bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions Between Shoot Age Structure, Nutrient Availability and Physiological Integration in the Giant Bamboo Phyllostachys pubescens
Authors: Li R. , Werger M. J. A. , de Kroon H. , During H. J. , Zhong Z. C.
Published: July 2002

Abstract: The age structure of adult shoots, the nutrient availability of the habitat, and their interaction, are important factors influencing the productivity of bamboo groves. In a field fertilization experiment over two years we examined the impact of physiological integration on the emergence, growth, and survival of new shoots of Phyllostachys pubescens, a giant woody bamboo. Impacts of physiological integration were compared using uniform and patchy fertilization treatments. The number of new shoots emerging per plot significantly increased with the application of fertilizer (NPK), but the increase was constrained by the age structure of adult shoots. In a year with a high proportion of shoots with new (first‐year) leaves many more new shoots emerged than in a year with a low proportion of new leaves. Mean survivorship of the new shoots was constant at 20 % for all treatments in both years of study. Surprisingly, fertilization did not increase DBH or height of the new shoots, suggesting that shoot size was fixed early in ontogeny. The pattern of fertilizer application, either uniform or patchy, did not affect the total number of new shoots produced. In the case of patchy application, more new shoots developed in unfertilized patches in comparison to uniformly unfertilized plots, probably because these parts of the clone received resources via the rhizomes from the adult shoots in adjacent fertilized patches. The production of new shoots in fertilized patches, in turn, was lower than that in uniformly fertilized plots as a result of this physiological integration. The results are discussed in the general context of the impact of integration on clonal plant performance in dense stands.
Trapping of Au in Si during pulsed laser irradiation: A comparison with ion beam induced segregation
Authors: Priolo F. , Poate J. M. , Jacobson D. C. , Batstone J. L. , Custer J. S. , Thompson Michael O.
Published: July 2002

Liquid phase nonequilibrium segregation and trapping of Au in Si induced by Q-switched laser irradiation are reported. Depending on the incident laser energy density, irradiation results in either amorphization or recrystallization of a near surface layer. In the latter case, at interface velocities of 9 m/s, the segregation coefficient is 0.1±0.02 and Au is trapped in near-substitutional lattice sites at concentrations of 0.5 at. %. These results are compared with recent data on solid phase, ion beam induced segregation, where Au at the amorphous-crystal interface is trapped on nonunique lattice sites.
Influence of growth temperature on crystalline structure in Ga0.5In0.5P grown by organometallic vapor phase epitaxy
Authors: Kondow Masahiko , Kakibayashi Hiroshi , Minagawa Shigekazu , Inoue Youji , Nishino Taneo , Hamakawa Yoshihiro
Published: July 2002

The relation between growth temperature and ordered structures in Ga0.5In0.5P grown using organometallic vapor phase expitaxy is investigated using transmission electron diffraction, electroreflectance, and Raman scattering measurements. It is found that generation of the ordered structure is not related to the immiscibility of this alloy and that the ordered structures do not simply represent ‘‘sublattice ordering.’’ The anomalous band gap may be a consequence of the variation in the atomic arrangement of neighboring atoms, but not of the long-range ordered structure itself.
Physical and electronic structure of amorphous silicon carbon hydrogen alloy
Authors: Sah Wen-Jyh , Tsai Hsiung-Kuang , Lee Si-Chen
Published: July 2002

The physical and electronic structure of hydrogenated amorphous silicon carbide (a-SiC:H) are identified by measuring its photoluminescence and infrared spectra at various stages of thermal annealing. It is found that Brodsky’s [Solid State Commun. 36, 55 (1980)] quantum well model can be successfully applied to explain the observed results, such as the double peak structure in photoluminescence spectrum and the physical origin of the optical gap widening due to carbon incorporation.
Displacement damage equivalent to dose in silicon devices
Authors: Dale C. J. , Marshall P. W. , Summers G. P. , Wolicki E. A. , Burke E. A.
Published: July 2002

Particle-induced displacement damage effects in silicon bipolar transistors, including those due to electrons and to fission neutrons, are correlated on the basis of the nonionizing energy deposited in the lattice by the primary knock-on atoms. Deviations from linearity between damage effects and energy deposition are in a direction opposite to those expected from defect cluster models but can be accounted for in terms of the fraction of vacancy-interstitial pairs initially formed that survive recombination.
Broadband 8–12 μm high-sensitivity GaAs quantum well infrared photodetector
Authors: Levine B. F. , Hasnain G. , Bethea C. G. , Chand Naresh
Published: July 2002

Broadband GaAs/AlxGa1−xAs quantum well infrared detectors grown by molecular beam epitaxy have been demonstrated which are sensitive over the λ=8–12 μm atmospheric window spectral region. These are the first high-detectivity bound state to extended state quantum well detectors which are peaked at λ=10 μm. The spectral bandwidth (Δν/ν) of these devices is three times larger than our earlier λ=8 μm device. The detectivity D* is background limited at T=50 K with D*=1×1010 cm (Hz)1/2 /W, and a noise equivalent temperature change of NEΔT=0.01 K.
Metalorganic chemical vapor deposition of [100] textured MgO thin films
Authors: Kwak B. S. , Boyd E. P. , Zhang K. , Erbil A. , Wilkins B.
Published: July 2002

We report on the results of a recent study on the deposition of [100] textured MgO films on fused quartz substrates by using the metalorganic chemical vapor deposition technique. Magnesium β-diketonate was used as the metal source and the growth rate of the film was about 0.4 μm/h at 740 °C in a horizontal warm wall reactor. X-ray diffraction experiments provided evidence that the MgO films on fused quartz were fully textured with [100] orientation perpendicular to the substrate surface. The films had a very smooth surface morphology and optical transparency with an index of refraction of 1.71.
Irradiation-induced enhancement of the critical current density of epitaxial YBa2Cu3O7−x thin films
Authors: Roas B. , Hensel B. , Saemann-Ischenko G. , Schultz L.
Published: July 2002

Thin films of YBa2Cu3O7−x have been prepared epitaxially on 〈100〉 SrTiO3 by laser evaporation in a single-step process. The resistivity of the films decreases linearly with temperature and is measured to 80 μΩ cm at 100 K. The samples are completely superconducting at 88 K. The critical current densities are as high as 5×106 A/cm2 at 77 K in strip lines of 8 μm width. Irradiation with 25 MeV 16O ions at 77 K combined with in situ measurements was applied to study the influence of lattice disorder on superconducting properties. The resistivity ρ increases, whereas the critical superconducting temperature Tc0 and the critical current density jc in the absence of a magnetic field decrease proportionally to the ion fluence. Contrary to this behavior, we observe an enhancement of jc in magnetic fields larger than 1 T. The maximum enhancement is about a factor of 2 at a fluence of 1014 16O/cm2. This increase is due to pinning at irradiation-induced pinning centers. Simultaneously the upper critical magnetic field Bc2 (T) exhibits an increasing positive curvature leading to a crossover with Bc2(T) of the unirradiated samples.
One electron in an orthogonalized cylindrical Penning trap
Authors: Tan Joseph , Gabrielse Gerald
Published: July 2002

Highest precision mass spectroscopy and other highly accurate measurements have been carried out in Penning traps with metal electrodes painstakingly shaped along hyperbolic contours. A single electron has now been observed in a much simpler, cylindrical trap with equally good signal-to-noise ratio, thus demonstrating the possibility of conducting such experiments in a more readily constructed apparatus and opening the possibility of some new experiments. An essential requirement is the careful choice of electrode lengths to make the size of the electric quadrupole potential insensitive to adjustments which minimize deviations from an electric quadrupole.
Fast anisotropic etching of silicon in an inductively coupled plasma reactor
Authors: Perry A. J. , Boswell R. W.
Published: July 2002

A 13.56 MHz rf inductively coupled diffusion plasma confined by a weak magnetic field is shown to produce high etch rates and high plasma densities. With a substrate bias of −160 V and 1 mTorr of pure SF6, silicon has been etched anisotropically at a rate of 0.7 μm min−1 with a selectivity to SiO2 of about 5.
Band-edge alignment in heterostructures
Authors: Schuermeyer Fritz L. , Cook Paul , Martinez Edgar , Tantillo John
Published: July 2002

Conduction-band and valence-band energies are presented for ternary III-V compounds in a novel way. These data are used to evaluate new material combinations for heterostructure devices.
Silicon vapor phase epitaxial growth catalysis by the presence of germane
Authors: Garone P. M. , Sturm J. C. , Schwartz P. V. , Schwarz S. A. , Wilkens B. J.
Published: July 2002

Experiments involving the epitaxial growth of GexSi1−x films by chemical vapor deposition have shown that the addition of germane greatly enhances the growth rate, compared to that seen with dichlorosilane alone. Careful analysis shows that the increase is not accounted for by summing the individual growth rates, but clearly indicates that the silicon growth rate is catalyzed. The magnitude of the effect increases at lower temperatures, with a two orders of magnitude increase seen at 625 °C.
Etch-tuned ridged waveguide magneto-optic isolator
Authors: Wolfe R. , Lieberman R. A. , Fratello V. J. , Scotti R. E. , Kopylov N.
Published: July 2002

Isolation ratios as large as 3000 to 1 (−35 dB) at wavelengths near 1.55 μm have been measured on ridged waveguide Faraday rotation isolators. These are the best results ever reported for any waveguide isolator. Single-mode, triple-layer bismuth yttrium iron garnet films were chemically etched to reduce the linear birefringence of the active top layer to zero at 1.49 μm. Ion implantation enhanced etching was used to create ridges 8 μm wide and 0.5 μm high. Using fiber coupled light from a tunable color center laser, isolation ratios of −25 dB or better were achieved over a wavelength range of ±0.03 μm near 1.5 μm. A silica overlayer was used to increase the effective thickness of the active layer and raise the optimum wavelength from 1.49 to 1.55 μm.
GaInP mass transport and GaInP/GaAs buried-heterostructure lasers
Authors: Groves S. H. , Liau Z. L. , Palmateer S. C. , Walpole J. N.
Published: July 2002

Mass transport of a semiconductor alloy has been demonstrated using Ga0.51In0.49P which is lattice matched to GaAs. Buried-heterostructure diode lasers with Ga0.51In0.49P as cladding and GaAs as the active layer have been made using this fabrication technique. Initial attempts produce devices with room-temperature lasing thresholds of ∼33 mA and 15% differential power efficiency per facet.
Structure at polymer interfaces determined by high-resolution nuclear reaction analysis
Authors: Chaturvedi U. K. , Steiner U. , Zak O. , Krausch G. , Schatz G. , Klein J.
Published: July 2002

We describe a method based on nuclear reaction analysis, using the reaction 2H(3He, 4He)1H, (Q=18.352 MeV) to determine composition profiles of deuterated polymer chains in thin films. By detecting the emitted α particles (4He) at forward angles (30°) we are able to achieve a spatial resolution of 7 nm half width at half maximum (HWHM) at the deuterated sample surface, and 15 nm HWHM at a depth of some 130 nm. We use our method to probe initial diffusional broadening at the interface between deuterated and protonated polystyrene films. Our measured profiles are in close agreement with earlier measurements (over larger spatial scales) and with mean field models for the diffusional process in this system.
Measurement of the impact ionization rates in Al0.06Ga0.94Sb
Authors: Kuwatsuka H. , Mikawa T. , Miura S. , Yasuoka N. , Kito Y. , Tanahashi T. , Wada O.
Published: July 2002

We measured impact ionization rates in AlxGa1−xSb at x=0.06, where the band-gap energy Eg equals the spin-orbital splitting energy Δ, in an electric field of 1.5×105–3.2×105 V/cm. By considering exact field profile in the depletion layer for each sample, the ionization rates of AlxGa1−xSb have been determined to be α=2.35×106 exp(−1.30×106/E) and β=9.02×105 exp(−9.03×105/E). Although our data have not shown the resonant enhancement of hole ionization rates described by O. Hildebrand, W. Kuebart, and M. Pilkuhn [Appl. Phys. Lett. 37, 801 (1980)], exact values of impact ionization rates have been established in practical electric fields required for designing AlxGa1−xSb avalanche photodiodes.
Large third-order optical nonlinearities in organic polymer superlattices
Authors: Jenekhe Samson A. , Chen Wen-Chang , Lo Saukwan , Flom Steven R.
Published: July 2002

Large second hyperpolarizabilities, 〈γxxxx〉, have been measured in solutions of two recently prepared organic polymer superlattices. These compounds have period aromatic and quinoidal structures and differ from each other by a side group substituent. The values observed are 1.6×10−29 esu for the parent copolymer and 3.7×10−30 esu for its acetoxy derivative. The corresponding values of χ(3)xxxx for the solid phase are estimated to be 2.7×10 −7 and 4.5×10−8 esu. Time-resolved degenerate four-wave mixing measurements, made at 532 nm, showed that the dynamics of the parent copolymer were faster than the 25 ps resolution of the instrument while the derivative exhibited an additional slower response component.
Chemical reaction at the ZnSe/GaAs interface detected by Raman spectroscopy
Authors: Krost A. , Richter W. , Zahn D. R. T. , Hingerl K. , Sitter H.
Published: July 2002

When ZnSe is deposited at temperatures commonly used for epitaxy onto GaAs, the possibility arises that selenium or zinc reacts with the substrate and thin interfacial layers consisting of a gallium selenide or a zinc arsenide are formed. In particular, Ga2Se3, which is thermodynamically the most stable, has been suggested as a likely candidate. In this study we present evidence for the formation of Ga2Se3 using Raman spectroscopy as a fingerprint technique. Ga2Se3 layers were grown on GaAs and the Raman spectra thereof were compared with those of ZnSe/GaAs heterostructures.
Composition and growth kinetics of ultrathin SiO2 films formed by oxidizing Si substrates in N2O
Authors: Ting W. , Hwang H. , Lee J. , Kwong D. L.
Published: July 2002

Chemical composition and growth kinetics of ultrathin SiO2 films formed by rapid thermal oxidizing Si substrates in N2O have been studied. Both Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) revealed nitrogen pile-up at the SiO2/Si interface. Nitrogen concentration at the oxide surface and throughout the bulk was found to be low, similar to reoxidized/nitrided oxides. The nitrogen 1s electron binding energy determined by XPS in the oxide also indicated that these nitrogen atoms were bonded to Si. Electrical characterization showed that N2O oxides exhibited less interface state generation under hot-electron stressing as compared with the control oxide. Growth kinetics study showed that after an initial stage of fast growth, the oxidation rate was reduced significantly due to the formation of a nitrogen-rich layer at the Si/SiO2 interface which blocked oxidant diffusion to the interface.
Propagation of picosecond electrical pulses on a silicon-based microstrip line with buried cobalt silicide ground plane
Authors: Roskos Hartmut , Nuss Martin C. , Goossen Keith W. , Kisker David W. , White Alice E. , Short Ken T. , Jacobson Dale C. , Poate John M.
Published: July 2002

A microstrip line with a highly conducting cobalt silicide (CoSi2) ground plane buried 7 μm below the surface of a single-crystal silicon wafer is presented. This new transmission line shows significantly reduced dispersion up to 100 GHz bandwidth compared to a conventional microstrip line with the ground plane on the back of the substrate, while being able to support active devices in the silicon dielectric. After propagating 5 mm, the rise time (10%–90%) of an electrical pulse increases only from 2.5 to 3.7 ps as opposed to an increase from 2.7 to 11.3 ps on a conventional microstrip line.
High-efficiency InGaP light-emitting diodes on GaP substrates
Authors: Stinson L. J. , Yu J. G. , Lester S. D. , Peanasky M. J. , Park Kwang
Published: July 2002

Very high brightness In(x)Ga(1−x)P light-emitting diodes (LEDs) have been fabricated on GaP substrates by hydride vapor phase epitaxy. LEDs operating at wavelengths from 650 nm (red) to 565 nm (green) have been demonstrated. The brightest encapsulated lamps emit at 592 nm and have external quantum efficiencies of 0.9%. These LEDs are the brightest yet reported for this material system and are several times brighter than commercially available GaAsP:N diodes. A device structure is described that minimizes self-absorption and is critical to obtaining these high-brightness emitters. Reliability studies show greatly improved light output stability over GaAsP:N LEDs through 1000 h of operation between −55 and +55 °C.
Selective excitation of single-mode acoustic waves by phase velocity scanning of a laser beam
Authors: Yamanaka Kazushi , Nagata Yoshihiko , Koda Toshio
Published: July 2002

A novel method for selective generation of single-mode acoustic waves in multimode media has been developed using a laser beam scanned at the phase velocity of a specified mode. In dispersive media, the acoustic frequency can be varied by changing the scanning velocity. The number of carriers in the generated wave packet is proportional to the difference between the phase and the group velocities. These features were experimentally verified in the fundamental symmetric and asymmetric Lamb waves on an aluminum plate generated by a long-pulse Nd:YAG laser. Applications to anisotropy and thickness measurements are discussed.
Totally relaxed GexSi1−x layers with low threading dislocation densities grown on Si substrates
Authors: Fitzgerald E. A. , Xie Y.-H. , Green M. L. , Brasen D. , Kortan A. R. , Michel J. , Mii Y.-J , Weir B. E.
Published: July 2002

We have grown compositionally graded GexSi1−x layers on Si at 900 °C with both molecular beam epitaxy and rapid thermal chemical vapor deposition techniques. Triple-crystal x-ray diffraction reveals that for 0.10<x<0.53, the layers are totally relaxed. GexSi1−x cap layers grown on these graded layers are threading-dislocation-free when examined with conventional plan-view and cross-sectional transmission electron microscopy. Electron beam induced current images were used to count the low threading dislocation densities, which were 4×105±5×104 cm−2 and 3×106±2×106 cm−2 Eq. 2×106 cm−2 for x=0.23 and x=0.50, respectively. Photoluminescence spectra from the cap layers are identical to photoluminescence from bulk GexSi1−x.
Comparative study of implantation-induced damage in GaAs and Ge: Temperature and flux dependence
Authors: Haynes T. E. , Holland O. W.
Published: July 2002

Damage accumulation during ion implantation of 100 keV Si+ into GaAs and Ge has been investigated. A comparison is made of the amount of damage created in GaAs and Ge and its dependence on dose, temperature, and dose rate. General similarities are observed in the dependence of damage in the two materials on dose and temperature. Both materials exhibit a well-defined transition temperature above which the damage decreases dramatically. This transition occurs near room temperature in GaAs and approximately 112 °C higher in Ge. Furthermore, a strong dose-rate effect on damage growth is demonstrated in both Ge and GaAs near their respective transition temperatures. The temperature dependence of the damage yield in both materials is compared to that given by the model of Morehead and Crowder [Rad. Eff. 6, 27 (1970)] for a range of ion doses.
Effect of doping on electron traps in metalorganic molecular-beam epitaxial GaxIn1−xP/GaAs heterostructures
Authors: Paloura E. C. , Ginoudi A. , Kiriakidis G. , Christou A.
Published: July 2002

The formation of trap centers in GaxIn1−xP/GaAs epitaxial layers grown by metal-organic molecular-beam epitaxy (MOMBE) is investigated by deep-level transient spectroscopy (DLTS). The undoped epitaxial layers are characterized by a deep electron trap with an activation energy that depends on the Ga mole fraction and takes values in the range 820 to 875 meV. This trap center is suppressed by S and Si doping, and a new trap at 300–345 meV appears in the doped samples with a capture cross section of 1×10−13–2×10−15 cm2, while the trap concentration increases with the dopant concentration. Persistent photoconductivity (PPC), which is present in all samples investigated, appears to be suppressed only by Si doping.
Electro-optic determination of second and third-order susceptibilities in poled polymer films
Authors: Röhl P. , Andress B. , Nordmann J.
Published: July 2002

An electro-optic measuring technique is reported by which higher-order susceptibilities of nonlinear optical polymer films can be determined. The basis of the evaluation is the separation of linear and quadratic electro-optic effects by means of a dc and ac modulated electric field in the experiment. The method is demonstrated with results for an unpoled and a poled polymer film.
New carbon related defects formed in nitrogen rich Czochralski silicon crystals
Authors: Hara Akito , Ohsawa Akira
Published: July 2002

We studied some electrical properties of silicon crystals containing carbon, nitrogen, and oxygen. Nitrogen-oxygen complexes are formed in nitrogen- and oxygen-rich silicon crystals. However, we found that carbon suppresses the formation of nitrogen-oxygen complexes. Moreover, new shallow effective-mass-like defects with g≂1.999, which includes carbon and nitrogen, were found. We could not observe the hyperfine interaction of nitrogen by electron spin resonance measurements even though the new defects contain nitrogen having nuclear spin. New effective-mass-like defects may be series-like defects, because two effective-mass-like defects are observed. These properties resemble those of both nitrogen-oxygen complexes and thermal donors.
Nanotips by reverse electrochemical etching
Authors: Fotino Mircea
Published: July 2002

A simple, two-stage procedure is shown to produce slender and ultrasharp tungsten tips of nanometer and subnanometer apex dimensions (nanotips). Tip sharpening is achieved by electrochemical etching through bubble dynamics induced by ac voltage in a novel configuration in which the wire end is oriented upward. Tip shape is characterized by high-resolution transmission electron microscopy.
New infrared injection-seeded optical parametric oscillator with high energy and narrow bandwidth output
Authors: Huisken F. , Kulcke A. , Voelkel D. , Laush C. , Lisy J. M.
Published: July 2002

We report on a new infrared injection-seeded optical parametric oscillator with narrow bandwidth (Γ≤0.2 cm−1) and high energy (E≥4 mJ/pulse) output between 2.5 and 4 μm which has been developed for cluster spectroscopy in molecular beams. The oscillator contains a LiNbO3 crystal pumped by the 1.064 μm fundamental of a Q-switched Nd:YAG laser. In order to reduce the linewidth and to increase the output energy, it is seeded with narrow bandwidth IR-radiation obtained by difference frequency mixing the output of a tunable dye laser with the second harmonic of the same Nd:YAG laser in a LiIO3 crystal.
Unipolar avalanche multiplication phenomenon in multiquantum well structures
Authors: Toivonen M. , Jalonen M. , Salokatve A. , Pessa M.
Published: July 2002

Unipolar electron impact ionization and multiplication in photodiodes consisting of GaAs/AlGaAs multiquantum well heterostructures have been observed. In these diodes, electrons generated by photon absorption and accelerated in the barrier regions scatter bound electrons from the donor-doped GaAs wells. Gain-per-well of 1.13±0.05 and total gain of 100 for the multiplication region have been demonstrated. The photodiodes exhibit high dark current which arises from thermionic emission and tunneling of electrons out of the wells.
In situ approach to realization of three-dimensionally confined structures via substrate encoded size reducing epitaxy on nonplanar patterned substrates
Authors: Madhukar A. , Rajkumar K. C. , Chen P.
Published: July 2002

We report the first realization of three-dimensionally confined semiconductor heterostructures via a one-step growth on nonplanar patterned substrate. Truncated pyramidal shaped mesas on GaAs (111)B patterned substrates are employed and a substrate encoded size reducing epitaxical growth process exploited to realize GaAs pinched-off pyramidal volumes of base ∼50 nm and height 13 nm.
Bias-stress-induced stretched-exponential time dependence of charge injection and trapping in amorphous thin-film transistors
Authors: Libsch F. R. , Kanicki J.
Published: July 2002

The threshold voltage instabilities in nitride/oxide dual gate dielectric hydrogenated amorphous silicon (a-Si:H) thin-film transistors are investigated as a function of stress time, stress temperature, and stress bias. The obtained results are explained with a multiple trapping model rather than weak bond breaking model. In our model, the injected carriers from the a-Si:H channel first thermalize in a broad distribution of localized band-tail states located at the a-Si:H/aSiNx:H interface and in the a-SiNx:H transitional layer close to the interface, then move to deeper energies in amorphous silicon nitride at longer stress times, larger stress electric fields, or higher stress temperatures. The obtained bias-stress-temperature induced threshold voltage shifts are accurately modeled with a stretched-exponential stress time dependence where the stretched-exponent β cannot be related to the β=TST/T0 but rather to β≂TST/T0*−β0 for TST≤80 °C; for TST≥80 °C, the β is stress temperature independent. We have also found that β is stress gate bias independent.
Half-integral constant voltage steps in high-T
c grain boundary junctions
Authors: Early E. A. , Clark A. F. , Char K.
Published: July 2002

A novel effect from microwave radiation near 9.3 GHz applied to high-TcYBa2Cu3O7−δ single grain boundary junctions was observed. In addition to the usual Shapiro steps resulting from the ac Josephson effect, constant voltage steps with voltages halfway between the voltages of the Shapiro steps were present. The widths of these ‘‘half-integral’’ steps were measured as a function of microwave power, and the influence of a magnetic field was investigated. From previous results on high-Tc grain boundary junctions and a comparison of the results presented here with single- and multiple-junction effects in low-Tc materials, we conclude that the half-integral steps are likely to be a result of grain boundaries being composed of multiple junctions in parallel.
Sublimed C60 films for tribology
Authors: Bhushan Bharat , Gupta B. K. , Van Cleef Garrett W. , Capp Cindy , Coe James V.
Published: July 2002

Fullerenes take the form of hollow, geodesic domes, which are formed from a network of pentagons and hexagons. The C60 molecule has the highest possible symmetry (icosahedral) and assumes the shape of a soccer ball. At room temperature, fullerene molecules pack in a face-centered-cubic lattice bonded with weak van der Waals attractions. Fullerenes can be dissolved in solvents such as toluene and benzene and easily sublimed. The resilience, high load bearing capacity, low surface energy, high chemical stability, and spherical shape of C60 molecules and weak intermolecular bonding offer great potential for various mechanical and tribological applications. Sublimed films of C60 have been produced and friction and wear performance of these films in various operating environments are the subject of this letter.
Structural characterization of nanometer SiC films grown on Si
Authors: Li J. P. , Steckl A. J. , Golecki I. , Reidinger F. , Wang L. , Ning X. J. , Pirouz P.
Published: July 2002

Continuous, ultrathin silicon carbide (SiC) films of less than 10 nm have been grown on Si by rapid thermal chemical vapor deposition carbonization with high propane flow rates at 1100–1300 °C. X-ray and electron diffraction techniques indicated a monocrystalline structure for these nanometer-scale films. High-resolution transmission electron microscopy reveals that five SiC planes are aligned with four Si planes at the SiC/Si interface. The Fourier transform infrared spectrum of the SiC films exhibits the characteristic Si-C absorption peak at around 800 cm−1, with a FWHM of 45 cm−1.
Epitaxial growth and surface-acoustic-wave properties of LiTaO3 films grown by pulsed laser deposition
Authors: Shibata Yoshihiko , Kaya Kiyoshi , Akashi Kageyasu , Kanai Masaki , Kawai Tomoji , Kawai Shichio
Published: July 2002

Untwinned epitaxial films of LiTaO3 are deposited on (001), (110), and (012) sapphire substrates using a pulsed excimer-laser ablation technique. Complete epitaxy in three dimensions is obtained under optimized conditions for each of the substrate orientations; (1) On (001) sapphire the (001) planes of the film are parallel to the (001) of the substrate [(001)LiTaO3 //(001)sapphire] and the [110] axis of the film is parallel to the [110] of the substrate ([110]LiTaO3//[110] sapphire); (2) (110)LiTaO3//(110)sapphire, [001]LiTaO3//[001]sapphire); (3) (012)LiTaO3//(012)sapphire, [01̄1]LiTaO3//[01̄1]sapphire. We have evaluated surface-acoustic-wave properties of these films.
Theoretical and experimental studies of the ZnSe/CuInSe2 heterojunction band offset
Authors: Nelson Art J. , Schwerdtfeger C. R. , Wei Su-Huai , Zunger Alex , Rioux D. , Patel R. , Höchst Hartmut
Published: July 2002

We report first-principles band structure calculations that show that ZnSe/CuInSe2 has a significant valence band offset (VBO, ΔEv): 0.70±0.05 eV for the relaxed interface and 0.60±0.05 eV for the coherent interface. These large values demonstrate the failure of the common anion rule. This is traced to a stronger Cu,d-Se,p level repulsion in CuInSe2 than the Zn,d-Se,p repulsion in ZnSe. The VBO was then studied by synchrotron radiation soft x-ray photoemission spectroscopy. ZnSe overlayers were sequentially grown in steps on n-type CuInSe2(112) single crystals at 200 °C. In situ photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In 4d and Zn 3d core lines. Results of these measurements reveal that the VBO is ΔEv=0.70±0.15 eV, in good agreement with the first-principles prediction.
Simple method for direct synthesis of YBa2Cu4O8 at atmospheric oxygen pressure
Authors: Khan Nawazish A. , Baber N. , Zafar Iqbal M. , ul Haq A.
Published: July 2002

A simple method for the synthesis of YBa2Cu4O8 superconductor at oxygen pressure of 1 atm is reported. The starting copper compound Cu2 (CN)2 makes it possible to synthesize near single phase material directly, without the use of reaction rate enhancers or wet chemical methods previously considered necessary. Resistivity and magnetic susceptibility measurements confirm the presence of bulk superconductivity at 81 K previously achieved only in YBa2Cu4O8 material synthesized at high oxygen pressure.
Growth of fcc Fe films on diamond
Authors: Pappas D. P. , Glesener J. W. , Harris V. G. , Idzerda Y. U. , Krebs J. J. , Prinz G. A.
Published: July 2002

The epitaxial growth of fcc iron films on the (001) face of diamond has been achieved. The films were studied by reflection high-energy electron diffraction and angle-resolved Auger electron diffraction. The studies show that 4–5 atomic layers of Fe on C(100) form a continuous film. The films as deposited at room temperature are disordered, and after a high-temperature anneal have a fcc structure at room temperature.
Relaxation of phosphor field in SrS:Ce thin film electroluminescent devices
Authors: Ohmi Koutoku , Inoue Satoshi , Tanaka Shosaku , Kobayashi Hiroshi
Published: July 2002

Capacitance-applied voltage and internal charge-phosphor field characteristics of SrS:Ce thin film electroluminescent devices have been studied. The average phosphor field of the SrS:Ce films reaches the maximum of 1.3 MV/cm and relaxes to 0.7 MV/cm, although the applied voltage increases. The turn-on voltage of the SrS:Ce thin film electroluminescent device decreases nonlinearly with increase of conduction charge and depends on the slew rate dV/dt. A large spike current is observed and is thought to correspond to the charge generation in the SrS:Ce layer, which results in the space charge, and causes a relaxation of phosphor field in the SrS:Ce films.
Subpicosecond time response of third-order optical nonlinearity of small copper particles in glass
Authors: Tokizaki Takashi , Nakamura Arao , Kaneko Shoji , Uchida Katsuaki , Omi Shigeyuki , Tanji Hiroaki , Asahara Yoshiyuki
Published: July 2002

Femtosecond pump-probe experiments with a time resolution of 100 fs have been performed for copper particles with a radius of 4 nm. Differential absorption spectra for a pump centered at 2.05 eV indicates the broadening of the absorption band due to the surface plasmon. The nonlinear response time derived from the recovery time of the nonlinear absorption is dependent on the pumping laser fluences, and is as short as 0.7 ps for 210 μJ/cm2. The relaxation dynamics of nonequilibrium electrons can be described by the usual electron-phonon coupling model.
Electron-temperature control for plasmas passing through a negatively biased grid
Authors: Kato Kohgi , Iizuka Satoru , Sato Noriyoshi
Published: July 2002

Electron-temperature control is performed on plasmas passing through a coarse mesh grid from a discharge region. By increasing a negative potential applied to the grid, the electron temperature is continuously decreased in a very wide range covering almost two orders of magnitude down to the value nearly equal to the background gas temperature in case of direct current argon or helium gas discharge. The temperature decrease is accompanied by an increase in the electron density. This method of electron-temperature control can also be applied to plasmas produced by radio-frequency and electron cyclotron resonance discharges.
Study of KTiOPO4 gray-tracking at 1064, 532, and 355 nm
Authors: Boulanger B. , Fejer M. M. , Blachman R. , Bordui P. F.
Published: July 2002

Photochromic ‘‘gray-track’’ damage occurring during 1064 nm second-harmonic generation (SHG) in KTiOPO4 is a significant limitation in many practical applications. Measurements of the evolution of gray-track damage during SHG, along with measurements of the 355 nm radiation simultaneously produced by non-phase-matched sum-frequency generation, are described. Comparison of these measurements with the gray-tracking induced by exposure to a single wavelength indicates that for the conditions investigated here, the gray-tracking during 1064 nm SHG is dependent only on the intensity of the 532 nm radiation. The dependence of the induced absorption on the 532 nm intensity is nonlinear, having a threshold of 80 MW/cm2, and an approximately linear increase for intensities above this threshold.
Fabrication of an InGaAs single quantum well circular ring laser by direct laser patterning
Authors: Shih M. C. , Hu M. H. , Freiler M. B. , Levy M. , Scarmozzino R. , Osgood R. M. , Tao I. W. , Wang W. I.
Published: July 2002

The fabrication of single quantum well (SQW) ridge waveguide ring laser in strained InGaAs is described which utilizes direct-write laser lithography followed by cryogenic UV laser-assisted etching. The laser has a threshold current of 270 mA and emits ∼14 mW of single-frequency output.
Performance of the Tokamak Fusion Test Reactor bolometers
Authors: Schivell J.
Published: July 2002

For the past year we have been making use of a horizontally viewing 19-channel array and a bolometer which views a narrow cross-sectional slice of the plasma. More recently, we have also obtained results from a second, vertically viewing array. Software has been developed to translate the data from general plasma and array locations to plasma minor radius and to do the Abel inversion with an antisymmetrical term included. Experience has been obtained on the noise and response-time characteristics, as well as the accuracy of total radiated power and radial profiles. Representative cases of radiated power profiles and local power balance are presented, as well as comparisons with other measurements of impurity concentration and trends with electron density and limiter coating. Although most of the ohmic-heating input power leaves by radiation, most of this loss occurs near the outer part of the plasma. Also, the behavior of power profiles during neutral beam injection is discussed briefly.
Tokamak Fusion Test Reactor horizontal high-resolution Bragg x-ray spectrometer
Authors: Hill K. W. , Bitter M. , Tavernier M. , Diesso M. , von Goeler S. , Johnson G. , Johnson L. C. , Sauthoff N. R. , Schechtman N. , Sesnic S. , Tenney F. , Young K. M.
Published: July 2002

A bent quartz-crystal spectrometer of the Johann type with a spectral resolution of λ/Δλ= 10000–25000 is used on the Tokamak Fusion Test Reactor (TFTR) to determine central plasma parameters from the spectra of helium-like and lithium-like metal impurity ions (Ti, Cr, Fe, and Ni). The spectra are observed along a central radial chord and are recorded by a position-sensitive multiwire proportional counter with a spatial resolution of 250 μ. Standard delay-line time-difference readout is employed. The data are histogrammed and stored in 64 K of memory providing 128 time groups of 512-channel spectra. The central ion temperature and the toroidal plasma rotation are inferred from the Doppler broadening and Doppler shift of the Kα lines. The central electron temperature, the distribution of ionization states, and dielectronic recombination rates are obtained from satellite-to-resonance line ratios. The performance of the spectrometer is demonstrated by measurements of the Ti xxi Kα radiation.
Production of solid D2 threads for dense Z-pinch plasmas
Authors: Grilly E. R. , Hammel J. E. , Rodriguez D. J. , Scudder D. W. , Shlachter J. S.
Published: July 2002

A liquid-He/liquid-N2 cryostat system has been developed to freeze D2 gas and extrude fibers of solid deuterium into a vacuum chamber. Fibers that are 40 μm in diameter and 10 cm long have been successfully and routinely produced. The fibers are observed to remain constant in physical dimensions for several minutes. A fiber will be used as the electrical load for a pulsed power machine in a program investigating the properties of dense, ohmically heated plasmas for controlled thermonuclear fusion.
Versatile microreactor for studies of gas–surface catalytic reactions between 10−7 and 1000 Torr
Authors: Vajo J. J. , Tsai W. , Weinberg W. H.
Published: July 2002

A microreactor system that is designed for studies of steady-state and batch heterogeneous reactions on a wire, foil, or single-crystal surface at pressures between 10−7 and 1000 Torr is described. The applicability of the continuous stirred tank reactor approximation that facilitates the calculation of absolute reaction rates is discussed. Results for the decomposition of ammonia on a polycrystalline platinum wire are used to illustrate the performance of the microreactor.
1000-V, 300-ps pulse-generation circuit using silicon avalanche devices
Authors: Benzel D. M. , Pocha M. D.
Published: July 2002

A Marx configured avalanche transistor string and a pulse rise-time peaking diode are used to generate pulses of >1000 V into a 50-Ω load with rise times of less than 300 ps. The trigger delay of this circuit is about 7–10 ns, with jitter <100 ps. This circuit has been used to generate pulses at a repetition rate up to 5 kHz.
Diamond anvil cell and cryostat for low-temperature optical studies
Authors: Silvera Isaac F. , Wijngaarden Rinke J.
Published: July 2002

A diamond anvil cell and cryostat suitable for optical studies from 1.1 K to room temperature at ultrahigh pressures is described. Special provisions and techniques for loading condensable gases (cryogases) are discussed.
New cavity design for a LiNbO3 optical parametric oscillator
Authors: Michael Daniel W. , Kolenbrander Kirk , Lisy James M.
Published: July 2002

A new cavity design for a Nd–YAG-pumped LiNbO3 optical parametric oscillator has been developed for resonating the low-frequency component between 2.2 and 4.0 μ. The design allows for rapid conversion between medium (0.8 cm−1) and high (0.06 cm−1) resolution configurations. The use of digital feedback servocontrols enables computer scanning over a range of 400 and 4 cm−1 in medium- and high-resolution modes, respectively.
Infrared light scattering tomography with an electrical streak camera for characterization of semiconductor crystals
Authors: Ogawa Tomoya , Nango Nobuhito
Published: July 2002

An electrical streak camera has been developed for IR imaging. Integration for noise reduction and subtraction of dark current were successfully performed using a 16-bit personal computer, improving the signal-to-noise ratio of a PbO–PbS visicon for IR detection. In this paper, the camera was applied to infrared light-scattering tomography for characterization of semiconductor crystals such as GaAs, InP, and CdTe crystals. In this streak camera, the IR detector can be replaced by a photodiode array such as HgCdTe, to detect even much longer wavelength radiation, which will be useful to study some electronic centers in semiconductors.
Bragg rotor spectrometer for tokamak diagnostics
Authors: Barnsley R. , Evans K. D. , Peacock N. J. , Hawkes N. C.
Published: July 2002

A high-throughput broadband (1–24-Å) x-ray spectrometer has been demonstrated on the divertor injection tokamak experiment (DITE) tokamak. A hexagonal rotor supporting six diffractors may be driven in several modes, ranging from a full spectral survey at ∼10 Hz to a stationary, monochromator mode. Wavelength resolution, 500≲λ/Δλ≲1000, is governed by gridded or slotted collimators. A multiwire gas proportional counter provides a measure of energy discrimination, which together with the large instrument aperture, gives sufficient sensitivity and signal/noise ratio to allow measurement of the continuum radiation from the tokamak. The instrument has a self-contained vacuum system which allows full spatial scans of the DITE plasma. Data acquisition and drive mechanisms for the rotor and filter selection, are controlled remotely from a computer. Results are presented of fast spectral surveys and time evolution of impurity emission during impurity injection.
Design and implementation of a control system for a deuterium pellet injector
Authors: Burris R. D. , Baylor L. R. , Greenwood D. E. , Stewart K. A.
Published: July 2002

The Oak Ridge National Laboratory is currently developing a deuterium pellet injector for installation on the tokamak fusion test reactor (TFTR). This paper describes the design and development of a stand-alone data acquisition and control system for that device. Major elements of the hardware are an Allen–Bradley PLC 2/30 programmable logic controller, a MicroVAX-II computer using the VMS operating system, CAMAC data acquisition and communication equipment, and special-purpose controllers for temperature and for the sequencing of pellet firing valves. The PLC performs all actual control actions and acquires data pertinent to those actions. The MicroVAX receives the data acquired by the PLC, displays it for the operator, prompts for and processes requests for action from the operator, and informs the PLC of those requests. The primary purpose of this paper is to describe the software operating in the MicroVAX, including the system architecture, major tasks, and ancillary and background tasks.
Ultrahigh vacuum sample mount for insulators
Authors: Marsh E. P. , Tabares F. L. , Bach G. A. , Cowin J. P.
Published: July 2002

An ultrahigh vacuum sample mount for insulators which allows both good thermal conduction to the mount and accurate temperature measurement is described: good thermal connection between sample and mount is made with an indium layer. By melting an edge of the sample a thermocouple can be inserted directly into the crystal for accurate temperature measurement.
Simultaneous measurements of radial and poloidal wave numbers using a heavy ion beam probe
Authors: Connor K. A. , Crowley T. P.
Published: July 2002

Experimental studies of density, temperature, or potential fluctuations in high-temperature plasmas have been limited by the inability of the available diagnostics to determine radial and poloidal wave numbers at the same plasma location. A technique is under investigation that can permit the heavy ion-beam probe to determine the wave number in two dimensions by adding a rapid, small-amplitude, square-wave voltage modulation to both the sweep plates and the accelerator that moves the measurement points along and perpendicular to the beam. k can then be determined for fluctuation frequencies limited only by the beam modulation and detector electronics.
Multichannel Thomson scattering systems with high spatial resolution (invited)
Authors: Johnson D. , Bretz N. , Dimock D. , Grek B. , Long D. , Palladino R. , Tolnas E.
Published: July 2002

Thomson scattering systems capable of providing snapshot profiles of electron temperature and density with high spatial resolution (>50 points) have become routine diagnostics on the Princeton large torus (PLT), Princeton divertor experiment (PDX), and tokamak fusion test reactor (TFTR) tokamaks. The design parameters of these systems are compared. Particular attention is given to describing those new components and techniques which have contributed most to improved data quality and reliability in the ten-year evolution of these systems. Examples of recent TFTR Te(R) and ne(R) profiles are presented.
High-power, twin-frequency FIR lasers for plasma diagnostic applications
Authors: Lehecka T. , Savage R. , Dworak R. , Peebles W. A. , Luhmann N. C. , Semet A.
Published: July 2002

The development of imaging interferometry and multichannel heterodyne scattering systems for fusion plasma diagnosis has dictated the development of high-power, stable twin-frequency sources in the 100→1000 μm spectral region. Output powers of 500 mW (185 μm), 150 mW (393 μm), 100 mW (496 μm), and 25 mW (1.22 mm) have been measured directly on a Scientech Calorimeter applying no correction factors. These powers have been achieved via the optimization of the CO2 and far infrared (FIR) laser cavities together with the use of buffer gases (to relieve bottlenecking) and variation of the pumped molecular gas temperature (to optimize the ground-state population). The source intermediate frequency (IF) jitter in twin-frequency FIR laser systems has also been investigated in detail. The effect of CO2 and FIR feedback on the IF frequency has been studied with the view of producing low-cost stable laser systems without complicated active stabilization. Finally a comparison between a novel twin-frequency laser involving a single optical cavity and a conventional system involving two separate cavities has been performed. The conclusions drawn from the above studies have been utilized in the design of laser systems operational on the TEXT tokamak and at UCLA.
Langmuir trough with four movable barriers
Authors: Miyano Kenjiro , Maeda Toshiteru
Published: July 2002

A new type Langmuir trough has been constructed, in which a monolayer on water is enclosed by four polytetrafluoroethylene (PTFE) tapes, independently movable, floating on the water. This arrangement allows a uniform film compression and a study of the stress inhomogeneity under purely compressional or shear strain. The system does not require a delicate water level adjustment. It is capable of sustaining a high surface pressure and easy to operate.