A new surface electron-emission mechanism in diamond cathodes

Abstract

An electron-emission mechanism for cold cathodes is described based on the enhancement of electric fields at metaldiamond-vacuum triple junctions. Unlike conventional mechanisms, in which electrons tunnel from a metal or semiconductor directly into vacuum, the electrons here tunnel from a metal into diamond surface states, where they are accelerated to energies sufficient to be ejected into vacuum. Diamond cathodes designed to optimize this mechanism exhibit some of the lowest operational voltages achieved so far.Conventional cathodes for applications from television to power transmitters use heat to boil electrons out of a metal into vacuum. However, these cathodes do not have the power efficiency or the dimensional stability to be used with micrometre-size structures, which are required for flat-panel displays and some power amplifiers. Cathodes that can be scaled to micrometre sizes use high electric fields instead of heat to pull electrons out of a solid into vacuum. The reliability and current density of these electric field emission cathodes depend upon both their geometry and the material used in their construction. Here we review field emission cathodes and show that a new cathode geometry which uses a novel material, diamond, has properties superior to those of previous cathodes.For the cold cathodes we discuss, emission is obtained with a large electric field that causes electrons to tunnel over a potential barrier out of a metal substrate into vacuum. Material and fabrication techniques have both been used to increase emission by enhancing the electric field and reducing the barrier over which the electrons must tunnel. Excellent low electric field electron emission has been reported from diamond and amorphous diamond-like films on metal substrates, but practical application of these cathodes is limited by a serious lack of reproducibility 1-3 and inconsistency (M. E. Kordesch, personal communications). Emission originates from a few localized sites, which were believed to be due to the inconsistent bulk properties of the cathode material. The enhanced emission at the interface between the diamond surface, a conductive region, and vacuum, a new emission mechanism, may explain the localization of emission sites. If so, a discontinuous diamond film that provides an abundance of interfaces should be a better electron emitter than a continuous diamond film 4,5 .We now describe two generally accepted emission mechanisms: geometric electric-field enhancement 6 , and Schottky diode with a negative-electron-affinity semiconductor 2,3 . Semiconductors and insulators have a negative electron affinity (NEA) if the minimum energy of electrons in the conduction band is above the minimum energy of electrons in vacuum. Experimental results are then described that cannot be explained by the previous emission mechanisms. A mechanism is proposed that combines the high electric fields that can be obtained at the intersection of a semiconductor surface, a metal substrate and vacuum (a so-called triple junction) 7,8 with t...

Electron emission from conduction band of diamond with negative electron affinity

“…The first was electron emission from heavily N-doped CVD diamond reported by one of the present authors (KO) in 1996 [15]. The second is the triple junction emission reported by Geis in 1998 [16]. Theoretical interpretations of these experimental results were made by many researchers, reflecting the importance of these two reports [17][18][19][20].…”

Electron field emission from excimer laser crystallized amorphous silicon

“…Furthermore, c-Si has size restrictions imposed by wafer manufacturability and large area displays are not feasible with such a technology. Since then flat emitter materials such as diamond, 2 amorphous carbon 3 (a-C), a-Si:H, 4 polycrystalline silicon, 5,7 ͑poly-Si͒ and silicon nanowires 6 have shown a wide range of possibilities for using thin film technology as cold cathodes. However, these flat films do not benefit from external geometric enhancement as compared to those with tip structures.…”

Chemical vapor deposition of novel carbon materials

“…The nanocrystalline diamond thin ®lms have several desirable characteristics, among them: (a) small grain size and surface roughness of the diamond ®lms, (b) low grain boundary angle, and (c) synthesis from argon domain plasma. These characteristics can be exploited for applications in the cold-cathode electron ®eld emitter for¯at panel displays [5], protective coating for vacuum pump sealing [4], diffusion barrier [6] for the Cu interconnect technology, and potential hard transparent coating on oxide or nitride materials for optical applications. In contrast to nanocrystalline diamonds, carbon nanotubes have been demonstrated to be another novel carbon related material, which has great potential applications in the advanced technology.…”