Comparative study of self-assembly of a range of monofunctional aliphatic molecules on magnetron-sputtered aluminium

The adsorption of a range of organic molecules from toluene onto the oxidized surface of magnetron-sputtered aluminium metal is studied using sessile drop water contact angle measurements. Molecules with different head group functionalities and various chain lengths are considered, including alkyl carboxylic acids, alkyl phosphonic acids, alkyl amines, alkyl trimethoxysilanes, alkyl trichlorosilanes and epoxy alkanes. Alkyl phosphonic and carboxylic acids are identified as readily forming the most well-packed monolayers on the aluminium surface, whereas the others adsorb less well and the chlorosilanes polymerize as a result of combination with moisture to form a thick deposit. The high-adsorption-density monolayers of alkyl phosphonic and carboxylic acids were studied using polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and x-ray photoelectron spectroscopy (XPS): PM-IRRAS reveals relatively poorer ordering of the C-10 alkyl carboxylic acid monolayer compared with that formed from the phosphonic acid, and XPS data suggest that this is likely to relate to a lower ability to displace preadsorbed volatile organic compounds. Copyright (C) 2004 John Wiley Sons, Ltd.