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Talks and Poster Presentations (without Proceedings-Entry):

L. Pardini, S. Löffler, G. Biddau, R. Hambach, U. Kaiser, C. Draxl, P. Schattschneider:
"Mapping atomic orbitals in the transmission electronic microscope: seeing defects in graphene";
Talk: 79th Annual Meeting of the DPG and Spring Meeting of the Condensed Matter Section, Berlin; 2015-03-15 - 2015-03-20.



English abstract:
The possibility of mapping atomic orbitals by using energy-filtered transmission electron microscopy (EFTEM) has been considered for a long time and was recently demonstrated from a theoretical point of view. With the example of graphene, we predict how this approach can be used to map orbitals of a particular character. To this purpose, we have investigated graphene in its pristine structure and with two different kinds of defects, namely an isolated vacancy and a substitutional nitrogen atom. We show that basically three different kinds of images are to be expected, depending on the orbital character as determined from the corresponding projected density of states. To judge the feasibility of mapping such orbitals in a real microscope, we investigate the effect of the optics´ aberrations, by simulating the lens system of two microscopes that are commonly used for electron energy loss spectrometry. We find that it should indeed be feasible to see atomic orbitals in a state-of-the-art EFTEM.

Electron magnetic chiral dichroism (EMCD) is the electron wave analogue of X-ray magnetic circular dichroism (XMCD). It offers the possibility to study magnetic properties at the nanoscale in a transmission electron microscope (TEM). In a `classical´ EMCD setup, the sample is illuminated with a plane electron wave and acts as a beam splitter. Although this method is meanwhile well established, only very few EMCD spectra were so far obtained from individual nanoparticles. We report on EMCD measurements on individual FePt nanocubes with a size of roughly 30 nm and compare our experimental findings with simulations. The dichroic signals at the L 3 and L 2 edges are expected to be as small as 10 % of the total scattering intensity. Our experiments are supported by simulations utilizing the WIEN2k program package, based on which FePt cubes with a thickness, that should provide maximal EMCD signals, are chosen for the experiments. The experiments indeed reveal a small but reproducible dichroic signal that agrees well with the results of the theoretical calculations.

Created from the Publication Database of the Vienna University of Technology.