Electrochemical and Charge Transport Behavior of Molybdenum-Based Metallic Cluster Layers Immobilized on Modified n- and p-Type Si(111) Surfaces

Octahedral molybdenum cluster cores [Mo6I8]4+ have been attached in apical positions to p- and n-type Si(111) surfaces through complexation with a pyridine-terminated organic monolayer (2 × 1014 cm−2), which was previously covalently bound to hydrogen-terminated Si(111). This grafting procedure resulted in about a 4 nm thick Mo6-terminated layer. Similar XPS results were found for p- and n-type samples, suggesting that the grafting efficiency and composition of the resulting layers do not depend significantly on the doping type of the surface. The cluster footprint of 10 nm2 indicates a fairly dense molecular packing on the Si(111) surface. The electrochemistry of such Mo6-modified surfaces in acetonitrile was characterized by a single irreversible oxidation peak at 0.92 V versus saturated calomel electrode (SCE) and flat band potential Efb values of −0.55 ± 0.05 V and 0.04 ± 0.05 V for the modified n- and p-type surfaces, respectively. The derivatization of silicon surfaces by Mo6 introduces surface stat...