Graphene – Optical Properties

Graphene – Optical Properties

Michael TsangUC Berkeley

Physics 141ASpring 2013

Lawrence Berkeley LabManchester Group

for monolayers

Graphene is a single layer of carbon packed in

hexagonal (honeycomb) lattice the first truly 2D material

What is Graphene



Graphene is a single layer of carbon packed in

hexagonal (honeycomb) lattice the first truly 2D material

What is Graphene


MoS2 .


Graphene has Covalent Bonding sp2 hybridization Remarkably high quality

A Closer Look at Graphene


0.142 nm


Familiar Carbon Structures Carbon Nanotubes, known since 1993 Buckeyballs C60, known since 1996 Graphite, known since … a long time



Konstantin Novoselov Andre Geim

Nobel Prize in Physics (2010)


Isolated large sheets in order to identify and characterize graphene and verify 2D properties


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”

Methods: Micromechanical Cleavage


The Optical Properties of Graphene




Optical Measurements Take prepared

macroscopic membranes of graphene

Shine light through the membrane

Detector measures light intensity



Optical Measurements

Ideal Dirac Fermions?

?



Dirac Fermions? “Dirac Fermions”

refers to electrons that race through the graphene structure

Relativistic Quantum Mechanics becomes important Dirac Equation

Richard Feynman, a founding father of quantum electrodynamics Michael Tsang

UC Berkeley


Understanding origins of πα

The universal conductivity implies that observable, optical transmittance is also universal

It was argued that conductivity for Dirac fermions is a universal constant, G



Ultrafast Nano-Optics Group

Changing the optical reflection of graphene from electrical gating

Optical determination of graphene electronic structure

Optical Properties in Berkeley Physics

Professor Feng Wang (left)

Prof Wang welcomes interested undergraduates and graduates into his lab


Other Properties of Graphene

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!



RecapGraphene:

2D, honeycomb lattice of carbons Pure, remarkable strength, conductivity “Mechanical Cleavage” πα = 2.3% Light Absorption First material observed with Dirac Fermions


Only 193 US Patents!

Whenever a new material is characterized, entire systems can change

Take home message,



http://www.condmat.physics.manchester.ac.uk/pdf/mesoscopic/publications/graphene/Science_2008fsc.pdf

http://archive.sciencewatch.com/inter/aut/2008/08-aug/08augSWGeim/

http://newscenter.lbl.gov/feature-stories/2010/10/15/the-noise-about-graphene/

http://www.nobelprize.org/nobel_prizes/physics/laureates/2010/advanced-physicsprize2010.pdf

http://blogs.ls.berkeley.edu/fengwang/research/graphene/

http://news.softpedia.com/news/Graphene-Can-Cool-Electronics-with-Great-Efficiency-263614.shtml

http://www.scientificamerican.com/article.cfm?id=carbon-wonderland

References



Graphene – Optical Properties

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