PNNL

Abstract

The optical properties and charge trapping phenomena observed on oxide nanoparticle ensembles can be strongly influenced by the presence of particle-particle interfaces. Powders of MgO nanocrystallites represent a convenient system to study these effects due to their well defined shape and adjustable size distributions. The spectroscopic properties of particle-particle interfaces are investigated by monitoring the dependence of absorption characteristics on the concentration of the interfaces in the nanopowders. The presence of interfaces is found to affect the absorption spectra of nanopowders more significantly than changing the size of the constituent nanocrystallites. We find a strong absorption band in the 4.0-5.5 eV energy range, which was previously attributed to surface features of individual nanocrystallites, such as corners and edges. These findings are supported by complementary first principles calculations. The possibility to directly address such interfaces by tuning the energy of excitation may provide new means for functionalization of nanostructures, chemical activation, and can help improve performance and reliability for many nanopowder applications, such as such as photo-catalysts and solar cells.