The authors have characterized field emission properties of freestanding, 1nm thick graphene layers, called carbon nanosheets (CNSs), which were grown perpendicular to the growth surface using a radio-frequency plasma-enhanced chemical vapor deposition technique. The CNSs are metallic impurity-free and have uniform height distribution (standard deviation of <10%). The authors have demonstrated reproducibility and stability of the CNSs for a period of >200h at 1.3mA emission current level. Over this time, no degradation has been observed, the variability of the individual I-V curves is small among 7216 voltage cycles, and the standard deviation at the maximum current was no more than 2.3%. A nanosheet-based backgated triode emission device has been developed to take advantage of the nanosheet field emission performance. Prototype devices have confirmed triode operation and stable electron emission.

Carbon nanosheets have recently evolved into useful edge emitters with high emission current densities, low threshold electric fields, and long lifetimes. In addition to further improvement in these characteristics, good stability and repeatability are also essential for these materials to be suitable for high vacuum applications such as microwave tubes and flat panel displays. Since the work function of graphite, carbon nanotubes, and amorphous carbon is relatively high, 4.6-4.8 eV, selective thin film coatings may offer significant advantages. Carbides are a good film choice for their corrosive resistance, chemical stability, and substantially lower work function. Approximately 3 ML ͑monolayer͒ ͑ϳ1 nm͒ of molybdenum were deposited on carbon nanosheets by physical vapor deposition and the carbide ͑Mo 2 C͒ formed by heating to Ͼ200°C at 1 ϫ 10 −8 Torr. The carbide stoichiometry was confirmed in situ by the characteristic Auger triple peak at 272 eV. A stoichiometric Mo 2 C calibration sample was used to acquire the Auger electron spectroscopy asymmetric ratio of 0.7 and this was used to determine the carbide growth as a function of temperature ͑from room temperature to 1000°C͒. Field emission currents of up to 400 A were compared with uncoated CNS at a given electric field. The Mo 2 C / CNS cathodes were shown to have greater than a factor of 100 increase in current and greater than 2 V / m decrease in threshold. The Fowler-Nordheim plots were exceptionally linear and quite repeatable ͑correlation coefficient R 2 = 0.999+͒. Using the slope and vertical intercept, an emission area for the 0.07 cm 2 Mo 2 C / CNS dot sample was determined to be ϳ3 ϫ 10 −9 cm 2 and the field enhancement factor was found to be ␤ ϳ 530.

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