bluuebunny/crossref_metadata_2025 huggingface dataset:
Deep center photoluminescence study of low-temperature InP grown by molecular beam epitaxy
Authors: Yu P. W. , Liang B. W. , Tu C. W.
Published: July 2002

Low-temperature grown (130–480 °C) InP was investigated using photoluminescence spectroscopy with changes of excitation intensity and temperature. Two deep broad photoluminescence bands at ∼0.8 and 1.06 eV are present in undoped and Be-doped materials, and their formation strongly depends on the growth temperature. PIn and VIn related centers are associated with the transitions at 0.8 and 1.06 eV bands via the deep donor PIn–Be acceptor pair and the conduction band-to-VIn acceptor transitions, respectively. A configuration coordinate model is used to locate the deep donor and acceptor levels.
Magnetic force microscopy utilizing an ultrasensitive vertical cantilever geometry
Authors: DiCarlo A. , Scheinfein M. R. , Chamberlin R. V.
Published: July 2002

We have developed a novel magnetic force microscope (MFM) utilizing a vertically cantilevered microtip probe. This new geometry provides maximum sensitivity while inhibiting uncontrolled vertical deflections (tip crashes). We demonstrate the capability of our MFM by imaging domain structure in prerecorded magnetic tape and domain walls in single-crystal iron whiskers. Good agreement is obtained between the observed magnetic contrast and predictions of a micromagnetic model.
Phonon mode study of near-lattice-matched InxGa1−xAs using micro-Raman spectroscopy
Authors: Estrera J. P. , Stevens P. D. , Glosser R. , Duncan W. M. , Kao Y. C. , Liu H. Y. , Beam E. A.
Published: July 2002

We identify the four allowable phonon modes in InxGa1−xAs on InP:InAs-like transverse optical (TO) (225±2 cm−1), InAs-like longitudinal optical (LO) (233±1 cm−1), GaAs-like TO (255±2 cm−1), and GaAs-like LO (269±1 cm−1), using the selectivity of first-order Raman scattering off the (100) normal surface and the (011) cleaved plane and detailed line-shape analysis employing a sequential simplex optimization procedure. Raman scattering off the (011) cleaved plane was achieved for the first time in thin-film InGaAs using microprobing capabilities (∼1 μm). We also identify another phonon mode R* at 244 cm−1 which is attributed to an alloy disorder mode in these films. For the five identified phonon modes, a linear relationship between the Raman frequencies and composition determined from x-ray diffraction was determined for near-lattice-matched conditions (0.42<1−x<0.52).
Fabry–Perot reflectance modulator for 1.3 μm from (InAlGa)As materials grown at low temperature
Authors: Fritz I. J. , Hammons B. E. , Howard A. J. , Brennan T. M. , Olsen J. A.
Published: July 2002

We report the first all-semiconductor Fabry–Perot-cavity reflectance modulators operating at wavelengths of 1.32–1.33 μm. These devices were grown on a GaAs substrate using an intermediate, linearly graded InGaAs buffer layer terminating in an In0.33Ga0.67As layer. The Bragg reflector stacks of the Fabry–Perot structure are composed of InGaAs and InAlAs layers lattice matched to the buffer, and the active cavity region is an In0.4Ga0.6As/In0.26Al0.35Ga0.39As strained-layer superlattice. The key to obtaining device-quality material was low temperature growth (∼400 °C) of the entire structure. For a device with a 0.38-μm-thick active region and a 4 dB insertion loss, we obtained a contrast ratio of ∼3:1 at 4 V bias.
Effect of annealing on the interfaces of giant-magnetoresistance spin-valve structures
Authors: Huang T. C. , Nozieres J.-P. , Speriosu V. S. , Gurney B. A. , Lefakis H.
Published: July 2002

Si/Ta/NiFe/Cu/NiFe/FeMn/Ta spin-valve layered structures were analyzed by x-ray reflectivity, before and after annealing at 240, 320, and 360 °C. Specularly reflected x-ray data were collected using a high-resolution reflectometer and were analyzed by least-squares refinement. The thicknesses of the individual layers in the NiFe/Cu/NiFe/FeMn magnetic sandwich remained essentially unchanged. With the exception of the FeMn/Ta interface, the widths of the buried interfaces increased rapidly with annealing temperature. The increase in widths at each of the NiFe/Cu and Cu/NiFe interfaces from 6.8 to 22.6 Å caused a fivefold increase in the magnetically inactive layer in NiFe and a tenfold decrease in magnetoresistance. An increase in the total film thickness with annealing temperature was found to be caused by the surface oxidation of the Ta capping layer and the growth of a Ta silicide layer between the Ta buffer layer and the Si substrate.
Anomalous temperature dependence of photoluminescence in porous silicon
Authors: Narasimhan K. L. , Banerjee S. , Srivastava A. K. , Sardesai A.
Published: July 2002

We have studied the temperature dependence of luminescence in porous silicon between 10 and 300 K. We find that above 60 K the luminescence has a temperature dependence opposite in sign from that of the band gap. Using a Gaussian decomposition procedure we have identified three different processes which dominate the luminescence at different temperatures. With a knowledge of the temperature dependence of the relative intensities of the three components we explain the blue shift of the luminescence peak with increasing temperature. We also present arguments to show that the luminescence in porous silicon is due to a complex.
Lateral transport in GaAs/AlGaAs quantum wells
Authors: Araújo D. , Oelgart G. , Ganière J.-D. , Reinhart F. K.
Published: July 2002

The lateral transport of excess carriers in metal organic chemical vapor deposition grown GaAs/AlxGa1−xAs(x=0.5) 20 Å thick single quantum well structures is studied by cathodoluminescence (CL) between 5 K≤T≤170 K. Impurity and native defect related transitions are found to take place around grown-in dislocations where well thickness variations are also found. The CL intensity of free excitons and/or transitions involving impurities and native defects is measured as a function of distance from the dislocation to the point of excitation. Using a simple diffusion model, we are able to determine the hole diffusion length, L=1.5 μm, in slightly n-doped SQW. This represents a novel method for the direct determination of the diffusion length in sufficiently defect-free material.
Analysis of wafer fusing for 1.3 μm vertical cavity surface emitting lasers
Authors: Ram R. J. , Yang L. , Nauka K. , Houng Y. M. , Ludowise M. , Mars D. E. , Dudley J. J. , Wang S. Y.
Published: July 2002

We report low densities of electrically active defects and low optical losses at the wafer fused interface between InP and GaAs. Electron beam induced current analysis shows electrically active defects with an average spacing of 4.5 μm at the interface and significantly lower densities 0.4 μm from the fused interface. Optical measurements of a Fabry–Perot resonator made by fusing an InP epilayer to a GaAs/AlAs mirror demonstrate a 3% increase in mirror transmission after fusing and negligible absorption at the fused interface. Based on these results, we present design considerations for fused surface emitting lasers.
Intermixing of GaInP/GaAs multiple quantum wells
Authors: Francis C. , Bradley M. A. , Boucaud P. , Julien F. H. , Razeghi M.
Published: July 2002

The intermixing of GaInP-GaAs superlattices induced by a heat treatment is investigated as a function of the annealing temperature and duration. Photoluminescence experiments reveal a large red shift of the effective band gap of the annealed quantum wells thus indicating a dominant self-diffusion of the group III atoms which is confirmed by secondary ion mass spectroscopic measurements. For long enough annealing durations, the red shift saturates and even decreases due to the competing slower self-diffusion of the group V atoms. Experiments are well understood based on a simple diffusion model.
Control of an unstable electron cyclotron resonance plasma
Authors: Jarnyk Mark A. , Gregus Jeffrey A. , Aydil Eray S. , Gottscho Richard A.
Published: July 2002

Although plasmas are used throughout the microelectronics industry for etching, deposition, and cleaning of thin films, control of plasma processes has been a long-standing problem. Because of the nonlinear properties of plasmas, such as the coupling between wave propagation, density profile, and power absorption, plasma reactors are prone to unstable operation, multiple steady states, and hysteresis. We report observation and suppression of an abrupt transition in the operating mode of an electron cyclotron resonance reactor that alters the ion flux to device wafers by more than twofold. While the origin of this mode change is not well understood, we show here that it is strongly correlated with the neutral gas density, which slowly decreases as the reactor temperature increases during a process or from run to run. By measuring the quartz liner temperature and adjusting the pressure to maintain an approximately constant neutral gas density, the mode change can be avoided indefinitely. In a simulated manufacturing process, where the plasma is pulsed on and off, a mode change occurs after several cycles unless the neutral density, instead of the pressure, is controlled.
Preparation and structure of PbZrO3 epitaxial films by metalorganic chemical vapor deposition
Authors: Bai G. R. , Chang H. L. M. , Lam D. J. , Gao Y.
Published: July 2002

Single-crystal PbZrO3 thin films have been grown on (001) SrTiO3 substrates by metalorganic chemical vapor deposition. The single-crystal nature of c-axis oriented PbZrO3 film is confirmed by x-ray diffraction, selective area electron diffraction, and transmission electron microscopy. The epitaxial relationship between the PbZrO3 film and the SrTiO3 substrate was found to be (001)[100]PbZrO3∥(001)[110]SrTiO3.
Ultrashallow depth profiling using ozone oxidation and HF etching of silicon
Authors: Lau W. M. , Huang L. J. , Chang W. H. , Vos M. , Mitchell I. V.
Published: July 2002

A new approach for semiconductor ultrashallow depth profiling is presented. In this technique, the compositional and structural properties in the near-surface region of a silicon sample were measured by Rutherford backscattering spectroscopy, and the chemical and electrical properties by x-ray photoelectron spectroscopy (XPS). The measurements were repeated after the removal of a few atomic layers of silicon via ozone oxidation followed by a hydrofluoric acid etch of the oxide. The depth distributions of composition and surface potential were then determined. The etch-depth per cycle of this treatment was estimated by measuring the oxide thickness formed in each ozone oxidation with XPS, and was calibrated to be 0.5 nm of silicon per cycle by applying the technique to a Si/Ge/Si sample with a known silicon overlayer thickness. This profiling technique, therefore, provides a depth resolution of better than 0.5 nm. The applicability of the technique is demonstrated by showing the compositional profiling results on a p-Si (100) sample treated with reactive ion etching, and the surface potential profiling data on an n-Si (100) sample bombarded by 1 keV Ar+.
Three-terminal conductance modulation of a quantum interference device using a quantum wire with a stub structure
Authors: Aihara K. , Yamamoto M. , Mizutani T.
Published: July 2002

We report the fabrication of a three-terminal quantum interference device using a quantum wire with a novel stub structure. The device achieves clear conductance modulation as a function of stub-tuner gate voltage, which controls the stub length independently of the Fermi energy. The observed conductance oscillations can be consistently explained by the quantum interference of electron waves in the stub.
Optically active three-dimensionally confined structures realized via molecular beam epitaxical growth on nonplanar GaAs (111)B
Authors: Rajkumar K. C. , Madhukar A. , Rammohan K. , Rich D. H. , Chen P. , Chen L.
Published: July 2002

We report the first realization on nonplanar patterned substrates of optically active three-dimensionally confined semiconductor volumes created in situ via a one-step molecular beam epitaxial growth. Growth is carried out on pyramidal mesas on (111)B substrates and in a regime that results in the emergence of three equivalent {110} side facets which overtake the as-patterned {100} side facets and lead to mesa pinch-off. Transmission electron microscopy along with spatially and spectrally resolved cathodoluminescence provide evidence for emission from laterally confined regions with lateral linear dimensions ≲100 nm.
Carrier distribution in silicon devices by atomic force microscopy on etched surfaces
Authors: Raineri V. , Privitera V. , Vandervorst W. , Hellemans L. , Snauwaert J.
Published: July 2002

The selective chemical etching of silicon containing an impurity profile was used to obtain surface topography related to the local carrier concentration. Atomic force microscopy (AFM) was then used to image this topography. Through a calibration curve of etched depth versus carrier concentration, established by etching uniformly doped epitaxial silicon layers, it is possible to convert the AFM topographical data into carrier concentration. The technique was applied to measure directly the carrier distribution in submicron devices.
Sputter-induced formation of an electron accumulation layer in In0.52Al0.48As
Authors: Maslar J. E. , Bohn P. W. , Agarwala S. , Adesida I. , Caneau C. , Bhat R.
Published: July 2002

Ar-sputtering of In0.52Al0.48As was investigated with room-temperature Raman and photoluminescence spectroscopy. A clear increase of carrier density in the near-surface region was observed in the Raman spectra. The PL intensity was found to depend in a complex way on plasma self-bias potential, incident laser irradiance, and InAlAs doping level, indicating that the recombination mechanisms dominating the PL response differ with changing experimental conditions. The observed trends can be explained by sputter-induced formation of an electron accumulation layer in the near-surface region.
Photopumped long wavelength vertical-cavity surface-emitting lasers using strain-compensated multiple quantum wells
Authors: Lin C. H. , Chua C. L. , Zhu Z. H. , Ejeckam F. E. , Wu T. C. , Lo Y. H. , Bhat R.
Published: July 2002

We report optically pumped long wavelength vertical-cavity surface-emitting lasers (VCSELs) made of strain-compensated multiple quantum wells. The structure of the VCSELs consists of 30 pairs of compressive strained wells and tensile strained barriers as the gain medium and Si/SiO2 dielectric mirrors. The lasers operate at 1.59 μm wavelength. The threshold power density was measured to be 3 kW/cm2 at room temperature, corresponding to a threshold current density of about 2 kA/cm2. The VCSELs have a characteristic temperature T0 of 90 K between 10 and 60 °C, and 60 K from 70 to 110 °C.
Hysteresis of trapped charge in AlGaSb barrier as a mechanism for the current bistability in AlGaSb/InAs/AlGaSb double-barrier structures
Authors: Buot F. A. , Rajagopal A. K.
Published: July 2002

A simple theory of charge buildup and bistability is used to show that the new hysteresis and bistability in the current-voltage behavior recently reported in AlGaSb/InAs/AlGaSb double-barrier structures is directly related to the bistability and hysteresis in the hole population of the AlGaSb barrier layer. This occurs well before the resonant-tunneling-current peak.
Effects of atomic clustering on the optical properties of III-V alloys
Authors: Mäder Kurt A. , Zunger Alex
Published: July 2002

Self-consistent electronic structure calculations together with a structural model are used to study the effect of short-range atomic order on the optical properties of otherwise random Al0.5Ga0.5As, Ga0.5In0.5P, and Al0.5In0.5As alloys. We find that clustering can reduce the direct band gap of these alloys by as much as 100 meV. Furthermore, sufficiently strong clustering is predicted to transform Al0.5Ga0.5As into a direct gap material.
Highly sensitive interfacial mass detection using ultracompact waveguiding films
Authors: Hoyer R. , Mangold C. , Fattinger Ch. , Heming M. , Danielzik B. , Otto J. , Lohmeyer M.
Published: July 2002

We demonstrate quantitative detection of interfacial mass changes with submonolayer sensitivity during the sorption of a small molecule at a planar surface. The optical transducer consists of a 140-nm-thick ultracompact waveguiding film of amorphous TiO2 prepared by low-temperature microwave plasma-impulse chemical vapor deposition.
Suppression of partition noise in infrared hot-electron transistors
Authors: Kuan C. H. , Choi K. K. , Chang W. H. , Farley C. W. , Chang F.
Published: July 2002

The noise properties of hot electrons in three different infrared hot-electron transistors have been characterized. We observed that there is a reduction of generation-recombination noise after the hot electrons passed through the built-in electron energy filters. The magnitude of the reduction depends on the band structure of the filters, and can be attributed to the lack of partition noise associated with the quantum transport of the hot electrons. Based on this observation, low noise infrared hot-electron transistors can be designed using appropriate filters.
Interfacial stages of the ZnTe/GaAs strained heterostructures grown by temperature-gradient vapor transport deposition at low temperature
Authors: Kim T. W. , Park H. L. , Lee J. Y.
Published: July 2002

A lattice-mismatched ZnTe epilayer on a GaAs (100) substrate was grown by the simple method of temperature-gradient vapor deposition. From the x-ray diffraction analysis, the grown layers were found to be ZnTe epitaxial films. The stoichiometry of the ZnTe films was investigated by Auger electron spectroscopy. Transmission electron microscopy measurements showed that there was a large lattice mismatch between the ZnTe epitaxial layer and the GaAs substrate. These results indicate that ZnTe epitaxial films grown on GaAs substrates at 320 °C have no significant interdiffusion problems, and that pseudomorphic, fully strained ZnTe layers are observed for deposits after ten molecular layers.
Cr4+:Gd3Sc2Ga3O12 passive Q-switch for the Cr3+:LiCaAlF6 laser
Authors: Kuo Yen-Kuang , Yang Yang , Birnbaum Milton
Published: July 2002

A Cr4+:Gd3Sc2Ga3O12 (Cr4+:GSGG) broad-band saturable absorber has been demonstrated to be an excellent passive Q-switch for the flashlamp-pumped tunable Cr3+:LiCaAlF6 (Cr:LiCAF) laser at room temperature. A single Q-switched laser output pulse of 11 mJ in energy and 37 ns in duration at 778 nm was obtained in a nonoptimized laser.
Photoconductively switched antennas for measuring target resonances
Authors: Rahman Arifur , Kralj David , Carin Lawrence , Melloch Michael R. , Woodall Jerry M.
Published: July 2002

Coplanar-strip horn antennas are switched photoconductively to generate picosecond bursts of freely propagating electromagnetic energy with bandwidth covering 15–75 GHz. The antennas are fabricated on GaAs grown by molecular beam epitaxy at low substrate temperatures. These antennas are used to perform transient scattering measurements from slit-coupled circular and coaxial cavities; Prony’s method [IEEE Trans. Antennas Propagat. 23, 777 (1975)] is used to extract cavity resonances from the measured late-time scattered signal.
Direct evidence of carbon precipitates in GaAs and InP
Authors: Moll A. J. , Haller E. E. , Ager J. W. , Walukiewicz W.
Published: July 2002

Raman spectra of carbon-doped GaAs and InP show two peaks which are characteristic of C clusters with sp2 bonding. The peaks are seen in C-implanted GaAs and InP following either rapid thermal annealing or furnace annealing. The peaks are also seen in heavily doped epilayers following furnace annealing. Various mechanisms for C precipitation are discussed. Experimental evidence suggests that the loss of the group V component at the surface during annealing may play a role in the precipitation of C.
As/P interdiffusion in ultrathin InAs/InP strained quantum wells
Authors: Sallese J. M. , Taylor S. , Bühlmann H. J. , Carlin J. F. , Rudra A. , Houdré R. , Ilegems M.
Published: July 2002

The intermixing process of ultrathin InAs/InP strained quantum well structures by thermal annealing at 730–830 °C is investigated by photoluminescence measurements. Analyzing the results using a microscopic model, the interdiffusion process is characterized by an activation energy close to 3.8±2.0 eV, leading to an interdiffusion coefficient close to 7±0.5×10−7 cm2/s at 830 °C.
Symmetry considerations in vertical-cavity surface-emitting lasers: Prediction of removal of polarization isotropicity on (001) substrates
Authors: Vakhshoori Daryoosh
Published: July 2002

The effects of crystalline and structural symmetry on the performance of vertical-cavity surface-emitting laser structures are studied by group theoretical techniques. It is shown that an asymmetrically designed active region (i.e., saw-tooth quantum wells) will make the gain anisotropic with respect to the two different transverse polarization on (001) substrates with eigenvectors along [110] and [11̄0] directions. Removal of gain degeneracies is also shown for tilted substrates with the corresponding tabulation of the eigendirections. The gain/loss anisotropicity is required to make polarization stablized lasers.
Relationship between radiation response and density of buried oxide in separation-by-implantation-of-oxygen material
Authors: Mrstik B. J. , McMarr P. J. , Lawrence R. K.
Published: July 2002

We show that the radiation response of separation-by-implantation-of-oxygen material is determined primarily by the density of the buried oxide. We also show that minor variations in process conditions can significantly affect the oxide density, although it is not yet clear which process parameters are most important.
Off-diagonal orthorhombic-symmetry elastic constants
Authors: Kim Sudook
Published: July 2002

We derive analytical expressions for off-diagonal elastic stiffnesses C12, C13, and C23 in terms only of easily and precisely measurable diagonal elastic stiffnesses and Young moduli. We verify the expressions for several symmetry classes: cubic (Li), hexagonal (Zn), tetragonal (In), orthorhombic (Ga), and a weakly orthorhombic fiber composite: B/Al.
Crystal morphology and three-dimensional-like growth model of DyBa2Cu3O7−d superconducting materials synthesized in situ in 0.6 T
Authors: Cloots R. , Vandewalle N. , Ausloos M.
Published: July 2002

This report discusses the crystal growth mechanism of 123 superconducting ceramics from scanning electron micrographs made on DyBa2Cu3O7−d superconducting materials synthesized by peritectic recombination under a magnetic field. Such a synthesis procedure is used only here in order to enhance the growth features of textured materials. The micrographs reveal that the crystal growth model must be strictly tridimensional. The proposed model, followed by computer simulations, can then explain all the microstructure data reported for such textured materials. The preferred growth direction in the a–b planes could also be expected to be the 〈100〉 direction.
Erratum: ‘‘As/P interdiffusion in ultrathin InAs/InP strained quantum wells’’ [Appl. Phys. Lett. 65, 341 (1994)]
Authors: Sallese J. M. , Taylor S. , Bühlmann H. J. , Carlin J. F. , Rudra A. , Houdré R. , Ilegems M.
Published: July 2002

The intermixing process of ultrathin InAs/InP strained quantum well structures by thermal annealing at 730–830 °C is investigated by photoluminescence measurements. Analyzing the results using a microscopic model, the interdiffusion process is characterized by an activation energy close to 3.8±0.2 eV, leading to an interdiffusion coefficient close to 7±0.5×10−17 cm2/s at 830 °C.
Scanning tunneling microscopy of etched HgTe/CdTe superlattices
Authors: Myers T. H. , Klymachyov A. N. , Vitus C. M. , Dalal N. S. , Endres D. , Harris K. A. , Yanka R. W. , Mohnkern L. M.
Published: July 2002

Scanning tunneling microscopy is demonstrated for determining the surface morphology of etched Hg-based semiconductors. Wet etching of HgTe/CdTe superlattices used a Br-based etch solution while dry etching used methyl-free radicals formed by electron cyclotron resonance in a reactive ion etching reactor. Both techniques produced smooth surfaces with random features over large regions. Features ranged in height from 1 to 5 nm for wet etching, while the smoothest dry etched sample had random features with an average height of 40 nm. Near mesa structures, evidence of differential etching was observed between the different composition layers in the HgTe/CdTe superlattices for both wet and dry etched samples.
Electron Hall mobility of n-GaN
Authors: Rode D. L. , Gaskill D. K.
Published: July 2002

It is known that recently published electron Hall mobility data by J. G. Kim, A. C. Frenkel, H. Liu, and R. M. Park [Appl. Phys. Lett. 65, 91 (1994)] for cubic GaN at 300 K are in excellent agreement with theoretical calculations of Hall mobility for uncompensated material. The Hall scattering factor is calculated and Hall effect free-electron concentration data are corrected for samples with free-electron concentrations of 7.24×1017 cm−3 and 1.74×1018 cm−3. The corresponding experimental/theoretical Hall mobility is 760/744 and 530/543. Hence, agreement between theory and experiment is demonstrated within 2.5%.
Fabrication of multilayer single-electron tunneling devices
Authors: Visscher E. H. , Verbrugh S. M. , Lindeman J. , Hadley P. , Mooij J. E.
Published: July 2002

A reliable process has been developed for the fabrication of multilevel single-electron tunneling (SET) devices. Using this process, we have fabricated SET devices with Au-SiO-Al and Al-AlOx-SiO-Al overlap capacitors. The SET transistors exhibit voltage gain and, despite the complex device structure, have a low charge noise (7×10−5e/√Hz). Moreover, the use of overlap capacitors in SET devices results in a reduction of cross capacitances down to 8%.
Sample positioner and deflection energy analyzer for measurements of photofield emission
Authors: Venus D. , Lee M. J. G.
Published: July 2002

A sample positioner and an electron energy analyzer for studies of photofield emission have been designed and constructed. The sample positioner allows photofield emission from every facet of a field emitter to be measured under illumination at arbitrary angles of light incidence and polarization. The electrons emitted from a selected facet are decelerated to a kinetic energy E0 by a series of cylindrical lenses and introduced into either one of two energy analyzers. The deflection energy analyzer, formed from two identical 127° cylindrical analyzers, is used when high-energy resolution is required. The full width at half-maximum height of the resolution function of this analyzer is proportional to E0 down to a minimum kinetic energy which is less than 0.5 eV, and is given by ΔEFWHM=(0.0390±0.0006)E0. The throughput depends on E0 due to a combination of resolution and aperturing effects, and varies as E3/20. The signal-to-noise ratio of the analyzer is limited to 2×104 by inelastic scattering of electrons. The retardation energy analyzer is used for aligning the system and for measuring the energy-integrated current.
High repetition rate operation of a closed-cycle rare-gas halide laser
Authors: Matera Manlio , Buffa Roberto , Burlamacchi Pio , Fini Lorenzo , Salimbeni Renzo
Published: July 2002

A rare-gas halide system operating at a pulse repetition rate up to 103 pps in a burst mode is described. A novel command charging high-voltage pulse generator has been used for the laser pumping. The transverse gas flow velocity required in the discharge region for stable operation is provided by a closed-cycle gas circulation system. The operating characteristics of the laser and the preliminary results of an investigation on the high pulse repetition rate limitations are reported.
Correlation of dielectric breakdown with hole transport for ultrathin thermal oxides and N2O oxynitrides
Authors: Hao M.-Y. , Chen W.-M. , Lai K. , Lee J. C. , Gardner M. , Fulford J.
Published: July 2002

In this letter, the dielectric breakdown characteristics of thermal oxides and N2O-based oxynitrides have been studied. A direct correlation was found between dielectric breakdown and the hole current generated within the gate dielectrics. The dependence of dielectric breakdown on oxide thickness was also studied. It was found that both charge-to-breakdown and hole-fluence-to-breakdown for the N2O oxynitrides were higher than those for the thermal oxides throughout the thickness range studied (33–87 Å). The results suggest that N2O oxynitrides can sustain more damage before breakdown and thus have superior dielectric integrity compared to the thermal oxides.
Time-resolved measurement of energy and species of an intense pulsed ion beam
Authors: Matsuzawa T. , Takahashi A. , Masugata K. , Ito M. , Matsui M. , Yatsui K.
Published: July 2002

A time-resolvable Thomson-parabola spectrometer is developed employing a microchannel-plate image intensifier, which acts as a high-speed shutter (∼5 ns) by gating the applied voltage. Using such a spectrometer, we have achieved the measurement of temporal behavior of beam energy for various ion species of an intense pulsed ion beam extracted from a dual-current-feed magnetically insulated diode. The energy of protons is found to be in a good agreement with the diode voltage.
Output voltage waveform improvement of the coaxial Marx-type high-voltage generator
Authors: Matsuzawa Hidenori , Akitsu Tetsuya
Published: July 2002

A metal ring was installed to each of the main capacitor modules of the coaxial Marx-type high-voltage generator to increase the stray capacitance between the main capacitors and the cylinder of the outer conductor. Improvements in build-up time of the output voltage were achieved and good agreements were obtained between the experimental and the simulated results.
Grid-to-plate current-voltage characteristics of a corona triode
Authors: Oliveira O. N. , Ferreira G. F. Leal
Published: July 2002

Measurements of the grid-to-plate current-voltage characteristics of the corona triode are reported. A space-charge-limited current (SCLC) characteristic is observed to hold for low values of the plate current IP, provided that the grid voltage Vg is corrected for a counter potential Vr. The analysis of experimental results indicates that Vr is due both to penetration of field lines through the grid and to the corona wind. However, departure from SCLC regime is observed at higher plate currents, when the ion supply from the corona current becomes insufficient to afford it. A simplified theory is developed in order to explain the results. In the calculation, a layer of recombination centers is substituted for the grid. The model fits the whole characteristics and leads to reasonable value of the parameters defined by the model.
Neutron diffraction of liquids to 20 kbar: An aluminum-alloy pressure vessel
Authors: Wu A. Y. , Whalley E. , Dolling G.
Published: July 2002

A pressure vessel for neutron diffraction of liquids up to 20 kbar is described. It was made of one or two aluminum-alloy cylinders, having ultimate strengths of ∼6.5 kbar, that were supported radially by three steel supporting rings, which left two 6-mm-wide gaps for the passage of neutrons. The cylinders were supported longitudinally by a force of 300 tonnes applied to the ends of the vessel by a hydraulic press. The experimental fluid was pressurized in another vessel and piped into the diffraction vessel.
Improved algorithm for the discrete Fourier transform
Authors: Froeyen M. , Hellemans L.
Published: July 2002

An alternative discrete (fast) Fourier transform algorithm with suppressed aliasing is presented. It is inspired by work done by Sorella and Ghosh [Rev. Sci. Instrum. 55, 1348 (1984)]. While using their idea of expanding the time function as a series (as Schütte [Rev. Sci. Instrum. 52, 400 (1981)] and Mäkinen [Rev. Sci. Instrum. 53, 627 (1982)] have done), it corrects a flaw in their method. The remarkable quality of the calculation is illustrated for an exponential decay by comparing the results to analytical values.
One-mile equivalent length interferometric pendulum for seismic noise reduction
Authors: Giazotto A. , Passuello D. , Stefanini A.
Published: July 2002

We describe the performances of a 100-kg, 1-m-long active pendulum provided with a reference arm to get rid of the effects of tilting of the ground. The pendulum displacement with respect to the suspension point is measured interferometrically. The phase signal, to be sent to the actuator which displaces the suspension point, is extracted from the interferometer using an analog phase follower. At 10 Hz we obtain a virtual pendulum length of 1.7 km with the reference arm locked and 1.2 km when the reference arm is free. This device can be used to reduce the seismic noise in an antenna for low-frequency gravitational wave detection.
Pulse modulated electron cyclotron resonance plasma for chemical vapor deposition of diamond films
Authors: Hatta A. , Kadota K. , Mori Y. , Ito T. , Sasaki T. , Hiraki A. , Okada S.
Published: July 2002

Pulse operation of electron cyclotron resonance plasma was performed for the fabrication of diamond films by chemical vapor deposition. With square wave amplitude modulation of microwaves at 500 Hz in frequency, the growth rate became twice as large as one of continuous operation with the same microwave power. Time resolved measurement of the optical emission from the pulse modulated plasma was also carried out.
Small permanent magnet for fields up to 2.6 T
Authors: Oldenbourg R. , Phillips W. C.
Published: July 2002

We describe a small permanent magnet (no dimension exceeds 8 cm) which produces a uniform magnetic field of 2 T in a volume of about 14 mm3. This magnet has been used to orient macromolecular assemblies for light microscopy, x-ray, and light-scattering studies.
Filtered x-ray diodes for imploding plasma experiments
Authors: Young F. C. , Stephanakis S. J. , Scherrer V. E.
Published: July 2002

Vacuum x-ray diodes with μm-thick filters have been developed to measure specific x-ray line emissions from plasmas imploded by megampere driving currents. Detector–filter combinations are presented for argon L-shell radiation (0.25–0.46 keV), for the 0.92-keV neon He-α line, and for the 1.13-keV sodium He-α line. For example, a power of 50 GW is measured in the neon He-α line.
Plasma density and poloidal field measurements on TEXT using an injected lithium beam (invited)
Authors: West W. P.
Published: July 2002

Spectroscopy of an injected Li beam has been used to determine both the plasma density profile and the poloidal field profile on the TEXT tokamak. The neutral Li beam is injected at energies up to 95 keV and both collisional and laser-induced fluorescence are observed during a tokamak shot. Radial and temporal profiles are obtained during a complete shot. The applicability of this technique to larger tokamaks depends on several parameters including (but not limited to) beam penetration, reliability, spatial/temporal resolution, and signal-to-noise ratio. Because this basic technique obtains local measurements, it is also applicable to nonsymmetric devices. Such applications will be discussed.
Microwave method for measurement of liquid film thickness in gas– liquid flow
Authors: Roy R. P. , Ku J. , Kaufman I. , Shukla J.
Published: July 2002

A simple microwave technique is described that accurately measures the instantaneous, local thickness of a film of liquid flowing down the inner wall of a tube while at the same time an adjacent current of gas flows in the opposite direction. Such a nonintrusive measurement technique is significant because of the extensive occurrence of similar liquid/gas flows in chemical process and energy systems.
Zero-field NMR and NQR spectrometer
Authors: Bielecki A. , Zax D. B. , Zilm K. W. , Pines A.
Published: July 2002

In comparison to high-field NMR, zero-field techniques offer advantages in terms of spectral interpretability in studies of polycrystalline or amorphous solids. This article describes a technique and apparatus for time-domain measurements of nuclear magnetism in the absence of applied fields (Fourier transform zero-field NMR and NQR). Magnetic field cycling and high field detection are employed to enhance sensitivity. The field cycling is accomplished with an air-driven shuttle system which moves the sample between regions of high and low magnetic field, in combination with switchable electromagnets in the low-field region. Sudden field steps or pulses are used to initiate coherent nuclear spin evolution in zero field and to monitor such evolution as a function of time. Experimental results are shown and analyzed. Possible variations on the basic method are described and their relative advantages are discussed.
Neutron diagnostics on TFTR utilizing the Campbelling technique
Authors: England A. C. , Hendel H. W. , Nieschmidt E. B.
Published: July 2002

Modified commercial equipment installed on the tokamak fusion test reactor (TFTR) at Princeton Plasma Physics Laboratory (PPPL) utilizes Campbell’s mean square voltage theorem to monitor the neutron source strength at neutron count rates orders of magnitude above the capability of the count rate mode. Campbelling uses the large amplitude fluctuations from neutron fission events in the detectors to discriminate against small amplitude γ ray and other noise events. Source strengths yielding equivalent count rates a factor of 5 greater than possible in the conventional count rate mode have been obtained to date. The concept of Campbelling is discussed and the particular application to TFTR is illustrated. Fundamental advantages are the extended useful range of the detectors by a factor of ∼104 and gamma rejection by a factor of ∼103. Some results are shown and the neutron source strengths obtained are compared to those from conventional counting circuits and from other detectors whose outputs have not yet suffered counting losses.
High-quality c-axis oriented superconducting Nd1+xBa2−xCu3O7−d thin films deposited by the laser ablation method
Authors: Badaye Massoud , Wang Furen , Kanke Yukio , Fukushima Kensuke , Morishita Tadataka
Published: July 2002

High-quality single phase Nd1+xBa2−xCu3O7−d thin films have been fabricated on SrTiO3 substrates by the laser ablation method. The resistivity of the deposited films are usually lower than that of the YBCO film. The Tc(onset) and Tc(R=0) in the optimized thin films are as high as 91 and 88 K, respectively. The crystallinity of our films are higher than the best YBCO films ever reported. The rocking curve FWHM of the (005) peaks in our thin films is typically 0.05°, which is superior to the best reported YBCO films.
Construction function for three-dimensional sinograms of the time-of-flight positron emission tomograph
Authors: Ishii Keizo , Orihara Hikonojo , Matsuzawa Taiju
Published: July 2002

A new method of image reconstruction for the time-of-flight positron emission tomograph (TOF-PET) has been developed. A construction function was found to reconstruct a positron image by directly convoluting three-dimensional sinograms. This construction function consists of the product of the well-known function for a conventional PET and the response function of time-of-flight measurement system for annihilation γ rays.
Device for high-pressure differential thermal analysis for liquid samples
Authors: Hiramatsu Nobuyasu , Inoue Tohru
Published: July 2002

The simple high-pressure DTA cell that can be used for liquid samples was constructed. The advantage of this device is the facility of its operation. The utility was demonstrated by measuring the freezing temperature of n-tetradecane under various pressures up to 300 MPa.
A superconducting coaxial transmission line for dilution refrigerators
Authors: Yucel S. , Alexander N. , Honig A.
Published: July 2002

A novel helium-gas-filled coaxial insert sealed with ceramic feedthroughs, which thermally grounds the superconducting niobium inner conductor of a coaxial transmission line at the 1.3-K pot of a dilution refrigerator, is described. This transmission line–insert combination overcomes the large heat leak associated with room temperature coaxial access to a dilution refrigerator and results in relatively unperturbed broadband transmission of radio-frequencies from room temperature to the mixing chamber, with a heat load of less than 1 μW. Two such lines are used to access a cw NMR system incorporated in an Oxford Instruments model 200 top-loading dilution refrigerator, resulting in a rise of the base temperature from 10 mK up to 12 mK. The thermal impedance of the insert with and without helium is analyzed between 1.5 and 6 K; it is shown that the heat leak can be further reduced by an order of magnitude with relatively minor modifications.
An investigation of microweighing with an eddy current transducer
Authors: Huai-ning Chen
Published: July 2002

A method of microweighing with the electromagnetic force and frequency characteristics of an eddy current transducer is presented. The amplitude of a rf current flowing through the eddy current transducer coil indicates the weight. A coil–plate system acts as the compensating electromagnetic force generator and as a displacement sensor. The advantage of the coil–plate system is that it can easily be placed in any desired orientation for lateral or vertical force measurements. Test results show that the basic principles of this system are sound.
Method for producing neutral and negative hydrogen particles applicable to hot plasma diagnosis
Authors: Ray N. R. , Sengupta S. N.
Published: July 2002

A method is described whereby a beam of positive hydrogen ions incident at grazing angles on an array of cesium-covered tungsten foils is used to produce H0 and H− particles by negative surface ionization. The results of these experiments indicate that the method can provide diagnostic beams of particles to hot plasmas and can also energy-analyze charge exchange neutrals emerging from hot plasmas.
Preparation of TFTR diagnostics for D–T break-even experiments
Authors: Johnson L. C. , Manos D. M. , Young K. M.
Published: July 2002

Although diagnostic systems for the tokamak fusion test reactor (TFTR) must be compatible with high-power experiments in deuterium–tritium (D–T) plasmas, it has been neither possible nor desirable to implement all the required features during the early phases of the facility. The research plan, the physical plant, instrumentation, and diagnostic techniques have all evolved during the past decade, and some of the original plans are no longer suitable. Preparations are now underway for D–T operation in TFTR in 1990. Among the activities necessary in support of the research plan are completion of the installation of the D–T diagnostic set, modification of diagnostic hardware to accommodate the ‘‘igloo’’ radiation shield of the torus, installation of auxiliary shielding for detectors and electronics, and enhancement of the reliability of specific components. These preparations and the final D–T diagnostic set for TFTR will be described.
Spectral analysis of nonstationary plasma fluctuation data via digital complex demodulation
Authors: Powers E. J. , Don H. S. , Hong J. Y. , Kim Y. C. , Hallock G. A. , Hickok R. L.
Published: July 2002

Digital complex demodulation techniques are used to generate time-varying auto- and cross-power spectra which, in turn, are useful in characterizing the time-frequency characteristics of nonstationary plasma fluctuation data. The approach is illustrated with fluctuation data measured with a heavy-ion beam probe on the TMX experiment.
TFTR epithermal neutron detector system: Recalibration and effect of nonisotropic neutron emission
Authors: Hendel H. W. , Jassby D. L. , Bosch H. S. , Barnes Cris. W. , Johnson L. C. , Murphy T. J. , Nieschmidt E. B. , Saito T. , Strachan J. D. , Tait G. D. , Young K. M.
Published: July 2002

The primary TFTR neutron source strength measurement system consists of seven fission detectors previously calibrated with D–D and D–T neutron generators and a 252Cf neutron source inside the TFTR vacuum vessel. A recalibration became desirable because of the addition of major components to the tokamak. The new calibration with the D–D neutron generator in situ is consistent with the detection efficiencies measured in the previous calibrations, within the uncertainties. Effects of the anisotropic emission of the neutron generator, due both to the variation of the differential D–D yield with angle (similar to that from beam–target and beam–beam reactions in the beam-driven TFTR plasma) and to scattering and absorption by the generator heads have been observed.
Trap-limited interstitial diffusion and enhanced boron clustering in silicon
Authors: Stolk P. A. , Gossmann H.-J. , Eaglesham D. J. , Jacobson D. C. , Poate J. M. , Luftman H. S.
Published: July 2002

Boron doped superlattices have been used to detect the diffusion of self-interstitials in Si. Interstitials were generated in the near-surface region by 40 keV Si implantation followed by diffusion at 670–790 °C. The interstitial diffusion profile at 670 °C is stationary for t≤1 h, demonstrating that the penetration depth of interstitials is limited by trapping. The concentration of traps is estimated to be ∼1017/cm3. For sufficiently long annealing times, interstitials diffuse beyond the trapping length with an effective trap-limited diffusivity ranging from ∼6×10−15 cm2/s at 670 °C to ∼1×10−12 cm2/s at 790 °C. The high interstitial supersaturation adjacent to the implant damage drives substitutional B into metastable clusters at concentrations below the B solid solubility limit.
Gyrotron collective Thomson scattering diagnostic for confined alpha particles in TFTR
Authors: Woskov P. P. , Machuzak J. S. , Myer R. C. , Cohn D. R. , Bretz N. L. , Efthimion P. C. , Doane J. L.
Published: July 2002

A 200-kW, ∼60-GHz gyrotron will be used on TFTR during D–T operation for collective Thomson scattering diagnostics of confined alpha-particle velocity distribution and density. Scattering angles of up to 120° are under consideration using x-mode propagation to increase the density cutoff limit. Useful signal-to-noise ratios will be possible in plasmas where ne≳5×1013 cm−3, nα≳2×1011 cm−3, and the background emission is ≲30 eV equivalent blackbody level.
Auger electron spectroscopy: Method for the accurate measurement of signal and noise and a figure of merit for the performance of AES instrument sensitivity
Authors: Seah M. P. , Hunt C. P.
Published: July 2002

The absolute signal and absolute noise behaviors of Auger electron spectrometers are analyzed for the pulse counting, analog amplification, beam blanking, and sinusoidally modulated differential modes. Measurements for a Varian 10-keV CMA system and a VG Scientific Microlab support the theoretical predictions in detail. Measurements using a 5-keV electron beam at 45° angle of incidence allow a figure of merit factor F to be derived such that the defined signal-to-noise ratio for the Cu L3M45M45 intense peak is given by F(It)0.5, where I is the beam current ( μA) and t is either the period averaging time or twice the exponential time constant (ms). It is shown that the F value using pulse counting is 20.5 times that using current amplification, 2 times that using beam blanking, and 3.3 times that using modulated differentiation. The F value, under specified conditions, allows a very broad characterization of the instrument’s sensitivity. The measured F values for the above instruments are all very similar and are equivalent to a value of 40 in the pulse counting mode.
Pressure profiles at multimegabar pressures in a diamond anvil cell using x-ray diffraction
Authors: Brister Keith E. , Vohra Yogesh K. , Ruoff Arthur L.
Published: July 2002

Pressure distributions in a diamond anvil cell with a rhenium gasket have been measured at various pressures up to 212±6 GPa using energy dispersive x-ray diffraction with a synchrotron source. Three sets of type IA yellow diamonds were used with bevels of 5°, 7°, and 10°. For the 7°-beveled tips, a 5-μm-diam collimated beam was used to a pressure of 206±6 GPa. In the other experiments, collimators of 10–30 μm were used. In the region of the 50-μm central flat, the pressure was essentially uniform. The effect of finite collimator size on the measurement of pressure profiles is also analyzed.