Ag deposited on TiO<sub>2</sub>(110) forms nanoclusters ~5 nm across and 2 nm in height, shown by STM. These nanoclusters
exhibit a plasmon loss at 3.8 eV as determined by EELS yet the substrate Fuchs-Kliewer phonon modes remain,
indicating that the exposed TiO<sub>2</sub> is not perturbed by the Ag clusters. Titania is grown on top of these clusters by
evaporation of Ti and subsequent oxidation and both EELS and optical measurements show that new excitations are
produced in the 1.5-2 eV range, a much better match to the solar spectrum than the 3.8 eV Ag plasmon. AFM
measurements indicate that the Ag clusters retain their morphology upon titania coating.
The conversion of 3D data sets of x-ray absorption images into 3D composition maps requires accurate mass absorption values, high-quality images, and a robust fitting algorithm. We evaluate the status of convenient x-ray absorption databases, the impact of various CCD parameters and imaging strategies (minimal vs over-determined), and styles of least-squares fits of the images (optionally including volume constraints). Concerns raised include the impact of NEXAFS features and limited CCD dynamic range. In the absence of these effects, the reduction of images to composition is fast and robust, as tested with simulations based on element-labeled Shepp-Logan phantoms. These studies allow one to evaluate a recent experiment in which synchrotron X-ray tomography is used to image a multicomponent sample. Those samples consisted of a mixture containing high-impact polystyrene (HIPS) and a two-component flame retardant, a brominated phthalimide dimer and a synergist, antimony oxide (Sb<sub>2</sub>O<sub>3</sub>). Complete tomography data sets were acquired at 3.34 micron spatial resolution using seven X-ray energies in the range of 12 to 40 keV, closely spanning Br and Sb 1s electron binding energies at 13.474 and 30.491 keV, respectively.
A tomography beamline has been built recently at the LSU CAMD synchrotron. The instrument consists of a Linux/LabVIEW-controlled CCD and Macintosh/LabVIEW controlled positioning stages. The two computers communicate via LabVIEW/TCP/IP. A Macintosh G4/Linux cluster has been installed for the purpose of on-site reconstruction. Instrument alignment and reconstruction programs are written in LabView, Matlab, and IDL. Applications to date are many. The blending of flame retardants (brominated aromatics, phosphates, and antimony oxide) in high-impact polystyrene is being studied with tomography; this work complements solid-state 81Br NMR. Also, several biological samples are to be studied as part of a multi-investigator project on biological visualization and computational studies. This project gives the tomography workers close access to an ImmersaDesk R2 and other computational resources.