Читать книгу Amorphous Nanomaterials - Lin Guo - Страница 23

Using in-situ imaging techniques (scanning electron microscope, transmission electron microscope, and atomic force microscope) to characterize the growth process, James J. De Yoreo of Pacific Northwest National Laboratory summarized the existing crystal growth modes and proposed the crystallization by particle attachment (CPA) theory [30]. He pointed out that, in addition to the monomer-by-monomer addition described in classical models, crystallization by addition of particles, ranging from multi-ion complexes to fully formed nanocrystals, is now recognized as a common phenomenon. Crystallization can occur by attachment of a wide range of species more complex than simple ions. These higher order species are collectively named as particles. They are broadly defined to include multi-ion complexes, oligomers (or clusters), and nanoparticles, whether crystalline, amorphous, or liquid. Compared to traditional growth models, the growth, assembly, and transformation of these particles seem to be the actual route in the formation of crystal particles.

In a real crystallization process, even if only considering the reaction mechanism of a specific system, multiple growth mechanisms can occur simultaneously. It depends on the values of global parameters such as supersaturation, local factors that include interface curvature, and materials parameters such as phase stability versus particle size. The growth process may include the traditional direct connection of atoms, the connection of crystal clusters, the connection of amorphous particles and the subsequent crystallization or maturation, and the oriented or non-oriented connection of crystal particles and recrystallization. Ostwald ripening can occur in all particles to provide free radicals for the main particles. At the same time, twins, stacking faults, and dislocations can result from the attachment of crystalline particles. It can be found that the predictive understanding of the theory of particle-connected crystallization is helpful for the further development of amorphous nanomaterial design and synthesis.