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R. Zenkyu, J. Yuhara, T. Matsui, S. Shah Zaman, M. Schmid, P. Varga:
"Composition and local atomic arrangement of decagonal Al-Co-Cu quasicrystal surfaces";
Physical Review B, 86 (2012), 1154221 - 1154228.

We investigated the composition of decagonal Al-Co-Cu surface by Auger electron spectroscopy (AES) and
low-energy ion scattering (LEIS). The surface composition after annealing was Al richer and Co poorer compared
to that after sputtering or bulk composition. Two types of the characteristic clusters were observed by scanning
tunneling microscopy (STM) and no bias voltage dependence of the image was observed. On the other hand,
scanning tunneling spectroscopy revealed a subtle difference of local density of states in unoccupied states
between different sites. Structural optimization using ab initio calculations based on density functional theory
(DFT) was performed on several compositional models, which are based on the W-(AlCoNi) bulk model. The
surface structures of two types of the characteristic clusters were determined by comparison of the STM image
and the simulated image of the structures obtained by DFT. The topmost layer was composed of Al and Cu atoms,
and the compositional ratio was consistent with the AES and LEIS results.