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

Abstract

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.

Electron ptychographic microscopy for three-dimensional imaging

“…This is consistent with the theory underlying the WDD, which makes use of the multiplicative approximation. For the experimental geometry used here, two < 0001> oriented graphite rods with a 24 nm thickness, the multiplicative assumption appears to break down at 60 kV, although we note that recent results using the WDD provide faithful reconstructions from crystalline samples at 200 kV 59 . Overall, the invMS approach provides depth-resolved sectioning, which is robust to multiple scattering, although the attainable resolution has yet to be shown to be competitive with that achieved using the WDD and a focused probe.…”

Imaging Beam‐Sensitive Materials by Electron Microscopy

“…As proposed by Rodenburg et al,2 electron ptychography is usually conducted with large sampling redundancy in the probe positions, followed a phase retrieval algorithm such as the extend ptychographic iterative engine (ePIE),283 difference map (DM),282,284 hybrid input–output (HIO)285 or Fourier‐based direct algorithms 157,286. Electron ptychography enables the recovery of structural information for both heavy and light elements in three‐dimensions and at atomic resolution 272,281,287–289. Typical pixelated detectors, including monolithic active pixel sensors (MAPS) and hybrid pixel array detectors (PADs),290 are both high throughput and suitable for ptychographic applications.…”

3D observation of large-scale subcellular dynamics in vivo at the millisecond scale

“…In addition, both the overlap in spatial domain induced by the scanning and the frequency aliasing in the angular domain facilitate the incoherent synthetic aperture during 3D reconstruction. As with the techniques sharing similar support constraints for recovery, such as ptychography 26,28 and Wigner-distribution deconvolution 29 , we can achieve the diffraction limit of the whole objective NA with iterative updates of a consistent volume (Supplementary Note 4, and Extended Data Fig. 4).…”