Highlights

First Applications of C_c Corrected Imaging for High-Resolution and Energy-Filtered TEM

Scientific Achievement

Chromatic aberration has been the limiting factor for TEM experiments in which the energy spread of the beam and the coefficient of chromatic aberration of the objective lens (C_c) determine the optical properties of the instrument.  This is the case for a wide scope of TEM application such as in-situ experiments, energy filtered TEM, Lorentz TEM, tomography and biological samples where the thickness is close to the transmissivity limit of the electron beam.  A first prototype of an electron optical system which can correct spherical as well as chromatic aberration has been designed and fabricated as part of the TEAM project.  Tests of this prototype have successfully demonstrated correction of C_c for the first time for a TEM with acceleration voltages between 80 and 300 kV.  C_c has been corrected from its initial value of 1.4 mm at 80kV down to 2 ?m which is an improvement by three orders of magnitude. The spatial resolution is enhanced by C_c-correction from 1.8 Å to 1.0 Å.

Energy filtering TEM (EFTEM) allows elemental and chemical mapping of large areas.  The resolution achievable by EFTEM mapping is limited to about one nanometer by the chromatic aberration of the objective lens.  Elemental maps of La have been measured at the interface LSAT/LaCoO₃ [1] with an uncorrected microscope and with a C_c-corrected instrument.  The width of the interface calculated from these maps is influenced by the resolution of the microscopes in EFTEM mode.  The C_c-corrected value was five times smaller than the interface width derived from the uncorrected measurement.

C_c-correction allows high resolution imaging using the background of the energy loss spectrum.  The imaging process of this mode is not fully understood but can be very useful for investigating soft matter and thick samples.

Significance

Demonstrating C_c-correction for the first time for TEM mode is a major break-through for charged particle optics and can have an impact not only for electron optical systems but also for ion optics.  Beyond the gain in resolution which has been demonstrated for elemental mapping in EFTEM mode and higher spatial resolution for low acceleration voltages we expect benefits for in-situ TEM, ultra-fast experiments, soft matter imaging, Lorentz TEM and visualizing thick samples.  A summary of these benefits of C_c-correction can be found in Adv. Imaging Electr. Phys. 153, 261-281 (2008).

Performers

B. Kabius, Argonne National Laboratory; P. Hartel, Maximilian Haider, CEOS GmbH, Heidelberg, Germany

[1] B. Kabius, P. Hartel, M. Haider, H. Müller, S. Uhlemann, U. Loebau, J. Zach, H. Rose, J. Electron Microsc., submitted.