Case of Substituted Alkyl Surfaces

Substituted alkyl chains can also be grafted on the hydrogenated silicon surface using the hydrosilylation route [37, 76, 101, 175-177]. Such is the case of fluorinated chains or of co-carboxyalkyl chains [69, 76, 178]. The thermal stability of such surfaces has been investigated by Faucheux et al. using IR spectroscopy [168]. In either case, important changes appear as compared to unsubstituted alkyl chains. 

Fluorinated chains were grafted by catalyzed hydrosilylation of Fl2C=CH-(CF2) -CFj. It was found that the IR bands characteristic of the CF groups disappear in the temperature range between 250 °C and 300 °C (about the same range as the vClTs of unsubstituted alkyl chains). However, in contrast to the case of unsubstituted alkyl chains, here the CH bands were found to survive up to temperatures of 350 °C [168]. 

This increased stability of the organic layer was attributed to a coupling of two chains at their ends, following the loss of the functional group [168]. 

The experimental data hardly allow to distinguish between the two schemes. 

The grafting of alkoxy groups on various silicon surfaces has been the subject of a number of studies [44-54]. It can most conveniently be obtained by reaction of the hydrogenated Si surface with alcohols [44-49,52,53]  

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