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

Abstract

The pseudo-tenfold surface of the ${\ensuremath{\xi}}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{Al}}_{77.5}{\mathrm{Pd}}_{19}{\mathrm{Mn}}_{3.5}$ crystal, an approximant of the icosahedral $\mathrm{Al}--\mathrm{Pd}--\mathrm{Mn}$ 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 $(1\overline{1}0)$ 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 $0.80\text{\ensuremath{-}}\mathrm{nm}$ high steps and occasionally by double steps. In contrast, the surface prepared with shorter annealing time exhibits highly perfect terraces with $0.80\text{\ensuremath{-}}\mathrm{nm}$-high steps and additional unusual steps of heights close to $0.40\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. All step heights observed for both preparation methods are consistent with interlayer spacings of the bulk model.