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  • 1
    Electronic Resource
    Electronic Resource
    "Magic number'' carbon clusters: Ionization potentials and selective reactivity (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3556-3562 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ionization potentials (IPs) of several large carbon clusters Cn (n≥48), including the enhanced abundance ("magic number'') clusters C50, C60, and C70, have been determined by Fourier transform ion cyclotron resonance (FTICR) mass spectrometric charge transfer bracketing experiments. The IPs of C50, C60, and C70 were bracketed by the same two charge transfer compounds, leading to a common value of 7.61±0.11 eV. The IPs of even numbered clusters adjacent to these magic number clusters were found to be lower by as much as 0.5 eV and all clusters between C50 and C200 were determined to have IPs greater than 6.20 eV. The reaction rates of C+60 and C+70 with metallocenes were anomalously slow in comparison to the other large carbon cluster ions. IP and reactivity results suggest that C50, C60, and C70 may indeed have different or more stable structures than neighboring clusters, which supports the hypothesis of closed-shell, spherical species. The implications of these results for the mechanism of C+n formation by direct laser vaporization are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459778
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  • 2
    Electronic Resource
    Electronic Resource
    ECRH absorption and propagation studies via collective Thomson scattering (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1980-1982 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Electron cyclotron resonance heating (ECRH) has made rapid progress over the last few years due primarily to improved gyrotron source technology. The unique ability of ECRH to deposit energy locally offers numerous advantages, such as the ability to preionize, initiate, control, and heat fusion plasmas. However, wave propagation and absorption mechanisms are not well understood and the fusion community would clearly benefit from a nonperturbing monitor of ECRF wave activity. The use of FIR collective Thomson scattering techniques on the upcoming ECRH experiment on TEXT is described. The intention is to probe both k⊥ and k(parallel) ECRF wave activity as well as simultaneously monitoring microturbulence levels. The existing source frequency of 245 GHz will experience a large frequency shift (∼60 GHz) after scattering from ECRF waves. This has a number of important consequences for the accurate interpretation of scattering data. These will be described in detail as well as alternative CO2 and FIR laser scattering schemes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138812
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  • 3
    Electronic Resource
    Electronic Resource
    Picosecond time-resolved electronic spectroscopy in plate impact shock experiments: Experimental development (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1743-1750 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An experimental method was developed to perform picosecond time-resolved electronic spectroscopy in single-event, plate impact, shock wave experiments. Several experimental difficulties had to be addressed due to the fast time resolution (100 ps) and short time duration (12.7 ns) of such experiments. Procedures are described to address the following experimental issues: (i) synchronization of the light source, detection equipment, and the shock event within the experimental duration, (ii) incorporation of a Nd:YAG laser (operative in a repetitive mode) into the experimental configuration, and (iii) sources of temporal dispersion. Representative results are shown from experiments performed on single crystal CdS. The developments described here are also expected to be useful for shock wave experiments involving Raman, fluorescence, or other types of spectroscopy which require the use of a laser. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149662
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  • 4
    Electronic Resource
    Electronic Resource
    Pyrolysis and laser ablation of plasma-polymerized fluorocarbon films: Effects of gold particles (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2462-2471 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma-polymerized fluorocarbon (PPFC) films were analyzed by thermogravimetric analysis (TGA), direct pyrolysis/mass spectrometry, and laser-ablation/electron-impact mass spectrometry. Fourier transform mass spectrometry was used to detect products. The films were made by plasma polymerizing tetrafluoroethylene in an argon plasma. Two types of films were studied: with and without fine gold particles incorporated in the PPFC films. TGA showed that gold-containing films decompose more rapidly and at lower temperature with increasing gold content. Pyrolysis products were determined as a function of temperature. The predominant positive product ions, using 20 eV electron-impact ionization, were C2F4+, CF3+ and a distribution of higher-mass unsaturated fluorocarbon species, CnFm+, up to at least n=14 and m≥n+1. The predominant negative ions, formed by electron attachment, were also unsaturated fluorocarbon ions which extended up to 1145 u in mass. These species are different from those observed from polytetrafluoroethylene pyrolysis. No dependence of the positive-ion mass spectral distributions of pyrolysis products on gold content of the films was observed. However, the negative-ion pyrograms had a dramatically different temperature dependence for films with and without gold. The results imply that the gold-containing films have regions of lower molecular weight, and a possible formation mechanism is suggested. Laser ablation formed low-mass neutral fluorocarbon species. Ablation of the gold-containing film under direct laser ionization conditions (higher laser power), produced a spectrum resembling the pyrolysis spectrum, suggesting that the gold particles affect the mechanism of the ablation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351592
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  • 5
    Electronic Resource
    Electronic Resource
    Operation of a Y-Ba-Cu-O rf SQUID at 81 K (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 617-618 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An rf superconducting quantum interference device (SQUID) has been made from bulk Y-Ba-Cu-O. The device displays quantum interference effects and operates with useful signal levels up to 81 K. The SQUID is formed from a ring of Y-Ba-Cu-O which is broken in the cryogenic environment and then recontacted. Estimates of the SQUID noise performance are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98365
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  • 6
    Electronic Resource
    Electronic Resource
    Electric-field-induced polarization current studies in guest–host polymers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1267-1285 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We apply polarization current measurements to study dipole reorientation of nonlinear chromophores that are embedded in a polymer matrix. In particular, we apply a step voltage to a thin film of poly(methyl methacrylate) that is doped with a well-known dipolar chromophore, Disperse Red 1, or an apparently centrosymmetric squarylium chromophore, and measure the isothermal temporal behavior of the current at several temperatures. By correlating the current with electric-field-induced second-harmonic generation, we find that at very early times, polarization current dominates, while at later times, charge hopping mechanisms probably dominate. For the centrosymmetric squarylium chromophore dopant, we find an early-time current suggesting polarization decay with no corresponding second-harmonic signal. This suggests that the squarylium molecule has a dipole moment that is perpendicular to the dominant axis of the polarizability tensor and is consistent with the presence of the cis isomer. A time–temperature–voltage complimentarity relationship is also observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356404
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  • 7
    Electronic Resource
    Electronic Resource
    Electrical transients during interfacial debonding and pullout of a metal rod from an epoxy matrix (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4808-4815 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We examine electrical transients which are produced during the propagation of a debonding crack along the interface of an axially loaded stainless-steel rod embedded in epoxy. Time-resolved correlations with fracto-emission signals and tensile strain in the rod are made to assist interpretation. We show that on microsecond time scales, the motion of the debonding crack as well as the initial pullout motion of the rod following debonding can be detected and followed. A model is developed which consistently describes the sign and amplitude of the detected electrical signals. These experimental data provide time-resolved information on the sequence of events leading to interfacial fracture and initial pullout of the rod from the epoxy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349046
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of temperature on data retention of silicon-oxide-nitride-oxide-semiconductor nonvolatile memory transistors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7115-7124 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The discharge behavior of silicon-oxide-nitride-oxide-semiconductor nonvolatile memory transistors is investigated for a range of programming and storage temperatures spanning −55 °C to 200 °C. A number of empirical observations strongly limit the nature of the mechanisms that govern charge injection and decay. Both electrons and holes contribute to the charge storage properties of the transistors, and the decay properties of both are thermally activated with a continuous distribution of activation energies (trap depths). Charge decay, for both charge states, is negligibly limited by mechanisms other than those which are strongly thermally activated. The programming temperature, relative to the storage temperature, significantly impacts the retention time of the excess electron state, while not affecting the long term decay of the excess hole state. The experimental results also have significant implications regarding proper retention screening techniques and nonvolatile ROM programming techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345062
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  • 9
    Electronic Resource
    Electronic Resource
    A comparison of three-dimensional multimode hydrodynamic instability growth on various National Ignition Facility capsule designs with HYDRA simulations (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1125-1132 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three similar cryogenic ignition capsule designs for the National Ignition Facility [J. Lindl, Phys. Plasmas 2, 3933 (1995)] are analyzed to determine surface roughness specifications required to mitigate the growth of hydrodynamic instabilities. These capsule utilize brominated plastic, polyimid and copper-doped beryllium ablator materials respectively. Direct three-dimensional numerical simulations with the HYDRA radiation hydrodynamic code [M. M. Marinak et al., Phys. Plasmas 3, 2070 (1996)] examine the growth of multimode perturbations seeded by roughness on the outer ablator and inner ice surfaces. The simulations, which showed weakly nonlinear behavior for optimized surfaces, were carried through ignition and burn. A three-dimensional multimode perturbation achieves somewhat larger amplitudes in the nonlinear regime than a corresponding two-dimensional simulation of the same rms amplitude. The beryllium and polyimid capsules exhibit enhanced tolerance of roughness on both the ice and ablator surfaces. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872643
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  • 10
    Electronic Resource
    Electronic Resource
    The formation of large polyaromatic hydrocarbons via carbon cluster ion reactions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 3267-3274 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Reactions of carbon cluster ions (C+n, 10〈n〈25) with polyaromatic hydrocarbons (PAHs) and substituted benzenes, studied using Fourier transform ion cyclotron resonance (FTICR) mass spectrometry, provide evidence for the formation of large, highly conjugated PAHs. Product ions consist of adducts formed by radiative association/collisional stabilization and adducts accompanied by the loss of a hydrogen. These two reaction pathways alternate between the even- and odd-numbered cluster ions dependent on reactant neutral employed. Adduct formation continues up to a maximum of five associations and to molecular weights in excess of 900 amu. Collisionally induced dissociation (CID) of product ions produced fragmentation indicative of species with multiply bonded carbon atoms and possibly fullerene-type structure. Complete dehydrogenation of the adduct ions was possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460884
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