Analysis and Characterization of Mixed Alkyl Silane Self-Assembled Monolayers on Metal and Oxide Surfaces

Alkyl silane amphiphiles form robust Self-Assembled Monolayers (SAMs) on stable oxide surfaces. Substrate surfaces of Ge, Si, and Ti can be modified by coating them with ultra-thin long-chain alkyl silane monolayers which are found to be very stable¹. Titanium is especially interesting as it is a light, corrosion-resistant metal used in aircraft, spacecraft, and medical devices.

In this study, mixed monolayers, composed of very similar alkyl silanes, differing only in chain length by about 5 angstroms (Å), were formed on silicon wafer substrates. Although the desired and expected result was random mixing of the monomers in the SAM, island aggregates of the longer monomer were observed with Atomic Force Microscopy (AFM). Since self-assembly of silanes on oxide is believed to be attained through strong covalent Si-O bonding at the substrate surface, inter-molecular thermodynamic forces between like molecules, or incomplete mixing of monomers may give rise to island formation.