The aim of this project is the development of a new method to obtain orbital information from element specific signals in the electron microscope. The combination of the theory to be developed with the experimental proof of principle that the energy filtered image carries orbital information (to be performed on the best available microscopes) is a prerequisite for future direct mapping of orbitals and bonds in the solid.

It is an international cooperation project between Austria and Germany. The partners are:

• Prof. Peter Schattschneider Vienna University of Technology (EELS methodology)
• Prof. Claudia Ambrosch-Draxl Humboldt University of Berlin (ab-initio calculations of solid-state properties)
• Prof. Ute Kaiser University of Ulm (experiment and theory)

The University of Ulm will contribute both experimentally (1) and theoretically (2).

Dr. Ralf Hambach is in charge of this project.

 

(1) Energy-filtered TEM imaging for graphene and other 2D materials

As bonding effects have been visualized recently in a direct TEM image [1], energy-filtered TEM might become one of the next challenges in electron microscopy. We will perform proof-of-principle EFTEM and diffraction experiments and evaluate those using TEM images calculations, which need to be further developed at the same time.

 

(2) TEM image simulations from first-principles calculations

By improving the resolution of aberration-corrected electron microscopes to sub-atomic dimensions, image simulations become more and more important for the understanding and interpretation of the observed contrast. At low acceleration voltage (like 20kV), one has to account for the subsequent elastic and inelastic scattering events of the electron beam in the target, which is a formidable task [2,3]. In close collaboration with the groups from Vienna and Berlin, we investigate how first-principles calculations can be used for image simulations using (a) density-functional theory for the elastic scattering potential [1,4] and (b) time-dependent density functional theory for the inelastic scattering kernel.

 

Literature

[1] J.C. Meyer, S. Kurasch, H.J. Park, V. Skakalova, D. Künzel, A. Groß, A. Chuvilin, G. Algara-siller, S. Roth, T. Iwasaki, U. Starke, J.H. Smet and U. Kaiser
Experimental analysis of charge redistribution due to chemical bonding by high-resolution transmission electron microscopy
Nature Materials, vol. 10, pp. 209–215 (2011).

[2] P. Schattschneider and B. Jouffrey
Channeling, localization and the density matrix in inelastic electron scattering
Ultramicroscopy, vol. 96, pp. 453-462 (2003).

[3] H. Müller, H. Rose and P. Schorsch
A coherence function approach to image simulation
Journal of Microscopy, vol. 190, pp. 73-88 (1998).

[4] Lee, Z., J.C. Meyer, H. Rose and U. Kaiser
Optimum HRTEM image contrast at 20kV and 80kV― exemplified by graphene
Ultramicroscopy accepted.