Z-contrast imaging of decagonal quasicrystals: an atomistic model of growth

The structure of Al–Ni–Co decagonal quasicrystals is studied by atomic-resolution Z-contrast imaging technique. We propose that the presence of “rotational ordering” is the key reason leading to the formation of the 2 nm clusters and the overlaps necessary in the coverage model. Every detail of the Z-contrast images of the 2 nm clusters can be reproduced by a superposition of rotational variants of the 2 nm clusters seen in the ordered τ2-inflated Al13Co4 approximant phase. Introducing this rotational ordering, it is clear how one cluster can nucleate neighboring clusters. Continuing this process automatically generates all the intercluster separations necessary for quasiperiodic tiling.