An electron emitter is formed by in situ growth from the vapor on catalyst clusters that are adhered by an adhesion layer to a conductive electrode. The emitter comprises hemispheroidal nanofiber clusters that emit electrons at low field strengths and high current densities, producing bright light by the interaction of the electrons and a fluorescent and/or phosphorescent film on an anode spaced across an evacuated gap. The nanofibers may be grown such that the nanofiber clusters are entangled, restricting movement of individual nanofibers.