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Aberration-corrected (AC) STEM, AC TEM and in situ X-ray absorption fine structure spectroscopy (XAFS) were used to characterize the Pt clusters present on a 0.35 wt % Pt on γ-alumina support after reduction in hydrogen at 700 °C. STEM high-angle annular dark field imaging shows that cluster formation takes place at temperatures up to approximately 350 °C, and this is followed by gradual growth in cluster size for heat treatments in hydrogen up to 700 °C. The STEM data show that after 700 °C reduction the Pt clusters are present in a narrow size distribution centered at 0.88 nm, and using a method involving a redistribution of the Pt atoms using a high electron dosage in the STEM, it is shown that the clusters are present in two-dimensional morphology. This conclusion is verified using intensity line scans. The in situ extended X-ray absorption fine structure data are in good agreement with these observations. High-resolution AC–TEM, which uses a broad coherent electron beam, and can thus offer advantages relative to STEM for structure determination of fine clusters, supported by image simulations of through-focus series, were used to analyze the structures of Pt particles. The structures determined by using AC–TEM are consistent with STEM and EXAFS data in having a flat two-dimensional morphology. Comparison of AC–STEM and AC TEM data for the same 700 °C reduced sample suggests that parallel-beam TEM mode of imaging may be advantageous because of the less pronounced beam-induced structural rearrangements that occur when imaging with a fine STEM probe.

X rays are a powerful probe for investigating metal and radionuclide transformations in soils, sediments, and groundwaters. In particular, synchrotron-based X-ray investigations can identify the changes in an element’s valence state and chemical speciation that often result from microbially mediated electron transfer. This chapter describes some of the synchrotron-based X-ray techniques (X-ray absorption spectroscopy, X-ray fluorescence, and X-ray microscopy) that can be used to improve understanding of metal transformations. The X-ray absorption near-edge structure (XANES) technique provides an in situ probe of an element’s oxidation state and clearly can contribute significantly to an understanding of the fate of elements in the environment, in both solid and solution phases. In addition to its utility, XANES is relatively easy to implement and has been perhaps the most commonly used synchrotron-based X-ray technique for monitoring metal transformations in environmental studies. XANES spectroscopy focuses on the energy range near an element's absorption edge, which is related to the element's valence state. Extended X-ray absorption fine-structure (EXAFS) focuses on the energy region well above the absorption edge and yields information on the local chemical environment of the absorbing element. Investigators can initiate the use of synchrotron radiation in their research in a number of ways.