Nano Graphene Nanotubes

7/31/2019 Nano Graphene Nanotubes

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Lectures 15-16

Graphene and

carbon nanotubes

Graphene is atomically thin crystal of carbon which is stronger than steel butflexible, is transparent for light, and conducts electricity (gapless semiconductor).


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D.I.Y.

GrapheneGeim & Novoselov(Manchester) 2004


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Graphene from a nanopensil


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Ultra-thin graphitic films mechanically exfoliated from

bulk graphite

Novoselov & Geim (Manchester)

Science 306, 666 (2004)

Geim & Novoselov - Nature Materials 6, 183 (2007) , , -

Geim & Kim, Scientific American 90-97 (April 2008)

10 nm


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h bridisation forms stron directed bonds2

s

Carbon has 4 electrons in the outer s-p shell

which determine a honeycomb lattice structure.

C

- bonds

*Strong hybridised bonds

make graphene mechanically strong.

It takes 48,000 kNmkg1

2sp empty

?- conduction properties(compare to best steel's 154 kNmkg1).

Also, it is chemically resilient.

strong covalentbonds full


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hexagonal Bravais lattice unit cell can be

chosen differently221121

ananR nn

sites


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h bridisation forms stron directed bonds2

s

Carbon has 4 electrons in the outer s-p shell

which determine a honeycomb lattice structure.

C

- bonds

z

eV3~0

*

eV10~pz-bands


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Bragg scattering conditions

Reciprocal lattice

MRG nn 2

221121NN121

nne

aGaG 1

2||

unitcell

aS

22

2unitcellS

222

Hexagonal Bravais lattice determines a

hexagonal reciprocal lattice, with

1G aa

GG32/3

|||| 221


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Reciprocal lattice

221121NN

21NN

reciprocal latticecorresponding to

Bravais lattice2G

1st Brilloun zone

1


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Fermi point

F

Ek )(


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Valle

'G


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is an atomically thin zero-gap

two-dimensional semiconductor

with linear dis ersion of

conduction and valence bandelectrons.

22cond yx

Electronic dispersion in the vicinity of the corner of

xyp

22val

the Brillouin zone: the same in both valleys.

yx


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high-energy photon

~ -

Simultaneous detection

of the energy, Eand

propaga on ang e o

photo-electrons

enables

to restorecompletely

the band structure.

EAp )( ||

work function

ng e-reso ve p oto-em ss on spectroscopy

of heavily doped graphene synthesized on silicon carbideA. Bostwicket al Nature Physics, 3, 36 (2007)


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DoS

Graphene: gapless semiconductor

gatecarriers Vn

o es e ec ron

Wallace, Phys. Rev. 71, 622 (1947)

Graphene-based field-effect transistor:

Geim and Novoselov, Nature Mat. 6, 183 (2007)


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Graphene-based pixels

When embedded in polymers,

ra hene reinforces them remainsgraphene

conducting and, since its thin, it ishighly transparent.

,

flexible liquid crystal screens

or to be used in conducting coating.Blake (Graphene Industries Ltd), et al

Nano Lett. 8, 1704, (2008)


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Graphene: state of the art in applicaitons

G exfoliated from bulkra hite into

G grown on copper andtransferred into various media

G sublimated oninch-size SiC is used

suspensions is used toenhance mechanical

properties of light-weight

is used for flexibleoptoelectronics,

LCD displays, touch screens.

for manufacturing THzcircuits. IBM & HRL (USA)IBM & HRL (USA)

materials (for aerospace

and medical implants ).

(Samsung)


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Carbon nanotubes

Iijima 1991

Smalley 1993

STM images of carbon nanotubesT.W. Odom, J.-L. Huang, P.Kim, C.Lieber, Nature 391 (1998)


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Nanotubes growth


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anotu e t e

armchair (n,n) metallic

z g-zag n, sem con uc or

c ra n,m sma -gap

with n-m=3 semiconductors


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Lyy

Li

)()0(

/2

Metallic nanotubes (n,n)

eL

2

~perimeter, 2r

L

y

22cond v 2

22

2

L

Mhpv

x

cond

n1

n

0nF

xyp

22

,....,,,xp

22

yx

val ppv 22

L

pv xval

n


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1M

Metallic nanotubes (m,m) with m=m

truly 1D conductors

0M

ens yof states

1M 1M||vx

v

DoS

0M

Yao et al(TUDelft)1999


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Semicondutor-type nanotubes(different n and m)

epen ng on ow e car on s ee s ro e n o ananotube, the resulting nanotube may have a gap in

the electron spectrum. A gap in the nanotube

spectrum is determined by its radiusr, which offers

a direct root towards engineering semiconductor

wires with a prescribed band gap, for use inelectronic and optoelectronic devices.

r

xp

tunnelling current

T.W. Odom, J.-L. Huang, P. Kim, C. Lieber, Nature 391 (1998)


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Potential applications of carbon nanotubes:

In surface tunnelling microscopy used as a tip.

Make excellent tips for field-effect electron guns for plasma.displays (SONY).e ui- otential lines


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NorthwestDoctoral Training Centre

in Nanoscience

Initial training designed to demonstrate the breadth and potential ofnanoscience be ore ocusin on one s eci ic area o the sub ect.

Research and training in fundamental nanoscience,

practical nano-engineering, and nanotechnology in medicine.

Interdisciplinary PhD projects which span from development and studies(exp and th) of fundamental properties of new materials and structuresto makin devices for a lications in electronics and medicine.

Development of skills in nanofabrication, low-temperature physics,materials science and data storage, synthetic chemistry, cell &tissue

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Nano Graphene Nanotubes