抄録
The observation of the tunnel formed on D. C. etched {100} highly ordered aluminum and analysis of the tunnel shape have been performed by using the oxide replica method. The tunnel widths (Wi) were measured as a function of the tunnel depth (li) for the tunnels obtained by D. C. etching in AlCl3, HCl+AlCl3, NaCl+AlCl3, H2SO4+AlCl3, LiCl, NaCl and KCl aqueous solutions. As has already been reported regarding HCl solution, Wi tapered exponentially with li, i. e., log (Wi/W10)=a·li, where W10 is the tunnel width at the depth of 10μm from the tunnel entrance, in all solutions examined in this study. In HCl+AlCl3 solution, Wi tapered rapidly with li compared to the case of HCl or AlCl3 solutions. The rapid decrease in Wi with li, in HCl+AlCl3 solution was considered to be caused by the increase in the concentration of Al3+and Cl- ions in the tunnel, followed by the hindrance of electrochemical dissolution of Al. On the other hand, for the tunnel obtained in LiCl, NaCl, or KCl solutions, Wi tapered with li, at the same rate. It was considered that Li+, Na+, and K+ ions play the same role in the formation of the tunnel.
