Appendix A. Supplementary data

Supplementary data associated with this article can be found,

in the online version, at doi:10.1016/j.carbon.2010.02.035.

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C A R B O N 4 8 ( 2 0 1 0 ) 2 3 6 1 – 2 3 8 0 2371

Lithographically defined site-selective growth of Fe filledmulti-walled carbon nanotubes using a modified photoresist

Joydip Sengupta a, Avijit Jana b, N.D. Pradeep Singh b, Chacko Jacob a,*

a Materials Science Centre, Indian Institute of Technology, Kharagpur 721302, Indiab Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India

A R T I C L E I N F O

Article history:

Received 27 January 2010

Accepted 24 February 2010

Available online 1 March 2010

A B S T R A C T

Partially Fe filled multi-walled carbon nanotubes (MWCNTs) were grown by chemical

vapor deposition with propane at 850 �C using a simple mixture of iron (III) acetylaceto-

nate (Fe(acac)3) powder and conventional photoresist. Scanning electron microscopy

revealed that catalytic nanoparticles with an average diameter of 70 nm are formed on

the Si substrate which governs the diameter of the MWCNTs. Transmission electron

microscopy shows that the nanotubes have a multi-walled structure with partial Fe filling.

A site-selective growth of partially Fe filled MWCNTs is achieved by a simple photolitho-

graphic route.

� 2010 Elsevier Ltd. All rights reserved.

Carbon nanotubes (CNTs) exhibit a unique combination of

electronic, thermal, mechanical and chemical properties,

which promise a wide range of potential applications in key

industrial sectors. In the last few years, chemical vapor depo-

sition (CVD) has been the preferred method among different

CNT growth methods because of its potential advantage to

produce a large amount of CNTs growing directly on a desired

substrate with high purity, large yield and controlled align-

ment. The CVD synthesis of CNTs on plain substrates gener-

0008-6223/$ - see front matter � 2010 Elsevier Ltd. All rights reservdoi:10.1016/j.carbon.2010.02.036

* Corresponding author: Fax: +91 3222255303.E-mail address: cxj14_holiday@yahoo.com (C. Jacob).

ally requires catalyst metal deposition over the substrate,

which is time consuming and the deposited area is also finite.

These limitations can be easily overcome by employing the

spin-coating of the catalyst material on the desired substrate.

Moreover, in recent times, magnetic metal encapsulated CNTs

are of huge interest as it has demonstrated widespread appli-

cations in magnetic force microscopy [1], high-density

magnetic recording media [2] and biology [3]. However,

there are many technical barriers to achieve magnetic metal

ed.

Fig. 1 – SEM micrograph of the catalytic nanoparticles prepared from Mod-PR film over the Si(1 1 1) substrate after annealing at

900 �C; (inset) the distribution histogram of the catalyst nanoparticles.

Fig. 2 – SEM micrograph of the MWCNTs synthesized using Mod-PR by CVD growth; (inset) the distribution histogram of the

external CNT diameter deposited by the CVD method.

2372 C A R B O N 4 8 ( 2 0 1 0 ) 2 3 6 1 – 2 3 8 0

encapsulated CNT-based electronic devices; especially the

placement of CNTs in the desired position is crucial for CNT

integration in such devices. In this regard, photolithography

is one of the most important and powerful patterning tech-

niques for microfabrication and is also widely used in inte-

grated circuit (IC) technology. Thus we have employed spin-

coating along with the lithographic approach for the site-

selective growth of magnetic material filled CNTs using a sim-

ple mixture of iron (III) acetylacetonate (Fe(acac)3) powder and

conventional photoresist (HPR 504, Fuji Film) as a starting

material.

706 mg of Fe(acac)3 was mixed with 10 ml of HPR 504 to ob-

tain a modified photoresist (Mod-PR) solution of concentra-

tion 0.2 M. Then the Mod-PR solution of concentration 0.2 M

was spin-coated with a rotation speed of 4000 rpm for 20 s

on the Si(1 1 1) substrate to get a thin layer of the Mod-PR.

The thin Mod-PR film was annealed in air for 10 min at

200 �C to improve the adhesion to the substrate. The sub-

strates were then loaded into a quartz tube furnace (ELEC-

TROHEAT EN345T), pumped down to 10�2 Torr and backfilled

with flowing argon to atmospheric pressure. Afterwards, the

samples were heated in argon up to 900 �C following which

the argon was replaced with hydrogen. Subsequently, the

samples were annealed in hydrogen atmosphere for 10 min.

Finally, the reactor temperature was brought down to 850 �Cand the hydrogen was turned off, thereafter propane was

introduced into the gas stream at a flow rate of 200 sccm for

1 h for CNT synthesis.

For lithographically selective growth of CNTs, after per-

forming the spin-coating of Mod-PR the samples were baked

at 90 �C for 15 min followed by an exposure step with a mask

aligner to make an array of patterns. The exposed specimens

Fig. 3 – TEM images of the Fe encapsulated CNTs grown by the CVD method using Mod-PR, (a) A catalytic nanoparticle is

encapsulated at the top of a CNT implying tip-growth mechanism; (b) TEM image of interlayer spacing of polyaromatic carbon

in CNT; (c–f) Fe nanoparticles encapsulated in CNTs.

C A R B O N 4 8 ( 2 0 1 0 ) 2 3 6 1 – 2 3 8 0 2373

were developed in the developer solution for 60 s and rinsed

in distilled water. Thereafter, the synthesis of CNT was

carried out on the pattern areas following the same procedure

as described earlier.

Fig. 1 shows the scanning electron microscopy (SEM) im-

age of the catalytic nanoparticles formed over the Si(1 1 1)

substrate after annealing the Mod-PR film at 900 �C. The sta-

tistical analysis of the size of the catalytic nanoparticles (inset

of Fig. 1) displays a Gaussian profile with a mean of 70 nm.

Fig. 2 shows the SEM image of the CNTs synthesized on the

Si(1 1 1) substrate by CVD using Mod-PR. The high-aspect-ra-

tio nanostructures had a randomly oriented spaghetti-like

morphology with high area density. We note that in Fig. 2

the outer diameters of CNTs are in the range of 30–130 nm

and the corresponding distribution profile (inset of Fig. 2) is

similar to the size distribution profile of the catalyst nanopar-

ticles (inset of Fig. 1). Thus, the size of the catalytic particles

largely determines the outer diameters of the CNTs. Several

bright catalyst particles were detected at the tip of the tubes

(indicated in Fig. 2 with white arrows) suggesting the tip-

growth mechanism.

Fig. 3 shows the transmission electron microscopy (TEM)

images of MWCNTs grown using Mod-PR. A catalytic nano-

particle of size nearly 80 nm is encapsulated at the tip of a

CNT (Fig. 3a) implying tip-growth mechanism. It can be

clearly seen that the CNT is well graphitized and have clear

well-ordered lattice fringes of polyaromatic sheets (Fig. 3b).

Fig. 3(c–f) demonstrate the presence of high-aspect-ratio

nanoparticles encapsulated inside the CNTs deposited

using Mod-PR. Chemical composition analysis confirms that

the elongated particles are of Fe (not shown here). The

growth model of partially Fe filled CNT can be explained

by emphasizing the role of the capillary action of the

liquid-like Fe particles that exist at the time of CNT

nucleation. The detail of the growth model is discussed

elsewhere [4].

Fig. 4 – Schematic representation of the direct photolithographic route for the selective growth of partially Fe filled MWCNTs.

Fig. 5 – Site-selective growth of partially Fe filled MWCNTs by direct photolithographic route using Mod-PR (a) SEM image of

Mod-PR pattern; (b) SEM image after CNT growth.

2374 C A R B O N 4 8 ( 2 0 1 0 ) 2 3 6 1 – 2 3 8 0

Acknowledgement

J. Sengupta is thankful to CSIR for providing the senior

research fellowship.

R E F E R E N C E S

[1] Winkler A, Muhl T, Menzel S, Koseva RK, Hampel S, LeonhardtA, et al. Magnetic force microscopy sensors using iron-filledcarbon nanotubes. J Appl Phys 2006;99:1049051–5.

[2] Kuo CT, Lin CH, Lo AY. Feasibility studies of magnetic particle-embedded carbon nanotubes for perpendicular recordingmedia. Diamond Relat Mater 2003;12:799–805.

[3] Palen EB. Iron filled carbon nanotubes for bio-applications.Mater Sci (Poland) 2008;26:413–8.

[4] Sengupta J, Jacob C. The effect of Fe and Ni catalysts on thegrowth of multiwalled carbon nanotubes using chemicalvapor deposition. J Nanopart Res. 2010;12:457–65.

C A R B O N 4 8 ( 2 0 1 0 ) 2 3 6 1 – 2 3 8 0 2375

Fig. 4 shows the schematic representation of the direct

photolithographic route adopted for the selective growth of

partially Fe filled MWCNTs. Fig. 5a is the SEM image of the

Fe-containing patterns produced by the general photolitho-

graphic process using Mod-PR whereas, Fig. 5b is the SEM im-

age of the CNTs grown from lithographically defined catalyst

patterns. This photolithography-based approach is simple

and yet robust process with excellent potential to fabricate

partially Fe filled CNTs at lithographically defined locations

in a reproducible manner.

In conclusion, we have demonstrated a simple and effec-

tive method to synthesize partially Fe filled CNTs using a mix-

ture of Fe(acac)3 powder and conventional photoresist and

successive CVD growth. The experimental results show that

the catalyst particle size effectively controls the diameter of

the partially Fe filled CNTs grown through a tip-growth mech-

anism. A simple photolithographic route has been devised for

the spatially selective synthesis of partially Fe filled MWCNTs,

which were grown only on a pre-defined surface in a manner

compatible with current IC technology.

Synthesis of multi-walled carbon nanotubes on ‘red mud’catalysts

Oscar M. Dunens *, Kieran J. MacKenzie, Andrew T. Harris

Laboratory for Sustainable Technology, School of Chemical and Biomolecular Engineering, Building J01, The University of Sydney, NSW 2006,

Australia

A R T I C L E I N F O

Article history:

Received 25 December 2009

Accepted 24 February 2010

Available online 1 March 2010

A B S T R A C T

Red mud, a toxic waste product from bauxite processing, was used as a catalyst for the syn-

thesis of multi-walled carbon nanotubes (MWCNTs) by fluidised bed chemical vapour

deposition. The products were analysed using thermogravimetric analysis, Raman spec-

troscopy, and transmission electron microscopy. Using ethylene at 650 �C a MWCNT yield

of 375% (with respect to Fe loading) was obtained. Carbon products were approximately

75% MWCNTs with an IG/ID ratio from Raman spectroscopy of 1.43. The production tech-

nique and reaction conditions used are conducive to large-scale CNT production, offering

a potential value-added commercial use for red mud.

� 2010 Elsevier Ltd. All rights reserved.

Red mud is a waste product from alumina (Al2O3) produc-

tion by the Bayer process. The composition of red mud is lar-

gely dependant on the bauxite source but typically contains

Fe2O3 (20–60%), Al2O3 (10–30%), SiO2 (3–50%), Na2O (1–10%),

CaO (2–8%) and TiO2 (trace – 10%) [1,2]. Red mud is highly

alkaline with a pH of 10–12.5 and radioactive due to concen-

trating naturally occurring 238U, 226Ra, 232Th and 40K [3]. Con-

sequently, the disposal and storage of red mud is a costly

industry challenge [4].

Global alumina production has been forecast to reach

124 Mt by 2017,1 the amount of red mud produced per ton of

alumina depends on the ore grade, ranging from 0.3 ton for

0008-6223/$ - see front matter � 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.carbon.2010.02.039

* Corresponding author: Fax: +61 2 9351 2854.E-mail address: oscar.dunens@sydney.edu.au (O.M. Dunens).

1 Global Alumina Corporation, 2009 (cited November 2009); Available from: http://www.globalalumina.com/ind_overview.php.