Asymmetric pentagonal cluster on an Al-Cu-Co quasicrystal surface

The 10-fold surface of a decagonal Al₆₆Cu₁₇Co ₁₇ quasicrystal has been studied by scanning tunneling microscopy (STM). Three kinds of characteristic pentagonal clusters are observed in the STM images. Clusters within a given terrace have the same orientation, while those in adjacent terraces have opposite orientations. We show that two of the pentagonal cluster types are part of the 2-nm cluster, which is considered to be the basic structural unit of the Al-Cu-Co quasicrystal. The local atomic arrangement in the 2-nm clusters is found to be asymmetric.