Controlled Oxidation, Biofunctionalization, and Patterning of Alkyl Monolayers on Silicon and Silicon Nitride Surfaces using Plasma Treatment

A new method is presented for the fast and reproducible functionalization of silicon and silicon nitride surfaces coated with covalently attached alkyl monolayers. After formation of a methyl-terminated I-hexadecyl monolayer on H-terminated Si(100) and Si(111)surfaces, short plasma treatments (1-3s) are sufficient to create oxidized functionalities without damaging the underlying oxide-free silicon. The new functional groups can, e.g., be derivatized using the reaction of surface aldehyde groups with primary amines to form imine bonds. In this way, plasma-treated monolayers on silicon or silicon nitride surfaces were successfully coated with nanoparticles, or proteins such as avidin. In addition, we demonstrate the possibility of micropatterning, using a soft contact mask during the plasma treatment. Using water contact angle measurements, ellipsometry, XPS, IRRAS, AFM, and reflectometry, proof of principle is demonstrated of a yet unexplored way to form patterned alkyl monolayers on oxide-free silicon surfaces.