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  • Oxford University Press  (351)
  • American Institute of Physics (AIP)  (117)
  • American Association of Petroleum Geologists (AAPG)
  • Periodicals Archive Online (PAO)
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  • 1
    Electronic Resource
    Electronic Resource
    Electron transfer reactions on Cs/MoS2(0002) with chlorine, oxygen, and water: High resolution x-ray photoelectron spectroscopy and theoretical study (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1636-1649 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Supra-valence electron transfer from surface Cs-doped MoS2(0002) to electron acceptor adsorbates was investigated by high resolution x-ray photoelectron spectroscopy (HRXPS) in the valence band region and above the valence band maximum (VBM). Deposition of a sub-monolayer amount of Cs onto the basal plane of MoS2 introduced a new electron density of states at ca. 1.25 eV above VBM. Angle-resolved HRXPS and theoretical analysis located this electron density in the MoS2 layer. Upon the reaction with Cl2, this Cs-induced photoelectron almost completely disappeared and the Cs 3d and Cl 2p core levels indicated the formation of a surface Cs-chloride species. The Cs-covered MoS2(0002) surface also reacted with O2 to form surface peroxides and superoxides, as evidenced by two distinct binding energies of the O 1s core level peaks. However, the reaction with water proved to be more difficult: Exposure of the Cs-covered MoS2(0002) surface to H2O at 10−5 Torr did not result in electron transfer reaction, but the Cs/MoS2(0002) surface exposed to H2O at 1 Torr showed a substantial decrease in the density of states above VBM as well as formation of a surface-hydroxide, indicated by the O 1s core level position. Theoretical calculations using a full-potential linearized augmented plane wave density functional theory (FLAPW-DFT) confirm the conclusion based on experimental intensity anisotropy of the new peak: the Cs 6s electron transfers into the MoS2 substrate, forming the Cs/MoS2 electron donor–acceptor complex with Csδ+. In addition, all phenomena observed during the adsorption of electron donor–acceptor molecules are quantitatively accounted by the theory. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479423
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  • 2
    Electronic Resource
    Electronic Resource
    Raman scattering study of GaN films (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4058-4062 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman spectra of GaN films grown by molecular-beam epitaxy and hydride vapor-phase epitaxy on GaAs and Al2O3 substrates have been studied. It was found that longitudinal phonon modes disappear from the spectra of n+ films due to screening by free carriers, but coupled plasmon phonon modes of the higher-energy branch are not observed because of strong damping of plasmons. Precise values for phonon frequencies and linewidths are presented. No differences in phonon frequencies for the films of different thicknesses grown on different substrates have been found which indicates that the strain due to lattice and thermal-expansion mismatch is relaxed by the formation of the dislocations very close to the substrate–film interface. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363367
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  • 3
    Electronic Resource
    Electronic Resource
    Deep level defects in GaAs on Si substrates grown by atomic hydrogen-assisted molecular beam epitaxy (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4770-4772 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electrical activity of defects in GaAs p+n diodes grown on Si and GaAs substrates by both conventional molecular beam epitaxy (MBE) and atomic hydrogen-assisted MBE (H-MBE) were characterized by deep level transient spectroscopy. The well-known electron traps typical of MBE-grown GaAs were detected without the presence of any new levels in the upper half of the band gap. The trap densities and diode reverse saturation currents are significantly reduced in the homoepitaxial GaAs grown by H-MBE compared to that grown by MBE. The trap densities for the heteroepitaxial GaAs-on-Si grown by H-MBE have values higher than those of homoepitaxial GaAs grown by H-MBE at 330 °C, which are possibly affected by the residual dislocation density and stress. The reduction of trap density is attributed to in situ passivation of these defects by atomic H during the growth. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363415
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  • 4
    Electronic Resource
    Electronic Resource
    Low-loss polycrystalline silicon waveguides for silicon photonics (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6120-6123 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photonic integrated circuits in silicon require waveguiding through a material compatible with silicon very large scale integrated circuit technology. Polycrystalline silicon (poly-Si), with a high index of refraction compared to SiO2 and air, is an ideal candidate for use in silicon optical interconnect technology. In spite of its advantages, the biggest hurdle to overcome in this technology is that losses of 350 dB/cm have been measured in as-deposited bulk poly-Si structures, as against 1 dB/cm losses measured in waveguides fabricated in crystalline silicon. We report methods for reducing scattering and absorption, which are the main sources of losses in this system. To reduce surface scattering losses we fabricate waveguides in smooth recrystallized amorphous silicon and chemomechanically polished poly-Si, both of which reduce losses by about 40 dB/cm. Atomic force microscopy and spectrophotometry studies are used to monitor surface roughness, which was reduced from an rms value of 19–20 nm down to about 4–6 nm. Bulk absorption/scattering losses can depend on size, structure, and quality of grains and grain boundaries which we investigate by means of transmission electron microscopy. Although the lowest temperature deposition has twice as large a grain size as the highest temperature deposition, the losses appear to not be greatly dependent on grain size in the 0.1–0.4 μm range. Additionally, absorption/scattering at dangling bonds is investigated before and after a low temperature electron-cyclotron resonance hydrogenation step. After hydrogenation, we obtain the lowest reported poly-Si loss values at λ=1.54 μm of about 15 dB/cm. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363686
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  • 5
    Electronic Resource
    Electronic Resource
    Intermolecular vibrations of naphthalene trimer by ionization-detected stimulated Raman spectroscopy (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11264-11276 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present nonlinear Raman spectra of intermolecular vibrational transitions in four naphthalene trimer isotopomers. The spectra, measured at 0.03 cm−1 by mass-selective ionization-loss stimulated Raman spectroscopy, reveal distinctly shaped pendular band contours, which, upon comparison to simulated pendular contours, lead to ready assignments for almost all of the observed bands. The results show clearly that the trimer has C3h (or very nearly C3h) symmetry with the naphthalenes arranged such that their long axes are parallel to one another. Comparison of the experimental results to the results of calculations of naphthalene-trimer intermolecular spectra performed by assuming harmonic intermolecular modes and by taking the intermolecular potential energy surface to be a pair-wise additive one reveals significant qualitative agreement. This agreement strongly suggests a relatively rigid cluster with no large amplitude intermolecular motions within 100 cm−1 of the zero-point level. Finally, the results highlight the dominance of librational motions in giving rise to scattering intensity in the intermolecular portion of the cluster's Raman spectrum. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479067
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  • 6
    Electronic Resource
    Electronic Resource
    Structure sensitivity of methane dissociation on palladium single crystal surfaces (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 4033-4043 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Palladium single crystals have been found to be active for the C–H bond dissociation of methane in the temperature range 400–600 K, and the activities of the presently investigated Pd(111) and Pd(311) surfaces are compared with previously studied Pd(679). Structure sensitivity is reported that spans an order of magnitude in terms of the rates in the order Pd(111)〈Pd(311)〈Pd(679), while the effective activation energies range from 32–34 kJ/mol for Pd(111) and Pd(311) to 44 kJ/mol for Pd(679). These data are analyzed with a model that involves unsymmetrical barriers, first by constructing a potential-energy surface for Pd(111), in which the reaction pathway is well-simulated by the Eckart barrier. The Eckart barrier is then shown to obey exactly the Marcus rule for exothermic or endothermic processes. This property is used in comparing the H–CH3 dissociation on the different crystal faces, with the result that the Pd(679) surface provides a driving force of some 26 kJ/mol due to the role of defects compared to smooth planar Pd(111) surface and 22 kJ/mol compared to the Pd(311) surface. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474759
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  • 7
    Electronic Resource
    Electronic Resource
    Hyperfine selectivity using multiquantum electron–nuclear–electron triple resonance (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 9644-9646 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Hyperfine selectivity is demonstrated in a continuous wave electron–nuclear double resonance (ENDOR) experiment. A multiquantum electron–electron double resonance (ELDOR) signal is monitored as a function of the nuclear radio frequency. The signs and relative intensities of the ENDOR lines permit separating the case where both ELDOR and ENDOR frequencies match hyperfine couplings from the cases where this condition is not satisfied. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471671
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  • 8
    Electronic Resource
    Electronic Resource
    The X-valley transport in GaAs/AlAs triple barrier structures (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 5199-5201 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron transport through the X valley of GaAs/AlAs triple-barrier structures (TBS) grown by molecular-beam epitaxy has been studied. Negative differential resistance is observed at 77 K in one type of TBS and is identified as the result of electron transport through both the Γ and X valleys of TBS. In another type of TBS, resonant tunneling through the X valley of GaAs/AlAs TBS is observed. The Γ and X energy-band profiles under bias have been calculated in order to identify the observed features.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343151
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  • 9
    Electronic Resource
    Electronic Resource
    Fast-responding thermionic chlorine analyzer for respiratory applications (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 3978-3983 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: To noninvasively determine the distribution of inhaled air pollutants in the intact human respiratory tract, a gas analyzer with a fast dynamic performance, small sampling flow, and high sensitivity is required. Such an analyzer was developed for chlorine (Cl2) by utilizing a commercially available transducer consisting of a thermionic catalytic source and a metallic collector. Operation of the transducer at 600–800 °C, an absolute pressure of 120 Torr, and a sampling flow rate of 0.6 l/min resulted in a sensitivity of 3–5 pA/ppm Cl2, a minimum detection limit of 0.04 ppm, a response time of less than 100 ms, and signal-to-noise ratios of approximately 10 and 40 at Cl2 mole fractions of 0.1 and 1.0 ppm, respectively. The calibration was linear in the range of 0.3 to 4.0 ppm Cl2 and insensitive to variations in temperature, CO2 content, and humidity which exist in respired air during a breathing cycle. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149208
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  • 10
    Electronic Resource
    Electronic Resource
    Bimodal loop-gap resonator (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1896-1904 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A bimodal loop-gap resonator for use in electron paramagnetic resonance (EPR) spectroscopy at S band is described. It consists of two identical one-loop–one-gap resonators in coaxial juxtaposition. In one mode, the currents in the two loops are parallel and in the other antiparallel. By introducing additional capacitors between the loops, the frequencies of the two modes can be made to coincide. Details are given concerning variable coupling to each mode, tuning of the resonant frequency of one mode to that of the other, and adjustment of the isolation between modes. An equivalent circuit is given and network analysis carried out both experimentally and theoretically. EPR applications are described including (a) probing of the field distributions with DPPH, (b) continuous wave (cw) EPR with a spin-label line sample, (c) cw electron–electron double resonance (ELDOR), (d) modulation of saturation, and (e) saturation-recovery (SR) EPR. Bloch induction experiments can be performed when the sample extends half way through the structure, but microwave signals induced by Mx and My components of magnetization cancel when it extends completely through. This latter situation is particularly favorable for SR, modulation of saturation, and ELDOR experiments, which depend on observing Mz indirectly using a second weak observing microwave source. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147001
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