Transcript Graphene * Optical Properties

Graphene – Optical Properties
for monolayers
Manchester Group
Physics 141A
Spring 2013
Lawrence Berkeley Lab
Michael Tsang
UC Berkeley
What is Graphene
Graphene is
 a single layer of carbon packed in hexagonal
(honeycomb) lattice
 the first truly 2D material
Physics 141A
Spring 2013
Michael Tsang
UC Berkeley
What is Graphene
Graphene is
 a single layer of carbon packed in hexagonal
(honeycomb) lattice
 the first truly 2D material
MoS2
Physics 141A
Spring 2013
Michael Tsang
UC Berkeley
.
A Closer Look at Graphene
Graphene has
 Covalent Bonding
 sp2 hybridization
 Remarkably high quality
0.142 nm
Physics 141A
Spring 2013
Michael Tsang
UC Berkeley
Familiar Carbon Structures
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Carbon Nanotubes, known since 1993
Buckeyballs C60, known since 1996
Graphite, known since … a long time
Physics 141A
Spring 2013
Michael Tsang
UC Berkeley
Nobel Prize in Physics (2010)
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Konstantin Novoselov
Andre Geim
Isolated large sheets in order to identify and
characterize graphene and verify 2D properties
Physics 141A
Spring 2013
Michael Tsang
UC Berkeley
Methods: Micromechanical
Cleavage
1. “You put scotch tape on graphite or mica
and peel the top layer. There are flakes of
graphite that come off your tape.
2. “Then you fold the tape in half and stick it
to the flakes on top and split again. And
you repeat this procedure 10 or 20 times.
Each time, the flakes split into thinner
and thinner flakes.”
3. “At the end you’re left with very thin
flakes attached to your tape. You dissolve
the tape and everything goes into
solution”
Physics 141A
Spring 2013
The Optical Properties of
Graphene
Physics 141A
Spring 2013
Michael Tsang
UC Berkeley
Optical Measurements
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Take prepared
macroscopic membranes
of graphene
Shine light through the
membrane
Detector measures light
intensity
Physics 141A
Spring 2013
Michael Tsang
UC Berkeley
Optical Measurements
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Ideal Dirac Fermions?
p e2
c
p e2
= pa ?
Physics 141A
Spring 2013
c
Michael Tsang
UC Berkeley
Dirac Fermions?
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“Dirac Fermions”
refers to electrons that
race through the
graphene structure
Relativistic Quantum
Mechanics becomes
important
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Dirac Equation
Richard Feynman, a founding father of
quantum electrodynamics
Physics 141A
Spring 2013
Michael Tsang
UC Berkeley
Understanding origins of πα
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It was argued that
conductivity for Dirac
fermions is a universal
constant, G
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The universal
conductivity implies
that observable,
optical transmittance
is also universal
æ 1 ö
T º (1+ 2p G / c)-2 = ç 1+ pa ÷
è 2 ø
Physics 141A
Spring 2013
-2
Michael Tsang
UC Berkeley
Optical Properties in Berkeley
Physics
Ultrafast Nano-Optics Group
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Changing the optical
reflection of graphene from
electrical gating
Optical determination of
graphene electronic
structure
Prof Wang welcomes interested
undergraduates and graduates into his
lab
Physics 141A
Spring 2013
Professor Feng Wang (left)
Michael Tsang
UC Berkeley
Other Properties of Graphene
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Density of: 0.77 mg/m2
Breaking Strength: 42 N/m
Conductivity: 0.96x106 Ω-1cm-1 ( > copper)
Thermal Conductivity: 10x greater than copper
According to the Nobel
Prize paper, a hammock
of graphene could hold a
cat (4kg) while weighing
the same as one of its
whiskers!
Physics 141A
Spring 2013
Michael Tsang
UC Berkeley
Recap
Graphene:
 2D, honeycomb lattice of carbons
 Pure, remarkable strength, conductivity
 “Mechanical Cleavage”
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πα = 2.3% Light Absorption
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First material observed with Dirac Fermions
Physics 141A
Spring 2013
Michael Tsang
UC Berkeley
Only 193 US Patents!
Take home message,
Whenever a new material is
characterized, entire systems can
change
Physics 141A
Spring 2013
Michael Tsang
UC Berkeley
References
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http://www.condmat.physics.manchester.ac.uk/pdf/
mesoscopic/publications/graphene/Science_2008fsc.p
df
http://archive.sciencewatch.com/inter/aut/2008/08aug/08augSWGeim/
http://newscenter.lbl.gov/featurestories/2010/10/15/the-noise-about-graphene/
http://www.nobelprize.org/nobel_prizes/physics/lau
reates/2010/advanced-physicsprize2010.pdf
http://blogs.ls.berkeley.edu/fengwang/research/grap
hene/
http://news.softpedia.com/news/Graphene-CanCool-Electronics-with-Great-Efficiency-263614.shtml
http://www.scientificamerican.com/article.cfm?id=ca
rbon-wonderland
Physics 141A
Spring 2013
Michael Tsang
UC Berkeley