Polytype formation in zirconium‐silicon thin films

The structure of zirconium silicide (ZrSi2, orthorhombic C49; a=0.369 nm, b=1.47 nm, c=0.366 nm) thin films has been investigated by high‐resolution electron microscopy. The crystals are heavily faulted in the 010 plane with an average distance between faults of 1.6 nm. The fault has been found to be a π/2‐rotation twin around the b axis, the habit plane lying between two silicon layers. The crystals contain an equal number of 〈a〉‐ and 〈c〉‐oriented slabs, giving rise to a strained lattice with an average a=c lattice parameter. On the basis of an elastic calculation, the fault energy is evaluated to be of the order of 5 ergs cm−2. This low energy explains the tendency to form polytypes which are mostly disordered, although some ordered sequences are favored at short range.