Investigation of the icosahedral quasicrystal Al68Pd23Mn9 by LEED and STM

The surface of icosahedral Al₆₈Pd₂₃Mn₉ was investigated by Low Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy (STM). Fivefold symmetric LEED patterns of this three dimensional (3D) quasicrystal were analysed in terms of the Fourier transform of a Fibonacci pentagrid. High resolution STM images of this surface prove the quasicrystalline nature ofi-Al₆₈Pd₂₃Mn₉ both laterally and vertically. Atomically flat terraces with nm-sized fivefold symmetric objects like fivefold stars and pentagonal holes were observed in real space. A Fibonacci pentagrid connecting the pentagonal holes was found to have line separations, which are within experimental errors identical to those derived from LEED data. The terraces are separated by steps of two incommensurable heights, whose succession forms part of the Fibonacci sequence. Cutting a 6D lattice yields lateral separations and step heights in 3D space, which agree with the experimentally determined values.