flatland: 2차원 세계의 물리학 - universitas sanata dharma · 2017. 4. 12. · edwin abbott...
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Flatland:Physics in 2-dimensional world
Hyeonsik Cheong
Department of Physics
Sogang University
Edwin Abbott Abbott
(1884)
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Flatland: THE FILM (2007)
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Dimensionality
• Our world is 3 dimensional.
• Einstein says, “No! There are 4 dimensions!”
• Superstring Theory: No, the world is in 10-
dimensional space!
High-dimensional Physics?
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Low Dimensional Physics
• Thin film, Quantum Well (2D)
2~10 nm
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Low Dimensional Physics
• Quantum Wire, Nanowire, Carbon
Nanotube (1D)
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Low Dimensional Physics
• Quantum Dot, Nanoparticle (0D)
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Physics in ‘real’ 2 dimension?
Ultimate 2D material.
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Graphene
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graphene
Diamond Graphite
Graphene
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Graphene – The Beginning
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Nobel Prize in Physics - 2010
Andre K. Geim Konstantin S. Novoselov
“for groundbreaking experiments regarding the two-dimensional material graphene”
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Nobel Prize in Physics - 2010
Scotch Tape!
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Peculiar Band Structure
Dirac pointkx
ky
E( ) FE vk k
2 22 21
2 2 2
pE mv k
m m ‘Nomal’ particles:
2 4 2 2 2 2 2 2E m c p c c m c k Relativistic particle:
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“Massless Dirac Fermion”
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Dirac Equation
Klein Tunneling
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Zeitschrift fur Physik 53, 157 (1929)
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Half-integer quantum Hall effect
2 21 1
4( ) , 0, 1, 2,2
xy
e eR n n
h h
K. S. Novoselov et al., Nature 438, 197 (2005)
Y. Zhang et al., Nature 438, 201 (2005)
B = 14 T, T = 4 K
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Graphene’s Superlatives• Thinnest imaginable material
• Largest surface-to-weight ratio (~2700m2 per gram)
• Strongest material ‘ever measured’ (theoretical limit)
• Stiffest known material (stiffer than diamond)
• Most stretchable material (up to 20% elastically)
• Record thermal conductivity (outperforming diamond)
• Highest current density at room T (106 times of copper)
• Highest intrinsic mobility (100 more times than in Si)
• Conducts electricity in the limit of no electrons
• Lightest charge carriers (zero rest mass)
• Longest mean free path at room T (micron range)
• Completely impermeable (even He atoms cannot squeeze through)
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(from Geim’s talk)
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But
Such small pieces of graphene
Are not very useful!
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PDMS
Ni deposition heating carbon deposition cooling graphene formation
Removal of Ni Etching Floating Transfer
Chemical Vapor Deposition (CVD)
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Keun Soo Kim et al.
Nature 457, 706 (2009)
Large area graphene
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Roll-to-Roll Process
Graphene on Cu foil
Polymer support
Cu etchant
Graphene on
polymer support
Target substrateGraphene on target
Released
polymer support
S. Bae et al. Nature Nanotech. 5, 574 (2010)
Large area graphene
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b
Fig. 2
c
1st
2nd
Before
heating
After
heating
a
8 inch
f
d
e
Stencil mask
Screen
printer
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Graphene touch screen
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Applications of graphene
• Replacement for silicon: electronic
devices
• Transparent electrode: display, touch
screen
• Anode material for lithium ion batteries
• Replacement for copper wires
• …
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Limitations of Si devices
• High-capacity, high-speed memories and
CPU’s more, smaller transitors
Heat problem
Typical Si MOSFET Cooling device for CPU
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Graphene’s Superlatives• Thinnest imaginable material
• Largest surface-to-weight ratio (~2700m2 per gram)
• Strongest material ‘ever measured’ (theoretical limit)
• Stiffest known material (stiffer than diamond)
• Most stretchable material (up to 20% elastically)
• Record thermal conductivity (outperforming diamond)
• Highest current density at room T (106 times of copper)
• Highest intrinsic mobility (100 more times than in Si)
• Conducts electricity in the limit of no electrons
• Lightest charge carriers (zero rest mass)
• Longest mean free path at room T (micron range)
• Completely impermeable (even He atoms cannot squeeze through)
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(from Geim’s talk)
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Transparent electrodes• Current technology ITO (Indium Tin Oxide)
on glass
– Scarcity of In
– Durability of glass
– Inflexible
• Advantages of graphene
– Flexible (1-atom thick)
– Good conductivity
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TV Commercial
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Courtesy BH Hong
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The Hype!
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Future Devices
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Other Applications
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ACS Nano, 2011, 5, 1321.
Graphene Application Materials PDP LED Low
Resistivity Graphene Heat Sink
Alibaba.com
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Importance in physics community
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Beyond Graphene
• Limitations of Graphene
– No band gap (Low on/off)
– Made of single element (Carbon)
• New class of 2-dimensional materials
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Beyond Graphene
• Limitations of Graphene
– No band gap (Low on/off)
– Made of single element (Carbon)
• New class of 2-dimensional materials
– Transition metal chalcogenides: MoS2, WSe2, MoTe2, GaSe
– Black Phosphorus, Hexagonal Boron Nitride
– Semiconductor, Superconductor, Magnetic, etc.
– Can complement graphene in future electronics
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Beyond Graphene
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MoS2
Nature Nanotechnology 6, 147 (2011).
On/off ratio > 108
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Black phosphorus
Liu et al., ACS Nano 8(4), 4033 (2014)
Li et al., Nat. Nanotech. 9(5), 372 (2014)
• Least reactive allotrope of phosphorus
• High carrier mobility ~ 1,000 V∙cm2/s & on/off ratio ~105
promising candidate for FET devices
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2D Heterostructures
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2D Heterostructures
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Major Research Centers
Research Centers of 2D Materials
Harvard/Columbia(Philip Kim)
U. Manchester(Geim & Novoselov)
Korea
Singapore
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EU Graphene Flagship
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€1 billion for 10 years
Manchester
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Singapore
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Korea
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Korea
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세계 그래핀 연구의 주요 중심지
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IF 9.611
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EU-Korea Workshop
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Summary
• Graphene and 2D materials show various
novel physical phenomena, many of
which are not understood yet.
• It is the task of the physicists to discover
useful properties among many 2D
materials.
• More research (and more people) is
needed…
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Terima kasih!
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