Chromatic Aberration Correction for Atomic Resolution TEM Imaging from 20 to 80 kV

Martin Linck, Peter Hartel, Stephan Uhlemann, Frank Kahl, Heiko Müller, Joachim Zach, Max. Haider, Marcel Niestadt, Maarten Bischoff, Johannes Biskupek, Zhongbo Lee, Tibor Lehnert, Felix Börrnert, Harald Rose, and Ute Kaiser

Phys. Rev. Lett. 117, 076101 – Published 9 August 2016

Abstract

Atomic resolution in transmission electron microscopy of thin and light-atom materials requires a rigorous reduction of the beam energy to reduce knockon damage. However, at the same time, the chromatic aberration deteriorates the resolution of the TEM image dramatically. Within the framework of the SALVE project, we introduce a newly developed $C_{c} / C_{s}$ corrector that is capable of correcting both the chromatic and the spherical aberration in the range of accelerating voltages from 20 to 80 kV. The corrector allows correcting axial aberrations up to fifth order as well as the dominating off-axial aberrations. Over the entire voltage range, optimum phase-contrast imaging conditions for weak signals from light atoms can be adjusted for an optical aperture of at least 55 mrad. The information transfer within this aperture is no longer limited by chromatic aberrations. We demonstrate the performance of the microscope using the examples of 30 kV phase-contrast TEM images of graphene and molybdenum disulfide, showing unprecedented contrast and resolution that matches image calculations.

Received 22 April 2016

DOI:https://doi.org/10.1103/PhysRevLett.117.076101

Physics Subject Headings (PhySH)

Beam optics

Transmission electron microscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Martin Linck^*, Peter Hartel, Stephan Uhlemann, Frank Kahl, Heiko Müller, Joachim Zach, and Max. Haider

Corrected Electron Optical Systems GmbH, Englerstrasse 28, D-69126 Heidelberg, Germany

Marcel Niestadt and Maarten Bischoff

FEI Company, Achtseweg Noord 5, 5651 GG Eindhoven, Netherlands

Johannes Biskupek, Zhongbo Lee, Tibor Lehnert, Felix Börrnert, Harald Rose, and Ute Kaiser

Central facility of electron microscopy, Ulm University, Albert-Einstein-Allee 11, D-89081 Ulm, Germany

^*linck@ceos-gmbh.de

Article Text (Subscription Required)

Click to Expand

Supplemental Material (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 117, Iss. 7 — 12 August 2016

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
TEM images of small gold clusters on thin carbon film at 20 kV with diffractograms obtained in (a) an uncorrected TEM, (b) a $C_{s}$ -only corrected TEM and (c) the $C_{c} / C_{s}$ -corrected SALVE TEM. Only panel (c) shows the Au clusters atomically resolved.
Reuse & Permissions
Figure 2
(a) Photograph of the SALVE $C_{c} / C_{s}$ corrector during installation into the TEM column. It adds 43 cm of length and about 185 kg of weight to the TEM column. (b) The corrector consists of eight multipoles. Here, the axial and off-axial rays in the $x$ section (blue) and the $y$ section (red) are overlaid to the corrector scheme.
Reuse & Permissions
Figure 3
The microscope’s resolution at (a) 80 kV, (b) 60 kV (c) 40 kV (d) 30 kV, and (e) 20 kV as determined by Young’s fringes on an amorphous tungsten sample. The FFTs of the images are equally scaled ( $10 {nm}^{- 1}$ scale bar) and show the results for two perpendicular directions (upper and lower half, respectively), indicating uniform information transfer exceeding 50 mrad (white half circle) for all accelerating voltages. (f) The measured aberration function $χ$ of the 20 kV setting shows that a uniform phase contrast transfer function (PCTF) can be tuned in the SALVE corrector [phase plate $χ$ to scale with (e); green color illustrates where $\sin χ > 0.5$ ]. The corresponding aberration coefficients are listed in the Supplemental Material [26].
Reuse & Permissions
Figure 4
(a) Achromaticity at 20 kV: In $C_{c}$ -uncorrected TEMs (red line: $C_{c} = 1.45 mm$ ) the defocus changes dramatically with a change of electron energy. In the SALVE microscope (black dots: measurement; dashed line: third-order fit) the energy-dependent defocus changes only due to the remaining quadratic and cubic chromatic aberrations. (b) Estimation of focus spread: The information transfer under axial illumination (solid profile) does not show any deterioration at all if the beam is tilted to 3° (52.4 mrad) (red line in profile).
Reuse & Permissions
Figure 5
Experimental and calculated $C_{c} / C_{s}$ -corrected 30-kV HRTEM images of graphene (A) and ${MoS}_{2}$ (B). The diffractograms (A1 and B1) of the experimental raw images of graphene (A2) and ${MoS}_{2}$ (B2) in bright-atom contrast (field of view $40 \times 40 {nm}^{2}$ ) indicate the achieved resolution. The magnified images (A3 and B3) directly allow for identifying the atomic structure. The averaged experimental images (A4 and B4) show a strong signal-to-noise improvement and are in good agreement with the simulated images (A5 and B5) as visible in the corresponding line profiles (A6 and B6). The scale bars in A5 and B5 correspond to 0.5 nm.
Reuse & Permissions

Physical Review Letters