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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6129-6135 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An ESR investigation is reported of oxygen radicals formed by UV radiation of silica gel surfaces in the presence of O2. The species O−2 and O−3 are identified. The O−2 radical shows a temperature dependent signal shape between −196 and 25 °C which is interpreted in terms of Brownian rotational surface diffusion about an axis perpendicular to the O–O bond and to the surface. Correlation times for surface diffusion are estimated from comparison of observed and computer simulated spectra, and an activation energy for surface diffusion of 2.4±0.8 kJ mol−1 calculated. Comparison with previously reported spectra for W/SiO2 and Ti/SiO2 surfaces indicates that the mobile O−2 species formed in all three systems must be located on the SiO2 support, and that the mobility is due to the absence of strong interaction with transition metal sites.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 2949-2960 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A particle-level simulation method is employed to study the dynamics of flowing suspensions of rigid and flexible fibers. Fibers are modeled as chains of prolate spheroids connected through ball and socket joints. By varying the resistance in the joints, both flexible and rigid fibers can be modeled. Repulsive interactions between fibers are included, but hydrodynamic interactions and particle inertia are neglected in this implementation. The motion of a fiber is determined by solving the translational and rotational equations of motion for each spheroid. Simulations of isolated fibers in shear flow demonstrate that the method can reproduce known dynamical behavior of both rigid and flexible fibers. The transient behavior in the suspension relative viscosity under simple shear flow was also investigated. An oscillatory response similar to the experimental observations of Ivanov et al. was obtained for rigid fibers. Fiber flexibility reduced the period of oscillation, but had little effect on steady-state viscosities. These results verify that rigid and flexible fibers can be modeled with linked rigid prolate spheroids. Modeling fibers with fewer elongated bodies, as opposed to many spheres, significantly reduces computation time and facilitates the study of suspensions of many interacting, long fibers. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5936-5941 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this work, the influence of surrounding ambient atmosphere on the stability of electroluminescent (EL) porous Si (PS) diodes is examined. We have fabricated electroluminescent porous Si layers from anodic oxidation of (1) epitaxially grown p-type layers on n-type Si substrates; (2) n-type substrates with Au/Pd contacts; (3) p-type substrates with Au/Pd contacts. These structures are characterized using photoluminescence (PL), EL, and infrared (IR) spectroscopies, as well as scanning electron microscopy (SEM). In the case of the porous Si structures fabricated from p-n junctions, such structures yield orange emission with maxima near 620 nm upon the application of moderate applied voltages (3–7 V). For each type of diode, it is found that in strong oxidizing environments, EL intensity degrades completely within 30 min; in contrast, the integrated intensity remains essentially unchanged in the same time frame in the presence of a vigorous flow of inert gases such as nitrogen and argon. Infrared spectroscopic studies strongly suggest that electroluminescence degradation is related to porous silicon surface oxidation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3416-3418 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this work, we report a method for the incorporation of rare-earth oxides onto silicon surfaces. This process uses a high-energy dc spark to convert salts of rare-earth ions such as europium and erbium to the corresponding oxide phase(s) with concomitant formation of a porous layer. Scanning electron micrographs of the silicon substrate show an irregular, pitted surface morphology for those areas exposed to spark processing. Photoluminescence, infrared spectroscopy, and electron microscopy of the spark-processed regions of the Si substrate are clearly consistent with the formation of the desired luminescent oxide phase. © 1996 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3851-3853 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a method of semiconductor nanostructure fabrication relying on the size and shape of a polynucleotide to dictate the overall structure of an assembly of individual nanoparticles. This is exemplified by our use of the 3455-basepair circular plasmid DNA molecule pUCLeu4 which, when anchored to a suitably derivatized substrate, yields an array of semiconductor nanoparticles matching the shape of the biopolymer stabilizer. The viability of the methodology was confirmed using data from high resolution transmission electron microscopy, selected area electron diffraction, and linear optical absorption spectroscopy. This is a unique demonstration of the self-assembly of mesoscale semiconductor nanostructures using biological macromolecules as templates. © 1996 American Institute of Physics.
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