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Deposition of Dense Siloxane Monolayers from Water and Trimethoxyorganosilane Vapor

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journal contribution
posted on 16.08.2011, 00:00 by Randall D. Lowe, Matthew A. Pellow, T. Daniel P. Stack, Christopher E. D. Chidsey
A convenient, laboratory-scale method for the vapor deposition of dense siloxane monolayers onto oxide substrates was demonstrated. This method was studied and optimized at 110 °C under reduced pressure with the vapor of tetradecyltris(deuteromethoxy)silane, (CD3O)3Si(CH2)13CH3, and water from the dehydration of MgSO4·7H2O. Ellipsometric thicknesses, water contact angles, Fourier transform infrared (FTIR) spectroscopy, and electrochemical capacitance measurements were used to probe monolayer densification. The CD3 stretching mode in the FTIR spectrum was monitored as a function of the deposition time and amounts of silane and water reactants. This method probed the unhydrolyzed methoxy groups on adsorbed silanes. Excess silane and water were necessary to achieve dense, completely hydrolyzed monolayers. In the presence of sufficient silane, an excess of water above the calculated stoichiometric amount was necessary to hydrolyze all methoxy groups and achieve dense monolayers. The excess water was partially attributed to the reversibility of the hydrolysis of the methoxy groups.