Surface ligand assisted valence change in ceria nanocrystals

In this report, we used x-ray absorption, electron energy-loss, and magnetic analyses to demonstrate the effect of modification of ceria (CeO _2-δ) nanocrystals with a particle size D= 3.5-14 nm by oleic acid surface ligands. We observe a shift of the electronic state of the cerium ions from tetra to trivalent state as the surface density of the ligand molecules is increased. The valence state of cerium in the nanocrystal is strongly correlated with the number of ligand molecules bound to the surface of the ceria nanocrystals. One oxygen vacancy is stabilized by 5-6 ligand molecules bound on a CeO_2-δ nanocrystal.