A Fibonacci-like terrace structure along a fivefold axis of i-Al 68 Pd 23 Mn 9 monograins has been observed by Schaub et al. with scanning tunneling microscopy. In the planes of the terraces they see patterns of dark pentagonal holes. These holes are well oriented both within and among terraces. In one of 11 planes Schaub et al. obtain the autocorrelation function of the hole pattern. We interpret these experimental findings in terms of the T * (2F) tiling decorated by Bergman and Mackay polytopes. Following the suggestion of Elser that the Bergman polytopes, clusters are the dominant motive of this model, we decorate the tiling T * (2F) with the Bergman polytopes only. The tiling T * (2F) allows us to use the powerful tools of the projection techniques. The Bergman polytopes can be easily replaced by the Mackay polytopes as the only decoration objects, if one believes in their particular stability. We derive a picture of ''geared'' layers of Bergman polytopes from the projection techniques as well as from a huge patch. Under the assumption that no surface reconstruction takes place, this picture explains the Fibonacci sequence of the step heights as well as the related structure in the terraces qualitatively and to a certain extent even quantitatively. Furthermore, this layer picture requires that the polytopes are cut in order to allow for the observed step heights. We conclude that Bergman or Mackay clusters have to be considered as geometric building blocks ͑just the polytopes͒ of the i-Al-Pd-Mn structure rather than as energetically stable entities ͑clusters͒. ͓S0163-1829͑99͒02829-5͔

By means of magneto-optical Kerr effect we observe spin reorientations from in-plane to out-ofplane and vice versa upon annealing thin Fe films on Ag(001) at increasing temperatures. Scanning tunneling microscopy images of the different Fe films are used to quantify the surface roughness. The observed spin reorientations can be explained with the experimentally acquired roughness parameters by taking into account the effect of roughness on both the magnetic dipolar and the magnetocrystalline anisotropy. 75.70.Ak, 75.30.Gw, 75.50.Bb, 61.16.Ch *

The Katz-Gratias-de Boissieu-Elser (KGdeBE) model for the icosahedral quasicrystals i-AlFeCu and i-AlPdMn is studied and applied to the surface structure of i-AlPdMn.

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A Cr͑001͒/Fe͑001͒ superlattice with ten bilayers grown by molecular beam epitaxy on a Ag͑001͒ substrate is studied by in situ scanning tunneling microscopy ͑STM͒ and ex situ x-ray diffraction ͑XRD͒. Layer-resolved roughness parameters determined from STM images taken in various stages of the superlattice fabrication are compared with average values reported in the literature or obtained from the fits of our XRD data. Good agreement is found for the rms roughnesses describing vertical roughness and for the lateral correlation lengths characterizing correlated as well as uncorrelated interface roughness if peculiarities of STM and XRD are taken into account. We discuss in detail ͑i͒ the possible differences between the STM topography of a free surface and the morphology of a subsequently formed interface, ͑ii͒ contributions due to chemical intermixing at the interfaces, ͑iii͒ the comparison of XRD parameters averaged over all interfaces versus layer-resolved STM parameters, and ͑iv͒ the question of the coherent field of view for the determination of rms values.