Carbon has been known as the king of elements because of its versatility and diversity in all areas. Currently, it has three allotropic forms viz., diamond, graphite and buckminsterfullerene (C 60 ) or bucky-ball, in short. Diamond has been prized for centuries as a gemstone of extraordinary beauty, brilliance and lustre. The word diamond derives its name from the alteration of the Latin word adamas meaning ‘untamable’ referring to its hardness. The name graphite comes from the greek verb graphian meaning ‘to write’. It has been used in lubricants, seals, insulators, filters, refractors, electrodes and writing material. Bucky-ball, the third form of carbon, was synthesised in laboratory by Smalley and Kroto (1985). Scientists have been speculating that bucky-ball might be formed every time we light a candle. They have also suggested that it might be abundant in clouds of interstellar dust (Smalley, 1996). The properties associated with two allotropic forms (diamond and graphite) of carbon have already been investigated thoroughly and researchers are well aware of the properties of these two forms (Gopalkrishnan and Subramanyam, Dec. 2002) and (Ravichandran, Sept. 2001). However, regarding the third new form (bucky-ball) of carbon, there is very little awareness among students till date. This has been realised during the supervision duty in intrernship programme of B.Sc. B.Ed. in different schools. Keeping the above in view, attempts have been made to highlight the properties and derivatives associated with the ‘bulky-ball’ and also to discuss its structural properties,synthesis methods and applications in this article. Allotropic Forms of Carbon and their Structures Carbon has three crystalline allotropic forms viz., diamond, graphite and bucky-ball. Their crystal structures are shown in Fig. 1(a), (b) and (c) respectively. Graphite is the carbon form that is stable at room temperature. Diamond is the stable form at very high pressures. Once formed, diamond continues to exist at atmospheric pressure and below about 900°C, because the transformation rate of diamond to graphite is virtually zero under these conditions. Graphite and diamond have widely differing properties, which lead to diverse applications (Table 1). For example, graphite is an electrical conductor whereas diamond is an insulator. LEARN MORE ABOUT BUCKY- BALL S.V S.V S.V S.V S.V. Sharma . Sharma . Sharma . Sharma . Sharma Lecturer in Physics Regional Institute of Education, NCERT Ajmer
Transcript
Carbon has been known as the king of elementsbecause of its versatility and diversity in all areas.Currently, it has three allotropic forms viz.,diamond, graphite and buckminsterfullerene (C
60)
or bucky-ball, in short. Diamond has been prizedfor centuries as a gemstone of extraordinarybeauty, brilliance and lustre. The word diamondderives its name from the alteration of the Latinword adamas meaning ‘untamable’ referring to itshardness. The name graphite comes from thegreek verb graphian meaning ‘to write’. It hasbeen used in lubricants, seals, insulators, filters,refractors, electrodes and writing material.Bucky-ball, the third form of carbon, wassynthesised in laboratory by Smalley and Kroto(1985). Scientists have been speculating thatbucky-ball might be formed every time we light acandle. They have also suggested that it might beabundant in clouds of interstellar dust (Smalley,1996). The properties associated with twoallotropic forms (diamond and graphite) of carbonhave already been investigated thoroughly andresearchers are well aware of the properties ofthese two forms (Gopalkrishnan andSubramanyam, Dec. 2002) and (Ravichandran,Sept. 2001). However, regarding the third newform (bucky-ball) of carbon, there is very little
awareness among students till date. This has beenrealised during the supervision duty in intrernshipprogramme of B.Sc. B.Ed. in different schools.Keeping the above in view, attempts have beenmade to highlight the properties and derivativesassociated with the ‘bulky-ball’ and also todiscuss its structural properties,synthesismethods and applications in this article.
Allotropic Forms of Carbon and their
Structures
Carbon has three crystalline allotropic forms viz.,diamond, graphite and bucky-ball. Their crystalstructures are shown in Fig. 1(a), (b) and (c)respectively. Graphite is the carbon form that isstable at room temperature. Diamond is the stableform at very high pressures. Once formed,diamond continues to exist at atmosphericpressure and below about 900°C, because thetransformation rate of diamond to graphite isvirtually zero under these conditions. Graphite anddiamond have widely differing properties, whichlead to diverse applications (Table 1). For example,graphite is an electrical conductor whereasdiamond is an insulator.
LEARN MORE ABOUT BUCKY- BALL
S.VS.VS.VS.VS.V. Sharma. Sharma. Sharma. Sharma. SharmaLecturer in Physics
Regional Institute of Education, NCERTAjmer
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School Science Quarterly Journal September - December 2012
Structure Covalent bonding withinlayers, Van der Waalsbonding between layers,Hexagonal crystal structure
Good electrical conductor
Thermal conductivitycomparable to metals
Lubricating agent,Mechanable. Bulk graphiteY = 27 G Pa ñ~2.25 g cm-3
Covalently bondednetwork. Cubic crystalstructure
Very good electricalinsulator
Excellent thermalconductor, about fivetimes more than Copper
The hardest materialY = 827 G Pa ñ = 3.25 gcm-3 except boron nitride
Covalently bonded C60
spheroidalmolecules held in an face centredcubic crystal structure by Vander Waals bonding
Semiconductor compounds withalkali metal (e.g. K
3C
60) exhibit
super-conductivity
Mechanically soft.Y = 18 G Pañ = 1.65 g cm-3
Mechanical
Thermal
Electrical
Table 1Table 1Table 1Table 1Table 1
Properties of three allotropic forms of CarbonProperties of three allotropic forms of CarbonProperties of three allotropic forms of CarbonProperties of three allotropic forms of CarbonProperties of three allotropic forms of Carbon
The FCC Unit Cell of the Bucky-ball Bucky-ball Molecule (C60
)
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The bucky-ball (C60
) is the most symmetricmolecule having icosaludral point group with 120symmetry operations. It has a shape of a soccerball in which 60 carbon atoms bond with eachother to form a perfect soccer ball type molecule.This molecule has 12 pentagons and 20 hexagons,joined together to form a spherical molecule witheach carbon atom at a corner as depicted inFigure 1 (c). It has been established that solid C
60
forms a face centred cubic (F.C.C.) lattice with alattice constant 14.17 A° at room temperature. Inthis structure the distance between the nearestneighbour C
60 cluster is 10A° and thus the
intercluster separation is 2.9A°. Scanningtunneling microscope (Fig. 2 a and b) andscanning electron microscope (Fig.3) picturesclearly show the hexagonal arrays of closelypacked spherical balls. (Grigoryan et. al. (1992),Sharma et. al. (1992), Kratschmer et. al. (1990) andBaggot (1991).) Table 2 provides x-ray diffractionparameters for a crystal of bucky-ball. The typicalproperties of bucky-ball are summarised inTable 3.
Fig. 2(a): Scanning tunneling micrograph of molecularlyresolved buckyball image in 3D perspective. Bias voltageand current are shown in scanning tunneling micrograph.
Fig. 2(b): Same micrograph at higher magnification
MeasuredMeasuredMeasuredMeasuredMeasured MeasuredMeasuredMeasuredMeasuredMeasured CalculatedCalculatedCalculatedCalculatedCalculated AssignmentAssignmentAssignmentAssignmentAssignment22222 Θ d spacingd spacingd spacingd spacingd spacing d spacingd spacingd spacingd spacingd spacing miller indicesmiller indicesmiller indicesmiller indicesmiller indices
(degree )(degree )(degree )(degree )(degree ) ( A ° )( A ° )( A ° )( A ° )( A ° ) ( A ° )( A ° )( A ° )( A ° )( A ° ) ( h k l )( h k l )( h k l )( h k l )( h k l )
10.2 8.70 8.68 (100)
10.81 8.18 8.18 (002)
17.69 5.01 5.01 (110)
20.73 4.28 4.28 (112)
21.63 4.11 4.09 (004)
28.1 3.18 3.17 (114)
30.8 2.90 2.90 (300)
32.7 2.74 2.73 (006)
Fig. 3: Scanning electron micrograph of a film of bucky-ball.Magnification, scale and operating voltage are shown on themicrograph.
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School Science Quarterly Journal September - December 2012
Table 3Table 3Table 3Table 3Table 3
Some properties of bucky-ball Some properties of bucky-ball Some properties of bucky-ball Some properties of bucky-ball Some properties of bucky-ball
Shape Spherical (20 hexagonsand 12 pentagons)
Dimensionality 3D
Density 1.7 g/cm3
Crystal structure Face centered cubic
C - C bond length 1.44 A°
State of Hybridisation Intermediate betweenSP2 & SP3
Nearest neighbour distance 10.04 A°
Diameter 7.1 A°
Lattice parameter 16.2 A°
Index of refraction 2.2
Infrared active modes 1429, 1183, 577, 528 cm-1
Bulk modules 18 giga Pascals
Ionisation potential 7.6 ev
Cohesive energy forC
60 molecule 1.5 ev
Cohesive energy for atom 7.4 ev
Electrical resistivity 1011-1014 ohm
Magnetic susceptibility 260 g ppm
Electron band gap 1.5 ev
Effective mass of conduction 1.3 me
Band electron
Superconducting transition 19K
Temperatures for K3C
60
Rb3C
6029K
Cs2 Rb C
6033K
Rb2.7
Tl2.3
C60
42.5K
Colour Black
Doping Intercalation of alkalimetal
Coherence length 100 A°
Penetration depth 2000-4000 A°
Fermi energy (Ef) 0.3 ev
Vf
~ 2×107 cm/s
Isotope effect 0.3 – 1.2
Critical magnetic field[H
e2(O)] 50 tesla
Density of states [N (EF)
RB3C
60/N(E
F) K
3C
60] 1.21
2Ä/KBT
C5.3
Synthesis of Bucky-ball (C60
)
Synthesis of bucky-balls has been carried out byusing mainly two techniques viz. (i) graphite arcwelding, and (ii) laser ablation.
Graphite Arc Welding Technique
In this technique graphite rods of spectroscopicpure grade are butted together and a high current
of the order of 100 amperes is passed throughthem in a controlled inert gas (He/Ar) atmosphere.
The apparatus consists of a vacuum chamber,which is evacuated and then filled with inert gas
(He). To the evaporated graphite condenses on theinner surface of a glass cylinder surrounding the
graphite electrodes from which it is scrapped off.It has been noticed that the He pressure is very
crucial for optimising the yield of bucky-ball (C60
))))).By this method solid C
60 is prepared in the form of
graphite soot. The C60
has been separated fromthe soot using liquid chromatography.
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Laser Ablation
Laser ablation deposition technique has also beenused to prepare the C
60 films. In this technique,
the laser beam enters the vacuum chamberthrough a window and is focused on a target ofgraphite of spectroscopic pure grade. Duringevaporation under the energy of the laser beam,the emitted matter forms a plume that carries thevaporised graphite to the substrate. The processworks in very high vacuum as well as in inertatmosphere. By this technique very good qualityhomogeneous films of bucky-balls have beenprepared.
Properties of Bucky-ball
Chemical properties of bucky-ball have depictedthat it is a highly stable molecule. Ion beamexperiments with 250 eV impact energy haveshown high inelasticity of the ions but gave noevidence of impact induced fragmentation. Bucky-ball possesses a vanishingly small ð-electron ringcurrent and hence has magnetic susceptibility farbelow that of graphite or benzene.Electrochemical studies have proved that bucky-ball is very strong oxidising agent and does notreact with electrofiles. Rather it is easily reducedand reacts readily with nucleophilic agents likealkali metals.
Superconductivity in Bucky-ball
Bucky-ball (C60
) doped with potassium formed anew metallic phase known as ‘buckide’ and
resulted in its maximum electrical conductivitywhen there were three potassium atomsintercalated to each bucky-ball. If too muchpotassium is added, however, the materialbecomes insulating. K
3C
60, a metal, becomes a
superconductor when cooled below 18K. Whenrubidium was substituted for potassium, thecritical temperature (T
c) was found to be 30K.
Recently, superconductivity at 42.5K forrubidium-thallium doped material has beenreported.
Derivatives of Bucky-ball
The synthesis of bucky-balls C60
to C266
in veryhigh yield (upto 44% extractable) by plasmadischarge technique has been reported byParker et. al. (1991). They have characterised theextracted samples by time of flight massspectrometry and Fourier transform massspectrometry and concluded that almost one-third of the extractable material is composed ofbucky-balls C
84 to C
200 (Parker et. al. 1991). Similar
to discovery of bucky-ball, a major breakthroughcame in 1991 when the synthesis of carbon nanotubes (CNTs) was announced by Ijiyama. Carefulanalysis revealed that these carbon nano tubesare long tubes made from a planar sheet ofgraphite that is wrapped into a seamless tube,nanometer in diameter and few microns inlength. They are very stable and found to be goodyield emitters and can be operated at lowerelectric field giving larger currents (Purandareand Patil, 2002).
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School Science Quarterly Journal September - December 2012
Future Projection and Application of
Bucky-ball
Bucky-ball research has immense scope innanoscience and technology. The mosttechnologically interesting property of bulkbucky-ball is electronic in various forms of thecompound. Since, By playing with the dopingconcentration of alkali-metal, it functions as aninsulator, conductor, semi-conductor and super-conductor. Bucky-ball and its derivatives andCNTs can be the potential source of use incatalytic chemistry, bimolecular recognition,nanoreactors, flat panel display technology,electron microscope and atom force microscopy.Also it can be used as molecular sieves and alsoas inhibitions to the activity of HIV virus. Somescientists even believe that the silicon technologymay be replaced in future by bucky-balls clusterbased devices.
Conclusion
The bucky-ball, hollow cage-shaped hugemolecule composed of 60 carbon atoms (thethird crystalline allotropic form of carbon afterwell known diamond and graphite), started toattract an increasing attention of scientificcommunity. The existence of higher derivatives(C
60 to C
266), synthesised by the time-of-flight
mass spectroscopy and Fourier transformmass and spectrometry. In future, the bucky-ball and its higher derivatives including carbonnano tubes can be considered as potentialcandidates for applications in electronics, nano-science, atom force microscopy, catalyticchemistry, etc. In particular, the occurrence ofsuperconductivity in alkali metal doped bucky-ball continues to be a fascinating aspect ofbucky-ball.
References
BAGGOTT, J. 1991. New Scientist. 34.
GOPALAKRISHNAN, B. and SUBRAMANYAM, S.V. 2002. Resonance, 7,10.
GRIGORYAN, L.S., CHAND, P., SHARMA, S.V. and MAJUMDAR, A.K. 1992. Solid State Communications, 81, 853.
IJIYAMA, S. 1991. Nature. 354, 56.
KRATSCHMER, W., LAMB, L.D., FOSTIROPOULOS. K. and HUFFMAN. D.R. 1990. Nature. 347, 354.
