Investigation of the cluster substructure of icosahedral Al-Pd-Mn quasicrystals by means of exit-plane wavefunction reconstruction in high-resolution electron microscopy

摘要

The exit-plane wave reconstruction technique has been used for the first time to investigate the structure of icosahedral Al-Pd-Mn quasicrystals. The complex-valued exit-plane wavefunction along a fivefold direction was reconstructed with a resolution of 0.135 nm on the basis of a series of high-resolution electron microscopy images taken at different defocus values of the objective lens. In contrast with the original electron microscopic images, the exit-plane wave-function is free from imaging artefacts. The result fits well with that expected from the Mackay-type cluster model for the Al-Pd-Mn icosahedral quasicrystal derived from X-ray and neutron diffraction structure investigations. Different columnar arrangements of clusters were identified; clusters whose projections barely interfere with those of other clusters display almost perfect tenfold symmetry, while the local symmetry of strongly overlapping projected clusters is degraded.