A novel, two step method for the modification of silicon surfaces with organic groups by chlorinated phosphazene plasma deposition and subsequent reaction in solution

Abstract In this work the surface of silicon substrates has been modified with organic ligands by exploiting chlorinated phosphazene as coupling agent. Hexachlorocyclophosphazene-derived thin films were deposited by Glow-Discharge-induced Sublimation (GDS) and then treated with an anhydrous tetrahydrofuran solution of trifluoroethanol and 4-cyanophenol as organic nucleophilic reagents. The sublimation of the chlorinated molecules and their interaction with the plasma ions and electrons have been studied in situ by mass spectrometry and by measuring the deposition rate using a quartz crystal microbalance. As deposited thin films and organically-modified surfaces were characterized by means of FT-IR analysis and XPS spectroscopy. Mass spectrometry points out that the sublimation of integer molecules takes place, while the deposition rate on the substrate is nearly constant as shown by microbalance measurements. The phosphazene chemical structure and its P–Cl bond content are partially maintained in the as deposited films, as assessed by FT-IR analysis and XPS spectroscopy. During the reaction in solution most part of the deposit is dissolved by the solvent, leaving a very thin surface-bonded insoluble phosphazene layer, where chlorine P–Cl atoms are almost completely substituted by the organic reagent residue.