Defect structures in TaSi2 thin films produced by co-sputtering

Phase transformation and defect structures in thin-film TaSi2 produced by co-sputtering have been investigated as a function of annealing temperature by transmission electron microscopy. Crystallization of amorphous TaSi2 thin films occurs at 400 deg. C without forming any metastable phases. Most of C40 TaSi2 crystallites contain planar faults parallel to (0001) basal planes. Convergent-beam electron diffraction (CBED) indicates that these planar faults are not simple stacking faults but are twin boundaries bounded by two adjacent enantiomorphically-related twin domains; i.e., domains belonging to the space groups P6222 (right-handed) and P6422 (left-handed) having the identical crystal orientation arrange alternatively separated by twin boundaries parallel to (0001). The formation of these enantiomorphically-related domains in TaSi2 thin films with the hexagonal C40 structures is discussed in comparison with the formation of twin-related domains in MoSi2 (the tetragonal C11b structure) and TiSi2 (the orthorhombic C54 structure) thin films. A new CBED method is proposed for identification of enantiomorphically-related crystals, in which asymmetry in the intensity of Bijvoet pairs of FOLZ disks in an experimental symmetrical zone-axis CBED pattern is compared with that in a computer simulated CBED pattern