Showing papers by "Ondrej L. Krivanek published in 2015"

Aberration-corrected STEM for atomic-resolution imaging and analysis.

Abstract: Aberration-corrected scanning transmission electron microscopes are able to form electron beams smaller than 100 pm, which is about half the size of an average atom. Probing materials with such beams leads to atomic-resolution images, electron energy loss and energy-dispersive X-ray spectra obtained from single atomic columns and even single atoms, and atomic-resolution elemental maps. We review briefly how such electron beams came about, and show examples of applications. We also summarize recent developments that are propelling aberration-corrected scanning transmission electron microscopes in new directions, such as complete control of geometric aberration up to fifth order, and ultra-high-energy resolution EELS that is allowing vibrational spectroscopy to be carried out in the electron microscope.

Vibrational phonon spectroscopy of boron nitride polymorphs: a comparison between theory and experiment

Abstract: 1 Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, U.K. 2 SuperSTEM Laboratory, STFC Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD, U.K. 3 School of Applied Sciences, RMIT University, Melbourne VIC 3001, Australia 4 Nion Company, 11511 NE 118 St., Kirkland, WA 98034, U.S.A. 5 STFC Rutherford Appleton Lab., Harwell Science and Innovation Campus, Didcot OX11 0QX, U.K. 6 Department of Physics, Royal Holloway, University of London, Egham TW20 0EX, U.K.

Hydrogen Analysis by Ultra-High Energy Resolution EELS

Abstract: 1. Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel 2. Department of Physics, ASU, Tempe, AZ 85287, USA 3. Center for Solid State Science, Arizona State University, Tempe, AZ 85287, USA 4. School for Engineering of Matter, Transport and Energy, ASU, Tempe, AZ 85287, USA 5. Nion Co., 11511 NE 118 St., Kirkland, WA 98034, USA 6. Structural Biology, Weizmann Institute of Science, Rehovot 76100, Israel 7. Physique des Solides, University of Paris-Sud, Orsay 91405, France

Name that Atom in 60 Seconds or Less: Energy Dispersive X-Ray Spectroscopy of Individual Heteroatoms in Low Dimensional Materials

Abstract: The feasibility of identification of individual Si atoms on single-layer graphene on the basis of energy dispersive x-ray spectroscopy (EDXS) in a scanning transmission electron microscope (STEM) has been demonstrated [1]. However, the employed measurement conditions, i.e., manual tracking of single Si atoms on single carbon sheets over collections time of 4 to 6 minutes greatly limited the applicability of the method for more wide-spread use. Under such conditions, there is no clear advantage of EDXS over the use of quantitative annular dark field image analysis, or electron energy loss spectroscopy (EELS). To be truly practical for samples such as supported catalyst nanoparticles or other low dimensional materials, single atom EDXS measurement conditions must allow for robust atom identification in seconds, in samples with variable thickness that contain combinations of multiple, unknown heteroatom species.

Zen-like Simplicity is Hard Work, and Other Secrets I Learned from Peter Swann

Abstract: This talent served him particularly well when he finished his Ph. D. studies at Cambridge, UK, and joined the research staff at the US Steel Research Center in Monroeville PA, USA. Unraveling the mysteries of dislocations and other defects in metals by imaging them in the newly available electron microscopes was a hot topic back then. Peter developed a double-tilt sample holder for a Siemens Elmiskop I electron microscope [1], which allowed crystals to be imaged in the precise orientation needed for g.b contrast of dislocations (g = chosen reflection, b = Burgers vector). This was a major step on a career path that Peter honed to perfection over the years: developing new capabilities for electron microscopes, preferably in areas that had hardly been touched.

STEM-EDXS System for Atomic-Sensitivity Elemental Mapping

Abstract: The Nion UltraSTEM aberration-corrected cold field emission scanning transmission electron microscope (AC-CFE-STEM) can focus a beam current of about 0.2 nA into an atom-sized (~1.5 Å large) electron probe at a primary energy of 60 keV (and about 1 nA at 200 keV). Using such an electron probe with an ultra-thin window silicon drift detector (SDD) of 30 mm (0.1 sr solid angle) in a Mark I system at 60 keV allowed energy dispersive X-ray spectroscopy (EDXS) to identify individual atoms while tracking their occasional hops to neighboring lattice sites [1]. Here we report on the design and performance of a Mark II STEM-EDXS system with about 10x higher efficiency, which allows single impurity atoms to be identified even when they are very mobile.