The determination of structure in small supported metal particles by scanning transmission electron diffraction

The crystallographic structure of small Pd particles formed during the earliest stages of vapor deposition onto refractory oxide supports was studied by energy filtered in situ UHV scanning transmission electron diffraction (STED). Although only the average structure of particles can be obtained by this high-precision, large area diffraction technique, its main advantage over high-resolution transmission electron microscopy (TEM) is the drastic reduction of radiation damage effects. On-line processed experimental diffraction data were compared to calculated elastic diffraction intensities and radial distribution functions obtained by Fourier transformation. The results show conclusive evidence that small Pd clusters of less than about 2 nm size prefer non-fcc icosahedral packaging over the standard fcc structure, which confirms earlier theoretical predictions for minimum energy cluster configurations. Standard fcc structures always dominate in later stages of growth with increasing particle size. © 1989, American Vacuum Society. All rights reserved.