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  • 1
    Electronic Resource
    Electronic Resource
    Lattice position of Si in GaAs determined by x-ray standing wave measurements (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 8161-8168 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The x-ray standing wave (XSW) technique was applied to determine the lattice location of Si impurity atoms in GaAs(100) crystals. The synchrotron radiation of X24A at the national synchrotron light source was utilized to set up backreflection XSW, an experimental geometry which drastically relaxes the otherwise stringent requirement on the lattice perfection. Specifically, the lattice sites were determined with respect to the [311] reflection planes which differentiate a Ga site from an As site. With the aid of an appropriate choice of the x-ray fluorescence filter, we were able to study GaAs(100) samples with very low levels of Si impurities. On a sample doped with 4×1018 cm−3 Si during the molecular-beam epitaxy growth, we found that the Si atoms predominantly occupied the Ga sites. On both an ion-implanted sample after annealing and a sample with Si impurities introduced by thermal diffusion, about 30% of the Si atoms occupied the Ga sites, and the rest occupied random sites. The As site occupation was less than 6%. Suggestions are made for further experiments with improved sensitivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353430
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  • 2
    Electronic Resource
    Electronic Resource
    Vibronic coupling and other many-body effects in the 4σ−1g photoionization channel of CO2 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 949-956 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational branching ratios and photoelectron angular distributions were measured for 4σ−1g photoionization of CO2 in the energy range 20–28 eV. Of particular interest are three vibrational components of the resulting CO+2 C˜ 2Σ+g state—the allowed (000) and (100) bands and the forbidden (101) band. The wavelength dependence of the beta parameter for the forbidden band deviated significantly from that of the two allowed bands, showing instead a strong resemblance to that of the B˜ 2Σ+u state. This behavior suggests that vibronic coupling to the B˜ 2Σ+u state is responsible for the appearance of the forbidden (101) band in the C˜ 2Σ+g state photoelectron spectrum. We also observe evidence for other many-body effects—shape-resonance-induced continuum–continuum coupling and doubly excited autoionizing resonances—in the present data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459985
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  • 3
    Electronic Resource
    Electronic Resource
    Vibrationally resolved photoelectron studies of the 7σ−1 channel in N2O (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1551-1556 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present vibrationally resolved photoelectron studies of the 000, 100, 200, and 001 modes of the A˜ state (7σ−1) of N2 O+ in the 17.4–26 eV photon-energy range. The vibrational branching ratios σ(100)/σ(000) and σ(001)/σ(000) agree very well with fluorescence measurements by Kelly et al. and qualitatively with recent theoretical predictions of Braunstein and McKoy. The large non-Franck–Condon variations in the σ(100)/σ(000) and σ(200)/σ(000) branching ratios are associated with a predicted 7σ→εσ shape resonance near 20 eV. Overall, the vibrational branching ratios imply lower resonant energies for the stretching modes (100 and 200) and a similar resonant energy for the asymmetric stretch (001), compared with the 000 mode. The vibrational asymmetry parameters (β) display a strong variation with energy which is qualitatively reproduced by theory; however, the experimental values for β(100) and β(001) exhibit additional structure around 20 eV. When combined with theory and recent fluorescence data, these results help to demonstrate a correlation of shape resonance energy with overall molecular length (RN–N+RN–O); this important result implies a resonant state which is localized on the entire triatomic molecular frame rather than on the N–N or N–O components.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456098
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  • 4
    Electronic Resource
    Electronic Resource
    Autoionization dynamics in the valence-shell photoionization spectrum of CO (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 812-819 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Autoionizing Rydberg series in the valence-shell spectrum of CO have been studied by determining the high resolution relative photoionization cross section of cooled CO in the energy region 14.0–20.0 eV and by determining the vibrational branching ratios and the photoelectron angular distributions for production of CO+ X 2Σ+, v+=0–2 in the energy region 16.75–18.75 eV. Of particular interest are three prominent spectral features between 17.0 and 17.5 eV that result from interactions involving Rydberg series converging to the excited A 2Π and B 2Σ+ states of the ion. The results are discussed in the context of recent two-step multichannel quantum defect theory calculations by Leyh and Raseev (the following paper).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455204
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  • 5
    Electronic Resource
    Electronic Resource
    Vibrationally resolved shape resonant photoionization of N2O (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1544-1550 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a vibrationally resolved dispersed fluorescence study of 7σ−1 shape resonant photoionization in N2O. Previous work indicates that there are two shape resonances in the εσ channel, and our results demonstrate that the lower energy shape resonance (hνexc≈20 eV) results in non-Franck–Condon vibrational branching ratios over a wide range. Moreover, the cross section curves for alternative vibrational modes behave differently, and we show that the symmetric stretch exerts a greater influence on resonance behavior than the asymmetric stretching vibration. Such comparisons of vibrationally resolved partial cross section curves provide qualitative insights into the shape resonant photoionization dynamics for polyatomic targets. The higher energy shape resonance is apparently masked by the presence of the dominant nonresonant επ channel. In addition to information on the photoionization dynamics, these results also provide spectroscopic data on the ionic potential surfaces. Specifically, we obtain ratios of Franck–Condon factors for N2O+ (A→X) transitions which are useful for testing calculated properties of the ion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456097
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  • 6
    Electronic Resource
    Electronic Resource
    Vibrationally resolved electronic autoionization of core–hole resonances (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4048-4053 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate the dynamics of molecular core–hole decay using dispersed fluorescence from an ionic valence–hole state in N2. A core–hole excited state is created via the N2(1s→1 π*g) transition, and this state electronically autoionizes to the N+2(B 2Σ+u) state. The vibrational branching ratios for the N+2(B 2Σ+u) state are then determined from N+2(B 2Σ+u→X 2Σ+g) fluorescence. Fundamental aspects of core–hole state decay emerge clearly from these measurements. In particular, interference effects due to lifetime broadening of vibrational levels of the core–hole state can be investigated quantitatively using this method. As a result, dispersed fluorescence detection serves as a powerful tool for investigating R-dependent aspects of molecular core–hole resonances. The experimental results do not agree with predictions based on previous theoretical developments, and possible causes for the discrepancy are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454838
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  • 7
    Electronic Resource
    Electronic Resource
    Strain and relaxation in InAs and InGaAs films grown on GaAs(001) (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3010-3012 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The strain and relaxation of InAs and InGaAs films grown on GaAs(001) have been examined by the x-ray standing wave and extended x-ray absorption fine-structure techniques. While 1 monolayer (ML) films of both InAs and InGaAs are found to be tetragonally distorted in accordance with the prediction of macroscopic-elastic theory, thicker InAs films are found to collapse to their natural-lattice constant past a critical thickness Tc, of ∼2 ML's. By 8 ML's, bond-length strain is no longer evident, and a large degree of structural disorder is observed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116680
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  • 8
    Electronic Resource
    Electronic Resource
    Zero kinetic energy proton and deuteron production from photoionization of H2 and D2 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 3912-3916 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A zero ion kinetic energy spectrometer has been developed to study the production of near zero energy protons and deuterons from dissociative photoionization of H2 and D2. Both H+ and D+ spectra show four peaks on top of a continuum. The continuum was found to be in excellent agreement with the single center Coulomb calculation for the direct dissociation through the X 2Σ+g state of H+2. The observed structures were shown to originate from autoionization of the doubly excited Q1 1Σ+g(1), Q1 1Σ+u(1), Q1 1Σ+u(2), and Q2 1Σ+u(1) states, of which the Q1 1Σ+g(1) state is dipole forbidden. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470692
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  • 9
    Electronic Resource
    Electronic Resource
    Resonance structure in the vibrationally resolved photoelectron branching ratios and angular distributions of the 2π−1 channel of NO (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 5125-5130 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report on vibrationally resolved measurements of photoelectron angular distributions and branching ratios for NO+(2π−1)X 1Σ+ using synchrotron radiation over hν=11.5–26 eV. Normally weak vibrational levels are strongly enhanced below 18 eV, and the photoelectron asymmetry parameters and branching ratios display a vibrationally dependent, broad spectral structure over hν(approximately-equal-to)11–18 eV. These observations may reflect the presence of the expected σ shape resonance, however, various interchannel coupling mechanisms may also be involved. Resonance structure in the photoelectron asymmetry parameters is also observed in the hν(approximately-equal-to)19–22 eV region. This structure is likely associated with Rydberg excitations from the 4σ orbital.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453680
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  • 10
    Electronic Resource
    Electronic Resource
    Photoelectron angular distributions from H"2 and D"2
    Amsterdam : Elsevier
    Journal of Electron Spectroscopy and Related Phenomena 26 (1982), S. 43-51 
    Details
    ISSN: 0368-2048
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0368-2048(82)87004-7
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