X-ray reflection fluorescence spectroscopy (XRFS)

Elemental analyses were pursued by EDXS, EELS, and XRFS as described earlier. [25–26, 29–30, 46] The field emission, scanning transmission, electron microscope FESTEM HB501 (Vacuum Generators) was equipped with the energy dispersive x-ray spectrometer (EDXS) (Noran) and post-column electron energy loss spectrometer (EELS) (Gatan). The cryo-energy filtering transmission electron microscope 912 Omega was equipped with the omega, in-column, electron energy loss spectrometer (EELS) and the energy dispersive x-ray spectrometer (EDXS) (Zeiss). The cryo-energy filtering transmission electron microscopes 410 and 430 Phillips were equipped with the post-column, electron energy loss spectrometers (EELS) and the energy dispersive x-ray spectrometer (EDXS) (Noran). The field emission, scanning electron microscope SEM1530 (Zeiss) was equipped with the energy dispersive x-ray spectrometer (EDXS) (Noran). The field emission, scanning electron microscope H3400 (Hitachi) was equipped with the energy dispersive x-ray spectrometer (EDXS) (Hitachi). The S2 Picofox XRFS spectrometer was equipped with a molybdenum (Mo) X-ray target and the Peltier cooled Xflash Silicon Drift Detector (Bruker). Scan times ranged up to 1000 seconds. The ICP standard of 1000 mg/l of mono-element Gallium or Gadolinium (CPI International) was added to 500 microL of each sample to the final concentration of 10 mg/l. Instrument control, data collection, and analysis were under the SPECTRA 7 software (Bruker).