IVC17 / ICSS13 and ICN+T 2007

Lead Adsorption on the pseudo-10-fold surface of the T-Al₃(Mn,Pd) approximant crystal and on quasicrystal surfaces
Ledieu, Julian¹; Addou, Rafik¹; Deniozou, Thalia¹; Smerdon, Joseph²; Wearing, Lisa²; Leung, Lydie²; McGrath, Ronan²; Heggen, Marc³; Feuerbacher, Michael³; Lograsso, Thomas⁴; Wu, Dongmei⁴; Gröning, Oliver⁵; Fournée, Vincent¹; Dubois, Jean-Marie¹ ¹France; ²United Kingdom; ³Germany; ⁴United States; ⁵Switzerland

Much of our understanding of condensed matter and surface science is based on studies of periodic crystals. In recent years, this has been extended through the study of quasicrystals and their surfaces, which, although well ordered, are aperiodic. Now, the growth of approximant systems, which are large unit cell complex metallic alloys close in composition to a related quasicrystalline phase, allows the direct comparison of structural and growth phenomena on related periodic and aperiodic surfaces.
We report the first study of the (010) surface of the complex metallic alloy T-Al3(Mn,Pd), approximant of the d-Al-Mn-Pd quasicrystal, using scanning tunnelling microscopy (STM), low energy electron diffraction (LEED) and x-ray and ultra-violet photoelectron spectroscopy (XPS, UPS). The T-Al3(Mn,Pd) belongs to the Pnma space group and has the following parameters: a=14.717Å, b=12.510Å, c=12.594Å.
As revealed by sharp LEED patterns, the T-Al3(Mn,Pd) surface is well ordered after cycles of sputtering and annealing to 850K. Among the numerous diffraction spots describing the orthorhombic mesh, ten more intense peaks are distributed on a decagonal ring (pseudo-10-fold). Our preliminary analysis using XPS and UPS, indicates a surface more metallic than the related quasiperiodic surface. Flat terraces separated by a unique step height (6.3±0.3Å) are observed by STM. The structural motifs recorded within terraces change considerably with the bias applied. When compared to planes present within the unit cell, several atomic arrangements can be recognised and will be presented here.
Finally, Pb adsorption on the T-Al3(Mn,Pd) surface has been carried out and characterised using the above techniques. A layer-by-layer growth mode is observed up to 4ML using STM. This result will be compared to our recent study on Pb adsorption on d-Al-Ni-Co, i-Al-Cu-Fe and i-Al-Pd-Mn quasicrystals. In these experiments, the sticking coefficient is decreasing drastically and approaching zero with the completion of the first monolayer. Consequently, only one quasiperiodic Pb monolayer can be deposited on these quasicristallines substrates.
The European network of Excellence on 'Complex Metallic Alloys', contract NMP3-CT-2005-500145, is acknowledged for its financial support.

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