Electrochemical impedance study of fresh and passivated macroporous silicon for sensors

As-etched macroporous silicon layers were passivated successful by electrochemical oxidation and then covered by a chemically deposited polyaniline layer. They were studied by Fourier transform infrared spectroscopy (FTIR) and Impedance electrochemical spectroscopy (IES). The results show that electrochemical method is an excellent alternative for silicon oxide growth within the porous structure, whereas for polyaniline deposition into the insulating structure the chemical route is the most suitable. The FTIR analysis reveals that polyaniline in its emeraldine state, which is the most conductive one, was successful deposited into the porous matrix. The electrochemical behavior of these samples was studied by the impedance electrochemical spectroscopy (IES) and shows that IES is sensitive to surface chemical properties variation at the film/electrolyte interface, as well as to the chemical composition of the electrolyte. The addition of low amounts of contaminants, in the order of ppb, promotes a shift of its real and imaginary impedance, showing that these samples can be used as excellent chemosensor for contaminants in ethanoic solution.