The (100) surface of the Al 13 Co 4 quasicrystalline approximant
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The (100) surface of the Al13Co4 quasicrystalline approximant Vincent Fournée1, Émilie Gaudry1, Marie-Cécile de Weerd1, Renee D. Diehl2 and Julian Ledieu1 1
Institut Jean Lamour, UMR 7198 CNRS – Université de Lorraine, Parc de Saurupt, 54011 Nancy Cedex, France. 2 Department of Physics, Penn State University, University Park, PA 16802, USA. ABSTRACT The structure of the (100) surface of the orthorhombic Al13Co4 quasicrystalline approximant is described based on a combined scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and density functional theory (DFT) study. We discuss the interplay between the surface structure and the cluster substructure of this approximant as well as possible offstoichiometry effects that could explain the discrepancies found in the literature on possible surface models. INTRODUCTION The interplay of the three-dimensional cluster structure of complex metallic alloys (CMA) with a two-dimensional surface is an exciting problem which was first introduced by the studies of quasicrystalline surfaces (for a review see Ref. [1]). However the relationship between the quasiperiodic layers exposed at quasicrystal (QC) surfaces and the three-dimensional arrangement of cluster building blocks is a very difficult problem to tackle in detail. A comprehensive amount of work has been published on this topic and a general conclusion is that quasicrystalline surfaces form at specific bulk planes characterized by a high atomic density and large interlayer spacing together with a high content of the lowest surface energy element (typically Al-rich planes in Al-based QCs) [2-6]. Such selection rules for surface terminations have no explicit relationship with the cluster substructure. It can only be said that all selected surface planes necessarily contain truncated clusters from the bulk structure. Therefore, the cluster substructure does not appear to play any obvious role on the QC surface structure but some more subtle relationship may be highlighted in the future. Surfaces of approximants can be regarded as a more tractable situation in this respect while being conceptually similar. In this paper, we focus on the (100) surface of the Al13Co4 quasicrystalline approximant. The surface has been studied by a combination of experimental methods and ab initio calculations [7,8]. We provide here a complete summary of our current knowledge of this surface. We discuss the relationship between its structure and the cluster substructure and we propose a possible mechanism that could reconcile contradictory results available in the literature on this particular surface [7-9]. The paper is organized as follows. Experimental details are provided in the next section. Then, results are presented and discussed in a last section before we conclude.
EXPERIMENTAL The Al13Co4 single crystal was grown using the Czochralski method. First, an ingot was prepared using an induction furnace under inert Ar atmosphere with a composition of Al84Co16 (in at.%) needed for the melt according to the phase diagr
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