Pulse-electroplated copper that contained a high density of {111}/<112> nanotwins was found to greatly improve the yield strength while maintaining good electrical conductivity. The thermal stability of nanotwins was a concern and was studied by in situ transmission electron microscopy characterization from 200 to 350C in the present work. It was found that the (11¯2) twin boundary in a junction of (111)/(11¯2)/(111) twins migrates to eliminate the (111) twin boundaries. It was proposed that it was the dominant mechanism that reduced the twin density in the range of temperature studied. The driving force was provided by the elimination of the two (111) boundaries. The inverse migration of the (11¯2) twin boundary driven by a high strain was possible if enough stress was applied to the copper, e.g., the strain introduced during pulsed electroplating. On the other hand, the migration of (111) twin boundary in the direction normal to the twin plane was not found. However, it was proposed that it could happen if a (11¯2) step migrated on the (111) surface, provided that there existed a driving force. The structure and mobility of (112) twin boundary was characterized by high resolution transmission electron microscopy. It was observed that the (112) step on (111) twin plane had a height of 3 atomic layers. It was a unique structural unit of the (112) twin.

Structure and Migration of (112) Step on (111) Twin Boundaries in Nanocrystalline Copper. L.Xu, D.Xu, K.N.Tu, Y.Cai, N.Wang, P.Dixit, J.H.L.Pang, J.Miao: Journal of Applied Physics, 2008, 104[11], 113717