RHEED and STM studies of the pseudo-tenfold surface of the ξ′-Al77.5Pd19Mn3.5 approximant crystal

The pseudo-tenfold surface of the ξ′-Al77.5Pd19Mn3.5 crystal, an approximant of the icosahedral Al–Pd–Mn quasicrystal, is investigated by reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy. The observed RHEED patterns of the surface after sputtering are found to be consistent with those of a simple cubic lattice with (11̅ 0) surface plane. The [001] and [110] axes of the surface plane are oriented along the principal low-index axes of the bulk. The RHEED patterns of the sputter-annealed surface consist of diffraction streaks with periodic spacings expected for the bulk truncated surface. The surface prepared under different preparation methods is found to exhibit different step-height distribution and terrace morphology. A longer annealing yields a high density of shallow pentagonal pits on terraces, separated predominantly by 0.80-nm high steps and occasionally by double steps. In contrast, the surface prepared with shorter annealing time exhibits highly perfect terraces with 0.80-nm-high steps and additional unusual steps of heights close to 0.40 nm. All step heights observed for both preparation methods are consistent with interlayer spacings of the bulk model