STUDY OF THE GROWTH OF RHODIUM PARTICLES ON DIFFERENT SUBSTRATES

We have investigated the growth of small supported rhodium particles o n different substrates (mica, Al2O3, NaCl). The particles were deposit ed in a vacuum from a special source permitting a low evaporation rate . The particle size, density and crystallographic structure dependenci es on mean deposit thickness, deposition rate and substrate temperatur e during the deposition were studied by transmission electron microsco py and diffraction (TEM and TED). The results showed that it is possib le to prepare a model Rh catalyst with a well-defined particle populat ion by vacuum vapour deposition. These catalysts form relatively stabl e systems with respect to the thermal treatment. It was observed that the particle density, the mean size and the size dispersion of Rh part icles 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.