On the transition-metal doping efficiency of zinc oxide nanocrystals

Using first-principles density functional theory calculations, we investigate the mechanism of doping colloidal ZnO nanocrystals with the transition-metal elements Mn, Co, and Ni. We find that the dopant atoms have high binding energies for adsorption onto the Zn-vacancy site of the (0001) surface and the O-vacancy site of the (000 (1) over bar) surface of the wurtzite-structure ZnO crystal; therefore, these surface vacancies provide viable sites for substitutional doping, which is consistent with experimental measurements. However, the doping efficiencies are affected by the strong tendencies of the transition-metal dopants to segregate at the nanocrystal surface facets. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3478216]