1989 年 55 巻 9 号 p. 1633-1638
The dissolution behavior on the tip and on the wall of tunnel pits formed on aluminum during DC etching in hot HCl solutions was studied. Initiated pits grow into a tunnel by crystallographic and auto-catalytic dissolution on the tip, independent of both the pH and the chloride ion concentration of a bulk solution. The tip dissolution proceeds under diffusion control at a rate of several μm/s, and then the tunnel growth abruptly stops at a limiting length when the tunnel tip may be repassivated. Although the tunnel walls must be passive during etching, they are subjected to general dissolution because of a high etching temperature. The tunnel widths increase continuously at a rate of several nm/s and the square cross section of the tunnels changes to circular shape.