QUANTITATIVE AND QUALITATIVE CHARACTERIZATION OF AQUATIC IRON OXYHYDROXIDE PARTICLES BY EF-TEM

Electron energy-loss spectroscopy (EELS) and elemental imaging under t he energy-filtered transmission electron microscope are powerful tools for the characterization of iron-rich particles present in natural wa ters. Features present in EEL spectra (Fe-M-2,M-3 Fe-L-2,L-3 and O-K i onization edges) of goethite (alpha-FeOOH) have been studied with an e nergy filter operated at 80keV to determine optimal quantification and elemental imaging of Fe-rich natural aquatic particles in the 30-200 nm range of thickness, For quantitative aims, the Fe-M-2,M-3 ionizatio n edge cannot be used easily, but the Fe-L-2,L-3 edge provides more ac curate results owing to a better background extrapolation. The partial cross-section of the Fe(III) M shell has been determined for iron oxi de. The use of two-windows (jump-ratio) and three-windows (background stripping) imaging methods is discussed in relation to the specimen th ickness.