A microfabricated electron phase shift element is used for modifying the
phase characteristics of an electron beam passing though its center
aperture, while not affecting the more divergent portion of an incident
beam to selectively provide a ninety-degree phase shift to the
unscattered beam in the back focal plan of the objective lens, in order
to realize Zernike-type, in-focus phase contrast in an electron
microscope. One application of the element is to increase the contrast of
an electron microscope for viewing weakly scattering samples while in
focus. Typical weakly scattering samples include biological samples such
as macromolecules, or perhaps cells. Preliminary experimental images
demonstrate that these devices do apply a ninety degree phase shift as
expected. Electrostatic calculations have been used to determine that
fringing fields in the region of the scattered electron beams will cause
a negligible phase shift as long as the ratio of electrode length to the
transverse feature-size aperture is about 5:1. Calculations are underway
to determine the feasibility of aspect smaller aspect ratios of about 3:1
and about 2:1.