Medium energy ion scattering (MEIS) study from the five-fold surface of icosahedral Ag-In-Yb quasicrystal

H R Sharma,J Parle,R Mcgrath,A P Tsai,P J Nugent,T C Q Noakes,J Smerdon

doi:10.1088/1742-6596/809/1/012017

Abstract

Medium energy ion scattering (MEIS) is employed to characterize the composition and structure of the five-fold surface of the icosahedral Ag42In42Yb16 quasicrystal. The composition of the surface after sputtering is dominated by Ag and In, and when the surface is annealed at temperatures approaching 430°C, Yb is restored at the surface. The composition is that expected from the bulk structure if the surface is formed at bulk planes involving the centre of rhombic triacontahedral clusters, the building blocks of the system. Structural analysis of MEIS results are also consistent with a surface after annealing that is in close agreement with bulk truncation intersecting the cluster centre.

Highlights

The discovery of the binary icosahedral (i-)Cd-Yb quasicrystal[1] has led to the development of a series of isostructural ternary quasicrystalline and approximant systems that are suitable for surface studies under ultra-high vacuum (UHV)
The main building blocks of the i-CdYb system are rhombic triacontahedral (RTH) clusters which consist of five successive atomic shells[8]
The cluster atoms comprise 93.8% of the total atoms in the crystal with the remaining ‘glue’ atoms filling the space between the RTH clusters

Summary

Introduction

The discovery of the binary icosahedral (i-)Cd-Yb quasicrystal[1] has led to the development of a series of isostructural ternary quasicrystalline and approximant systems that are suitable for surface studies under ultra-high vacuum (UHV). These systems include i-Ag-In-Yb and Ag-In-RE 1/1 approximants (RE: rare earth element Yb, Gd, Yb). We employed medium energy ion scattering (MEIS) to characterise the structure and chemical composition of the five-fold surface of i-Ag-In-Yb. The main building blocks of the i-CdYb system are rhombic triacontahedral (RTH) clusters which consist of five successive atomic shells (an outer-most RTH shell composed of 92 Cd atoms, a 30atom Cd icosidodecahedron, a smaller 12-atom Yb icosahedron, a smaller 20- atom Cd dodecahedron, and an inner 4-atom Cd tetrahedron)[8]. Energy spectra typically provide information on the depth dependent composition, while angular spectra provide crystallographic information.[11]

Results and Discussion

Structural Analysis

Conclusions