Structure and Reactivity of Alkylsiloxane Monolayers Formed by Reaction of Alkyltrichlorosilanes on Silicon Substrates

摘要

Long-chain alkyltrichlorosilanes, C13Si (CH2)nX, adsorb from solution onto silicon-silicon dioxide (Si/SiO2) substrates and form ordered alkylsiloxane monolayer films. These films were characterized by wettability, ellipsometry, and XPS. Except for very short chains (n = 0,1,2), the wetting of these monolayers was approximately independent of chain length. The presence of small amounts of water was necessary for the formation of these films. The alkylsiloxane monolayers were stable in common organic solvents, water, and acid, but were destroyed by prolonged exposure to base. Simple reactions on vinyl-terminated monolayers generated alcohol-, carboxylic acid-, and bromine-terminated films whose contact angles were lower than the starting monolayers, but whose lengths were largely unchanged. Measurements of the contact angle of acid-terminated interfaces as a function of pH indicated that ionization of soluble carboxylic acids. Monolayers containing mixtures of methyl- and carboxyl-functionalities exhibited wetting properties that mirrored the composition of the interface. (AW)