Open Access Nano Express

Assessment of a nanocrystal 3-D morphology by the analysis of single HAADF-HRSTEM images

Daniel G Stroppa123*, Ricardo D Righetto14, Luciano A Montoro1, Lothar Houben2, Juri Barthel2, Marco AL Cordeiro5, Edson R Leite5, Weihao Weng6, Christopher J Kiely6 and Antonio J Ramirez13

Author Affiliations

1 Brazilian Nanotechnology National Laboratory, Campinas, São Paulo 13083-970, Brazil

2 Ernst Ruska Centre, Forschungszentrum Jülich GmbH, Jülich 52425, Germany

3 Mechanical Engineering School, University of Campinas, Campinas, São Paulo 13083-860, Brazil

4 School of Electrical and Computer Engineering, University of Campinas, Campinas, São Paulo 13083-852, Brazil

5 Department of Chemistry, Federal University of São Carlos, São Carlos 13565-905, Brazil

6 Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015, USA

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Nanoscale Research Letters 2013, 8:475  doi:10.1186/1556-276X-8-475

Published: 13 November 2013

Abstract

This work presents the morphological characterization of CeO2 nanocrystals by the analysis of single unfiltered high-angle annular dark-field (HAADF)-high-resolution scanning transmission electron microscopy (HRSTEM) images. The thickness of each individual atomic column is estimated by the classification of its HAADF integrated intensity using a Gaussian mixture model. The resulting thickness maps obtained from two example nanocrystals with distinct morphology were analyzed with aid of the symmetry from the CeO2 crystallographic structure, providing an approximation for their 3-D morphology with high spatial resolution. A confidence level of ±1 atom per atomic column along the viewing direction on the thickness estimation is indicated by the use of multislice image simulation. The described characterization procedure stands out as a simple approach for retrieving morphological parameters of individual nanocrystals, such as volume and specific surface areas for different crystalline planes. The procedure is an alternative to the tilt-series tomography technique for a number of nanocrystalline systems, since its application does not require the acquisition of multiple images from the same nanocrystal along different zone axes.

Keywords:
3-D morphology; HAADF; HRSTEM; Nanocrystal modeling