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  • 1
    Electronic Resource
    Electronic Resource
    Fluorescence studies of the vacuum ultraviolet, synchrotron radiation-induced photochemistry of polystyrene (1993)
    s.l. : American Chemical Society
    Macromolecules 26 (1993), S. 3262-3266 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00065a003
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  • 2
    Electronic Resource
    Electronic Resource
    Production of excited neutral and ionic photofragments following core-level excitation in molecules (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 5196-5200 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed the first experiments to examine the neutral fragmentation paths following direct core-level excitation in a molecule. Using monochromatized synchrotron radiation in the range 100–140 eV, we have monitored the dispersed UV/optical fluorescence resulting from excitation of a Si 2p electron in SiF4. The main features in the fluorescence spectrum have been identified as emission from the SiF+4 D state and from excited SiF, Si, F, and Si+. Features in the fluorescence excitation spectra are assigned to excitation of a Si 2p electron to unoccupied valence orbitals, Rydberg orbitals, and shape resonances. There is a large enhancement in the yield of excited-state fragments following core-to-Rydberg excitation, which is due to the greater probability of the core-excited Rydberg state decaying, via a resonant Auger process, to highly excited, unbound states of SiF+4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458554
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  • 3
    Electronic Resource
    Electronic Resource
    The soft x-ray photochemistry of physisorbed SiF4. II. Mechanisms and kinetics (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 10366-10377 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an analysis of the extensive photolysis of an adsorbate resulting from adsorbate core-level excitation. The system studied was SiF4 adsorbed on Ge(100) at 30 K. Photolysis fragments and molecular species (identified with Si 2p soft x-ray photoemission spectroscopy) were measured as a function of monochromatic (140-eV) photon exposure and adsorbate coverage. The photolysis cross sections for 55–140-eV photons were determined and the neutral photon-stimulated desorption cross section for a selected SiF4 excitation is also presented. In the Si 2p absorption region, it was found that the photolysis cross section was one to three times the preedge value and comparable in magnitude to that of gas phase photoabsorption, while the total yield increased at most by a factor of 1.4. Both of these observations indicate that direct core excitation of the adsorbate is a major path by which photolysis occurs as opposed to an indirect, substrate-driven one. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470703
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  • 4
    Electronic Resource
    Electronic Resource
    The soft x-ray photochemistry of physisorbed SiF4. I. Reactions of the molecular species through desorption and dissociation (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 10356-10365 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present evidence that demonstrates photolysis of SiF4 adsorbed on Ge(100) at 30 K. Silicon 2p soft x-ray photoemission spectroscopy (PES) indicates that upon irradiation, the molecularly adsorbed SiF4 dissociates into SiFn species (where n=0,1,2,3) and desorbs as molecular SiF4. Also, the Si 2p PES from undissociated molecules exhibits a number of distinct kinetic-energy shifts. These are attributed to anisotropic adsorption in which different molecular sites have different apparent Si 2p binding energies. A structure of the adsorbate layer is proposed to account for the varying core hole screening. Examination of the gas phase during irradiation confirms molecular desorption and shows the system to have a significant neutral molecular desorption yield. Changes in the valence-level photoemission structure and signal intensity are consistent with the observed fragmentation and desorption, both of which lead to disappearance of the molecularly adsorbed species. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469873
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  • 5
    Electronic Resource
    Electronic Resource
    Observations on the surface and bulk luminescence of porous silicon (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6335-6340 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using the x-ray excited optical luminescence technique, we have investigated the soft x-ray induced photoluminescence of porous silicon in the optical region (200–900 nm) and the Si K-edge x-ray absorption fine structures of porous silicon in the near edge region. It is found that while porous silicon prepared at low current density (20 mA/cm2 for 20 min) exhibits a single broad luminescence band, porous silicon prepared at high current density (200 mA/cm2 for 20 min) exhibits three optical luminescence channels; i.e., in addition to the broad peak characteristic of all porous silicon, there are at least two additional optical luminescence channels at shorter wavelengths, one with modest intensity at ∼460 nm and the other a weak and very broad peak at ∼350 nm. These optical channels have been used to monitor the Si K-edge absorption of porous silicon in the near edge structure region. Analysis of the data shows that while the band at ∼627.5 nm corresponds to the bulk emission, the other channels are of a surface origin. These observations and their implications are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355156
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  • 6
    Electronic Resource
    Electronic Resource
    Synchrotron radiation studies of diamond nucleation and growth on Si (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5481-5491 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Valence-band as well as Si(2p) and C(1s) core-level photoemission, Auger, and near-edge x-ray-absorption fine-structure spectroscopies were used to follow the surface chemistry associated with diamond film deposition with a filament-assisted chemical-vapor-deposition reactor on atomically clean and diamond polished Si(100) and Si(111) surfaces. Raman spectroscopy and atomic force microscopy (AFM) were also used ex situ to characterize the deposited films. Within 3 min of deposition, a carbon-rich SiC layer, at least 13 A(ring) thick, was observed to develop. At early stages of growth (〈10 min of deposition), no differences were observed between the clean and diamond-polished surfaces. With additional deposition, a 20–30-A(ring)-thick amorphous carbon overlayer was deposited on the clean Si surfaces: The amorphous carbon layer did not promote diamond nucleation. Deposition of an a-C:H layer on top of the amorphous carbon layer also did not promote diamond nucleation. In contrast, ∼500 A(ring) diamond films were deposited within 45–60 min on the diamond-polished surfaces. Two types of nuclei were observed following 20 min of deposition by atomic force microscopy: (1) large (200–300 nm in diameter) nuclei, randomly distributed on the surface; and (2) smaller (50–100 nm) nuclei that show a preference for forming along the scratches. Atomic force micrographs of the originally clean surface show the formation of sharp relief structures on the surface. These structures, combined with the amorphous carbon overlayer, may be responsible for the few sites that do nucleate diamond on unpolished Si surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357166
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  • 7
    Electronic Resource
    Electronic Resource
    Chemistry and electronic structure of the H2 plasma passivated surface of CdTe (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1632-1637 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of low energy H2 plasma exposure on the surface defect chemistry and the electronic structure of CdTe were studied by synchrotron radiation soft x-ray photoemission spectroscopy and optical emission spectroscopy as a function of substrate temperature. The low energy H2 plasma was generated with a commercial electron cyclotron resonance plasma source using pure H2 with the plasma exposure being performed at ambient temperature, 100 °C, and 200 °C. Plasma species were identified with optical emission spectroscopy. In situ photoemission measurements were acquired after each plasma exposure in order to observe changes in the valence band electronic structure as well as changes in the Cd 4d and Te 4d core lines. The results were correlated in order to relate the plasma species and characteristics to changes in surface defect chemistry and electronic structure. These measurements indicate that the H2 plasma exposure type converts the CdTe(100) surface from p- to n-type and passivates defect states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356376
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  • 8
    Electronic Resource
    Electronic Resource
    Synchrotron-radiation-induced deposition of boron and boron carbide films from boranes and carboranes: Decaborane (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4103-4109 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Boron has been deposited successfully on Si(111) from the synchrotron-radiation-induced decomposition of decaborane (14), i.e., B10H14. The rate of deposition is limited by the adsorption rate of decaborane (14) on the surface. In addition there is some indication that there is an activation barrier to dissociative adsorption. The synchrotron-radiation- induced growth rate of boron thin films from decaborane (14) is linear with coverage for a large range of thickness, suggesting a constant sticking coefficient for decaborane adsorption at room temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348422
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  • 9
    Electronic Resource
    Electronic Resource
    Continuum channel coupling of shape resonances in N2 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2740-2744 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured vibrational branching ratios for 2σ−1u photoionization of N2 in an effort to elucidate fundamental aspects of continuum channel coupling. Calculations have shown that photoejection of a 2σu electron from N2 should be influenced by a shape resonance in the 3σg →εσu photoionization channel and that this continuum channel coupling can result in deviations from Franck–Condon behavior for the resulting N+2(B 2Σ+u) ion. In the present study, the N2 molecules are ionized by monochromatic synchrotron radiation (25〈hν〈55 eV) and dispersed fluorescence is measured to determine the vibrational branching ratios v'=1/v'=0 and v'=2/v'=0 for the N+2(B 2Σ+u) state. The observed branching ratios are enhanced at hν≈30 eV and we attribute this Franck–Condon breakdown to continuum coupling between the 2σ−1u and 3σ−1g ionization channels. However, our results exhibit significant discrepancies with theory. The areas of agreement and disagreement suggest useful avenues of further study to clarify the nature of continuum channel coupling in molecular photoionization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462022
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  • 10
    Electronic Resource
    Electronic Resource
    Vibrationally resolved shape resonant photoionization of SiF4 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 23-27 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured vibrationally resolved fluorescence from SiF+4(D˜ 2A1) photoions to determine the vibrational branching ratio σ[v=(1,0,0,0)]/σ[v=(0,0,0,0)] in the excitation energy range 22〈hν〈70 eV. The branching ratio shows pronounced enhancements at hν=25 and 45 eV. The deviation from Franck–Condon behavior at higher energy (hν=45 eV) is attributed to a shape resonance and it appears that a shape resonance is also responsible for the lower energy feature (hν=25 eV). However, the present results in this lower energy region conflict with interpretations of previous vibrationally unresolved work. Applications of these results to general problems in polyatomic photoionization are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462511
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