Fine structure on flat surfaces of quasicrystalline Al-Pd-Mn

We have analyzed the fine structure revealed by scanning tunneling microsco py for a flat (within 0.8 Angstrom) fivefold surface of i-Al-Pd-Mn. Even th ough features in the image appear to be arranged randomly, self-similar fea tures are separated by distinct distances. The distribution of such distanc es is compatible with the separations between pseudo-Mackay icosahedra tang ent to the topmost layer, and with separations between other cluster-based units. We propose that the fine structure is due to electronic structure im posed by the clusters. [S0163-1829(99)01035-8].