| Abstract: | HREM, image calculations and small probe diffraction/AEM have been used to characterize structure and contrast of supported small metal particles of ≤5 nm diameter. Such small particles are thought to be active species in industrial applications such as in heterogeneous catalysis where, in general, the particles employed as catalysts are supported. Image calculations (HREM and diffraction contrast) carried out at both 200 keV and 400 keV at various defoci and support thicknesses have shown that in HREM, particle images are obscured by the support contrast with the loss of edge definition and particles appear to be smaller than they actually are. The particle visibility is better at 400 keV. The calculations have also indicated that particle shape varies as a function of support thickness and defocus. The results have clear implications for identification and interpretation of surface structure of the supported small particles accurately by HREM if not performed under controlled conditions and for determining their size and shape. |
