Evaluation of the coherence of electron beam from low temperature field emitter

Summary form only given. Multi-walled carbon nanotubes (MWCNT) have been known to function as nano-biprism in projection microscope. Here we measure the transverse coherence length (Lt) of electron beam (e-beam) from tungsten field emitter by using the nano-biprism. A MWCNT is irradiated by an e-beam radially propagating from a field emitter and its magnified image is projected on the screen. Tip approach enlarges the image and beautiful interference patterns always show up as shown. With decreasing the source temperature from RT to 78K, the visibility of the interference fringe increases by a factor of 3, and the bandwidth of interference pattern widens by a factor of 5. This enhancement of coherence with temperature fall strongly suggests the direct relationship between the coherences of electronic state inside the field emitter and e-beam. Now we are preparing experiments at liquid helium temperature with conventional tungsten tips and superconducting niobium tips, which will provide further enhancement of the coherence of e-beam.