Making Microholes in Glass by Electrochemical Local Acidification of Fluoride-Containing Solution

When water is oxidized at an anode, protons are produced together with oxygen bubbles. As a result, in a solution containing fluoride ions, hydrofluoric acid is produced in a limited region near an electrode. By placing the electrode on the glass substrate, a microhole was formed in a glass substrate due to local etching by hydrofluoric acid produced near the tip of the electrode. However, oxygen bubbles may have increased the sizes of holes formed in the glass plate because the bubbles agitate the solution near the anode. To suppress the formation of oxygen bubbles, we added sulfite ions to the solution because protons are produced without generation of dioxygen when sulfite ions are oxidized into sulfate ions. Sulfite ions are also useful to suppress the diffusion of protons because they function as pH buffers.