Nucleation lays the foundation for the nanoparticle synthesis. Initial nuclei play a vital role on the size and shape of the nanoparticles that will ultimately form by acting as templating nuclei for the nanoparticle itself. Long-term stability is also determined by the initial nucleation procedures. Homogeneous nucleation occurs when nuclei form uniformly throughout the parent phase and is less common. Heterogeneous nucleation, however, forms on areas such as container surfaces, impurities, and other defects. Crystals may form simultaneously if nucleation is fast, creating a more monodisperse product. However, slow nucleation rates can cause formation of a polydisperse population of crystals with various sizes. Controlling nucleation allows for the control of size, dispersity, and phase of nanoparticles.
The process of nucleation and growth within nanoparticles can be described by nucleation, Ostwald ripening or the two-step mechanism-autocatalysis model.