Stabilization Mechanism of ZnO nanoparticles by Fe doping
  Surprisingly low solubility and toxicity of Fe-doped ZnO nanoparticles is elucidated on the basis of first-principles calculations. Various ZnO surfaces that could be present in nanoparticles are subject to substitutional Fe doping. We show that Fe stabilizes polar instable surfaces, while non-polar surfaces, namely (1010) and (1120), remain intact. Polar surfaces can be stabilized indirectly through Fe2+-Fe3+ pair assisted charge transfer, what reduces surface polarity and therefore, the solubility in polar solvents. 
Jianping Xiao, Agnieszka Kuc, Thomas Frauenheim, Thomas Heine
cond-mat.mtrl-sci