Fabrication and characterization of high-current-density carbon-nanotube cold cathodes

doi:10.1016/j.apsusc.2005.03.185

Applied Surface Science

Volume 251, Issues 1–4, 15 September 2005, Pages 249-253

https://doi.org/10.1016/j.apsusc.2005.03.185 Get rights and content

Abstract

In this paper, we report a recent experimental observation of high field-emission current density (6.5 A/cm²) from carbon nanotube emitters. Carbon nanotubes are grown on Ni catalyst coated on Si substrates using chemical vapor deposition of C₂H₂ gas at 700 °C. Our research shows that it is beneficial for getting the high-current density in our experiment that Au film was deposited onto Si substrate before evaporating a Ni catalyst dot onto the substrate. We compared the field emission characteristics of CNTs cathodes grown on the Ni films with different thickness of 50, 70, 100 nm. The thickness of the Ni film is very important for the growth of CNTs, which will affect the field emission properties very much. The Fowler-Nordheim plot showed a good linear fit, indicating that the emission current of carbon nanotubes follows Fowler-Nordheim behavior. The calculated field enhancement factor was 2370.

Introduction

Since being discovered in 1991 [1], carbon nanotubes (CNTs) have attracted the interest of researchers because of their many possible applications especially in field emission [2], [3] where CNTs have been used as cold electron emitters [4]. High-current field emission is necessary for the application of microwave power amplifier tubes requiring at least 500 mA/cm². However, the reported current densities of CNTs are still low, typically, 80 mA/cm² [5] to 4 A/cm² [6]. The reason for this includes the damage of CNTs due to heating or ion bombardment under high field emission current, and the electrostatic field shielding between the closely packed nanotubes. In this paper, we present a recent experimental result of high field-emission current density (6.5 A/cm²) from carbon nanotube emitters.

Section snippets

Experimental

The substrates were prepared by evaporating a Ni catalyst dot (0.13 mm in diameter) with a mask onto Au film that has previously been deposited onto Si substrates. In the experiments, we evaporate the Ni films with different thickness of 50, 70 and 100 nm, respectively. CNTs growth was carried out by CVD in a quartz tube furnace with flowing mixture of C₂H₂ (10.1%) and N₂ (89.9%) at 700 °C after the reduction by H₂ at 500 °C.

The field emission properties were measured using diode structure at room

Results and discussion

Fig. 1 shows SEM images of the Ni particles resulted from the reduction of the Ni films with thickness of 50, 70 and 100 nm, respectively. The average particle size increases with the thickness of the Ni films. However, the particle density decreases with the increase of thickness of the Ni film. For the Ni film with thickness of 50 nm, there are some places where no Ni film exists, as shown in Fig. 1a. This might be attributed to the capillarity of the film at high temperature.

Fig. 2a and b show

Conclusion

We get the high field-emission current density (6.5 A/cm²) from carbon nanotube emitters by depositing Au film onto Si substrate before evaporating a Ni catalyst dot and compared the field emission characteristics of CNTs cathodes grown on the Ni films with different thickness of 50, 70 and 100 nm. The high field-emission current density is mainly resulted from the use of Au film and the fit thickness of Ni films. Apart from this, the proper size of the CNT array also increases the fringe field

Acknowledgement

This work is carried out under the support from National Key Basic Research Program (No. 2003CB314706), Foundation of Doctoral Program of Ministry of Education (No. 20030286003), and Foundation of Science and Technology of Southeast University (No. 9206001270 and No. 9206001271).

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Fabrication and characterization of high-current-density carbon-nanotube cold cathodes

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusion

Acknowledgement

Solid State Electron

Curr. Appl. Phys.

Nucl. Instrum. Methods A

Ultramicroscopy

Nature (London)