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  • 2020-2024  (7)
  • 1995-1999  (81)
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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results are reported from an investigation of the effects of selected processing parameters on the morphology and properties of YBa2Cu3O7−δ (YBCO) superconducting thin films grown directly on polycrystalline silver substrates by chemical-vapor deposition (CVD). These results were achieved through a set of experimental studies which examined: (i) recrystallization mechanisms of polycrystalline silver and their effect on the deposition of YBCO thin films; and (ii) CVD processing conditions leading to the growth of high-quality YBCO films. The samples were analyzed using dynamic impedance, four-point resistivity probe, x-ray diffraction, Rutherford backscattering, and scanning electron microscopy. These studies showed that substrate temperature played a critical role not only in the formation of YBCO films, but also in the recrystallization of silver substrates, which in turn greatly influenced film growth. The studies also led to the identification of a two-stage processing scheme for the growth of YBCO films on silver. The first processing stage consisted of a substrate conditioning cycle which involved a 10 min ramping from room temperature to deposition temperature where the substrates were held for an additional 10 min in a flow of 70 sccm O2 at a reactor working pressure of 2 Torr. The second processing stage involved actual film deposition at 760–800 °C for 3–10 min (depending on desired film thickness) in a mixed flow of 70 sccm O2 and 210 sccm N2O at a reactor working pressure of 4 Torr. Samples thus produced were highly oriented along the c axis perpendicular to the substrate with a zero resistance transition temperature of 87 K and a critical current density of 2×104 A/cm2 (77 K, B=0). The films had a thickness of 200–700 nm depending on the length of the growth cycle, which corresponded to the growth rates in the range 65–130 nm/min. A growth mechanism for YBCO on polycrystalline silver, which emphasized the role of silver recrystallization, was consequently proposed and discussed.
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  • 2
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 9428-9437 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Classical Monte Carlo and molecular dynamics (MD) simulations were carried out to investigate the structures, the infrared spectra, and the rigid–nonrigid transitions of small methanol clusters (CH3OH)n for n=3–6. The study was motivated by experimental results for these clusters from size specific infrared (IR) dissociation spectroscopy. The MD simulations revealed the following transitions: The trimer passes from a rigid ring configuration into a series of nonrigid open chain structures starting at 197 K. For n=4 and 5 such transitions occur between rings and rapidly fluctuating ring structures at T=357 and 243 K, respectively. For n=6 first a pure isomeric transition between the two energetically lowest isomers of S6 and C2 symmetry is found at 35 K, and then a similar transition to a nonrigid behavior as is observed for n=4 and 5 is seen at 197 K. The measured spectra display in all cases the rigid lowest energy configurations.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4072-4076 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The behavior of radiation-induced carbon-related defects in high-resistivity silicon detectors has been investigated. The defects were introduced by α-particle irradiation and investigated by deep-level transient spectroscopy. An unusual defect behavior consists in low-temperature annealing, including self-annealing at room temperature, of the interstitial carbon Ci with a simultaneous increase of the Ci-Oi-complex concentration. The kinetic parameters of the process have been determined from the increase of the Ci-center concentration versus time. Two annealing velocities have been observed, which arise from different heat treatments during the detector fabrication process.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3215-3217 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The depth distribution of Ge implanted into thermally grown SiO2 films has been studied after annealing using transmission electron microscopy, Rutherford backscattering spectrometry, and x-ray diffraction. At annealing temperatures above 900 °C a significant redistribution of the as-implanted Ge profile was found. Crystalline Ge nanoclusters embedded in the SiO2 matrix are formed within a cluster band with well defined boundaries. The evolution of nanoclusters can be explained qualitatively by a model based on nucleation, growth and Ostwald ripening of Ge precipitates. Besides, chemical and interface reactions lead to the formation of additional Ge peaks near the surface and at the Si/SiO2 interface. © 1997 American Institute of Physics.
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  • 6
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A technologically useful chemical vapor deposition process with high growth rate ((approximately-greater-than)4 μm/h) was developed for the epitaxial growth of YBa2Cu3O7−x (YBCO) thin films. Even at the high growth rate used in this process, a spiral growth mechanism was observed and the films grown had electrical (Tc=92 K, Jc of 2×106A/cm2 at 77 K) and structural properties equal to films produced by physical vapor deposition.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1862-1879 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ultrafast state-selective dynamics of diatomic molecules in the electronic ground state under the control of infrared picosecond and femtosecond shaped laser pulses is investigated for the discrete vibrational bound states and for the dissociative continuum states. Quantum dynamics in a classical laser field is simulated for a one-dimensional nonrotating dissociative Morse oscillator, representing the local OH bond in the H2O and HOD molecules. Computer simulations are based on two approaches — exact treatment by the time-dependent Schrödinger equation and approximate treatment by integro-differential equations for the probability amplitudes of the bound states only. Combination of these two approaches is useful to reveal mechanisms underlying selective excitation of the continuum states and above-threshold dissociation in a single electronic state and for designing optimal laser fields to control selective preparation of the high-lying bound states and the continuum states. Optimal laser fields can be designed to yield almost 100% selective preparation of any prescribed bound state, including those close to the dissociation threshold. State-selective preparation of the highest bound state may be accompanied by the appearance of a quasi-bound molecular state in the continuum with the kinetic energy of the fragments being close to zero. The respective above-threshold dissociation spectrum contains an additional, zero-order peak. The laser-induced dissociation from selectively prepared high-lying bound states is shown to be very efficient, with the dissociation probability approaching the maximal value. Flexible tools of state-selective laser control are developed which enable one to achieve selective control of the dissociation spectra resulting in time-selective and space-selective control of the dissociation fragments. © 1996 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9425-9431 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared photodissociation spectra of the mixed complexes C2H4–CH3COCH3 and C2H4–(CH3COCH3)2 have been observed after size selecting them by scattering from a helium beam combined with mass spectrometric detection. The excitation of the ν7-out of plane symmetric wagging mode of ethene near its gas phase frequency at 949.3 cm−1 with a cw-CO2 laser leads to a characteristic depletion of the cluster beam. The dissociation spectrum of the 1:1 complex can be explained by two peaks at 950.8 and 961.6 cm−1. Calculations of minimum energy configurations and band shifts based on an empirical site–site potential show that these frequencies can be attributed to the absorption of two different isomers. They correspond to the two different binding patterns of the H atoms of ethene to the O atom of acetone and those of acetone to the C–C group of ethene, respectively. For the 1:2 complex, a large peak at 958.5 cm−1 and a smaller one around 940.5 cm−1 are found which can be explained in a similar manner by several isomers found in the structure calculations.
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  • 9
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The biconversion of [14C]atrazine to deaikyt-ated and hydroxylated products was studied in heteroirophic cell-suspension cultures of carrot (Daucus caroia L.), Agrostemma githago L. (corn cockle). Digitalis purpurea L. (purple foxglove), soyabean (Giycine max L. Merr; four different cultivars). Datura stramonium L. (thorn-apple) and wheat (Tritician aestivum L.). During 48 h of incubation, the herbicide was biotransformed by all species; turnovers yields differed considerably and were between 10.1% and 88.0% of applied 14C. Differences were also observed among the soyabean cultivars (10.1-73.5%). Hydroxy-atrazine, de-ethyl-, deisopropyl- and de-ethyt-deisopropylatrazine formed in the cultures were identified by thin-layer chromatography (tlc) (co-chromatography with reference compounds); deaikyiated metabolites were also proved by gas chromatography–mass spectrometry (gc–ms). In addition, highly polar transformation products emerged that were not identified. Portions of non-extractable residues were below 5% (one soyabean cultivar: 8.9%). Atrazine was metabolized by the cells, mainly to its dealkylated derivatives and hydroxyatrazine (totals of 9.4-54, 5%), whereas portions of highly polar products were lower (0.1-26.1%). Exceptions were A. githago (26.0 and 33.6%, respectively) and D, purpurea (4.5 and 25.2% respectively). Thus, plants generally contribute to the environmental degradation of atrazine.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    European journal of nutrition 10 (1970), S. 111-114 
    ISSN: 1436-6215
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Medicine
    Description / Table of Contents: Summary 1. In aqueous phosphate buffer diacetyl tartaric acid monoglyceride is hydrolyzed to glyceride and tartaric acid. 2. Orally administered14C-labeled emulsifier to rats is absorbed to 26–31% of the activity given. 3. 21–20% are oxidized to14CO2, 8–13% are excreted in the urine, 2% are retained in the carcass.
    Notes: Zusammenfassung 1. Die vorliegende Substanz wird in geringem Umfang, maximal zu 10–20%, im wäßrigen Medium gespalten. 2. Im Organismus der Ratte wird rd. 1/3 der14C-Aktivität der Substanz resorbiert. 3. Die Ausscheidung der14C-Aktivität erfolgt zu 12–20% via Lunge, zu 8–13 % via Niere, während der im Körper verbleibende Anteil nur 2% ausmacht.
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