Molecular Grafting to Silicon Surfaces in Air Using Organic Triazenes as Stable Diazonium Sources and HF as a Constant Hydride-Passivation Source

Aryl molecules were covalently grafted to hydride-passivated Si(100) surfaces (Si−H) by the in situ conversion of aryldiethyltriazenes into aryldiazonium salts using 2% HF, followed by spontaneous surface grafting of the aryl species to the silicon surface. Major advances are as follows:  first, reactive diazonium species need not be isolated, and second, by using aqueous HF as the triazene-to-diazonium conversion promoter, the entire process can be carried out in air since any Si-oxide is continuously converted to the Si−H species. Molecular layers from a monolayer to 200 nm thick could be formed depending on the reaction conditions used. In one case where the molecule bore an α-triazene and ω-aniline (6), after grafting of the molecular layer onto Si−H via the triazene, the remaining aniline moiety was converted into a diazonium salt in situ with NOBF₄ and then permitted to react with functionalized single-walled carbon nanotubes (SWNTs), thereby covalently attaching nanotubes to the silicon surface using the aryl molecular layer as a tethering unit.