Magic-size equilibrium shapes of nanoscale Pb inclusions in Al

We show that the equilibrium shapes of small solid Pb inclusions embedded in an Al matrix are size dependent. Using high resolution electron microscopy we have observed that small inclusions a few nanometers in size adopt equilibrium shapes with smooth {111} facets. Inclusion dimensions follow preferred sizes shown to result from the nature of the residual strain which oscillates and decreases with size. As a result, the inclusion shape is Controlled by the residual strain energy at small sizes and by the interface energy at larger sizes.