Surface structures of cleaved icosahedral Al-Pd-Mn single quasicrystals after heat treatment

Surfaces produced by in situ cleavage fracture in ultrahigh vacuum of Czochralski-grown icosahedral Al-Pd-Mn single quasicrystals were investigated by scanning tunneling microscopy and by scanning electron microscopy at ambient temperature and after heat treatments of up to 670 ^∘{}C. It is found that the evolution of the surface structure with temperature depends very sensitively on the local stoichiometry. In areas of suitable composition a cluster-subcluster structure similar to that observed at room temperature is maintained whereas in areas of slightly different composition a terrace structure atomically flat over relatively large areas develops. The results are discussed in the general framework provided by current models of quasicrystal formation.