High-resolution electron microscopy of quasicrystals

Our present knowledge on the structure of icosahedral and decagonal quasicr ystals has strongly profited from the combined information inferred from el ectron diffraction patterns and high-resolution transmission electron micro scopy (HRTEM) images. Many structural properties of quasicrystals can be re cognized and quantified by the analysis of electron diffraction patterns al one. Nevertheless, a much more complete understandings of the real structur e of quasicrystals can be achieved by the additional analysis of the HRTEM images. Compared to only diffraction-based techniques, transmission electro n microscopy offers several advantages. Especially for decagonal quasicryst als, 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 quasi crystals are periodic along one direction and the atoms thus form periodic atom columns as in crystalline materials. Accordingly, the imaging theory e stablished for crystals can also be applied to the HRTEM images of decagona l 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 be tween a random tiling acid perfect quasiperiodicity. The structural analysi s of icosahedral quasicrystals by HRTEM is briefly, but critically, analyze d and applications for icosahedral Al-Mn-Pd quasicrystals are discussed. (C ) 2000 Elsevier Science B.V. All rights reserved.