Formation of Multilayers by Self-Assembly

Monolayer and multilayer films were formed by self-assembly of methyl 23-(trichlorosilyl)tricosanoate (1) from organic solution. In agreement with published results, this compound was found to form good quality, close-packed monolayers on silicon surfaces. We have, however, found that films significantly thicker than the three monolayers previously obtained can be formed from continued chemisorption of monolayers of this compound followed by reduction of the surface ester with LiAlH₄in THF to form an “alcohol surface”. The quality of monolayer formation in the multilayer films was monitored in detail by ellipsometry, contact angle, and FTIR measurements, and, although generally increasing disorder can be detected, films of up to 25 discrete monolayers can be successfully made. These results indicate that self-assembly is a viable alternative to the Langmuir-Blodgett transfer technique for the construction of relatively thick (0.1-μm scale), ordered, multilayer films.