Comparative Experimental Study of X-Ray Absorption Spectroscopy and Electron Energy Loss Spectroscopy on Passivated U Su
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0986-OO02-06
Comparative Experimental Study of X-Ray Absorption Spectroscopy and Electron Energy Loss Spectroscopy on Passivated U Surfaces Art J. Nelson1, W. J. Moberlychan1, R. A. Bliss1, W. J. Siekhaus1, T. E. Felter1, and J. D. Denlinger2 1 CMS MSTD, LLNL, 7000 East Avenue, Livermore, CA, 94550 2 ALS, LBL, 1 Cyclotron Road, Berkeley, CA, 94720 ABSTRACT X-ray absorption spectroscopy and electron energy loss spectroscopy are complementary analytical techniques on energy and spatial resolution. These techniques are based on the same fundamental physical process of core excitation with either an incident photon or incident electron. In the proper experimental configuration the electron and photon inelastic scattering amplitudes are comparable and thus the x-ray and electron absorption edges look identical. We have applied these two complementary analytical techniques to investigate the electronic structure of C ion implanted U. Implantation of C+ ions into U238 has been shown to produce a physically and chemically modified surface layer that passivates the surface preventing further air oxidation and corrosion. Comparison of the resultant spectra reveal that transitions between the initial state and a series of final states yield numerous strong features at the absorption edge that can provide structural information and information on the local chemical environment, including the character of the U 5f state. INTRODUCTION Emerging science involving small structures, structure property relations controlled at the nanoscale, and chemical research at the molecular scale require small probe characterization capabilities in the sub-micron to near atomic level coupled with elemental and chemical specificity. In addition, knowledge of the surface reactions of uranium metal on the nanoscale with various environmental and atmospheric agents, and the subsequent degradation processes, are vitally important in 21st century nuclear technology. Inelastic electron scattering techniques have the potential for elucidating these processes. Synchrotron radiation based x-ray absorption spectroscopy (XAS) is a highly developed capability for characterizing the electronic structure of materials. However, this technique has had limited spatial resolution while technological advancements now require nanoscale spatial resolution. Electron energy loss spectroscopy (EELS) has developed in parallel but has the advantage of atomic resolution when combined with transmission electron microscopy (TEM). XAS and EELS are complementary analytical techniques on energy and spatial resolution. These techniques are based on the same fundamental physical process of core excitation with either an incident photon or incident electron. XAS has only dipole allowed transitions, but both dipole and non-dipole transitions are observed with EELS. However, for small momentum transfer or for small scattering angles, electron and photon inelastic scattering amplitudes are comparable and thus the x-ray and electron absorption edges look identical. [1-4] We have appli
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