Towards semiconducting nano-engineered photocathodes for electron microscopy applications

The growing field of pulsed electron microscopy (PEM) currently suffers from technical challenges, many of which are related to the inefficiency of present pulsed emitters. In this research, we explore semiconductor photoemitters as a replacement of conventional emitters with improved quantum efficiency and brightness. P-doped diamond and GaN are investigated as photoemitter materials. Both have been shown to present efficient photoemission through the phenomenon of Negative Electron Affinity (NEA): at H-terminated surfaces for diamond, and by Caesium activation for GaN. We develop the idea of replacing these surface treatments by Electric-field-induced NEA at the surface of nanostructured emitters. Emitter nanostructuration in the form of sharp tips, akin to thermal-field or Cold-Field electron emitters found in today's microscopes, will ensure a high beam brightness and allow electric field enhancement capable of creating the field-induced-NEA. To characterize the performances of photoemitters, we build a projection chamber setup providing the same environment as a time-resolved electron microscope gun, driven by a wavelength-tunable femtosecond laser, and equipped with a faraday cup for current measurements.