Public Physic Colloquium in the Winter Terms 2010/2011 in Münster
Place:     Germany, 48149 Münster, Wilhelm-Klemm-Str. 10, IG I, HS 2
Time:     Thursday, 14.10.2010  16:00 h c.t.
Colloquium Coffee at 15:45 h  at the Lecture Hall

Circular dichroism in the electron microscope: Principle and progress

P. Schattschneider, University Service Centre for Transmission Electron Microscopy and Institute of Solid State Physics, Vienna University of Technology

Electron Energy-Loss Spectroscopy (EELS) and X-ray Absorption Spectroscopy (XAS) probe the same transitions from core-shell states to unoccupied states above the Fermi energy. Recently, this equivalence was used to establish a new TEM technique called EMCD (Electron energy-loss magnetic chiral dichroism) [1,2], allowing to do XMCD (X-ray Magnetic Circular Dichroism) on the nanometer scale.

Among the particular obstacles in EMCD that do not exist for synchrotron radiation is the notoriously low signal and the very particular scattering conditions necessary to observe a chiral dichroic signal. In spite of that, impressive progress was made in the last years. The signal strength could be considerably increased, and some innovations such as using a convergent beam have been introduced. EMCD has evolved into several techniques, which make full use of the versatility of the TEM and energy filtering, spectroscopy or STEM conditions.

We present an overview of the current situation in EMCD, stressing recent results such as nanometric resolution [3] and new image simulation software [4]. We also propose experiments to map electron spins of individual atomic columns under HR-TEM conditions.

References

[1] P. Schattschneider et al., Nature. 441 (2006), 486.

[2] S. Rubino et al., J. Mat. Res. 23 (2008), 2582.

[3] P. Schattschneider et al., Phys. Rev. B 78 (2008), 104413.

[4] J. Verbeeck et al., Ultramicroscopy 109 (2009), 350.

Invited from: Prof. Dr. H. Kohl