Study of the self-assembling of n-octylphosphonic acid layers on aluminum oxide from ethanolic solutions

One of the molecules which has been noted to form self-assembled monolayers on aluminium oxide is the phosphonic acid molecule. A variety of chain lengths and solvents have been discussed in state of the art literature. No global consensus about the adsorption mechanism and its limitations has been found yet. In this study, we present the continuation of previous analysis of the adsorption of n-octylphosphonic acids on chemically and morphologically optimised aluminium oxides. An ex situ analysis approach, using atomic force microscopy, X-ray photoelectron spectroscopy and Visible Ellipsometry (VISE) is presented. It can be seen that from ethanol, the molecules adsorb on the surface. This occurs in a very unstable way, creating defects at the surface. Through modeling of ellipsometry data, it is found that the oxide film itself is attacked by the acids, resulting in non homogeneous organic overlayers. It seems that, from an ex situ point of view, ethanol is not suitable for the creation of n-octylphoshonic acid monolayers. The reaction of the phosphonic acids with the aluminium hydroxyls creates local aqueous environments, which are, in combination with dissolved acids, hazardous for the oxide surface. Copyright (c) 2012 John Wiley & Sons, Ltd.