Transforming the Transmission Electron Microscope into an Electron Interferometer

Here we extend electron interferometric capabilities to older model transmission electron microscopes (TEM) which continue to use lower quality thermionic electron sources. Currently, conventional electron interferometry can be done using the Mollenstedt biprism, but the spatial coherence requirements needed to conduct such experiments is demanding as the electron beam must be spatially coherent over much of the electron beam. Instead, we suggest the use of a nanofabricated grating to act as an amplitude-splitting beam splitter. The spatial coherence requirement is less demanding and need only be coherent across two or more grating bars for diffraction to take place. We place the nanofabricated grating in the condenser aperture of the TEM where we can then use the microscopes condenser lens system to form well focused, spatially separated, diffraction orders in the specimen plane. Using post specimen lenses, we are able to interfere the diffraction orders to form an image of the grating, giving rise to a path separated electron interferometer similar to that of the optical Mach Zehnder.