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-co ntrast tomography, in which, by use of a field-emission gun scanning transm ission electron microscope equipped with a high-angle annular dark-field de tector, 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 nano particles 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.