GRAPHENE
Team #3
Phillip Keller
Krista Melish
Micheal Jones
James Kancewick
http://www.nanotech-now.com/images/Art_Gallery/ASgraphene.jpg
Further Applications and Research
Overview

Introduction
Graphene’s mechanical properties
 Graphene’s electrical properties
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Carbon Vs Silicon
Supercapacitors and Graphene
Gas Detection using low-temperature reduced
graphene oxide sheets
Ultrafast graphene photodetector
Electronics and Magnetism of Patterned Graphene
Nanoroads
General Conclusions
Introduction


Advances in electronics have been the result of
the continuous miniaturization or ‘scaling’ of
electronic devices, particularly of silicon-based
transistors, that has led to denser, faster and
more power-efficient circuitry.
http://www.scc.spokane.edu/_ima
ges/elect/circuit.gif
The realization of the approaching limits has inspired a
worldwide effort to develop alternative device technologies.
Some approaches involve spin-based devices, while others
replace a key component of the device, the conducting
channel, with carbon nanomaterials, which have superior
electrical properties.
Charlier, J.-C., Blase, X., & Roche, S. Electronic and transport properties of nanotubes.
Rev. Mod. Phys.
Introduction

Among these carbon nanomaterials is graphene. Graphene
is a two dimensional allotrope of carbon arranged like a
honeycomb structure made out of hexagons and plays an
important role since it is the basis for the understanding of
the electronic properties in other allotropes.
http://www.lbl.gov/Science-Articles/Archive/sabl/2007/Nov/assets/img/lrg/graphene_sheet.jpg
History of Graphene




Wallace in 1947
 Created 2D structure to help in the understanding of 3D
Graphite
Single layers of graphite grown epitaxially on metallic substrates
in the 1970s
 Tightly bound to substrate, distorted properties
Term “graphene” coined in 1987
2004, Geim and Novoselov mechanically exfoliated sheets of
graphene from graphite
 Transferred to charge neutral silicon substrate
 First successful electrical properties measured
Geim, A. K. & MacDonald, A. H. (2007). "Graphene: Exploring carbon flatland". Physics Today.
A Closer Look at Graphene

2D hexagonal carbon crystal lattice


Infinite boundaries
Actual 2D structure is debatable



Naturally occurring



Graphene sandwich
Thermal effects
Multilayer in graphite
Nanospecs in soot from exhaust
Currently one of the most researched
materials


http://www.nanotechnow.com/images/Art_Gallery/ASgraphene.jpg
Unique physical and electrical
properties
Wide array of potential uses
Ziegler, K., Robust transport properties in graphene. Phys. Rev. Lett.
Graphene Mechanical Properties



Breaking strength 200 times
greater than steel

Thermal properties exceed
those of diamond
Youngs modulus of ~ 1 tPa

Incredible rigidity lends
themselves to nanoscale
pressure sensors
 Nanoscopic graphene
flakes bend with increasing
pressure which alters their
electrical conductivity which
can be related to the
pressure

Excellent conductor of heat
Phonon dominated although it
can be shown that at certain
conditions the electrical portion
is significant
http://www.kinectrics.com/images/CableSp
an.JPG
John Scott Bunch. Mechanical and Electrical Properties of Graphene. Cornell University 2008.
Graphene Electrical Properties



Anomalous Quantum Hall Effect
 Quantization of the Hall effect
Dirac fermions
 Carriers have zero effective
mass
Room temperature electron mobility
of 15,000 cm2/V*s
 Theoretically higher conductivity
at room temp than silver, but
unknown forces are limiting
 Possible optical phonon
scattering from attached
substrate


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

Both P and N-type transistors
have been created
Recent announcement by IBM
that graphene transistor was
operated at a terahertz
frequency
Tunable band gap from 0 to
0.25 eV
Excellent conductivity makes
graphene ideal for electrical
leads in sensors/capacitors or
use in touch screens because of
its mechanical strength
Graphene ribbons have tunable
electrical conductivity
depending on the shape
http://www.atwillett.com/li
ghting_pictures/lightningbo
lt_closeup.jpg
Charlier, J.-C., Blase, X., & Roche, S. Electronic and transport properties of nanotubes.
Rev. Mod. Phys.
Electrical Component: Transistor


A transistor's operation speed depends on the size of the
device — smaller devices can run faster — and the speed
at which electrons travel in it. This size dependence has been
one of the major driving forces for making ever smaller
silicon transistors.
The Consortium of International Semiconductor Companies in
its 2001 International Technology Roadmap for
Semiconductors projected that transistors have to be smaller
than 9 nanometers by 2016 in order to continue the
performance trend.
Charlier, J.-C., Blase, X., & Roche, S. Electronic and transport properties of nanotubes.
Rev. Mod. Phys.
Carbon vs. Silicon


Figure (a) is Intel’s 45 nm
silicon transistor which uses a
Hafniun based dielectric.
Figure (b) is a wafer of the
45 nm transistors
photographed with a dime.
The processors incorporate
410 million transistors for
each dual core chip, and 820
million for each quad core
chip.
http://www.intel.com/pressroom/kits/45nm/photos.htm.
Carbon vs. Silicon

Graphene could offer a way forward. As well as
being extremely thin and a semiconductor,
electrons move through graphene at extremely
high speeds.

The cutting edge of silicon-based
transistors is at 32 nanometers.
http://mayang.com/textures/Manmade/images/Plastics%
20and%20Related/electronic_circuit_board_9131073.JP
G

Graphene has the potential to fabricate transistors only a
few atoms across. British researchers have unveiled the
world’s smallest transistor, which measures one atom thick
and ten atoms across. This is in the sub-10 nanometer range
Geim, A. K. & Novoselov, K. S. The rise of graphene. Nature Mater.
Performance Characteristics for
Carbon-Based Transistor
Ambipolar transfer characteristics [current versus gate voltage]:
drain bias increases from –0.1 V to –1.1 V in –0.2 V steps. Red line
represents -0.1 V and the pink line is -1.1 V. Step size is -0.2 V
Left Inset: Schematic of
the band structure of a
Schottky barrier
semiconducting carbon
nanotube in a field
effect transistor under
negative gate bias.
Holes are
injected from the source
[S].
Right Inset: Schematic of
the band structure of a
Schottky barrier
semiconducting carbon
nanotube in a field
effect transistor under
positive gate bias.
Electrons are
injected from the drain
[D].
Anantram, M. P. & Leonard, F. Physics of carbon nanotube electronic devices. Rep. Prog. Phys.
Electrical Component: Supercapacitors

Supercapacitors are energy storage systems that are
able to store and deliver energy at relatively high rates.

They are able to store and deliver energy beyond those
accessible by batteries. This is because the mechanism of
energy storage is the simple charge-separation at the
electrochemical interface between the electrode and the
electrolyte.
>
http://www.johnhenryshammer.com/WO
W/willWebPics/battery/superCap.jpg
http://carolinepond.files.wordpress.
com/2008/12/energizer-bunny.jpg
Chen, Y. et al. Supercapacitor Devices Based on Graphene Materials. J. Phys. Chem. C 2009
Supercapacitors

An advantage for supercapacitors is that they have
several orders of magnitude higher energy density than
that of conventional dielectric capacitors.

Furthermore, the deficiencies of other power sources, such as
batteries and fuel cells, could be complemented by
supercapacitors, owning to their long cycle life and rapid
charging and discharging at high power densities.
+
http://www.johnhenryshammer.com/WO
W/willWebPics/battery/superCap.jpg
http://carolinepond.files.wordpress.
com/2008/12/energizer-bunny.jpg
Chen, Y. et al. Supercapacitor Devices Based on Graphene Materials. J. Phys. Chem. C 2009
Supercapacitors

When
the
practical
use
of
electrochemical capacitors for the
storage of electrical charge was
demonstrated and patented by
General Electric, supercapacitors have
generated great interest for a wide
and growing range of applications
such as:
http://i.thisislondon.co.uk/i/pix/200
8/07/general-electric-415x275.jpg

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
Links to pictures
are in notes

Load cranes
Forklifts
Electric vehicles
Electric utilities
Factory power back
up
Kotz, R.; Carlen, M. Electrochim. Acta 2000, 45, 2483.
Supercapacitors

Different materials such as various carbon materials,
mixed metal oxides, and conducting polymers have
been used as supercapacitor electrode materials.
 Particularly
http://www.easycalculation.com/chem
istry/elements/images/carbon.jpg
carbon, in its various
forms, has been used as electrode
materials of supercapacitors, aiming
at high specific capacitance together
with high power density.
Pandolfo, A. G.; Hollenkamp, A. F. J. Power Sources 2006, 157, 11.
Supercapacitors

Although porous carbon materials have high specific
surface area, the low conductivity of porous carbon
materials is limiting its application in high power density
supercapacitors.

Carbon nanotubes (CNTs), with excellent electrical
conductivity and high surface areas, have been fabricated
https://www.opassoap.com/o
for supercapacitors since 1997.
passtore/media/catalog.jpg
http://www.t12.lanl.gov/home/afv/nanotube.singleframe.begin.gif
Diederich, L.; Barborini, E.; Piseri, P.; Podesta, A.; Milani, P. Appl. Phys. Lett. 1999, 75, 2662.
Supercapacitors

However, CNT-based
supercapacitors have not met the
expected performance; one
possible reason is probably due
to the observed contact resistance
between the electrode and current
collector.

Hence, many studies have focused
on the morphology of the carbon
materials to boost the
performance of the capacitor, such
as growing CNTs directly on bulk
metals to eliminate the contact
resistance.
http://fc05.deviantart.net/fs24
/f/2008/018/e/3/Smoke_Sto
ck_002_by_mross5013.jpg
http://www.deskpicture.com/DPs/Tec
hnology/CircuitBoard_2.jpg
Shaijumon, M. M.; Ou, F. S.; Ci, L. J.; Ajayan, P. M. Chem. Commun. 2008, 2373.
Supercapacitors

Graphene is emerging as a unique morphology carbon
material with potential for electrochemical energy storage
device applications due to its superb characteristics of
chemical stability, high electrical conductivity, and large
surface area.

Fig (a). Schematic diagram of
graphene-based supercapacitor
device
Recently, it has been proposed that
graphene should be a competitive
material for supercapacitor
application. Graphene with less
agglomeration should be expected
to exhibit higher effective surface
area and thus better supercapacitor
performance.
Chen, Y. et al. Supercapacitor Devices Based on Graphene Materials. J. Phys. Chem. C 2009
GAS DETECTION USING
LOW-TEMPERATURE REDUCED
GRAPHENE OXIDE SHEETS
By
Ganhua lu
Leonidas E. Ocola
Junhong Chen
Gas Detection using reduced graphene
sheets



high-performance gas
sensors made of partially
reduced graphene oxide
sheets
obtained through lowtemperature step
annealing at 300 °C in
argon flow at atmospheric
pressure
Was tested with low
concentration NO2
http://www.engineerlive.com/media/images/large/large_111
2_D12_Image.JPG
W. Frank, J. Vac. Sci. Technol. B 25, 2558 2007
Background



The 2D structure of graphene makes
every carbon atom a surface atom so
that electron transport can be highly
sensitive to adsorbed molecules.
Mechanically exfoliated graphene has
demonstrated a potential ability to
detect gases down to the single
molecular level
The gas sensing mechanism of
graphene is generally attributed to the
adsorption/desorption of gaseous
molecules which act as donors or
acceptors on the graphene surface,
leading to changes in the conductance
of graphene
http://c0378172.cdn.cloudfiles.rackspaceclou
d.com/graphene-interconnects.jpg
S. Novoselov, Y. Zhang, I. V. Grigorieva, and A. A. Firsov, Science 306, 666 2004.
Chemically Reduced Graphene Oxide
using Hydrazine


Has been used for the detection
of acetone, warfare agents, and
explosive agents at parts per
billion concentrations
Using Hydrazine for sensor
fabrication involves toxic
chemicals and introduce extra
nitrogen functional groups which
may slow the response of the
sensor.
Below is graphene prepared with
Hydrazine
http://2.bp.blogspot.com/_VyTCyizqrHs/SRoCXZgYZxI/A
AAAAAAABoU/64fpjTGIJjw/s1600h/graphene_sheet.jpg
Yang, A. Velamakanni, G. Bozoklu, S. Park, M. Stoller, R. D. Piner, S. Stankovich, I. Jung, D. A. Field,
C. A. Ventrice, Jr., and R. S. Ruoff, Carbon 47, 145 2009.
Modified Hummers Method
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Was used for the creation of the graphene oxide sheets
used for sensors
Graphite is first synthesized by oxidative treatment
Then is exfoliated in water to produce suspension of
single graphene oxide sheets
For a detailed explanation of Hummer’s method please visit
http://pubs.acs.org/doi/abs/10.1021/ja01539a017
Chemistry
http://www.air-intakes.net/Hummer.gif
http://www.physics.umanitoba.ca/~tapas
h/nano/molecule-graphene.jpg
Park, J. An, R. D. Piner, I. Jung, D. Yang, and R. S. Ruoff, Chem. Mater. 20, 6592 2008.
Fabrication of the Sensing Device


The graphene oxide was
suspended with Au
interdigitated electrodes.
 Both finger width and
interfinger spacing of 1 µm
Drops of the graphene oxide
suspension where then placed
on the wafer.
http://www.physics.upenn.edu/yodhlab/images/resea
rch_CMP_Solubilization.jpg
H. Lu, L. E. Ocola, and J. H. Chen, J. Nanomater. 2006, 60828 2006
The Fabrication of the Electrodes

The Au interdigitated electrodes were
fabricated using electron-beam lithography on
a Silicon wafer.
http://www.cnst.nist.gov/nanofab/nanofab_equipment/images/leica.
jpg
The Sensor
Figure obtained from article
FIG. 1. Color online SEM image of a GO sheet bridging two neighboring Au fingers of an
interdigitated electrode. Gases are detected by measuring the change in the current while
applying a constant dc bias to the device.
Leonidas E. Ocola, et al, Gas detection using low-temperature reduced graphene oxide sheets
2009 American Institute of Physics, 2009
How it works
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

When different gases absorb to
it the electrical conductance of
the Graphene Oxide changes
and is used to detect certain
gases as extremely low
concentrations
For this experiment it was tested
using NO2
After the annealing process at
300 °C absorption sites opened
allowing for low concentrations of
N02 to cause a change in the
resistance of the sensor.
http://www.durawear.com/images/cat
alog/live/imageLibrary/35314ECE15
17585314A3B395639BAE23M.jpg
Gomez-Navarro, R. T. Weitz, A. M. Bittner, M. Scolari, A. Mews, Nano Lett. 7, 3499 2007.
The sensor
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
Can detect a single atom of N02 which is shown in
the figure below
When the N02 binds to the
graphene the electrical
properties change and this can
be detected
http://www.rsc.org/images/GrapheneNO
2-250_tcm18-95542.jpg
24H. A. Becerril, J. Mao, Z. Liu, R. M. Stoltenberg, Z. Bao, and Y. Chen, ACS Nano 2, 463 2008.
Problems that need further research

Exploring methods to enhance
sensor recovery
 Currently
it takes the sensors longer
than 30 minutes to recover under
normal conditions
 Methods to be explored
 Low
temperature heating
 UV illumination
http://dkamhi.com/uv%20600x450.jpg
Leenaerts, B. Partoens, and F. M. Peeters, Phys. Rev. B 77, 125416 2008
ULTRAFAST GRAPHENE
PHOTODETECTOR
By
Fengnian Xia
Thomas Mueller
Yu-ming Lin
Alberto Valdas-Garcia
Phaedon Avouris
http://img.directindustry.com/images_di/ph
oto-g/photodetector-27819.jpg
Graphene’s photonic abilities
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

Ability to absorb ~ 2% of
incident light over a broad
wavelength
Multiple graphene layer
absorb additively
The absorption range of a
http://www.nanotechsystem can be tuned by
now.com/images/NANOIDENTPhotodetectorFunction300.jpg
changing the Fermi energy
using an external gate field
Wang, F. et al. Gate-variable optical transition in graphene. Science 320, 206–209 (2008).
Field-Effect Transistors (FETs)


Zero bandgap,large-area single or few-layers of
graphene as FETs are used in this paper
Internal fields are shown in this paper to produce
an ultrafast photocurrent response in graphene
http://rocky.digikey.com/weblib/ST%2
0Micro/Web%20Photos/New%20Phot
os/POWERSO-10jpg.jpg
http://images.iop.org/objects/phw/news/thum
b/14/2/10/graph1.jpg
Xia, F. et al. Photocurrent imaging and efficient photon detection in a graphene
transistor. Nano Lett. 9, 1039–1044 (2009).
Applications of Photonic applications
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High-speed optical communications
Interconnects
Terahertz detection
Imaging
Remote sensing
Surveillance
http://www.eecs.umich.edu/o
ptics/html/pics/opticsSpectroscopy
main4.jpg
http://www.delen.polito.it/var/
http://www.sflp.co.uk/xhtmlcss/images/surveillance1.jpg
Geim, A. K. & Novoselov, K. S. The rise of graphene. Nature Mater. 6, 183–191 (2007).
SEM and optical images of Highbandwidth graphene photodetector
Figure obtained from article



The graphene shown here has two to three layers
Two types of wirings are shown: ground–signal (G–S) and ground–signal–ground(G–S–G)
Optical bottom left, SEM is the remaining black and white image
Chuang, S. Physics of Optoelectronic Devices (Wiley, 1995).
Schematic of a Photodetector



Device schematics and
electrical model in the
high-frequency domain
The green symbols, from
top to bottom, represent
Cp, Cg and Rg,
respectively
The purple sheet
represents the graphene,
and a pair of dark red
strips denote the
microwave probe tips
Image was obtained from paper
Ishibashi, T. et al. InP/InGaAs uni-travelling-carrier photodiodes. IEICE Trans.
Electron. E83-C, 938–949 (2000).
The High speed Impedance


Impedance – is an important relation of the physical set up of
the device in order to filter out the low frequency signals from
registering on the device
This equation is what sets the gate bias for the photodetector.
Ryzhii, V., Mitin, V., Ryzhii, M., Ryabova, N. & Otsuji, T. Device model for
graphene nanoribbon phototransistor. Appl. Phys. Exp. 1, 063002 (2008).
Photodetectors
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
Magnitude of the photocurrent is
strong function of the location of
the optical illumination and also
on the gate bias which are
calculated with the impedance
equation
The figure to the right displays
the absolute a.c. photoresponse
as a function of light intensity
modulation frequency up to 26
GHz with the gate bias varying
from -40 to 80V
Meric, I. et al. Current saturation in zero-bandgap, top-gated graphene fieldeffect
transistors. Nature Nanotech. 3, 654–659 (2008).
Future research for Photodetectors


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
Enhancing the ability of the photodetectors to
detect a broader light position.
The incorporation of photodetectors into use
Large scale manufacture of photodetectors
Use of photodetectors as transistors
http://research.microsoft.com/en-us/um/people/jpwang/full_images/led_brdf.jpg
ELECTRONICS AND MAGNETISM OF
PATTERNED GRAPHENE
NANOROADS
By
Abhishek K. Singh
Boris I. Yakobson
http://www.blogcdn.com/www.engadget.com/media/2010/04/graph
ene-20100402.jpg
Nanoroads


Carving Graphene roads out of fully hydrogenated
carbon sheets create “Nanoroads”
This is a method in which the individual
characteristics depending upon the zigzag and
orientation can be studied to their corresponding
affects.
Graphane is shown to the left and is
full hydrogenated graphene
ceramics.org/ceramictechtoday/tag/graphene/
Chen, Z.; Lin, Y.; Rooks, M. J.; Avouris, P. Physica E 2007, 40, 228.
Graphene Vs. Graphane
http://www.afs.enea.it/project/cmast/Documenti/web/foto/Pulci_fig1.jpg
Papers Concept


Can hydrogenation be used to form geometrical
areas, such as “roads” of pristine graphene with the
desired electronic properties?
This would be done to receive the same electrical
properties of graphene nanoribbons without having
to cut the graphene.
http://images.google.com/imgres?imgurl=http://
ceramics.org/ceramictechtoday
Hod, O.; Barone, V.; Peralta, J. E.; Scuseria, G. E. Nano Lett. 2007, 7, 2295.
Armchair and Zigzag orientation
Relaxed structure of
(a) armchair nanoroad
(b) zigzag nanoroad
Na and Nz are the width
measured by the number of
pristine sp^2 carbon dimerlines or zigzag chains
respectively
Figure obtained from article
Son, Y.; Cohen, M.; Louie, S. Nature 2006, 444, 347.
Conclusions of Paper


In order for the nanoroads to be well
defined, the sharpness of the
interfaces between hydrogenated
and pristine graphene is important.
Conducting and semiconducting
nanoroads can in principle be
patterned on a graphene by
hydrogenation
Dewar, M. J. S.; Dougherty, R. C. The PMO Theory of Organic Chemistry, 1st ed.; Plenum: New York,
1975
Conclusions of Paper Continued


Antiferromagnetic state is semiconducting, the
ferromagnetic state is metallic with a widthindependent moment of 0.80 μB/unit cell
The possibility of having metallic and
semiconducting roads on the same planar geometry
can be an advantage in certain applications
Dewar, M. J. S.; Dougherty, R. C. The PMO Theory of Organic Chemistry, 1st ed.; Plenum: New York,
1975
Further Research



Achieve a rough patterns and directionality by the
masked exposure to a reagent transforming sp2
carbon into sp3, while further energy minimization
of the interface
The magnetism in wider nanoroads should display
better stability and this should be researched
Applications of this technology also is in need for
research
Potential Issues



An inability to produce graphene
of consistent sizes and consistent
electronic properties.
Difficulty integrating graphene
into electronic devices using
processes suitable for volume
production.
High electrical resistance that
produces heating and energy loss
at junctions between graphene
and the metal wires connecting
them.
http://www.thelocal504.com/wpcontent/uploads/2009/05/
broken_computer.jpg
Anantram, M. P. & Leonard, F. Physics of carbon nanotube electronic devices. Rep. Prog. Phys.
Further Research



Incorporating diamond as a semiconductor in hightemperature, high-power applications.
Accurate mass production techniques.
Essentially developing an entire electronic computing
system with carbon-based electronics.
←
→
http://www.cnanorhonealpes.org
/IMG/gif/BuckyTube_s.gif
http://www.deskpicture.com/DPs/Tec
hnology/CircuitBoard_2.jpg
http://www.absolutediamonds
.co.za/images/diamonds.jpg
Conclusion

Bearing excellent material properties, such as high
current-carrying capacity and thermal conductivity,
graphene and other carbon based allotropes are
ideally suited for creating components for
semiconductor circuits and computers. Its planar
geometry allows the fabrication of electronic
devices and the tailoring of a variety of electrical
properties. Because it is only one-atom thick, it can
potentially be used to make ultra-small devices and
further miniaturize electronics.