Optimizing Catalyst Nanoparticle Distribution To Produce Densely-Packed Carbon Nanotube Growth

CARBON

4 7 ( 2 0 0 9 ) 1 9 8 9 –2 0 0 1

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journal homepage: www.elsevier.com/locate/carbon

Optimizing catalyst nanoparticle distribution to produce
densely-packed carbon nanotube growth
´
E. Terrado, I. Tacchini, A.M. Benito, W.K. Maser, M.T. Martınez*
´
Instituto de Carboquımica, CSIC, Miguel Luesma Castan 4, 50018 Zaragoza, Spain
´

ARTICLEINFO

ABSTRACT

Article history:

The experimental parameters involved in the formation of the Ni catalytic nanoparticles on

Received 23 August 2008

Si/SiO2 substrates that seed carbon nanotube growth were investigated. It was found that

Accepted 20 March 2009

after deposition of a nickel film on the substrate, the temperature and time of the thermal

Available online 27 March2009

and reduction catalyst pre-treatment steps are crucial variables for optimized nanoparticle
distribution with different average diameters, depending on the initial film thickness. Densely-packed carbon nanotube forests with interesting potential applications have been
grown from this nanoparticle distribution.
Ó 2009 Elsevier Ltd. All rights reserved.

1.

Introduction

Carbonnanotubes (CNTs) can become a key element in the
nanotechnology development since their unique size and
structure determine their electronic complexity and excellent
physical and chemical properties [1,2] making them promising candidates for interesting applications in such different
areas as electronic, material science or medicine [3,4].
Nevertheless, the ability to grow CNTs with specificdiameter and chirality directly on a substrate is the real challenge
from a technological point of view. This control would allow
the integration of the grown nanotubes into functional electronic devices including field emission displays, gas sensors,
resonators or supercapacitors. In the development of such
applications, chemical vapour deposition (CVD) processes appear to be the most suitabletechnique for direct CNT growth
on substrates owing to their versatility in terms of the type of
catalyst, carbon sources, environmental gases and process
variables (pressure, temperature, reaction time) [5,6] that
can be utilized.
The CVD process for CNT growth on a supported catalyst is
made up of several steps, one of the most important being the
preparation of the metal nanoparticles on thesubstrate [7].

Once the hydrocarbon gas is let into the furnace, the carbon
feedstock molecules decompose on the metal surface of the
nanoparticle at a temperature ranging from 600 to 1100 °C.
The role of such metal nanoparticles is very complex [8] and
essential for CNT growth. In-depth knowledge of the function
of these catalyst nanoparticles encompasses many factors
such as theircomposition and morphology, size, density
and distribution directly derived from their preparation method, the catalyst–substrate interaction and the pre-treatment
conditions. All of the mentioned parameters as a whole determine the final catalytic properties of the metal nanoparticles.
Since each nanoparticle acts as a seed for a nanotube, controlling catalyst nanoparticles is the shortest way ofachieving
the controlled growth of CNTs.
The catalyst can be deposited onto the substrate by a
chemical method [9,10] through the use of metal containing
solutions or a physical method [7]. Physical methods include
several techniques such as electron gun evaporation [11],
thermal evaporation [12], ion-beam sputtering [13] and magnetron sputtering [14] that are suitable to deposit thin catalystfilms with a thickness under 20 nm. Subsequent heating and
reduction steps allow small metal nanoparticles able to promote CNT growth to be obtained quickly and easily [7]. These

* Corresponding author: Fax: +34 976733318.
E-mail address: mtmartinez@icb.csic.es (M.T. Martınez).
´
0008-6223/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carbon.2009.03.045...