title: Toward single mode, atomic size electron vortex beams.
abstract: 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.
authors.affiliation: 1Nion Co.,1102 8th St. Kirkland,WA 98033,USA.
authors.forename: Ondrej L
authors.initials: OL
authors.lastname: Krivanek
authors.affiliation: 2Department of Physics and Astronomy,Uppsala University,SE-751 20 Uppsala,Sweden.
authors.forename: Jan
authors.initials: J
authors.lastname: Rusz
authors.affiliation: 3Center for Nanophase Materials Sciences,Oak Ridge National Laboratory,Oak Ridge,TN 37831,USA.
authors.forename: Juan-Carlos
authors.initials: JC
authors.lastname: Idrobo
authors.affiliation: 1Nion Co.,1102 8th St. Kirkland,WA 98033,USA.
authors.forename: Tracy J
authors.initials: TJ
authors.lastname: Lovejoy
authors.affiliation: 1Nion Co.,1102 8th St. Kirkland,WA 98033,USA.
authors.forename: Niklas
authors.initials: N
authors.lastname: Dellby