In-Situ TEM Annealing of Nanocrystalline Copper Thin Films S. Simões * , R. Calinas ** , P.J. Ferreira *** , F. Viana * , M. T. Vieira *** , M.F. Vieira * * GMM/IMAT, Dep. de Engenharia Metalúrgica e Materiais, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal ** ICEMS, Departamento Engenharia Mecânica, Faculdade de Ciências e Tecnologia da Universidade de Coimbra, R. Luís Reis Santos, 3030-788 Coimbra, Portugal *** Materials Science and Engineering Program, University of Texas at Austin, Austin, TX 78712, USA Grain growth in nanocrystalline metals has been observed well below the temperatures needed to promote grain growth in coarse grained materials; in some cases, even at room temperature [1]. In this regard, the study of grain growth in nanocrystalline metals is crucial for the development of new nanocrystalline materials with outstanding mechanical properties. Of particular interest is to understand and monitor the kinetics of grain growth. In-situ TEM techniques are invaluable for understanding and characterizing dynamic microstructural changes. In this fashion, the mechanisms and kinetics of grain growth in the aforementioned nanocrystalline copper thin films can be observed and studied in real time. In this work, nanocrystalline sputtered Cu thin films with an average grain size of approximately 43 ± 2 nm were produced by sputtering. Specimens were subsequently annealed in-situ in a transmission electron microscope at 100, 300, 500 ºC during 1, 3 and 5 hours. An increase in grain size and fraction of twins as temperature increases is evident. Specimens annealed revealed that the average grain size at 100, 300 and 500ºC after 5 hours is 70 ± 4 nm, 106 ± 6 nm and 278 ± 10 nm, respectively. As expected, the kinetics of grain growth is significantly faster at 500ºC. Figure 1 shows the microstructural evolution observed during in-situ TEM annealing at the temperature of 500ºC. This sequence of images shows clearly the grain growth process and the formation and growth of one twin (see short black arrow) inside a large grain (labelled A in Figure 1). The value obtained for grain growth exponent n is close to 3 which mean that volume diffusion controls the grain growth. This value is in close agreement with the ones reported for nanocrystalline materials in the literature. The activation energy for grain growth was found to be 35 kJ/mol and is significantly lower than the activation energy found for polycrystalline copper [2] and nanocrystalline copper [3]. In these cases, the value for the activation energy was found to be about 100kJ/mol. On the other hand, other grain growth studies carried out in nanocrystalline copper found a value for the activation energy of around 30kJ/mol [4]. The reason for this discrepancy is not fully understood at this point. One possibility we are considering is that in nanocrystalline materials, the number of atoms that need to jump across the grains, in order for the grain boundary to move, is significantly less than those needed to jump in a polycrystalline material. References [1] C. Detavernier, D. Deduytsche, R. L. Van Meirhaeghe, J. De Baerdemaeker, and C. Dauwe, Appl. Phys. Lett. 82 (2003) 1863 [2] I.M. Ghauri, M.Z. Butt, and S.M. Raza, J. Mater. Sci. 25 (1990) 4782 [3] L. Lu, N. R. Tao, L. B. Wang, B. Z. Ding, and K. Lua, J. Appl. Phys. 89 (2001) 6408 [4] S.K. Ganapatchi, D.M. Owen, and A. H. Chokshi, Scripta Metall. Mater. 25 (1991) 2699. 574 CD DOI: 10.1017/S1431927607078622 Copyright 2007 Microscopy Society of America Microsc Microanal 13(Suppl 2), 2007