bluuebunny/crossref_metadata_2025 huggingface dataset:
High-reflectivity visible-wavelength semiconductor native oxide Bragg reflectors grown by metalorganic chemical vapor deposition
Authors: Holmes A. L. , Islam M. R. , Chelakara R. V. , Ciuba F. J. , Dupuis R. D. , Ries M. J. , Chen E. I. , Maranowski S. A. , Holonyak N.
Published: July 2002

The growth and fabrication of high-quality vertical distributed Bragg reflectors (DBRs) utilizing layers of InAlP and the AlAs native oxide are reported. The III–V epitaxial structures employed in this work consist of alternating layers of InAlP and AlAs grown on GaAs substrates by low-pressure metalorganic chemical vapor deposition (MOCVD). The DBR mirrors are formed by selective lateral oxidation of the AlAs layers (H2O vapor + N2, 450 °C) resulting in a layered structure of single-crystal InAlP and amorphous AlxOy. The oxidized vertical DBR mirrors having only 4.5 pairs exhibit high reflectivity in the 96%–99% range over a wide spectral region (Δλ∼200 nm). The structural and optical properties of these DBR mirrors have been measured and show that the reflectors are of high quality.
Observation of enhanced photoluminescence in erbium-doped semiconductor microdisk resonator
Authors: Chu D. Y. , Ho S. T. , Wang X. Z. , Wessels B. W. , Bi W. G. , Tu C. W. , Espindola R. P. , Wu S. L.
Published: July 2002

We report experimental results from an erbium-doped gallium phosphide microdisk resonator pumped by a Ti-sapphire laser at 980 nm. Fabrication and characterization of the microdisk resonator are discussed. Enhanced Er+3 intra-4f-shell photoluminescence was observed in the microdisk resonator due to microcavity effect and compared to a thin film sample. At low pumping power intensity, the photoluminescence from erbium-doped gallium phosphide microdisks is an order stronger than that from a thin film sample.
Temperature-dependent dry cleaning characteristics of GaAs (111)B surfaces with a hydrogen electron cyclotron resonance plasma
Authors: Weegels L. M. , Saitoh T. , Kanbe H.
Published: July 2002

The cleaning of the GaAs (111)B surface with a hydrogen electron cyclotron resonance discharge plasma is investigated at temperatures between 200 and 500 °C and compared with the GaAs (100) surface. It is found that during the exposure the GaAs (111)B is etched in a non-Arrhenius way with a higher etch rate at low temperatures. For temperatures 300–500 °C, the surface is severely roughened after exposure, while the (100) surface remains smooth in all cases. The near-surface crystalline quality of GaAs (111)B remains higher than that of (100).
N-channel polycrystalline silicon thin film transistors using as-deposited polycrystalline silicon and ion doping
Authors: Lim Hong Joo , Ryu Bong Yeol , Jang Jin
Published: July 2002

Polycrystalline silicon (poly-Si) thin film transistors (TFTs) were fabricated using as-deposited poly-Si and ion doping. The poly-Si was prepared by a remote plasma chemical vapour deposition at the substrate temperature of 280 °C using a mixture gas of SiF4, SiH4, He, and H2. The n-channel poly-Si TFTs using as-deposited poly-Si and ion doping exhibited a field effect mobility of 12 cm2/V s, a threshold voltage of 4 V, and a gate voltage swing of 1.80 V/decade.
Subquantum limit Josephson magnetometry
Authors: Jeffery Mark
Published: July 2002

A reactive dc Josephson inductive kinetic amplifier (IKA) has been proposed to measure weak dc magnetic fields with high sensitivity. In this letter the quantum noise intrinsic to the IKA is analyzed and the device is shown to operate as a back-action evasion magnetic flux amplifier capable of subquantum limit detection of weak dc magnetic fields.
Grain boundary misorientations and percolative current paths in high-J
c powder-in-tube (Bi,Pb)2Sr3Ca3Cu3Ox
Authors: Goyal A. , Specht E. D. , Kroeger D. M. , Mason T. A. , Dingley D. J. , Riley G. N. , Rupich M. W.
Published: July 2002

Grain orientations and grain boundary misorientations in high-Jc, powder-in-tube (PIT) (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) were determined using electron backscatter Kikuchi diffraction and x-ray microdiffraction. Data collected from over 113 spatially correlated grains, resulting in 227 grain boundaries, show that over 40% of the boundaries are Σ1 or small angle (less than 15°). In addition, 8% of the boundaries are within the Brandon criterion for CSLs (sigma larger than 1 and less than 50). Grain boundary ‘‘texture maps’’ derived from the electron microscope image and orientation data reveal the presence of percolative paths between low energy boundaries.
Growth of cubic BN films on β-SiC by ion-assisted pulsed laser deposition
Authors: Mirkarimi P. B. , Medlin D. L. , McCarty K. F. , Barbour J. C.
Published: July 2002

Cubic BN(c-BN) films were deposited on cubic SiC (β-SiC) films on Si(100) by ion-assisted pulsed laser deposition. The films were nearly phase pure, with c-BN fractions of up to ∼90% as determined by infrared spectroscopy. Cross-sectional transmission electron microscopy showed that much of the film/substrate interface had a thin amorphous layer next to the β-SiC, followed by hexagonal/turbostratic BN (h-BN/t-BN), and then polycrystalline c-BN, as commonly observed on Si substrates. However, there are also c-BN crystals that extend to within 10 Å of the SiC interface, with no intervening h-BN/t-BN layer. A sharp falloff in c-BN content was observed for substrate temperatures <150 °C, and below 100 °C c-BN did not form for any ratio of the ion current flux to the deposition flux. At a different ion-to-substrate angle (20° closer to glancing incidence) the falloff in c-BN content for T<150 °C was less sharp. The existence of a critical temperature for c-BN formation does not result from a nitrogen deficiency at low temperature since film stoichiometry did not change with temperature.
Common origin of thermal and light-induced defect kinetics in amorphous silicon
Authors: Schumm G.
Published: July 2002

Based on thermodynamic equilibration between free carriers, defects, and defect-free configurations, a correlation between the various rates of thermal and light-induced defect kinetics in hydrogenated amorphous silicon (a-Si:H) is derived. The presented rate equation is shown to be a direct extension of, and consistent with, an earlier stationary solution describing steady-state defect densities in thermal equilibrium and under external perturbations.
Carbon doping of GaAs: Compensation effects
Authors: Schmidt T. M. , Venezuela P. P. M. , Caldas M. J. , Fazzio A.
Published: July 2002

We study the carbon substitutional impurity in GaAs at both cation and anion sites. We use first-principle nonlocal pseudopotentials, and we find for the acceptor CAs impurity the expected shallow-level defect behavior. The CGa impurity, however, behaves as a deep amphoteric impurity, not as a shallow donor, and in the neutral and negative charge states should cause virtually no lattice shrinking. We expect that this unusual behavior is the reason why the center was not directly detected up to now, although compensating for the shallow acceptor is known to occur with high carbon concentrations.
Damping effect on the radio frequency induced voltage steps in a Josephson tunnel junction
Authors: Kim Kyu-Tae , Niemeyer Jürgen
Published: July 2002

The phase-lock stability of a Josephson tunnel junction to the external rf frequency (ω1) is the most important feature of the Josephson voltage standard. The junction plasma frequency (ωP) should be much lower than ω1 to avoid any chaotic instability. But we found that the moderate junction damping can support the phase-lock stability so that a larger step size reaching the Bessel function values can be achieved even in the region where ωP≂ω1. Measurements of a moderately damped tunnel junction confirm the simulation results.
Transport critical-current characteristics of (Bi,Pb)2Sr2Ca2Cu3Ox silver-sheathed pressed and rolled tapes
Authors: Sun Yuping , Du Jiaju , Lu Zi , Xu Guoyang , Zhang Yuheng , Duan Zhenzhong , Tang Xiande , Xi Zhengping , Zhou Lian
Published: July 2002

We have measured the dependence of the transport critical-current density on magnetic fields and temperatures close to Tc of high-Jc Bi(2223) Ag-sheathed pressed (Jc=2.1×104 A/cm2, 77 K, 0 T) and cold rolled tapes (Jc=1.8×104 A/cm2, 77 K, 0 T). It is found that the transport critical current of the two kinds of tapes follows the relation Jc=Jco (1−αT+βT2). The results can be explained according to the thermally activated flux creep model. The dependence of Jc on H for two kinds of tapes is compared as H is parallel and perpendicular to the tape surface. It is found that the cold rolled tapes have a weaker field dependence of Jc for the H⊥ tape surface at higher fields (≳0.2 T). The difference of Jc(H) between the pressed and cold rolled tapes seems to originate from the difference in their microstructure defects.
Submicron, soft x-ray fluorescence imaging
Authors: La Fontaine Bruno , MacDowell Alastair A. , Tan Zhengquan , White Don L. , Taylor Gary N. , Wood Obert R. , Bjorkholm John E. , Tennant Don M. , Hulbert Steven L.
Published: July 2002

Submicron fluorescence imaging of soft x-ray aerial images, using a high resolution fluorescent crystal is reported. Features as small as 0.1 μm were observed using a commercially available single-crystal phosphor, STI-F10G (Star Tech Instruments Inc. P. O. Box 2536, Danbury, CT 06813-2536), excited with 139 Å light. Its quantum efficiency was estimated to be 5–10 times that of sodium salicylate and to be constant over a broad spectral range from 30 to 400 Å. A comparison with a terbium-activated yttrium orthosilicate fluorescent crystal is also presented. Several applications, such as the characterization of the aerial images produced by deep ultraviolet or extreme ultraviolet lithographic exposure tools, are envisaged.
Ferroelectric/(La,Sr)2CuO4 epitaxial heterostructure with high thermal stability
Authors: Watanabe Yukio , Tanamura M. , Matsumoto Y. , Asami H. , Kato A.
Published: July 2002

Three-dimensionally aligned epitaxial (Pb,La)(Zr,Ti)O3/(La,Sr)2CuO4 multilayers were grown on SrTiO3 (100) single crystals by pulse laser deposition. A cube-on-cube epitaxial relationship of these multilayers was confirmed by the θ-2θ diffraction profile and the pole figure. The stability of their interfaces was confirmed by depth profiles and x-ray diffractometry of the as-deposited and the annealed multilayers having 100–300-Å-thick (La,Sr)2CuO4 layers. The results suggest that the multilayers can be applied to the ferroelectric field-effect transistor.
Calculations on modulation transfer function of a read-only optical disk system with super resolution
Authors: Wu Yihong , Noor Yusoff bin Mohamed
Published: July 2002

Simulations have been performed for signal reproduction from a read-only super resolution optical disk using a beam splitting method, in which a collimated laser beam generated by a laser diode is split into two beams with orthogonal polarizations and then recombined using polarizing beamsplitters. The beam with a higher power is used to raise the temperature of the mask layer, while the one with a lower power is employed to reproduce the recorded data. Tilting one of the laser beams against the other results in two laser spots partially overlapped at the focal plane, and the distance between the center of the two spots can be controlled by a galvanomirror. This allows signal readout with maximum resolution independent of the disk rotation speed.
Third-order nonlinear optical response in a multilayered phthalocyanine composite
Authors: Mandal Braja K. , Bihari Bipin , Sinha Arun K. , Kamath Manjunath , Chen Lin
Published: July 2002

The third-order nonlinear optical properties of multilayered films containing 23% by weight of an axially modified silicon phthalocyanine derivative have been measured by degenerate four-wave mixing at 532 nm with 70 ps full width at half maximum pulses. The average χ(3)of the films measured at (1.33±0.15) ×10−11 esu using CS2 as a standard and the cubic hyperpolarizability 〈γ〉 was calculated at (1.97±0.22)×10−32esu. The degenerate four-wave mixing signal profile indicates that the films have a response time better than 70 ps.
Influence of a longitudinal variation of dB/dt on the magnetic field distribution of superconducting accellerator magnets
Authors: Krempasky L. , Schmidt C.
Published: July 2002

Unexpected periodic variations of the magnetic field were recently found along the axis of superconducting accellerator magnets, which reduces the field quality of the magnets. The field modulation shows a complicated time dependence containing very long time constants. In this letter it is shown that an inhomogeneous distribution of dB/dt along the superconducting cable leads to superposed coupling currents flowing over long lengths, which can explain the observed effects. The solution of the diffusion equation allows one to calculate the space and time dependence of the currents and hence of the amplitude of the field modulation.
Submillimeter wave responses in NbN/AlN/NbN tunnel junctions
Authors: Uzawa Yoshinori , Wang Zhen , Kawakami Akira , Komiyama Bokuji
Published: July 2002

The submillimeter wave frequency responses of NbN/AlN/NbN tunnel junctions have been investigated using quasioptical coupling techniques and an optically pumped far-infrared laser. A two junction array was integrated at the feeds of a bowtie antenna. Measurements on the junctions were made by monitoring photon-assisted tunneling steps induced in the current–voltage characteristics. These n=±1 photon steps were clearly observed with irradiation at 303, 594, 693, and 762 GHz. The results suggest it will be possible to realize submillimeter wave mixers by using these junctions.
Threshold carrier density in vertical cavity surface emitting lasers
Authors: Bae J. W. , Shtengel G. , Kuksenkov D. , Temkin H. , Brusenbach P.
Published: July 2002

A combination of spontaneous emission lifetime and spectral measurements is used to estimate the threshold carrier density in small diameter gain guided vertical cavity surface emitting lasers. Differential spontaneous emission lifetimes measured below threshold are extrapolated to a τth=0.4 ns at threshold. The corresponding threshold carrier density is Nth=7.9×1018 cm−3. The measured carrier densities are used to calculate spontaneous emission spectra. These are in agreement with the edge emission spectra obtained on cleaved laser chips. For the measured carrier density, we estimate the threshold gain at the emission wavelength of g=1640 cm−1.
2×2 Mach–Zehnder interferometric switch based on hetero-n-i-p-i quantum wells
Authors: Leijtens X. , Yoffe G. W. , Haverkort J. E. M. , Karouta F. , Brubach J. , Eijkemans T. , Kaufmann L. M. F. , Smit M. K. , Stegemann J. A. A. , Zhu Y. C. , Wolter J. H.
Published: July 2002

A 2×2 Mach–Zehnder interferometric switch has been developed employing 3 dB multimode interference (MMI) couplers and laterally contacted hetero-n-i-p-i quantum wells as the active material providing refractive index changes. Switching over a 4π range between the cross state and the bar state with an on/off ratio of 17:1 has been observed. A record voltage-length product for switching is observed of less than 1 V mm. By exploiting the quadratic nature of the quantum confined Stark effect, a differential switching voltage as low as 0.2 V mm is observed in the push–pull configuration.
Correlation of molecular hydrogen dissociation and the film quality of diamondlike carbon in plasma enhanced chemical vapor deposition
Authors: Cheshire R. C. , Graham W. G. , Morrow T. , Kornas V. , Döbele H. F. , Donnelly K. , Dowling D. P. , O’Brien T. P.
Published: July 2002

The ground state atomic hydrogen density in a hydrogen/acetylene discharge is compared with the diamondlike carbon (DLC) film quality as determined from in situ ellipsometry measurement of the refractive index. Two-photon laser-induced fluorescence (LIF) was employed for the detection of the ground state atomic hydrogen in the rf generated discharge. Absolute atomic hydrogen number densities were determined by calibrating the LIF detection system using a transfer standard. A direct correlation was found between the level of molecular hydrogen dissociation in the plasma and the refractive index of the DLC film.
Electron relaxation and capture in InGaAsP quantum well laser structures
Authors: Marcinkevičius S. , Olin U. , Wallin J. , Landgren G.
Published: July 2002

Experimental investigations of electron relaxation in the confinement region and capture into the quantum wells are reported for InGaAsP/InP laser structures. The measurements are performed by time-resolved photoluminescence using upconversion. The value for the electron capture of 1.4 ps is obtained. No dependence on the potential profile of confining layers has been observed.
InAsP phase formations during the growth of a GalnAsP/lnP distributed feedback laser diode structure on corrugated lnP using metalorganic vapor phase epitaxy
Authors: Jang Dong Hoon , Kim Jeong Soo , Park Kyung Hyun , Nahm Sahn , Lee Seung Won , Lee Jung Kee , Cho Ho Sung , Kim Hong Man , Park Hyung-Moo
Published: July 2002

An InAsP phase formed during the heatup time to the growth temperature of MOVPE was investigated by transmission electron microscopy and energy dispersive spectroscopy. The thickness of the InAsP phase on the concave regions of corrugation is increased with increased AsH3 partial pressure and heat-up time. The arsenic composition in InAsP was also increased with the increase of AsH3 partial pressure during the heat-up time. Dislocations and defects were not generated below an AsH3 partial pressure of 2.4×10−3 Torr, although strain was induced according to the thickness and composition of InAsP formed on the concave regions of corrugation.
Two-dimensional laser-induced fluorescence imaging of non-emissive species in pulsed-laser deposition process of YBa2Cu3O7−x
Authors: Nakata Yoshiki , Kumuduni Wanniarachchi K. A. , Okada Tatsuo , Maeda Mitsuo
Published: July 2002

Two-dimensional laser-induced fluorescence spectroscopy has been applied to visualize the behavior of non-emissive species in pulsed-laser deposition process of YBa2Cu3O7−x. Behavior of Ba atoms at different oxygen gas pressures and near the substrate is presented. Based on this observation, oxidation of Ba atoms is discussed. The distributions of BaO molecules are also shown and compared with those of Ba atoms.
Formation of covalent solid CNx compounds by high dose nitrogen implantation into carbon thin films
Authors: Xin Huoping , Xu W-ping , Shi Xiaohong , Zhu Hong , Lin Chenglu , Zou Shichang
Published: July 2002

Our preliminary studies show that covalent solid CNx compounds can be synthesized by high dose nitrogen implantation into carbon thin films. 100 keV N+ ions at a dosage of 1.2×1018 cm−2 were implanted at different temperatures. The samples were evaluated by x-ray photoelectron spectroscopy (XPS), x-ray diffraction analysis, and Fourier transform infrared absorption spectroscopy (FTIR). N(1s) core level line XPS analyses show the existence of two different N(1s) bonding states, corresponding to the nitrogen of the C–N covalent bonding state and free state nitrogen, respectively. More importantly, it can be clearly seen that the content of C–N covalent bonding state in the samples is increased with increasing of the implanting temperature of samples. When implantation was performed at 500 °C, C(1s) XPS studies show the existence of three different C(1s) bonding states, corresponding to graphite, i-carbon, and the carbon of C–N covalent bonding state, respectively, and FTIR analyses indicate that there is an absorption band near 2200 cm−1 assigned to the C≡N covalent bonding.
Measurement of penetration depths in superconducting films
Authors: Rowlands George
Published: July 2002

A closed expression is obtained for the mutual inductance of any arrangement of stacked circular coils between which a thin film of superconducting material is inserted.
Stability of Pb doped Bi2Sr2Ca1Cu2O8+δ and the growth of Bi2Sr2Ca2Cu3O10+δ
Authors: Xu Ming , Finnemore D. K. , Balachandran U. , Haldar Pradeep
Published: July 2002

In situ high-temperature x-ray measurements have been used to follow the crystallographic changes that occur as Pb-doped Bi2Sr2Ca1Cu2O8+δ plus other phases transform to Bi2Sr2Ca2Cu3O10+δ in a powder-in-tube process for forming tape conductors. On the initial ramp to the reaction temperature, the Bi2Sr2Ca1Cu2O8+δ x-ray lines first diminish in amplitude, by about a factor of 2 or more, and then begin to grow again above 700 °C. In the 790–795 °C range, a transient new phase is seen. Finally, at temperatures as low as 790 °C, the Bi2Sr2Ca2Cu3O10+δ phase begins to grow as the Pb-doped Bi2Sr2Ca1Cu2O8+δ disappears. Separate studies of a Pb-doped Bi2Sr2Ca1Cu2O8+δ pellet without the Ca2Cu1O3 and CuO present show essentially the same peak intensity changes during the temperature ramp to 700 °C.
Deposition of cubic SiC films on silicon using dimethylisopropylsilane
Authors: Boo J.-H. , Yu K.-S. , Lee M. , Kim Y.
Published: July 2002

We have grown cubic SiC films on the Si(100) and Si(111) substrates in the temperature range of 750–970 °C by low pressure organometallic chemical vapor deposition (LP-OMCVD) using dimethylisopropylsilane (CH3)2CHSiH(CH3)2 as a single molecular precursor. On a carbonized Si(100) substrate, a polycrystalline cubic SiC film was obtained at 960 °C. Cubic-type SiC films were also grown on uncarbonized Si(100) surfaces at 850 °C. At lower temperatures, amorphous SiC films were formed. These growth temperatures are much lower than those reported previously by others. On an uncarbonized Si(111) substrate, however, strongly oriented growth of cubic SiC film in the [111] direction was observed at the growth temperature of 970 °C.
New design approach to precision thermostats at liquid-helium temperature
Authors: Komiyama B.
Published: July 2002

A precision liquid-helium temperature proportional thermostat designed for use with a superconducting cavity stabilized oscillator is described, where temperature of the X-band superconducting Nb cavity mounted inside a vacuum can is regulated at the temperature below 2 K. By noticing the fact that the time for establishment of thermal equilibrium is very short at liquid-helium temperature and thermal transfer properties can, therefore, be measured in the frequency domain, the frequency domain technique rather than the conventional time domain technique is used to design and measure feedback loops of a thermostat. The application of a second-order loop to the design of thermostats is discussed in order to obtain better transient and steady-state performance. In the thermostat constructed, temperature is measured with a germanium resistance thermometer in the ac Wheatstone bridge, a commercial lock-in amplifier is used as a null detector, and the second-order loop is used. The loop characteristics were confirmed by measuring the Bode plot of the feedback loop which also contains the frequency response of the thermal interface, and the gain crossover frequency and the phase margin were 26 Hz and 52°, respectively, at the operating temperature near 1.7 K. The thermostat has achieved the long-term temperature drift of less than 3.2 μK, where the drift caused by the instability of the bridge itself is excepted, in the presence of the liquid-helium temperature fluctuation of 35 mK for periods more than 10 h; it has also shown very fast and good transient response. In addition, the Bode plots of the closed loops have shown that the loop is stable to the variation of the gain crossover frequency of more than four octaves. It has been shown that the method of designing a precision thermostat by measuring its thermal properties in the frequency domain can be useful and can give very reliable results at liquid-helium temperature.
New target cell design for alkali and alkaline earth vapor scattering experiments
Authors: Coggiola M. J. , Peterson J. R. , Leon R. L.
Published: July 2002

A scattering cell is described that is suitable for use with targets of alkali and alkaline earth vapors in beam-static gas collision experiments. A novel feature of this vapor oven design is that the entire assembly can be rapidly moved into and out of the projectile beam path. When used with fixed beam defining apertures, this arrangement results in greatly simplified total scattering cross-section measurements using an attenuation technique. Examples of cross sections measured in this way are presented for electron capture and loss by D+/D− in a Cs target between 0.1 and 4.0 keV/amu.
Effects of thermal loading on pressure measurement in a combustion bomb
Authors: Kach R. A. , Adamczyk A. A.
Published: July 2002

The effects of thermal loading on the measurement of gas pressure during combustion and cool down of a constant volume reactor, 25 to >1000 ms, and the methods to reduce these effects were investigated. Four piezoelectric pressure transducers—a Kistler 6121, a Kistler 6123, a Kistler 603B, and an AVL 8QP500c—were tested with four levels of thermal protection: (1) no protection; (2) RTV placed on the front of the transducer; (3) the transducer placed behind a flame arrestor to prevent the flame from reaching the transducer with no RTV; and (4) the transducer behind a flame arrestor with RTV on the front. The results show that the application of RTV to the front of the transducers significantly reduces the differences between the pressure traces recorded by the Kistler 603B and traces recorded by the Kistler 6121, the Kistler 6123, or the AVL 8QP500c. However, the effect of RTV on reducing the differences made between the Kistler 6121, the Kistler 6123, and the AVL 8QP500c is minimal. Placing the transducers behind flame arrestors with ‘‘good’’ gas exchange properties resulted in four indistinguishable pressure traces recorded by the four pressure transducers.
Phaedrus diagnostic system
Authors: Breun R. , Brouchous D. , Ferron J. , Golovato S. , Hershkowitz N. , Pew J. , Brooker P. , Persing H. , Ross S. , Sing D.
Published: July 2002

The Phaedrus diagnostic system makes optimum use of probes and miniature gridded energy analyzers to measure detailed parameters such as density, plasma potential, and electron and ion energy. This requires miniaturization and provision for flexible access. Other diagnostics are made as flexible as possible. A multiple-aperture, end-loss analyzer is rotatable, allowing complete mapping of the end wall loss contours. Self-emissive probes are used to measure plasma potential contours in the end plugs. A single-channel neutral energy analyzer is movable and can be swept in energy. Secondary emission detector arrays supplement the neutral energy analyzer and give a measure of the ion energy versus pitch angle. Calibrated diamagnetic loops are used to measure the total plasma energy and its axial extent in each cell. Both permanent and insertable fast ion gauges are available. Completing the diagnostic system is a computerized data-acquisition system that is flexible and receptive to the time varying demands of the many ongoing experiments.
Thermal capacitance spectroscopy of epitaxial 3C and 6H-SiC pn junction diodes grown side by side on a 6H-SiC substrate
Authors: Saddow Stephen E. , Lang Manfred , Dalibor Thomas , Pensl Gerhard , Neudeck Philip G.
Published: July 2002

The fabrication of 3C-SiC and 6H-SiC pn junction diodes, grown side by side on low-tilt-angle 6H-SiC substrates via a chemical vapor deposition (CVD) process, has recently been reported. Admittance spectroscopy and deep-level transient spectroscopy (DLTS) measurements were made on one of these diodes to compare the defect structure of 3C- and 6H-SiC CVD epitaxial layers grown under the same conditions. The 6H-SiC layers revealed a single minority carrier level and a deeper broad majority carrier peak. The minority level is due to the boron-related D center, whereas the broad majority level was identified as a double peak by a DLTS simulation. DLTS measurements on the 3C-SiC layers revealed only one deep level impurity consistent with the boron-related D center. Shallow donor levels observed using admittance spectroscopy correspond with the known shallow nitrogen donor in both 3C- and 6H-SiC epitaxial layers. This confirms that both 3C- and 6H-SiC polytypes were simultaneously formed on the same 6H-SiC substrate.
Doping of chemically deposited intrinsic CdS thin films to n type by thermal diffusion of indium
Authors: George P. J. , Sánchez A. , Nair P. K. , Nair M. T. S.
Published: July 2002

CdS thin films deposited from chemical bath containing citratocadmium(II) and thiourea are intrinsic and highly photosensitive. In the present letter, we discuss the conversion of such films to n type by thermal diffusion of indium from an evaporated 50 nm indium film deposited on the CdS thin film. The process which takes place in the temperature range of 250 °C–350 °C involves the formation of an In2O3 surface layer which acts as a barrier preventing the outdiffusion of indium. This allows indium to diffuse into the CdS film and results in an indium-doped CdS thin film. The electrical conductivity of such films is about 300 Ω−1 cm−1. All beneficial optical properties of chemically deposited CdS thin films for application as a window material in heterojunction optoelectronic devices are retained.
Medium energy ion implantation of germanium into heated 〈100〉 silicon
Authors: Tissot P. E. , McCoy J. C. , Hart R. R.
Published: July 2002

The potential of the heated implant technique was investigated for 〈100〉 germanium silicon layers. Germanium silicon layers with increasing germanium peak concentrations (1% to 16%) were implanted at different energies (40 keV, 60 keV), dose rates (1 μA/cm2, 0.1μ A/cm2) and at different substrate temperatures (24 °C, 300 °C, 380 °C). The layers were subsequently annealed for 10 minutes at 1010 °C. The final crystalline quality of the annealed layers was investigated by 300 keV alpha and 150 keV proton channeling spectrometry. For room temperature implants, regrown layers with peak concentrations up to 6.5% showed good crystalline quality while the high concentration layers (16% peak concentration) showed significant residual damage. The final quality of the heated implants was consistently and substantially lower than that of the room temperature implants. Varying the implant temperature, dose rate and energy did not produce significant improvements nor did a modification of the annealing schedule. The fact that the room temperature implants produced consistently better final quality layers than the heated implants for 〈100〉 layers is in contrast with results obtained previously for 〈111〉 layers.
Waveguiding without a waveguide: Local-mode exciton polaritons in multiple quantum wells
Authors: Citrin D. S.
Published: July 2002

Exciton polaritons are considered in infinite multiple quantum wells which are periodic except that one well (impurity) has a different well width from the others (host). Under certain circumstances it is possible to have a long-lived exciton-polariton mode localized about the impurity. From the viewpoint of the electromagnetic field, this corresponds to waveguide modes in the vicinity of an exciton resonance in such structures.
Heat transport properties of semiconductors under nonuniform stress
Authors: Aflatooni K. , Nathan A.
Published: July 2002

The effects of an inhomogeneous stress field on the heat transport in semiconductors are qualitatively studied. Stress-induced spatial variations in lattice constant results in changes in phonon frequency and hence, in the phonon distribution leading to diffusion of phonons which constitutes heat flux at the macroscopic level. It is also found that this leads to a fractional change in thermal conductivity that is linear with the local stress tensor.
Coimplantation of carbon implanted GaAs: Energy and dose rate observations
Authors: Morton R. , Zhu B. , Lau S. S. , Poker D. B.
Published: July 2002

Coimplantations of carbon implanted GaAs at doses of mtsp;5×1013 and mtsp;5×1014 cm−2 were performed at room temperature using argon, gallium, arsenic, and krypton ions with varying beam intensity. The electrical activation of carbon implanted gallium arsenide as a function of coimplanted dose, energy, and dose rate has been studied. For moderate carbon and coimplant doses of mtsp;5×1013 cm−2 increasing the dose rate of the coimplant improved the carbon activation, while at high carbon and coimplant doses of mtsp;5×1014 cm−2 the opposite trend was observed. The dose rate effects were found to be similar in magnitude as the well-known stoichiometric effects for coimplantation. This study illustrates the importance of damage production and placement for carbon activation.
Hall probe for measuring high currents in superconducting coils
Authors: Ferendeci Altan M.
Published: July 2002

Constructional details of a compact Hall probe for measuring high currents in superconducting coils are given. The Hall probe is easy to assemble and can be inserted or removed from the system without breaking the superconducting loop. Upper current limit of the probe can be increased by using larger magnetic core material. Shielding becomes necessary if the probe holder is to be placed near large current dependent magnetic fields.
Plasma implantation technique for incorporation of foreign elements into polymer films
Authors: Liu F. Y. , Kim S. H. , Liu D. , Kao K. C.
Published: July 2002

A plasma formed in a gas containing desired foreign elements dissociates molecules, and activates and ionizes foreign elements. These reactive foreign elements are then implanted into a polymer film under an appropriate bias field and substrate temperature. We report that nitrogen and silicon are well incorporated into polyethylene films using this technique.
Fiducial monitor for an x-ray streak camera
Authors: Popil R. , Fedosejevs R. , Offenberger A. A.
Published: July 2002

A fiducial monitor system that has been adapted and utilized for a commercial x-ray streak camera is described. The fiducial allows an unambiguous temporal synchronization of the incident KrF UV laser pulse with the features of the x-ray emission streak as required in ablation rate studies involving multilayered targets. The linearity of the fiducial record was confirmed by recording the laser pulse simultaneously with an UV streak camera.
Use of an electrical surface potential probe for the measurement of capillary and gravity water waves
Authors: Lange P. A. , Hühnerfuss H.
Published: July 2002

Capillary and short gravity water waves generated in the range of 7–45 Hz by pulsating air from a loudspeaker have been measured using an electrical surface potential probe placed a fixed distance of 0.4 mm above the mean water surface. The surface potential wave gauge (measuring wave amplitude) is compared to a wire resistance-type gauge (measuring wave amplitude) and a laser gauge (measuring wave slope). The wave gauges show good agreement for the capillary waves measured. Gravity water waves with frequencies of 1.0, 1.5, and 1.8 Hz and heights of 1–3 cm could also be successfully measured with the surface potential probe fixed 2.5 cm above the mean water surface. Measurements of waves generated by 2.5-, 4.0-, and 6.0-m/s winds showed that spectra recorded by the surface potential probe qualitatively agree with those of the wire wave gauge when the surface potential probe’s height above the mean water surface is adjusted in accordance with the wind speed.
Mass spectrometer controlled electron beam evaporation synthesis of multilayered materials
Authors: Sevenhans W. , Locquet J.-P. , Bruynseraede Y.
Published: July 2002

A UHV apparatus equipped with two high-power electron guns is extended with a multichannel quadrupole mass spectrometer which accurately controls the deposition rate. A rotating substrate holder is used for deposition of multilayers at room temperature; a fixed substrate holder enables one to prepare layered structures at liquid N2 temperature. A home-built load lock in combination with an extended travel sample manipulator permits a rapid change of the samples without breaking vacuum. The system has been used to deposit Nb/Cu and Pb/Ge multilayers and preliminary structural measurements indicate the samples are of high quality.
Calculation of resonant absorption and photoresponse measurement in p-type GaAs/AlGaAs quantum wells
Authors: Szmulowicz Frank , Brown Gail J.
Published: July 2002

The bound-to-continuum absorption in p-type GaAs/AlGaAs quantum wells is calculated based on the electronic structure, wave functions, and optical matrix elements obtained from an 8×8 envelope-function approximation (EFA) calculation without the use of an artificial large box to enclose the entire system; as such, the present work represents the first true continuum calculation. We show that, for an aluminum content of 30%, the well width of 48 Å (and not the 30 or 40 Å wells used previously) optimizes the linear absorption coefficient for bound-to-continuum absorption due to the presence of a resonant LH2 (second light-hole) state at the top of the well.
Developments in small electrostatic accelerators (invited)
Authors: Rathmell Robert D.
Published: July 2002

Today’s application for small accelerators are spin-off technologies of nuclear physics research. Many of these applications have gained such wide utility that accelerators are developed specifically for them. This paper will review the new generation of small electrostatic accelerators which are being built as diagnostic and production tools.
Status of the University of Washington superconducting booster
Authors: Amsbaugh J. F. , Connolly R. C. , Corcoran D. T. , Cramer J. G. , Howe M. A. , Storm D. W. , Swanson H. E. , Trainor T. A. , Vandenbosch R. , Van Houten L. P. , Weitkamp W. G. , Will D. I.
Published: July 2002

We are approximately half-way through the construction phase of the superconducting booster linac. Contracts have been placed for all major items, and many of these have been delivered. The high-beta resonator development has been successful and we are going ahead with construction of these.
Scaling of the optical parameters for the JAERI tandem accelerator
Authors: Hanashima S. , Minehara E.
Published: July 2002

A scaling rule of the beam optical parameters was adopted for computer-aided beam transport in the JAERI tandem accelerator. Tests have shown that the computer program can transport a specified beam in a short time using a reference parameter set. Problems of ion source control and accuracy of the optical devices are also discussed.
Nondestructive depth profile measurement of a Co/Ti bilayer using refracted x-ray fluorescence
Authors: Roberts T. A. , Ko D. H. , Gray K. E. , Wang Y. Y. , Chang R. P. H. , Ogawa S.
Published: July 2002

The depth profile of a Co (300 Å)/Ti (50 Å) bilayer on Si(100) is studied by nondestructive refracted x-ray fluorescence before and after annealing. Following annealing, the angular distribution of the x-ray fluorescence indicates an inversion of the Co and Ti layers and the formation of CoSi2. These were confirmed by cross-section transmission electron microscopy and x-ray nanoprobe measurements. This success suggests that refracted x-ray fluorescence, which can be used as an in situ probe, may be ideally suited for analysis of thin-film reactions and interdiffusion.
Stepwise equilibrated graded GexSi1−x buffer with very low threading dislocation density on Si(001)
Authors: Kissinger G. , Morgenstern T. , Morgenstern G. , Richter H.
Published: July 2002

We have grown stepwise equilibrated graded GexSi1−x(x≤0.20) buffers with threading dislocation densities between 102 and 103 cm−2 in their unstrained cap layers. The Ge content of the buffer was increased stepwise. The equilibrating treatment was performed as an in situ annealing in hydrogen at 1050 °C after each and every layer of the buffer. Subsequently, the buffer was grown relaxed layer by relaxed layer. The extreme low threading dislocation density was present on the whole area of 4 in. wafers.
Practical sound-reducing enclosure for laboratory use
Authors: Hils D. , Faller J. E. , Hall J. L.
Published: July 2002

We describe the design of a sound-reducing laboratory enclosure. The unit fits directly over the experiment and is hoisted to the ceiling during setup and adjustment stages. The advantages of the design are its modest cost, saving of space, and the fact that no door is required. The average sound isolation achieved is 30 dB, typical for a wall mass per unit area of 35 kg/m2.
Improved Lyman-alpha hygrometer for small-scale atmospheric turbulence measurements. Part I: Miniaturizing the sampling volume
Authors: Mestayer Patrice , Rebattet Claude , Goutail Florence
Published: July 2002

An improved Lyman-alpha hygrometer has been developed in order to measure high-frequency small-scale fluctuations of water vapor concentration in the lower atmosphere and in tunnels (e.g., IMST large air–sea interaction simulation tunnel). The sampling volume is reduced to 3 mm in diameter by aerodynamic shaping; the signal-to-noise ratio is largely increased by designing special UV sources and using a photomultiplier connected to a low-noise electrometer; parasitic sensitivities are reduced by a precise control of the variable path length and by filtering the UV beam with an oxygen cell. This article describes the problems and improvements related to reducing the sampling volume and presents some characteristic spectral functions obtained in IMST tunnel, up to 200 Hz. A further article will describe the O2 filtering technique, the control of sensitivity, and the data reduction procedures.
Matched impedance, low-voltage vacuum-arc centrifuge
Authors: Prasad Rahul R. , Krishnan Mahadevan
Published: July 2002

A matched-impedance, low-voltage vacuum-arc centrifuge is described. The centrifuge is a magnetized plasma column, 1 m long, 4 cm in diameter, with ne∼1015 cm−3 and Ti∼3 eV. Rigid rotor frequencies ∼105 rad/s lead to radial, centrifugal separation between isotopes. The source of this rotating plasma column is a vacuum-arc discharge between a negative cathode and a grounded mesh anode at one end of a 2-m-long vacuum chamber. The discharge is driven by an L–C ladder network of 40-mΩ characteristic impedance, which sees the discharge directly as its load, giving a critical damped, flat-topped current pulse of 10-ms duration, with 90% efficient power transfer. An externally applied axial magnetic field, with less than ±1% axial variation, collimates the plasma and induces rotation. Measured cathode erosion rates suggest that such a centrifuge is capable of converting solid into plasma at a rate of 200 mol/day. A piezoelectrically scanned Fabry–Perot interferometer is used to measure ion temperature, Ti, and angular rotation velocity, ω.
Inexpensive instrument for programmed multiple development in thin-layer chromatography
Authors: Wandruszka R. von , Gottschalk F.
Published: July 2002

A programmed multiple thin-layer chromatography (TLC) developer of new design has been constructed and tested. It is controlled by a programmable delay timer and supported by other common solid-state components. The system is dedicated to ‘‘Mode 1’’ operation and features a hard-wired drying interval. Solvent removal is effected by a cold-air blower and the elution chamber includes a solvent pump. This ensures rapid solvent vapor saturation of the TLC atmosphere after a drying cycle. The instrument is relatively inexpensive and can be constructed with facilities provided by many laboratories.
Alternating current transport and magnetic losses in Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox wires
Authors: Fukunaga T. , Abe T. , Oota A. , Yuhya S. , Hiraoka M.
Published: July 2002

The ac losses are investigated on the Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox superconducting wires in the rod and tape forms through an ac transport method and an ac magnetic method at 77 K. Experimental results show that the ac losses at 50 Hz for both rod and tape samples are mainly dominated by the hysteresis loss independent of the measuring method. However, the tape sample yields ac transport losses larger than the ac magnetic losses by about one order of magnitude, while the rod sample shows no difference between them. This discrepancy is explained by the difference in the geometry between both samples, which affects only the ac magnetic losses.
Position-sensitive photodetector based on hydrogenated amorphous silicon p-i-n junctions
Authors: Chumak V. A. , Bertolotti M. , Ferrari A. , Bartoloni F. , Evangelisti F.
Published: July 2002

A position-sensitive photodetector is discussed using the transverse photoeffect and a particular geometry in a hydrogenated amorphous silicon (a-Si:H) junction. A comparison with a more conventional device using the lateral photoeffect in a-Si:H is made and it is shown that the new device has better characteristics.
Thin-film bolometer with fast response
Authors: Regelsberger M. , Wernhardt R. , Rosenberg M.
Published: July 2002

A short summary on recent developments in semiconducting temperature sensors is given. A thin-film germanium resistor is described in detail, which is used for fast and accurate thermometry in a nonadiabatic microcalorimeter. The use of only standard vapor deposition techniques makes this sensor also available to research groups lacking access to semiconductor technology. The general good performance and its good mechanical properties have the potential of numerous applications in fast and accurate low-temperature thermometry.
High-voltage switching for in-flight capture of keV antiprotons in a Penning trap
Authors: Fei X. , Davisson R. , Gabrielse G.
Published: July 2002

The recently observed in-flight capture of keV antiprotons and protons in a Penning trap requires that the −3-kV potentials on electrodes of a Penning trap near 4.2 K be switched on and off with switching times less than 20 ns. These rapidly switched potentials are applied via transmission lines which are not terminated at the trap, thereby avoiding unacceptable heat load on the helium Dewar. Simple high-voltage switching circuits are constructed using krytrons and reed relays. A krytron provides the rapid switching and stays on just long enough for a reed relay to kick in and maintain the switched state indefinitely.
Ring wire anemometer—Part II: Measurement of small-scale turbulence
Authors: Mestayer Patrice , Giovanangeli Jean-Paul , Chambaud Pierre
Published: July 2002

The ring wire, a circular hot-wire anemometer probe, orientated normal to the flow, is useful to measure turbulent scales in the dissipative range. It is less sensitive to angular positioning errors than straight wire sensors. Following the rationale of Wyngaard [J. Phys. E. 52, 1, 1105 (1968)], theoretical expressions are derived for the high wave number attenuation due to spatial resolution (line averaging). The expressions are applied to the estimation of longitudinal velocity spectrum and dissipation rate. The ring wire is shown to present much smaller attenuations than the straight wire of the same length or, inversely, to have a much higher sensitivity and frequency response than the straight wire of similar spatial resolution. The theoretical results are confirmed by experimental data.
Low-power persistent switch for superconducting magnet
Authors: Uchiyama T. , Mamiya T.
Published: July 2002

A low-power persistent switch module for a superconducting magnet in an adiabatic demagnetization experiment is presented. It performs with heater power as low as 25 mW and has a small decay rate 1.1 ppm/h when the persistent current is 60 A.