Zhiming Lin

Surface charges and optical characteristic of colloidal cubic SiC nanocrystals

Colloidal cubic silicon carbide (SiC) nanocrystals with an average diameter of 4.4 nm have been fabricated by anisotropic wet chemical etching of microsized cubic SiC powder. Fourier transform infrared spectra show that these cubic SiC nanocrystals contain carboxylic acid, SiH, CH, and CHx groups. UV/Vis absorption and photoluminescence (PL) spectroscopy clearly indicate that water and ethanol colloidal suspensions of the as-fabricated colloidal samples exhibit strong and above band gap blue and blue-green emissions. The cubic SiC nanocrystals show different surface charges in water and ethanol solutions due to the interaction of water molecules with polar Si-terminated surfaces of cubic SiC nanocrystals. The results explain the distinctive optical characteristics of colloidal cubic SiC nanocrystals in water and ethanol, and reveal that quantum confinement and surface charges play a great role in determining the optical characteristics of colloidal cubic SiC nanocrystals.

Effect of dopants on the crystallite growth of superfine zirconia powder

Abstract Crystallites can grow in superfine zirconia powder during calcination. It is found that, in addition to calcination temperature and holding time, the crystallite size or crystallite growth rate can apparently also be affected by doping. Undoped powder has the largest crystallite size and the size decreases as the dopant content increases under the same calcination conditions. The effect of crystallite growth suppression is also dependent on dopant types, and it is explained by the dopants surface energy reduction effect, which is related to their ability to stabilize tetragonal and/or cubic phases of zirconia and to their surface-enriching and solute-dragging effects.