Unique shapes of micro-pits formed in an Al-Pd-Mn icosahedral quasicrystal by anodic etching

Abstract

The shapes of micro-pits formed in an Al-Pd-Mn icosahedral quasicrystal have been examined by alternating sequence of electrochemical etching and scanning electron microscopy (SEM) observations. Anodic etching was executed on fivefold and twofold surfaces of the single-quasicrystal. Prolonged anodic etching in a solution of CH3OH+HNO3 (volume ratio 3:1) followed by SEM observations has revealed that two different types of micro-pits, i.e. pre-existing micro-voids and electrochemical etch-pits, develop into the same regular shape. The micro-pits develop into a pentagonal pyramid on the fivefold surface, and a flat-bottomed rhombic pyramid on the twofold surface. It is shown that these two polyhedral etch-figures correspond to two different sections of a regular rhombic triacontahedron.