Low-temperature field emission system for development of ultracoherent electron beams

Here, we present the design and test-operation performance of a low-temperature field emission (FE) system which can be employed to image and characterize the FE beam from low-temperature tips. Three radiation shields cooled by liquid helium and liquid nitrogen cryostats surround the FE tips and anodes completely. Once the FE system is cooled down to 5 K, experiments can run for more than 15 h without interruption. The design allows not only for the exchange of tips and anodes by load-lock equipment but also for the adjustment of tip-anode distance using a piezo-tube. Test runs in projection microscopy mode have presented clear diffraction-fringe patterns near the shadows of nano objects at temperatures from room temperature to 5.5 K, indicating that the system is well suited for the investigation of the coherence of electron beam from FE tip.