Structure of Decagonal Quasicrystals

Abstract

Recent discoveries made in synthesizing stable quasicrystals allows us to apply conventional techniques in growing macroscopic single grains and use conventional probes to study the complex structure of this novel form of matter. The decagonal quasicrystals in particular appears to have a far less complicated phase diagram and an extreme phase stability compared to their three dimensional icosahedral counterparts. We have grown several millimeter size single grains and studied the structure of stable A165Co20Cu15 Decagonal quasicrystals, using High Resolution X-ray Diffraction (HRXD) and Scanning Tunneling Microscopy (STM). Unlike diffraction probes which provide large volume reciprocal space information, STM is a local probe and provides direct real-space information with atomic resolution. The two techniques are therefore complimentary and when combined becomes very powerful in structure determinations of complex systems like quasicrystals. We have been able to prepare clean single grain surfaces in UHV and resolve individual atoms in quasiperiodic ordering with STM. Images of 10-fold quasiperiodic surfaces exhibit very well defined five sets of mass density lines, separated by multiples of 72 degree rotations. Near perfect quasiperiodic order seem to extend beyond thousands of angstroms, and can be modeled by a Penrose lattice. All atomic layers observed have identical local structure unlike the two dissimilar layers of the approximant Al13Fe4 phase. High resolution x-ray scattering from single grains finds 2000 angstroms size defect free quasicrystalline layers stacked periodically.