AVS 52nd International Symposium
    Thin Films Wednesday Sessions
       Session TF+EM-WeM

Paper TF+EM-WeM4
Twin Boundaries can be Moved by Step Edges during Film Growth

Wednesday, November 2, 2005, 9:20 am, Room 310

Session: In-Situ/ Ex-Situ & Real- Time Monitoring
Presenter: N.C. Bartelt, Sandia National Laboratories
Authors: N.C. Bartelt, Sandia National Laboratories
W.L. Ling, Sandia National Laboratories
K.F. McCarty, Sandia National Laboratories
C.B. Carter, University of Minnesota
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Considerable effort has been devoted to minimizing twins in a film's microstructure because they typically degrade a film's performance. Twins are generally believed to originate from the nucleation stage of film growth. That is, when film islands nucleate, not all of them contain the same stacking sequence of film layers. Twin boundaries then occur where islands with different stacking sequence impinge. Attempts to reduce the density of twins are usually based on minimizing their nucleation or by removing them by annealing. We track individual twin boundaries in Ag films on Ru(0001) using low-energy electron microscopy (LEEM). We find that twin boundaries can move readily during film growth but relatively little during annealing. The growth-driven motion of twin boundaries occurs as film steps advance across the surface -- as a new atomic Ag layer approaches an fcc twin boundary, the advancing step edge carries along the boundary, which intersects the film thickness. This process can produce twin-free regions that are over 10 µm wide. These observations show that there can be a close connection between morphological evolution and microstructural evolution in thin films. This work was supported by the Office of Basic Energy Sciences, Division of Materials Sciences of the U.S. DOE under Contract No. DE-AC04-94AL85000.