17 October 2011 NZ Institute of Physics Conference VICTORIA UNIVERSITY OF WELLINGTON Te Whare Wānanga o te Ūpoko o te Ika a Māui Alan B. Kaiser Shrividya Ravi and Chris Bumby * MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington * Now at Industrial Research Ltd, Gracefield
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17 October 2011
NZ Institute of Physics Conference
VICTORIA UNIVERSITY OF WELLINGTON
Te Whare Wānanga o te Ūpoko o te Ika a Māui
Alan B. Kaiser
Shrividya Ravi and Chris Bumby *
MacDiarmid Institute for Advanced Materials and Nanotechnology,
Victoria University of Wellington
* Now at Industrial Research Ltd, Gracefield
polyacetylene
(CH)n
intrinsic conductivity
similar to metals
carbon-based
electronics
typical nanofibre
diameter 20 ~ 40 nm
electrode separation
~ 150 nm
Polyacetylene (conducting polymer) nanofibre
Yung Woo Park et al.
2
Nobel prize for Physics 2010
Andre Geim and Kostya Novoselov
Awarded 2010 Nobel Prize for Physics for their ground- breaking
experiments on the two-dimensional material graphene
- Demonstrated novel physics of electrons in graphene owing to
unusual band structure around Fermi level.
3
Bulk graphite 4
loosely bound layers
of carbon atoms
Graphite flakes in pencil marks:
Including flakes only one atom
thick!
Discovered by Andre Geim and
his group, 2004
Gate voltage Vg shifts Fermi
energy up (or down)
Resistance per square
of graphene:
electrons conduct
5
holes conduct
Mobility can extremely high - up to 120,000 cm2/Vs at 240 K
in suspended graphene
(Andrei et al. 2008, Bolotin, Kim et al. 2008, Geim, Novoselov et al. 2008)
- higher than any semiconductor (mean free path up to 1 mm)
Re
sis
tan
ce
(kW
)
charge neutrality point
6
Resistance of graphene flake
-20 -15 -10 -5 0 5 10 15 20
1
2
3
4
5
before T-cycle
after T-cycle
R (
kW
)
Gate Voltage (V)
Viera Skákalová, Max Planck Institute, Stuttgart
charge neutrality point
Mesoscopic “Universal
Conductance
Fluctuations” very
persistent in graphene
- up to > 50 K
0 50 100 150 200 2500.6
0.8
1.0
1.2
1.4
high
energy
phonons fluctuations
acoustic phonons
residual resistance
Resis
tan
ce (
kW
)
Temperature (K)
low temperature
anomaly
- monotonic but
can be up or down
7
Graphene: temperature dependence of resistance
R(T) above 50K
consistent with
scattering by
acoustic and high-
energy phonons
(as shown by Chen
et al., Morosov et al.
2008)
Skakalova, Kaiser et al. Phys. Rev. B (2009)
1) Flakes from graphite crystal: lift off with sticky tape, or rub
graphite crystallite on Si/SiO2 substrate (Geim, Novoselov 2004)
2) Epitaxial films from SiC: heat to remove Si at surface, leaving C
layer (Berger, de Heer 2006)
3) Chemically-derived by forming graphene oxide sheets (which
disperse in water), depositing them and then removing oxygen by
chemical reduction (Burghard, Kaner 2007)
– can deposit as macroscopic graphene films
4) Chemical vapour deposition on thin Ni layers (Kim et al. 2009)