Spectroscopic analysis of the interface chemistry of ultra-thin plasma polymer films on iron

The bonding of organosilanes to iron surfaces was analysed on three model samples using FTIR-reflection absorption spectroscopy (IRRAS) for the layer characterisation and ToF-SIMS to characterise specific fragments that are commonly interpreted as the proof for a covalent +Si–O–Me-bonding. On an ultra-thin HMDSO plasma polymer coated specimen, characteristic fragments of a covalent bonding of organosilanes to iron oxide surfaces as discussed by other authors could be reproduced, whereas on the pure iron substrate no such peaks could be observed. On an iron surface dip-coated from a diluted polydimethylsiloxane solution, the discussed characteristic fragments of a covalent bonding could be found. This arises questions on the validity of the common interpretation, since in the case of pure physical adsorption of a non-reactive long-chain siloxane, no such bonds should be detectable. Additionally, ToF-SIMS sputter depth profiles on the HMDSO plasma polymer coated iron surface and of the iron surface covered with polydimethylsiloxane could be shown to behave qualitatively identical.