Cuboctahedra

Clusters with cuboctahedral structures are particles with fcc symmetry (cf. Wulff [36] and Herring [37]). The magic numbers are the same as those for icosahedra. An Ns-shelled cluster consists of No atoms:

Therefore, the magic numbers are 13, 55, 147, 309,____As mentioned before, there is a relation between the diameter of the cluster and the number N0 for closed-shell cubic particles assuming a spherical surface:

D = a 33N0/2w a is the cubic lattice parameter (21)

Figure 3 shows a five-shelled cuboctahedron consisting of 561 atoms. Figures 4 and 5 show computer simulations (top) and experimental images (bottom) in the [110] and [001] orientations, respectively. The PS are displayed on the right-hand side. The computer simulation is performed for seven-shelled cuboctahedra (1415 atoms). Calculations and experiments are performed for Cu at room temperature. No image processing is performed in the present case. The particles were prepared with the inert gas aggregation technique. Generally, it was concluded that larger Cu clusters, that is, larger than about 5 nm critical cluster diameter, show the bulk fcc structure, whereas, as shown later, the smaller Cu clusters have icosahedral or decahedral structures. Examples thereof will be given later. This finding is in good agreement with molecular dynamical calculations by Valkealahti and Manninen [38]. A similar behavior but with different critical cluster sizes also exists for Au, Ag, Pd, etc.

0 0

Post a comment