Self-assembled monolayers on silicon oxide

We evaluated the wet-chemical formation of octa-decyltrichlorosilane (OTS) self-assembled monolayers on silicon substrates with a silicon oxide layer. Our investigations were focussed on the influence of the reaction time on the surface energy. The surface energy was thereby calculated by measuring the static contact angle of two probe liquids on the surface. We found that only high reaction times of several hundred minutes yield a high quality monolayer with a minimal surface energy. A clear increase of the dispersive part of the surface energy for short reaction times is found. This can be explained by a high ratio of gauche-conformation within the alkyl chains accompanied by a rather slow rearrangement of the chains inside the monolayer to form a densely packed alltrans conformation. [GRAPHICS] Image of a water droplet on an OTS self-assembled monolayer-terminated silicon oxide surface. The contact angle is about 111 degrees indicating a high quality of the OTS monolayer. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim