S-Induced Destabilization of Aluminum Oxide at the Fe(poly)–S–Al2O3 Interface

Abstract

Auger measurements reveal that, under UHV conditions, interfacial sulfurinduces the destabilization of an aluminum oxide overlayer at theFe–Al₂O₃ interface at temperatures above400 K. One monolayer deposition of Al onto Fe/S results in the insertion ofAl at the Fe–S interface. Exposure of Fe–Al–S to oxygenat 300 K gives rise to the complete oxidation of the aluminum adlayer asevidenced by the disappearance of the Al⁰ Auger signal and thestoichiometric formation of the aluminum oxide. When the resultingFe–S–Al₂O₃ is annealed progressively tohigher temperatures between 400 and 900 K, analysis of the Auger spectrashows a dramatic decline in the Al/O Auger intensity ratio. This declineis accompanied by the appearance of a small signal due to Al⁰,which maintains a constant intensity as the total Al signal (due mainly toAl³⁺) decreases. The appearance of the Al⁰ Augersignal accompanied by the attenuation of the Al³⁺ signalsignifies the chemical conversion of Al³⁺ into Al⁰,probably followed by diffusion of Al into the bulk. The possibility ofalumina dewetting and island formation, however, cannot be ruled out onthe basis of the present data. In the absence of interfacial sulfur, the alumina–Fe interface is stable to 900 K.