Atomic resolution imaging of oxygen atoms close to heavy atoms by HRTEM and ED, using the superconductor SmFeAsO0.85F0.15 as an example

• Light atoms O, adjacent to relative heavier atoms Sm at a very close distance (1.17 Å) in superconductor SmFeAsO0.85F0.15 are revealed by a novel approach.
• This approach includes deconvolution processing, phase extension and electron-diffraction intensity correction.
• The effect of contrast transfer function is corrected by image deconvolution.
• A structure projection of SmFeAsO0.85F0.15 is restored by combining the corrected electron diffraction data.
• We demonstrate imaging of O atoms adjacent to the heavier atoms at a very close distance (1.17 Å) by this approach.

Imaging of light atoms has always been a challenge in high-resolution electron microscopy. Image resolution is mainly limited by lens aberrations, especially the spherical aberration of the objective lens. Image deconvolution could correct for the image distortion by lens aberrations and restore the structure projection, the resolution of which is limited by the information limit of the microscope. Electron diffraction unrestricted by lens aberrations could overcome this resolution limit. Here we show a combination of electron diffraction and image deconvolution to reveal simultaneously the atomic columns of O and considerably heavier Sm at a very close distance (1.17 Å) in iron-based superconductor SmFeAsO0.85F0.15 using a conventional 200 kV electron microscope. The approach used here, starting from an image and an electron diffraction pattern, has an advantage for those radiation-sensitive samples. Besides, it can be applied to simultaneously imaging light and heavy atoms, even though they have a big difference in atomic number and a much smaller atomic distance than the microscope resolution.