Onset of oxidation of Al(111) at low temperatures: A study by electron-energy-loss spectroscopy and Auger electron spectroscopy

The early stages of oxygen adsorption and oxide formation on Al(111) have been studied at 135 K using a combination of electron-energy-loss spectroscopy and Auger electron spectroscopy. Both surface and subsurface binding sites are occupied at 135 K, even at an oxygen exposure as low as 1.8×{}10¹⁵ molecules/cm². Further oxygen exposure preferentially increases the population of subsurface sites. When a sufficient number of oxygen atoms occupy surface and subsurface sites in close proximity, clustering occurs, resulting in Al₂{O}₃$ formation. Aluminum oxide is characterized by a three-peak vibrational spectrum with a characteristic loss feature at 325--425 ${cm}^{{{-}}1}$ and a distinct Auger transition at 54 eV. Surface spectroscopic studies of Al(111) oxidation are facilitated at low temperatures where kinetic retardation permits separation of the processes of chemisorption, penetration, and oxide formation.