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...

This letter reports, diamond field emitters, Cs treated, air stable, that emit electrons at the lowest reported field, <0.2 V μm−1. Field emission from B-, Li-, P-, and N-doped diamonds and carbonized polymer was characterized as a function of surface treatment. A treated with an O2 plasma, coated with Cs, heated, and exposed to O2 exhibited increased emission for all samples except for B-doped diamond. The best emission was obtained from N-doped diamond samples, followed by carbonized polymer, the Li-doped, and polycrystalline P-doped diamond. Li- and N-doped samples treated with Cs were stable in laboratory air for several days. This stability of the surface-activated diamond is believed to be due to the formation of a diamond–O–Cs salt. If the sample is treated with a H2 plasma instead of an O2 plasma, the Cs-enhanced emission degrades with heat and exposure to O2. Subbands formed by Li and N impurities are believed to be responsible for this enhanced emission. The surface treatment on N-doped diamond results in emission at fields as low as 0.2 V μm−1.

Optically sampled analog-to-digital converters (ADCs) combine optical sampling with electronic quantization to enhance the performance of electronic ADCs. In this paper, we review the prior and current work in this field, and then describe our efforts to develop and extend the bandwidth of a linearized sampling technique referred to as phase-encoded optical sampling. The technique uses a dual-output electrooptic sampling transducer to achieve both high linearity and 60-dB suppression of laser amplitude noise. The bandwidth of the technique is extended by optically distributing the post-sampling pulses to an array of time-interleaved electronic quantizers. We report on the performance of a 505-MS/s (megasample per second) optically sampled ADC that includes high-extinction LiNbO 3 1-to-8 optical time-division demultiplexers. Initial characterization of the 505-MS/s system reveals a maximum signal-to-noise ratio of 51 dB (8.2 bits) and a spur-free dynamic range of 61 dB. The performance of the present system is limited by electronic quantizer noise, photodiode saturation, and preliminary calibration procedures. None of these fundamentally limit this sampling approach, which should enable multigigahertz converters with 12-b resolution. A signal-to-noise analysis of the phase-encoded sampling technique shows good agreement with measured data from the 505-MS/s system.