Quasicrystalline Antimony Thin Films

Introduction

The discovery of the thermally stable binary icosahedral (i) Cd−Yb¹ quasicrystal opened up a new area of research in the field of aperiodic materials. Unlike other common quasicrystals, which largely consist of three elements and are based on Al, the i-Cd−Yb quasicrystal is composed of only two elements, allowing for a complete structural determination to be made.² This material is constructed from an aperiodic array of Rhombic Triacontrahedral (RTH) clusters with adjoining glue atoms, which gives it a different structure than the Al-based quasicrystals, whose building blocks are Mackay and Bergman clusters.³

However, Cd−Yb is not suitable for surface studies under ultra-high vacuum (UHV) conditions due to the high vapor pressure of Cd. By replacing Cd with Ag and In, it has been possible to grow the isostructural Ag−In−Yb quasicrystal in a large single grain with high structural quality,⁴ enabling UHV surface studies of this phase.^5-9 It has been shown that all three high symmetry surfaces of i-Ag−In−Yb form at bulk planes that intersect the RTH cluster centers.^{5, 8, 9}

The search for aperiodic structures that possess less chemical complexity than the bulk quasicrystals has led to the discovery of novel epitaxial structures.^{10, 11} These structures include noble metal films with fivefold-twinned structure,¹⁰ magic height Bi and Ag films influenced by quantum size effects,^12-14 and quasiperiodically modulated multilayer Cu structures.^15-17 Furthermore, it has been found that the quasicrystalline structure of the substrate can be transmitted to a film of a single element. The quasicrystalline structure is not only limited to a monolayer but may extend up to a few atomic layers of the film. The observed quasicrystalline monolayers include Bi,^{18, 19} Sb,¹⁸ Sn,²⁰ and Pb^{21, 22} on various Al-based quasicrystals. A multilayer quasicrystalline structure has been observed in Pb deposited on i-Ag−In−Yb,²³ Sn deposited on i-Al−Pd−Mn²⁴ and Na on i-Al−Pd−Mn.²⁵ There has been a theoretical prediction of a quasicrystalline bilayer with a sparse second layer of alkaline metals on i-Al−Pd−Mn,²⁶ but such a structure has not been experimentally realized.

In this paper we present scanning tunneling microscopy (STM) and x-ray photoelectron spectroscopy (XPS) studies of Sb thin film growth on the fivefold i-Ag−In−Yb surface. Antimony was chosen to examine the possibility of pseudomorphic growth on i-Ag−In−Yb because of the following reasons: Sb has a similar atomic size to Sn and is also in the same periodic group as Bi, possessing a similar electronic configuration, and previously these three elements Sn,²⁰ Bi,^{18, 19} and Sb¹⁸ were successfully grown in a quasicrystalline monolayer on the Al-based quasicrystals. Another element Pb, which is next to Bi and in the same column as Sn in the periodic table, also yields a quasicrystalline monolayer on the Al-based quasicrystal^{21, 22} and a quasicrystalline multilayer on i-Ag−In−Yb.²³ All these four elements have low surface free energy. The choice of Sb was also motivated by a consideration that the covalent bonding between Sb and the substrate In may induce a quasicrystalline structure in the adlayer.