bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomically layered heteroepitaxial growth of single-crystal films of superconducting Bi2Sr2Ca2Cu3Ox
Authors: Eckstein J. N. , Bozovic I. , von Dessonneck K. E. , Schlom D. G. , Harris J. S. , Baumann S. M.
Published: July 2002

Atomic layering of high-temperature superconducting compounds has been employed to grow films of Bi2Sr2Ca2Cu3Ox, in situ, on SrTiO3 substrates. Atomic monolayers of the constituent atoms were sequentially deposited by shuttering the fluxes from thermal effusion cells, and oxidation of the film was accomplished using a beam of ozone. The films were superconducting as-grown, with complete resistive transitions as high as 86 K. Moreover, reflection high-energy electron diffraction patterns observed during growth, as well as post-growth analysis by x-ray diffraction and high-resolution scanning electron micrography, indicate the films to be single crystal and heteroepitaxial, with in-plane a-b twinning.
Cross-sectional transmission electron microscopy observation of Nb/AlOx-Al/Nb Josephson junctions
Authors: Imamura Takeshi , Hasuo Shinya
Published: July 2002

A study of microstructure of Nb/AlOx-Al/Nb Josephson junctions by cross-sectional transmission electron microscopy yielded much information regarding the junction barrier region. Both thick Nb and several-nanometer Al form polycrystalline films with columnar structures. Nb is oriented to the (110) plane, and Al is (111). The 200 nm lower Nb has a wavy surface with ∼5 nm smoothness, but its surface is planarized by several nanometers Al deposited on it. Thus AlOx with a smoothness under 1 nm can be formed on Al. The upper Nb has a good crystalline structure even just above the AlOx barrier.
Fabrication of GaAs photodiode using laser selective area epitaxy
Authors: Liu H. , Roberts J. C. , Ramdani J. , Bedair S. M. , Farari J. , Vilcot J. P. , Decoster D.
Published: July 2002

Laser-assisted chemical vapor deposition offers a new approach for the integration of optoelectronic devices. We report for the first time the selective deposition and fabrication of a GaAs p-i-n photodetector. The detector, fabricated on a 200×200 μm mesa, shows an impulse response with a full width at half maximum of 150 ps and external quantum efficiency (no AR coating) of 60% both at 0 and −1.4 V bias. These results show that the p-i-n detector has a performance comparable to that achieved by metalorganic chemical vapor deposition and molecular beam epitaxy for similar device dimensions.
Size-dependent electroabsorptive properties of semiconductor microcrystallites in glass
Authors: Cotter D. , Girdlestone H. P. , Moulding K.
Published: July 2002

Pronounced differences of behavior are seen in the electroabsorptive properties of semiconductor microcrystallites in glass, depending on their size. A rapid transition from confined ‘‘quantum-dot’’ properties to well-developed ‘‘bulk-crystal’’ behavior is observed.
Photoluminescence lifetime of AlAs/GaAs disordered superlattices
Authors: Kasu Makoto , Yamamoto Teiji , Noda Susumu , Sasaki Akio
Published: July 2002

Time-resolved photoluminescences (PL) of AlxGa1−xAs (0≤x≤0.5) bulk alloys, AlAs/GaAs ordered superlattices, and AlAs/GaAs disordered superlattices are measured at 77 K and compared. The PL lifetimes of the AlAs/GaAs disordered superlattices were always shorter than those of the Al0.5Ga0.5As bulk alloy and the AlAs/GaAs ordered superlattices with indirect band gaps. These shorter PL lifetimes of the disordered superlattices suggest a relaxation of the momentum conservation during radiative recombination by intentional disordering.
Electron dephasing due to Coulomb interaction
Authors: Fasol Gerhard
Published: July 2002

The electron-electron scattering time τee for a hot electron with excess energy Δ above the Fermi surface of a two-dimensional (2D) electron gas is calculated as a function of temperature, carrier density, and excess energy Δ for a typical heterostructure. τee increases with decreasing temperature and saturates for temperatures below kT<Δ. The electron-electron scattering length lee limits the size of electron quantum interference devices. We show that electron-electron scattering lengths lee around 1 mm should be possible at temperatures T below 1 K and electron energies Δ below 0.1 meV.
Investigation on the growth rate enhancement by Ge during SiGe alloy deposition by chemical vapor deposition
Authors: Ning Bob M. H. , Crowell John E.
Published: July 2002

The desorption of deuterium from clean and Ge-covered Si(100) surfaces has been studied using temperature-programmed desorption. The Ge/Si(100) surfaces were prepared using the dissociative adsorption of digermane on Si(100). The presence of Ge on Si(100) dramatically lowers the deuterium (or hydrogen) desorption temperature. The desorption maxima shift to lower temperature with increasing Ge coverage until a new low-temperature desorption state becomes dominant. The lowering of the deuterium desorption energies due to the presence of Ge on the Si(100) surface is used to explain the acceleration in growth rate observed during GexSi1−x alloy growth by chemical vapor deposition upon the introduction of germane to the Si source gas.
Renormalization of the one-dimensional π-π* band gap on the Ge(111) 2×1 surface
Authors: Haight R. , Baeumler M.
Published: July 2002

Using angle resolved laser photoemission spectroscopy we have measured the transient narrowing of the surface state band gap on the cleaved Ge(111) 2×1 surface. The reconstruction of this surface results in the formation of one-dimensional π bonded chains of atoms which give rise to bonding and antibonding bands whose energy/wave vector dispersions are one-dimensional as well. Photoexcitation of this surface produces a transient π* population which, in turn, leads to an observed narrowing of the surface band gap. We have investigated this renormalization as a function of surface carrier density and laser excitation fluence.
Nanometer-scale electrochemical deposition of silver on graphite using a scanning tunneling microscope
Authors: Li Wenjie , Virtanen Jorma A. , Penner Reginald M.
Published: July 2002

Silver pillars, 10–30 nm in diameter and 4–10 nm in height, were generated on graphite surfaces using a scanning tunneling microscope. These structures were produced following the application of tip(+), 6 V×50 μs bias pulses in dilute, aqueous silver fluoride. A pit on the graphite surface is formed during the first 5μs of the pulse, followed by nucleation and electrochemical deposition of silver at this pit. This two-step mechanism allows silver pillars to be located with a high lateral precision on the graphite surface−independent of the proximity of the tip to preexisting nucleation sites such as step edges.
C60 sensitization of a photorefractive polymer
Authors: Silence S. M. , Walsh C. A. , Scott J. C. , Moerner W. E.
Published: July 2002

The fullerene molecule C60 is shown to act as a useful sensitizer of a recently discovered photorefractive polymer. Measurements of the steady-state diffraction efficiency, grating growth rate, and other photorefractive properties are presented as a function of C60 concentration, writing intensity, and applied electric field. The dc photoconductivity, grating growth rate, and steady-state diffraction efficiency all increase by as much as a factor of 20 upon doping with up to 0.2 wt % C60. The sensitization appears to result from a small increase in the carrier generation efficiency and a larger increase in the useful optical absorption at the operating wavelength, 647 nm.
Low-pressure, low-temperature, and remote-plasma deposition of diamond thin films from water-methanol mixtures
Authors: Singh R. K. , Gilbert D. , Tellshow R. , Holloway P. H. , Ochoa R. , Simmons J. H. , Koba R.
Published: July 2002

We have deposited diamond thin films remote from the active plasma region using an electron cyclotron resonance chemical vapor deposition technique. Diamond films were fabricated at temperatures in the range of 550–650 °C and gas pressures between 25 and 60 mTorr. The volume ratio of water to methanol was varied from 1:20 to 1:5 to optimize diamond film growth. High methanol content resulted in multiple nucleation in the growing diamond film, while higher water content led to complete etching of the film. A positive electrical bias was found to be essential for diamond thin film growth remote from the plasma region. The films were characterized by x-ray diffraction, micro-Raman, and scanning electron microscopy for phase identification, surface morphology, and bonding characteristics.
Ellipsometric study of silicon surface damage in electron cyclotron resonance plasma etching using CF4 and SF6
Authors: Haverlag M. , Vender D. , Oehrlein G. S.
Published: July 2002

In situ ellipsometry has been used to measure in real time the surface damage introduced during electron cyclotron resonance (ECR) plasma etching of silicon as a function of rf bias to the substrate. CF4 and SF6 plasmas were employed. For all ECR plasma operating conditions, the amount of Si surface damage increases with the rf bias voltage, without an apparent damage threshold. It is shown that the surface damage depends on the ion current to the substrate and the gas, with SF6 plasmas resulting in the least surface damage.
Elastic misfit stress relaxation in heteroepitaxial SiGe/Si mesa structures
Authors: Fischer A. , Richter H.
Published: July 2002

We present a two-dimensional analysis of the in-plane misfit stress and its elastic relaxation in rectangular patterned heteroepitaxial SiGe structures on the Si substrate. Based on the generally acknowledged model of relaxing film stress we calculate the distribution of the misfit stress versus distance from the free surface of a mesa edge. By superposition of the isolated stress fields of the mesa edges, we obtain the biaxial misfit stress distribution in a finite heteroepitaxial SiGe mesa on silicon substrate. The formalism developed permits the determination of the variation of stress values as a function of material and size characteristics of the patterned layer-substrate system. A main result of this letter is that the elastic misfit stress is relaxed appreciably in small square SiGe/Si mesa structures, but not in a narrow/long pattern. Furthermore, the theoretical analysis can be applied to most of the pseudomorphic and heteroepitaxial material systems of current interest.
Spontaneous bonding of hydrophobic silicon surfaces
Authors: Ljungberg Karin , Söderbärg Anders , Bäcklund Ylva
Published: July 2002

The initial attraction of silicon surfaces etched in aqueous and buffered HF solutions have been studied, by observing the spontaneity and velocity of the contact wave. Also, the effect of a following water rinse was investigated. The bond strengths were determined by measuring the surface energy of the bonds at room temperature. Surfaces etched in an aqueous HF solution, with no subsequent water rinse before drying and contacting, bond spontaneously. If water rinsing is performed after the etch, the spontaneity is lost and the surfaces bond only if a pressure is applied. Surfaces etched in a buffered HF solution did not bond.
Optical response of an ultrathin film and a large-angle grain-boundary in superconducting YBa2Cu3O7−δ
Authors: Bhattacharya S. , Xi X. X. , Rajeswari M. , Kwon C. , Mao S. N. , Li Qi , Venkatesan T.
Published: July 2002

We have investigated the optical response of epitaxial ultrathin (3 nm) YBa2Cu3O7−δ film on NdGaO3 substrate and thin (50 nm) film of YBa2Cu3O7−δ on a bicrystal SrTiO3 substrate. While the current-voltage characteristics of the ultrathin film indicate a Kosterlitz–Thouless transition (associated with vortex–antivortex unbinding) at a temperature TKT, we do not observe any optical response at or below TKT. An enhanced optical response with nonbolometric characteristics was observed from the grain-boundary as compared to the bolometric optical response of the epitaxial film at the resistive transition. These results indicate that the grain-boundary weak links play a significant role in the enhanced optical response near Tc.
Femtosecond optical dynamics of C60 and M3C60
Authors: Fleischer S. B. , Ippen E. P. , Dresselhaus G. , Dresselhaus M. S. , Rao A. M. , Zhou P. , Eklund P. C.
Published: July 2002

The initial, ultrafast scattering of optically excited carriers in M3C60 for M=K, Rb is investigated by femtosecond pump–probe measurements. An initial fast response (τ≊0.2 ps) of similar magnitude for both Rb3C60 and K3C60 is observed, while τ for undoped C60 is more than an order of magnitude longer. These results are discussed in terms of the molecular character of C60 and the bandlike character of M3C60.
Detection of 11BF and 10BF by resonance-enhanced multiphoton ionization spectroscopy
Authors: Irikura Karl K. , Johnson Russell D. , Hudgens Jeffrey W.
Published: July 2002

The mass-resolved, one-color, 2+1 resonance-enhanced multiphoton ionization (REMPI) spectrum of the BF radical between 304 and 337 nm is reported and rotationally analyzed. The B 1∑+ (3s)←←X 1∑+ origin is observed to have a strong Q branch and much weaker O and S branches. Since they are forbidden in one photon, these rotational branches have not been previously observed. This is the first REMPI study of any boron-containing radical. We find that 2+1 REMPI is a convenient method for the detection of boron monofluoride, having sensitivity better than 108 cm−3.
Whispering-gallery-mode dye lasers in blue, green, and orange regions using dye-doped, solid, small spheres
Authors: Taniguchi Hiroshi , Fujiwara Tamiya , Yamada Hiroshi , Tanosaki Shinji , Baba Mamoru
Published: July 2002

A whispering-gallery-mode (WGM) dye laser in blue, green, and orange regions is reported using dye-doped, solid, small spheres. A WGM dye laser is pumped by a transversely excited atmospheric UV N2 laser. Some features of the WGM dye laser are demonstrated.
Continuous-wave, fourfold upconversion laser
Authors: Xie P. , Rand S. C.
Published: July 2002

We report a new Er3+:LiYF4 cryogenic upconversion laser pumped by a fourfold upconversion process. Excitation at 1.5 μm results in laser emission at 701.5 nm on a transition with an upper state at nearly four times the pump photon energy. Mechanisms and the concept of cooperative upconversion enhancement are examined.
Laser dehydrogenation/crystallization of plasma-enhanced chemical vapor deposited amorphous silicon for hybrid thin film transistors
Authors: Mei P. , Boyce J. B. , Hack M. , Lujan R. A. , Johnson R. I. , Anderson G. B. , Fork D. K. , Ready S. E.
Published: July 2002

A low temperature process for laser dehydrogenation and crystallization of hydrogenated amorphous silicon (a-Si:H) has been developed. This process removes hydrogen by laser irradiations at three energy steps. Studies of hydrogen out-diffusion and microstructure show that hydrogen out-diffusion depends strongly on film structure and the laser energy density. Both high quality and low leakage bottom gate polycrystalline silicon and a-Si:H thin film transistors were monolithically fabricated on the same Corning 7059 glass substrate with a maximum process temperature of only 350 °C.
Hydrogenation effects on n+-p InP solar cell
Authors: Min Suk-Ki , Choi Won Chel , Cho Hoon Young , Yamaguchi M.
Published: July 2002

The hydrogenation effects on the solar cell property have been investigated in the sulfur (S) diffused n+-p solar cell. In the plasma-hydrogenated n+-p junction at 150 °C for 30 min, the carrier concentration of p-type substrate (Zn doped) decreased by one order of magnitude as the distance from the junction region becomes 0.7 μm. This indicates that the hydrogen passivation by atomic hydrogen is due to the form of the neutral hydrogen-Zn acceptor complex near the junction region. The InP solar cell properties, especially the conversion efficiency and the short circuit current of the solar cell, were remarkably improved by 150 °C hydrogenation. The mechanism for the hydrogen passivation effects on the InP solar cell is also discussed. It is shown that the increase of the solar cell efficiency and short circuit current after hydrogenation may be due to the formation of the n+-p−-p structure by the hydrogen-defect incorporation and adequate control of the carrier density in the p-type substrate.
Densification effect on the microstructure and critical current density in (Bi,Pb)2Sr2Ca2Cu3OxAg sheathed tape
Authors: Satou M. , Yamada Y. , Murase S. , Kitamura T. , Kamisada Y.
Published: July 2002

The density of oxide core in (Bi,Pb)2Sr2Ca2Cu3OxAg sheathed tape was estimated from Vickers hardness and found to be increased to as high as 93% of the theoretical density with increasing the degree of cold working. During heat treatment, this densification before heat treatment promoted the formation of a strong linked microstructure which is characterized by dense microstructure, a high degree of orientation of oxide crystal and smooth interface between the Ag sheath and oxide core. Consequently, we obtained high values of critical current density: 66 000 A/cm2 at 0 T and 14 500 A/cm2 at 1 T for 77 K.
Ultrabroadband second-harmonic generation in organic and inorganic thin crystals
Authors: White J. O. , Hulin D. , Joffre M. , Migus A. , Antonetti A. , Toussaere E. , Hierle R. , Zyss J.
Published: July 2002

Organic thin crystals of 2-methyl-4-nitroaniline (MNA) have been used to frequency double simultaneously all components of a broadband continuum using a non-phase-matched configuration. A 1 μm sample of MNA permits to convert, in a single pulse, wavelengths in the band 600–1400 nm to the 300–700 nm band. Using the same technique, we also evidence the remarkably large bandwidth of a 100-μm-thick KDP, when used in the wavelength noncritical phase-matched region centered around 1.03 μm. The conversion efficiencies of the 1-μm-thick MNA sample and of the 100-μm-thick phase-matched KDP crystal are shown to be comparable. The results are of interest to the processing and measurement of femtosecond pulses.
Structural origin of the 5.16 eV optical absorption band in silica and Ge-doped silica
Authors: Tsai T. E. , Friebele E. J. , Rajaram M. , Mukhapadhyay S.
Published: July 2002

The origin of the 5.16 eV absorption band observed in silica and Ge-doped silica was studied using optical and electron spin resonance (ESR) measurements. The band was observed only in samples containing Ge, suggesting that it is related to the Ge impurity in silica, while a lack of correlation between the ESR intensity of the induced hydrogen-associated doublet and the absorption coefficient of the 5.16 eV band indicates that it is not related to two-coordinated Si or Ge. The observation of the absorption coefficient increased as the square root of the Ge concentration demonstrates that the 5.16 eV band is not related to two-coordinated Ge defects but that it is an oxygen deficiency center of the divacancy type associated with Ge.
Observation of near-band-gap luminescence from boron nitride films
Authors: Taylor C. A. , Brown S. W. , Subramaniam V. , Kidner S. , Rand S. C. , Clarke R.
Published: July 2002

We report results from cathodoluminescence spectroscopy of boron nitride films grown on Si(100) substrates by ion-source-assisted magnetron sputtering of a hexagonal BN target. Three main peaks are observed in the near-band-gap region for hexagonal boron nitride films at energies of 4.90, 5.31, and 5.50 eV. We also report deep-level emission spectra of predominantly cubic boron nitride films which are correlated with sample growth conditions. In particular we show that the emission intensity, position, and linewidth are strongly dependent on the substrate bias voltage used during sample growth.
Properties of YBa2Cu3O7−x/YBa2Cu2.79Co0.21O7−x/YBa2 Cu3O7−x edge junctions
Authors: Char K. , Antognazza L. , Geballe T. H.
Published: July 2002

We report the properties of YBa2Cu3O7−x/YBa2Cu2.79Co0.21O7−x/YBa2 Cu3O7−x junctions in an edge junction geometry as a function of temperature and barrier thickness. The barrier material used in this work, YBa2Cu2.79Co0.21O7−x, is an underdoped version of YBa2Cu3O7−x, which has a lower carrier density, a lower Tc, and a higher anisotropy than YBa2Cu3O7−x. The resistances of the junctions are proportional to the thicknesses of their barriers, suggesting the presence of very little interface resistance. The temperature dependences of critical currents and junction resistances show behavior consistent with that predicted by the conventional proximity effect.
Real-time electron cyclotron oscillations observed by terahertz techniques in semiconductor heterostructures
Authors: Some D. , Nurmikko A. V.
Published: July 2002

We demonstrate the application of optoelectronically generated terahertz electromagnetic transients to real-time detection of coherent oscillations by free electrons in modulation doped semiconductor heterostructures, due to the cyclotron resonance. The damping of these oscillations gives a direct measure of the electron dephasing which can be compared with scattering rates obtained from dc transport measurements.
Nonguiding half-wave semiconductor microcavities displaying the exciton-photon mode splitting
Authors: Abram I. , Iung S. , Kuszelewicz R. , Le Roux G. , Licoppe C. , Oudar J. L. , Rao E. V. K. , Bloch J. I. , Planel R. , Thierry-Mieg V.
Published: July 2002

We present a monolithic epitaxially grown λ/2 semiconductor microcavity that contains two InGaAs quantum wells in its AlAs spacer. This particular design displays greatly reduced coupling of the quantum well emission to the in-plane guided modes. The reflection and luminescence spectra of this structure at 77-K display an exciton-photon splitting of 4 meV with as few as two quantum wells, indicating the possibility of a strong coupling of the spontaneous emission of the excitons to the vertical cavity modes. This cavity design should thus be well suited for improving the coupling efficiency of the spontaneous emission to the lasing mode in vertically emitting structures.
YBa2Cu3O7 ramp-type junctions and superconducting quantum interference devices with an ultrathin barrier of NdGaO3
Authors: Grundler D. , Krumme J.-P. , David B. , Dössel O.
Published: July 2002

We have fabricated ramp-type Josephson junctions and SQUIDs (superconducting quantum interference devices) using an ultrathin barrier layer of NdGaO3 as weak contact between the YBa2Cu3O7 electrodes. The junctions operate up to 82 K, exhibiting current-voltage characteristics of the resistively-shunted-junction type. A normal-state resistance of up to 30 Ω at a junction width of 5 μm and a characteristic voltage in excess of 100 μV at 77 K are obtained. We find hysteretic behavior below 70 K and an intrinsic junction capacitance of about 0.15 μF/cm2 at 4 K. SQUIDs show a transfer function δ V/δ Φ of 50 μV/Φ0 at an inductance of 40 pH at 77 K. Thus we observe excellent Josephson properties at a thickness of the NdGaO3 barrier of 2 nm.
Subsurface hydrogenated amorphous silicon to μc-hydrogenated silicon transformation during magnetron sputter deposition determined by spectroscopic ellipsometry
Authors: Yang Y. H. , Katiyar M. , Feng G. F. , Maley N. , Abelson J. R.
Published: July 2002

We use in situ spectroscopic ellipsometry to analyze the microstructure of the μc-Si:H/a-Si:H interface deposited by reactive magnetron sputtering of a Si target in (Ar+H2). We increase the hydrogen pressure to promote μc-Si:H formation and observe several effects. Initially, H penetrates ∼45 Å into the a-Si:H substrate and increases its hydrogen content. Then ∼55 Å of hydrogen-rich a-Si:H deposits. Finally, μc-Si:H nucleates on top of this ∼100 Å thick, high H-content a-Si:H interface layer. As μc-Si:H grows, the thickness of the amorphous interface layer decreases by ∼40 Å; the void fraction in the μc-Si:H layer is always ≤15 vol %, ruling out the possibility that the a-Si:H is etched away. These results suggest that a-Si:H can be transformed into μc-Si:H in a subsurface region under appropriate conditions.
Multichannel Schwinger study of C 1s photoionization of acetylene
Authors: Lin Ping , Lucchese Robert R.
Published: July 2002

We have studied the C 1s photoionization of acetylene using single- and multichannel scattering calculations including the core and selected shakeup channels. Our calculation found a shape resonance occurs in the 1σg−1 channel. However, this resonance is not the dominant feature in photoabsorption spectrum due to strong shake-up intensities at about the same position, in agreement with the high-resolution photoelectron spectra. The 1σg−1 and 1σu−1 channels have been identified as having different dynamics in the core ionization process. The calculated intensity ratio between these two channels agrees well with the recent measurement. Electron correlation in the target states is found to have a great impact on the computed cross sections and asymmetry parameters. In the coupled-channel scattering calculation, an insufficient treatment of target electron correlation leads to exaggerated channel coupling effects. A multi-electron resonant process via the doubly excited state (1σg−11πu−11πg+2) was also found in the multichannel calculation. Results are also presented for ionization leading to some shake-up states.
Meandering grain boundaries in YBa2Cu3Oy bi-crystal thin films
Authors: Miller D. J. , Roberts T. A. , Kang J. H. , Talvacchio J. , Buchholz D. B. , Chang R. P. H.
Published: July 2002

Artificially induced [001] tilt grain boundaries in epitaxial YBa2Cu3Oy (YBCO) thin films were prepared by deposition onto SrTiO3 bi-crystal substrates and subsequently examined by transmission electron microscopy and atomic force microscopy (AFM). It was found that the YBCO grain boundary deviated from the path defined by the underlying substrate boundary, with the ‘‘meandering’’ YBCO boundary only generally following the path defined by the boundary in the underlying substrate. The AFM studies suggest this ‘‘meandering’’ behavior is related to the nucleation and growth mechanisms of the film, and based on this, we were able to vary the magnitude of the meandering by changing the growth conditions. The implications of this meandering behavior are significant, suggesting potential variations in electrical behavior from point to point along these boundaries. This effect is likely to be exacerbated by reduced junction linewidths and may lead to inconsistent behavior in devices which utilize this type of boundary.
TARA diagnostic set
Authors: Sevillano E. , Brau K. , Goodrich P. , Irby J. , Mauel M. , Post R. S. , Smith D. K. , Sullivan J.
Published: July 2002

The TARA Tandem Mirror Experiment has recently begun operation. The set of diagnostics available at this time is discussed. The following diagnostics are now in use: diamagnetic loops, a multichord microwave interferometer, Langmuir and emissive probes, pick-up loops, and secondary-emission detectors. End-loss diagnostics include net current detector arrays, Faraday cup arrays, swept particle analyzer arrays, and calorimetry. Light-emission measurements are made in the visible and VUV regions. A multichord fiber-optic array for plasma position detection is also used. In addition, a three-channel charge exchange analyzer, a hard x-ray system, and fast pressure gauges are available.
Extraction of volume-produced H− ions
Authors: Bacal M. , Hillion F. , Nachman M.
Published: July 2002

The results of an investigation on the extraction of volume-produced H− ions from several plasma sources, characterized by different magnetic multicusp configurations, as well as from a plasma source with no magnetic containment field, are presented. In all these configurations the extracted negative ion current can be increased and the electron current reduced by a suitable choice of the plasma electrode area and positive bias and of the extraction aperture area. This indicates that the variation of the extracted negative ion current due to the plasma electrode bias is an electrostatic effect. A significant effect of the plasma electrode bias upon the electron density and temperature is only observed in the neighborhood of the plasma electrode, while in the plasma center the negative ion and electron density are unaffected.
E∥B end-loss-ion analyzer for Tandem-Mirror Experiment-Upgrade
Authors: Foote J. H. , Coutts G. W. , Pedrotti L. R. , Schlander L. , Wood B. E.
Published: July 2002

We are constructing and testing a diagnostic instrument to investigate, in detail, ions emanating along magnetic field lines from the plasma region of the TMX-U tandem-mirror experiment. This analyzer (of Tokamak Fusion Test Reactor design) contains parallel electric and magnetic fields, which yield ion mass and energy spatial separation, respectively. A two-dimensional array of 128 copper collector plates detects the particles. The entering ion flux is first well collimated and then focused onto the detector plane during the 180° bending in the magnetic field. This instrument is designed to measure higher particle energies than the present gridded end-loss analyzers as well as determine the energy spectra more accurately. Tandem-mirror plasma parameters to be investigated with this analyzer include end-plug potential, average central-cell-ion energy, and plasma potential in the thermal barrier and nearby regions. We plan a time resolution of up to 2 kHz for each detector.
TFTR Thomson scattering system
Authors: Johnson D. , Dimock D. , Grek B. , Long D. , McNeill D. , Palladino R. , Robinson J. , Tolnas E.
Published: July 2002

The TFTR Thomson scattering system has been operational since January 1984. The diagnostic uses two ruby lasers and two spectrometer-detector systems to provide profiles at two times in a discharge. The two scattering lines consist of 76 spatial channels which span the 200-cm vacuum vessel along a major radius. The detectors are gated, intensified CCD arrays with single photoelectron sensitivity. Te(R) and Ne(R) profiles are presented.
Potential measurement by use of a negative-ion source
Authors: Ishii K. , Yamashita Z. , Mase A. , Miyoshi S.
Published: July 2002

A negative-ion beam and the neutralized beam are used for plasma potential measurement. Advantages of this method are discussed and the method is applied to measure the plasma potential in GAMMA-6 and GAMMA-10 tandem mirror devices.
Development and application of multichannel collective scattering systems
Authors: Park H. , Brower D. L. , Peebles W. A. , Luhmann N. C. , Savage R. L. , Yu C. X.
Published: July 2002

The numerous applications of cw collective Thomson scattering in fusion plasmas are greatly enhanced by the addition of a multichannel capability. This permits the determination of the dispersive properties (ω vs k) of waves on a single tokamak discharge. This paper describes the development, calibration, and application of such systems in the far-infrared spectral region. The measurement of the wave dispersion of externally excited ion Bernstein waves leads to the determination of ion temperature in a tokamak plasma. In addition, the study of naturally occurring microturbulence has produced a series of unique observations which has both motivated theoretical effort and clarified the role of density fluctuations in anomalous transport.
TEA CO2 laser with a SiC anode
Authors: Beaupere D. , Helias G. , Bettinger A.
Published: July 2002

It is demonstrated that the use of a SiC plane anode and a Dumanchin–Farcy type cathode in the TEA CO2 laser system yields very uniform glow discharges producing high specific peak power.
Top-loading unit for closed-cycle refrigeration systems
Authors: Eychmüller A. , Grellmann K. H. , Dräger H.
Published: July 2002

The design and the properties of a top-loading unit for a closed-cycle refrigerator are discussed. Liquid solution cells are cooled in this unit with a carrier gas under normal pressure. Heat transfer problems encountered on cooling a cell under vacuum with conductive grease in a closed-cycle refrigerator without top-loading unit are briefly reported.
High-resolution picosecond transient absorption spectrometer utilizing dye emission and a streak camera
Authors: Jang Du-Jeon , Kelley David F.
Published: July 2002

A high-resolution picosecond transient absorption spectrometer utilizing dye emission and a streak camera is presented and compared with other methods of picosecond transient absorption measurements. Typical transient absorption and ground-state bleach recovery kinetics measured with this spectrometer are shown. Single wavelength transient absorption or ground-state bleach recovery kinetics are determined on the basis of a single laser shot with this spectrometer, so that the samples are relatively free from decomposition by irradiation. Excellent kinetics may be obtained from the near UV to the near IR and are not subject to interference from luminescence of samples. The sensitivity of this spectrometer is very high and it is reasonably easy and convenient to set up and use.
Spatially resolved matrix isolation spectroscopy I: Visible spectra
Authors: Lang Valerie I. , Winn John S.
Published: July 2002

An apparatus is described for measuring visible absorption spectra across the lateral dimension of a cryogenic matrix isolation sample. By exploiting the rigidity of the matrix, the spatially resolved spectra can be parametrically labeled by another experimental variable, such as photolysis wavelength from dispersed radiation, resulting in a multiplex advantage in data collection rates. Alternatively, the apparatus can be used to measure the visible absorption spectrum of a spatially uniform sample in ≤1 second, a speed which is important for photochemically active samples.
Magnetically driven micropositioners
Authors: Smith Douglas P. E. , Elrod Scott A.
Published: July 2002

Several designs are presented for micropositioners which use permanent magnets and current carrying coils to attain controlled displacements down to 5 nm while possessing a dynamic range of several centimeters. Angular displacements of less than 10−3 rad are also possible.
140-GHz pulsed Fourier transform microwave spectrometer
Authors: Kolbe W. F. , Leskovar B.
Published: July 2002

A pulsed microwave spectrometer operating in the vicinity of 140 GHz for the detection of rotational transitions in gaseous molecules is described. The spectrometer incorporates a tunable Fabry–Perot cavity and a subharmonically pumped superheterodyne receiver for the detection of the molecular emission signals. A 70-GHz source supplying a high-efficiency frequency doubler which is pulse modulated at 30 MHz produces sidebands of sufficient power at 140 GHz to excite the molecules. The cavity is tuned to one of the modulation sidebands. The operation of the spectrometer is illustrated by the detection of emission signals from the 6(2, 4)–6(1, 5) transition of SO2 gas. The generation of the electric dipole analog of nuclear-magnetic-resonance (NMR) ‘‘spin-echo’’ signals by a π/2−π pulse sequence is also described.
Computer-controlled pulsed electron-paramagnetic-resonance spectrometer
Authors: Mailer C. , Danielson J. D. S. , Robinson Bruce H.
Published: July 2002

A computer-controlled electron-paramagnetic-resonance spectrometer for pulse and cw experiments is described. Particular features include: (i) a TWT microwave amplifier for high-power pump operation; (ii) a low-noise microwave amplifier for signal-to-noise improvement; (iii) the use of SPDT microwave switches, to allow independent setting of pump and observer power; (iv) computer control of data acquisition; (v) extensive data processing and graphics display system based on a PDP 11/23 computer. Detailed schematics and program software are available from the authors upon request.
Spectral averaging and low-frequency sampling modifications for the IQS 401 fast Fourier transform spectrum analyzer
Authors: Smith Steven W.
Published: July 2002

The IQS 401 spectrum analyzer, a commercial addition to the Apple II and III personal computers, can be modified for low-cost power spectrum measurements of random noise signals and similar waveforms. The IQS basic control program is changed to perform low-frequency sampling, spectral averaging, and spectrum scaling. External analog filtering must be provided on the lowest sampling rates; however, no change is made to the original IQS hardware. Resolution of 0.5 dB is obtainable from 10−4 Hz to 20 kHz.
Absolute determination of molecular-beam intensities
Authors: Kern Klaus , Lindenau Bernd , David Rudolf , Comsa George
Published: July 2002

A new type of detector for the determination of absolute molecular-beam intensities is described. The intensity is obtained from the work done on a cylindrical rotating body by the torque exerted by the impinging beam particles. The detector takes advantage of the very low and constant bearing friction of magnetically suspended rotors and of the complete particle momentum accommodation on uncleaned surfaces. The detection limit of the present design is Imin0 =1.2×1015/Mṽ, where M is the atom mass and ṽ the average velocity of the beam particles in ms−1. The molecular-beam detector turns out to be an absolute instrument. Principle, experimental performance, and measurements with helium nozzle beams are reported.
Electro-optical position measurement for active magnetic bearing
Authors: Sridharan G.
Published: July 2002

As active magnetic bearings and suspensions are position servomechanisms, accurate measurement of the position of the suspended rotor is very important. The various position sensing devices that have been in use are: optical, inductance, capacitance, and eddy current transducers. In this paper the optical measurement technique is revived using modern, solid-state infrared devices. In general, this method results in simplicity of sensor interface, adequate sensitivity and linearity, and cost effectiveness. This article describes the mechanical design feature of the electro-optics, the sensor circuitry, and the transfer characteristics of the sensor subsystem. Results of actual performance of the sensor in an electromagnetic bearing are also given.
Hematoporphyrin-derivative optical-fluorescence-detection instrument for localization of bladder and bronchous carcinoma i
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Authors: Mattiello James , Hetzel Fred W.
Published: July 2002

The use of hematoporphyrin derivative (HpD), a drug which concentrates in cancer cells, causes a cytotoxic effect on these cells when irradiated with the appropriate wavelength of light. The HpD will fluoresce at a wavelength of 630 nm when excited by 405-nm light. Instruments which are able to cause and detect this fluorescence will assist the surgeon to locate regions of neoplasms which contain HpD. Once the neoplastic region is located, the surgeon can treat this region destroying the neoplastic cells. The recent construction and successful operation of a photodetection instrument for the localization of early carcinoma in situ of the bladder and bronchous in humans is discussed. This instrument is in some ways similar to previously described devices with major improvements due to the use of available electro-optical equipment and elimination of the need for modification or manufacture of special surgical ‘‘scopes,’’ thereby minimizing construction costs.
Flash x-ray computed tomography facility for microsecond events
Authors: Zoltani C. K. , White K. J. , Di Bianca F. A.
Published: July 2002

A new computed tomography imaging device that allows four orders of magnitude improvement in temporal resolution over currently available systems is described. Using 21 simultaneously triggered flash x-ray sources and 21 detector arrays, density resolution of several percent for a 1-cm region, lateral spatial projection resolution of 2 mm on a 200-mm object, and a temporal resolution of 10−6 s are predicted. To achieve this time resolution with only 21 views, both the spatial and contrast resolution are degraded when compared with medical CT systems. The system has multislice capability when used with film/screen detectors. The design, construction, and projected capabilities of the facility are detailed.
X-ray TV camera at 4.5 nm
Authors: Germer R. , Meyer-Ilse W.
Published: July 2002

An imaging CCD (charge coupled device) camera for soft x-ray detection has been constructed. The principle used is the conversion of x-rays to visible light in a GdO2S:Tb screen which covers the CCD surface. The achieved detective quantum efficiency was about 9% at the wavelength λ=4.5 nm.
Heterodyne technique for measuring photodetector frequency response without rf interference
Authors: Sapir E. , Schacham S. E. , Finkman E.
Published: July 2002

For heterodyning two optical beams it is necessary to obtain two almost coherent waves. Rather than using an extremely stable laser source, it is possible to split the beam from a single source and use a modulator to shift the frequency of one of the waves. The heterodyne signal generated is at the frequency of modulation, thus, it is susceptible to rf interference by the high modulation voltage. Using two electro-optical modulators, one can utilize the signal at the sum or difference frequency at which no high voltage is present. It is shown that using a single source and two modulators one obtains a signal without any interference leakage. Thus it is possible to measure easily the frequency response of photodetectors up to high frequencies. This configuration also doubles the frequency range obtainable from a single modulator. The theoretical expressions for the intensities at the various frequencies are presented. Noise equivalent power (NEP) measurements of heterodyne signals performed using this setup are very close to the theoretical limit.
High-power radio-frequency plasma source
Authors: Petty C. Craig , Smith Donald K.
Published: July 2002

A high-power radio-frequency plasma source was built and tested for an antenna frequency of 2.45 MHz. A puff valve fed hydrogen gas into a plasma chamber made from 4-in.-diam Pyrex tubing. A helical antenna was wound directly around this chamber. The plasma source was surrounded by a magnetic bucket which used a longitudinal line-cusp geometry. For 20 kW of rf input power, the peak electron density was 2.0×1019 m−3, the electron temperature was 2.0 eV, the ion temperature was 0.9 eV, and the atomic hydrogen density was 4.4×1019 m−3. For 90 kW of rf input power, the peak electron density was 8.9×1019 m−3, the electron temperature was 2.5 eV, the ion temperature was 3.0 eV, and the atomic hydrogen density was 2.3×1019 m−3. The plasma source had a typical current efficiency of 6 A/kW. A theoretical model for the plasma loading resistance was developed.
Bimorph-driven x–y–z translation stage for scanned image microscopy
Authors: Matey J. R. , Crandall R. S. , Brycki B. , Briggs G. A. D.
Published: July 2002

We have developed an x–y–z scanning stage for mechanically scanned microscopy. The stage is constructed of ‘‘double-S’’ mode piezoelectric bimorphs. The prototype unit has a deflection sensitivity of 0.3 μm/V and a travel in each of the three axes of ±60 μm. The lowest mechanical resonances of the stage are at 190, 220, and 360 Hz, corresponding to the x, y, and z axes of the stage, respectively. The noise level of the stage, when mounted on an isolation table, is ∼0.1 nm. The performance of the stage can be understood in terms of a simple lumped element model which can be used to optimize such stages for particular applications.
Use of a light emitting diode as a current sensor for electrostatic double probes
Authors: Tendys J.
Published: July 2002

A light emitting diode has been used as a convenient current sensor for electrostatic double probes under conditions of very high common mode voltages at frequencies around 1 MHz. A simple probe circuit permitted the signal to be transmitted optically to a remote conditioning and detection circuit. A calibration curve was used to correct the nonlinearities in the system.
Timing control unit for enhancing vidicon linearity in pulsed laser spectroscopy with the OMA 1205
Authors: Menzel Ralf
Published: July 2002

A special timing control unit to synchronize the OMA 1205 with a SIT vidicon for a pulsed laser apparatus has been developed. Under special timing conditions the range of linearity of the vidicon response can be enhanced by a factor of 25. The results for the vidicon response as a function of illumination intensity under the realistic conditions of a transient state measurement are presented together with reference data obtained without utilizing the unit. In both cases optimum linearity is achieved with counting rates of about 20 counts/shot only.
Hydrogen permeation apparatus with surface modification and characterization capabilities
Authors: Swansiger W. A. , Folk D. R.
Published: July 2002

A new ultrahigh-vacuum hydrogen permeation system is described which permits modification and characterization of the sample surface while the permeation experiment is in progress. The sample cell is mounted on a manipulator which allows it to be moved to various stations within the vacuum chamber. The sample can be modified by: (1) argon sputter cleaning; (2) sputter deposition of various materials; (3) chemical vapor deposition; and (4) exposure to various gases using a doser. XPS and AES are used for in situ surface characterization. For most experiments the inside of the sample cell is pressurized with hydrogen or deuterium and the effects of modifying the downstream surface are monitored using a quadrupole mass spectrometer, which measures the permeating flux. It is also possible to measure permeation in the opposite direction by sealing a cell to the UHV face of the sample assembly and pressurizing it with tritium. Results are reported for the permeation of deuterium through polycrystalline iron as a function of the AES oxygen to iron ratio. As the O/Fe ratio increased to 1.5, the deuterium permeability decreased by a factor of 14 at 313 K.
Characteristics of compact solid-target charge exchange analyzers for energetic ion diagnostics on tokamaks
Authors: Beiersdorfer P. , Roquemore A. L. , Kaita R.
Published: July 2002

Compact electrostatic charge exchange analyzers (18×18×13 cm) have been constructed for installation in areas of high magnetic fields and restricted access near tokamak fusion devices. The analyzers employed carbon stripping foils, and have been calibrated for proton and deuteron energies between 1 and 70 keV. They have been successfully used to study charge exchange losses in auxiliary-heated tokamak plasmas and were found to be ideally suited to supplement the larger and more complex gas-cell analyzers by providing additional spatial and temporal information at a modest effort and cost.
Development of a 1.5-tonne niobium gravitational radiational antenna
Authors: Veitch P. J. , Blair D. G. , Linthorne N. P. , Mann L. D. , Ramm D. K.
Published: July 2002

A 1.5-tonne Nb gravitational radiation antenna is described. Problems associated with a noncontacting magnetically levitated parametric upconverter transducer are discussed, and a system using a bonded microwave reentrant cavity and bonded mechanical impedance transformer is described and analyzed in detail. It is shown that such an antenna can be expected to achieve a noise temperature of ∼1 mK. An ultralow phase noise tunable microwave source for the transducer pump signal is described, as well as precision bonding techniques which yield a mechanical positioning accuracy of 10−6 m, and a reproducibility of 10−8 m.
Rapid scanning fluorescence spectroscopy using an acousto-optic tunable filter
Authors: Kurtz Ira , Dwelle R. , Katzka P.
Published: July 2002

A new method for rapidly acquiring fluorescence spectra from optical probes using an acousto-optic tunable filter (AOTF) has been developed. The AOTF consists of a piezoelectric transducer bonded to a birefringent crystal. Acoustic waves are generated in the crystal by an applied radio frequency. For a given radio frequency, only a narrow band of optical frequencies will be diffracted. Unlike normal Bragg diffraction which can only be used with collimated light, the AOTF has a large angular aperture (up to 28 deg) and can therefore be coupled to an uncollimated broadband white light source, photomultiplier tube, or camera. Using the device and a xenon–mercury arc lamp, excitation and emission spectra of the fluorescent pH probe BCECF were acquired in 17 ms (spectral resolution=4 nm). Rapid wavelength switching or modulation of selected wavelengths was achieved at ∼105 Hz. The device is also capable of spectral imaging with a spatial resolution of greater than 100 lines/mm.