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  • American Institute of Physics (AIP)  (161)
  • American Meteorological Society (AMS)
  • 2000-2004  (43)
  • 1985-1989  (118)
  • 1
    Electronic Resource
    Electronic Resource
    The effects of a dynamic lattice on methane self-diffusivity calculations in AlPO4-5 (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 3345-3350 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Canonical ensemble molecular dynamics simulations were conducted for methane diffusion in AlPO4-5 in order to assess the role of the lattice motion on adsorbate diffusivity in straight pore zeolites. Both a static lattice model and a full dynamic lattice model were used at a loading of 1.5 methane/unit cell at 295 K. Although recent simulation work has asserted that there should be a difference, we show that there is little difference in the observed methane diffusivity (1.26×10−7 m2/s) and passing frequency (0.305) when a static lattice approximation is used over a full dynamic lattice (1.33×10−7 m2/s and 0.328). Furthermore, we introduce a methodology for handling lattice motion in molecular simulations by utilizing the normal vibrational modes in a harmonic crystal approximation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480917
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  • 2
    Electronic Resource
    Electronic Resource
    Laser spectroscopy of jet-cooled ethyl radical: Infrared studies in the CH2 stretch manifold (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 1823-1834 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A glow discharge, slit supersonic expansion in conjunction with direct infrared laser absorption methods has been utilized to record high resolution vibration–rotation spectra of the CH3–CH2 ethyl radical. The slit supersonic expansion results in efficient rotational cooling from discharge temperatures down to Trot(approximate)14 K, permitting unambiguous rotational assignment and spectral analysis for the first time. Furthermore, a discharge on/discharge off data collection scheme permits clean discrimination between spectral contributions from radical vs precursor absorption. Spectra for both symmetric and asymmetric CH2 stretch manifolds are observed. Least-squares fits of transition frequencies out of the K=0 ground state manifold to a near prolate top model Hamiltonian reproduce the data to within the 7 MHz experimental uncertainty and provides rotational constants for both ground and vibrationally excited symmetric/asymmetric CH2 stretch states. The band origins for the CH2 stretch vibrations [3037.018 96(12) cm−1 and 3128.693 69(13) cm−1] are in reasonable agreement with ab initio theory; though predictions for relative intensities of the two bands are off by nearly an order of magnitude and indicate that the transition moment vector is tilted 33° away from each C–H bond toward the C–C bond axis. Structural analysis based on the measured B and C rotational constants imply a C–C bond distance of 1.49 Å. This is consistent with partial ((approximate)15%) double bond character for the ethyl radical carbon frame and in excellent agreement with theoretical predictions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480746
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  • 3
    Electronic Resource
    Electronic Resource
    Femtosecond stimulated emission pumping: Characterization of the I2− ground state (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 8847-8854 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Femtosecond stimulated emission pumping in combination with femtosecond photoelectron spectroscopy is used to characterize the potential energy function of the I2−(X˜ 2Σu+) ground state up to vibrational energies within 2% of the dissociation limit. The frequency and anharmonicity of this state are measured at a series of vibrational energies up to 0.993 eV by coherently populating a superposition of ground state vibrational levels using femtosecond stimulated emission pumping, and monitoring the resulting wave packet oscillations with femtosecond photoelectron spectroscopy. The dissociative I2−(A˜′ 2Πg,1/2) state is used for intermediate population transfer, allowing efficient population transfer to all ground state levels. Using the measured frequencies and anharmonicities, the X˜ 2Σu+ state has been fit to a modified Morse potential with the β-parameter expanded in a Taylor series, and the bond length, well depth, and υ=0–1 fundamental frequency set equal to our previously determined Morse potential [J. Chem. Phys. 107, 7613 (1997)]. At high vibrational energies, the modified potential deviates significantly from the previously determined potential. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481499
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  • 4
    Electronic Resource
    Electronic Resource
    Crossed beams studies of Mo(a 7S3) and Mo*(a 5S2) collisions with CH4 and C2H6 (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 4634-4643 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interactions of Mo(a 7S3) and Mo*(a 5S2) with methane, CH4, and ethane, C2H6, were studied under single collision conditions using the crossed molecular beams technique. Ground state Mo(a 7S3) atoms were found to be unreactive at all collision energies studied up to 〈Ecoll〉=35.4 kcal/mol. Nonreactive scattering of Mo(a 7S3) with methane and ethane was studied and compared to collisions with Ne and Ar. A forward peaking center-of-mass angular distribution, T(aitch-theta), was necessary to simulate the elastic collisions with inert gases as well as inelastic collisions with the alkanes. At a collision energy of 14.4 kcal/mol with CH4 and 21.0 kcal/mol with C2H6, inelastic collisions were found to transfer ∼10% and ∼19% of the initial kinetic energy into alkane internal energy, respectively. For collisions of Mo*(a 5S2)+CH4, the dehydrogenation product, MoCH2, was observed at all collision energies studied down to 2.1 kcal/mol. The reaction Mo*(a 5S2)+C2H6→MoC2H4+H2 was observed down to 〈Ecoll〉=4.5 kcal/mol. For a given total energy (electronic+translational), it was found that electronic energy is highly effective in promoting this reaction whereas translational energy is ineffective. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481018
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of Al and Ti interlayers on Sb/(HgCd)Te interface behavior (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3435-3440 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of 0.1 and 0.5-nm Al and 0.02-nm Ti interlayers on the Sb/(HgCd)Te system have been investigated with photoelectron spectroscopy using synchrotron radiation. With no interlayer, the Sb forms an abrupt, uniform overlayer with a stoichiometric interface and causes no change in the band bending induced during the cleaving process. With the two Al interlayers Sb exhibits less uniform deposition and diffuses into the semiconductor enough to reverse the additional band bending caused by Al in-diffusion. It also reacts with the elemental Al of the 0.5-nm interlayer to form AlSb. The increased disruption of the (HgCd)Te surface by the Ti interlayer leads to enhanced out-diffusion of Te in addition to Sb clustering and in-diffusion. In this case, Sb is able to compensate for the inversion occurring during cleavage and returns the surface to a nearly flat-band condition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342662
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  • 6
    Electronic Resource
    Electronic Resource
    SiGe/Si superlattices on implanted buried-oxide structures (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1505-1509 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In an attempt to reduce the number of threading dislocations propagating through a silicon epitaxial layer grown on an implanted buried-oxide structure, a SiGe/Si superlattice was placed between the initial silicon surface layer and the subsequently grown silicon epitaxial layer. Both the superlattice and the silicon epitaxial layer were formed by molecular-beam epitaxy. Some of the threading dislocations are bent parallel to the superlattice as they propagate through the structure. Some of these are annihilated by interacting with other dislocations while others bend toward the surface again after propagating parallel to the superlattice for some distance. The effect of the superlattice is limited, and many of the dislocations continue propagating through the superlattice toward the surface of the silicon epitaxial layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342965
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  • 7
    Electronic Resource
    Electronic Resource
    Chemical vapor deposition and characterization of 6H-SiC thin films on off-axis 6H-SiC substrates (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2672-2679 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-quality, monocrystalline 6H-SiC thin films have been epitaxially grown on 6H-SiC {0001} substrates which were prepared 3° off-axis from 〈0001〉 towards 〈112¯0〉 at 1773 K via chemical vapor deposition (CVD). Essentially, no defects were generated from the epilayer/substrate interface as determined by cross-sectional transmission electron microscopy (XTEM). Double positioning boundaries which were observed in β-SiC grown on 6H-SiC substrates were eliminated as confirmed by plan-view TEM. A strong dependence of the surface morphology of the as-grown thin films on the tilting orientation of the substrates was observed and reasons for this phenomenon are discussed. The unintentionally doped 6H-SiC thin films always exhibit n-type conduction with a carrier concentration on the order of 1016 cm−3. Au-6H-SiC Schottky barrier diodes were fabricated on the CVD 6H-SiC thin films and it was found that the leakage current at a reverse bias of 55 V was only 3.2×10−5 A/cm2. This is compared to SiC films grown on other substrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341608
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  • 8
    Electronic Resource
    Electronic Resource
    Electrical properties of ion-implanted p-n junction diodes in β-SiC (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 922-929 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mesa structure junction diodes prepared via high-temperature ion implantation of Al+ (100 keV, 4.8×1014 Al/cm2) in n-type or N+ (90 and 180 keV, 0.9 and 1.3×1014 N/cm2) in p-type β-SiC thin films were electrically characterized as a function of temperature using current-voltage and capacitance-voltage measurements. In either case, rectification was observed to the highest measurement temperature of 673 K. Closer examination of the device current-voltage characteristics yielded diode ideality factors greater than 2. Additionally, the log dependence of these two parameters indicated space-charge-limited current in the presence of traps as the dominant conduction mechanism. From the temperature dependence of log-log plots, trap energies and densities were determined. Two trapping levels were observed: (1) 0.22 eV with a density of 2×1018 cm−3 and (2) 0.55 eV with a density of 2×1016 cm−3. The former is believed to be ionized Al centers (in the case of Al-implanted sample) and the latter a compensating acceptor level, both of which lie within the bottom third of the band gap. Reverse currents at low biases were characteristic of generation in the depletion region. At intermediate biases an ohmic dependence was observed, whereas at high biases the current appeared to be space-charge limited. Capacitance-voltage measurements indicated both types of diodes were abrupt junctions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340034
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  • 9
    Electronic Resource
    Electronic Resource
    Optical, mechanical, and thermal properties of barium borate (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 1968-1983 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report measurements of all the material constants necessary to fully characterize barium borate as a nonlinear optical material. All data was taken on crystals supplied by Professor Chuangtien Chen, Fuzhou, People's Republic of China. We have determined the crystal structure, the optical absorption, the refractive indices from the UV to the near IR, the thermo-optic coefficients, the nonlinear optical or coefficients, the resistance to laser damage, the elastic constants, the thermal expansion, thermal conductivity and dielectric constants, and the fracture toughness. This data is used to evaluate barium borate for a variety of applications. We find that, in general, barium borate has a low acceptance angle, and that despite its higher optical nonlinearity, it is therefore not significantly more efficient than other commonly available materials, except in the UV below 250 nm. On the other hand, it has a high damage threshold, it is physically robust, it has good UV and IR transparency, and it has excellent average power capability. It permits deep UV generation, and has great potential for generating tunable visible and IR light as an optical parametric amplifier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339536
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  • 10
    Electronic Resource
    Electronic Resource
    Photoluminescence spectroscopy of ion-implanted 3C-SiC grown by chemical vapor deposition (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 2011-2016 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature photoluminescence (PL) spectroscopy has been used to characterize as-grown and ion-implanted 3C-SiC films grown by chemical vapor deposition on Si(100) substrates. The D1 and D2 defect PL bands reported previously in ion-implanted Lely-grown SiC were also observed in the as-grown chemical vapor deposited films, and the effects of annealing (1300–1800 °C) on these PL bands as observed in as-grown films and films implanted with B, Al, or P have been studied. As reported previously for Lely-grown SiC, the spectral details of the defect PL bands and their annealing characteristics were found to be independent of the particular implanted-ion species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337997
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