Selective growth of carbon nanotubes on Si microfabricated tips and application for electron field emitters

Abstract

In this article, we present the results on the synthesis and electron emission characteristics of an individual and a carbon nanotube ͑CNT͒ bundle on a Si tip. The Si tip with diameter of about 20 nm at the apex and the tip height of 5 m was fabricated using Si microfabrication process. Individual and carbon nanotubes bundle were selectively grown at the apex of the Si tip using a hot-filament chemical vapor deposition with a mixture of C 2 H 2 and H 2 gases under a negative substrate biasing. Electron field emission characteristics of the Si tips with and without the individual CNT on the same substrate were measured in a vacuum of 1.7ϫ10 Ϫ4 Pa. Threshold or turn on voltages defined at the emission current of 10 pA of approximately 40 V ͑4 V/m͒ and 200 V ͑20 V/m͒ were found for the Si tips with and without the individual CNT, respectively. Emission current and emission light pattern of the emitted electrons from the carbon nanotubes bundle were also studied.

Characterizing field emission from individual carbon nanotubes at small distances

“…Hence, less voltage is necessary to establish a sufficient electric field at the CNT tip to produce emission. Similar observations were reported in prior studies with tungsten tips by Olson and Panitz 44 and with CNTs grown on silicon tips by Minh et al 14 The dependence of emission on separation distance is further evidenced by a reduction in the turn-on voltage ͑voltage to emit 1 nA͒ as illustrated in Fig. 6.…”

“…Table I summarizes results reported by others after conducting field emission studies with individual CNTs or carbon nanofibers at small distances. Of these studies, only Minh et al 14 and Bonard et al 27 reported I͑V͒ data for multiple distances. Minh et al 14 measured I͑V͒ data for an individual CNT on a silicon tip.…”

“…Of these studies, only Minh et al 14 and Bonard et al 27 reported I͑V͒ data for multiple distances. Minh et al 14 measured I͑V͒ data for an individual CNT on a silicon tip. Bonard et al 27 used a roaming anode technique within a scanning electron microscopy ͑SEM͒ to measure I͑V͒ curves from individual nanotubes protruding from a CNT film.…”

“…The technique is demonstrated with an individual multiwall CNT, and the sensitivity of the field amplification factor and turn-on voltage V to to changes in the separation distance s is determined. The values are determined over a range of separation distances between 1.4 and 13.5 m, which lies between the ranges reported by Bonard et al 27 and Minh et al 14 Unfortunately, the data cannot be correlated directly due to the differences in the size and geometry of the electrodes.…”

“…8,9 Structural changes in the nanotube 10 and failure mechanisms 11 are also observable since emitters can be inspected with highresolution microscopy during or after emission tests. Techniques previously used to study emission from individual nanotubes include the measurement of I͑V͒ curves, [12][13][14] measurement of electron energy distribution, 15,16 field emission microscopy, [17][18][19] in situ studies within a transmission electron microscope, [20][21][22][23] and roaming anode techniques. [24][25][26][27][28][29] Field emission studies from individual nanotubes are often conducted with distances between the anode and cathode exceeding several millimeters.…”