Planar and cluster structure of icosahedral quasicrystals

Twofold-, threefold-, and fivefold-symmetry elements are observed in the ne ar-surface region of the quasicrystal Al70Pd20Mn10 using a real-space imagi ng technique based on secondary-electron emission. The observed icosahedral point-group symmetry implies the presence of atomic clusters within the an alyzed region of the solid. The same surface produces perfect low-energy el ectron diffraction patterns typical for well-defined crystallographic plane s. We present a model which reconciles this dual structural nature of quasi crystals. Our model is constructed from an icosahedral seed followed by con centric symmetry-preserving "growth" to form the macroscopic solid.