Nanocrystallization

Nanocrystallization is the formation of crystalline particles on the nanometer scale, producing nanocrystals with dimensions typically from 1 to 100 nanometers. It can occur from melts, solutions, or vapors and is governed by nucleation and growth. The kinetics and thermodynamics depend on supersaturation, temperature, and the environment at interfaces, with high surface area and possible size-dependent properties distinguishing nanocrystals from bulk crystals.

Mechanisms include homogeneous and heterogeneous nucleation, followed by growth on existing nuclei. Common bottom-up routes are colloidal synthesis in solution, solvothermal or hydrothermal methods, precipitation, and templated or epitaxial growth. Vapor-phase crystallization and thin-film deposition are also used for anisotropic nanocrystals. Surface ligands and substrates help stabilize small sizes and direct shape.

Characterization focuses on size, phase, and crystallinity. Techniques include X-ray diffraction, transmission electron microscopy, and SAED for structure; UV-Vis or photoluminescence for optical properties; dynamic light scattering for size distribution; and elemental analysis like EDS. Challenges include controlling size dispersion, achieving high crystallinity, preventing ripening or aggregation, and ensuring chemical stability.

Applications span catalysis, electronics, photovoltaics, sensing, and biomedicine. Quantum dots are used in displays and imaging; semiconductor nanocrystals enable tailored optoelectronic properties; metal nanocrystals serve in catalysis and plasmonics. Realizing consistent performance requires precise control of size, shape, and surface chemistry and attention to safety and environmental issues.