Spatial and temporal oscillation at Si(111) electrodes in aqueous fluoride-containing solution

The oscillatory behavior of single crystalline n-Si(111) in dilute ammonium and sodium fluoride solutions is investigated. Simultaneous in-situ Fourier transform infrared analyses performed in the multiple internal reflection (FTIR-MIR) mode and photocurrent measurements show a pronounced variation in the integrated Si-O signal during photocurrent oscillations and corresponding changes in minority excess carrier concentration. The resulting oxide thickness changes are +/-5 monolayers (ML), assuming an average thickness value of 22 ML (as a lower limit due to the inaccessibility of Si-F vibrations in the FTIR experiment). The investigation of the initial oxidation by light-generated holes shows the formation of oxide in two stages. Electrolytic coupling of the oscillations is demonstrated in experiments in which oscillations of electrodes with spatially separated areas on their surfaces are studied.