Step structure on the fivefold Al–Pd–Mn quasicrystal surface, and on related surfaces J. Ledieu a , E.J. Cox a , R. McGrath a , N.V. Richardson b , Q. Chen b , V. Fourne ´e c,1 , T.A. Lograsso c , A.R. Ross c , K.J. Caspersen c,2 , B. Unal c , J.W. Evans c , P.A. Thiel c, * a Surface Science Research Centre, The University of Liverpool, Liverpool L69 3BX, United Kingdom b School of Chemistry, University of St. Andrews, North Haugh KY16 9ST, United Kingdom c Departments of Chemistry, Materials Science and Engineering, and Mathematics, and Ames Laboratory, Iowa State University, Ames, IA 50011, USA Received 11 October 2004; accepted for publication 8 February 2005 Available online 2 March 2005 Abstract We compare step morphologies on surfaces of Al-rich metallic alloys, both quasicrystalline and crystalline. We pres- ent evidence that the large-scale step structure observed on Al-rich quasicrystals after quenching to room temperature reflects equilibrium structure at an elevated temperature. These steps are relatively rough, i.e., have high diffusivity, compared to those on crystalline surfaces. For the fivefold quasicrystal surface, step diffusivity increases as step height decreases, but this trend is not obeyed in a broader comparison between quasicrystals and crystals. On a shorter scale, the steps on Al-rich alloys tend to exhibit local facets (short linear segments), with different facet lengths, a feature which could develop during quenching to room temperature. Facets are shortest and most difficult to identify for the fivefold quasicrystal surface. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Equilibrium thermodynamics and statistical mechanics; Scanning tunneling microscopy (STM); Step formation and bunching; Alloys; Stepped single crystal surfaces 1. Introduction Quasicrystals are non-periodic intermetallics possessing long-range order. Their existence poses a fundamental question for the scientific commu- nity: whether and how their properties—often 0039-6028/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2005.02.012 * Corresponding author. Tel.: +1 5152948985; fax: +1 5152944709. E-mail address: thiel@ameslab.gov (P.A. Thiel). 1 Present address: Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544. 2 Present address: LSG2M, CNRS-UMR 7584, Parc de Saurupt, F-54042 Nancy, France. Surface Science 583 (2005) 4–15 www.elsevier.com/locate/susc