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 report the first application of valence-band photoemission to a quantum-dot system. Photoemission spectra of cadmium sulfide quantum dots, ranging in size from 12 to 35 Å 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.

The surface electronic states of $\mathrm{W}(110)\mathrm{\text{−}}(1\times 1)\mathrm{H}$ 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 $\overline{\mathrm{S}}$ symmetry point. In contrast, no measurable polarization of nearby bulk states is observed.

Angle-resolved photoemission extended fine structure from adsorbate core levels yields complete, accurate surface structures without resort to trial-and-error comparisons to theory. Scattering peaks from individual substrate atoms were observed with use of $\mathrm{S}\mathrm{}\left(1s\right)\mathrm{}$ photoemission from $c(2\mathrm{}\times 2)\mathrm{S}/\mathrm{Ni}\mathrm{}\left(001\right)\mathrm{}$ and $p(2\mathrm{}\times 2)\mathrm{S}/\mathrm{Cu}\mathrm{}\left(001\right)\mathrm{}$, along [011]. Fourfold-hollow site geometries were found for both systems, with interatomic distances of $R(\mathrm{S}-\mathrm{N}\mathrm{i})=2.24\mathrm{}\left(3\right)\mathrm{}$ Å and $R(\mathrm{S}-\mathrm{C}\mathrm{u})=2.28\mathrm{}\left(3\right)\mathrm{}$ Å.

Synchrotron-radiation-based x-ray absorption, electron energy-loss spectroscopy in a transmission electron microscope, multielectronic atomic spectral simulations, and improved first-principles calculations (generalized gradient approximation in the local density approximation) have been used to investigate the electronic structure of the light actinides: $\alpha \text{−}\mathrm{Th}$, $\alpha \text{−}\mathrm{U}$, and $\alpha \text{−}\mathrm{Pu}$. 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 $\alpha \text{−}\mathrm{Th}$, $\alpha \text{−}\mathrm{U}$, and $\alpha \text{−}\mathrm{Pu}$, has been determined using the branching ratio of the white line peaks of the $N_{4,5}$ edges, which correspond to $4d\to 5f$ transitions. Examination of the branching ratios and spin-orbit interaction shows that the apparent spin-orbit splitting is partially quenched in $\alpha \text{−}\mathrm{U}$, but is strongly dominant in $\alpha \text{−}\mathrm{Pu}$. 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 $\alpha \text{−}\mathrm{Th}$, $\alpha \text{−}\mathrm{U}$, and $\alpha \text{−}\mathrm{Pu}$, which in turn are supported by a previous bremsstrahlung isochromat spectroscopy experiment.