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MBE Growth and Characterization of Graphene on Well-Defined Cobalt Oxide Surfaces: Graphene Spintronics without Spin Injection

Description: The direct growth of graphene by scalable methods on magnetic insulators is important for industrial development of graphene-based spintronic devices, and a route towards substrate-induced spin polarization in graphene without spin injection. X-ray photoelectron spectroscopy (XPS), low energy electron diffraction LEED, electron energy loss spectroscopy (EELS) and Auger electron spectroscopy (AES) demonstrate the growth of Co3O4(111) and CoO(111) to thicknesses greater than 100 Å on Ru(0001) surfaces, by molecular beam epitaxy (MBE). The results obtained show that the formation of the different cobalt oxide phases is O2 partial pressure dependent under same temperature and vacuum conditions and that the films are stoichiometric. Electrical I-V measurement of the Co3O4(111) show characteristic hysteresis indicative of resistive switching and thus suitable for advanced device applications. In addition, the growth of Co0.5Fe0.5O(111) was also achieved by MBE and these films were observed to be OH-stabilized. C MBE yielded azimuthally oriented few layer graphene on the OH-terminated CoO(111), Co0.5Fe0.5O(111) and Co3O4(111). AES confirms the growth of (111)-ordered sp2 C layers. EELS data demonstrate significant graphene-to-oxide charge transfer with Raman spectroscopy showing the formation of a graphene-oxide buffer layer, in excellent agreement with previous theoretical predictions. XPS data show the formation of C-O covalent bonding between the oxide layer and the first monolayer (ML) of C. LEED data reveal that the graphene overlayers on all substrates exhibit C3V. The reduction of graphene symmetry to C3V – correlated with C-O bond formation – enables spin-orbit coupling in graphene. Consequences may include a significant band gap and room temperature spin Hall effect – important for spintronic device applications. The results suggest a general pattern of graphene/graphene oxide growth and symmetry lowering for graphene formation on the (111) surfaces of rocksalt-structured oxides.
Date: August 2017
Creator: Olanipekun, Opeyemi B
Partner: UNT Libraries

Carbon K-Shell X-Ray and Auger-Electron Cross Sections and Fluorescence Yields for Selected Molecular Gases by 0.6 To 2 .0 MeV Proton Impact

Description: Absolute K-shell x-ray cross sections and Auger-electron cross sections are measured for carbon for 0.6 to 2.0 MeV proton incident on CH₄, n-C₄H₁₀ (n-Butane), i-C₄H₁₀ (isobutane), C₆H₆ (Benzene), C₂H₂ (Acetylene), CO and CO₂. Carbon K-shell fluorescence yields are calculated from the measurements of x-ray and Auger-electron cross sections. X-ray cross sections are measured using a variable geometry end window proportional counter. An alternate method is described for the measurement of the transmission of the proportional counter window. Auger electrons are detected by using a constant transmission energy Π/4 parallel pi ate electrostatic analyzer. Absolute carbon K-shell x-ray cross sections for CH₄ are compared to the known results of Khan et al. (1965). Auger-electron cross sections for proton impact on CH₄ are compared to the known experimental values of RΦdbro et al. (1979), and to the theoretical predictions of the first Born and ECPSSR. The data is in good agreement with both the first Born and ECPSSR, and within our experimental uncertainties with the measurements of RΦdbro et al. The x-ray cross sections, Auger-electron cross sections and fluorescence yields are plotted as a function of the Pauling charge, and show significant variations. These changes in the x-ray cross sections are compared to a model based on the number of electrons present in the 2s and 2p sub shells of these carbon based molecules. The changes in the Auger-electron cross sections are compared to the calculations of Matthews and Hopkins. The variation in the fluorescence yield is explained on the basis of the multiconfiguration Dirac-Fock model.
Date: August 1986
Creator: Bhalla, Raj P. (Raj Pal), 1948
Partner: UNT Libraries

Xenon N4,500 Auger spectrum - a useful calibration source

Description: In the xenon N4,5OO Auger spectrum there are 19 prominent lines ranging from 8 to 36 eV that provide a convenient set of standards for calibrating electron spectrometers. Combining optical data with recent measurements of this spectrum gives energies for these lines that are absolutely accurate to 11 meV. For most lines the relative accuracy is better than 1 meV; for a few it is about 3 meV. The spin-orbit splitting of the xenon 4d lines is measured to be 1979.0 +- 0.5meV.
Date: February 6, 2002
Creator: Carroll, T.X.; Bozek, J.D.; Kukk, E.; Myrseth, V.; Saethre, L.J.; Thomas, T.D. et al.
Partner: UNT Libraries Government Documents Department

X-ray fluorescence/Auger-electron coincidence spectroscopy of vacancy cascades in atomic argon

Description: Argon L{sub 2.3}-M{sub 2.3}M{sub 2.3} Auger-electron spectra were measured in coincidence with K{alpha} fluorescent x-rays in studies of Ar K-shell vacancy decays at several photon energies above the K-threshold and on the 1s-4p resonance in atomic argon. The complex spectra recorded by conventional electron spectroscopy are greatly simplified when recorded in coincidence with fluorescent x-rays, allowing a more detailed analysis of the vacancy cascade process. The resulting coincidence spectra are compared with Hartree-Fock calculations which include shake-up transitions in the resonant case. Small energy shifts of the coincidence electron spectra are attributed to post-collision interaction with 1s photoelectrons.
Date: December 1, 1996
Creator: Arp, U.; LeBrun, T.; Southworth, S.H.; Jung, M. & MacDonald, M.A.
Partner: UNT Libraries Government Documents Department

Interpreting X-ray and auger resonant Raman spectra

Description: We discuss resonant Raman Scattering in atoms within the context of conservation of energy, arguing that energy conservation determines the principal features of spectra taken at a resolution comparable to the natural widths of the transitions involved. Example systems applicable to atoms or solids are calculated using the model by Tulkki and Aberg, and the model is discussed in terms of energy conservation. Finally, results for X-ray resonant Raman scattering in Xe and Auger resonant Raman scattering in Ar are presented and the two processes are contrasted.
Date: December 31, 1996
Creator: Lebrun, T.
Partner: UNT Libraries Government Documents Department

Resonant Auger studies of metallic systems

Description: Results of resonant Auger spectroscopy experiments are presented for Cu, Co, and oxidized Al. Sub-lifetime narrowing of Auger spectra and generation of sub-lifetime narrowed absorption spectra constructed from Auger yield measurements, were observed. Resonant Auger yields are used to identify three valence states of oxidized Al. Partial absorption yield spectra were derived giving detailed electronic information and thickness information for the various chemical states of the bulk metal, the passivating aluminum oxide layer, and the metal-oxide interface region. In addition, the total absorption yield spectrum for the oxidized Al sample was constructed from the partial yield data, supporting the consistency of the authors method.
Date: October 21, 1999
Creator: Coulthard, I.; Antel, W. J., Jr.; Frigo, S. P.; Freeland, J. W.; Moore, J.; Calaway, W. S. et al.
Partner: UNT Libraries Government Documents Department

Sodium Depletion on Glass Surfaces During Auger Analysis

Description: The kinetics of the depletion of sodium on glass surfaces during Auger Electron Spectroscopic analysis is investigated. The decay process is mathematically represented as a sum of two single decaying exponential functions. This behavior may be described by a mechanism that accounts for the neutralization of sodium ions by the electron beam. Sodium ions and neutral sodium atoms are depleted by several known processes.
Date: April 22, 1981
Creator: Whitkop, P.G.
Partner: UNT Libraries Government Documents Department

Irradiation-assisted stress corrosion cracking behavior of austenitic stainless steels applicable to LWR core internals.

Description: This report summarizes work performed at Argonne National Laboratory on irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels that were irradiated in the Halden reactor in simulation of irradiation-induced degradation of boiling water reactor (BWR) core internal components. Slow-strain-rate tensile tests in BWR-like oxidizing water were conducted on 27 austenitic stainless steel alloys that were irradiated at 288 C in helium to 0.4, 1.3, and 3.0 dpa. Fractographic analysis was conducted to determine the fracture surface morphology. Microchemical analysis by Auger electron spectroscopy was performed on BWR neutron absorber tubes to characterize grain-boundary segregation of important elements under BWR conditions. At 0.4 and 1.4 dpa, transgranular fracture was mixed with intergranular fracture. At 3 dpa, transgranular cracking was negligible, and fracture surface was either dominantly intergranular, as in field-cracked core internals, or dominantly ductile or mixed. This behavior indicates that percent intergranular stress corrosion cracking determined at {approx}3 dpa is a good measure of IASCC susceptibility. At {approx}1.4 dpa, a beneficial effect of a high concentration of Si (0.8-1.5 wt.%) was observed. At {approx}3 dpa, however, such effect was obscured by a deleterious effect of S. Excellent resistance to IASCC was observed up to {approx}3 dpa for eight heats of Types 304, 316, and 348 steel that contain very low concentrations of S. Susceptibility of Types 304 and 316 steels that contain >0.003 wt.% S increased drastically. This indicates that a sulfur related critical phenomenon plays an important role in IASCC. A sulfur content of <0.002 wt.% is the primary material factor necessary to ensure good resistance to IASCC. However, for Types 304L and 316L steel and their high-purity counterparts, a sulfur content of <0.002 wt.% alone is not a sufficient condition to ensure good resistance to IASCC. This is in distinct contrast to the behavior of their high-C ...
Date: January 31, 2006
Creator: Chung, H. M.; Shack, W. J. & Technology, Energy
Partner: UNT Libraries Government Documents Department

Vibrational structure and partial rates of resonant Auger decay ofthe N 1s ->2pi core excitations in nitric oxide

Description: High-resolution resonant Auger electron spectra of NO measured in the vicinity of the N 1s {yields} 2{pi} core excitations are presented. The open shell electronic configuration of the molecule results in four excited electronic states, three of which are populated in the photoabsorption spectrum, {sup 2}{Delta}, {sup 2}{Sigma}{sup -} and {sup 2}{Sigma}{sup +}. Electron emission spectra obtained at different vibrational levels of the three N 1s core-excited states of NO are reported. Recently reported ab initio calculations [J. Chem. Phys. 106, 4038(1997)] are used to generate theoretical spectra for comparison with the experimental results taking lifetime vibration interference and Auger resonant Raman effects into account. Very good agreement is found for the lowest energy X {sup 1}{Sigma}{sup +} final ionic state. Spectra of the higher energy final ionic states are decomposed into contributions from the different 5{sigma}{sup -1}2{pi}{sup 1} and 1{pi}{sup -1}2{pi}{sup 1} configurations for comparison of the calculated and experimental partial Auger decay rates. A revised value for the adiabatic ionization energy of the {sup 1}{Delta} ionic state results from the deconvolution.
Date: July 6, 2000
Creator: Kukk, Edwin; Snell, Gyorgy; Bozek, John D.; Cheng, Wei-T. & Berrah, N.
Partner: UNT Libraries Government Documents Department