Effect of placement of aluminium foil on growth of etch tunnels during DC etching

• The limiting length of tunnel is different under the various placement.
• Many sub tunnels are formed when Al is etched in face-down placement.
• A new etching model is proposed by considering the electrocapillary effect.
• Hydrogen bubbles in the tunnel have a great influence on the tunnel growth.

The tunnel growth behaviour of aluminium foil etched in different placement has been investigated. The limiting length of tunnel of specimens in increasing order is: face-down, vertical, and face-up placement. Many sub tunnels branch on the wall surface of the main tunnel when aluminium is etched in face-down placement, while much fewer sub tunnels are formed when aluminium is etched in face-up placement. A novel etching model has been proposed to interpret the phenomenon, by considering the electrocapillary effect. It reveals that the status and transport of hydrogen bubbles inside the tunnel has a great influence on the tunnel growth.