CHARACTERIZATION OF (1(1)OVER-BAR-01) TWIN DISLOCATION-STRUCTURES IN EVAPORATED TITANIUM THIN-FILMS BY HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY

The structure of {1101BAR} twin dislocations in Ti films evaporated on NaCl substrates at 250-degrees-C has been examined and characterized by high-resolution transmission electron microscopy. The results have revealed that a twin dislocation structure with a step height 4d(K1), where d(K1) is the spacing of the {1101BAR} twin planes, actually dissociates into two {1101BAR} twin dislocations with step heights of d(K1) and 3d(K1). The twin dislocation with a step height of 3d(K1) contains an edge dislocation in the core, while that with a step height of d(K1) is a simple classical twin-dislocation structure. Twin dislocations with a step height of 2d(K1), including an edge dislocation in the core, also occur. The atomic-scale core structures of {1101BAR} twin dislocations may be derived by analysis of the high-resolution images. The relative mobilities of the three types of twin dislocations are then discussed.