A mild functionalization route to robust molecular electroactive monolayers on Si(100)

Abstract

Light-assisted surface anchoring to H-terminated n- and p-Si(100) wafers has resulted in the production of molecular electroactive monolayers from Si–C bound vinylferrocene (VFC). The resulting hybrids have been characterized by means of X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and electrochemically. White-light photoactivated anchoring has resulted in a mild route. The functionalized Si surface results negligibly oxidized, and the C/Fe atomic ratio is close to the value for the precursor. Electrochemical methods have been applied to investigate the role played by a covalent Si–C anchoring mode towards substrate–molecule electronic communication, a crucial issue for future molecular electronics devices. The response from cyclic voltammograms (cv's) for p-Si(100) functionalized electrodes, run in the dark and under illumination, has shown that the electron transfer is not limited by the number of charge carriers, confirming the occurrence of electron transfer via the Si valence band. The hybrids have shown a noticeable electrochemical stability and reversibility under cyclic voltammetry, and the trend in peak current intensity vs. the scan rate was linear. The molecule–Si bond is preserved for thousands voltammetric cycles, although both the coverage, evaluated from cv and XPS, and the electron transfer rate constant decrease with electrode ageing. VFC/p-Si resulted in the best-to-date large-area charge storage hybrid device responding to AC with no dissipation up to 100 Hz.