A central problem in materials is the tailoring of the grain structure (or more generally nano/microstructure) to achieve the properties required for desired performance in engineered systems. Studies of grain growth in materials date back to the 1920's – therefore, grain growth, is, in some sense, an old problem that should have been understood and solved by now. Indeed, the problem is old enough to have rudimentary explanations provided in undergraduate level materials text books. However, truly predictive theories of grain growth that incorporate experimentally-determined grain boundary properties and satisfy the thermodynamic and topological constraints of the grain boundary network are not yet available – but they are perhaps a little closer given the recent generalization of the von Neumann-Mullins "n-6 rule" for growth of grains in two dimensions to three dimensions by MacPherson and Srolovitz. In this talk, I will review a decade’s worth of experimental studies in Al and Cu films carried out in our group. I will compare the experimental results with those from two-dimensional simulations that do and do not incorporate drag and pinning mechanisms. My aim is to leave you not only with an appreciation of how difficult the problem of grain growth is, but also how very puzzling its stagnation in thin films is.

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