Hexagonal Particles

Examples of two different preparations described above are given for CdS ligand stabilized clusters, that is, one preparation for sphere-like clusters (Figs. 6-9) and the other for flat triangular clusters (Fig. 10). For the spherical particles computer simulations are also performed as shown at the top of the images. For simplicity the calculations are performed for hcp clusters consisting of only one type of atom, whereas the experimental images consist of two types of atoms. Therefore, more reflections appear in the PS of the experimentally obtained CdS images. This is due to the lowering of the symmetry for these samples. The PS in Figures 6-8 are a convincing demonstration thereof. The same applies for the PS of the triangular particle in Figure 10. The calculations are performed for seven-shelled clusters consisting of 2037 atoms. The orientations of the particles are

Figure 3. Model of a cuboctahedron consisting of five shells, 561 atoms.

Figure 4. Computer simulation (top) and electron micrograph (bottom), together with the PS on the right-hand side of a Cu cuboctahe-dron consisting of seven shells, 1415 atoms in the [110] orientation.

[001] (Fig. 6), [011] (Fig. 7), [100] (Fig. 8), [211] (Fig. 9), and [001] (Fig. 10B). It is well known that bulk CdS exists in two structures, sphalerite (cubic) and wurtzite (hexagonal) [17]. In the case of spherical particles both structures were observed. However, only hexagonal examples are shown here. For the triangular particles, however, only hexagonal structures could be observed. To exclude also cubic structures with stacking faults, computer simulations for CdS with different numbers of stacking faults were performed (cf. Fig. 11). The structures, stapling, and orientations for the images in Figure 11a-e (from top to bottom) are as follows:

a: cubic, abc abc abc, orientation [111]

b: cubic, abc abc ab, orientation [111]

Figure 5. Computer simulation (top) and electron micrograph (bottom) together with the PS on the right hand-side of a Cu cuboctahedron consisting of seven shells, 1415 atoms in the [001] orientation.

Figure 3. Model of a cuboctahedron consisting of five shells, 561 atoms.

Figure 5. Computer simulation (top) and electron micrograph (bottom) together with the PS on the right hand-side of a Cu cuboctahedron consisting of seven shells, 1415 atoms in the [001] orientation.

Figure 6. Computer simulation (top) of a hcp structure and electron micrograph (bottom) of CdS and the PS on the right-hand side in the [001] orientation. The simulation consists of seven shells, 2037 atoms.

Figure 8. Computer simulation (top) of a hcp structure and electron micrograph (bottom) of CdS and the PS on the right-hand side in the [100] orientation. The simulation consists of seven shells, 2037 atoms.

Figure 6. Computer simulation (top) of a hcp structure and electron micrograph (bottom) of CdS and the PS on the right-hand side in the [001] orientation. The simulation consists of seven shells, 2037 atoms.

Figure 8. Computer simulation (top) of a hcp structure and electron micrograph (bottom) of CdS and the PS on the right-hand side in the [100] orientation. The simulation consists of seven shells, 2037 atoms.

c: cubic, abc ab ab, orientation [111] d: cubic, ab ab ab, orientation [001]

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