Evidence for a Unique Chain Organization in Long-Chain Silane Monolayers Deposited on 2 Widely Different Solid Substrates


David L. Allara, Atul N. Parikh, Francis Rondelez, Langmuir 11, 2357 (1995)

We address the longstanding issue of substrate effects in alkylsiloxane monolayer self-assembly. With proper substrate prehydration, we observe formation of identical quality, compact, quasi-crystalline monolayers on oxidized silicon and gold substrates with widely different chemical character, the former capable of covalent bonding to the adsorbed molecules via silanol groups and the latter devoid of reactive surface sites. Infrared spectroscopy, ellipsometry, and wetting measurements show identical average film structures consisting of highly extended chains tilted at 10 (+/-2)degrees with significant end-gauche defect content. This observed substrate independence is consistent with our previous hypothesis that substrate-bound water promotes the decoupling of the organic film from the underlying solid surface.