Nonlinear analysis: the intermodulated differential immittance spectroscopy.

Intermodulation is used for the analysis of the nonlinear behavior of electrochemical and electronic systems. As a matter of fact, different than the passive elements, electrochemical systems have a highly nonlinear character, which can be used to obtain information on the reaction mechanism and structure of the double layer. The setup for measuring and analyzing the intermodulated sidebands is discussed in detail, using a commercial Schottky diode as the ideal system. A general intermodulated differential immitance spectroscopy technique was consequently defined as the analysis of the variation of the immittance elements as a function of the stimulus frequency, and its transfer function was called differential immittance spectrum. Through a simple model, it was possible to precisely calculate the flat band voltage and the doping level of the Schottky diode from a single differential immittance spectrum. The differential immitance spectra of a dummy cell containing passive elements demonstrated the resolution limits of the technique.