L.E. Cox

The band structure of UO2: An angle resolved and resonant photoemission study☆

Abstract A detailed study of angle resolved photoemission of UO2 〈100〉 in the normal emission configuration is presented. The results are compared with a semirelativistic linearized augmented plane wave (LAPW) band calculation with the actual calculated empty bands used in the data reduction. Excellent agreement is found with calculations both for filled states as well as critical points in the empty states with no adjustment of bands, f-p Hybridization is found at the leading edge of the valence band and not at the bottom of the valence band, p-d Hybridization is found throughout the valence bands.

Valance-Band photoemission intensities in thorium dioxide

Abstract Resonant photoemission spectra of the O 2p-derived valence band of insulating ThO2 are compared to linear muffin-tin orbital (LMTO) density-of-state (DOS) and XPS intensity calculations. At Th 5d corelevel threshold energies (85 ⩽ hv ⩽ 120 eV), resonance is greatest at the bottom of the O 2p band where calculated p/d hybrid states are greatest; p/f hybrid content is weak by comparison. We conclude that the dominant hybridization is between O 2p states and Th 6d.

Resonance photoelectron spectroscopy using a tunable laser plasma light source

We report the first resonance photoemission experiments on plutonium metal, with surface preparation accomplished by means of laser ablation. The photoemission experiments were conducted using the newly commissioned tunable light source for transuranic research at Los Alamos. The light source is a tunable, laser plasma system capable of producing photons in the energy range 30-150 eV, with a photon flux of order 10 9 photons s -1 at 0.1% bandwidth. First results on δ-phase plutonium reveal the 5d-5f resonance enhancement to be maximum at a photon energy of 113 eV. Lower energy photoemission results show a narrow peak very near the Fermi level, with a linewidth of order 100 meV. This peak is verified by resonance photoemission to be of 5f character but also having strong 6d-7s contributions. The combination of high-energy resolution, tunable energies for orbital character determination and surface sensitivity of the UPS energy range make the laser plasma light source ideal for surface and interface studies.

An XPS study of the valence levels of alpha plutonium

Abstract The X-ray photoelectron spectum of the valence levels (0–25eV binding energy) of α-Pu has been obtained. The 5f bandwidth (1.8eV) results from significant 5f-5f overlap in the monoclinic phase.

Photoemission and inverse photoemission studies on actinide materials - Does any model work?

An overview is given of issues in the comparison of theory and experiment for actinide 5f electron spectra, with new experimental results on the photon energy dependence of 5f photoemission in UAl2 and the 4f core levels of the four phases of Pu metal.

ARPES in strongly correlated 4f and 5f systems: Comparison to the periodic Anderson model (PAM)

Abstract The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow, nearly temperature-independent bands (i.e., no spectral weight loss or transfer with temperature). A small dispersion of the f-bands above the Kondo temperature is easily measurable so that a Kondo resonance, as defined by NCA, is not evident. Preliminary results, however, indicate that the Periodic Anderson Model (PAM) captures some of the essential physics. Angle-integrated resonant photoemission results on δ-Pu indicate a narrow 5f feature at E F , similar in width to f-states in Ce and U compounds, but differing in that PES cross-section as a function of h ν suggests substantial 6d admixture.

Calculated lattice relaxation in Pu-Ga alloys

Abstract Hellman-Feynman forces on atoms in Pu 32 and Pu 31 Ga supercells are calculated with the full-potential LMTO method in the local density approximation. These forces are minimized by adjusting atomic positions using an iterative Broyden scheme. A Pu 32 supercell shows no tendency to relax from a perfect fcc lattice. In Pu 31 Ga the nearest-neighbor shell of plutonium atoms relaxes inward by 1.04% of the initial theoretical bond length (2.86 A) compared with a measured (EXAFS) value of 3.7% for an alloy with similar composition. Possible sources of the discrepancy between theory and experiment are discussed.

CORE-LEVEL AND VALENCE-BAND X-RAY PHOTOELECTRON DIFFRACTION IN UO2 (100)

Abstract X-ray photoelectron diffraction (XPD) effects have been studied in the U 4f, 0 1s and valence-band spectra of UO 2 (100). A simple nearest-neighbor forward-scattering model adequately explains the intensity modulations which occur with changes in polar angle, θ. In the valence band, the U 5f and U 6p 3 2 peaks and the 0 2p band show very similar angular intensity variations showing that the 0 2p bands intensity is largely U-orbital derived.

Solid-state Power Controller for Electrothermal Atomizers

The usefulness of electrothermal atomizers (ETA) is attested to by the recent publication of an increasing number of papers dealing with various aspects of the technique. Very high sensitivity with small sample volumes is its most noteworthy asset.