XPS, AES and EELS studies of Al surfaces

XPS, AES and EELS spectroscopies are used to study the surface and near-surface composition of ambient-exposed Al metal. Large-area averaged XPS analysis shows that after prolonged etching the sample consists of Al metal and anhydrous, virtually stoichiometric Al2O3. The intensities of the first bulk plasmon and surface plasmon signals lying below the Al2p peak are used to observe the incoherence of the alumina overlayer, as well as derive estimates of both its coverage and thickness. An Auger parameter, α2Al, involving the ALVV transition is considered which marks the difference between Al0 and Al2O3 with a chemical shift which is more than twice as great as that associated with the AlKLL-related Auger parameter used in the literature for characterizing the aluminum chemistry. Both AES and EELS highlight lateral chemical heterogeneities over the surface at different depths of analysis, with AES proving a more powerful indicator of chemical state changes. EELS-to-AES signal intensity ratios, calculated as a function of primary electron energy and analyzer resolution, are considered as a reference for anticipating the contrast obtainable in chemical imaging of Al0-containing surfaces by reflected electron energy loss microscopy and scanning Auger microscopy.