Performing Electron Interferometry Using a Transmission Electron Microscope with an Thermionic Source

Here we demonstrate the capability of the FEI Tecnai Spirit Transmission Electron Microscope (TEM) to perform electron interferometry. This TEM, like many other older models, uses a thermionic emission source with low spatial coherence. Presently, electron interferometry can be performed in a TEM using methods such as the Mollenstedt Biprism, but such methods require much higher spatial coherence than can be attained with lower-end TEMs. By using a nanofabricated grating as a beam splitter, we are able to perform electron interferometry with much lower spatial coherence. The goal of this experiment was to verify that older TEMs could be used to study the properties of electron-transparent materials using this method. Gratings were milled with a pitch of 200 nm and a diameter of 20 μm using a focused ion beam. The grating was placed in the aperture of the TEM and was used to split the electron beam into spatially separated, well-focused diffraction orders at the specimen plane. By refocusing these diffraction orders we obtained an image of the grating in which the sinusoidal features on the grating were visible, suggesting that electron interferometry can be performed in TEMs with thermionic emission sources.