Berlin 2005 – scientific programme

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M: Metallphysik

M 30: Symposium Tomographic Methods in Materials Research

M 30.4: Talk

Monday, March 7, 2005, 12:00–12:20, TU H1058

Electron Tomography of Nanoparticles: towards atomic resolution? — •Sara Bals¹, Christian Kisielowski², Mihail Croitoru¹, and Gustaaf Van Tendeloo¹ — ¹EMAT-University of Antwerp, Groenenborgerlaan 171, Antwerp B-2020, Belgium — ²National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley CA 94720, USA

The use of bright field imaging for electron tomography in physical sciences is often hampered by the presence of Bragg diffraction. Reconstructions of Pt nanoparticles (5-7 nm) show that the morphology is not remarkably hampered, but artificial cavities are observed inside the particles. To understand the formation of these artifacts, we have used multislice calculations to simulate the different projections in a tomography series. From this we can conclude that strong scattering and channeling effects are possible reasons for the formation of the cavities. One of the experimental possibilities to overcome this problem is to combine electron tomography with annular dark field TEM. Here, the central beam and all electrons scattered up to a certain semi-angle are excluded from imaging by an annular objective aperture. In this manner, a mass-thickness contrast is generated that depends exponentially on sample thickness. Using this technique, we have successfully obtained a 3D reconstruction of CdTe tetrapods, which also allows us to locate the CdSe seed that is used during growth.