Defect structures in cosputtered thin films of transition-metal disilicides with C11_b, C40 and C54 structures

Defect structures in crystallites of the stable phases in thin films of transition-metal (TM) disilicides (C11_b 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 C11_b 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 C11_b 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.