INVESTIGATION OF THE ICOSAHEDRAL QUASI-CRYSTAL AL68PD23MN9 BY LEED AND STM

The surface of icosahedral Al68Pd23Mn9 was investigated by Low Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy (STM). F ivefold symmetric LEED patterns of this three dimensional (3D) quasicr ystal were analysed in terms of the Fourier transform of a Fibonacci p entagrid. High resolution STM images of this surface prove the quasicr ystalline nature of i-Al68Pd23Mn9 both laterally and vertically. Atomi cally flat terraces with nm-sized fivefold symmetric objects like five fold stars and pentagonal holes were observed in real space. A Fibonac ci pentagrid connecting the pentagonal holes was found to have line se parations, which are within experimental errors identical to those der ived from LEED data. The terraces are separated by steps of two incomm ensurable heights, whose succession forms part of the Fibonacci sequen ce. Cutting a 6D lattice yields lateral separations and step heights i n 3D space, which agree with the experimentally determined values.