carbon nanotubes asignmnt

8/3/2019 Carbon Nanotubes Asignmnt

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QUEENY DASGUPTAM.TECH NANOTECHNOLOGYENROLMENT NO.: 10551011PHYSICS OF NANOMATERIALS

ASSIGNMENT I:CARBON NANOTUBES

SUBMITTED TO: DR. K L YADAV



1.How would one classify carbon nanotubes? What are the variouskinds of carbon nanotubes?

Ans: Carbon nanotubes are of three types on the basis of configurationsthey undertake when they are rolled along the tube axis.

1. Zigzag.2. Armchair.3. Chiral.

The structure of a cylindrical tube is best described in terms of a tubulediameter d and a chiral angle θ. The chiral vector C = na 1 + ma 2 alongwith the two parameters d and θ define the tube. The unit vectors a1 and

a2 define the graphene sheet. In a planar sheet of graphene (a single sheetof graphite), carbon atoms are arranged in a hexagonal structure, witheach atom being connected to three neighbors.

There are numerous ways in which the tubes can be rolled. While the (n,0) tubes are called ‘zigzag tubes’ where θ is zero, the (n, n) tubes arecalled ‘armchair tubes’ where θ is 30°. These two types of tubes havehigh symmetry and a plane of symmetry perpendicular to the tube axis.

Any other tube (n, m) is a chiral tube, which can be either left-handed or right-handed.



(3) As the diameter increases, tubes resemble graphite, which can be metallic.

4.Why is it not possible to insert an arbitrary tube into a given tube?

Ans: It is not possible to fit any arbitrary tube in a given tube due to lack of space. For a tube to fit into another there must be a gap of at least 3.44Å between the layers. We can fit a (10, 0) tube in a (19, 0) tube, but notin a (18, 0) tube. This is because in order to insert a 7.94 Å diameter tube, the larger diameter tube has to have a diameter of 14.82 Å or larger [(7.94) + 2(3.44) Å]. The diameters of (19, 0) and (18, 0) tubes are 15.09Å and 14.29 Å, respectively.

5.What are the other materials which can form nanotubes?

Ans: Any planar structure should be able to curl and make a tubular structure. Certain clays such as christolite and imogolite are found intubular form. The structural characteristics of CNTs such as helicity androtational disorder, are found in these clays too.e.g WS2 and MoS2. Avariety of polyhedral and tubular structures of WS2 have been obtained

by heating a thin tungsten film in H2S. The curling of a graphite-likesheet of WS2 leads to the creation of defects.

6.Are there specific properties of nanotubes which will be differentin multiwalled and single-walled nanotubes?

Ans:FEATURES SWNT MWNT

(1)No. of nanotubes Single Many, one rolled insideanother.

(2)Growthmechanism

Presence in catalyzedconditions.

Presence in uncatalyzedconditions.

(3)Electronicstructure

The 1s resonance in theinner shell electronenergy loss spectrum

Distinctly different inSWNTs.



shows features at 285and 291 eV, due to1s→π * and 1s→σ *resonances. These aresimilar to graphite inMWNTs

(4)Density 1.8 g/cm3 0.8 g/cm3

7.What are the unique properties of nanotubes and how would onestudy those?

Ans: A carbon nanotube is produced by curling a graphene sheet.

(1)Electronic Properties : Nanotubes can have distinctly differentelectronic properties depending on the chirality. Early calculations predicted that they can be semiconducting or metallic depending on thetype of structure. While armchair tubes are always metallic, others can be semiconducting or metallic. The presence of defects on the body of the tube can alter the electronic structure and can make regions of specific electronic properties, such as metallic and semiconducting.

CNTs exhibit plasmon features at 7 and 25 eV, nanotubes also showfeatures in the range of 10–16 eV. This is attributed to the lowdimensionality of the tubes and also to the dimensional cross-over fromone to three dimensions.

Raman scattering is found to be highly diameter-dependent. Thereare specific vibrations in the 100–1600 cm–1 region which are stronglydiameter dependent.

(2) Transport properties: The band gaps of the nanotubes vary from0.2 to 1.2 eV.The gap varies along the tube body and reaches aminimum value at the tube ends. This is due to the presence of localizeddefects at the ends due to the extra states. The conductive behaviour of MWNTs was consistent with the weak two-dimensional localization of the carriers. The inelastic scattering of carriers from lattice defects ismore significant than carrier–carrier or carrier–phonon scattering. In



SWNTs, conduction occurs through discrete electronic states that arecoherent between the electrical contacts.

(3)Mechanical Properties : Nanotubes are the ultimate high strengthcarbon fibres. The value of Young’s modulus is 1.8 TPa. withstandextreme strain in tension (up to 40 per cent). The tubes can recover fromsevere structural distortions. The resilience of a graphite sheet ismanifested in this property, which is due to the ability of carbon atomsto rehybridize. Any distortion of a tube will change the bonding of thenearby carbon atoms and in order to come back to the planar structure,the atoms have to reverse to sp2 hybridization. If the tube is subjected toelastic stretching beyond a limit, some bonds are broken. The defect is

then redistributed along the tube surface.(4) Physical properties: Nanotubes have a high strength-to-weight ratio(density of 1.8 g/cm3 for MWNTs and 0.8 g/cm3 for SWNTs). Nanotubes are highly resistant to chemical attack. It is difficult tooxidize them and the onset of oxidation in nanotubes is 100°C higher than that of carbon fibres. The surface area of nanotubes is of the order of 10–20 m2/g. Nanotubes have a high thermal conductivity and the

value increases with decrease in diameter.

8. Can one extend the knowledge of the chemistry of fullerenes intocarbon nanotubes? What are such properties?

Ans.: (a) The synthesis procedures are similar.(b) Nanotubes are mostly found with closed ends on either side,

though open tubes are also seen. Thus these are three-dimensionalclosed-cage objects, and may be considered as elongated fullerenes. Thehexagons make the elongated body of the tube and the ends contain bothhexagons and pentagons, with a minimum of six pentagons on each face.That is like in the case of fullerenes, CNTs are also composed of hexagons and pentagons.

Such properties are (i) Filling properties



(ii) Structural properties

10. From the everyday examples of macroscopic objects similar totubes, such as iron pipes, suggest a few properties of nanotubeswhich could be investigated.Ans.: Comparing nanotubes with Iron pipes or other such macroscopicobjects of everyday use, the following properties maybe studied:-

(1) Hardness(2) Tensile strength(3) Elasticity

carbon nanotubes asignmnt

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