Harald Rose

Ulm University

Aberration correction can be considered as a quantum step in the development of the electron microscope. The correction of spherical aberration, the improved electrical and mechanical stability of the basic instrument, the development of monochromators, detectors, and corrected energy filters have transformed the electron microscope from a crude imaging instrument into a high-performance analytical instrument providing sub-eV spectroscopic information and sub-Angstroem spatial resolution at voltages above about 80kV. The additional correction of the chromatic aberration and the off-axial coma has further improved the performance of the microscope, giving atomic resolution down to 20kV. The requirements necessary for achieving successful aberration correction are illustrated by outlining  the evolution of correctors starting from simple systems and ending with the most advanced corrector employed in the SALVE microscope. This microscope has reached a resolution limit of 15λ which is about seven times smaller than the resolution limit of a non-corrected TEM. The improvement of resolution and contrast in the SALVE microscope by means of the Cc/Cs corrector will be documented by experimental results. The correction of chromatic aberration enables the use of elastically and inelastic scattered electrons for image formation without loss of intensity and degradation of resolution. This possibility is especially important for imaging dose-limited objects. Moreover, the action of other correctors will be shown for different microscopes operating in the range between 10V and 300kV.  Perspectives will be suggested to further increase the information on the atomic structure of radiation-sensitive objects and to enable optical sectioning with atomic resolution.