Popov V.N., Lambin P. (eds.) Carbon Nanotubes

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*To whom correspondence should be addressed. Th. Dikonimos Makris; e-mail:

dikonimos@casaccia.enea.it

V.N. Popov and P. Lambin (eds.), Carbon Nanotubes, 57–58.

CARBON NANOTUBES GROWTH AND ANCHORAGE TO CARBON

FIBRES

TH. DIKONIMOS MAKRIS,* R. GIORGI, N. LISI,

E. SALERNITANO

ENEA Casaccia Research Centre, 00060 Rome, Italy

M. F. DE RICCARDIS, D. CARBONE

ENEA Brindisi Research Centre, 72100 Brindisi, Italy

Abstract. A novel material made of carbon fabrics with a uniform three-

dimensional (3D) distribution of carbon nanotubes (CNTs) on the surface was

synthesized by an electrochemical deposition (ELD) process.

Keywords: carbon nanotubes; electrochemical deposition

The CNT exceptional tensile strength and modulus are deemed to improve the

tensile properties of a polymeric matrix composite. In order to fully utilise the

mechanical properties and the lightness of CNT, a sufficient volume fraction

should be dispersed into the matrix.

The problems are connected with the CNT

aggregation and floating. The 3D distribution achieved by coating fabrics of

carbon fibres with CNT could provide a way for dispersing the CNT across the

composite. Moreover, CNT could further enhance the mechanical properties of

composite materials traditionally reinforced with carbon fibres by enhancing the

interfacial bonding between polymer and carbon fibre acting as fillers of

micropores.

ELD process was used to deposit Ni catalyst on PAN and Pitch based

carbon fibres. Different deposition conditions were tested in order to optimise

the dimension, morphology, and density of the Ni clusters.

3,4

A Hot Filament

assisted CVD reactor was used for the CNT growth.

5,6

On both PAN and Pitch

based carbon fibres, independently of the cluster size, density and morphology,

clean CNT with low impurity content and rather smooth walls were grown.

high density of CNT was obtained on carbon fibres fabric (see Fig. 1, left), even

at the critical cross over regions, as shown in Fig. 1, center. This result indicates

that all fabric fibres were coated by the catalyst giving rise to such a dense CNT

network. Mechanical test usually performed to measure the adhesion of thin

films on a substrate are not reliable in this case due to the peculiar nature of the

substrate and the coating itself. Pseudo-mechanical tests, based on the idea of

exposing the three-component material (carbon fibre plus metallic cluster plus

carbon nanotubes) to stressing environments were performed.

Samples were

treated by immersion, magnetic stirring, centrifugation and ultrasonic bath in

four different liquids (deionised water, ethanol, n-butanol, and acetone). After

the treatment, the Ni clusters remained anchored to the fibres. As illustrated in

Fig. 1, right, for the ultrasonic bath test in acetone, CNT were still present with

high density on the fibre surface.

Figure 1. Left and center: high density CNT grown on carbon fibres fabrics. Right: carbon fibres

after ultrasonic bath in acetone for 5 minutes.

References

1. C. Bower, R. Rosen, L. Jin, J. Han, and Q. Zhou, Deformation of carbon nanotubes in

nanotube-polymer composites, Appl.Phys.Lett.74(22), 3317-3319 (1999).

2. E. T. Thostenson, W. Z. Li, D. Z. Wang, Z. F. Ren, and T. W. Chou, Carbon

nanotube/carbon fibre hybrid multiscale composites, Journal of Applied Physics 91, 6034-

6037 (2002).

3. E. Gómez, R. Pollina, and E. Vallés, Morphology and structure of nickel nuclei as function

of the conditions of electrodeposition, J. of Electroanalytical Chemistry 397, 111-118

(1995).

4. E. Gómez, R. Pollina, and E. Vallés, Nickel electrodeposition on different metallic

substrates, J. of Electroanalytical Chemistry 386, 45-46 (1995).

5. Th. Dikonimos Makris, R. Giorgi, N. Lisi, L. Pilloni, E. Salernitano, F. Sarto, and M.

Alvisi, Carbon nanotubes growth by HFCVD: effect of the process parameters and catalyst

preparation, Diamond and Related Materials 13, 305-310 (2004).

6. Th. Dikonimos Makris, R. Giorgi, N. Lisi, L. Pilloni, E. Salernitano, and F. De Ricardis,

Carbon nanotubes growth on PAN and Pitch based carbon fibres by HFCVD, Fullerenes,

Nanotubes and Carbon Nanostructures 13(1), 383-392 (2005).

7. M. F. De Riccardis, D. Carbone, Th. Dikonimos Makris, R. Giorgi, N. Lisi, and E.

Salernitano, Anchorage of carbon nanotubes grown on carbon fibres, Carbon (2005)

(submitted).

*To whom correspondence should be addressed: Th. Dikonimos Makris; e-mail:

dikonimos@casaccia.enea.it

V.N. Popov and P. Lambin (eds.), Carbon Nanotubes, 59–60.

CVD SYNTHESIS OF CARBON NANOTUBES ON DIFFERENT

SUBSTRATES

TH. DIKONIMOS MAKRIS, L. GIORGI, R. GIORGI, N. LISI,

E. SALERNITANO

ENEA Casaccia Research Centre, 00060 Rome, Italy

M. ALVISI, A. RIZZO

ENEA Brindisi Research Centre, 72100 Brindisi, Italy

Abstract. Carbon nanotubes (CNTs) were grown using three different chemical

vapor deposition (CVD) processes. Optimized conditions were studied.

Keywords: carbon nanotubes; chemical vapor deposition process

CNTs were grown on differently supported Ni catalytic nanoparticles on flat

and bulk substrates using H

and CH

as precursors. The different behavior of

the same metal catalyst in the presence of the same precursor varying the gas

activation by different energy sources, using Hot Filament, Plasma Enhanced

(PE), and pure Thermal CVD processes, was studied. By properly choosing the

process parameters, dense CNTs were grown by HFCVD on 3 nm Ni thin film

deposited by Evaporation and Radio-frequency (RF) Sputtering onto flat Si

substrates coated with an intermediate SiO

layer

(Fig. 1a). Prior to the growth,

the samples were heated in H

atmosphere and the Ni clusters distribution

shown in Fig. 2a was obtained. No CNT growth was obtained on the same

sample in the thermal CVD reactor, but only cluster coalescence was observed

(Fig. 2b). CNT grew sparsely in the PE CVD reactor. The different results were

ascribed to: i) the catalytic decomposition of the precursors was more efficient

where an additional activation source was present; ii) weak interaction between

the Ni cluster and the SiO

substrate could favour cluster coalescence, which

was the dominant effect in the thermal CVD process.

Flat Al

substrate coated by a 3nm Ni film, deposited by RF Sputtering,

were subjected to the same clustering and CNT growth process in Thermal and

PE CVD. The thermal process failed as in the previous case giving rise to

aggregation of Ni clusters distributed on alumina grain surfaces. On the

opposite, in the PE reactor, a dense distribution of Ni nanoclusters was obtained

(Fig. 2c), followed by a dense CNT growth (Fig. 1b).

The commercial catalyst, consisting of Ni nanoparticles supported on alumina

microparticles, was tested in the thermal CVD process for CNT growth (Fig. 1c).

This catalyst exhibited a high productivity and a yield of 15mgC/mgNi was

obtained.

The reason for this could be attributed to the higher metal dispersion on

highly porous material. Moreover, the stronger interaction existing between the

catalyst and the support prevented metal particles from aggregating and forming

unwanted large particles. It could not be excluded that even an electronic interaction

existed and it was responsible for the lowering of the catalyst activation barrier.

Figure 1. CNT growth on Ni/SiO

/Si flat sample in HFCVD (a), on Ni/Al

flat sample in

PECVD (b) and on Ni/Al

pellet in Thermal CVD (c).

Figure 2. Cluster distribution on Ni/SiO

/Si flat sample in HFCVD (a) and Thermal CVD (b) and

on Ni/Al

flat sample in PECVD.

References

1. S. Hoffmann, B. Kleinsorge, C. Ducati, A. C. Ferrari, and J. Robertson, Low-temperature

plasma enhanced chemical vapour deposition of carbon nanotubes, Diamond and Related

Materials 13, 1171-1176 (2004).

2. K. Hernadi, Z. Konya, A. Siske, J. Kiss, A. Oszko, J. B. Nagy, and I. Kiricsi, On the role of

the catalyst support and their interaction in synthesis of carbon nanotubes by CCVD, Mater.

Chem.Phys. 77, 536-541 (2002).

3. Th. Dikonimos, R. Giorgi, N. Lisi, E. Salernitano, L. Pilloni, M. Alvisi, and F. Sarto, Carbon

nanotubes growth by HFCVD: effect of the process parameters and catalyst preparation,

Diamond and Related Materials 13, 305-310 (2004).

4. Th. Dikonimos, L. Giorgi, R. Giorgi, N. Lisi, and E. Salernitano, CNT growth on alumina

supported nickel catalyst by thermal CVD, Diamond and Related Materials 14, 815-9

(2005).

V.N. Popov and P. Lambin (eds.), Carbon Nanotubes, 61–62.

INFLUENCE OF THE SUBSTRATE TYPES AND TREATMENTS ON

CARBON NANOTUBE GROWTH BY CHEMICAL VAPOR

DEPOSITION WITH NICKEL CATALYST

R. RIZZOLI, R. ANGELUCCI, S. GUERRI, F. CORTICELLI

CNR - IMM Bologna, via P. Gobetti 101, 40129 Bologna, Italy

M. CUFFIANI, G. VERONESE

Department of Physics, University of Bologna, viale Berti Pichat

6/2, 40127 Bologna, Italy

Abstract. Our investigation aimed at the development of a process capable of

producing well ordered, vertically aligned carbon nanotubes (CNTs) arrays,

with reproducible properties, for applications such as a position particle detector

and a cold cathode emitter for storage devices. The results on catalyst

nanoparticles formation from a thin Ni film evaporated on SiO

and Si

substrates are presented. The substrate-catalyst layers have been processed in

several gaseous atmospheres and in the temperature range 700-900°C in order

to obtain the most appropriate morphology, size and density of the

nanoparticles for the subsequent CNTs growth. The smallest nanoparticles have

been obtained on the SiO

substrate in H

atmosphere and at the lowest

temperature 700°C. However, the best vertically aligned and well graphitized

CNTs resulted from the NH

annealing process followed by the deposition of

CNTs at 900°C in C

and NH

Keywords: Carbon nanotubes; Ni catalyst; chemical vapor deposition synthesis

Ni thin films, 2 nm thick, were deposited by e-gun evaporation on SiO

/ Si and

/Si substrates. The Ni nanoparticles (NPs) formation was studied varying

the gas atmosphere (Ar, NH

and H

) and the temperature (in the range 700°C-

900°C) applied during the warm-up and annealing steps prior to the CNTs

deposition step. Vertically aligned CNTs were grown by atmospheric pressure

chemical vapor deposition in C

+ NH

gas mixtures at temperatures in the

range 750-900°C.

The investigation on the formation of Ni NPs, starting from a 2 nm thick Ni

film, showed that the NP dimensions are mainly affected by the nature of the

substrate layer. The NPs average diameter is smaller on SiO

than on Si

substrates. The use of a reducing (H

or NH

) or inert (Ar) gas atmosphere

during the NPs thermal treatment had a strong impact on their properties: size,

morphology and chemical composition of subsurface layers both of the NPs and

of the underlying substrate. For each gas atmosphere, with increasing the

annealing temperature in the range 700° - 900°C on Si

substrates, the NPs

size decreases, while on SiO

, it remains almost unchanged. The smallest NPs,

shown in the SEM image of Fig. 1, were obtained on SiO

after annealing in H

at 700°C (scale bar on the bottom left side corresponds to 100 nm).

Figure 1. SEM images of Ni NPs on a SiO

substrate after annealing at 700°C in H

However, the best multiwalled CNTs, vertically aligned and well

graphitized, resulted from the NH

annealing process followed by the

deposition of CNTs in 5% C

in NH

at 900°C, on a SiO

substrate. SEM and

HRTEM images of these CNTs are displayed in Fig. 2.

Figure 2. Left: cross-section SEM image of CNTs grown in C

+ NH

at 900°C on Ni NPs

formed in NH

; Right: HRTEM micrograph of one of these MWNTs.

*To whom correspondence should be addressed: Jorg J. Schneider

V.N. Popov and P. Lambin (eds.), Carbon Nanotubes, 63–64.

NON CATALYTIC CVD GROWTH OF 2D-ALIGNED CARBON

NANOTUBES

NADEZDA I. MAKSIMOVA, JORG ENGSTLER, JORG J.

SCHNEIDER*

Dept of Chemistry, Eduard-Zintl Inst. of Inorganic and Physical

Chemistry, Tech. University, 64287 Darmstadt, Germany

Abstract. Aligned carbon nanotubes (CNTs) were grown in the channels of

porous alumina membranes via a non-catalytic chemical vapor deposition

(CVD) method. The morphology of the samples was studied.

Keywords: carbon nanotubes; non-catalytic chemical vapor deposition method

Carbon nanotubes (CNTs) produced by catalytic methods contain metal

nanoparticles that cannot be removed completely and may have negative effect

on the performance of the CNTs for microelectronic applications.

Herein, we

present an optimized synthesis procedure for well-aligned CNT arrays. It

includes a new post-process purification approach to remove carbonaceous by-

products.

Aligned CNT arrays were grown in the tubular channels of porous anodic

alumina oxide (PAOX) membranes (Anodisc 25, Whatman) with different pore

diameters at 900qC by a CVD method based on propylene decomposition.

The

morphology of the samples was examined using scanning electron microscopy

(Philips XL-30 FEG).

In the non-catalytic CVD process, the carbon atoms or reactive -C-

fragments within a PAOX template are directly deposited on the surface of

PAOX membrane (Fig. 1, left). In this case, the growth of CNTs is mainly

controlled by the shapes of the membrane pores and the catalytic action of the

PAOX template.

Besides the CNT growth inside the pores (Fig. 1, center),

there is deposition of carbon by-products on the PAOX membrane surface that

cannot be prevented. This carbon deposit has to be removed before any

application of CNTs could be considered. The presence of at least three carbon

layers on the PAOX surface, i.e., a thick amorphous carbon overgrowth layer, a

layer of high molecular hydrocarbons (tar, pitch, resin, etc.) penetrated on the

PAOX surface, and a surface graphitic overlayer, was detected (Fig. 1, right).

This allowed us to develop a controllable removal of PAOX template: (i) the

surface carbon layer was oxidized in a controlled fashion at 550°C in air; (ii)

high molecular hydrocarbon by-products were removed by boiling in benzene

for 3 hours; (iii) the PAOX template was removed via dissolution in

concentrated HF or H

during 4 hours. After these procedures, free-standing

CNTs were obtained, however, still stuck to each other and connected via a

surface graphitic overlayer.

The complex structural composition of the

deposited carbon products is an evidence for the complicated mechanism of the

non-catalytic metal-free CVD process containing only one precursor.

Figure 1. Scheme of the mechanism of CNT growth within the pores of a PAOX membrane by

CVD with (left) and without catalyst (center). Right: cross-section of the PAOX membrane with

CNTs inside the pores (a); scheme of carbon layers on the PAOX membrane surface (b).

In the present work, CNTs were produced within the pores of PAOX

membranes by a non catalytic CVD method. The presence of three different

carbon layers on the PAOX membrane surface after CVD process was proven

and the three-step purification procedure was developed to receive the free-

standing aligned CNT arrays.

We acknowledge support of the Volkswagen Foundation (grant no.

53200034).

References

1. W. A. de Heer, A. Chatelain and D. Ugarte, A Carbon Nanotube Field-Emission Electron

Source, Science 270, 1179-1180 (1995).

2. J. J. Schneider, N. I. Maksimova and J. Engstler (unpublished).

3. L. Zhi, J. Wu, J. Li, U. Kolb, and K. Müllen, Carbonization of disclike molecules in porous

alumina membranes: Toward carbon nanotubes with controlled graphene-layer orientation,

Angew. Chem. Int. Ed. 44, 2120-2123 (2005).

precursor gas flow

Membrane

(b)

precursor gas flow

Membrane

(b)

*To whom correspondence should be addressed. Kseniia Katok, Institute of Surface Chemistry of National

Academy of Sciences of Ukraine 17 Naumov Str., 03164 Kyiv, Ukraine; e-mail: smpl@ukr.net

V.N. Popov and P. Lambin (eds.), Carbon Nanotubes, 65–66.

PYROLYTIC SYNTHESIS OF CARBON NANOTUBES ON Ni, Co,

Fe/ɆɋɆ-41 CATALYSTS

KSENIIA KATOK,* SERGIY BRICHKA, VALENTYN

TERTYKH, GENNADIY PRIKHOD’KO

Institute of Surface Chemistry of National Academy of Sciences of

Ukraine, 17 Naumov Str., 03680 Kyiv-164, Ukraine

Abstract. The purpose of the accomplished work was to use the advantages

(ordered porous structure and high surface area) of mesoporous ɆɋɆ-41

silicas in the pyrolytic synthesis of carbon nanostructures. MCM-41 matrices

were used for chemisorption of volatile nickel, cobalt, and iron acetylacetonates

with following metal reduction. The synthesis of carbon nanotubes was carried

out by two routes: (a) ɆɋɆ-41 treatment with Ni(acac)

or Co(acac)

vapor at

150qɋ, metal reduction with H

at 450qɋ, C

pyrolysis over the catalyst at

700qɋ; (b) ɆɋɆ-41 modification with Co(acac)

or Fe(acac)

, reduction of

supported metal complexes with C

, and pyrolysis at 700qɋ (in situ

reduction). The TEM data showed that carbon nanotubes were formed with

external diameter 10-35 nm for Ni-, 42-84 nm for Co-, and 14-24 nm for Fe-

containing matrices. In the absence of metals, low yield of nanotubes (up to

2%) was detected.

Keywords: mesoporous MCM-41 silica; metal acetylacetonates; acetylene; pyrolysis;

carbon nanotubes; in situ reduction

The unique properties of the carbon nanotubes and the prospects of their

possible applications continue to attract the attention of the researchers. The

pyrolysis of hydrocarbons on the surface of inorganic matrices is one of the

possible routes of carbon nanotubes synthesis. In this regard, the ordered

mesoporous matrices, such as ɆɋɆ-41, are of great importance.

The synthesis of carbon nanotubes was carried out by two routes: (a) ɆɋɆ-

41 treatment with Ni(acac)

or Co(acac)

vapour at 150qɋ, metal reduction with

at 450qɋ, C

pyrolysis over the catalyst at 700qɋ; (b) ɆɋɆ-41

modification with Co(acac)

or Fe(acac)

, reduction of supported metal

complexes with C

, and pyrolysis at 700qɋ (in situ reduction). During the

pyrolysis of acetylene, a deposition of decomposition products of black color on

silica matrices was observed. The synthesized composite was treated with a

solution of hydrofluoric acid at ambient temperature for removal of the silica

phases. As a result, insoluble carbon fraction was obtained. The carbon

nanotubes were identified using a transmission electron microscope.

Cetyltrimethylammonium bromide was used as a template for the synthesis

of MCM-41 silica with specific surface area905 m

-1

and total volume of

pores 0.87 cm

-1

. The average diameter of the pores, determined by the ȼJH-

method, was about 39 Å. The characterization of the mesoporous silica was

performed by nitrogen adsorption measurements at 77 K.

In order to provide the homogeneous catalyst deposition, the silicas were

treated with volatile cobalt (II) nickel (II) and iron (II) acetylacetonates at

moderate temperature. At these conditions, acetylacetonates of metals are

chemisorbed on the silica surface due to reaction with the surface silanol groups

with eliminating one of the ligands.

The removal of the ligands from the metal complexes supported on the

silica was studied in air by the thermogravimetric technique. The destruction of

the residual ligands of acetylacetonates (after interaction with silanol groups)

occurred at about 445qC. As a result, formation of complex oxides of cobalt and

iron occurred on the silica surface.

The pyrolysis of acetylene on the surface of ɆɋɆ-41 silicas containing

metallic catalysts was studied. The application of matrices with supported

metals as catalysts enabled us to attain rather high yields of carbon

nanostructures (2030% of the process product). The electron microscopy data

provided evidence for the formation of nanotubes with an external diameter of

4284 nm in the case of cobalt catalyst and 1424 nm in the case of iron

catalyst. The formation of carbon fibers with diameters in the interval 80110

nm for nickel catalyst was also observed. Here it is appropriate to mention that

in the absence of a catalyst on such matrices, small yields (up to 2%) of carbon

nanotubes were attained.