| Application of a Novel Differential XAFS Approach for Determination of Coordination Geometries |
JAN 97 |
5 pages |
| Authors:
D. E. Ramaker; H. Sambe; X. Qian; W. E. O'Grady; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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 | A novel differential XAFS approach has been developed which allows the determination of small distortions in coordination geometry (distortions in bond lengths and angles) about the absorber. The approach requires taking the difference, delta-X, between the XAFS of the sample and a reference material. The Fourier transform of delta-X directly reveals the average of the altered path lengths between the sample and the reference. More importantly, the amplitude of delta-X ... |
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| The Oxidation State of Ni in the Nickel Oxide Electrode and Related Nickel Oxide Compounds: I. Spectroscopic Evidence |
JAN 97 |
21 pages |
| Authors:
H. Sambe; T. M. Nabi; D. E. Ramaker; A. N. Mansour; W. E. O'Grady; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| The electronic structures of the nickel oxide electrode, NiO(x)(OH) (2-x) for x=0-1.6, and related nickel oxide materials, Li-substituted NiO, Li(y) Ni(2-y)O2 for y=0-1 and 'Ni(4+)' compounds, KNiO2(IO4) and BaNiO3, have been investigated using Ni 2p XPS (X-ray photoemission spectroscopy) and Ni K-edge XAS (X-ray absorption spectroscopy) data. Three aspects of the Ni 2p XPS spectra (the main peak energy, satellite energy separation, and main-line shape) and three aspects of the ... |
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| A NEXAFS Study on the Coordination Geometry of Aluminum in Minerals and Y Zeolite. Comparison of Experiment and Theory |
JAN 97 |
9 pages |
| Authors:
J. A. Van Bokhoven; H. Sambe; D. C. Koningsberger; D. E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| Curved-wave multiple scattering cluster calculations using the FEFF6 code were successfully used to interpret experimental Al K edge NEXAFS spectra of various minerals and Y zeolites. starting about 5 eV above threshold. The Al octahedral, tetrahedral and square planar geometries can be easily distinguished from each other utilizing the NEXAFS data. Semi-empirical molecular orbital calculations were used to interpret the whitelines below 5 eV in the data. A new assignment ... |
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| The Oxidation State of Ni in the Nickel Oxide Electrode and Related Nickel Oxide Compounds: II. Geometric Evidence |
JAN 97 |
30 pages |
| Authors:
H. Sambe; T. M. Nabi; D. E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| The electronic structures of the nickel oxide electrode (NOE), NiOx(OH)(2-x) for x=0-1.6 and the related nickel oxide materials including the NiO- LiNiO2 - NiO2 series and the 'Ni(4+)' compounds, KNiO2(IO4) and BaNiO3, have been investigated utilizing geometric data such as the Ni-OH and Ni-O bond lengths published in the literature. The electronic structures deduced from these bond lengths agree with those found using spectroscopic data, which were presented in the ... |
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| Quantitative Interpretation of K-Edge NEXAFS Data for Various Nickel Hydroxides and the Charged Nickel Electrode |
JAN 96 |
26 pages |
| Authors:
X. Qian; H. Sambe; D. E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| A quantitative interpretation of Ni K-edge NEXAFS data for beta- Ni(OH)2, beta-NiOOH, and BaNiO3, and in situ data for a charged Ni electrode is reported. We have performed curve wave multiple scattering calculations utilizing the FBFF6 code on clusters approximating these materials. These theoretical results reproduce the experimental changes with oxidation remarkably well. Our interpretation of the NEXAFS line shape for the charged electrode indicates that large amounts of Ni+4 ... |
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| Two-Center, Two Electron Excitations Identified in NEXAFS for Solid Ne |
SEP 94 |
12 pages |
| Authors:
H. Sambe; X. Qian; D. E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| Experimental K-edge NEXAFS (near edge X-ray absorption fine structure) data for solid Ne are compared with theoretical results. Seven features in the experimental spectrum that are not reproduced by the theoretical results are found to be attributable to two-electron excitations. Five of them are usual one-center excitations, but the remaining two are found to be novel two-center excitations involving resonant orbitals as opposed to the usual bound orbitals. In contrast, ... |
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| Identification of Resonant, Two-Electron, and Inter-Atomic Features in K and L(sub23) NEXAFS Spectra |
SEP 94 |
9 pages |
| Authors:
H. Sambe; X. Qian; David E. Ramaker; W. E. O'Grady; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| Experimental Cl K NEXAFS spectra for Cl- hydrated in H20, and on passivated Al electrodes (below and above the pitting potential) have widely different spectral line shapes. Experimental K-and L23-edge NEXAFS data for the alkali halides and rare gas solids are compared with FEFF6 calculated results to optimize code input parameters, test code validity, and identify many-body features in these model systems. Differences are shown to arise from many-body shake-up ... |
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| Angle Resolved Auger Electron Spectroscopy: An Alternate Tool for Identifying Electronic Excitation Processes in Solids |
SEP 94 |
13 pages |
| Authors:
David E. Ramaker; R. A. Fry; Y. U. Idzerda; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| Angle resolved Auger electron spectroscopy (ARAES) is shown to be a useful tool for obtaining unique electronic structure information and identifying satellite excitation processes in solids. Although relatively unexplored, ARAES is an attractive tool which may complement the more conventional energy resolved AES. The ARAES method is successful because the diffraction patterns exhibited in ARAES at fixed energy are strongly dependent on the l-wave of the emitted electron and its ... |
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| Similarity Solutions and Numerical Modeling in Buoyancy Controlled Turbulent Diffusion Flames |
03 FEB 94 |
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| Authors:
David E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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 | The objective of this research was to develop a fundamental understanding of the behavior of buoyancy controlled axisymmetric diffusion gas flames and liquid pool fires. Specifically, we attempted to simulate two- dimensional axisymmetric profiles of the velocity, temperature, and species and soot concentrations. Knowledge of these profiles allowed us to determine the main characteristics of the flame; i.e., the heat feed back, which in turn determines the mass burning rate ... |
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| Resonance Electron Scattering by O(2) Monolayers on Graphite: Reinterpreted |
DEC 93 |
4 pages |
| Authors:
Hideo Sambe; David E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| Electron angular distributions of inelastic electron scattering from O2 physisorbed on graphite have been studied extensively by Palmer and coworkers. Their results have been published in more than eight papers over the past four years and summarized in two recent review articles. We have reinterpreted their data and in some aspects come to different conclusions.... Inelastic electron scattering, Molecular oxygen, Resonant states. |
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| Accurate Determination of Auger Line Shape Binding Energies |
JAN 93 |
16 pages |
| Authors:
N. H. Turner; D. E. Ramaker; F. L. Hutson; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| A quantitative comparison between an experimental and a theoretical description of any Auger spectrum requires a common energy reference point such as the Fermi level. With non-conductors this is problematic, since the Fermi level is not well defined and charging may shift the Fermi level. A common approach to overcome this problem employs spectra containing the Auger peak, core, and valence band (VB) photoemission peaks. One then has only to ... |
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| Resonance Electron Scattering by O2 Monolayers on Graphites: Reinterpreted |
JAN 93 |
4 pages |
| Authors:
Hideo Sambe; David E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
|
| Electron angular distributions of inelastic electron scattering from 02 physisorbed on graphite have been studied extensively by Palmer and coworkers. Their results have been published in more than sight papers over the past four years and summarized in two recent review articles. We have reinterpreted their data and in some aspects come to different conclusions.... Inelastic electron scattering, Molecular oxygen, Resonant states. |
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| Corrosion Control by Vitreous Films on Aluminum and High T sub c Superconductors |
31 DEC 92 |
7 pages |
| Authors:
David E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| Electron spectroscopy has become one of our most important tools for the study of electronic structure of solids and at surfaces. Under this contract, we studied the passivation and inhibition of corrosion, utilizing the spectroscopic techniques of XPS, AES, and NEXAFS. In particular, we studied the passivation of Al and Al-alloys towards attack by Cl(-), and the utility of Zr- Ir alloys to serve as diffusion/reaction barriers on silicon and ... |
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| Non-Adiabatic Curve Crossings in Dissociative Electron Attachment of Condensed O2 |
DEC 92 |
40 pages |
| Authors:
Hideo Sambe; David E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| Previously published data on electron stimulated desorption (ESD) from condensed O2 or O2+ in matrices have been analyzed. Dissociative electron attachment (DEA) via the 2 Sigma sub g(+) resonant state can result in two different dissociation products (i.e. by proceeding to the dissociation limits O(3p) + O(-)(2-P) and O* (1D) + O(-)2(P). The O* (1D) product requires dissociation via a non-adiabatic curve crossing. O (1D) is the dominant DEA product ... |
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| Auger Line Shapes as a Probe of Electronic Structure in Covalent Systems |
JAN 92 |
14 pages |
| Authors:
David E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| Our goal has been to develop a generally applicable, semi-empirical approach for quantitatively interpreting Auger line shapes for covalently bonded systems. In this regard we examine four main topics. First, because the Cini- Sawatzky theory was originally derived for initially filled, single bands in metals, we present our grounds for applying it to covalent systems. Second, we examine the problem of unfilled bands, and third, emphasize the importance of satellites. ... |
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| Dissociative Electron Attachment of O2: A Solid-State Effect on Potential Curve Crossing |
JAN 92 |
11 pages |
| Authors:
Hideo Sambe; David E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| Previously published data on electron stimulated desorption (ESD) from condensed oxygen or oxygen solid matrices are reanalyzed. In the gas phase, the resonant state at 8.5 eV is known to dissociate predominantly into the second lowest limit. In this paper we point out that this dissociation requires a non-adiabatic curve crossing. In the condensed phase or solid matrices, this resonant state is found to dissociate adiabatically into the lowest limit ... |
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| X-Ray Photoelectron Spectroscopy Study on the Double Layer at an Al2O3- Al Interface |
JAN 92 |
13 pages |
| Authors:
David E. Ramaker; Hideo Sambe; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| Upon oxidation of a clean Al Aluminum surface, and electrical double layer (EDL) is formed at the aluminum-aluminum oxide interface. This EDL is investigated using X-ray Photoelectron Spectroscopy data available in the literature. The EDL strength, measured as a potential difference across the EDL, depends on the Al surface and the oxidation process. The polarity of the EDL is however invariably the same: the Al2o3 side of the Al-Al203 interface ... |
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| Quantitative Interpretation of Auger Lineshapes and Electron/Photon Stimulated Desorption |
28 FEB 91 |
7 pages |
| Authors:
David E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| This project has involved a quantitative theoretical interpretation of electron spectroscopic data with a view toward elucidating the chemical environment and electronic structure of atoms in the bulk and adsorbed on solid surfaces. We have most recently examined XPS, XAS, and AES data for the high temperature superconductors, and CEELS, AES, and NEXAFS data for chemisorbed carbon species on metals. Electron/photon stimulated desorption (ESD/PSD) was also of interest. Here, an ... |
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| Evidence for Vertical C2 on Ni as a Precursor for Graphite Nucleation |
JAN 91 |
16 pages |
| Authors:
David E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| We interpret previously published C K edge CEELS and NEXAFS data for carbon Ni between 500-700K. The C K CEELS data for CO/Ni at 500K reveal the presence of C-C bonding on the surface, i.e. horizontal Cn(n=2,3..). The CEELS data for carbon at 620K reveal that some of the C2 species flip up at this temperature, while the others dissociate. Evidence for vertical C2 is seen only at higher carbon ... |
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| CEELS as a Probe of the Carbide to Graphite Transformation on Ni |
JAN 91 |
11 pages |
| Authors:
David E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| Recent effective medium theory calculations indicate that a nucleation step must be involved in the carbide to graphite transformation on Ni, and that vertical C2 may be a precursor to this nucleation step. A similar nucleation site could also be involved in diamond formation on metals. We interpret previously published C K edge CEELS and NEXAFS data for carbon/Ni between 500-700K. We make comparison with theoretical DOS calculations, and utilize ... |
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| The Past, Present, and Future of Auger Lineshape Analysis |
JAN 91 |
169 pages |
| Authors:
David E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| This review critically evaluates the suitability of Auger spectral line shape analysis as a source of electronic structure information. Methods for extracting the true Auger line shape from the raw data and a theoretical framework for semiquantitative interpretation of that line shape are presented. A wide range of recent applications, concentrating on the line shapes of the low Z metals (Be, Li, Na, Mg, and A1), the line shapes of ... |
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| Correlation of Burning Rates and Energy Transport Mechanisms in Open and Enclosed Liquid Pool Fires |
28 FEB 88 |
17 pages |
| Authors:
David E. Ramaker; GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY
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| A full scale fire model for an enclosed environment needs a quantitative description of the fire source itself. This is because of the time dependent power output of a flame arising from oxygen depletion. The objective of this research was to develop a quantitative understanding of the behavior of simulated gas flames and liquid pool fires of low initial momentum (buoyancy controlled) in a two-dimensional, axi-symmetric situation. Specifically, we predicted ... |
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