Field emission properties of carbon nanotubes

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Abstract
We have investigated the field emission properties of nanotube thin films deposited by a plasma enhanced chemical vapor deposition process from 2% CH4 in H2 atmosphere. Depending on the deposition of the metallic catalyst [Fe(NO3)3 in an ethanol solution or sputtered Ni] the nanotube films showed a nested or continuous dense distribution of tubes. The films consisted of multiwalled nanotubes (MWNTs) with diameters ranging from 40 down to 5 nm, with a large fraction of the tubes having open ends. The nanotube thin film emitters showed a turn-on field of less than 2 V μm−1 for an emission current of 1 nA. An emission site density of 10 000 emitters per cm−2 is achieved at fields around 4 V μm−1. The emission spots, observed on a phosphorous screen, show various irregular structures, which we attribute to open ended tubes. A combined measurement of the field emitted electron energy distribution (FEED) and the current-voltage characteristic allowed us to determine the work function at the field emission site....