Vapour phase formation of amino functionalised Si 3N 4 surfaces

Abstract

Self-assembled monolayer (SAM) formation of silanes on SiO 2 surfaces has been extensively studied. However, SAMs formed on silicon nitride (Si 3N 4) substrates have not been explored to the same level as SiO 2, even though they are of technological interest with a view to the chemical modification of microelectromechanical systems (MEMS). Therefore, this article presents the formation and characterisation of 3-aminopropyltrimethoxysilane (APTMS) SAMs on Si 3N 4 substrates from solution phase and vapour phase, compared to the well characterised APTMS SAMs formed on SiO 2 surfaces. Contact angle, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and ellipsometric data indicate the formation of APTMS SAMs (0.55 nm ellipsometric thickness) after 60 min immersion of either SiO 2 or Si 3N 4 substrates in APTMS solution (0.5 mM in EtOH). By comparison Si 3N 4 substrates exposed to APTMS vapour, at 168 mbar for 60 min, result in the formation of the equivalent of a bi or trilayer of APTMS.