High-resolution electron microscopy of quasicrystals

Abstract

Our present knowledge on the structure of icosahedral and decagonal quasicrystals has strongly profited from the combined information inferred from electron diffraction patterns and high-resolution transmission electron microscopy (HRTEM) images. Many structural properties of quasicrystals can be recognized and quantified by the analysis of electron diffraction patterns alone. Nevertheless, a much more complete understanding of the real structure of quasicrystals can be achieved by the additional analysis of the HRTEM images. Compared to only diffraction-based techniques, transmission electron microscopy offers several advantages. Especially for decagonal quasicrystals, the HRTEM has been very successful in analyzing the atomic as well as the long-range structure. This is linked with the fact that decagonal quasicrystals are periodic along one direction and the atoms thus form periodic atom columns as in crystalline materials. Accordingly, the imaging theory established for crystals can also be applied to the HRTEM images of decagonal quasicrystals taken with the electron beam parallel to the 10-fold axis. The HRTEM images of decagonal Al–Mn–Pd and Al–Co–Ni quasicrystals have been used to distinguish between disorder and order: such as, the difference between a random tiling and perfect quasiperiodicity. The structural analysis of icosahedral quasicrystals by HRTEM is briefly, but critically, analyzed and applications for icosahedral Al–Mn–Pd quasicrystals are discussed.