An in situ second harmonic generation study of the electrochemical oxidation of silicon in fluoride media

The electrochemical oxidation of p-type Si in fluoride solutions has been studied by in situ second harmonic generation (SHG) with the SHG signal being recorded simultaneously with the cyclic voltammogram. The SHG signal is shown to change in tandem with the electrochemical response enabling the identification of transition points between different surface conditions such as hydrogen-terminated, hydrated oxide and oxide. Interpretation of the changes in SHG suggests that the initial response is due to the electric field-induced second harmonic (EFISH) due to the electric field gradient at the interface. It then becomes dominated by the variation in the resonant surface non-linear susceptibility as the changes in local bonding affect the response. SHG signals display a much greater sensitivity to surface conditions than the voltammetric response and allow the real-time identification of the potentials at which significant changes take place in the state of the surface.