Electron ptychographic phase imaging of light elements in crystalline materials using Wigner distribution deconvolution

• Published in: Ultramicroscopy 2017-09, Vol.180 (C), p.173-179
• Main Authors: Yang, Hao, MacLaren, Ian, Jones, Lewys, Martinez, Gerardo T., Simson, Martin, Huth, Martin, Ryll, Henning, Soltau, Heike, Sagawa, Ryusuke, Kondo, Yukihito, Ophus, Colin, Ercius, Peter, Jin, Lei, Kovács, András, Nellist, Peter D.
• Format: Article
• Language: English
• Subjects: 4D-STEM; MATERIALS SCIENCE; Phase retrieval; Pixelated detectors; Ptychography; Wigner distribution deconvolution
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/j.ultramic.2017.02.006

•The ptychographic Wigner-distribution deconvolution method is applied to crystalline samples at atomic resolution.•This technique provides interpretable phase images for imaging light elements in crystalline specimens.•This technique allows the measurement and correction of residual lens aberrations from the recorded 4D-data of relatively thin crystalline specimens. Recent development in fast pixelated detector technology has allowed a two dimensional diffraction pattern to be recorded at every probe position of a two dimensional raster scan in a scanning transmission electron microscope (STEM), forming an information-rich four dimensional (4D) dataset. Electron ptychography has been shown to enable efficient coherent phase imaging of weakly scattering objects from a 4D dataset recorded using a focused electron probe, which is optimised for simultaneous incoherent Z-contrast imaging and spectroscopy in STEM. Therefore coherent phase contrast and incoherent Z-contrast imaging modes can be efficiently combined to provide a good sensitivity of both light and heavy elements at atomic resolution. In this work, we explore the application of electron ptychography for atomic resolution imaging of strongly scattering crystalline specimens, and present experiments on imaging crystalline specimens including samples containing defects, under dynamical channelling conditions using an aberration corrected microscope. A ptychographic reconstruction method called Wigner distribution deconvolution (WDD) was implemented. Experimental results and simulation results suggest that ptychography provides a readily interpretable phase image and great sensitivity for imaging light elements at atomic resolution in relatively thin crystalline materials.