CRYSTALLINE SURFACE-STRUCTURES INDUCED BY ION SPUTTERING OF AL-RICH ICOSAHEDRAL QUASI-CRYSTALS

Low-energy electron diffraction patterns, produced from quasicrystal s urfaces by ion sputtering and annealing to temperatures below similar to 700 K, can be assigned to various terminations of the cubic CsCl st ructure. The assignments are based upon ratios of spot spacings, estim ates of surface lattice constants, bulk phase diagrams vs surface comp ositions, and comparisons with previous work. The CsCl overlayers are deeper than about five atomic layers, because they obscure the diffrac tion spots from the underlying quasicrystalline substrate. These patte rns transform irreversibly to quasicrystalline(like) patterns upon ann ealing to higher temperatures, indicating that the cubic overlayers ar e metastable. Based upon the data for three chemically identical, but symmetrically inequivalent surfaces, st model is developed for the rel ation between the cubic overlayers and the quasicrystalline substrate. The model is based upon the related symmetries of. cubic close-packed and icosahedral-packed materials. The model explains not only the sym metries of the cubic surface terminations, but also the number and ori entation of domains. [S0163-1829(98)00239-2].