For three dimensional investigations on the nanometer scale we use the LIBRA 200 transmission electron microscope for tomography. The sample is stepwise titled in the special sample holder from about +70 to -70 degrees and at each angle the projected and magnified image is recorded. The three dimensional data set is subsequently retrieved from these images using dedicated reconstruction software. Further software packages allow for visualization and quantification.
Electron tomography can be combined with the various imaging and analytical tools of the TEM:
TEM tomography in bright field mode is sensitive to absorption.
STEM tomography yields information about the mean atomic number.
Energy filtered TEM allows to record the three dimensional distribution of specific elements.
Currently, we use electron tomography to study the morphological properties of metal catalyst particles and of their supporting carbon black. The image on the right displays a tomographic slice through a reconstructed data set (image width 78 nm). Dark ruthenium particles of a few nanometer size can be seen at the circumference of the supporting carbon black. By accessing the three dimensional structure we can unambiguously shown that there are no catalysts particles within the carbon black.