Spherical-aberration-corrected HRTEM of Al-Ni-Co decagonal quasicrystals

EcoTopia Science Institute, Nagoya University* Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Japan** HREM Research Inc., Japan***
○Koh Saitoh* Nobuo Tanaka* Pang Tsai An** Kazuo Ishizuka***

Quasicrystals (QCs) have a complex structural order, which are neither of ordinary crystals due to their non-crystallographic rotational symmetry, nor of amorphous solids by their long range order. Many electron microscope studies have been performed for various types of QCs and have provided valuable structural information of the QCs [1-3]. Hiraga et al. first took high-resolution transmission electron microscope (HRTEM) images of decagonal quasicrystals (DQC) at an accelerating voltage of 400kV [2]. The images show the arrangement of atom-clusters and atoms inside the cluster in atomic resolution. However, the 400 kV HRTEM has a problem that the high-energy electron beam inevitably introduces severe damages. 200 kV HRTEM is considered to be desirable for avoiding such beam induced damages. However, the resolution of the 200kV images is not sufficient to resolve all the atomic columns of QCs, even though the current highest-resolution objective lens is used.
In the present study, spherical aberration (Cs) corrected HRTEM [4,5] was applied to DQC. A significant improvement of the resolution from that with Cs-uncorrected 200kV HRTEM was observed. When Cs was set at nearly 0 μm (±1 μm) and the defocus was at a slightly negative value (underfocus), the images appear to be very similar to those taken at 400kV by Hiraga et al. Exit plane wave reconstruction was applied to defocus series of Cs-corrected HRTEM images [6].

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