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SUMMARY:Improving electron microscope capabilities through the design of n
 ew cold field emission electron source
DTSTART:20220127T140000
DTEND:20220127T150000
DTSTAMP:20260407T215705Z
UID:7765deccf6c9fc103c85ca9e3c658689bbf2fd36d2827c17c6efeeb8
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr. Florent Houdellier - CEMES CNRS\nAbstract:\n\nThe electro
 n microscope (Transmission EM or Scanning EM)\, like other machines\, is m
 ade up of several critical components such as the electron source\, lenses
 \, and detectors. Each of these elements has a significant impact on the n
 umber of applications accessible and the quality of the data captured. For
  example\, the precise design of the objective lens magnetic circuit will 
 substantially influence the instrument's resolution as well as the useable
  area available around the sample to interact with it\, whether in traditi
 onal TEM or Scanning EM (STEM or SEM). The influence of geometrical aberra
 tions of the lens will "naturally" rise when this essential space is incre
 ased\, resulting in a worsening of the instrument resolution. For many yea
 rs\, this well-known intrinsic feature of magnetic electron lenses severel
 y hampered TEM capabilities\, but it was solved in the early twenty-first 
 century with the advent of multipole lenses-based aberration correctors. [
 1\, 2]. \nThe introduction of the Cs corrector had a favorable side effec
 t of reviving instrumental innovations and stimulating a new period of inv
 entiveness in the electron optics field. [3\, 4].\n \nIf the objective le
 ns is the instrument's "heart\," the electron source is its "brain\," isol
 ated in a highly sensitive environment (high voltage and vacuum) and havin
 g a significant impact on all of the machine's outcomes. The electron sour
 ce based on electron cold field emission from a metallic nanotip is the br
 ightest of a large family of electron sources [5]. \nWhen high beam coher
 ence is required in TEM or high probe current with minimal energy spread i
 s required in STEM and electron spectroscopic techniques\, the brightness 
 is an appropriate figure of merit. The brightness of the simplest CFE sour
 ce assembly\, i.e. a fine tip and a large round anode\, is optimal due to 
 its short virtual source size in the nm range. In an electron microscope\,
  however\, this virtual source size must be imaged properly and with enoug
 h flexibility to generate either a coherent collimated beam on the sample 
 in TEM or a narrow-focused probe in STEM/SEM.\nElectrostatic gun lenses ar
 e usually employed before the accelerating tube\, followed by magnetic con
 denser/objective lenses. However\, geometrical aberrations of these elemen
 ts will gradually deteriorate the optimum beam brightness\, provided by th
 e first virtual cross\, over in each consecutive image plane. In this well
 -known mechanism shown by a progressive distortion of the emittance figure
  in each related conjugate plane\, the electrostatic optic design\, compos
 ed of the extraction anode and the gun lens assembly above the accelerator
 \, is critical. Many source design options have been offered to improve th
 e tip area\, extractor\, or gun lens assembly to provide an optimization o
 f the final emittance.\nWe started addressing these concerns a few years a
 go alongside Aurélien Masseboeuf and Marc Monthioux in CEMES\, by replaci
 ng the tip material from the original monocrystalline W <310> oriented nan
 otip to a new form of carbon nanocone to boost the holography capabilities
  of our FE-TEM [6\,7]. This first instrumental achievement allowed us to i
 ncrease the brightness and beam current stability of an old 200keV CFE sou
 rce. Together with Arnaud Arbouet\, we recently succeeded in generating br
 illiant and ultrashort electron pulses by mixing a traditional W nanotip c
 athode with a femtosecond laser\, allowing us to implement coherent techni
 ques in an ultrafast TEM\, such as electron holography. [8\, 9]. \nThe st
 rength of these two original developments\, as usually in CFE technology\,
  is heavily influenced by the qualities of the initial pre-accelerator ele
 ctrostatic optic. \nDuring my presentation\, I will quickly summarize the
 se developments and discuss our ongoing research efforts to improve the em
 ittance characteristic of a CFE source and overcome the limitations of our
  previous designs.\n\n\n[1] M Haider\, S Uhlemann\, E Schwan and B Kabius
 \, Development of a spherical corrected 200 kV TEM. Proc. Dreiländert
 agung\, Regensburg\, Germany. 1997\, Optik 106\, 7\n[2] O.L Krivanek 
 \, P.D Nellist\,N Dellby\,M.F Murfitt and Z Szilagyi Towards sub-0.5 Å
  electron beams. 2003 Ultramicroscopy 96\, 229–237\n[3] N Shibata\,
  Y Kohno\, A Nakamura et al. Atomic resolution electron microscopy in a 
 magnetic field free environment. 2019 Nat Commun 10\, 2308\n[4] F Börr
 nert\, F Kern\, F Harder\, T Riedel\, H Müller\, B Büchner\, A Lubk\, Th
 e Dresden in-situ (S)TEM special with a continuous-flow liquid-helium cr
 yostat\,Ultramicroscopy. 2019\, 203\, 12-20\,\n[5] A.V Crewe\, D.N Eggenb
 erger\, J Wall and L.M Welter An electron gun using a field emission sour
 ce. 1968\, Rev. Sci. Instr.39:4.\n[6] F Houdellier\, A Masseboeuf\, M Mo
 nthioux\, M.J. Hÿtch. New carbon cone nanotip for use in a highly coheren
 t cold field emission electron microscope. Carbon. 2012\, 50 (5)\, 2037-2
 044\n[7] S Mamishin\, Y Kubo\, R Cours\, M Monthioux\, F Houdellier. 200
  keV cold field emission source using carbon cone nanotip: Application t
 o scanning transmission electron microscopy. Ultramicroscopy. 2017\, 182\
 , 303 - 307\n[8] F. Houdellier\, G.M. Caruso\, Sébastien J. Weber\, M. K
 ociak\, A. Arbouet. Development of a high brightness ultrafast Transmissio
 n Electron Microscope based on a laser-driven cold field emission source.
  Ultramicroscopy. 2018\, 186\, 128 - 138.\n[9] F. Houdellier\, G.M. Car
 uso\, S. Weber\, M.J. Hÿtch\, C. Gatel\, A. Arbouet Optimization of off
 -axis electron holography performed with femtosecond electron pulses. Ult
 ramicroscopy\, 2019\, 202\, 26-32\n\n\nAbout the speaker:\n\n2006 : Thesis
  at CEMES and Favard Prize of the French Society of Microscopies\n2007 : J
 oining the CNRS\, head of the TEM department at CEMES\n2009 : Recovery of 
 the first HF2000: towards instrumentation\n2018-2022 : Director of the joi
 nt laboratory HC-IUMi between Hitachi High Technologies and CNRS\n2019 : E
 rnst Ruska Prize of the German Society of Microscopies
LOCATION:https://epfl.zoom.us/j/2019908135
STATUS:CONFIRMED
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