LAUSR

Phase-contrast imaging plays a crucial role in imaging many types of materials, especially those with weak scattering potentials or low damage-threshold doses. With the recent advances in detector technology, phase-contrast imaging techniques in scanning transmission electron microscopy (STEM) are experiencing a renaissance. One widely used method, differential phase contrast (DPC) imaging, has been applied both for the atomic resolution crystal structures and nanometer scale electromagnetic field. However, accurate phase or field quantification via DPC requires caution as the probe shape effects can be very significant, especially at atomic resolution [1-2]. Ptychography via a Wigner-distribution deconvolution (WDD) method allows for correction of small residual geometric aberrations [3] but structural information beyond the aperture-limit has yet to be realized. Iterative ptychographic algorithms such as ePIE [4] or maximum likelihood (ML) [5,6] have the flexibility to correct a wide range of experimental uncertainties. Recently, using a high-dynamic-range electron microscope pixel array detector (EMPAD) [7] and ePIE ptychography with an in-focused probe illumination, we have achieved a 0.39 Å resolution phase-contrast image at 80 keV, 2.5 times that of the aperture-limited resolution for STEM annular dark-field (ADF) images or standard WDD [8].