Optical and electrochemical characterization of self-assembled octadecyltrichlorosilane monolayer on modified silicon electrode

Abstract With the aim of developing physical basis for the design of semiconductor biosensors, n-doped silicon substrates are first functionalised with thin layers of silicon dioxide grown by wet oxidation method. The electrical properties of treated silicon in contact with electrolyte are studied by impedance spectroscopy. The SiO 2 layers are then functionalized with self-assembled monolayers (SAM) of octadecytrichlorosilane (OTS; C 18 H 37 SiCl 3 ) to rend the surface hydrophobic. The analysis of the impedance spectra in terms of equivalents circuits of the Si/SiO 2 /electrolyte and Si/SiO 2 /SAM/electrolyte interface allows to determine the thickness of the silane monolayer. Ellipsometry is also used to determine the thickness of the OTS and confirms the result of impedance spectroscopy. Furthermore, the molecular structure of the OTS monolayer is studied by Fourier-transform infrared (FTIR) spectroscopy.