Is There a Stable Bucky-diamond Structure for SiC Clusters?

We have carried out an extensive search for the SiC Bucky-diamond structure to confirm not only that a pair of Si and C atoms can form sp2- as well as sp3-type bonds but also that these two types of bonds can co-exist in the same SiC-based structure. The successful and surprising discovery of the SinCm Bucky-diamond structure at the specific composition of n=68 and m=79 is the result of the relaxation of the truncated bulk 3C-SiC network to yield a SinCm cluster with m +n=147. It highlights the important role played by the composition in determining the structure and hence other properties of SiC-based nano-structures. We have also shed light on the mechanism behind the formation of the Bucky-diamond structure. The formation process is initiated by the induced bonds between pairs of surface carbon atoms of the initial configuration of the Si68C79 cluster obtained by truncating bulk 3C-SiC network. This action then continuously incorporates atoms in the six outer shells of the Si68C79 clusters to form the 112-atom Fullerene shell through nearest neighbor Si-C interactions. Because the 35-atom inner core with five completely filled shells only interacts weakly with the Fullerene shell through the six atoms on its "surface", the diamond-like inner core is barely perturbed and is suspended inside the Fullerene shell. We have also suggested a likely route of synthesizing the SiC Bucky-diamond structure based on the result of our simulation.