5 to 6-fold symmetry transition and T-dependent stacking of Xe adsorbed on a quasicrystal surface

The ordering of Xe films on an Al$_{73}$Ni$_{10}$Co$_{17}$ quasicrystals surface is studied using Grand Canonical Monte Carlo simulations with Lennard-Jones interatomic potentials and an empirical adsorption potential. Isotherms and layer density profiles show interesting phenomena. The study confirms the experimental layer-by-layer growth in the explored temperature (T) range (70-280K). By increasing the pressure at low temperatures (70-110K) the first layer, which forms following the 5-fold ordering of the substrate, evolves continuously assuming a 6-fold hexagonal symmetry before the condensation of the second layer. Thereafter, further layers have 6-fold symmetry. The 6-fold axes are aligned with the 5-fold axes of the quasicrystal, in agreement with experiment. However, at low T (70K) the layer stacking is ABC, consistent with fcc(111) experimental observations, while at higher T (160K) the stacking is AB, indicating a possible fcc to hcp transition of the adsorbate. Research supported in part by NSF.