title: Ultrafast Elemental and Oxidation-State Mapping of Hematite by 4D Electron Microscopy.
abstract: We describe a new methodology that sheds light on the fundamental electronic processes that occur at the subsurface regions of inorganic solid photocatalysts. Three distinct kinds of microscopic imaging are used that yield spatial, temporal, and energy-resolved information. We also carefully consider the effect of photon-induced near-field electron microscopy (PINEM), first reported by Zewail et al. in 2009. The value of this methodology is illustrated by studying afresh a popular and viable photocatalyst, hematite, α-Fe2O3that exhibits most of the properties required in a practical application. By employing high-energy electron-loss signals (of several hundred eV), coupled to femtosecond temporal resolution as well as ultrafast energy-filtered transmission electron microscopy in 4D, we have, inter alia, identified Fe4+ions that have a lifetime of a few picoseconds, as well as associated photoinduced electronic transitions and charge transfer processes.
authors.affiliation: Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Zixue
authors.initials: Z
authors.lastname: Su
authors.affiliation: Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: J Spencer
authors.initials: JS
authors.lastname: Baskin
authors.affiliation: School of Chemistry, University of St Andrews , St Andrews, Fife KY16 9ST, U.K.
authors.forename: Wuzong
authors.identifier: 0000-0001-9752-7076
authors.initials: W
authors.lastname: Zhou
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge , Cambridge CB3 0FS, U.K.
authors.forename: John M
authors.initials: JM
authors.lastname: Thomas
authors.affiliation: Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Ahmed H
authors.initials: AH
authors.lastname: Zewail