Surface structure and structural transition of decagonal Al-Ni-Co quasicrystal

X-ray photoelectron diffraction (XPD) and reflection high-energy electron diffraction (RHEED) measurements have been performed to investigate the surface structure of the decagonal Al₇₂Ni₁₂Co₁₆ quasicrystal, which is known as a two dimensional quasicrystal. RHEED patterns for the surface parallel to the quasiperiodic planes are almost identical to the selected area electron diffraction (SAD) patterns taken along the twofold axes of the bulk sample. The XPD images show clear tenfold-symmetric patterns consistent with the long range orientational order of the decagonal quasicrystal. These facts suggest that the surface has the same quasiperiodic structure as in the bulk. The surface phase transition induced by Ar⁺ ion bombardment is also investigated.