  Electron beams can acquire designed phase modulations by passing through
nanostructured material phase plates. These phase modulations enable electron
wavefront shaping and benefit electron microscopy, spectroscopy, lithography,
and interferometry. However, in the fabrication of electron phase plates, the
typically used focused-ion-beam-milling method limits the fabrication
throughput and hence the active area of the phase plates. Here, we fabricated
large-area electron phase plates with electron-beam lithography and
reactive-ion-etching. The phase plates are characterized by electron
diffraction in transmission electron microscopes with various electron
energies, as well as diffractive imaging in a scanning electron microscope. We
found the phase plates could produce a null in the center of the bright-field
based on coherent interference of diffractive beams. Our work adds capabilities
to the fabrication of electron phase plates. The nullification of the direct
beam and the tunable diffraction efficiency demonstrated here also paves the
way towards novel dark-field electron-microscopy techniques and tunable
electron phase plates.
