Heterogeneous nucleation and microstructure formation in binary colloidal systems

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We experimentally investigate heterogeneous nucleation and subsequent microstruc-ture formation in binary two-dimensional super paramagnetic colloidal systems. Nu-cleation is induced by rotating external magnetic fields which allows the systematic variation of the particle interactions and the corresponding nucleation barriers. In combination with scanning optical tweezers being controlled by acoustic-optical de-flection systems we can configure any initial position of the bigger particles which act as nucleation seeds for the smaller ones. In addition, nucleation centers with arbitrary shapes and sizes can be created. Because nucleation is initiated by an external field and thus sets in at a well-defined instant, this allows us to explore the full temporal development of heterogeneous nucleation starting from a homogeneous initial state until the very late stages of Ostwald ripening and microstructure formation.