Field Transmission Electron Microscopy Images Research Articles

Electron microscopy investigation of structure and morphology of small supported metal particles of palladium

The morphology and crystallographic structure of small palladium particles prepared by condensation onto NaCl(001) and mica substrates were investigated using electron diffraction and high resolution defocused dark field and strong beam and weak beam dark field transmission electron microscopy imaging techniques. Sample tilting through large angles was used to characterize particles with a rhombic outline and with irregular outlines. Thus, under conditions with very low deposition rates, it is possible to obtain decahedral or icosahedral particles of which a very high proportion have f.c.c. structure. These results are the opposite of previous ones. On NaCl(001) substrates, the proportion of decahedral particles is about 90% and the size can reach 2000 Å. On mica substrates, the proportion of icosahedral particles 150 Å in size is about 95%.

Formation of iron sulfide fine particles by evaporation in argon gas

Fine particles of iron sulfides were prepared by means of evaporation in argon gas in the pressure range of 5 to 100 Torr in order to study the early stages of growth. Bright and dark field transmission electron microscopy images and scanning micro diffraction patterns show: (i) The iron sulfide particles grow in chains of three types, which are commonly observed to form far from the evaporation source through the experiments with different argon gas pressures. One of the chains is composed of hollow particles, which are characterized by two parts of a hollow core and polycrystalline crust. The second chain is composed of well defined particles which have some facets and edges indicating hexagonal symmetry. The third chain is composed of particles which exhibit the characteristics shape of an octopus-pot. The hollow particles were mainly prepared in the lower argon pressure range (5, 35 Torr), while the other two types of particle whose size increased with the argon pressure were grown in the higher pressure range up to 100 Torr. It was found that the respective particles were coalesced into one long chain by the ferrimagnetic interaction between the particles. (ii) Some film-like products were also observed in the immediate vicinity of the evaporation source.