A PEEM STUDY OF SMALL AGGLOMERATES OF COLLOIDAL IRON OXIDE NANOCRYSTALS

A common limitation in nanostructure research is often the requirement to perform experiments on ensembles of nanoparticles, therefore averaging over inherent distributions with respect to particle size and shape, chemical composition, crystallinity and defect structure. This limitation can be overcome by studying the properties of a single nanostructure individually, which will allow one to truly correlate scaling laws of material properties with changes in size. Here we report the first experiments to explore the feasibility of spectromicroscopy using a photoemission electron microscope (PEEM) to record the X-ray absorption spectra of single nanocrystals. Colloidal iron oxide nanocrystals with an average diameter and standard deviation of 13 nm and 2 nm, respectively, were deposited on graphite (HOPG) forming small islands of agglomerated γ- Fe 2 O 3 nanocrystals (4–30 particles) as determined by scanning electron microscopy. Spatially resolved soft X-ray absorption spectra at the Fe L 3,2 edges of these individual islands were recorded with the PEEM2 instrument of the Advanced Light Source (ALS).