Nucleation of nanocrystals in solution: confinement by the amorphous networks

摘要: Recent advances show that nucleation of crystalline phases from dilute solutions often involves the formation of intermediate disordered states: clusters, droplets, amorphous nanoparticles, polymorphs etc [1]. It remains unclear how the intermediate states affect the predictions of the classical single-step nucleation theory, in terms of activation barrier, rate of nucleation, or critical cluster sizes. Progress is hampered by the difficulty to reach sufficient resolutions (<1nm, <<1s), without perturbing the metastable process. Here, we overcome this issue using in situ x-ray scattering, and report nucleation rates upon formation of different nanocrystals in solution (luminescent YVO4:Eu, magnetite Fe3O4), where an intermediate nanostructured amorphous network is evidenced [2,3]. We find how the amorphous precursor impedes nucleation at the nanometer scale, and limits the size of the nanocrystals. The clarification of the role of the intermediate nanostructure clarifies why the predicted nanocrystal sizes are overestimated by several orders of magnitude by classical theories.