STRUCTURE AND MORPHOLOGY OF SMALL PALLADIUM PARTICLES (2-6 NM) SUPPORTED ON MGO MICRO-CUBES

Small MgO cubes were prepared in a controlled atmosphere and protected against air contamination. Their clean surfaces were used as supports for Pd particles (2-6 nm) vacuum-deposited from a Knudsen cell in the same chamber. The Pd particles epitaxially oriented on the substrate were observed by HRTEM, microdiffraction and convergent-beam electron diffraction. An isotropic lattice expansion was determined by microdiffraction on isolated particles, increasing between 2% and 8% for particle sizes decreasing from 6 to 2 nm. From the HRTEM images of particles observed in two directions, parallel and perpendicular to the interface with the MgO substrate, the particles were characterized as single crystals with fcc structure and octahedral shape. The octahedra are truncated by (001) planes at the top and at the interface. © 1990.