Info

Figure 22. Detail of a Cu rod with the PS to the right. Reflections 1-8 in the PS represent lattice parameters: dj = 0.211 nm, d2 = 0.332 nm, d3 = 0.566 nm, d4 = d7 = 0.184 nm, d5 = d6 = 0.252 nm, d8 = 0.148 nm. The angle between planes representing reflections 5 and 6 is 27°. Reprinted with permission from [13], A. Lisiecki et al., Phys. Rev. B 61, 4968 (2000). © 2000, American Physical Society.

can be observed along the long axis. This suggests a fcc structure with stacking faults [44, 45]. Computer simulations, however, showed that reflections 5 and 6 with an angle of 27° could not be explained by such a structure. This is also true for reflections 1, 4, and 7. Furthermore, the repetition of the reflection pattern and in the images at ±36° and ±18° could also not be explained by an fcc structure with stacking faults. As was demonstrated above, small Cu clusters prepared by inert gas aggregation show the structure of decahedra or icosahedra (cf. also [46]). Therefore, truncated decahedral particles were calculated in different orientations. Figure 23 shows models, computer simulations, and PS for such a structure. From left to right one obtains: viewed along the 5-fold axis, viewed along 0, and ±36° and ±18°. The tilt angles are defined in the model of Figure 24. As can be seen from the images and from the PS, the struc-

Figure 23. Models, computer simulations, and PS of a truncated decahedron. The orientation is (from left to right) 5-fold axis, [001] direction, and [1-10] direction (parallel to a (001) plane), that is, 0° and 18°, perpendicular to the 5-fold axis for the latter two. Reprinted with permission from [13], A. Lisiecki et al., Phys. Rev. B 61, 4968 (2000). Fig. 8. © 2000, American Physical Society.

Figure 23. Models, computer simulations, and PS of a truncated decahedron. The orientation is (from left to right) 5-fold axis, [001] direction, and [1-10] direction (parallel to a (001) plane), that is, 0° and 18°, perpendicular to the 5-fold axis for the latter two. Reprinted with permission from [13], A. Lisiecki et al., Phys. Rev. B 61, 4968 (2000). Fig. 8. © 2000, American Physical Society.

Figure 24. Model of a decahedron viewed along the 5-fold axis with labeled subunits tj-t5. The arrows indicate the direction of the electron beam. (a) Tilt 0, ±36°. (b) Tilt ±18°. Reprinted with permission from [13], A. Lisiecki et al., Phys. Rev. B 61, 4968 (2000), Fig. 7. © 2000, American Physical Society.

ture represents exactly the results of the different tilts This is also demonstrated in the model of Figure 24, where the different subunits are labeled T1-T5, which are responsible for the different reflections. The different subunits cause single and multiple scattering reflections, all of which can be completely explained. A detailed description is given in [13]. The prepared cylinders show the same structure as the rods. The needles and cylinders show a remarkable behavior under heating. Partial premelting and an extreme lowering of the melting point compared with the bulk are observed. This is discussed in [14, 15].

0 0

Post a comment