , Rana Farhan , Chan Kevin , Shi Leathen , Hanafi Hussein
Published: July 2002

Use of nano-crystals of silicon in close proximity (1.5–4.5 nm) of a transistor channel lead to structures with pronounced memory where effects due to discrete number of electrons, confinement-induced subbands in inversion layers and discrete energy states in quantum dots, random charge distribution in quantum dots, and transmission through a strong barrier are very important. Experimental results show plateaus in threshold voltage at low temperatures, spaced nearly equally apart, and indicative of single electron effects. Varying the oxide thickness shows strong influence on speed and charge retention. We confirm the strength of confinement effects and discuss the underlying considerations in the operation of the memory that are related to the reduced volume, strength of the barrier, and random distribution of the trapped charge in nano-crystals.
Correlation between visible and infrared (1.54 μm) luminescence from Er-implanted porous silicon
Authors: Wu X. , Hömmerich U. , Namavar F. , Cremins-Costa A. M.
Published: July 2002

A photoluminescence excitation (PLE) study was performed of Er-implanted porous Si with two different porosities. Erbium was implanted at a dose of 1×1015 cm−2 at 380 keV and the samples were annealed for 30 min at temperatures from 650 to 850 °C. We observed that PLE spectra from Er3+ at 1.54 μm are nearly identical to those from the visible-emitting porous Si layers. Our results provide the first direct experimental evidence that infrared photoluminescence at 1.54 μm arises from Er3+ ions in porous Si and that ions are excited through the recombination of excess carriers spatially confined in Si nanograms.
X-ray photoelectron spectroscopy study of Al/Ta2O5 and Ta2O5/Al buried interfaces
Authors: Chen K. , Yang G. R. , Nielsen M. , Lu T. M. , Rymaszewski E. J.
Published: July 2002

Buried interfaces of thin Al/Ta2O5 and Ta2O5/Al films were studied using the x-ray photoelectron spectroscopy technique. The peak decomposition technique was employed to identify the composition and chemical states at the interface region. It was observed that there is an “intermixing layer” at the Al/Ta2O5 interface, where Ta2O5 has been reduced to lower binding energy states due to the reaction of Al with Ta2O5 during deposition. On the other hand, the Ta2O5/Al interface is relatively stable, consisting of Ta2O5 and Al2O3 interfacial layers. Based on a uniform multilayer structure model, the thickness of the interfacial layers was estimated by using the relative photoelectron intensities.
Large photoluminescence enhancements from epitaxial GaAs passivated by postgrowth phosphidization
Authors: Harrison D. A. , Arès R. , Watkins S. P. , Thewalt M. L. W. , Bolognesi C. R. , Beckett D. J. S. , SpringThorpe A. J.
Published: July 2002

Dramatic enhancements of over 300× in the room temperature photoluminescence signal obtained from high purity GaAs epitaxial layers were recorded after a brief heat treatment in tertiarybutylphosphine vapor. Low temperature photoluminescence spectra indicate that, unlike other passivation techniques, the surface layer formed during this simple treatment does not induce any appreciable strain on the underlying epilayer. The increases in photoluminescence intensity are indicative of a reduction in surface recombination brought about by the formation of a very thin GaP layer that protects against surface oxidation.
High minority carrier lifetime in phosphorus-gettered multicrystalline silicon
Authors: Cuevas Andrés , Stocks Matthew , Armand Stephane , Stuckings Michael , Blakers Andrew , Ferrazza Francesca
Published: July 2002

The electronic quality of multicrystalline material produced by directional solidification has been evaluated by means of photoconductance techniques. Very high minority carrier lifetimes, in the vicinity of 200 μs, have been measured in p-type 1.5 Ω cm material that had received a phosphorus diffusion gettering treatment. The measurements correspond to an effective lifetime averaged over an area of 3 cm2 that includes several grain boundaries and reflects the combined bulk, grain boundary and surface recombination mechanisms. The high lifetime (15 μs) also obtained in low resistivity 0.2 Ω cm wafers has allowed the fabrication of solar cells with an open-circuit voltage of 657 mV (AM1.5 G, 100 mW/cm2, 25 °C), probably the highest ever reported for multicrystalline silicon.
Control of silicon nanocrystallite shape asymmetry and orientation anisotropy by light-assisted anodization
Authors: Polisski G. , Averboukh B. , Kovalev D. , Koch F.
Published: July 2002

It is shown that the different and conflicting results on the strength of polarization memory effect on porous Si result from the influence of light on the electrochemical etching process. Illumination in general reduces the memory effect by decreasing the particle shape asymmetry. Linearly polarized light can both enhance or reduce the effect. It is accompanied by an in-plane orientation anisotropy of the memory parameter for (100) porous Si. This effect is evidence for a preferential alignment of the crystallite asymmetry axis normal to the light polarization.
Direct-injection high-Tc dc-SQUID with an upper YBa2Cu3O7−x ground plane
Authors: Terai H. , Hidaka M. , Satoh T. , Tahara S.
Published: July 2002

We have fabricated direct-injection high-Tc superconducting quantum interference devices (SQUIDs) with integrated YBa2Cu3O7−x (YBCO) ground planes in the upper part of structure. The YBCO/PrBa2Cu3O7−x(PBCO)/YBCO edge junctions with 10-nm-thick PBCO barriers showed RSJ-like current-voltage (I–V) characteristics before and after the ground plane formation. We measured the voltage modulations of these SQUIDs with two different hole sizes to evaluate the line inductance. At a temperature of 30 K, the estimated line inductance under the ground plane was about 1.0 pH/□, while the estimated line inductance without the ground plane was 2.8 pH/□.
Two-dimensional micromechanical bimorph arrays for detection of thermal radiation
Authors: Manalis S. R. , Minne S. C. , Quate C. F. , Yaralioglu G. G. , Atalar A.
Published: July 2002

We demonstrate that two-dimensional arrays of micromechanical bimorphs can be used as thermal sensors to image infrared (IR) radiation. A density of 100 pixels per mm2 is achieved by coiling a bimorph beam into the shape of a flat spiral. Temperature variations of a given spiral are converted to modulations of visible light by illuminating the spiral array with a visible source. The optical properties of the spiral resemble a Fresnel zone plate when light reflected off neighboring rings of the spiral is focused. When a spiral is heated through the absorption of IR radiation, thermally induced bending of the bimorph degrades the focusing efficiency by distorting the spiral. This reduces the optical intensity at the focal point. Arrays of spirals can be monitored with a commercial CCD camera. At 40 Hz, the temperature resolution and noise equivalent power of a 75 μm diam spiral are 50 μK/√Hz and 20 nW/√Hz, respectively, and the thermal response time is 270 μs.
Low-loss hydrogenated buried waveguide coupler integrated with a four-wavelength distributive Bragg reflector laser array on InP
Authors: Allovon M. , Talneau A. , Rao E. V. K. , Huet F. , Alexandre F. , Ougazzaden A. , Slempkes S. , Theys B. , Chevallier J.
Published: July 2002

An approach is proposed to realize the integration of a 4>1 passive coupler with butt-jointed buried ridge structure distributive Bragg reflector lasers and transparent buried waveguides for Bragg section. The butt coupling facilitates an independent optimization of gain and Bragg sections and the proposed additional processing step, namely, localized hydrogenation of coupler regions, permits reducing dramatically the losses due to free holes in the p+-InP cladding layer. With a coupling efficiency of ∼90% and losses as low as ∼0.4 dB/mm, the integrated emitter with uncoated facets yielded output powers up to 0.4 mW for each wavelength at 100 mA.
Improvement of leakage current characteristics of Ba0.5Sr0.5TiO3 films by N2O plasma surface treatment
Authors: Cho Hag-Ju , Oh Sejun , Kang Chang Seok , Hwang Cheol Seong , Lee Byoung Taek , Lee Ki Hoon , Horii Hideki , Lee Sang In , Lee Moon Yong
Published: July 2002

The effects of plasma surface treatment, using N2O gas, of Ba0.5Sr0.5TiO3 (BST) film on the leakage current characteristic of a Pt/BST/Pt capacitor were investigated. As a result of exposure of BST film to the plasma, the leakage current density of the BST capacitor decreased by two orders of magnitude in the high voltage region, and higher onset voltage of an abrupt increase in leakage current was observed. The improvement of leakage properties of BST films can be attributed to the elimination of the bulged curve in the leakage current characteristics. Thermal desorption spectroscopy showed that the elimination was closely related to the reduction of carbon content in the BST film.