Abstract
We investigate the electronic properties of nanocrystalline cerium oxide films, grown by various techniques, and we establish universal relations between them and the film structure, composition, and morphology. The nanocrystalline films mainly consist of grains, while a considerable concentration of trivalent is distributed at the grain boundaries forming amorphous A small portion of is also located around O-vacancy sites. The optical properties of the films are considered, taking into account the reported band-structure calculations. The fundamental gap of is due to the indirect electronic transition along the L high-symmetry lines of the Brillouin zone and it is correlated with the content, explaining the redshift of in nanostructured which is due to the at the grain boundaries and not due to the quantum-size effect itself. We also correlate the energy position of the electronic transition, which varies up to 160-meV wide, with the lattice constant of the grains. We also show that the higher-order transitions are more sensitive to film composition. The refractive index, far below is explicitly correlated with the film density, independently of the and O concentrations, grain size, and lattice parameter. The density is also found to be the major factor affecting the absolute value of the peak, which corresponds to the electronic transition.
- Received 23 December 2002
DOI:https://doi.org/10.1103/PhysRevB.68.035104
©2003 American Physical Society