In-situ observation of chemical states of a Si electrode surface during a galvanostatic oscillation in fluoride electrolytes using infrared absorption spectroscopy

Abstract

We have investigated a galvanostatic oscillation phenomenon during anodization of a silicon (Si) crystal electrode in fluoride electrolytes using infrared absorption spectroscopy in multiple internal reflection geometry (MIR-IRAS). We confirm that the electrode surface is covered with a thin oxide layer during the course of galvanostatic oscillation. We observe a weak oscillation of the oxide thickness that synchronizes with the oscillation of an anodic potential. We also find that when the anodic potential falls to its minimum, hydrogen-substituted oxide (suboxide, Si(O3)–H) forms on the electrode surface, and it diminishes before the anodic potential reaches its maximum. We propose a model of galvanostatic oscillation in which it is assumed that a decrease in the anodic potential is due to the formation of pits in the oxide overlayer and low-quality oxides containing Si(O3)–H species are preferentially formed at pit sites because of the concentration of the anodic current at those sites. We suggest that formation of an inhomogeneous oxide layer plays a crucial role for the galvanostatic oscillation phenomenon.