Rapid Interpretable Incoherent Imaging with Dynamic Hollow-Cone Illumination TEM

Transmission electron microscopy (TEM) is an exceedingly powerful technique to understand nanoscale and atomic structure, and is increasingly being used to characterize materials and devices under operando conditions in response to a variety of applied stimuli. Scanning transmission electron microscopy (STEM) imaging has become increasingly the default modality used in materials science applications, in part because the incoherent nature of HAADF and ABF-STEM imaging aids in the interpretation of imaging data [1], especially at high resolution. However, the frame rate of in-situ imaging is often a crucial parameter to capture structural changes on the timescale of perturbation, and the limitations of scanning speeds and linearity tend to limit STEM-based frame rates in the &lt;20 Hz range. Conversely, recent advances in electron detectors have made TEM frame rates in the kHz range routine, and frame rates approaching 100kHz are now accessible.<br/><br/>A technique leveraging the ability of TEM to simultaneously image wide fields-of-view at high frame rates combined with the advantage of STEM to produce directly interpretable images of light and heavy atoms in crystalline materials would greatly benefit in-situ studies at high resolution. Dynamic hollow cone illumination (DHCI-TEM) is a technique whereby conventional TEM illumination is precessed azimuthally through an angle just inside a post-specimen objective aperture [2]. This has been previously demonstrated to suppress dynamical scattering and diffraction-contrast from bend contours that may obscure fine details of an image [3]. Through reciprocity [4], DHCI-TEM is equivalent to the ABF-STEM imaging, implying interpretable incoherent contrast of crystalline materials at high resolution.<br/><br/>We have recently demonstrated simultaneous, interpretable atomic resolution contrast of both heavy (Sr, Ti) and light (O) atoms using DHCI-TEM combined with quantitative multislice simulations [5]. Interpretable atomic contrast is preserved even for relatively thick specimens (&gt;70nm), which is especially promising for potential imaging through electronic device structures or thicker samples relevant to in-situ mechanical deformation. We will discuss the demonstrated advantages and limitations of the atomic resolution DHCI-TEM technique, and present preliminary applications of the technique to in-situ imaging.<br/><br/>References<br/>[1] Findlay, S. D., et al. "Robust atomic resolution imaging of light elements using scanning transmission electron microscopy." <i>Applied Physics Letters </i>95.19 (2009): 191913.<br/>[2] Kunath, W., F. Zemlin, and K. Weiss. "Apodization in phase-contrast electron microscopy realized with hollow-cone illumination." Ultramicroscopy 16.2 (1985): 123-138.<br/>[3] Rebled JM, Yedra Ll., Estrade S, Portillo J & Peiro F “A new approach for 3D reconstruction from bright field TEM imaging: Beam precession assisted electron tomography,” <i>Ultramicroscopy</i> 111, 1504–1511 (2011)<br/>[4] Pogany, A. P., and P. S. Turner. "Reciprocity in electron diffraction and microscopy." <i>Acta Crystallographica Section A: Crystal Physics, Diffraction, Theoretical and General Crystallography </i>24.1 (1968): 103-109.<br/>[5] Brown, Hamish G., and Jim Ciston. "Atomic Resolution Imaging of Light Elements in a Crystalline Environment using Dynamic Hollow-Cone Illumination Transmission Electron Microscopy." <i>Microscopy and Microanalysis </i>26.4 (2020): 623-629.