The branching ratio of core-valence transitions in electron energy-loss spectroscopy and x-ray absorption spectroscopy is linearly related to the expectation value of the spin-orbit operator of the valence states. Here, we analyze the branching ratio of the N(4,5) edges in the actinides and find that the spin-orbit sum rule gives an accurate result without the need to include the core-valence interactions. The branching ratio is not only useful to study the variations in the 5f spin-orbit interaction, it also allows us to constrain the 5f count for given angular-momentum coupling conditions.

We present the first results from studies of liquid water microjets by soft X-ray absorption spectroscopy. Near the oxygen K-edge (∼530 eV) a fine-structure pattern very similar to that found for gaseous water monomers is observed when the surface-selective total ion yield (TIY) is measured, but a broadened and blue-shifted spectrum emerges when detecting the bulk-sensitive total electron yield (TEY). TIY EXAFS measurements produce a nearest neighbor O-O distance for surface molecules (3.00 Å) slightly longer than that of the isolated water dimer (2.98 Å), whereas the O-O distance extracted from TEY EXAFS corresponds to that accepted for bulk water (2.85 Å). Together, these results evidence an equilibrium liquid water surface dominated by water molecules interacting weakly at longer distances than in the bulk, thus supporting predictions from computer simulations.

We report the first application of valence-band photoemission to a quantum-dot system. Photoernission spectra of cadmium sulfide quantum dots, ranging in size from 12 to 35 A radius, were obtained using photon energies of 20 to 70 eV. The spectra are qualitatively similar to those obtained for bulk cadmium sulfide, but show a shift in the valence-band maximum with size.PACS numbers: 73.20.Dx, 71.20.Fi, 79.60.Eq The electronic structure of semiconductor quantum dots is strongly size dependent when the dot diameter is comparable to or smaller than the bulk exciton diameter. ' Theoretical studies of such systems have predicted many interesting effects in semiconductor cluster electronic structure including discrete, well-defined states near the edges of the band.Optical studies have confirmed these models of quantum confinement.

The surface electronic states of W(110)-(1 x 1)H have been measured using spin- and angle-resolved photoemission. We directly demonstrate that the surface bands are both split and spin-polarized by the spin-orbit interaction in association with the loss of inversion symmetry near a surface. We observe 100% spin polarization of the surface states, with the spins aligned in the plane of the surface and oriented in a circular fashion relative to the Smacr; symmetry point. In contrast, no measurable polarization of nearby bulk states is observed.

Synchrotron-radiation-based x-ray absorption, electron energy-loss spectroscopy in a transmission electron microscope, multielectronic atomic spectral simulations, and improved first-principles calculations ͑general-ized gradient approximation in the local density approximation͒ have been used to investigate the electronic structure of the light actinides: ␣-Th, ␣-U, and ␣-Pu. It will be shown that the spin-orbit interaction can be used as a measure of the degree of localization of valence electrons in a material. The spin-orbit interaction in the light actinide metals ␣-Th, ␣-U, and ␣-Pu, has been determined using the branching ratio of the white line peaks of the N 4,5 edges, which correspond to 4d → 5f transitions. Examination of the branching ratios and spin-orbit interaction shows that the apparent spin-orbit splitting is partially quenched in ␣-U, but is strongly dominant in ␣-Pu. These results are fully quantified using the sum rule. This picture of the actinide 5f electronic structure is confirmed by comparison with the results of electronic structure calculations for ␣-Th, ␣-U, and ␣-Pu, which in turn are supported by a previous bremsstrahlung isochromat spectroscopy experiment.

X-ray magnetic circular dichroism (XMCD) measurements on Yb14MnSb11 provide experimental evidence of a moment of 5 microB on Mn, with partial cancellation by an opposing moment on the Sb4 cage surrounding each Mn ion. The compound is isostructural to Ca14AlSb11, with Mn occupying the Al site in the AlSb4(9-) discrete tetrahedral, anionic unit. Bulk magnetization measurements indicate a saturation moment of 3.90 +/- 0.02 microB/formula unit consistent with four unpaired spins and implying a Mn3+, high-spin d4 state. XMCD measurements reveal that there is strong dichroism in the Mn L23 edge, the Sb M45 edge shows a weak dichroism indicating antialignment to the Mn, and the Yb N45 edge shows no dichroism. Comparisons of the Mn spectra with theoretical models for Mn2+ show excellent agreement. The bulk magnetization can be understood as Mn with a moment of 5 microB and a 2+ configuration, with cancellation of one spin by an antialigned moment from the Sb 5p band of the Sb4 cage surrounding the Mn.

Many materials have been theoretically predicted to be half-metallic, and hence suitable for use as pure spin sources in spintronic devices. Yet to date, remarkably few of these predictions have been experimentally verified. We have used spin polarized photoelectron spectroscopy to study one candidate half-metallic system, Fe(3)O(4). Such experiments are normally hampered by difficulties in producing clean stoichiometric surfaces with a polarization that is truly representative of that of the bulk. However, by utilizing higher photon energies than have traditionally been used for such experiments, we can study polarization in 'as received' samples, essentially 'looking through' the disrupted surface. High quality, strain relieved, ex situ prepared Fe(3)O(4) films have been thoroughly characterized by diffraction, transport and magnetometry studies of their crystallographic, electronic and magnetic properties. The spectroscopic results are found to agree fairly closely with previously published experimental data on in situ grown thin films and cleaved single crystals. However, despite the higher photoelectron kinetic energies of the experiment, it has not been possible to observe 100% polarization at the Fermi level. Hence, our data do not support the claim of true half-metallicity for Fe(3)O(4).

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