Researchers at CEMES-CNRS in Toulouse have developed a new ultrafast electron source based on a cold-field emission gun for applications in time-resolved electron microscopy and interferometry. These results were published in the journal Applied Physics Letters.
In Transmission Electron Microscopy, cold field emission electron sources are the first choice for the most demanding applications. They consist in a metallic nanotip placed in an electric field which is strong enough to allow the emission of electrons by quantum-mechanical tunneling. Since the emission of electrons is confined to the apex of the metal tip, these sources have the highest brightness and spatial coherence of all available electron sources. They are therefore ideally suited for instance for the quantitative investigation of electric, magnetic or strain fields in nanostructures using electron interferometry or holography.
During the last ten years, significant efforts have been made to combine the atomic spatial resolution of transmission electron microscopes with the femtosecond temporal resolution of ultra-short laser sources. These developments have allowed important advances in the exploration of the properties of nano-objects with excellent spatio-temporal resolution. However, almost all of this work is based on the use of electron packets emitted by flat photocathodes illuminated by femtosecond laser pulses. The poor brightness of these sources limits their range of application. Researchers at CEMES-CNRS have designed and developed a new ultrafast electron source combining a cold-field emission gun with a femtosecond laser. This new source of ultra-short electron packets will exceed the limits of photocathodes and paves the way towards demanding applications such as time-resolved electronic interferometry. These results were published in the journal Applied Physics Letters.