Selective synthesis of double helices of carbon nanotube bundles grown on treated metallic substrates (original) (raw)

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Carbon nanotube bundles self-assembled in double helix microstructures

Carbon, 2012

Double helix microstructures consisting of two parallel strands, each composed of hundreds of multiwalled carbon nanotubes (MWCNTs) are synthesised by chemical vapour deposition (CVD) of ferrocene/toluene vapours on thermochemically treated metal substrates, such as steel, Cu, Al and W. The thermochemical treatment produces a thin and brittle layer of SiO x . During the CVD process, carbon nanotubes (CNT) grow adhered to this layer, and as growth progresses, small SiO x microparticles detach from the substrate, directing the helical development of the growing MWCNTs double strands. This growth model for the helical microstructures is compared in the manuscript with models previously reported for coiled carbon fibres grown in the gas phase. A unique aspect of these double helices when they are composed of carbon nanotubes is that they grow on top of a forest of aligned CNTs.

Synthesis and characterisation of coiled carbon nanotubes

Catalysis Today

Recent results from our group and from literature data are summarized. Emphasis is put on the various supported catalysts that can lead to the formation of helical (or coiled) carbon nanotubes. Detailed analysis of transmission electron microscopy images reveals that not all types of nanotubes -having any type of coil pitch and coil diameter -are equally probable: stability islands can be found in the 3D representation of the number of nanotubes as a function of both coil pitch and coil diameter. In most of the cases the coils are formed by introducing pairs of five-membered and seven-membered rings into the nanotubes containing the basic six-membered rings. Possible applications of the helical carbon nanotubes are discussed.

Structural origin of coiling in coiled carbon nanotubes

Carbon, 2005

The statistical distribution of a large number of helically coiled carbon nanotubes was analyzed in a cross-correlated way in their geometrical configuration space defined by diameter and pitch. Stability islands were identified, in which the number of coils exceeds about 15-10 times the value corresponding to a uniform distribution. When comparing our data with data from literature, a good agreement is found. The statistical findings are interpreted as indirect evidence that the geometric configuration of coiled carbon nanotubes is rather decided by the atomic structure of carbon layers building up the coils than by the external parameters which on the other hand may induce the particular conditions under which coiling occurs. The possible effect of impurities like N and S on the incorporation of non-hexagonal rings and tubular growth is pointed out.

A Review of the Properties and CVD Synthesis of Coiled Carbon Nanotubes

Materials, 2010

The CVD route for carbon nanotube production has become a popular method to make large amounts of multiwall carbon nanotubes. The structure, morphology and size of carbon materials depend critically on the catalyst preparation and deposition conditions. According to current knowledge, CVD method is the only process which can produce carbon nanocoils. These nanocoils are perfect candidates for nanotechnology applications. One might indeed hope that these coils would have the extraordinary stiffness displayed by straight nanotubes. Based on theoretical studies, regular coiled nanotubes exhibit exceptional mechanical, electrical, and magnetic properties due to the combination of their peculiar helical morphology and the fascinating properties of nanotubes. In spite of its technological interest, relatively low attention has been paid to this special field. In this paper we attempt to summarize results obtained until now.

Review A Review of the Properties and CVD Synthesis of Coiled Carbon Nanotubes

2010

The CVD route for carbon nanotube production has become a popular method to make large amounts of multiwall carbon nanotubes. The structure, morphology and size of carbon materials depend critically on the catalyst preparation and deposition conditions. According to current knowledge, CVD method is the only process which can produce carbon nanocoils. These nanocoils are perfect candidates for nanotechnology applications. One might indeed hope that these coils would have the extraordinary stiffness displayed by straight nanotubes. Based on theoretical studies, regular coiled nanotubes exhibit exceptional mechanical, electrical, and magnetic properties due to the combination of their peculiar helical morphology and the fascinating properties of nanotubes. In spite of its technological interest, relatively low attention has been paid to this special field. In this paper we attempt to summarize results obtained until now.

Growth mechanism of coiled carbon nanotubes

Synthetic Metals, 1996

A growth mechanism on a catalyst particle at a molecular level is described, leading to perfect carbon tubules and tubule connections. The suggested mechanism explains the formation of curved (chiral or achiral) nanotubes, tori or coils using the heptagon-pentagon construction proposed by Dunlap.

Coiled carbon nanotube structures with supraunitary nonhexagonal to hexagonal ring ratio

Physical Review B, 2002

By assembling azulene units ͑fused pentagon-heptagon pairs͒ and hexagons, and applying specific wrapping rules to these structures resembling some recently-proposed Haeckelite structures ͓Terrones et al., Phys. Rev. Lett. 84, 1716 ͑2000͔͒, a large variety of toroidal, coiled, screwlike, and double-helix structures can be generated. In particular, the coiling appears naturally by rolling up stripes made of heptagons, hexagons and pentagons. In the structures examined here, the ratio of nonhexagonal rings to hexagonal units varies from 4:1 to 4:3. In the coiled nanotubes produced actually by catalytic chemical vapor deposition, it is not impossible that such a high concentration of nonhexagonal units in the nanotube structure be the result of a fast kinetic leading to metastable states that cannot anneal out due to the low growth temperatures used.

Application of carbon nanotubes as template for self-assembled nanowires

Diamond and Related Materials, 2009

The aim of this research is to investigate the method of white X-ray irradiation (WXI) for forming nano particles or wires mostly inside multi-walled carbon nanotubes (MWCNTs). WXI approach which uses the energy of light to react with MWCNTs in aqueous solution has not yet been found. This study is mainly focusing on white X-ray irradiation technique which illustrates MWCNTs can be used as template for selfassembled nanowires. WXI synthesis technique is compared with the traditional method of heat treatments for various structures of nano hybrid materials. The research indicates that the traditional heat treatment results in nano particles being on the surfaces of MWCNTs; while the WXI keeps them inside MWCNTs. Accordingly, a model of lightheat transformation for MWCNTs is proposed to explain the mechanism of reaction inside MWCNTs. It is also found that the approach of WXI can fill nanoparticles inside MWCNTs in a comparatively shorter time.

Structure and stability of coiled carbon nanotubes

physica status solidi (b), 2012

Helically coiled carbon nanotubes are modeled using topological coordinate method which is based on the toroidal triply connected graphs, containing pentagons, hexagons, and heptagons. Their regular incorporation into the hexagonal carbon net induces transition from the straight to the helical geometry. Relaxation of the structural model is performed in two steps: Firstly, molecular dynamics based on the Brenner potential is applied and then the coil parameters are, once again, optimized within symmetry preserving density functional tight binding (DFTB) method. Model of smooth regularly helically coiled single-walled nanotube structure is obtained. Correlations between the helical angle, tubular and helical diameter are found. Cohesive energy of the coiled structure is calculated by DFTB method within symmetry based POLSym code. Its dependence on the diameter of the coil is shown. The calculated energies range from 7.5 to 8.0 eV/atom.