Electron emission from chemical vapor deposited diamond and amorphous carbon films observed with a simple field emission
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Electron emission from chemical vapor deposited (CVD) diamond and amorphous carbon (a-C) films was observed with a simple field emission device (FED). Both diamond and a-C films were prepared with microwave plasma-enhanced CVD techniques. Electron emission in the field strength range +10 to —10 MVrrT 1 was studied, and the field emission source was confirmed by a diode characteristic of the I-V curve, a straight line in the Fowler-Nordheim (F-N) plot, and direct observation of light emission from a fluorescent screen. The turn-on field strength was ~ 5 MVm~\ which was similar for both kinds of carbon films. The highest current density for diamond films, observed at a field strength of 10 MVirT 1 , was ~15 /iAcrrT 2 . Diamond films yielded a higher emission current than a-C films. The reasons for the observed field emission are discussed.
With the rapid development of diamond deposition with chemical vapor deposition (CVD) techniques in recent years, there has been an increasing interest in the application of CVD diamond films as electronic materials due to the unique electronic properties and outstanding chemical inertness of diamond.1-2 One important and probably the most promising application is the use of CVD diamond films as electron emitters or cold cathodes for vacuum microelectronics2"6 utilizing diamond's so-called "negative electron affinity" on the {111} planes.7 Two different techniques have been used to investigate electron emission of diamond and CVD diamond films. Geis et al? fabricated cold cathodes (mesa-etched diodes) with semiconducting diamond/diamond films. With this technique, electrons are ejected into vacuum from the p side of the diode with forward biasing, provided that diamond has a negative electron affinity. Electron emission was indeed observed and a current density of 1 Acm~ 2 was estimated with the maximum forward bias of ^100 V. This compares favorably with uncoated Si cold cathodes. Using a field emission microscope, Wang et al.4 investigated electron emission of CVD diamond films deposited on molybdenum (Mo). With this technique, electric field strength of a few MVm" 1 was applied, and electron emission from a circular area of 50 /mm in diameter was observed with turn-on electric field strengths as low as 3 MVm" 1 . This is much smaller than those used for typical metal emitters, demonstrating that CVD diamond films are promising candidates for cold electron emitters. Using similar field emission techniques, Xu et al,5 and Okano et al.6 also observed electron emission from CVD diamond films deposited on Mo substrates and CVD J. Mater. Res., Vol. 10, No. 7, Jul 1995 http://journals.cambridge.org
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diamond emitters, respectively. Very recently, Davis et al.% reported electron emission from diamond-like carbon films prepared with intense ion beams produced by laser ablation of graphite. In the work described here, a much simpler field emission device (FED) was employed, and electron emission from both diamond and a-C films prepared with microwave plasma-enhanc
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