CHARACTERIZATION OF NANOPHASE AL-OXIDE AL POWDERS BY ELECTRON-ENERGY-LOSS SPECTROSCOPY

Al nanoparticles were prepared by the inert gas condensation method. A fter passivation with oxygen and air exposure we obtained a powdered s ample of an Al-oxide/ Al nanocomposite material, In the present paper we describe the use of the electron energy-loss spectroscopy (EELS) te chnique in a transmission electron microscope to characterize such nan ostructured powders compared with a microcrystalline commercial alumin ium foil. Energy-filtered images showed the presence of an alumina ove rlayer of = 4 nm covering the aluminium nanoparticles (23 nm in diamet er), EELS analysis enabled us to determine the total amount of Al2O3 a nd metallic Al and the structure of the alumina passivation overlayer in the sample. Tn particular, the extended energy-loss fine structure analysis of the data showed a major presence of Al tetrahedrally coord inated with oxygen in the alumina passivation layer of Al nanoparticle s instead of the octahedral coordination found for a conventional Al f oil. This surprising effect has been attributed to the nanoscopic char acter of the grains. The analysis of the electron-loss near-edge struc ture also determines the presence of a certain degree of aggregation i n this kind of powdered sample as result of the coalescence of the nan ocrystalline grains. The procedure presented here may have the potenti al to solve other problems during characterization of nanostructured m aterials.