Electronic transfer mechanism in self-assembled monolayers of silicon

Abstract

This work presents a theoretical-experimental study on electronic transfer mechanism on crystal silicon surface modified with redox molecules derived from ferrocene. The surface modification consists in the reaction of hydrogenated silicon with decyl bromide (10-bromo-1-decene) activated with white light, and its subsequent reaction with monolithio-ferrocene. The samples were analyzed by X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. The layers formed are electrochemically active and present a quasi-reversible electrochemical process which is attributed to the ferrocene molecules bound to the silicon surface. In the experimental results, we found an apparent discrepancy, with respect to the results of the cyclic voltammetry, indicating that the redox centers have a diffusive behavior, like to molecules in solution, in spite of these molecules are linked to the silicon surface. While another technique indicates that these redox centers could be attached to the substrate. To understand these results, we have formulated a phenomenological model, based on a cellular automaton, that describes the mechanism of electronic transfer in molecules attached to the substrate. The parameters of the model are obtained from calculations of first principles, based on the density functional theory (DFT). Our results show that the electronic transfer mechanism is influenced by the movement of the redox centers of the molecules attached to the substrate. The latter would explain the apparent discrepancy in the experimental results.