bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of H and O passivation on photoluminescence from anodically oxidized porous Si
Authors: Shih S. , Jung K. H. , Kwong D. L. , Kovar M. , White J. M.
Published: July 2002

We have studied the mechanism of photoluminescence (PL) change in porous Si layers (PSLs) by gradually replacing the hydrogen-terminated surface with an oxygen-terminated surface by anodic oxidation at room temperature. The observed PL change did not follow the change in the silicon hydrides detected by transmission Fourier transform spectroscopy (FTIR). FTIR spectra show that the silicon hydrides decreased while the PL increased. The results of this study show that the polysilane species is not solely responsible for efficient luminescence from PSLs. In addition, an enhancement of PL intensities after laser exposure was observed from anodically oxidized PSLs.
Low temperature synthesis and properties of lithium niobate thin films
Authors: Joshi V. , Roy D. , Mecartney M. L.
Published: July 2002

Thin films of lithium niobate were deposited on silicon (100) by a sol-gel technique and were annealed in oxygen at 400 °C. The annealed films were characterized by x-ray diffraction and transmission electron microscopy which showed crystallization to LiNbO3, a preferred orientation of the films, and an average grain size of about 0.5 μm. Electrical characterization of the films in the metal-ferroelectric-semiconductor configuration showed evidence for ferroelectricity via the hysteresis loop. The dielectric constant and dissipation factor were measured at frequencies from 10 Hz to 10 MHz with a dielectric constant of 35 and dissipation factor of 0.004 at 100 kHz. The current-voltage characteristics of the films exhibited asymmetric behavior, indicating a possible Schottky barrier and showed a leakage current density of 1.1×10−4 A/cm2 at 3 V.
Photoluminescence of high-quality SiGe quantum wells grown by molecular beam epitaxy
Authors: Wachter M. , Schäffler F. , Herzog H.-J. , Thonke K. , Sauer R.
Published: July 2002

A variety of SiGe quantum well (QW) samples were grown by solid-source molecular beam epitaxy (MBE) to study the influence of growth temperature TG and QW width Lz on the photoluminescence (PL) properties. For all growth temperatures investigated (350 °C≤TG≤750 °C) we found intense, well-resolved PL signals from the SiGe QWs. The PL intensity increases with TG, and the stability against measurement temperature becomes better. A formerly reported PL band below the SiGe band edge is either completely absent, or very weak in the 4.2 K spectra of our samples. Thus, the defects or complexes responsible for this signal are obviously not inherent properties of MBE growth.
Strain relief mechanism for damage growth during high-dose, O+ implantation of Si
Authors: Zhou D. S. , Holland O. W. , Budai J. D.
Published: July 2002

Ion-induced damage accumulation and growth during separation by implantation of oxygen (SIMOX) processing were studied. Silicon wafers were implanted with 450 keV oxygen ions at an elevated temperature with doses of 0.8×1018 and 1.1×1018 cm−2. At the lower dose, the silicon overlayer was found to be highly strained but free of dislocations, while a distinct band of dislocations was observed in the top Si layer at the higher dose. The occurrence of this band is shown to correlate with strain relief in the overlayer. Rutherford backscattering spectrometry, cross-section transmission electron microscopy, and x-ray diffraction were used to characterize this damage so that its role in releasing the accumulated strain during ion implantation could be better understood. Additional insight was gained into the nature of the damage formed at the different doses by studying the thermal stability at 900 °C. Markedly different thermal behaviors were observed and are correlated to changes in the strain state of each sample. These results strongly suggest that dislocation formation in the Si overlayer during the SIMOX process is in response to strain accumulation in the lattice and that dislocation-free layers can be formed by appropriate intervention prior to the yield point. This mechanism for dislocation formation is thought to be generally operative under extreme irradiation conditions and, therefore, will be important to other ion-beam synthesis processes such as buried silicide formation.
Epitaxial growth of Si by ArF laser-excited supersonic free jets of Si2H6
Authors: Motooka T. , Abe H. , Fons P. , Tokuyama T.
Published: July 2002

Epitaxial growth processes of Si from ArF laser-excited Si2H6 supersonic free jets have been investigated using reflection high-energy electron diffraction, growth rate, and atomic force microscopy measurements. Layer-by-layer epitaxial growth was observed at substrate temperature Ts=670 °C regardless of the laser excitation. However, it was found that island growth was predominant at Ts=550 °C without the laser excitation, while layer-by-layer growth occurred by using the ArF laser-excited Si2H6 jet probably due to an enhancement of surface reactions induced by precursor species obtained from laser-excited Si2H6 .
Properties of the quantum wires grown on V-grooved Al0.3Ga0.7As/GaAs substrate by atmospheric pressure metalorganic chemical vapor deposition
Authors: Lee Min-Suk , Kim Yong , Kim Moo-Song , Kim Seong-II , Min Suk-Ki , Kim Young Duk , Nahm Sahn
Published: July 2002

We report the successful growth of quantum wire (QWR) structures of AlxGa1−xAs/ GaAs /AlxGa1−xAs on a V-grooved Al0.3Ga0.7As/GaAs substrate. The samples are studied by photoluminescence spectra. The structures are grown by atmospheric pressure metalorganic chemical vapor deposition (MOCVD). The GaAs QWRs are fabricated on a V-grooved Al0.3Ga0.7As/GaAs substrate instead of GaAs substrate. Due to the effect of the Al0.3Ga0.7As layer, a necking area is formed in the side quantum wells (QWLs) near the bottom of the V groove. This results in a reduction of the lateral widths of the QWRs. Also, the luminescence of the QWRs is greatly enhanced in spite of low packing density. It is the first structure made in attempts to produce the quantum-size effects on a V-grooved substrate with non-(111) facets.
Unidirectional semiconductor ring lasers with racetrack cavities
Authors: Hohimer J. P. , Vawter G. A.
Published: July 2002

We report the development of racetrack-cavity semiconductor ring lasers that operate unidirectionally by means of an active crossover waveguide. These racetrack-cavity lasers show improved performance over previous circular-cavity unidirectional ring lasers with continuous-wave single-frequency output powers of ≥10 mW, and with up to 99% of the lasing output emitted from the preferred ring direction.
Ion implantation of porous silicon
Authors: Peng C. , Fauchet P. M. , Rehm J. M. , McLendon G. L. , Seiferth F. , Kurinec S. K.
Published: July 2002

We have investigated the properties of light-emitting porous silicon after ion implantation and successive annealing through continuous-wave photoluminescence (CWPL) and time dependent photoluminescence (TDPL) spectroscopies. Implantation was performed with phosphorus, boron and silicon ions of different doses and energies. Low dose dopant implantation keeps or even increases the CWPL intensity and increases the TDPL decay time. High dose dopant implantation and silicon self-implantation reduce the CWPL intensity and slightly decrease the TDPL decay time.
Sintered aerosol masks for dry-etched quantum dots
Authors: Deppert Knut , Maximov Ivan , Samuelson Lars , Hansson Hans-Christen , Weidensohler Alfred
Published: July 2002

We report on a sintering step in producing ultra-fine silver aerosol particles to serve as etch masks for semiconductor quantum-dot structures. Our experiments found heating conditions that reshape the Ag particles, resulting in a spherical shape and very good size uniformities. Using this improved aerosol generation technology, we have dry etched InP columns with 24±5 nm diameter and with very good uniformity, with nearly every aerosol particle resulting in a column. Column arrays with a density as high as 3×109 cm−2 could be produced.
Second-harmonic generation in bulk and waveguided LiTaO3 with domain inversion induced by electron beam scanning
Authors: Gupta Mool C. , Kozlovsky William , Nutt Alan C. G.
Published: July 2002

Bulk quasi-phase-matched frequency doubling experiments are reported for a lithium tantalate crystal which was periodically poled through its 0.5 mm thickness by electron beam scanning. The measured phase-matching bandwidth of 1 nm for the 2-mm-long domain inverted section was close to the theoretical value of 0.4 nm, although the conversion efficiency was lower than theoretically expected. Chemical etching revealed domain duty-cycle variations and incomplete inversions which are likely to have caused the lower conversion efficiency. Frequency doubling in waveguides fabricated in this material produced a normalized conversion efficiency of 290%/W cm2 and a phase matching bandwidth of 0.3 nm for a 1-mm-long domain inverted region.
Pd/Ge ohmic contacts to n-type GaAs formed by rapid thermal annealing
Authors: Lai Jiun-Tsuen , Lee Joseph Ya-Min
Published: July 2002

Pd/Ge ohmic contact to n-type GaAs is obtained by using the rapid thermal annealing (RTA) method. The best specific contact resistivity of ohmic contacts annealed at 400–500 °C is on the order of 10−6 Ω cm2. Secondary ion mass spectrometry (SIMS) measurement shows that these ohmic contacts are very shallow. Gallium dissociation from GaAs is observed. It is found that there is a correlation between a gallium SIMS signal bump and good ohmic contact behavior. A model is proposed for this phenomenon. This RTA ohmic contact method has been successfully applied to the fabrication of charge injection transistor/negative resistance field-effect transistor devices.
Nanosecond time-scale semiconductor photoexcitations probed by a scanning tunneling microscope
Authors: Gallagher Mark J. , Ruskell Todd G. , Chen Dong , Sarid Dror , Jenkinson Howard
Published: July 2002

The high-frequency response of scanning tunneling microscopy of a semiconductor is demonstrated by using the beat frequencies of the longitudinal modes of a HeNe laser at the tunneling junction. We present a comparison of the slow and fast optical response of photoexcited charge carriers in the layered structure semiconductors n-type MoS2 and p-type WSe2 using this method.
Formation of luminescent silicon by laser annealing of a-Si:H
Authors: El-Kader K. M. A. , Oswald J. , Kočka J. , Cháb V.
Published: July 2002

We report the preparation of luminescent Si by laser annealing of amorphous hydrogenated silicon (a-Si:H) deposited on a silica substrate by glow-discharge deposition. For this process, we have used XeCl excimer laser pulses with an energy density in the range of 0.3–0.7 J/cm2. While no visible photoluminescence (PL) has been observed at room temperature from the unirradiated a-Si:H the PL comparable to the PL spectra of porous Si occurs in the irradiated part. The electron microscope studies reveal a microstructure which is a function of the pulse number and the pulse energy density.
Smooth etching of single crystal 6H-SiC in an electron cyclotron resonance plasma reactor
Authors: Flemish J. R. , Xie K. , Zhao J. H.
Published: July 2002

Single-crystal 6H-SiC has been etched using a CF4/O2 gas mixture in an electron cyclotron resonance (ECR) plasma reactor. ECR etching results in SiC surfaces which are extremely smooth, without the problematic micromasking effects which have been reported to result from reactive ion etching in capacitively coupled radio-frequency plasma reactors. The effects of microwave power, total pressure, substrate temperature, and substrate bias on the etch rate, surface morphology, etch profile, and etch selectivity have been evaluated. The etch rate increases with increasing power and bias, and decreasing pressure. However, high biases lead to enhanced etching in regions adjacent to sidewall features. Improved etch profiles and selectivity are obtained with lower applied substrate bias.
Optical near-field imaging with a semiconductor probe tip
Authors: Mertz J. , Hipp M. , Mlynek J. , Marti O.
Published: July 2002

We present an optical near-field detection mechanism based on optical modulation of the image force between a semiconducting probe tip and a glass surface. The modulation stems from a phenomenon called surface photovoltage. The performance of the mechanism for near-field imaging is demonstrated by using a scanning force microscope over a standing evanescent light wave. The lateral resolution is found to be 170 nm (subwavelength) and a representative minimum detectable power is 0.1 pW/√Hz in air. We develop a simple theoretical model and discuss some possible applications.
Depleted double-heterojunction optical thyristor
Authors: Kuijk M. , Heremans P. L. , Borghs G. , Vounckx R.
Published: July 2002

A novel double-heterojunction PnpN optical thyristor is presented in which both the center n-layer and the center p-layer are completely depleted at equilibrium. This structure is an extremely attractive optoelectronic switch, because it allows the marriage of two usually incompatible features: speed and optical sensitivity. The speed results from the fact that our PnpN-structure can be reset to equilibrium, from any point on the current-voltage characteristics, in less than 10 ns by means of a simple negative anode-to-cathode voltage pulse. The optical sensitivity is a direct consequence of the center n- and p-layers being completely depleted of free carriers at equilibrium. We show experimental evidence of this reset operation by studying the dynamics of the free-carrier extraction from the center n- and p-layers.
Femtosecond reflectivity measurements and second harmonic generation in nonresonant excitation of photoconductive switches
Authors: Keil U. D. , Dykaar D. R. , Kopf R. F. , Darack S. B.
Published: July 2002

Field dynamics in a coplanar photoconductive switch are investigated by voltage dependent reflectivity measurements. The comparison of femtosecond pulsed and cw probe beams resolves both linear and nonlinear electro-optic effects. To avoid carrier effects, measurements were performed with below band gap light. We also report the observation of second harmonic generation near the positive electrode for below band gap excitation.
Studies of GaAs:Er impact excited electroluminescence devices
Authors: Chang S. J. , Takahei K.
Published: July 2002

We report on the study of impact excitation of Er ions in GaAs. The metalorganic chemical vapor deposition grown, p+-n structured electroluminescence (EL) devices were fabricated by growing, at different temperatures, GaAs:Er layers on top of the n+ GaAs substrates. P+ layers of GaAs were made by Zn diffusion from the top surfaces. When we forward biased these diodes, the EL spectra were similar to the respective photoluminescence (PL) spectra of each sample. The spectra of the samples differed for the various growth temperatures. However, when we reverse biased these diodes, the EL spectra are the same for all samples but different from the PL spectra. These results indicate that the Er center(s) excited by direct impact is different from the Er center(s) excited through electron-hold recombination and the subsequent energy transfer.
High sensitivity double relaxation oscillation superconducting quantum interference devices
Authors: Adelerhof Derk Jan , Kawai Jun , Uehara Gen , Kado Hisashi
Published: July 2002

Double relaxation oscillation superconducting quantum interference devices (SQUIDs) (DROSs) have been fabricated with estimated relaxation frequencies up to 14 GHz. Both the intrinsic flux noise and the performance in a flux locked loop with direct voltage readout have been studied. In flux locked loop, a noise level of 0.55 μφ0/√Hz corresponding to an energy sensitivity of 34 h has been obtained for a DROS with a SQUID inductance of 29 pH. The intrinsic sensitivity improves with increasing relaxation frequency, leveling off to a value of 13 h at relaxation frequencies higher than about 3 GHz.
Luminescence efficiency enhancement in laser soaked hydrogenated amorphous carbon films
Authors: Koós M. , Pócsik I. , Tóth L.
Published: July 2002

An unexpected effect of laser soaking was observed on the properties of annealed a-C:H films. The photoluminescence (PL) intensity was increased up to six times and, the spectrum was blue shifted in samples exposed to an unfocused Ar+ laser beam. The time dependence of the PL intensity increase was found to be exponential up to saturation with characteristic times around 103 s. The observed changes were influenced by illumination intensity and sample properties. These results are corroborated by a PL mechanism when excitation and recombination take place on π-bonded clusters.
Influence of Coulombic broadened DX center energy levels on free electron concentration in δ-doped AlxGa1−xAs/GaAs quantum wells
Authors: Brunthaler G. , Seto M. , Stöger G. , Köhler K.
Published: July 2002

The achievable two-dimensional (2D) electron concentration in a δ-doped quantum well depends on the Al content in the doping layer and is considerably lower than the nominal doping concentration. This behavior has been so far attributed to different incorporation probabilities of Si atoms depending upon the Al content. In this work, we show instead that the energy levels of the DX center together with the Coulomb interaction account for this behavior. We present calculations of the DX center density of states which are broadened by the Coulomb interaction and show that the estimated 2D carrier concentrations agree well with experiment.
Correlation of oscillations in a quantum dot with three contacts
Authors: Kumar A. , Eugster C. C. , Orlando T. P. , Antoniadis D. A. , Kinaret J. M. , Rooks M. J. , Melloch M. R.
Published: July 2002

Results of transport measurements on a GaAs quantum dot are presented in which the gate geometry allows the dot to be accessed by three, rather than two, contacts. In the Coulomb blockade regime, conductance oscillations periodic in gate voltage are measured concurrently at two contacts in response to a small excitation voltage at the third contact. When the dot is in the strongly blockaded regime, we obtain the expected result from single electron tunneling theory that oscillations at the two output contacts are correlated with each other in gate voltage. As the tunnel barriers are made softer by changing the gate voltage, a strikingly different phenomenon is observed: conductance peaks at the two output leads evolve from perfect correlation to perfect anticorrelation with each other.
In situ x-ray diffraction analysis of the C49–C54 titanium silicide phase transformation in narrow lines
Authors: Roy R. A. , Clevenger L. A. , Cabral C. , Saenger K. L. , Brauer S. , Jordan-Sweet J. , Bucchignano J. , Stephenson G. B. , Morales G. , Ludwig K. F.
Published: July 2002

The transformation of titanium silicide from the C49 to the C54 structure was studied using x-ray diffraction of samples containing arrays of narrow lines of preformed C49 TiSi2. Using a synchrotron x-ray source, diffraction patterns were collected at 1.5–2 °C intervals during sample heating at rates of 3 or 20 °C/s to temperatures of 1000–1100 °C. The results show a monotonic increase in the C54 transition temperature by as much as 180 °C with a decreasing linewidth from 1.0 to 0.1 μm. Also observed is a monotonic increase in (040) preferred orientation of the C54 phase with decreasing linewidth. The results demonstrate the power of in situ x-ray diffraction of narrow line arrays as a tool to study finite size effects in thin-film reactions.
Plastic stress relaxation in highly strained In0.30Ga0.70As/GaAs structures
Authors: Androussi Y. , Lefebvre A. , Delamarre C. , Wang L. P. , Dubon A. , Courboulès B. , Deparis C. , Massies J.
Published: July 2002

The evolution of surface roughness and the subsequent plastic relaxation mechanisms have been studied by transmission electron microscopy (TEM) as a function of the thickness of highly strained In0.30Ga0.70As layers on GaAs(001). The following stages have been observed: formation of coherent islands, coalescence of islands, and nucleation of dislocations at the troughs of the surface ripples. Dislocations are thus systematically generated where the highest stress concentrations are expected, according to recent theoretical predictions. It is the first time such a plastic relaxation mechanism has been observed in highly strained semiconductor heterostructures.
Deep levels in undoped In0.5Ga0.5P and In0.5Ga0.5P0.99As0.01 grown on GaAs (100) substrates
Authors: Lan Sheng , Yang Cheng-Qing , Cui De-Long , Xu Wan-Jing , Liu Hong-Du
Published: July 2002

High-quality In0.5Ga0.5P and In0.5Ga0.5P0.99As0.01 epitaxial layers on the GaAs (100) substrate have been grown by liquid phase epitaxy (LPE). Special attention is paid to the deep level transient spectroscopy (DLTS) and transient photoresponse in these samples. It is found that the epitaxial layers grown under the optimum P vapor pressure are free from deep levels and show a much longer photocarrier lifetime. We suggest that the deep level may be attributed to interstitial P atoms. From the photocarrier lifetime of different samples, we can conclude that the interstitial P atoms act as recombination centers.
Temporal and mode structure of the interband p-germanium laser emission
Authors: Bespalov A. V.
Published: July 2002

We have studied the emission of a far-infrared interband p-germanium laser using a terahertz range Schottky diode detector. The temporal structure of the emission was investigated with a resolution of 250 ps. We observed short intense spikes that arose due to laser mode beating. The mode structure of the laser emission was obtained by transforming the temporal signal into the frequency domain. It was found that four transversal modes were excited during the laser action. The frequency separation between transversal and longitudinal modes was 52.6 and 657 MHz, respectively.
Photothermal reflectance investigation of implanted silicon: The influence of thermal annealing
Authors: Seas Antonios , Christofides Constantinos
Published: July 2002

Photothermal reflectance (PTR) measurements on phosphorus implanted and annealed silicon wafers are reported. The ability to measure the dependence of the photothermal signal on doping and annealing temperature is discussed. The great sensitivity of the PTR technique on the short and long range disorder as well as on the residual defects, in combination with its nondestructive nature make this technique very promising toward the thermal and optoelectronic characterization of implanted and annealed wafers. Furthermore, PTR measurements have been proved to be very sensitive in the study of the annihilation process of defects.
H− and electron production in a magnetic multipole source
Authors: Holmes A. J. T. , Dammertz G. , Green T. S.
Published: July 2002

An investigation has been made of the yield of H− ions and electrons extracted from a magnetic multipole, or bucket, ion source as a function of the parameters of the source. Under optimum conditions the H− current density attains a value equal to half of the positive ion current density (H+3) measured at the extraction plane. The experimental results indicate that, while the H− current rises linearly with arc current, the extracted electron current shows a quadratic dependence. There is also a strong dependence of the electron current on the magnetic field applied across the extraction aperture, and source filling pressure. Probe measurements within the plasma volume show considerable axial variation of the fluxes of electrons, H− ions and H+3 ions.
Two-dimensional space-resolved soft x-ray spectroscopy of hot dense plasmas
Authors: Kiuttu G. F. , Degnan J. H. , Richter-Sand R. J. , Woodall D. M.
Published: July 2002

Two-dimensional spatially resolved K shell spectra from hot (Te≂40–400 eV), dense (ne≂1019–1021 cm−3) aluminum plasmas have been recorded using a convex curved KAP crystal spectrograph in a dispersion mapping mode with an orthogonal imaging slit. The approximately 1-cm-diameter, 2-cm-long cylindrical source was viewed on end, yielding axially and temporally integrated spectra. The relative intensities of the lines and recombination continua were used to estimate local temperatures and densities. The measurement technique is reviewed and representative analysis and results are presented in this paper.
Charge exchange neutral particle mass and energy analyzer for the JT-60 tokamak
Authors: Hayashi K. , Hashimoto K. , Yamato H. , Takeuchi H. , Miura Y. , Nishitani T. , Shiho M. , Maeda H.
Published: July 2002

Design considerations and experimental results are described for a charge exchange neutral particle mass and energy analyzer for JT-60, which analyzes H, D, and He simultaneously up to a maximum energy of 110 keV. The analyzer has separately a 180° deflection magnet for momentum analysis and an electrostatic deflector for mass analysis. The way to control the effect of the electric fringe fields in order to expand the detectable energy range is studied by numerical simulation. The deflector is then designed, made of two triangular plates and three additional electrodes for the control of the fringe fields. The effect of the deflector is demonstrated experimentally. Energy and mass resolution and the relation between the incident ion energy and the magnetic field strength are measured. The results of the calibration experiments agree with the designed value.
Calculated second-harmonic susceptibilities of BN, AlN, and GaN
Authors: Chen Jian , Levine Zachary H. , Wilkins John W.
Published: July 2002

We report calculations for the dielectric constant ε∞ and the second-harmonic susceptibility d for BN, AlN, and GaN in both zincblende and wurtzite structures within the Kohn–Sham local-density approximation. For wurtzite AlN and GaN, the computed dxxz(w) and dzzz(w) closely agree with experiment. For zincblende AlN and GaN as well as zincblende and wurtzite BN, we predict d. Our results show that the simple relation between the independent components of d predicted by bond additivity works for BN, breaks down for GaN, and completely fails for AlN.
Development of a photoacoustic probing technique to study the sedimentation of humic acid
Authors: Wylie Ian W. , Lai Edward P. C.
Published: July 2002

This work shows the feasibility of the application of a pulsed laser photoacoustic probe and photoacoustics in general to the study of the sedimentation of particles of molecular or macroscopic dimensions under gravity or in an ultracentrifuge. Sedimentation trials under gravity on particulate humic acid in ethanol and alkaline H2O were performed with the probe. These trials were compared to similar ones carried out on a UV/visible absorption spectrometer. They show that the photoacoustic sedimentation data, unlike the absorption data, are not obscured by interference from light scattering. Approximate sedimentation coefficients for humic acid were calculated and were compared to literature values to calculate an approximate average particle size for particles settling out during the trial.
New apparatus for simultaneous determination of phase equilibria and rheological properties of fluids at high pressures: Its application to coal pastes studies up to 773 K and 30 MPa
Authors: Cohen Albert , Richon Dominique
Published: July 2002

In this article, we present a new apparatus based on a static method to simultaneously measure rheological properties of a dense (liquid or liquid+solid) medium and sample phases (dense and gaseous) for analysis purposes. It was especially designed to study coal pastes in the working conditions of hydroliquefaction processes. It can also be used to study other mediums such as asphalts and polymers. The rheometer part of the apparatus was already tested and results published in a previous paper. The ability of the new apparatus to get reliable vapor–liquid equilibrium data in the range of thermal stability of chemical materials is shown as a result of measurements on the nitrogen-n-heptane system at 497.1 K and the methane-n-hexadecane system at 623.1 K and comparison to literature’s data. Reproducibility tests have displayed very small data dispersion.
Problems with cryogenic operation of piezoelectric bending elements
Authors: Duffield C. L. , Moreland John , Fickett F. R.
Published: July 2002

Piezoelectric bimorphs constructed from lead titanate-zirconate (PZT) ceramic bonded to a brass sheet have been tested at cryogenic temperatures to determine their suitability for use in a low-temperature micropositioner. Experimental data are presented on bimorph sensitivity (displacement per volt) as a function of the number of temperature cycles. Results indicate that bimorphs of this type cannot be calibrated because of irreversible changes in the bending characteristics that occur while cycling from room temperature to 4 K.
Simple concepts in the measurement of the energy distribution and spin polarization of an electron beam
Authors: Drouhin H.-J. , Eminyan M.
Published: July 2002

A comprehensive study of a compact electron spectrometer coupled with a Mott polarimeter is presented. This device is operated in ultrahigh vacuum (1×10−10 Torr) and optimized to investigate the polarized photoemission from negative electron affinity semiconductors. The electron energy dispersing device is made up of two 90° cylindrical electrostatic deflectors. It combines optimum geometry to allow spin-polarization measurements with high resolution (∼20 meV) and high luminosity (peak output current up to 5 nA). Emphasis is placed on practical hints, limiting factors, and simple criteria to optimize the design of the electron selector, the electron optics, the power supplies, and the current detection. The proposed solutions lead to a very convenient, easy to operate, and low-cost apparatus. Also the way of obtaining optimal performances is discussed. A new and simple method to measure the energy resolution of an electron spectrometer is described in detail. The problem of energy calibration is considered and some experimental results, obtained on gallium arsenide, are shown for illustration.
High-speed programmable detector system for plasma spectroscopy
Authors: Mai H. H. , Larsen J. M. , Dimoff K. , Castracane J.
Published: July 2002

Special electronic scanning circuits have been built to increase the resolution time of an intensified photodiode array assembly used for detecting EUV emission. The system can operate at 1-MHz sampling rate to provide data readout on two parallel output lines. The scanning time of a 1000-element array can be reduced to 500 μs. The system is programmable and can function sequentially at three different frequencies within a single scan. The device is CAMAC compatible and operated remotely by computer. It has been used to record spatial as well as temporal development of EUV radiation from the TEXTOR tokamak plasma.
Commissioning of the 8-UD injector for VICKSI
Authors: Busse W. , Martin B. , Michaelsen R. , Pelzer W. , Renner D. , Ziegler K.
Published: July 2002

The project to add an 8-MV tandem accelerator to the VICKSI facility is nearing completion. The status of the project is given and the tests and their results during commissioning of the tandem are described.
ANL high-resolution injector
Authors: Minehara E. , Kutschera W. , Hartog P. Den , Billquist P. , Liu Z.
Published: July 2002

The ANL (Argonne National Laboratory) high-resolution injector has been installed to obtain higher mass resolution and higher preacceleration, and to utilize effectively the full mass range of ATLAS (Argonne tandem linac accelerator system). Preliminary results of the first beam test are reported briefly. The design and performance, in particular a high-mass-resolution magnet with aberration compensation, are discussed.
Status report on the Florida State linac project
Authors: Fox John David , Wright Lon
Published: July 2002

The Florida State University superconducting linear accelerator booster will consist of three cryostat modules, each with four β=0.105 resonators and two superconducting solenoids, and buncher and rebuncher resonators in individual cryostats. The first cryostat module was recently completed and is described.
Improved rf modulation technique for bunched beam detection
Authors: Waterson M. , Clifft B. E.
Published: July 2002

The system used for sensing and controlling the timing of the bunched ion beam in the ATLAS accelerator has been modified to improve its beam detection capability through the addition of a secondary phase modulation to the reference signal. Exciting a resonant structure with this reference and the bunched ion beam generates a vector sum of the two signals containing phase and beam signal strength information as amplitude modulation components. A linear relationship between one of the modulation components and the average beam current is used in generating a beam monitor signal. The resulting system exhibits sensitivity to beams of 0.3 nA (electrical), dynamic range of 104, beam phase jitter of less than 20 ps at the subharmonic buncher, and is insensitive to environmental changes.
Post-mortem—An autopsy of an NEC column post
Authors: Weisser D. C. , Brinkley T. A. , Clarkson G. P. , Malev M. D. , Ophel T. R. , Turkentine R. B.
Published: July 2002

Cracks in ceramic components of NEC column posts pose a serious threat to the 14UD in Canberra. The failed posts have been examined with a view toward identifying the probable cause of puncture and deciding a strategy to contain the problem.
Junction parameters of mtsp;YBa2Cu3O7 step edge junctions on mtsp;LaAlO3 substrates from Fiske resonances
Authors: Yi H. R. , Winkler D. , Claeson T.
Published: July 2002

Strong Fiske type resonance peaks have been observed in current–voltage curves of mtsp;YBa2Cu3O7 step edge junctions on mtsp;LaAlO3 substrates. We determined effective shunting capacitances from the voltages of the resonances. These data compare well with those obtained from the McCumber constant mtsp;βc. Typical values of the shunting capacitance per unit area for these junctions were estimated to be in the range of 20–30 mtsp;fF/μm2. The surface resistance normalized to 1 GHz at the conjugating junction interfaces was estimated to be in the range of 1–3 μΩ.
Preparation of planar multilayered targets for laser ablation studies
Authors: Popil R. , Haromy A. , Fedosejevs R. , Offenberger A. A.
Published: July 2002

A method is described for the reliable production of reproducible multilayered targets for laser ablation rate studies using time-resolved x-ray spectroscopy. The targets consist of alternating layers of plastic and evaporated metals whose thickness and uniformity were examined by weighing and by SEM micrography to be suitable for experiments. The plastic layers are deposited by a dipping technique using various concentrations of polystyrene and Formvar solutions. The resulting thickness of the films versus the concentration of the solutions is reported. In addition, an application of submicrometer Formvar films for use as sub-keV x-ray filters is described.
Design of a single-axis platform for balloon-borne remote sensing
Authors: Coyle L. M. , Aurilio G. , Nystrom G. U. , Bortz J. , Nagy B. G. , Chance K. V. , Traub W. A.
Published: July 2002

We describe the design of two telescope pointing systems for remote optical sensing of the stratosphere from a balloon-borne gondola. The telescope pointing accuracy is ±0.02° in elevation, from a gondola which has static and dynamic tilts up to ±3°. Each system consists of a telescope, an elevation control subsystem, and a pitch-stabilized single-axis reference platform. The Mark I unit has performed successfully on each of its two balloon flights, for a total of over 16 h in the stratosphere; the Mark II unit is currently under construction. The single-axis platform is referenced to a rate-integrating gyroscope and an inclinometer for high- and low-frequency pitch-angle variations, respectively. The Mark I platform is supported by ball bearings, driven by a brush-contact torque motor, and is subject to a small, permanent pitch angle error which depends directly on the gyro drift rate. The Mark II platform uses flex-pivot supports, a brushless motor, and for even a relatively large gyro drift rate, is designed to asymptotically approach zero angular offset error.
Gas heating effects in the neutralizers of neutral beam injection lines
Authors: Paméla J.
Published: July 2002

Measurements of neutralization efficiencies in a powerful neutral deuterium beam line have evidenced neutralizer gas linear density values much lower than expected from conductance measurements made without the beam. This can be explained by gas heating phenemona in the presence of the beam. These phenomena are included in a model whose purpose is the gas linear density prediction [a detailed presentation of this model is given elsewhere (J. Paméla, ‘‘Gas Heating Effects in the Neutralizers of Neutral Beam Injection Lines,’’ EUR-CEA-FC 1279, Sept. 1985)].
Ultrahigh-vacuum field emitter array wafer tester
Authors: Gray H. F. , Ardis L. , Campisi G. J.
Published: July 2002

The device reported here allows the researcher the opportunity of gaining primitive yield information, threshold voltages, emission stability, and other information, e.g., gas effects, on field emitter arrays (FEA) which are microminiature ‘‘vacuum tubes’’ fabricated by microelectronic processing methods on silicon wafers, without scribing, dicing, and mounting each device on individual vacuum-compatible headers. This device also speeds up the entire data-acquisition process by requiring only one ultrahigh-vacuum pumpdown and one set of vacuum feedthroughs.
Schlieren method for measuring the particle density distribution in fusion plasma
Authors: Lisitano G.
Published: July 2002

This paper describes a measuring system which automatically selects and identifies angularly deflected electromagnetic rays of a pencil beam exploring a dispersive medium. The schlieren deflection is dependent on the refractivity gradient transverse to the ray path. This yields fairly localized measurement of material inhomogeneities. Applied for the first time to a tokamak plasma, this schlieren method yields fast time and good spatial resolution measurement of the particle density distribution. Without any need for data inversion this method also delivers monitor signals of the center-core peak density and flattening of the parabolic particle density distribution. Schlieren measurements of magnetohydrodynamic particle density perturbation give an insight into plasma transport and collapse mechanisms.
Optical multichannel analyzer-based high-resolution, multipoint spectroscopic apparatus
Authors: Antoniades J. A. , Peyser T.
Published: July 2002

A high-wavelength resolution (Δλ≤0.02 Å) spectroscopic apparatus has been developed and applied to the measurements of spectral line profiles emitted by thermonuclear plasmas yielding important plasma parameters, such as ion temperature and fluid velocity. The experimental apparatus consists of a spectrometer, an optical multichannel analyzer (OMA), and a lens. It allows precise wavelength measurements (Δλerror≤0.02 Å) when a computer and a ThI electrodeless discharge lamp (EDL) are used to calibrate the instrument. The apparatus yields single-shot space and time-resolved spectra for radiation in the 2000–8000-Å range.
Correction of fluorescence detected circular dichroic photoselection artifacts using light collecting ellipsoidal mirrors
Authors: Bicknese S. E. , Maestre M. F.
Published: July 2002

Ellipsoidal mirrors are used to collect the emitted light from fluorophores in fluorescence detected circular dichroic (FDCD) measurements and to deliver this light to a photomultiplier tube (PMT) at 90° to the excitation beam. These mirrors collect light over a symmetrical 71% of the emission sphere centered on the sample cell, and thereby eliminate most of the nonuniformity in detected emission resulting from the anisotropy of photoselection. Furthermore, even with reflectance and path length losses, the amount of fluorescent emission reaching the PMT is increased by a factor of approximately 18. Elimination of photoselection artifacts in UV FDCD spectra is demonstrated by comparing spectra of L-tryptophan in glycerol with its spectra in water. Validity of the values measured is verified through calibration with a d10 camphorsulfonic acid (d10 CSA) standard.
Charcoal-pumped 3He cryostats for storage Dewars
Authors: Swartz E. T.
Published: July 2002

We have designed a 3He cryostat which can be inserted into a storage Dewar. This cryostat requires no external gas-handling system and has the advantages of extremely low (and recoverable) helium consumption, fast cooldown and warm-up times, excellent temperature range and stability, and low vibrational and electrical noise. The freedom from an external gas-handling system allows for portability and flexibility in its uses. Design and construction of the cryostat are presented, and operation and performance are discussed in some detail. To demonstrate performance of the cryostat, we present thermal boundary resistance measurements between 0.4 and 170 K for a solid–solid interface (Rh:Fe/sapphire).
Rapid-frequency-scan laser for instantaneous line-profile measurements in fluorescence spectroscopy
Authors: Honda Chikahisa , Maeda Mitsuo , Muraoka Katsunori , Akazaki Masanori
Published: July 2002

Rapid-frequency-scan (RAFS) dye lasers have been developed for determination of instantaneous line profiles of neutral atoms and molecules. Two types of rapid-frequency scanners are examined and their scanning performances are compared. One scanner is an étalon driven by a PZT piezoelectrical element, and the other is an electro-optical (EO) filter with a KDP crystal. The PZT scanner takes 4–5 μs to scan over the free spectral range (FSR), and the EO scanner can make faster scanning. The maximum scanning range is limited by FSR, and the static bandwidth is approximately 1/100 of FSR in both cases. In fast scanning, however, the dynamic bandwidth increases. The error in the single shot measurement is evaluated, based on an experimental result of the line-profile measurement of Fe atoms.
Linear capacitive displacement sensor with frequency readout
Authors: Fritsch Klaus
Published: July 2002

A simple, inherently linear technique for measuring changes in the separation of the mirrors of an optical cavity is reported. The capacitor made up of the reflective metallic coatings is part of a feedback loop which adjusts the frequency of an oscillator to be proportional to the mirror separation. A linearity of 0.2% full scale was achieved for separations up to 0.5 mm with a resolution of 10 nm.
Picosecond fluorimeter using the optical Kerr effect for the direct and automatic recording of a whole time-resolved emission spectrum
Authors: Gilabert E. , Declémy A. , Rullière C.
Published: July 2002

Using an optical Kerr shutter and sophisticated automatization procedure, we have shown that it is possible to record routinely, with a good accuracy, and in an experiment consuming a comfortable time, time-resolved emission spectra of short-lived species in the time scale of 10 ps and in the spectral range 3900–9000 Å. This system will allow us to obtain a better understanding of ultrafast dynamics in solution, where time spectral changes provide new insight.
Solid state cesium ion guns for surface studies
Authors: Souzis A. E. , Carr W. E. , Kim S. I. , Seidl M.
Published: July 2002

Three cesium ion guns covering the energy range of 5–5000 V are described. These guns use a novel source of cesium ions that combine the advantages of porous metal ionizers with those of aluminosilicate emitters. Cesium ions are chemically stored in a solid electrolyte pellet and are thermionically emitted from a porous thin film of tungsten at the surface. Cesium supply to the emitting surface is controlled by applying a bias across the pellet. A total charge of 10.0 C can be extracted, corresponding to greater than 2000 h of lifetime with an extraction current of 1.0 μA. This source is compact, stable, and easy to use, and produces a beam with >99.5% purity. It requires none of the differential pumping or associated hardware necessary in designs using cesium vapor and porous tungsten ionizers. It has been used in ultrahigh-vacuum (UHV) experiments at pressures of <10−10 Torr with no significant gas load. Three different types of extraction optics are used depending on the energy range desired. For low-energy deposition, a simple space-charge-limited planar diode with a perveance of 1×10−7 A/V3/2 is used. Current densities of 10.0 μA/cm2 at the exit aperture for energies ≤20 V are typical. This type of source provides an alternative to vapor deposition with the advantage of precise flux calibration by integration of the ion current. For energies from 50 to 500 V and typical beam radii of 0.5 to 0.2 mm, a high perveance Pierce-type ion gun is used. This gun was designed with a perveance of 1×10−9 A/V3/2 and produces a beam with an effective temperature of 0.35 eV. For the energy range of 0.5 to 5 keV, the Pierce gun is used in conjunction with two Einzel lenses, enabling a large range of imaging ratios to be obtained. Beam radii of 60 to 300 μm are typical for beam currents of 50 nA to 1.0 μA. Results are presented and discussed for UHV studies of ion implantation, electronic surface changes induced by adsorbates, and negative secondary-ion mass spectrometry.
Continuous density measurement of atomic hydrogen by means of a bolometer
Authors: Mertig M. , Luppov V. G. , Roser T. , Vuaridel B.
Published: July 2002

We developed a device which allows continuous measurement of the density of low-temperature stabilized atomic hydrogen by means of a bolometer. This density monitor was tested in a large open-storage cell during microwave-induced extraction of polarized atoms.
High-speed optical pulse generation using single-mode optical fiber networks
Authors: Sampson D. D. , Jackson D. A.
Published: July 2002

We demonstrate an inexpensive and easily fabricated, high-performance system for the generation of single and multiple optical pulse bursts. The system, which is comprised of commercially available components, provides single pulses as short as 190 ps full width half maximum. Used as an active, very low jitter, delay line for application to fast coincidence timing experiments, delays of much less than 1 ns to in excess of 1 μs are possible using 1300 nm standard telecommunications fiber. Optical fiber ladder networks containing differential fiber delays, connected together using single-mode fiber connectors have been used to construct flexible and reconfigurable optical burst generators. Precise delay time determination (±5 psecs) allows very accurate, discretely variable burst frequencies demonstrated at up to 3 GHz. Instruments capable of 4, 8, and 16 pulse trains are also demonstrated. A conservative estimate indicates pulse trains consisting of 128 pulses at 8 μW per pulse should be possible with a simple extension to the present apparatus.
Monte Carlo convolution method for simulation and analysis of fluorescence decay data
Authors: Chowdhury Fahmida N. , Kolber Zbigniew S. , Barkley Mary D.
Published: July 2002

A Monte Carlo convolution method for simulating time-correlated single photon counting data is presented. The random convolution automatically produces the Poisson statistics of the real experiment. The new simulation technique offers realistic treatment of various aspects of the single photon counting experiment, including pulse pileup. The random convolution is also incorporated in a data analysis technique using a reference fluorophore. Illustrative examples comparing the Monte Carlo and conventional simulation methods are given and the conceptual differences are discussed.