Elsevier

Carbon

Volume 47, Issue 6, May 2009, Pages 1555-1560
Carbon

Enhanced field emission of an electric field assisted single-walled carbon nanotube assembly in colloid interstices

https://doi.org/10.1016/j.carbon.2009.02.001Get rights and content

Abstract

A novel method for fabrication of vertically aligned single-walled carbon nanotubes (SWCNTs) on indium–tin oxide glass substrates modified with self-assembly monolayer has been developed by using a supporting frame composed of a monolayer of monodispersed silica beads and an alternating current electric field. We have found that SWCNTs can be implanted into the interstices of the colloidal superlattices, which function as supporting scaffold to prevent the SWCNTs from falling down and maintain the SWCNTs at low density. As a result, this vertically aligned SWCNT assembly exhibits enhanced field emission.

Introduction

The use of single-walled carbon nanotubes (SWCNTs) as field emission source is one of the most promising aspects among SWCNT-based applications [1], [2], [3], [4], [5], [6], [7], [8]. In the application of carbon nanotubes (CNTs) to field emission display (FED), many efforts have been made to prepare vertically aligned CNTs on a large scale. Vertically aligned CNT films can be prepared by chemical vapor deposition (CVD) [9], [10], [11], [12], [13]. In order to obtain free-standing CNTs, substrate bias generated by applied direct current (DC) [14], [15], magnetic field [16], or porous alumina templates [17] have been integrated into the thermal CVD method. As a typical paradigm, freestanding CNT arrays were synthesized on Ni dot arrays by DC plasma-enhanced CVD [18], [19]. However, both the direct and the modified CVD methods show disadvantages in the high temperature (850–1000 °C) required in synthesis and the remaining of catalyst residue in the resultant vertically aligned CNT films or arrays.

As a post-treatment approach, screen-printing is commonly used to fabricate SWCNT cathodes for FEDs [20], [21], [22], but this approach still suffers from short lifespan of the FED devices and low resolution due to the ununiformity of SWCNTs and organic contaminants. As an alternative post-treatment approach, self-assembly method is easy and shows promising prospect for preparing vertically aligned SWCNTs at room temperature. Several self-assembly methods such as chemical assembly onto various surfaces have been used to prepare SWCNT films [23], [24]. Although this method has great potential for the surface modification and functionalization with SWCNTs, the alignment degree of the resulting SWCNTs is not sufficient for practical applications, which results in low emission performance.

In this paper, we present a novel self-assembling method, which makes use of a colloidal monolayer as supporting frame in the presence of an alternating current (AC) electric field, for preparing vertically aligned SWCNTs in the application of high-efficient FED devices. It is shown that the interstices of the colloidal particle assembly can maintain the vertical alignment of the SWCNTs after the electric field is removed. This method affords vertically aligned SWCNTs on self-assembly monolayer (SAM) modified indium–tin oxide (ITO) substrates at room temperature, resulting in highly efficient use of SWCNTs and large area deposition of SWCNTs. The field emission property was characterized, and the field emission devices prepared by using these SWCNT assemblies exhibit high performance in field emission property.

Section snippets

Purification and treatment of SWCNTs

As-prepared SWCNTs (HiPco, Carbon Nanotechnologies Inc.) were purified and end functionalized by using hydrochloric acid and piranha solution, respectively [25], [26]. Before the end functionalization process, the purified SWCNTs were annealed at 800 °C for 1 h under the protection of Ar in order to reduce the defect content on the side-wall surfaces. The end functionalized SWCNTs were dispersed in N,N-dimethylformamide (DMF) (20 mg L−1) by ultrasonication for 4 h. The solution was centrifuged at

Results and discussion

Raman spectroscopy was used to verify the dispersibility of the SWCNTs in DMF suspension with a concentration of less than 10 mg L−1. For the efficiently dispersed SWCNTs in DMF solution, the radial breathing mode band shows an up-shift of 9 cm−1 with respect to the solid SWCNT sample: 189 cm−1 for the as-prepared and purified SWCNTs at solid state and 198 cm−1 for the functionalized SWCNTs dispersed in DMF (Fig. 2a). This up-shift upon debunding results from the decreased energy spacing of the Van

Conclusions

We have developed a new method for the fabrication of vertically aligned SWCNTs on SAM-modified ITO substrates by using a well dispersed SWCNT solution, a supporting frame composed of a monodispersed silica monolayer, and an AC electric field. The use of the colloidal monolayer as the supporting frame contributes to both the vertical alignment of the SWCNTs on the ITO substrate and the low density of the aligned SWCNTs, resulting in enhanced field emission. This approach can potentially lead to

Acknowledgements

This work was supported by the National Research Laboratory Program (KOSEF), the Center for Nanoscale Mechatronics & Manufacturing, and the IT Leading R&D Support Project from the Ministry of Knowledge Economy through IITA. SM Yang acknowledges the support of a Creative Research Initiative Program Grant (KOSEF).

References (36)

  • J. Geng et al.

    Influence of single-walled carbon nanotubes induced crystallinity enhancement and morphology change on polymer photovoltaic devices

    J Am Chem Soc

    (2006)
  • J. Geng et al.

    Synthesis of SWCNT rings by non-covalent hybridization of porphyrins and single-walled carbon nanotubes

    J Phys Chem C

    (2008)
  • J. Geng et al.

    Effect of SWCNT defects on the electron transfer properties in P3HT/SWCNT hybrid materials

    Adv Funct Mater

    (2008)
  • H. Dai et al.

    Controlled chemical routes to nanotube architectures, physics, and devices

    J Phys Chem B

    (1999)
  • S.H. Jung et al.

    Vertically aligned carbon-nanotube arrays showing schottky behavior at room temperature

    Small

    (2005)
  • K. Hata et al.

    Water-assisted highly efficient synthesis of impurity-free single-walled carbon nanotubes

    Science

    (2004)
  • D. Zilli et al.

    Effect of alignment on adsorption characteristics of self-oriented multi-walled carbon nanotube arrays

    Nanotechnology

    (2006)
  • T. Hirata et al.

    Magnetron-type radio-frequency plasma control yielding vertically well-aligned carbon nanotube growth

    Appl Phys Lett

    (2003)
  • Cited by (0)

    1

    Both authors are equally contributed to this work.

    View full text