Ultra-small nanocrystals are nanoscale materials. Since the size of ultra-small nanocrystals is comparable to or even smaller than the Bohr exciton diameter of the materials, ultra-small nanocrystals exhibit significant enhanced physical properties, such as magnetic, optical and electronic properties. As the size of a nanocrystal becomes smaller quantum effects, increased astoichiometry, and defects can give rise to many interesting property transitions, including a metal to semiconductor transition, and a diamagnetic to ferromagnetic transition. Facile colloidal synthesis of ultra-small...