Ivan Lazić (Eindhoven / NL), Carsten Sachse (Jülich / DE; Düsseldorf / DE), Maarten Wirix (Eindhoven / NL), Max Leo Leidl (Munich / DE; Jülich / DE), Daniel Mann (Jülich / DE), Maximilian Beckers (Jülich / DE; Heidelberg / DE), Evgeniya V. Pechnikova (Eindhoven / NL), Knut Müller-Caspary (Munich / DE; Jülich / DE), Arno Meingast (Eindhoven / NL), Anna Carlsson (Eindhoven / NL), Felix de Haas (Eindhoven / NL), Eric G.T. Bosch (Eindhoven / NL)
Abstract text (incl. figure legends and references)
Historically, beam sensitive materials have been imaged using conventional transmission electron microscopy (CTEM) applying parallel electron illumination. Through single particle analysis (SPA) and cryo CTEM has found its way towards life science (LS) and biological applications. In these directions, scanning TEM (STEM) applying focused electron illumination, has played considerably smaller role, especially in revealing nano particle structures at atomic and near atomic resolution.
With integrated differential phase contrast (iDPC) STEM [1] mode a strong capacity to image light next to heavy elements at atomic resolution [2, 3, 4, 5] has been revealed, also within structures that are highly sensitive to electron radiation [6, 7]. Experimentally, capability to image metal organic frameworks (MOF-s) [6] and zeolites including single molecules [7, 8] with unprecedented resolution has been proven. In Fig. 1a, an iDPC-STEM image of a MOF, MIL-101 structure is shown with resolution of 2 Å using total electron dose of 42 e-/Å2, while in Fig. 1b, an image of MOF, UiO-66 structure is shown with resolution of 1.4 Å obtained using electron dose of 54 e-/Å2. This strongly encourages STEM investigation in LS applications [9], including imaging of biological cryo nano particles at near-atomic resolution [10]. For example, iDPC-STEM imaging of Keyhole Limpet Hemocyanin (KLH) protein and Tobacco Mosaic Virus (TMV), well-known and in-depth studied specimens [11] are shown in Fig. 2. The iDPC-STEM micrographs show complete signal transfer to high resolution, enabling 3D structure SPA reconstruction at 3.5 Å.
iDPC-STEM is utilized as the integration of the DPC vector field to resolve the iDPC scalar field [1]. For a thin sample the DPC vector field represents the projected electric field, which, when integrated into iDPC, yields the projected electrostatic potential field of the sample [1, 2]. Consequently, iDPC-STEM is directly interpretable since the potential field has maxima at the atomic core positions.
Here, iDPC-STEM low dose specifics and imaging of various extremely beam sensitive organic and inorganic materials (as in Fig. 1) will be shown, as well as LS cryo-EM specimens (as in Fig. 2) at near atomic resolution.
Figure 1. 200kV iDPC-STEM with 10 mrad convergence semi-angle (CSA) beam (Sample courtesy: Prof. Y. Han, KAUST Catalysis Center) a) Image of MOF, MIL-101, el. dose 42 e-/A2, resolution 2 Å b) Image of MOF, UiO-66, el. dose 54 e-/Å2, resolution 1.41 Å
Figure 2. 300kV iDPC-STEM with 3.5 mrad CSA beam, el. dose 35 e-/Å2, cryo SPA. Top: KLH a) 2D projections b) 3D reconstruction at 6.5 Å resolution Bottom: TMV c) iDPC-STEM micrograph d) 3D reconstruction and molecular model fit at 3.5 Å resolution
References:
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[10] I. Lazić, et. al., Nature Methods, accepted, (2022), preprint https://doi.org/10.1101/2021.10.12.464113
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