Diffraction contrast as a sensitive indicator of femtosecond sub-nanoscale motion in ultrafast transmission electron microscopy

Daniel R. Cremons, Karl B. Schliep, David J. Flannigan

Research output: Chapter in Book/Report/Conference proceedingConference contribution

4 Scopus citations

Abstract

With ultrafast transmission electron microscopy (UTEM), access can be gained to the spatiotemporal scales required to directly visualize rapid, non-equilibrium structural dynamics of materials. This is achieved by operating a transmission electron microscope (TEM) in a stroboscopic pump-probe fashion by photoelectrically generating coherent, well-timed electron packets in the gun region of the TEM. These probe photoelectrons are accelerated down the TEM column where they travel through the specimen before reaching a standard, commercially-available CCD detector. A second laser pulse is used to excite (pump) the specimen in situ. Structural changes are visualized by varying the arrival time of the pump laser pulse relative to the probe electron packet at the specimen. Here, we discuss how ultrafast nanoscale motions of crystalline materials can be visualized and precisely quantified using diffraction contrast in UTEM. Because diffraction contrast sensitively depends upon both crystal lattice orientation as well as incoming electron wavevector, minor spatial/directional variations in either will produce dynamic and often complex patterns in real-space images. This is because sections of the crystalline material that satisfy the Laue conditions may be heterogeneously distributed such that electron scattering vectors vary over nanoscale regions. Thus, minor changes in either crystal grain orientation, as occurs during specimen tilting, warping, or anisotropic expansion, or in the electron wavevector result in dramatic changes in the observed diffraction contrast. In this way, dynamic contrast patterns observed in UTEM images can be used as sensitive indicators of ultrafast specimen motion. Further, these motions can be spatiotemporally mapped such that direction and amplitude can be determined.

Original languageEnglish (US)
Title of host publicationUltrafast Imaging and Spectroscopy
PublisherSPIE
Volume8845
ISBN (Print)9780819496959
DOIs
StatePublished - Jan 1 2013
EventUltrafast Imaging and Spectroscopy - San Diego, CA, United States
Duration: Aug 25 2013Aug 26 2013

Other

OtherUltrafast Imaging and Spectroscopy
CountryUnited States
CitySan Diego, CA
Period8/25/138/26/13

Keywords

  • Bragg condition
  • Ewald sphere
  • Pump-probe
  • Relrod
  • Stroboscopic
  • UTEM
  • Wavevector

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