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.
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Corresponding author: Junji Yuhara. Reprints also available from M. Schmid (schmid).