5.4 Stimulated Nano-Cluster Transformations

It has already been discussed that large cubic aluminium clusters with (001) oriented surfaces build a rather stable phase while smaller cubes with the same face orientation show more or less extended meta-stable states which finally transit into stable configurations with mainly (111) structured surfaces.

As an example, without external influence an Al ₂₉₁₆ cluster (upper most picture of Fig. 5.24) does never leave such a "stable" state. This has been proofed for several initial conditions and periods of up to 150 ps. Since the considered MD models mirror ideal situations only, where no interactions with the environment take place (absolute vacuum), the question arises, whether an external stimulation can trigger a structural transformation in the same way as has been observed for smaller clusters without external influence.

Figure 5.24: The upper most picture shows a "pseudo stable" state of an Al ₂₉₁₆ cluster (the layers are colored red and green for a more instructive visualization of the structure) that can be stimulated to transit into finally stable states by a collision with another cluster (in this case an Al ₆₃ cube which is colored blue). The final structure strongly depends on the impact parameters. Several cases are illustrated, each from three different viewing angles (front, top and impact direction), about 3 ps after the cluster collision: (a) The impact velocity of the Al ₆₃ cluster is 1000 m/s. (b) The impact velocity is 2000 m/s with the same impact target as...