WORK FUNCTION AT THE TIPS OF MULTIWALLED CARBON NANOTUBES

R.P. Gao, Z.W. Pan, Zhong L. Wang

School of Materials Science and Engineering, Georgia Institute of Technology,

Atlanta, GA30332-0245, USA

The unique geometrical structure of carbon nanotubes suggests that they are likely to be an ideal field emitter for panel display application. Indeed, numerous field emission measurements show that the carbon nanotubes exhibit superior field emission performance with required electric field much lower than those of many other field emitters. For carbon nanotube emitters, most of the electrons are emitted from the tips of the tubes, and it is the local work function that matters to the properties of the tube field emission. Since the lack of suitable technical method to measure the work function of carbon nanotubes, the value of work function of carbon nanotubes used in the literatures is mainly from the well-studied carbon or graphite. Thus, it is necessary to experimentally measure the work function of carbon nanotubes.

In this study, we present experimental measurements of tip work functions of individual carbon nanotubes. The experiment was done by a novel in-situ transmission electron microscopy technique [1,2]. Our results indicate that the tip work function show no significant dependence on the diameter of the nanotubes in the range of 14-55 nm. Majority of the nanotubes (~75%) have a work function of 4.6-4.8 eV at the tips, which is 0.2-0.4 eV lower than that of carbon. A small fraction of the tubes (~25%) have a work function of ~5.6 eV, about 0.6 eV higher than that of carbon. This discrepancy is suggested due to the metallic and semiconductive characteristics of the tubes.

Key words: carbon nanotubes, work function, field emission

References:

[1] P. Poncharal, Z.L. Wang, D. Ugarte and W.A. De Heer, Science 283, 1513 (1999).

[2] R.P. Gao, Z.W. Pan, Zhong L. Wang, Appl. Phys. Letts., in press.

Corresponding author:

Zhong L. Wang

School of Materials Science and Engineering

Georgia Institute of Technology

Atlanta, GA 30332-0245

e-mail: Zhong.wang@mse.gatech.edu

Tel: 404-894-8008

Fax: 404-894-9140