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  • 1
    Electronic Resource
    Electronic Resource
    Diffusion-induced defects in GaAs by zinc and the effects of post-diffusion anneal (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3494-3502 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The crystallographic defects generated during the diffusion of zinc into GaAs have been studied using transmission electron microscopy and chemical etching techniques. By observing the effects of arsenic pressure on the defect density and the zinc penetration, the annihilation of the diffusion-induced defects in relation to the surface stoichiometry was investigated. It was found that the dissolution of the defects within the crystal is mainly caused by the out-diffusion of the diffusion-induced Ga interstitials to the surface. This is also supported by results obtained from post-diffusion annealing of the samples under different arsenic pressures. In addition, the possible inclusion of arsenic atoms in the interstitial dislocation loops found in GaAs is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348490
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  • 2
    Electronic Resource
    Electronic Resource
    Role of point defects in the silicon diffusion in GaAs and Al0.3Ga0.7As and in the related superlattice disordering (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2225-2237 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanism of silicon diffusion in GaAs, Al0.3Ga0.7As, and the silicon diffusion-induced layer disordering of multiquantum wells have been studied by photoluminescence, secondary-ion-mass spectroscopy, and transmission electron microscopy across a corner of a wedge-shaped sample. The diffusion source was a grown in highly Si-doped layer. The main photoluminescence properties of point defects in GaAs and Al0.3Ga0.7As are reviewed to interpret the experimental data. The depth profile of the photoluminescence allows the spatial correlation between the luminescence spectra and the Si concentration profile obtained from secondary-ion-mass-spectroscopy measurements. On the basis of the photoluminescence results, the physical processes occurring during the Si diffusion are discussed. Frenkel defects (pairs of element-III vacancies and interstitials) are generated in the highly Si-doped region. The element-III interstitials rapidly diffuse towards the surface where they react with the element-III vacancies generated at the surface when annealing is performed in an external As pressure. This induces a supersaturation of element-III vacancies in the Si-doped region which drives the Si diffusion. Annealing in vacuum reduces the oversaturation of element-III vacancies and, hence, reduces the Si diffusion. A domination of the Si donor–element-III vacancy complex emission band was found in the spectra taken in the Si-diffused region. This gives evidence for the vacancy-assisted mechanism in the Si diffusion and in the impurity-induced disordering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351120
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  • 3
    Electronic Resource
    Electronic Resource
    Photoreaction dynamics of CO oxidation on Pt(111) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6307-6310 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of the surface aligned photoreaction between submonolayers of O2 and CO coadsorbed on a Pt(111) surface at 25 K and laser irradiated at 308 nm are explored by measurement of angle-resolved translational energy distributions for the CO2 photoproduct.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462621
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  • 4
    Electronic Resource
    Electronic Resource
    Photoinduced dissociative electron attachment of CH3Br on Pt(111): The role of the local work function (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 9114-9121 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoinduced dissociative electron attachment of CH3Br on Pt(111) has been examined by measuring CH3 photofragment translational energy distributions from CH3Br adsorbed on Xe multilayers deposited upon CH3Br covered Pt(111). Subvacuum level, photoexcited substrate electrons produced by 308 nm laser irradiation were found to propagate through the Xe layer where attachment to CH3Br led to fragmentation. A simple model for surface dissociative electron attachment, DEA, was found to quantitatively predict the observed fragmentation dynamics for the CH3Br/Xe/CH3Br/Pt(111) system. The role of the local work function in surface DEA processes was explored by examining the dependence of the photofragment yield upon the thickness of the intermediate Xe layer and the fractional coverage of the Pt(111) bound first layer of CH3Br. Three dimensional variation of the local work function above the substrate was required to account for the observed DEA dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462220
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  • 5
    Electronic Resource
    Electronic Resource
    Photofragmentation dynamics of submonolayers of CH3Br adsorbed on Pt(111) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3957-3965 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Angle-resolved, photofragment translational energy distributions, Pcursive-theta(ET)s, arising from 308 nm laser irradiation of CH3Br adsorbed on Pt(111) are presented. Methyl photofragments were observed with translational energies extending to 2 eV and with Pcursive-theta(ET)s which varied sharply with angle of exit from the surface. The fragmentation dynamics were consistent with a mechanism of dissociative electron attachment of subvacuum level, photoexcited substrate electrons to adsorbed CH3Br. The CH3 Pcursive-theta(ET)s and the angular variation of the CH3 yield gave evidence that submonolayers of CH3Br form islands on Pt(111).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461898
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  • 6
    Electronic Resource
    Electronic Resource
    Photochemical hydrogenation of methyl radicals on Pt(111) (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5971-5973 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Submonolayers of methyl bromide and hydrogen were coadsorbed on a 25 K Pt(111) surface and laser irradiated at 308 nm. Photoinduced dissociative electron attachment of methyl bromide produced energetic methyl radicals that reacted with hydrogen to form methane. The photoreaction dynamics is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464856
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  • 7
    Electronic Resource
    Electronic Resource
    Annealing effects on Si-doped GaAs grown on high-index planes by molecular-beam epitaxy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3151-3157 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A photoluminescence study of the effects of annealing on Si-doped (∼1016 cm−3) GaAs grown on (311)A-, (111)A-, (111)B-, and (100)-oriented substrates by molecular-beam epitaxy has been performed. The anneal temperatures were 873, 973, and 1098 K. All the anneals were of 24 h duration. Detailed assessment of the low-temperature photoluminescence spectra suggests that site switching (Si switching from Ga site to As site) only occurs in the n-type samples [(100) and (111)B samples] and not in the p-type ones [(111)A and (311)A samples].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356994
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  • 8
    Electronic Resource
    Electronic Resource
    A statistical model for activated dissociative adsorption: Application to methane dissociation on Pt(111) (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 1564-1581 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A statistical model of activated dissociative adsorption is developed using microcanonical, unimolecular rate theory. Dissociation is treated as occurring through energy randomizing collisions between incident molecules and local clusters of surface atoms. The predictions of the statistical model are found to be in remarkable accord with existent experimental data for methane dissociative adsorption and the thermal hydrogenation of methyl radicals on Pt(111). Perhaps surprisingly, the "over the barrer'' statistical model adequately describes the known kinetics of these reactions without any explicit provision for quantum tunneling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468476
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  • 9
    Electronic Resource
    Electronic Resource
    Single hop diffusion of CO from bridge to top sites on Pt(111) (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 1730-1733 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The isothermal kinetics of single hop diffusion of CO from bridge sites to top sites of Pt(111) have been examined by reflection absorption infrared spectroscopy over the temperature range from 37–42 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468435
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  • 10
    Electronic Resource
    Electronic Resource
    Small-angle X-ray scattering in carbon fibers (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 627-636 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small-angle X-ray scattering (SAXS) has been used as an analytical tool to study microporosity in polyacrylonitrile- (PAN-) and pitch-based carbon fibers. Microporosity in carbon fibers consists primarily of needle-shaped voids whose long axes are oriented preferentially along the fiber axis. This preferred orientation is seen to be independent of the nature of the fiber precursor and is the major deciding factor in controlling the modulus of carbon fibers. As the modulus increases, the general trend for both PAN- and pitch-based fibers is to move from a system consisting of many small pores to one with few larger pores. At very small angles, the steep rise in scattered intensity is due to reflection effects for PAN-based fibers and multiple scattering effects from voids for pitch-based fibers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188989400227X
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