Quasicrystalline Structure of Icosahedral Al68Pd23Mn9 Resolved by Scanning Tunneling Microscopy

Abstract
For the first time the surface structure of an icosahedral quasicrystal could be resolved in direct space by scanning tunneling microscopy. The surface was found to form terraces with their normals being parallel to a fivefold axis. On the terraces fivefold stars and pentagonal holes were observed. Both the step heights and the distances between pentagonal holes obey Fibonacci sequences. The distribution of the holes locally resembles a Penrose tiling and is correlated up to long distances indicating a quasiperiodic order. A simple model yields an autocorrelation function very similar to the experiment.