Structure, microstructure and electronic characterisation of the Al 2O 3/SiO 2 interface by electron spectroscopies

Abstract

Al 2O 3 has been deposited by evaporation and post-oxidation of Al on a flat SiO 2 substrate. The obtained films have been analysed by X-ray photoemission spectroscopy (XPS) and reflection electron energy loss spectroscopy (REELS). It has been found that the modified Auger parameter of Al varies by ∼2.2 eV between a low coverage situation (below an equivalent monolayer) and the bulk material. This change has been attributed to variations in the coordination state of the aluminium atoms. Some minor contributions due to bonding and polarisation effects are also detected. Valence band photoemission and REELS have shown that the band gap energy of the deposited Al 2O 3 increases as the coverage decreases. These effects are discussed in terms of the bonding interactions between the SiO 2 and Al 2O 3 at the interface between the two oxides. Sandwich structures formed by approximately one equivalent monolayer of Al 2O 3 intercalated between SiO 2 present Auger parameter and band gap energy values which are larger than those of a monolayer-like Al 2O 3 thin film supported on SiO 2. Also, it has been shown that the energy of the plasmon losses behind the Al KLL Auger peak can be used as a fingerprint to discriminate between supported Al 2O 3 thin films or layers of this material embedded within a sandwich structure of two SiO 2 layers.