title: Four-Dimensional Ultrafast Electron Microscopy: Insights into an Emerging Technique.
abstract: Four-dimensional ultrafast electron microscopy (4D-UEM) is a novel analytical technique that aims to fulfill the long-held dream of researchers to investigate materials at extremely short spatial and temporal resolutions by integrating the excellent spatial resolution of electron microscopes with the temporal resolution of ultrafast femtosecond laser-based spectroscopy. The ingenious use of pulsed photoelectrons to probe surfaces and volumes of materials enables time-resolved snapshots of the dynamics to be captured in a way hitherto impossible by other conventional techniques. The flexibility of 4D-UEM lies in the fact that it can be used in both the scanning (S-UEM) and transmission (UEM) modes depending upon the type of electron microscope involved. While UEM can be employed to monitor elementary structural changes and phase transitions in samples using real-space mapping, diffraction, electron energy-loss spectroscopy, and tomography, S-UEM is well suited to map ultrafast dynamical events on materials surfaces in space and time. This review provides an overview of the unique features that distinguish these techniques and also illustrates the applications of both S-UEM and UEM to a multitude of problems relevant to materials science and chemistry.
authors.affiliation: King Abdullah University of Science and Technology , KAUST Solar Center, Division of Physical Sciences and Engineering, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Aniruddha
authors.initials: A
authors.lastname: Adhikari
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Minnesota , 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States.
authors.forename: Jeffrey K
authors.initials: JK
authors.lastname: Eliason
authors.affiliation: King Abdullah University of Science and Technology , KAUST Solar Center, Division of Physical Sciences and Engineering, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Jingya
authors.initials: J
authors.lastname: Sun
authors.affiliation: King Abdullah University of Science and Technology , KAUST Solar Center, Division of Physical Sciences and Engineering, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Riya
authors.initials: R
authors.lastname: Bose
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Minnesota , 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States.
authors.forename: David J
authors.identifier: 0000-0002-1829-1868
authors.initials: DJ
authors.lastname: Flannigan
authors.affiliation: King Abdullah University of Science and Technology , KAUST Solar Center, Division of Physical Sciences and Engineering, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Omar F
authors.identifier: 0000-0001-8500-1130
authors.initials: OF
authors.lastname: Mohammed
mesh_terms: D008854:Microscopy, Electron; D046590:Spectroscopy, Electron Energy-Loss; D013057:Spectrum Analysis
keywords: 4D ultrafast electron microscopy; atomic resolution; charge carrier dynamics; electron impact dynamics; energy loss mechanism; surface dynamics