Study of the growth of rhodium particles on different substrates

We have investigated the growth of small supported rhodium particles on different substrates (mica, Al₂O₃, NaCl). The particles were deposited in a vacuum from a special source permitting a low evaporation rate. The particle size, density and crystallographic structure dependencies on mean deposit thickness, deposition rate and substrate temperature during the deposition were studied by transmission electron microscopy and diffraction (TEM and TED). The results showed that it is possible to prepare a model Rh catalyst with a well-defined particle population by vacuum vapour deposition. These catalysts form relatively stable systems with respect to the thermal treatment. It was observed that the particle density, the mean size and the size dispersion of Rh particles are controlled by either atom diffusion or by particle migration on the substrate. The diffusion of atoms and clusters increases with the substrate temperature and the growth takes place also by particle coalescence.