Correlation between hydroxyl fraction and O/Al atomic ratio as determined from XPS spectra of aluminium oxide layers

A set of five different aluminium oxide layers has been investigated using XPS. The oxide layers were made by oxidizing aluminium in a vacuum, with an alkaline and acidic pretreatment and in boiling water. Hydroxyl fractions of the aluminium oxide layers ranging from 0.0 to 0.5 were determined by constrained curve‐fitting of the O 1s peak. The O/Al atomic ratios of the aluminium oxide layers, ranging from 1.5 to 2.0, were determined from the O 1s and Al 2p photoelectron intensities. A method is presented to account for the attenuation of the photoelectron intensities by the contamination overlayer. For the studied oxide layers, a linear relation is observed between the hydroxyl fraction and the O/Al atomic ratio of the aluminium oxide layers. It is concluded that the results obtained by the curve‐fitting procedure are reliable. Furthermore, a linear relation is observed between the hydroxyl fraction and the O 1s peak width. The O 1s binding energies of the O 2− and OH − components of the oxide layers correspond to 531.0 ± 0.1 eV and 532.4 ± 0.1 eV, respectively. Only pseudoboehmite showed 0.5 eV lower binding energies for these components. Angle‐resolved XPS analysis showed that most of the studied oxides are enriched in hydroxyl groups at their outermost surface. Copyright © 2004 John Wiley & Sons, Ltd.