Synchrotron Characterization of Texture and Stress Evolution in Ag Films
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1027-D01-01
Synchrotron Characterization of Texture and Stress Evolution in Ag Films Aaron Vodnick1, Michael Lawrence1, Bethany Little2, Derek Worden2, and Shefford Baker1 1 Department of Materials Science and Engineering, Cornell University, Ithaca, NY, 14853 2 Department of Physics, Houghton College, Houghton, NY, 14744
ABSTRACT
Real-time in-situ synchrotron x-ray diffraction measurements were performed at the Cornell High Energy Synchrotron Source to characterize both the texture evolution and stresses within the individual texture components of Ag films during texture transformations. As deposited films had a nearly perfect (111) fiber texture. During isothermal anneals, stress and texture were characterized in real time as the texture evolved into a strong (001) fiber. An Avrami analysis of the evolving texture fractions yielded very different activation energies for films on different barrier layers, suggesting that different governing mechanisms were responsible for secondary grain growth. The strains were used to test a common model for texture prediction that assumes the same strain within each texture component. It was found that secondary (001) grains were able to grow primarily strain free. Selection for this strain energy minimizing orientation occurred during the nucleation process during which texture interactions play an important role. By using real time x-ray diffraction measurements, we are able to show that driving forces for texture transformations in metal films may not be as simple previously described.
INTRODUCTION
The mechanical behavior of metal films is highly dependent on their microstructures. FCC metal films tend to have highly oriented columnar grains with either the or crystal orientation normal to the film plane. It is widely accepted that these two orientations arise due to a minimization of interface or strain energy, respectively1. The preferred orientation will minimize the total energy of the film, which depends on the relative contributions of the surface ( Wγ = ∆γ h ) and strain energies ( Wε = ∆Yε 2 ), where ∆γ and ∆Y are the difference in interface energies and biaxial moduli between (111) and (001) orientations, respectively, h is the film thickness, and ε is the applied strain. Improvements to this model have been made by considering the different yield stresses2, 3 for the different texture components, and the effect of changing strain due to grain growth3, though the latter has been utilized much less. These energy models for texture selection predict a critical thickness at which a sharp texture transition occurs, but in real films the texture transition often occurs over a wide thickness range (e.g. [2]). The mixed texture observed in many films is also not explained using this model. Mixed texture may be explained by interactions between anisotropic texture components, which may significantly affect the strain energies in both orientations. For instance, recent work showed the strain energies within the (111) and (001) grain orientations in a 500 nm annealed copp
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