First principles study on structure and property of Si₂CN₄(010) surface

The structure and property of Si₂CN₄(010) surface with different terminations were studied systemically by first principles calculation. The calculated cleavage energies of each possible surface showed that the Si-N II bond located at the SiN layer was the strongest, while the Si-N I bond connected with the carbodiimide was the weakest. As a result, the surface with the Si/N I termination was the easiest to form. We have compared the atomic structure and electronic properties of un-optimized and optimized surface models. During the optimization of structure, the unsaturated surface atom, especially the N I atoms at the surface would bond with each other to decrease the surface energies, since there are prominent density of states existing at the Fermi level of N I atom. At the same time, the unsaturated C atoms do not have the tendency of bonding with each other, since their electronic state are more stable than N I atom.