The invention relates to an electron source comprising a conductive substrate, a conductor disposed facing the substrate, the electron source emitting an electron beam when the conductor is positively biased with respect to the substrate, and an electrically insulating crystal arranged on the substrate, facing the conductor, the substrate defining with the crystal a void including at least one peak located at a distance from the crystal, the crystal having, in a plane parallel to the substrate, dimensions of less than 100 nm and a thickness of less than 50 nm.