Well-defined long Cu rods having a length of the order of 1 m and diameters of several nanometers were prepared by reduction of copper compounds. After deposition on amorphous carbon films, high-resolution transmission electron microscopy and electron diffraction were performed in order to explain the structure of the rods. By applying computer simulations with multislice calculations, the particle structure was obtained. The rods were held to be truncated decahedra with a fivefold symmetry. It could be shown that most particles were oriented in the ͓001͔ direction with respect to the substrate for one of the five deformed tetrahedral subunits, i.e., the fivefold axis very often was parallel to the surface of the substrate. It was also proven that the Cu fcc bulk structure containing stacking faults had to be excluded as a possible structural model. Also, truncated icosahedral structures or icosahedra with additional intermediate planes did not serve to explain the experimental process. Icosahedra are often observed together with decahedral structures for particles with a spherical-like morphology. Due to the presence of surfactant, only growth in the direction of the fivefold axis of decahedra was possible, resulting in long needlelike rods.
Equilateral CdS nanocrystals with 10-nm sides are produced in a Cd(AOT)2/isooctane/water reverse
micellar solution. The structures of individual nanocrystals are determined by TEM and HRTEM, and
these data were compared with computer simulations and power spectra calculations. This shows that the
particles are crystallized in a hexagonal (wurtzite) form. The thickness of these equilateral nanocrystals
(around 5 nm) is estimated from optical measurements. These nanocrystals are not highly stable as the
coated surfactant desorbs, and they coagulate, forming particles with a cubic structure (zinc blende).
The annealing process of truncated decahedral cylindrical copper particles with 5-fold symmetry (7.5 × 20.5 nm) is presented. The melting point of the cylinders lies below the melting point of the bulk phase. During the annealing process, various stages of surface diffusion, premelting, and melting take place. Depending on the particle coating with the surfactant, two behaviors are observed. When the nanocrystals are well-coated, they disappear completely at 520 °C. At the opposite, when they are not well-coated and are placed closely together during the premelting phase (at 380 °C), a percolation process leads to the formation of large aggregates which tend to crystallize again at a melting point far above 520 °C.
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