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  • 1
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    Molecular hydrogen messengers can lead to structural infidelity: A cautionary tale of protonated glycine (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-09-15
    Description: The effects of tagging protonated glycine with either He or between 1 and 14 H 2 molecules on the infrared photodissociation spectra and the ion structure were investigated. Differences in the IR spectra with either a single He atom or H 2 molecule attached indicate that even a single H 2 molecule can affect the frequencies of some vibrational bands of this simple ion. The protonation site is the preferred location of the tag with He and with up to two H 2 molecules, but evidence for H 2 attachment to the hydrogen atom of the uncharged carboxylic acid is observed for ions tagged with three or more H 2 molecules. This results in a 55 cm −1 red shift in the carboxylic acid OH stretch, and evidence for some structural isomers where the hydrogen bond between the protonated nitrogen and the carbonyl oxygen is partially broken; as a result H 2 molecules attached to this site are observed. These results are supported by theory, which indicates that H 2 molecules can effectively break this weak hydrogen bond with three or more H 2 molecules. These results indicate that large spectral shifts as a result of H 2 molecules attaching to sites remote from the charge can occur and affect stretching frequencies as a result of charge transfer, and that tagging with multiple H 2 molecules can change the structure of the ion itself.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    The late time structure of high density contrast, single mode Richtmyer-Meshkov flow (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-07-23
    Description: We study the late time flow structure of Richtmyer-Meshkov instability. Recent numerical work [F. J. Cherne et al. “On shock driven jetting of liquid from non-sinusoidal surfaces into a vacuum,” J. Appl. Phys. 118 , 185901 (2015)] has suggested a self-similar collapse of the development of this instability at late times, independent of the initial surface profile. Using the form of collapse suggested, we derive an analytic expression for the mass-velocity relation in the spikes, and a global theory for the late time flow structure. We compare these results with fluid dynamical simulation.
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Concentration, chemical bonding, and etching behavior of P and N at the SiO2/SiC(0001) interface (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-12-18
    Description: Phosphorous and nitrogen are electrically active species at the SiO 2 /SiC interface in SiC MOSFETs. We compare the concentration, chemical bonding, and etching behavior of P and N at the SiO 2 /SiC(0001) interface using photoemission, ion scattering, and secondary ion mass spectrometry. Both interfacial P and N are found to be resistant to buffered HF solution etching at the SiO 2 /SiC(0001) interface while both are completely removed from the SiO 2 /Si interface. The medium energy ion scattering results of etched phosphosilicate glass/SiC not only provide an accurate coverage but also indicate that both the passivating nitrogen and phosphorus are confined to within 0.5 nm of the interface. Angle resolved photoemission shows that P and N are likely situated in different chemical environments at the interface. We conclude that N is primarily bound to Si atoms at the interface while P is primarily bound to O and possibly to Si or C. Different interface passivating element coverages and bonding configurations on different SiC crystal faces are also discussed. The study provides insights into the mechanisms by which P and N passivate the SiO 2 /SiC(0001) interface and hence improve the performance of SiC MOSFETs.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Dissipation in monotonic and non-monotonic relaxation to equilibrium (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-02-19
    Description: Using molecular dynamics simulations, we study field free relaxation from a non-uniform initial density, monitored using both density distributions and the dissipation function. When this density gradient is applied to colour labelled particles, the density distribution decays to a sine curve of fundamental wavelength, which then decays conformally towards a uniform distribution. For conformal relaxation, the dissipation function is found to decay towards equilibrium monotonically, consistent with the predictions of the relaxation theorem. When the system is initiated with a more dramatic density gradient, applied to all particles, non-conformal relaxation is seen in both the dissipation function and the Fourier components of the density distribution. At times, the system appears to be moving away from a uniform density distribution. In both cases, the dissipation function satisfies the modified second law inequality, and the dissipation theorem is demonstrated.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    Investigating crystalline-polarity-dependent electronic structures of GaN by hard x-ray photoemission and ab-initio calculations (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-10-31
    Description: Crystalline-polarity-dependent electronic structures of gallium nitride (GaN) were studied by photoemission spectroscopy (PES) using soft and hard x-rays with different linear polarizations. A peak located near the valence band (VB) maximum was enhanced for a (0001) surface compared with that for a ( 000 1 ¯ ) surface regardless of photon energy. Comparison of the VB density of states obtained by ab-initio calculations with the observed VB-PES spectra indicates that the crystalline-polarity dependence is associated with the Ga 4 p and N 2 p states. The most plausible origin of the crystalline-polarity-dependent VB feature is based on the photoemission phenomena of electrons in the p z -orbitals due to spontaneous electric polarization along the c -axis of GaN.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 6
    Electronic Resource
    Electronic Resource
    Dynamics of surface-aligned photochemistry (theory). I. Trajectory study of H&drarr;+BrH'(ad) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3363-3371 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The displacement reaction H↘+BrH'(ad)→HBr(g)+H' resulting from the photoinduced interaction of adsorbed HBr molecules on a LiF(001) substrate has been modeled by a quasiclassical trajectory (QCT) calculation. This process constitutes "surface-aligned photoreaction'' (PRXN) in which atomic H↘ photoejected from HBr(ad) approaches an adjacent HBr(ad) with a restricted range of impact parameters b in either linear or bent (90°) configurations. The surface alignment (whether linear or bent) was found to eliminate the reaction pathway to yield H2 product, of major importance in the gas. Product HBr energy and angular distributions, as well as excitation functions Pr(ET), were obtained for each geometry at initial relative translational energies ET spanning 8–40 kcal mol−1. These distribution functions were compared to the gas. For both PRXN variants, linear or bent, reaction occurred with high probability, Pr(ET) rising sharply in each case from threshold to unity within a narrow range of ET. By contrast, Pr(ET) for the gas was broader and smaller. Product (HBr) vibrational excitation for PRXN exceeded that for gas-phase reaction; linear PRXN showed the greatest enhancement. Product rotational distributions were substantially narrower than for the gas-phase reaction, with P(J') for bent PRXN exhibiting bimodality attributable to the occurrence of reaction with either positive or negative impact parameters. The computed HBr angular distributions from PRXN were markedly narrower than for the gas-phase reaction, and were specific to the reagent configuration (linear or bent). The existence of a reference plane in PRXN (the crystal surface) governing the plane of reaction, has the consequence that product angular distributions with respect to each polar angle Pr(θ's) and Pr(φs), embody information concerning the reaction dynamics. It is evident that PRXN by restricting reagent parameters renders product attributes more informative.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453931
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  • 7
    Electronic Resource
    Electronic Resource
    Structure of adsorbates on alkali halides (theory). I. HBr on LiF(001) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 978-996 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a first computation of the geometry of HBr adsorbed on a LiF(001) substrate. The interaction energy of 200 HBr molecules with periodic boundary conditions was determined with respect to adsorbate–substrate and adsorbate–adsorbate electrostatic interaction (point charges in HBr simulated its dipole and multipoles) as well as a short-range "core'' potential (comprising dispersion forces and repulsive overlap). The monolayer heat of adsorption at T=100 K according to this model was 0. 27 eV, which was also the experimental value [E. B. D. Bourdon, et al., J. Chem. Phys. (submitted)]. The major contribution to this energy came from electrostatic binding. The preferred HBr location at all surface coverages (0.25, 0.50, and 1.0 ML) in the temperature range T=70–130 K was with Br over Li+ and H almost eclipsing one of the four neighboring F−. In this configuration, Br–H is tilted down by 23 ° from the crystal plane in an arrangement resembling a Br–H– –F− hydrogen bond. This computed geometry agrees well with recent experimental findings for HBr/LiF(001) using polarized infrared spectroscopy [P. M. Blass et al.; J. Chem. Phys. (submitted)], and is also in qualitative accord with the observed angular distribution of fast H from the photolysis of HBr adsorbed on LiF(001). At the separations dictated by the LiF(001) lattice, the net adsorbate–adsorbate interaction is attractive, leading to a tentative prediction of island formation at lower coverages under equilibrium conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459937
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  • 8
    Electronic Resource
    Electronic Resource
    Optical characterization of GaAs pyramid microstructures formed by molecular beam epitaxial regrowth on pre-patterned substrates (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 475-480 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Arrays of GaAs pyramids with square (001) bases of length 1–5 μm have been fabricated by molecular beam epitaxy regrowth on pre-patterned GaAs (001) substrates. The optical properties of the pyramid faces have been studied by microreflection and microtransmission imaging measurements with light (λ=900–1000 nm) incident through the pyramid base. Digitized charge coupled device images indicate that total internal reflection occurs at the {110} pyramid facets and that their reflectivities are greater than 80%, provided overgrowth of the facets does not occur. These properties suggest that such structures may be suitable as the top mirror in novel micron-scale vertical microcavity devices. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1376419
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  • 9
    Electronic Resource
    Electronic Resource
    Chemical vapor deposition of CoGa and PtGa2 thin films from mixed-metalorganometallic compounds (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2760-2762 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new process for deposition of thin metal films from organometallic precursors of limited volatility has been demonstrated. Short path vapor transport of the complexes dichloro(tetracarbonylcobalt)gallium(III) tetrahydrofuranate, (CO)4CoGaCl2(THF), or platinum(bis-dimethylglyoximato)(bis-dimethylgallium), Pt{(N2C2(CH3)2O2)(GaMe2)}2, each under a stream of hydrogen, leads to the films of the intermetallic compounds CoGa and PtGa2, respectively, on substrates such as Si (100) wafer or a glass slide at 500 °C. The compounds were identified and characterized by x-ray diffraction, Auger electron and x-ray photoelectron spectroscopies. The films are crystalline and highly reflective. The CoGa film is single phased; the PtGa2 film shows a minor constituent of Pt2Ga3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102370
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  • 10
    Electronic Resource
    Electronic Resource
    Effects of surface treatments on Schottky barrier formation at metal/n-type CdTe contacts (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 137-139 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nature of n-CdTe surfaces prepared by various chemical treatments has been studied by x-ray photoelectron spectroscopy. In parallel experiments Schottky barrier heights have been measured for Sb and Au contacts deposited on surfaces prepared in an identical manner. Reducing etches are found to leave the surface rich in Cd, and for these surfaces Sb and Au always produce barrier heights of 0.93±0.02 eV. Bromine in methanol solutions leaves the surface rich in Te and gives rise to two valued barrier heights of 0.93 and 0.72 eV. It is found that the probability of generating contacts with the higher value of barrier height increases as the surface becomes richer in Cd.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101208
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