Quasicrystals are materials with long-range ordering but no periodicity. We report scanning tunneling microscopy (STM) observations of quasicrystalline molecular layers on 5-fold quasicrystal surfaces. The molecules adopt positions and orientations on the surface consistent with the quasicrystalline ordering of the substrate. Carbon-60 adsorbs atop sufficiently separated Fe atoms on icosahedral Al–Cu–Fe to form a unique quasicrystalline lattice, whereas further C60 molecules decorate remaining surface Fe atoms in a quasi-degenerate fashion. Pentacene (Pn) adsorbs at 10-fold symmetric points around surface-bisected rhombic triacontahedral clusters in icosahedral Ag–In–Yb. These systems constitute the first demonstrations of quasicrystalline molecular ordering on a template.

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We present a study of the surface structure of the Ag-In-RE (RE: rare-earth elements Gd, Tb, and Yb) complex intermetallics using scanning tunneling microscopy and low-energy electron diffraction. The surface of the Ag-In-Yb approximant prepared by sputter-annealing methods under ultrahigh-vacuum conditions produces a flat (100) surface with no facets. However, the Ag-In-Gd and Ag-In-Tb 1/1 approximants, which have a surface miscut of about 12• relative to the (100) plane, develop surface facets along various crystallographic directions. The structure of each facet can be explained as a truncation of the rhombic triacontahedral clusters, i.e., the main building blocks of these systems. Despite their differences in atomic structure, symmetry, and density, the facets show common features. The facet planes are In rich. The analysis of the nearest-neighbor atom distances suggests that In atoms form bonds with the RE atoms, which we suggest is a key factor that stabilizes even low-density facet planes.

Scanning tunneling microscopy is employed to characterise the structure and morphology of the (100) surface of the Ag-In-Gd 1/1 approximant. The surface prepared by the usual method of sputter-annealing produces stepterrace structure. Observed step heights are consistent with the lattice constant of the bulk. Scanning tunneling microscopy on terraces reveals cluster-like protrusions arranged with a square unit cell as expected from the bulk. It has not been possible to assign the terraces to the specic bulk planes because of lack of atomic resolution on terraces.

We will present several interesting structures of thin films grown on Tsai-type quasicrystal, icosahedral (i)-Ag-In-Yb, studied by various experimental techniques including scanning tunnelling microscopy (STM). The results include three dimensional quasicrystalline films of single elements [1] and molecular films [2] (Figure 1).