Electrochemistry on Si(100) in a hydrofluoric acid solution at cathodic potential regions

We have investigated the electrochemistry of Si(100) electrode surfaces under the negative bias condition in hydrofluoric acid (HF) solution using infrared absorption spectroscopy (IRAS) in the multiple internal reflection geometry (MIR-IRAS). We observe that immediately after the potential of -0.20 V is applied to a Si(100) electrode, dihydride (SiH₂) and trihydride (SiH₃) species increased their surface densities, while monohydride (SiH) decreases its density. When further applying a negative potential, no spectral changes were observed. We propose that the constrained bonds of surface hydride species are attacked by the hydrogen ion (H⁺) or the hydronium ion (H₃O⁺) to generate more Si-H bonds in the vicinity of the surface, leading to an increase in the surface density of dihydride or trihydride species.