Andrew Evans, Justin Matson, Mohannad Bukhamseen , Wakaas Shafi papers: - Spatial control of defect creation in graphene at the nanoscale
- Nanoparticle structures served up on a tray
(Billinge 453-54)

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Substance composed of pure carbon, with atoms arranged in a regular hexagonal pattern similar to graphite, but in a one-atom thick sheet. It is very light, with a 1-square-meter sheet weighing only 0.77 milligrams.
honeycomb lattice made of carbon atoms.
Carbon atom, credit: protondecay.blogspot.com
Picture Credit: AlexanderUIS

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Why create defects in graphene?
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Defects in graphene alter:
1) electrical properties
2) chemical properties
3) magnetic properties
4) mechanical properties
Defects
Defect in Graphene
Credit: http://nextbigfuture.com/2010/11/g raphene-produced-withcontrolled.html

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Why create defects?
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We can intentionally make use of its altered properties
How do we create defects?
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Ion irradiation can induce atomic defects in graphene.
Ion irradiation facility
Credit: http://www.dreebit.com/en/products/ion_ irradiation_facility_m_31/

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Describe a method to control defects in a sheet of Graphene.
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Dope a sheet of graphene with a material that is used as a catalyst, such as an Iridium substrate.
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Lay the Iridium atoms on the sheet.Study the structure and the arrangement of the
Iridium nanoparticles.
Vacancies in a sheet of Graphene (orange) are filled with Iridium atoms (blue).
When Iridium is placed on the doped sheet, it is arranged in a specific pattern and structure.
Nature Materials 9,291 –292 (2010 )doi:10.1038/nmat2733
Iridium(111)

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What we know: o Catalysts reduce the rate of a reaction by providing a surface of nanoparticles for the reagents to react on.
o The atoms at the surface of the catalyst rearrange to increase the surface area and decrease the surface energy. This changes the reactivity and the interactions between the reagents.
o The catalyst is not consumed during the process.
Molecule bonding on a catalyst foundation
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What we don't know: o How the nanoparticles at the surface are arranged.
o What the surface structure looks.
Nature 430 , 730 (12 August 2004) | doi:10.1038/430730a; Published online 11 August 2004

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Basis for "20-30% of the GNP" (Gross National
Product)
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Used Everywhere: o Processing of fuels o fertilizers o polymers o pharmaceuticals o energy
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Need for new catalysts for energy conversion http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/ publications/the_changing_face_of_transportation/im ages/figure_01_us_gross_national_product.gif
Catalysts lower activation energy for reactions.
Credit: ch302.cm.utexas.edu
* Maxwell, Stud. Surf. Sci. Catal.
101, 1 (1996)

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The Challenge: o To develop a molecular level picture of the way surfaces catalyze chemical transformations. o To use these images to understand how the nanoparticles are arranged on the surface of the catalysts.
o To understand how do the nanoparticle's arrangement translate to a lower activation energy during reactions?
o To use this insight to produce and design new catalysts for better energy conversion.
Separate molecules react while bonded to the catalyst foundation.

Enabling nanoscale catalysts
Resources
Possibilities for Society
Energy
Chemical
Production
I n this transmission electron micrograph of the mesoporous nanospheres, the nano-scale catalyst particles show up as the dark spots. Using particles this small (~ 3nm) increases the overall surface area of the catalyst by roughly 100 times.
.
http://www.thebioenergysite.com/news/contents/08-08-14Nano.jpg
Environmental
Protection

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It was shown that the binding and molecular absorption of Pt nanoparticles onto a sheet of graphene can be controlled by inducing defects on graphene
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By doping the graphene sheet with nitrogen the Pt nanoparticles can tolerate
CO more when the particles are deposited on the nitrogen induced graphene sheet
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Creating defects that can affect the binding and absorption of nanoparticles on graphene, can help us design a construct new and more efficient catalysts for our everyday chemical processes http://pubs.acs.org/appl/literatum/publisher/achs/journals/c ontent/ancac3/2011/ancac3.2011.5.issue-
2/nn1017395/production/images/medium/nn-2010-
017395_0006.gif
Image above shows catalytic performance, particularly tolerance against CO poisoning and particle migration, of Pt nanoparticles dispersed on graphene using ab initio calculations.
http://cdn.physorg.com/newman/gfx/news/hires/graphenecatalyst.jpg

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Catalytic efficiency is highly dependent on surface geometry
Understanding that geometry can inform efficient catalyst production
Analyzing surface geometry on nanoscale catalysts is extremely difficult
A catalyst in action with a highly ordered surface geometry
E xample of a nanocatalyst: Credit: research.che.tamu.edu
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The surface atoms can be studied with the use of synchrotron X-ray sources. However, the atoms can only be seen if they are arranged in a periodic manner.
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Note that an alternate solution would be developing more sophisticated methods for observing nanoscale geometries
To be able to study the atoms, we need to have a surface that will allow the catalyst atoms to be arranged periodically.
http://media.wiley.com/Lux/52/287752.image0.jpg
Periodic layers and moire pattern.
Credit: http://iop science.iop.org/
0953-
8984/24/31/314
210/article

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Ion radiation is not the best method to induce defects because the defects are randomly scattered over large distances.
We need more accuracy, so we look to: exposing graphene to an electron beam.
http://www.nature.com/ncomms/journal/v3/n10/images/ncomms2141-f1.jpg
Broad beam (no defects) Focused beam Broad beam (with defects)

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The knock-on damage threshold of Graphene is 86 KeV. Subjecting a monolayered sheet of
Graphene to an electron beam irradiation with a potential higher than that will form defects.
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Reports show that setting the electron beam irradiation potential to 80 KeV, while varying the beam current density (BCD) and the exposure time, can make the process of creating defects in
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Graphene controllable, and confined to an area of 10X10 nm^2
It was found that when the sheet is exposed to a (BCD) of ~10^8 e−1 nm−2 s−1 for 30 seconds a divacancy was created. a) AC-TEM image of a pristine graphene sheet before 30 s exposure to a focused electron beam. b) Divacancy formed in exposure area directly after irradiation.
Images of three different 30 s exposures, resulting in: (c) a divacancy.
(d) a divacancy having undergone a single stone-Wales bond rotation and
(e) two linked divacancies along the armchair direction.
Nat. Commun. 3:1144 doi: 10.1038/ncomms2141 (2012).

Images of defects formed after 60s of focussed electron beam irradiation: a) Three linked divacancies.
[Nat. Commun. 3:1144 doi: 10.1038/ncomms2141 (2012) ] b) A divacancy after a SW transformation. c) Defects clustered around one of a pair of dislocations.
Images of defects formed after 120 s of focussed electron beam irradiation: g) An enclosed, rotationally misaligned core of six hexagons, surrounded by a complete loop of pentagons and heptagons. h) A larger, partially completed loop, isolating several rotated hexagons. A gap in the loop, filled by two hexagonal rings, is highlighted in red. The arrow marks an adatom, which inhibits direct interpretation of the area bordered in black due to localized lattice distortion arising from the adatom. i) Two divacancy defects, each having been transformed via two sW rotations, leading to a single isolated, rotated hexagon.

Normalized Defect Value
Total Beam Dose (e^-1 nm^-2)
A bar chart parameterizing the effect of exposure time on defect complexity, defined here as the number of non-six-membered carbon rings plus any rotationally mismatched sixmembered rings in the irradiated area, parameterized as the NDV.
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To dope the Graphene sheet with Iridium, 30s exposure is needed.
It creates vacancies that are small, and can be kept under control.

3D rendering of a graphene hole imaged on TEAM 0.5 shows that the carbon atoms along the edge assume either a zigzag or an armchair configuration.

Creating controlled defects with an electron beam
A) A broad beam used to image graphene before defect formation (typical beam current density ~105 e − 1nm − 2 s − 1)
C) A broad beam used to image graphene after defect formation. (BCD goes back to ~105 e − 1 nm − 2 s − 1)
B) A focused probe with a high current density used to form defects.
(BCD goes up to~108 e − 1 nm − 2 s − 1)
Robertson, A.W. et al. Spatial control of defect creation in graphene at the nanoscale. Nat. Commun. 3:1144 doi:
10.1038/ncomms2141 (2012).

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How do we achieve a periodic arrangement that can be observed by synchrotron x-ray sources?
A 3-D representation of a doped sheet of Graphene (black layer) with the Iridium atoms (yellow) arranged periodically on top of it .
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It was found that layering a sheet of graphene over an iridium substrate formed the perfect base for causing a periodic arrangement in identical 82atom nanoparticles of iridium
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This periodic arrangement (called a "moire arrangement") is observable with existing techniques.

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Once the iridium forms a moire arrangement on the graphene sheet, observation and analysis is possible.
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Specifics of the geometry can be observed o
Interaction between the particles and the substrate can be analyzed
Understanding how the substrate is structured and how it interacts allows us to make nanoscale improvements to the catalyst.
Moire arrangement on a graphene sheet
Credit: Johann Coraux
Website: http://perso.neel.cnrs.f
r/johann.coraux/index
_en.html

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We can use Iridium catalysts to increase reaction rates.
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We can study the structure and arrangement of nanoscale Iridium catalysts using Graphene sheets.
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We can make changes to the reactivity and interactions between the reagents.
Graphene sheet
Endless applications for graphene

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Study of the nanoscale structure in a temporally and spatially resolved way in a complex, heterogeneous system.
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How to create defects in a controlled area with variable complexity, opens up the possibility for enhanced engineering of graphene.

-Billinge, Simon. "Nanoparticle structures served up on a tray." Nature. 28 MAR
2013: 453-54. Web. 14 Apr. 2013. < http://www.nature.com/nature/journal/v495/n7442/full/495453a.html
-Robertson, A.W. et al. Spatial control of defect creation in graphene at the nanoscale. Nat. Commun. 3:1144 doi: 10.1038/ncomms2141 (2012)