Advances in near-field electron ptychography

Over the past few years, ptychography has drawn considerable attention for its ability to
recover high contrast and ultra-high resolution images without the need for high quality
optics. In its conventional form, it is a type of scanned-probe microscopy, in which a
convergent beam – the ptychographic probe – illuminates a small patch of a sample, and then
scans through a grid of positions to cover a region of interest, recording diffraction patterns
at each point in the grid. Near-field ptychography, originally proposed as a tool to image a
larger field of view, was first demonstrated with X-ray and quickly extended to visible light
and electron microscopy. In X-ray and visible light community, the near-field ptychography
was well explored and combined with multislice and tomography to image three-dimensional
samples.
Previously, near-field electron ptychography has been proved to be able to image a much
larger field of view with fewer diffraction patterns. This thesis keeps exploring the
performance of the near-field ptychography with electron microscopy. Our novel design of
the amplitude diffuser together with the new experimental arrangement make better use of
electron dose and reduce inelastic scattering. The variable magnifications are possible in this
geometry, via appropriate adjustment of condenser and projection lens settings. Next, our
setup is extended to image the magnetic sample in Lorentz TEM mode. Finally, we make the
first attempt at achieving atomic resolution and imaging biological specimens under low
voltage conditions using this technique.