HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY STUDIES OF STRUCTURAL DEFORMATIONS AT THE INTERFACE BETWEEN PD PARTICLES AND MGO SURFACES

Pd clusters were condensed on the surfaces of MgO microcubes, prepared in situ and observed by high-resolution transmission electron microscopy (HRTEM) in order to see directly both the profiles of the particles and the Pd-MgO interfaces. The HRTEM images in cross-sectional view were studied by numerical analysis. Small (1-2 nm) particles, with homogeneously expanded lattice distances, are perfectly accommodated to the MgO substrate and the dilatations are isotropic. In large (5-6 nm) particles, some dilatations of the d200 distances were measured only at the interface, the top and the edges. Theoretical images of these particles (5 nm) were simulated by the multislice method. They provide evidence that the large Pd particles keep the bulk parameter, except in the first three deposited layers, which are expanded and progressively accommodated to the substrate. The deformations observed at the top and the edges are only artefacts of microscopy.