Kirkland, WA, United States
Kirkland, WA, United States

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Lovejoy T.,Nion Co. | Rez P.,Arizona State University | Dellby N.,Nion Co.
Ultramicroscopy | Year: 2017

This article is a short biographical sketch of the life and times of Ondrej Krivanek. The story starts with his early days in Prague, Czechia, and briefly outlines various events from a PhD in Cambridge to post-docs in Kyoto, Bell Labs, and building his first spectrometer at UC Berkeley. Ondrej's pioneering contributions to electron microscopy as Assistant Professor at Arizona State University and later as Director of R&D at Gatan are covered, as well as his return to academia and focusing on aberration correction. The story wraps up with the founding of Nion, the early success of the Nion aberration correctors, and subsequent progress such as building a complete cutting-edge electron microscope and later a record-breaking monochromator. Ondrej continues to be actively involved in design and in running Nion, and while this article ends at the present, further breakthroughs can be expected from him. © 2017 Elsevier B.V.


Susi T.,University of Vienna | Kotakoski J.,University of Vienna | Kotakoski J.,University of Helsinki | Kepaptsoglou D.,Daresbury Laboratory | And 10 more authors.
Physical Review Letters | Year: 2014

We demonstrate that 60-keV electron irradiation drives the diffusion of threefold-coordinated Si dopants in graphene by one lattice site at a time. First principles simulations reveal that each step is caused by an electron impact on a C atom next to the dopant. Although the atomic motion happens below our experimental time resolution, stochastic analysis of 38 such lattice jumps reveals a probability for their occurrence in a good agreement with the simulations. Conversions from three- to fourfold coordinated dopant structures and the subsequent reverse process are significantly less likely than the direct bond inversion. Our results thus provide a model of nondestructive and atomically precise structural modification and detection for two-dimensional materials. © Published by the American Physical Society.


Krivanek O.L.,Nion Co. | Dellby N.,Nion Co. | Murfitt M.F.,Nion Co. | Chisholm M.F.,Oak Ridge National Laboratory | And 3 more authors.
Ultramicroscopy | Year: 2010

Aberration correction of the scanning transmission electron microscope (STEM) has made it possible to reach probe sizes close to 1. Å at 60. keV, an operating energy that avoids direct knock-on damage in materials consisting of light atoms such as B, C, N and O. Although greatly reduced, some radiation damage is still present at this energy, and this limits the maximum usable electron dose. Elemental analysis by electron energy loss spectroscopy (EELS) is then usefully supplemented by annular dark field (ADF) imaging, for which the signal is larger. Because of its strong Z dependence, ADF allows the chemical identification of individual atoms, both heavy and light, and it can also record the atomic motion of individual heavy atoms in considerable detail. We illustrate these points by ADF images and EELS of nanotubes containing nanopods filled with single atoms of Er, and by ADF images of graphene with impurity atoms. © 2010 Elsevier B.V.


Krivanek O.L.,Nion Co. | Dellby N.,Nion Co. | Murfitt M.F.,Nion Co.
Journal of Physics: Conference Series | Year: 2011

The scanning transmission electron microscope (STEM) has been able to image individual heavy atoms in a light matrix for some time. It is now able to do much more: it can resolve individual atoms as light as boron in monolayer materials; image atomic columns as light as hydrogen, identify the chemical type of individual isolated atoms from the intensity of their annular dark field (ADF) image and by electron energy loss spectroscopy (EELS); and map elemental composition at atomic resolution by EELS and energy-dispersive X-ray spectroscopy (EDXS). It can even map electronic states, also by EELS, at atomic resolution. The instrumentation developments that have made this level of performance possible are reviewed, and examples of applications to semiconductors and oxides are shown.


Krivanek O.L.,Nion Co.
NATO Science for Peace and Security Series B: Physics and Biophysics | Year: 2012

Aberration-corrected scanning transmission electron microscopes (STEMs) are versatile instruments that can perform many types of investigations. The main use of such microscopes has so far been in direct imaging and analysis, but they are equally well suited to performing diffraction studies and combined diffraction+imaging experiments. The various optical modes needed for such operating modes are reviewed. They include producing electron beams with angular spreads as narrow as a few μrad, and conical precession scans with scan angles >50 mrad. © 2012 Springer Science+Business Media Dordrecht.


Pennycook T.J.,Daresbury Laboratory | Pennycook T.J.,University of Oxford | Lupini A.R.,Oak Ridge National Laboratory | Yang H.,University of Oxford | And 4 more authors.
Ultramicroscopy | Year: 2015

We demonstrate a method to achieve high efficiency phase contrast imaging in aberration corrected scanning transmission electron microscopy (STEM) with a pixelated detector. The pixelated detector is used to record the Ronchigram as a function of probe position which is then analyzed with ptychography. Ptychography has previously been used to provide super-resolution beyond the diffraction limit of the optics, alongside numerically correcting for spherical aberration. Here we rely on a hardware aberration corrector to eliminate aberrations, but use the pixelated detector data set to utilize the largest possible volume of Fourier space to create high efficiency phase contrast images. The use of ptychography to diagnose the effects of chromatic aberration is also demonstrated. Finally, the four dimensional dataset is used to compare different bright field detector configurations from the same scan for a sample of bilayer graphene. Our method of high efficiency ptychography produces the clearest images, while annular bright field produces almost no contrast for an in-focus aberration-corrected probe. © 2014 Elsevier B.V.


Noel T.,University of Washington | Dietrich M.R.,University of Washington | Dietrich M.R.,Argonne National Laboratory | Kurz N.,University of Washington | And 5 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We report on an experimental investigation of rapid adiabatic passage (RAP) in a trapped barium ion system. RAP is implemented on the transition from the 6S 1/2 ground state to the metastable 5D 5/2 level by applying a laser at 1.76 μm. We focus on the interplay of laser frequency noise and laser power in shaping the effectiveness of RAP, which is commonly assumed to be a robust tool for high-efficiency population transfer. However, we note that reaching high state transfer fidelity requires a combination of small laser linewidth and large Rabi frequency. © 2012 American Physical Society.


Krivanek O.L.,Nion Co. | Rusz J.,Uppsala University | Idrobo J.-C.,Oak Ridge National Laboratory | Lovejoy T.J.,Nion Co. | Dellby N.,Nion Co.
Microscopy and Microanalysis | Year: 2014

We propose a practical method of producing a single mode electron vortex beam suitable for use in a scanning transmission electron microscope (STEM). The method involves using a holographic fork aperture to produce a row of beams of different orbital angular momenta, as is now well established, magnifying the row so that neighboring beams are separated by about 1 μm, selecting the desired beam with a narrow slit, and demagnifying the selected beam down to 1-2 Å in size. We show that the method can be implemented by adding two condenser lenses plus a selection slit to a straight-column cold-field emission STEM. It can also be carried out in an existing instrument, the monochromated Nion high-energy-resolution monochromated electron energy-loss spectroscopy-STEM, by using its monochromator in a novel way. We estimate that atom-sized vortex beams with ≥20 pA of current should be attainable at 100-200 keV in either instrument. Copyright © 2014 Microscopy Society of America.


Krivanek O.L.,Nion Co. | Lovejoy T.C.,Nion Co. | Murfitt M.F.,Nion Co. | Skone G.,Nion Co. | And 2 more authors.
Journal of Physics: Conference Series | Year: 2014

A monochromator we have introduced is improving the attainable energy resolution of electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) by more than 2x relative to what has been available until recently. Here we briefly review the design and the performance attained so far. We then investigate the ultimate resolution limits of our system and show that it should be able to reach an energy resolution of <10 meV. © Published under licence by IOP Publishing Ltd.


A high resolution energy-selecting electron beam apparatus and method for improving the energy resolution of electron-optical systems by restricting the energy range of admitted electrons, and optionally also for improving the spatial resolution by correcting chromatic and geometric aberrations. The apparatus comprises a plurality of magnetic or electrostatic prisms that disperse an electron beam according to the energies of the electrons into an energy spectrum, a plurality of magnifying lenses such as electromagnetic or electrostatic quadrupoles that increase the energy dispersion of the energy spectrum, an energy-selecting slit that selects a desirable range of energies of the electrons, and optionally also sextupole, octupole and higher-order lenses that correct chromatic and geometric aberration of the electron-optical system. The apparatus also comprises further magnetic or electrostatic prisms and electron lenses arranged such that the energy dispersion of the electron beam emerging from the apparatus is cancelled.

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