EVIDENCE FOR A UNIQUE CHAIN ORGANIZATION IN LONG-CHAIN SILANE MONOLAYERS DEPOSITED ON 2 WIDELY DIFFERENT SOLID SUBSTRATES

We address the longstanding issue of substrate effects in alkylsiloxan e monolayer self-assembly. With proper substrate prehydration, we obse rve formation of identical quality, compact, quasi-crystalline monolay ers on oxidized silicon and gold substrates with widely different chem ical character, the former capable of covalent bonding to the adsorbed molecules via silanol groups and the latter devoid of reactive surfac e 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 c ontent. This observed substrate independence is consistent with our pr evious hypothesis that substrate-bound water promotes the decoupling o f the organic film from the underlying solid surface.