Post on 05-Apr-2018
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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
, ,your choice!