carbon nanotube - a burgeoning field in …

www.wjpr.net

295

Sonali Jayronia et al. World Journal of Pharmaceutical Research

CARBON NANOTUBE - A BURGEONING FIELD IN

NANOTECHNOLOGY

*Sonali Jayronia, Anu Hardenia, Sanjay Jain

Assistant Professor, Manavta Nagar, Kanadiya Road, Indore.

ABSTRACT

The increased current interest in carbon nanotubes is a direct

consequence of the development of buckminsterfullerene’s and its

derivatives thereafter. The result of research that carbon could form

stable, ordered structures other than graphite and diamond stimulated

many researchers in the world to search for other allotropes of carbon.

The small dimensions, proper physical properties of these structures

make them very unique with many promising applications. The

properties and characteristics of Carbon Nanotubes are still being

researched heavily and scientists have barely begun to tap the potential

of these structures. They can pass through membranes, carrying

therapeutic drugs, vaccines and nucleic acids deep into the cell to

targets previously unreachable. Overall, recent studies regarding Carbon Nanotubes have

shown a very promising glimpse of what lies ahead in the future of medicines. In this review

the Properties and Structure of carbon Nanotubes is discussed. So as the applications are

given.

KEYWORDS: Carbon Nanotubes, Allotropes, Membranes.

INTRODUCTION

Carbon is a versatile element and it can form various allotropes, including graphite, diamond

and fullerene-like structures. In the well-known layered structure of graphite, there is a large

difference in chemical bonding within the layers and between them. The σ-bonds connecting

each C atom with its three neighbors within the layers are created by sp2 hybridization. They

are possibly the strongest existing chemical bonds. The remaining fourth delocalized electron

in graphite is responsible for the very weak π-bonds acting between the layers. It also

determines the “semimetallic” character of graphite.1 The difference in the bond strength is

World Journal of Pharmaceutical research

Volume 3, Issue 1, 295-310. Review Article ISSN 2277 – 7105

Article Received on 20 October2013 Revised on 24 November 2013, Accepted on 30 December 2013

*Correspondence for

Author:

Sonali Jayronia,

Assistant Professor, Manavta

Nagar, Kanadiya Road, Indore.

[email protected]

www.wjpr.net

296


reflected in the different bond distances: 0.142 nm between the neighboring C atoms within

the layers, as opposed to 0.335 nm between the layers. Due to the large difference in the bond

strength, the layers behave in a rather “independent “way and are termed “graphene” layers.

With the study of C60 and C70, it was soon realized that an infinite variety of closed

graphitic structures could be formed, each with unique properties. All that was necessary to

create such a structure was to have 12 pentagons present to close the hexagonal network (as

explained by the Euler theorem). Since C70 was already slightly elongated, tubular fullerenes

were imagined.

CNTs are allotropes of carbon. They are tubular in shape, made of graphite. CNTs possess

various novel properties that make them useful in the field of nanotechnology and

pharmaceuticals. They are nanometers in diameter and several millimeters in length and have

a very broad range of electronic, thermal, and structural properties. These properties vary

with kind of nanotubes defined by its diameter, length, chirality or twist and wall nature.

Their unique surface area, stiffness, strength and resilience have led to much excitement in

the field of pharmacy.

HISTORY

Carbon Nanotubes were discovered long before researchers even imagined that carbon may

exist in such a form. It was in 1952 when Radushkevichand Lukyanovich reported the

discovery of “worm-like” carbon formations1. These were observed during their study of the

soot formed by decomposition of CO on iron particles at 600 ˙C. On the basis of many

experiments and TEM images, the authors conclude that the formed product consisted of long

filamentary or needle-like carbon crystals with diameters of about 50 nm (the narrowest seen

in their TEM images were about 30 nm), probably hollow, growing from iron compound

(probably carbide) particles. In other words, the products were carbon nanotubes. The

discovered carbon nanotubes (CNTs), as we know today, were in fact multi-walled

(MWNTs), but the resolution of their TEM was too low (5–6 nm) to enable the authors to see

the arrangement of graphenes in then a no tube walls. It is interesting that the authors also

found couples of intertwined nanotubes, resembling at the first sight the DNA double helix

structure. The discovery of nanotubes passed almost unnoticed, like a number of other studies

before and after it.2

A paper by Oberlin, Endo, and Koyama published in 1976 clearly showed hollow carbon

fibers with nanometer-scale diameters using a vapor-growth technique3. Furthermore, in

www.wjpr.net

297


1979, John Abrahamson presented evidence of carbon nanotubes at the 14th Biennial

Conference of Carbon at Penn State University. The conference paper described carbon

nanotubes as carbon fibers which were produced on carbon anodes during arc discharge4. In

1981 a group of Soviet scientists published the results of chemical and structural

characterization of carbon nanoparticles produced by a thermocatalytical disproportionation

of carbon monoxide. Using TEM images and XRD patterns, the authors suggested that their

“Carbon multi-layer tubular crystals”were formed by rolling graphene layers into cylinders.

In 1987, Howard G. Tennent of Hyperion Catalysis was issued a U.S. patent for the

production of "cylindrical discrete carbon fibrils" with a "constant diameter between about

3.5 and about70 nanometers, length 10² times thediameter, and an outer region of multiple

essentially continuous layers of ordered carbon atoms and a distinct inner core"5. A large

percentage of academic and popular literature attributes the discovery of hollow, nanometer

sized tubes composed of graphitic carbon to SumioIijima of Nippon Electric Company in

1991. A 2006 editorial written by Marc Monthioux and Vladimir Kuznetsov in the journal

Carbon has described origin of the carbon nanotube.

CARBON STRUCTURE

Carbon has various elemental strutures.

CARBON

Graphite Fullerenes Nanotubes carbyne{chaoite} Diamond

Para crystalline Rhombic Hexagonal Cubic Hexagonal

Figure 1: Carbon elements

The arrangement of carbon atoms in each crystal is the fundamental difference between the

various structures. The three most important carbon structures are cubic diamond, fullerene

(C60) and hexagonal graphite Diamond is a stable form of carbon and can be synthesized

from graphite at high temperatures and pressures. Graphite is characterized by double bounds

www.wjpr.net

298


between sp2 hybridized carbon atoms. Fullerene, discovered in 1985, was the first discovered

form of carbon that had a cage like structure. The main derivatives of fullerene include buck

onions and nano tubes.

Structure of CNTs (Carbon Nanotubes)

CNTs are sheets of graphite rolled into tubes and tubes and have excellent due to their

symmetric structure. The two limiting cases, the armchair and zig-zagnanotubes, can be

obtained depending on the direction in which the sheet is rolled, as illustrated in Figure 2.

The structure of a nanotube is described by the chiral vector (ch), which is often referred to as

the rolled-up vector, and the chial angle (C). The chiral vector (n, m) is defined by the

following equation:

Ch= na1 +ma2

Figure 2: Roll-up a graphene sheet leading to the three different type of CNTs2

If the graphite sheet is rolled in all direction, then zig-zag nanotubes will be obtained. A

rolled graphite sheet in chiral vector (Ch) direction results in an armchair nanotubes.

Thesetwo structure are the limiting cases which occur which at chiral angles of the (zig-

zag)and 300 (armchair). The chiral vector of the zig-zagnanotubes is (n, 0) while the chiral

vector of the armchair nanotube is (n, n) (Thotenson et al, 2001). A SWCNT can be classified

as either metallic or semi-conducting based on its chiral vector (n, m).ASWCNT will be

metallic if the difference n-m is a multiple of three. Unlike MWCNTs, the atoms of SWCNTs

from of a singal covalently bound arry. Consequently, SWCNTs have more distinctive

electrical and optical properties when compared to MWCNTs and are typically used in

electronic components.

www.wjpr.net

299


METHODOLOGY

Types of carbon nanotubes and related structures

Single-walled

Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer, with

a tube length that can be many millions of times longer. The structure of a SWNT can be

conceptualized by wrapping a one-atom-thick layer of graphite called graphene into a

seamless cylinder. The way the graphene sheet is wrapped is represented by a pair of indices

(n, m). The integer’s n and m denote the number of unit vectors along two directions in the

honeycomb crystal lattice of graphene. If m = 0, the nanotubes are called zigzag nanotubes,

and if n = m, the nanotubes are called armchair nanotubes. Otherwise, they are called chiral.

The diameter of an ideal nanotubes can be calculated from its (n, m) indices as follows

Where a = 0.246 nm.

SWNTs are an important variety of carbon nanotubes because most of their properties

change significantly with the (n,m) values, and this dependence is non-monotonic. In

particular, their band gap can vary from zero to about 2 eV and their electrical conductivity

can show metallic or semiconducting behavior. Single-walled nanotubes are likely candidates

for miniaturizing electronics. The most basic building block of these systems is the electric

wire, and SWNTs with diameters of an order of a nanometer can be excellent

conductors6. One useful application of SWNTs is in the development of the first

intermolecular field-effect transistors (FET). The first intermolecular logic gate using

SWCNT FETs was made in 20017. A logic gate requires both a p-FET and an n-FET.

Because SWNTs are p-FETs when exposed to oxygen and n-FETs otherwise, it is possible to

protect half of an SWNT from oxygen exposure, while exposing the other half to oxygen.

This results in a single SWNT that acts as a NOT logic gate with both p and n-type FETs

within the same molecule. Single-walled nanotubes are dropping precipitously in price, from

around $1500 per gram as of 2000 to retail prices of around $50 per gram of as-produced 40–

60% by weight SWNTs as of March 2010

Figure 3: Single wall carbon nanotube7

www.wjpr.net

300


Multi-walled

Multi-walled nanotubes (MWNT) consist of multiple rolled layers (concentric tubes) of

graphene. There are two models that can be used to describe the structures of multi-walled

nanotubes. In the Russian Doll model, sheets of graphite are arranged in concentric cylinders,

e.g., a (0,8) single-walled nanotubes (SWNT) within a larger (0,17) single-walled nanotubes.

In the Parchment model, a single sheet of graphite is rolled in around itself, resembling a

scroll of parchment or a rolled newspaper. The interlayer distance in multi-walled nanotubes

is close to the distance between graphene layers in graphite, approximately 3.4 Å. The

Russian Doll structure is observed more commonly. Its individual shells can be described as

SWNTs, which can be metallic or semiconducting. Because of statistical probability and

restrictions on the relative diameters of the individual tubes, one of the shells, and thus the

whole MWNT, is usually a zero-gap metal.

Double-walled carbon nanotubes (DWNT) form a special class of nanotubes because their

morphology and properties are similar to those of SWNT but their resistance to chemicals is

significantly improved. This is especially important when functionalization is required (this

means grafting of chemical functions at the surface of the nanotubes) to add new properties to

the CNT. In the case of SWNT, covalent functionalization will break some C=C double

bonds, leaving "holes" in the structure on the nanotubes and, thus, modifying both its

mechanical and electrical properties. In the case of DWNT, only the outer wall is modified.

DWNT synthesis on the gram-scale was first proposed in 2003 by the CCVD technique, from

the selective reduction of oxide solutions in methane and hydrogen8.

The telescopic motion ability of inner shells and their unique mechanical properties permit to

use multi-walled nanotubes as main movable arms in coming nanomechanical devices9.

Retraction force that occurs to telescopic motion caused by the Lennard-Jones

interaction between shells and its value is about 1.5 nN.

Figure 4: Triple-walled armchair carbon nanotube8

www.wjpr.net

301


Torus

In theory, a nanotorus is a carbon nanotube bent into a torus (doughnut shape). Nanotori are

predicted to have many unique properties, such as magnetic moments 1000 times larger than

previously expected for certain specific radii Properties such as magnetic moment, thermal

stability, etc. vary widely depending on radius of the torus and radius of the tube.10

Figure 5: A Torus stable structure8

Nanobud

Carbon Nanobud is a newly created material combining two previously discovered allotropes

of carbon: carbon nanotubes and fullerenes. In this new material, fullerene-like "buds" are

covalently bonded to the outer sidewalls of the underlying carbon nanotubes. This hybrid

material has useful properties of both fullerenes and carbon nanotubes. In particular, they

have been found to be exceptionally good field emitters. In composite materials, the attached

fullerene molecules may function as molecular anchors preventing slipping of the nanotubes,

thus improving the composite’s mechanical properties

Figure 6: A nanobud stable structure9

Graphenated carbon nanotubes (g-CNTs)

Graphenated CNTs are a relatively new hybrid that combines graphitic foliates grown along

the sidewalls of multiwalled or bamboo style CNTs. Yu et al. reported on "chemically

bonded graphene leaves" growing along the sidewalls of CNTs11. Stoner et al. described

these structures as "graphenated CNTs" and reported in their use for enhanced

www.wjpr.net

302


supercapacitor performance12. The foliate density can vary as a function of deposition

conditions (e.g. temperature and time) with their structure ranging from few layers

of graphene (< 10) to thicker, more graphite-like.13

The fundamental advantage of an integrated graphene-CNT structure is the high surface area

three-dimensional framework of the CNTs coupled with the high edge density of

graphene. Graphene edges provide significantly higher charge density and reactivity than the

basal plane, but they are difficult to arrange in a three-dimensional, high volume-density

geometry. CNTs are readily aligned in a high density geometry (i.e., a vertically aligned

forest) but lack high charge density surfaces—the sidewalls of the CNTs are similar to the

basal plane of graphene and exhibit low charge density except where edge defects exist14.

Depositing a high density of graphene foliates along the length of aligned CNTs can

significantly increase the total charge capacity per unit of nominal area as compared to other

carbon nanostructures.

Peapod

A Carbon peapodis a novel hybrid carbon material which traps fullerene inside a carbon

nanotube. It can possess interesting magnetic properties with heating and irradiating. It can

also be applied as an oscillator during theoretical investigations and predictions.15-18

Cup-stacked carbon nanotubes

Cup-stacked carbon nanotubes (CSCNTs) differ from other quasi-1D carbon structures,

which normally behave as quasi-metallic conductors of electrons. CSCNTs exhibit

semiconducting behaviors due to the stacking microstructure of graphene layers.

Extreme carbon nanotubesS

Figure 7: Cycloparaphenylene9

The observation of the longest carbon nanotubes (18.5 cm long) was reported in 2009. These

nanotubes were grown on Si substrates using an improved chemical vapor deposition (CVD)

method and represent electrically uniform arrays of single-walled carbon nanotubes.

www.wjpr.net

303


The shortest carbon nanotube is the organic compound cycloparaphenylene, which was

synthesized in early 2009.

The thinnest carbon nanotube is armchair (2,2) CNT with a diameter of 3 Å. This nanotube

was grown inside a multi-walled carbon nanotube. Assigning of carbon nanotube type was

done by combination ofhigh-resolution transmission electron microscopy (HRTEM), Raman

spectroscopy and density functional theory (DFT) calculations.19

The thinnest freestanding single-walled carbon nanotube is about 4.3 Å in diameter.

Researchers suggested that it can be either (5, 1) or (4, 2) SWCNT, but exact type of carbon

nanotube remains questionable. (3, 3), (4, 3) and (5, 1) carbon nanotubes (all about 4 Å in

diameter) were unambiguously identified using more precise aberration-corrected high-

resolution transmission electron microscopy. However, they were found inside of double-

walled carbon nanotubes.

PROPERTIES

Hardness

Standard single-walled carbon nanotubes can withstand a pressure up to 24GPa without

deformation. They then undergo a transformation to superhard phase nanotubes. Maximum

pressures measured using current experimental techniques are around 55GPa. However, these

new superhard phase nanotubes collapse at an even higher, albeit unknown, pressure.

The bulk modulus of superhard phase nanotubes is 462 to 546 GPa, even higher than that of

diamond (420 GPa for single diamond crystal) 20.

Kinetic properties

Multi-walled nanotubes are multiple concentric nanotubes precisely nested within one

another. These exhibit a striking telescoping property whereby an inner nanotube core may

slide, almost without friction, within its outer nanotube shell, thus creating an atomically

perfect linear or rotational bearing. This is one of the first true examples of molecular

nanotechnology, the precise positioning of atoms to create useful machines. Already, this

property has been utilized to create the world's smallest rotational motor. Future applications

such as a gigahertz mechanical oscillator is also envisaged.

Optical activity

Theoretical studies have revealed that the optical activity of chiral nanotubes disappears if the

www.wjpr.net

304


nanotubes become larger21.Therefore, it is expected that other physical properties are

influenced by these parameters too. Use of the optical activity might result in optical devices

in which CNTs play an important role.

Electrical conductivity

Depending on their chiral vector, carbon nanotubes with a small diameter are either semi-

conducting or metallic. The differences in conducting properties are caused by the molecular

structure that results in a different band structure and thus a different band gap. The

differences in conductivity can easily be derived from the graphene sheet properties.It was

shown that a (n,m) nanotubes is metallic as accounts that: n=m or (n-m) = 3i, where i is an

integer and n and m are defining the nanotubes. The resistance to conduction is determined by

quantum mechanical aspects and was proved to be independent of the nanotube length. For

more, general information on electron conductivity is referred to a review by Ajayan and

Ebbesen.

Mechanical strength

Carbon nanotubes have a very large Young modulus in their axial direction. The nanotube as

a whole is very flexible because of the great length. Therefore, these Compounds are

potentially suitable for applications in composite materials that need anisotropic properties.

Chemical reactivity

The chemical reactivity of a CNT is, compared with a graphene sheet, enhanced as a direct

result of the curvature of the CNT surface. Carbon nanotube reactivity is directly related to

the pi-orbital mismatch caused by an increased curvature. Therefore, a distinction must be

made between the sidewall and the end caps of a nanotube. For the same reason, a smaller

nanotube diameter results in increased reactivity. Covalent chemical modification of either

sidewalls or end caps has shown to be possible. For example, the solubility of CNTs in

different solvents can be controlledthis way. Though, direct investigation of chemical

modifications on nanotube behavior is difficult asthe crude nanotube samples are still not

pure enough.

Thermal properties

All nanotubes are expected to be very good thermal conductors along the tube, exhibiting a

property known as "ballistic conduction", but good insulators laterally to the tube axis.

Measurements show that a SWNT has a room-temperature thermal conductivity along its axis

www.wjpr.net

305


of about 3500 W·m−1·K−1, Compare this to copper, a metal well known for its good thermal

conductivity, which transmits 385 W·m−1·K−1. A SWNT has a room-temperature thermal

conductivity across its axis (in the radial direction) of about 1.52 W·m−1·K−1,which is about

as thermally conductive as soil. The temperature stability of carbon nanotubes is estimated to

be up to 2800 °C in vacuum and about 750 °C in air.22, 23

Defects

As with any material, the existence of a crystallographic defect affects the material

properties. Defects can occur in the form of atomic vacancies. High levels of such defects can

lower the tensile strength by up to 85%. An important example is the Stone Wales defect,

which creates a pentagon and heptagon pair by rearrangement of the bonds. Because of the

very small structure of CNTs, the tensile strength of the tube is dependent on its weakest

segment in a similar manner to a chain, where the strength of the weakest link becomes the

maximum strength of the chain.

Crystallographic defects also affect the tube's electrical properties. A common result is

lowered conductivity through the defective region of the tube. A defect in armchair-type

tubes (which can conduct electricity) can cause the surrounding region to become

semiconducting, and single monoatomic vacancies induce magnetic properties.

Crystallographic defects strongly affect the tube's thermal properties. Such defects lead

to phonon scattering, which in turn increases the relaxation rate of the phonons. This reduces

the mean free path and reduces the thermal conductivity of nanotube structures. Phonon

transport simulations indicate that substitutional defects such as nitrogen or boron will

primarily lead to scattering of high-frequency optical phonons. However, larger-scale defects

such as Stone Wales defects cause phonon scattering over a wide range of frequencies,

leading to a greater reduction in thermal conductivity24.

SYNTHESIS

CNTs are generally produced by three main techniques, arc discharge, laser ablation and

chemical vapor deposition.

Arc discharge

Arc dischargeinitially used to for producing C60 fullerenes, is the most common and easiest

way to produce CNTs. This method creates CNTs through arc- vaporization of two carbon

www.wjpr.net

306


rods placed end to end, separated by approximately 1mm, in an enclosure that is usually filled

with inert gas at low pressure. A direct current of 50 to 100 A, driven by a potential

difference of approximately 20 V, creates a high temperature discharge between the two

electrodes. The discharge vaporizes the surface of one of the carbon electrodes, and forms a

small rod-shaped deposit on other electrode (Figure 8).

Figure 8: Arc Discharge setup for synthesis and growth of nanotube12

Laser ablation

In Laser ablation laser vaporization pulses were followed by a second pulse, to vaporize the

target more uniformly. The use of two successive laser pulses minimizes the amount of

carbon deposited as soot. The second laser pulse breaks up the larger particles ablated by the

first one, and feeds them into the growing nanotubes structure (Figure 9). The material

produced by this method appears as a mat of “ropes”, 10-20 nm in diameter and upto 100µm

or more in length.

Figure 9: Laser Ablation setup for nanotube 19

www.wjpr.net

307


Chemical Vapor Deposition

Chemical Vapor Deposition of hydrocarbons over a metal catalyst is a classical method that

has been used to produce various carbon materials like carbon fibers and filaments. Large

amount of CNTs can be formed by catalytic CVD (Figure 10) of acetylene over cobalt and

iron catalysts supported on silica or zeolite. High yields of single walled nanotubes have been

obtained by catalytic decomposition of an H2/CH4 mixture all over well dispersed metal

particles such as cobalt ,nickel and iron on magnesium oxide at 10000C.The reduction

produces very small transition metal particles at a temperature of usually >8000C. The

decomposition of CH4 over the freshly formed nanoparticlesprevents their further growth,

and thus results in a very highproportion of SWNTsand few MWNTs.

Figure 10: Diagrammatical representation of Chemical vapor deposition (CVD) setup

for nanotubes synthesis and growth25

APPLICATIONS25, 26

Various applications of CNTs are as follows:

1) Carrier for Drug delivery: Carbon nanohorns (CNHs) are the spherical aggregates of CNTs

with irregular horn like shape. Research studies have proved CNTs and CNHs as a potential

carrier for drug delivery system.

2) Functionalized carbon nanotubes are reported for targeting of Amphotericin B to Cells.

3) Cisplatin incorporated oxidized SWNHs have showed slow release of Cisplatin in aqueous

environment. The released Cisplatin had been effective in terminating the growth of human

lung cancer cells, while the SWNHs alone did not show anticancer activity.

www.wjpr.net

308


4) Anticancer drug Polyphosphazeneplatinum given with nanotubes had enhanced

permeability, distribution and retention in the brain due to controlled lipophilicity of

nanotubes.

5) Antibiotic, Doxorubicin given with nanotubes is reported for enhanced intracellular

penetration

6) The gelatin CNT mixture (hydro-gel) has been used as potential carrier system for

biomedical.

7) CNT-based carrier system can offer a successful oral alternative administration of

Erythropoietin (EPO), which has not been possible so far because of the denaturation of EPO

by the gastric environment conditions and enzymes.

8) They can be used as lubricants or glidants in tablet manufacturing due to nanosize and

sliding nature of graphite layers bound with van der Waals forces.

TOXICITY OF CNT

Harmful effect of nanoparticles arises due to high surface area and intrinsic toxicity of the

surface. CNT, in the context of toxicology, can be classified as ‘nanoparticles’ due to their

nanoscale dimensions, therefore unexpected toxicological effects upon contact with

biological systems may be induced. The nanometer-scale dimensions of CNT make quantities

of milligrams possess a large number of cylindrical, fibre-like particles, with a concurrent

very high total surface area. The intrinsic toxicity of CNT depends on the degree of surface

functionalization and the different toxicity of functional groups. Batches of pristine CNT

(non-purified and/or non-functionalised) readily after synthesis contain impurities such as

amorphous carbon and metallic nanoparticles (catalysts: Co, Fe, Ni and Mo), which can also

be the source of severe toxic effects. On the basis of recent studies with carbon derived

nanomaterials showed that platelet aggregation was induced by both single and multi-wall

carbon nanotube but not by the C60- fullerenes that are used as building blocks for these

CNT.

REFERENCES

1. Scharff P. New carbon materials for research and technology. Carbon, 1998; 36 (5-6):

481-6.

2. Wang X, Li Q, Xie J, Jin Z, Wang J, Li Y, Jiang K, Fan S. Fabrication of ultralong and

electrically uniform single-walled carbon nanotubes on clean substrates. Nano Lett, 2009;

9(9): 3137-41.

www.wjpr.net

309


3. Oberlin A, Endo M, Koyana T. Filamentous growth of carbon through benzene

decomposition. J Cryst Growth, 1976; 32: 335-349.

4. Abrahamson J, Wiles PG, Rhodes B. Structure of carbon fibers found on carbon arc

anodes. Carbon, 1999; 37: 1873-1875.

5. Carbon fibrils method of producing same and compositions containing same. US

PATENT, 4663230.

6. Mintmire JW, Dunlap BI, White CT."Are Fullerene Tubules Metallic? ". Phys. Rev. Lett,

1992; 68 (5): 631–634.

7. Derycke R, Lavoie V, Appenzeller C, Chan J, Tersoff K, Avouris J. "Ambipolar

Electrical Transport in Semiconducting Single-Wall Carbon Nanotubes". Phys. Rev. Lett,

2001; 87 (25): 256-70.

8. Flahaut E, Bacsa, Revathi, Peigney, Alain, Laurent, Christophe. "Gram-Scale CCVD

Synthesis of Double-Walled Carbon Nanotubes". Chemical Communications, 2003;

12 (12): 1442–1443.

9. Treacy MJ, Ebbesen TW, Gibson JM. "Exceptionally high Young's modulus observed for

individual carbon nanotubes". Nature , 1996; 381 (6584): 678–680.

10. Liu L, Guo G, Jayanthi C, Wu S. "Colossal Paramagnetic Moments in Metallic Carbon

Nanotori". Phys. Rev. Lett, 2002; 88 (21): 206- 217.

11. Kehan, Ganhua Lu, Zheng Bo, Shun Mao, Junhong Chen. "Carbon Nanotube with

Chemically Bonded Graphene Leaves for Electronic and Optoelectronic Applications". J.

Phys. Chem. Lett, 2011; 13 2 (13): 1556–1562.

12. Stoner, Brian R, Akshay S, Raut, Billyde B, Charles B, Parker, Jeffrey T. Glass

"Graphenated carbon nanotubes for enhanced electrochemical double layer capacitor

performance". Appl. Phys. Lett, 2011; 99 (18): 183104.

13. Parker, Charles B, Akshay S. Raut, Billyde B, Brian R, Stoner, Jeffrey T. Glass "Three-

dimensional arrays of graphenated carbon nanotubes". J. Mater. Res, 2012; 27 (7): 1046–

53.

14. Cui, Hong T, Zhou O, Stoner B. "Deposition of aligned bamboo-like carbon nanotubes

via microwave plasma enhanced chemical vapor deposition". J. Appl. Phys,

2000; 88 (10): 6072–4.

15. Smith, Brian W, Monthioux, Marc, Luzzi, David E. "Encapsulated C-60 in carbon

nanotubes". Nature ,1998, 396: 323–324.

16. Smith, Luzzi BW. "Formation mechanism of fullerene peapods and coaxial tubes: a path

to large scale synthesis". Chem. Phys. Lett, 2000; 321: 169–174.

www.wjpr.net

310


17. Su H, Goddard WA, ZhaoY. "Dynamic friction force in a carbon peapod

oscillator". Nanotechnology, 2006; 17 (22): 5691–5695.

18. Wang M, Li CM. "An oscillator in a carbon peapod controllable by an external electric

field: A molecular dynamics study".Nanotechnology, 2010; 21 (3): 035704.

19. Zhao X, Liu Y, Inoue S, Suzuki T, Jones R, Ando Y. "Smallest Carbon Nanotube is 3 Å

in Diameter". Phys. Rev. Lett, 2004; 92(12): 125502.

20. Popov M, Kyotani M, Nemanich R, Koga Y. "Superhard phase composed of single-wall

carbon nanotubes". Phys. Rev. 2002; 65 (3): 033408.

21. Damnjanovic M, Milosevic I, Vukovic T, Sredanovic R, Physical Review B, 60, (4),

2728- 2739, 1999

22. Sinha, Saion, Barjami, Saimir, Iannacchione, Germano, Schwab, Alexander, Muench,

George. "Off-axis thermal properties of carbon nanotube films". Journal of Nanoparticle

Research, 2005; 7 (6): 651–657.

23. Thostenson, Erik, Li C, Chou T. "Nanocomposites in context". Composites Science and

Technology, 2005; 65 (3–4): 491–516.

24. Mingo N, Stewart DA, Broido DA, Srivastava D. "Phonon transmission through defects

in carbon nanotubes from first principles". Phys. Rev. B, 2008; 77 (3): 033418.

25. Barroug A, Glimcher M. Hydroxyapatite crystals as a local delivery system for cisplatin:

adsorption and release of cisplatin in vitro. J Orthop Res, 2002; 20: 274-280.

26. Pai P, Nair K, Jamade S, Shah R, Ekshinge V, Jadhav N. Pharmaceutical applications of

carbon tubes and nanohorns. Current Pharmaesearch Journal, 2006; 1:11-15.

carbon nanotube - a burgeoning field in …

Documents