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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Selective area, synchrotron radiation induced, delta doping of silicon (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4795-4798 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used broadband synchrotron radiation to induce selective area surface doping of boron into silicon. The source of the boron was nido-decaborane (B10H14) adsorbed on Si(111) at 100 K. Irradiation caused decomposition of the adsorbed molecule which lead to an enhanced concentration of free boron in the irradiated area. Using Si 2p core level photoelectron spectroscopy, the surface chemical composition and Fermi level position in both the irradiated and unirradiated regions were determined. The downward movement of the Fermi level was greater in the irradiated region than in the unirradiated region, and greater for n-type than for p-type Si.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350619
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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    X-ray fluorescence detection of low-Z elements using a microchannel plate detector (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2193-2194 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We demonstrate the utility of a simple, inexpensive, microchannel plate (MCP) detector for monitoring the x-ray fluorescence (XRF) yield in the soft x-ray region. The detector consists of a dual MCP array, and appropriately biased grids. We compare the Al 2p XRF yield to the total-electron yield (TEY) (obtained with the same detector) of single-crystal sapphire. These measurements show that the XRF yield has the following advantages over TEY for monitoring absorption spectra in the soft x-ray region: (1) a greater bulk sensitivity, (2) an insensitivity to charging.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143137
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  • 8
    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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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Selective area deposition of boron on Si(111) induced by synchrotron radiation (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 607-609 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed the first deposition of boron on Si(111) induced by broadband synchrotron radiation (SR). Contamination-free thin films were grown at room temperature using decaborane (B10H14) as the source gas. After deposition the films were examined using photoelectron microscopy, which showed that film growth was limited to the region illuminated by SR. The temperature of the substrate rose less than 10 K. These results indicate that gas-phase excitations are not important and that the films are deposited by a nonthermal, photoinduced mechanism. Masked exposures demonstrate the potential of this technique for patterned deposition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104571
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