Electron field emission from soluble carbon nanotube films treated by hydrogen plasma

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Abstract

Large-scaled and homogeneous multi-wall carbon nanotube (MWNT) films have been fabricated using the soluble octadecylamine (ODA) modified multi-wall carbon nanotubes at room temperature by a spin-coating method. The characterization, by means of electron microscopy and micro-Raman spectroscopy, shows that the surfaces of MWNTs-ODA with hydrogen plasma treatment are covered by the carbon nanoparticles. The field emission test indicates that the treated MWNTs-ODA film has low turn-on emission field of 0.5 V/μm at 0.1 μA/cm2 of current density, high-emission luminescent site density of about 104/cm2.

Introduction

In recent years, the emission of electron from carbon nanotubes (CNTs) has attracted considerable attention due to their excellent field emission properties, i.e., good emission stability, long emitter lifetime and high-current density. These properties offer potential applications in cold cathode for field emission displays (FEDs) [1], [2], [3], [4]. For a high-resolution flat panel display, large-scaled homogeneous CNT film with uniform, high-emission site density and low-operation voltage is required. However, the homogeneity of the large-scaled CNT film is hard to control in processing for growth techniques [5]. Most recently, we have prepared a soluble octadecylamine modified multi- wall CNTs (MWNTs-ODA). This MWNT-ODA material can be solubilized homogeneously in common organic solvent (chloroform, dichloromethane, benzene, etc.). It could be applied to fabricate the large-scale and homogeneous CNT thin films on a variety of substrates at room temperature by spin-coating or spray-coating method. In order to enhance effectively the field emission of the CNT films, the samples are treated by means of hydrogen plasma (HP) treatment. As a result, the emission site density is greatly increased and the threshold field is lowered. In this Letter we report about an investigation of the field emission properties of the MWNT-ODA films treated by hydrogen plasma.

Section snippets

Experimental

The soluble MWNT samples can be prepared via functionalization with octadecylamine. The multi-walled carbon nanotubes were produced by vacuum chemical vapor deposition, using Ni–phthalocyanine as a starting material. The octadecylamine (ODA) was purchased from Fluka. The obtained MWNTs were purified and shortened with the mixture of nitric acid and sulfuric acid (1:3) according to the literature [6], and carboxyl groups were imported onto the surface of MWNTs in this step. Shortened MWNTs (1.0

Results and discussion

Fig. 1a shows a SEM micrograph of the original MWNT-ODA deposited film. A number of round holes with several micrometers in diameter appear on the surface of the film, which is shown in the inset of Fig. 1a. These holes are produced due to the chloroform volatilization. The remnant octadecylamine and impurities are left over on the upper layer of the films and MWNTs-ODA are deposited in the lower one. The MWNTs-ODA are observed in holes, indicating the existence of nanotubes.

The surface

Acknowledgements

The authors acknowledge the financial support from the NSF of China (No. 69925409), a Key Basic Research and Development Program of China Grant (973) and the PSF of Shandong Province, China (No. Y2001 G02). They also thank Prof. Qun Chen’s help for this work.

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