Electron Tomography of Nanoparticle Catalysts on Porous Supports: A New Technique Based on Rutherford Scattering

We report a new variant of three-dimensional (3D) electron microscopy, Z -contrast tomography, in which, by use of a field-emission gun scanning transmission electron microscope equipped with a high-angle annular dark-field detector, images are formed by Rutherford scattered electrons. The intensity of such electrons is approximately proportional to Z 2 ( Z being the atomic number of the scattering atom) so that the technique preferentially images high- Z materials distributed over low- Z supports. The 3D structure of nanoparticles catalysts, as well as that of the porous support (and especially the precise location of the former on the latter), is reconstructed from a tilt series of 2D projections by a (real space) tomography procedure using a weighted back projection approach.