Growth of Ultrasmooth Octadecyltrichlorosilane Self-Assembled Monolayers on SiO2

Ultrasmooth octadecyltrichlorosilane (OTS) monolayers (2.6 ± 0.2 nm thick, RMS roughness ∼1.0 A) can be obtained reproducibly by exposing clean native SiO2 surfaces to a dry solution of OTS in Isopar-G. A clean room is not required. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), contact angle data, and ellipsometry show that film formation occurs through a “patch expansion” process and terminates once a single monolayer is formed, after about 2 days. These monolayers are suitable as substrates for high-resolution electron beam and AFM or STM lithography. Further observations highlight the importance of controlling water content during deposition of siloxane self-assembled monolayers. OTS covers the surface much faster when there is a little water in the OTS solution; contact angle and ellipsometry data indicate formation of a hydrophobic, 2.6 nm thick film after about 2 h. However, these OTS films have a totally different growth mechanism than films grown from dry solutions and are...