Field emission from Mo2C coated carbon nanosheets

Abstract

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.

Atomic layer deposition of titanium dioxide nanostructures using carbon nanosheets as a template

“…7). This can be explained by the fact that edges of the as-deposited CNS are H-terminated [15,16] since the deposition is carried out in a methane/hydrogen atmosphere. These H-terminated edges are not very reactive adsorption sites.…”

Hyperthermal atomic hydrogen and oxygen etching of vertically oriented graphene sheets

“…Using the standard Fowler-Nordheim theory, the field enhancement factor, ␤, can be calculated from the slope and gives ␤ ϳ 1320, and is consistent with previous analysis of CNS samples. 30 The linear least mean square fits of RGA data as a function of current are shown in Fig. 6 with 95% confidence bounds as an indication of the spread in the data.…”

Energy distributions of field emitted electrons from carbon nanosheets: Manifestation of the quantum size effect

“…The sheets are consisting of several graphene layers and stand roughly vertical to the substrate. It has been found that CNSs have good field emission characteristics with promising applications in vacuum microelectronic devices [3,4,5,6]. High emission total current at low threshold field enables using CNSs as an effective cold cathode material.…”