In situ TEM observation of dislocation motion in thermally strained Al nanowires

Al thin films deposited epitaxially on (0001) alpha-Al2O3 substrates, have been thinned cross-sectionally to form Al nanowires. The Al wires, consisting of two Sigma3 twin variants, have been strained in situ by differential thermal expansion between the Al wires and the Al2O3 substrate during transmission electron microscopy heating. Dynamical observations show that maximum dislocation activity occurs in the first heating cycle up to 400degreesC, with decreasing activity during further cycles. The {111} Al parallel to (0001) alpha-Al2O3 interface acts as a source of dislocation half-loops. The motion of threading dislocations along the wires generates long trailing dislocation segments parallel to, and offset from, the {111} Al parallel to (0001) alpha-Al2O3 interface. Dislocation multiplication occurs by the reaction of half-loops and extended threading dislocation segments at the wire boundaries and substrate interface. The Sigma3 twin grains bisecting the wires are observed to be stable during thermal cycling to 400degreesC, and their {2 (11) over bar} boundaries are weak pinning sites. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.