Multi-cluster model of Al–Co–Ni Co-rich quasicrystal

Abstract

We studied the surface modification of Al–Co–Ni Co-rich quasicrystals by Co or Ni deposition, using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). After depositing 0.2 monolayers (ML) of Co or Ni with post-annealing, no clear changes were observed in the spot intensity or pattern of LEED. Only the uppermost surface was successfully modified. Based on the STM images of the modified surface, we found that excess Co atoms modified the 2-nm Co clusters to form 0.47-nm clusters and that excess Ni atoms only formed 0.29-nm Ni clusters on the Al–Co–Ni Co-rich quasicrystal surface. Finally, based on the STM images of a clean Co-rich surface, the Al positions proposed by transmission electron microscopy has been modified to match the STM image. To account for the data, we propose a multi-cluster model - based in part on the Hiraga model – composed of three main clusters for both A and B stacking layers.

Keywords:

• Al–Co–Ni
• quasicrystals
• structure analysis
• surface
• cluster-assembled materials
• scanning tunneling microscopy

Acknowledgement

We gratefully acknowledge the technical assistance of T. Sumi at the machine workshop at the School of Engineering, Nagoya University.