Grain Boundary and Impurity Interactions in Colloidal Crystals

Doping of a metallic crystal by addition of impurity atoms yields well known phenomena such as embrittlement and changes in the electronic band structure. While many impurities have been experimentally observed to be located at grain boundaries within crystals, the methods by which impurities find themselves so located are still obscure. To illuminate the particle-scale processes that enable impurity segregation to grain boundaries, we study 2D colloidal crystals of micron-diameter spheres doped with small densities of larger particles. Using particle tracking image analysis techniques, we track the motions of both grain boundaries and impurity particles to investigate the mutual interactions between these two types of disorder. Our measurements help elucidate the underlying mechanisms that drive impurity segregation, which plays a critical role in stabilizing grain structures.