Archiviertes Physik-Kolloquium:

24. Apr. 2014, 16:15 Uhr, Gebäude NW1, Raum H3

The Structure of Low-D Materials Explored by Low-Voltage TEM

Prof. Dr. Ute Kaiser, Universit├Ąt Ulm, Electron Microscopy Group of Materials Science

The structure of Low-D materials explored by low-voltage TEM The study of properties of low-dimensional materials is currently one domain of aberration-corrected high-resolution transmission electron microscopy at lower accelerating voltages of 80keV. The susceptibility to radiation damage both challenges the interpretation of the structure at the atomic level and allows at the same time the study of the dynamics of transformations. We report atom-by-atom on the direct formation of structures such as fullerenes, nanoribbons, nanotubes and 2D-layers, which are stimulated by the electron beam and/ or by heat. Moreover, under the influence of the e-beam during its imaging process, the creation and motion of point defects, dislocations, grain boundaries and phase transitions can be observed and allow an unprecedented view into their atomic nature and properties, if combined by atomistic simulations. We show in addition that the monochromatic low-energy electron beam enables the acquisition of EELS spectra with exceptionally low background noise and report on the dispersion behavior for π and π+σ plasmons in free-standing single-layer graphene. Imaging the pristine structure of beam-sensitive materials, however, still remains a challenging task. We show that fullerenes inside carbon nanotubes at 20kV can stand a 2 order of magnitude higher dose compared to the case at 80kV. We report on our theoretical results of contrast calculation at voltages as low as 20kV and show first experiments obtained with the Cs-Cc corrected SALVE II machine.