Vapour phase formation of amino functionalised Si3N4 surfaces

Self-assembled monolayer (SAM) formation of silanes on SiO2 surfaces has been extensively studied. However, SAMs formed on silicon nitride (Si3N4) substrates have not been explored to the same level as SiO2, 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 Si3N4 substrates from solution phase and vapour phase, compared to the well characterised APTMS SAMs formed on SiO2 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 SiO2 or Si3N4 substrates in APTMS solution (0.5 mM in EtOH). By comparison Si3N4 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.