LEED Studies of the 10-Fold Surface of d-Al-Ni-Co and Xe Adsorption

N. Ferralis[a], K. Pussi[b], M. Gierer[c], C. J. Jenks[d], I. Fisher[d], R. McGrath[e], and R. D. Diehl[a]

[a] Department of Physics and Materials Research Institute, Penn State University, University Park, PA 16802, USA

[b] Institute of Physics, Tampere University of Technology, Box 692, Tampere, Finland

[c] Institut fuer Kristallographie und Mineralogie der Universitaet Muenchen, Theresienstr. 41, D-80333 Muenchen, Germany

[d] Ames Laboratory, Iowa State University, Ames, IA 50011, USA

[e] Surface Science Centre, University of Liverpool, Liverpool L69 3BX, UK

A dynamical low-energy electron diffraction (LEED) study of the structure of the clean 10-fold surface of Al₇₂Ni₁₁Co₁₇ at 50 K indicates that the surface structure is consistent with a truncation of the bulk structure determined by x-ray diffraction [1]. This model consists of periodically stacked planes, each of which has a structure based on a Penrose tiling having 5-fold symmetry, with each plane is rotated by º/5 relative to the next, in an ABAB stacking sequence. LEED intensity data were measured over the energy range 20-450 eV. The calculational approach was similar to that used previously for icosahedral quasicrystal surfaces [2,3]. Aside from a small amount of surface relaxation in the top surface layers and some intraplanar rumpling, the best-fit structure is very similar to a bulk truncation. Xe adsorbed onto this surface produces a LEED pattern having 30-fold symmetry, indicative of close-packed Xe islands nucleating and growing in alignment with the quasicrystal structure. Adsorption isobars indicate that the growth is layer-by-layer for at least two layers, and that the hexagonal ordering first occurs upon adsorption of the second layer. The isosteric heat of adsorption for the monolayer was measured to be 247 meV.

[1] W. Steurer, T. Haibach, B. Zhang, S. Kek, R. L¸ck, Acta. Cryst. B 46 (1993) 661.

[2] M. Gierer, M. A. Van Hove, A. I. Goldman, Z. Shen, S. -L. Chang, P. J. Pinhero, C. J. Jenks, J. W. Anderegg, C. -M. Zhang and P. A. Thiel, Phys. Rev. B 57 (1998) 7628.

[3] T. Cai, F. Shi, Z. Shen, M. Gierer, A. I. Goldman, M. J. Kramer, C. J. Jenks, T. A. Lograsso, D. W. Delaney, P. A. Thiel and M. A. Van Hove, Surf. Sci. 495 (2001) 19.