Deakin Research

Institute for Frontier Materials

Carbon Nanotubes

Patterned Growth

Focused ion beam milling as a universal template technique for patterned growth of carbon nanotubes

Ying Chen, Hua Chen, Jun Yu, James S. Williams and Vince Craig

APPLIED PHYSICS LETTERS 90, 093126 (2007)

Abstract: Focused ion beam (FIB) milling system has been used to create nanosized patterns as the template for patterned growth of carbon nanotubes on Si substrate surface without predeposition of metal catalysts. Carbon nanotubes only nucleate and grow on the template under controlled pyrolysis of iron phthalocyanine at 1000 C. The size, growth direction, and density of the patterned nanotubes can be controlled under different growth conditions and template sizes. Atomic force microscopy and electron microscopy analyses reveal that the selective growth on the FIB template is due to its special surface morphology and crystalline structure.

(a) SEM image of parallel trenches created by FIB without CNT coating, (b) typical AFM scan image of a FIB trench, (c) SEM image of selective growth of CNTs in the patterns created using FIB, and (d) SEM image showing the formation of CNT clusters along the trenches under a high-pressure vapor condition  (a) SEM image showing selective deposition on two crossed FIB trenches under a low vapor density and at a lower temperature, (b) SEM image revealing nanotube growth from many nanoparticles deposited on a FIB trench, and (c) SEM image showing a nanotube growing out from a large deposition particle sitting at the edge of the trench


Patterned growth of carbon nanotubes on Si substrates without predeposition of metal catalysts

Y. Chen and J. Yu

APPLIED PHYSICS LETTERS 87, 033103 (2005)

Abstract: Aligned carbon nanotubes (CNTs) can be readily synthesized on quartz or silicon-oxide-coated Si substrates using a chemical vapor deposition method, but it is difficult to grow them on pure Si substrates without predeposition of metal catalysts. We report that aligned CNTs were grown by pyrolysis of iron phthalocyanine at 1000 C on the templates created on Si substrates with simple mechanical scratching. Scanning electron microscopy and x-ray energy spectroscopy analysis revealed that the trenches and patterns created on the surface of Si substrates were preferred nucleation sites for nanotube growth due to a high surface energy, metastable surface structure, and possible capillarity effect. A two-step pyrolysis process maintained Fe as an active catalyst.

SEM images of patterned CNTs grown on a Si substrate: (a) Three letters, ANU, written with a diamond pen covered by CNTs,  (b)-(d) SEM images taken from the letter N area with higher magnifications showing selective and patterned growth of CNTs  SEM images of vertically aligned and patterned CNTs on Si substrates: (a)  top view, (b)  side view, (c)  precisely deposited CNTs, and (d) a higher magnification image of (c).




Controlled Growth

Improved growth of aligned carbon nanotubes by mechanical activation

Y. Chen and L.T. Chadderton

Journal of Materials Research, Vol. 19, No. 10, Oct 2004

Abstract: Straight aligned carbon nanotubes with multiwalled cylindrical structure have been produced by pyrolysis of iron phthalocyanine (FePc) after ball milling treatment. The pre-ball milling treatment prevented the formation of curved nanotubes with bamboo or conelike structures. X-ray diffraction analysis revealed that the milled FePc has an activated and disordered structure, which contributes a lower vaporization temperature determined by thermal gravimetric analysis. The low formation temperature and an increased nanotube growth rate are favorable to the formation of cylindrical structure than bamboo tubes.

(a) SEM image of as-synthesized Carbon nanotubes produced by pyrolysis of iron phthalocyanine (FePC), (b) SEM image of as-synthesized Carbon nanotubes produced by pyrolysis of pre-ball milling treated FePC  (a) TEM image of as-synthesized Carbon nanotubes produced by pyrolysis of iron phthalocyanine (FePC), (b) TEM image of as-synthesized Carbon nanotubes produced by pyrolysis of pre-ball milling treated FePC




Solid-state Formation

The nucleation and growth of carbon nanotubes in a mechano-thermal process

Y. Chen, M.J. Conway, J.D. FitzGerald, J.S. Williams, L.T. Chadderton

Carbon, 42 (2004) 1543

Abstract: Separate nucleation and growth processes of carbon nanotubes were found in a mechano-thermal method in which carbon nanotubes are produced by first mechanical milling of graphite powder at room temperature and subsequent thermal annealing up to 1400 C. The ball-milled graphite contains nucleation structures (nanosized metal particles and deformed (0 0 2) layers containing pentagons), and disordered carbon as a free carbon atom source. The subsequent annealing activates the growth of two types of multi-walled nanotubes in the absence of carbon vapor. Thin nanotubes (diameter <20 nm) are formed via crystallization of the disordered carbon with the preferred formation of the (0 0 2) basal planes. Thick nanotubes (diameter >20 nm) are formed through a metal catalytic solution-precipitation process (solid-liquid-solid). In both cases, carbon nanotubes grew out from disordered carbon particles with closed tips.

TEM images of multi-walled carbon nanotubes produced from graphite. (a) The edge of a cluster of nanotubes and nanoparticles, (b) high-resolution image recorded from the tip of one nanotube showing
multi-walled tubular structures. The arrow indicates flat caps of the two innermost tubes; (c) two single-wall short extruders (tubes) with amorphous coating on the external surface. The possible faceted caps of each nanotube are illustrated  TEM image of metal catalytic formation of thick carbon nanotubes containing a Fe particle at the tip. The insert high-resolution TEM image was taken from the wall area of one nanotube

Substrate characteristics beneath self-aligned carbon-nanotube forests

Dai, XJ; Skourtis, C.

J. Appl. Phys. 2008, 103, 12.

Forests of carbon nanotubes (CNTs) can be grown in which each nanotube is only about 10-20 nm (1-2x10-5mm) in diameter but more than one mm in length. It has been found that some of these forests can be drawn off into continuous ribbons or sheets of fibres and twisted into yarns. There was considerable confusion in the literature over what conditions were needed for such fast-growing forests free of contaminants. It turned out that just like real forests what was needed was the right "soil", good seeds, and a suitable growing environment. Key requirements were an oxidized layer on the silicon substrate that causes the right type, size and distribution of metal catalysts to form followed by suitable temperature and gas conditions. This improved understanding has made controllable CNT forest growth possible and these forests can be used in a remarkable variety of applications including biomedical, electrical and composite materials.

(a)AFM image of the oxidized iron catalyst formed on SiO2/Si surface after suitable conditions;
(b)CNT forests; (c) XPS-spectra showing the changes in the chemical state of the iron catalyst

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20th February 2012