Molecular and electronic properties transferred to silicon via wet-chemistry surface nanofunctionalization: Ethynylferrocene on Si(100)

In the frame of our research activity on covalent anchoring of functional molecules on Si oriented surfaces, we report here on the hybrid species resulting from the reaction of ethynylferrocene with H-Si(100) either in a single, direct step, or after production of a self-assembled α,ω-bifunctional alkyl monolayer. In the former approach, a short Si-C covalent bond is established through visible-light activation of the unsaturated side arm of ethynylferrocene via an extra-mild approach. In the latter case, an azide-alkyne Huisgen cycloaddition reaction ("click" chemistry) is induced between the C=C group of the molecule and the -N ₃ terminations of undecyl hydrocarbon chains pre-assembled onto H-Si(100). These two routes lead to electroactive monolayers wherein the ferrocene head groups are respectively located close to or far from the Si surface. This allows for a fine tuning of the properties of the resulting hybrids on Si, in terms of distinct redox potentials, electron transfer rate constants, oxidation resistance. The different reaction steps have been monitored with X-ray Photoelectron Spectroscopy (XPS), in order to evaluate the presence and the chemical nature of the anchored species, while electrochemical measurements have evidenced reversible redox responses of the resulting SAMs.