Title:
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Super Resolution Tilt Series Exit Wave Restoration from Aberration Corrected Images
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Conventionally, the resolution of a transmission electron microscope is limited to the
axial information limit. Higher resolution information may be transferred by tilting the
incident illumination, which shifts the region of Fourier space that contributes to the
image. This super resolution is highly directional, but may be extended in all directions
by restoring the exit wave from images with a complimentary set of beam tilts. Although
this may be achieved using a conventional microscope, an instrument where the primary
aberrations are corrected electron optically provides significant advantages.
This thesis explores the optimal conditions for achieving super resolution using the
technique of tilt series restoration from aberration corrected images. The results
demonstrate that for a tilt defocus data set of aberration corrected images acquired using
the JEOL 2200FS 200 kV transmission electron microscope, the tilt induced changes in
the coherent and incoherent aberrations limits the optimal tilt magnitude to 25 mrad or 19
mrad respectively. However, the optimal tilt magnitude will in most cases be limited to
approximately 16 mrad by the thickness of the sample itself due to geometric parallax.
The need for fundamental microscope stability and an appropriate detector set up is also
discussed.
Experimental exit wavefunction restorations from tilt defocus data sets of aberration
corrected images are then presented for three specimens; <111> oriented strontium
titanate, <123:> oriented gold and <112> oriented silicon. These restorations are
compared to restorations using a standard focal series data set acquired immediately
subsequent to the tilt defocus series. These results demonstrate that by the inclusion of
tilted images in the exit wavefunction restoration data set an improvement in the
continuous information transfer from 0.11 nm to 0.071 nm can be achieved at 200 kV.
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