The hydrogen-terminated surface of porous silicon (PS) is sufficiently reactive for the uncatalyzed hydrosilation of alkenes and alkynes. These modifications produce dramatic changes to both the physical and chemical properties of the PS.

Complementary strands and redox intercalators can be self‐assembled into nanoscale structures capable of charge transfer at the electrode surface from DNA oligomers synthesized directly at covalently modified semiconductor silicon surfaces (see schematic representation).

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Functional monolayers containing ferrocenylphosphines have been assembled at silicon surfaces by reaction with the hydrogen-terminated layer.The hydrogen terminated silicon surface formed on etching with aqueous ammonium fluoride or hydrofluoric acid is an integral step in the fabrication of semiconductor devices. 1 Despite the fact that this surface has been very well characterised, it is only comparatively recently that studies examining its functional group reactivity have been reported. 2-9 However, to date, despite the variety of synthetic routes explored, the types of molecules that have been attached to silicon have generally been simple alkyl and aryl groups. The development of chemicallysensitive devices based on silicon requires chemical routes for the covalent attachment of molecules capable of various functions to the semiconductor surface. These may include redoxactive molecules, reactive groups and ligands. Towards this end we have previously shown that redox-active monolayers based on ferrocenyl derivatives can be assembled via a two-stage process involving initial formation of a reactive monolayer (terminated with an bromoalkyl headgroup) to which the ferrocenyl group was subsequently attached through alkylation of (dimethylaminomethyl)ferrocene. 6 We recently reported syntheses of the ferrocenyl(hydroxymethyl)phosphine, [Fe(η 5 -C 5 H 5 ){η 5 -C 5 H 4 CH 2 P(CH 2 OH) 2 }] 1 and its oxide, [Fe(η 5 -C 5 H 5 ){η 5 -C 5 H 4 CH 2 P(O)(CH 2 OH) 2 }] 2, and sulfide, [Fe(η 5 -C 5 H 5 ){η 5 -C 5 H 4 CH 2 P(S)(CH 2 OH) 2 }] 3; these derivatives combine a redox centre and ligating donor groups (P, S or O) coupled with a suitable functional group, OH, for attachment to H-terminated silicon surfaces in a single molecule. 10 In this report we demonstrate that covalently attached monolayers incorporating these functionalities can be formed in one step on either porous silicon or single-crystal wafers as a result of the reactivity of the hydrogen terminated silicon surface towards the PCH 2 OH group.A typical procedure for covalent modification involved refluxing a freshly etched piece of (100) oriented Si wafer in a dry acetonitrile solution of the ferrocenyl derivative (0.02 -0.07 , typically 95 mg in 5 ml solvent) for 3 h under nitrogen. Following this reaction, the wafers were washed repeatedly with dichloromethane and dried in a stream of nitrogen. For comparison ferrocenylmethanol-derived monolayers 6 were also prepared, in this case the solvent used was dry hexanes. After monolayer formation ohmic contact was made to the back of the wafers with an In-Ga eutectic and a copper contact wire attached with silver-loaded epoxy. The wafers were then sealed onto glass slides with a silicone rubber such that only the polished face was exposed to solution to enable characterisation by cyclic voltammetry.