title: Measuring bandgap states in individual non-stoichiometric oxide nanoparticles using monochromated STEM EELS: The Praseodymium-ceria case.
abstract: We describe a method to perform high spatial resolution measurement of the position and density of inter-band impurity states in non-stoichiometric oxides using ultra-high energy resolution electron energy-loss spectroscopy (EELS). This can be employed to study optical and electronic properties of atomic and nanoscale defects in electrically-conducting and optically-active oxides. We employ a monochromated scanning transmission electron microscope with subnanometer diameter electron probe, making this technique suitable for correlating spectroscopic information with high spatial resolution images from small objects such as nanoparticles, surfaces or interfaces. The specific experimental approach outlined here provides direct measurement of the Pr inter-band impurity states in Pr0.1Ce0.9O2-δ via valence-loss EELS, which is interpreted with valence-loss spectral simulation based on density of states data to determine the energy level and character of the inter-band state. Additionally, observation of optical color change upon chemically-induced oxygen non-stoichiometry indicates that the population of the inter-band state is accompanied by an energy level shift within the bandgap.
authors.affiliation: School for the Engineering of Matter, Transport and Energy, Arizona State University, 501 E. Tyler Mall, Tempe, AZ 85287-6106, United States.
authors.forename: W J
authors.initials: WJ
authors.lastname: Bowman
authors.affiliation: Laboratoire de Physique des Solides, Université Paris-Sud, CNRS, UMR 8502, 91405 Orsay Cedex, France.
authors.forename: K
authors.initials: K
authors.lastname: March
authors.affiliation: School for the Engineering of Matter, Transport and Energy, Arizona State University, 501 E. Tyler Mall, Tempe, AZ 85287-6106, United States.
authors.forename: C A
authors.initials: CA
authors.lastname: Hernandez
authors.affiliation: School for the Engineering of Matter, Transport and Energy, Arizona State University, 501 E. Tyler Mall, Tempe, AZ 85287-6106, United States. Electronic address: crozier@asu.edu.
authors.forename: P A
authors.initials: PA
authors.lastname: Crozier
keywords: Cerium dioxide (CeO(2)); Electron energy-loss spectroscopy (EELS); Inter-band states; Monochromated scanning transmission electron microscopy (STEM); Single scattering distribution