Defect structures in cosputtered thin films of transition-metal disilicides with C11b, C40 and C54 structures

Defect structures in crystallites of the stable phases in thin films of transition-metal (TM) disilicides (C11b MoSi2, C40 TaSi2, and C54 TiSi2) produced by cosputtering and subsequent annealing have been investigated by transmission electron microscopy (TEM). Crystallites in thin films of MoSi2, TaSi2, and TiSi2 all contain planar faults parallel to hexagonally arranged TMSi2 planes, which are a characteristic feature commonly observed in all three crystal structures. These planar faults are twin boundaries in all cases. Twins in thin films of these disilicides, thus, have a common characteristic that the twin habit plane is parallel to hexagonally arranged TMSi2 stoichiometric planes. For twins in thin films of C11b MoSi2, and C54 TiSi2, the twining elements can be deduced and the twin habit plane is found not to be parallel to the twinning (K1) plane, but to be perpendicular to it. Twins formed in C40 TaSi2 thin films are different from those formed in C11b MoSi2 and C54 TiSi2 thin films, in that the crystal orientation of the twin is exactly the same as that of the matrix, since they are racemic twins that are only enantiomorphically (space groups of P6222 or P6422) related to each other.