Reinhard Schneider
Laboratory for Electron Microscopy (LEM), Karlsruhe Institute of Technology (KIT)
Inelastic scattering of electrons passing through a thin sample in a transmission electron microscope (TEM) is not only of disadvantage, i.e. leading to a blurring of image contrast, but it also yields additional information about such sample properties like thickness, optical and electronic characteristics, and above all its chemical composition. The energy loss and scattering angle of inelastically scattered electrons can be measured by dedicated electron spectrometers, and the related technique is called electron energy loss spectroscopy (EELS) (see, e.g., [1]).
In the last decades, besides energy-dispersive X-ray spectroscopy (EDXS), EELS in combination with TEM has become a widely used technique for materials characterization. In comparison to EDXS, EELS is especially able to detect light elements at high efficiency, since the ionization cross sections increase with decreasing atomic number Z. Therefore, both analytical techniques, namely EELS and EDXS, should be combined at one and the same TEM in order to perform chemical analyses at high spatial resolution. Moreover, because of the high energy resolution of EELS being in the order of 1 eV and better, the bonding state of a chemical element can be identified, too. This can be done by analyzing energy loss near-edge fine structures (ELNES) of ionization edges. Furthermore, the functionality of an EEL spectrometer can be extended to record two-dimensional element maps by the use of particular electron optics, which is energy-filtered TEM (EFTEM).
In the introductory part of the lecture, the physical fundamentals of inelastic electron scattering will be briefly discussed. Then, the instrumentation needed for EELS/EFTEM experiments is presented. Here, the difference between in-column and post-column imaging energy filters is also explained. The typical features of an EEL spectrum and their application possibilities for materials investigations will be exemplified in detail. In the main part, the way is illustrated how to get information about the element composition as well as the chemical-bond state by combined EELS/EFTEM nanoanalytics. This will be shown on the basis of results obtained from different advanced materials, including Si nanowires, metal-oxide nanoparticles, ZnO-based diluted magnetic semiconductors and diamond layers.
[1] R.F. Egerton, Electron Energy-Loss Spectroscopy in the Electron Microscope, 2nd edition, Plenum Press, New York, 1996
Speaker：PD Dr. rer. nat. habil. Reinhard Schneider
Hoster：Prof. ZHANG Yuegang
Time: Monday 10:00a.m., 8th June.
Place: A718 SINANO
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