The structure of dodecagonal (Ta,V)1.6Te imaged by phase-contrast scanning transmission electron microscopy

• Published in: Journal of solid state chemistry 2012-10, Vol.194, p.106-112
• Main Authors: Krumeich, F., Müller, E., Wepf, R.A., Conrad, M., Reich, C., Harbrecht, B., Nesper, R.
• Format: Article
• Language: English
• Subjects: Aberration-correction STEM; Approximants; Clusters; Computer simulation; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Image contrast; Imaging; Phase contrast; Physics; Quasicrystals; Reciprocity theorem; Scanning electron microscopy; Scanning transmission electron microscopy; Semi-periodic solids; Structure of solids and liquids; crystallography; Tiling
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2012.04.050

While HRTEM is the well-established method to characterize the structure of dodecagonal tantalum (vanadium) telluride quasicrystals and their periodic approximants, phase-contrast imaging performed on an aberration-corrected scanning transmission electron microscope (STEM) represents a favorable alternative. The (Ta,V)151Te74 clusters, the basic structural unit in all these phases, can be visualized with high resolution. A dependence of the image contrast on defocus and specimen thickness has been observed. In thin areas, the projected crystal potential is basically imaged with either dark or bright contrast at two defocus values close to Scherzer defocus as confirmed by image simulations utilizing the principle of reciprocity. Models for square–triangle tilings describing the arrangement of the basic clusters can be derived from such images. PC-STEM image of a (Ta,V)151Te74 cluster. [Display omitted] ► Cs-corrected STEM is applied for the characterization of dodecagonal quasicrystals. ► The projected potential of the structure is mirrored in the images. ► Phase-contrast STEM imaging depends on defocus and thickness. ► For simulations of phase-contrast STEM images, the reciprocity theorem is applicable.