Effect of reaction temperatures and media on crystal structure of colloidal nanocrystals synthesized from an aerosol flow system.

The CdSe and CdTe nanocrystals were successfully synthesized from the ultrasonic-assisted aerosol flow system using a surfactant/solvent system of oleic acid (OA)/trioctylphosphine (TOP)/trioctylphosphine oxide (TOPO)/octadecene (ODE). A comprehensive examination on the control of the CdSe and CdTe crystal structures and optical properties was performed as functions of reaction temperatures and amount of reaction media in the aerosol flow system. CdSe nanocrystals with spherical shape and having zinc blende structure were produced. It was found that the crystal structure and shape of CdSe are not affected by reaction temperature. However, it was found that reaction temperature significantly affects the crystal structure and morphology of CdTe. Zero-dimensional CdTe nanocrystals with spherical shape and having zinc blende structure were obtained at the temperature higher than 300 degrees C. Three-dimensional tetrapod-shaped CdTe nanocrystals having wurtzite structure were obtained at the temperature lower than 250 degrees C. Furthermore, the anisotropic growth was observed to be enhanced as increasing the amount of OA used at the temperature of 250 degrees C.