Type of presentation: Oral

MS-12-O-1709 3 dimensional elemental mapping of epitaxially grown Fe-Co nanodumbbells

Altantzis T.1, Liakakos N.2, Gatel C.3, Blon T.2, Lentijo-Mozo S.2, Lacroix L. M.2, Respaud M.2, Soulantica K.2, Bals S.1, Van Tendeloo G.1
1EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium , 2INSA, UPS, CNRS, LPCNO, Université de Toulouse, 135 avenue de Rangueil, 31077, Toulouse, France, 3Centre d’Elaboration de Matériaux et d’Etudes Structurales (CNRS), 29, rue Jeanne Marvig, 31055, Toulouse, France
thomas.altantzis@uantwerpen.be

New developments in the field of nanotechnology drive the need for advanced quantitative characterization techniques in three dimensions that can be applied to complex nanostructures. Such nanostructures are often composed of different compounds, since the co-existence of different materials on the same nano-object increases its functionalities, or changes its original properties thanks to a synergy between the constituents. When magnetically “soft” Fe cubes grow on magnetically “hard” Co nanorods, the overall effective magnetic anisotropy is drastically reduced compared to the bare Co nanorod.

Here, we investigated the 3 dimensional (3D) structures of Fe-Co hybrid nanodumbbells using electron tomography. In materials science, electron tomography measurements are typically performed in High Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM) mode (Figure 1).1 We can clearly observe that cubes with concave facets are attached on a nanorod. Although the morphology of the nanodumbbells is clear, the small difference in atomic number Z between Co and Fe does not allow to distinguish between the two components in the final 3D reconstruction. New developments concerning the design of EDX detectors enabled us to combine EDX and electron tomography,2 leading to a 3D visualization of the chemical structure as presented in Figure 2. In this figure, Fe is presented using a transparent visualisation and the segregation between Fe and Co is clear. The Co nanorods penetrate into the Fe nanostructures and a limited amount of Fe has been deposited on the Co rod close to the Fe cube. It must be noted that this information could not be obtained from conventional HAADF-STEM reconstructions. Therefore, the use of EDX tomography will be of great potential in the investigation of a broad range of complex nanostructures.

1. S. J. Pennycook. Annual Review of materials Science, 1992, 22, 171-195

2. P. Schlossmacher et al. Microscopy Today, 2010, 18, 14

The authors acknowledge financial support from European Research Council (Grant COUNTATOMS and Grant COLOURATOMS) and the European Union Seventh Framework Programme - ESTEEM2.

Fig. 1: a) HAADF-STEM image of the dumbbell, which is part of the tilt series. b, c and d) 3D representation of the reconstructed volume presented along different viewing directions. The distribution of Fe and Co in the structure cannot be distinguished.

Fig. 2: a, b and c) 2D EDX maps from the same particle revealing the distribution of the elements in the structure. d) 3D representation of the reconstructed volume by using EDX-tomography. We clearly see the segregation between Fe (green) and Co (blue).