Graphene Syntheis and Characterization for Raman Spetroscopy At High Pressure

High-Pressure Spectroscopy LabDivision of Physics, TFMLuleå University of Technology

Single- and Double-Layer Graphene

for in-situ High-Pressure Raman scattering

Synthesis and Characterization of Carbon-based Nanomaterials

Nicolas MORAL

Supervisor: Pr. Alexander SOLDATOV

High-Pressure Spectroscopy LaboratoryDivision of Physics, Luleå Tekniska Universitet, 971 87 Luleå, SWEDEN

Department of Applied Physics and Mechanical Engineering

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Table of contents

Introduction• Carbon-based Nanomaterials• Resonance Raman Scattering• High-Pressure experiments

Review & Motivation

Methods and Materials• 2 routes to graphene at High-Pressure

Results & Discussions

Conclusion


Introduction

Carbon-based Nanomaterials

Raman scattering

High-Pressure

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Carbon NanoTubes (CNTs)• ~1D objects (1*1000 nm)

- High property-to-weight ratios

• Applications- Composites, Nanoelectronics, Heat transfer- Fuel cells and drug delivery

Fullerenes• ~0D objects (ø 0.7nm)

• Applications- Nanoelectronics, Transistors- Catalyst for diamond production

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Graphene

Graphite, Graphene• Single-Layer graphene

- 2D object

- One-atom-thick

- Sp² bonds

- Honeycomb lattice

• Origin of other Carbon allotropes- Cylinder = CNT

- Sphere = Fullerenes

- Stacks = Graphite

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Graphene

Graphene• Properties

- Young’s modulus 0.5 TPa- “high” optical opacity (2.3%)

- High thermal conductivity (103 W.m-1.K-1)- Ballistic thermal/electronic behavior- Quantum Hall effect

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Graphene

Graphene• Applications

- Nanoribbons and spintronics- Ultracapacitors

- Single-molecule detection

- Bio-devices


Introduction


Raman scattering

High-Pressure

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Raman scattering

Principle• Laser excitation ν0

• Phonons scattering Rayleigh ν0 +Raman ν0± νm

• Resonance Raman

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Raman Scattering

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High-Pressure

Principle• Diamond Anvil Cell

- Simple equipment

- High pressures (up to 50GPa)

Objective• SLG: probe the hardest bond

in the world, sp² in 2D

• DLG: experiment the isolated interplane interaction


Motivation of the thesis

Preparation of in-situ HP

Resonance Raman Spectroscopy

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Motivation of the thesis

Synthesis of Graphene• SLG, DLG, FLG; reliable and reproducible

Characterization of Graphene• Optical Microscope• Atomic Force Microscope• Electronic Microscope• Raman• …


Methods and materials

Source Materials, Equipment, Protocols

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Methods and Materials

References samples (courtesy of Dr K. Novoselov, Manchester)

• Graphene on SiO2 (tape method)

Source Material• Supported Graphene

- Si/SiO2 substrates

- Mechanical exfoliation = “Tape Method”

• Free-Standing Graphene- Cu grid

- Epitaxially grown

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Equipment: Optical Microscope• Olympus BX51• 10X, 20X, 100X magnifications

Equipment: Atomic Force Microscope• AFM/STM NT-MDT Ntegra

Equipment: Scanning Electron Microscope• Materialteknik Jeol JSM 6460LV

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Equipment: Raman stage• WiTec confocal Raman imaging system CRM200

- High signal-to-noise ratio

- 1cm-1 resolution

• Lasers- Green 532nm (2.33eV) _ SpectraPhysics Millenium IV

Powers 200mW up to 5W – 15mW on stage Power densities up to 300 kW/cm²

- Red 632.8nm (1.96eV) _ Coherent Powers up to 50mW – 8mW on stage Power densities up to 150 kW/cm²

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First route: Supported Graphene• Deposition cycle: Substrates cleaning / exfoliation / deposition• Optical observation / substrate mapping• Spectral confirmation

• Transfer into the DAC of SPECIFIC flakes (SLG/DLG)

Second route: Free-Standing Graphene• Provided by Manchester University’s collaborator

- Macroscopic sample (ø3 mm)

• Transfer into the DAC



Route 1: Supported Graphene

Route 2: Free-Standing Graphene

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Optical observation• Specific optical interference thanks to Si/SiO2 substrate

Spectral confirmation• Using Raman spectra and comparison to reference samples

Transfer• Protocol involving HoleyCarbonFilms (Quantifoil ™)

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Loading into the DAC• “Sandwiching” the flake• Cutting the sandwich (sample chamber <200µm)

• Loading into the DAC- Pressure-transmitting medium: ethanol-methanol





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Source Material: Free-Standing Single-Layer Graphene• Epitaxial growth on Ni substrate• Covered by PMMA• Ni etching in acid

• PMMA-SLG fishing with Copper grid• PMMA etching in acetone

Loading into the DAC• Sandwich method

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100 µm


Results and discussions

Route 1: Supported GrapheneDeposition Cycle

Optical Observation

Spectral Confirmation

Transfer

Route 2

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Supported Graphene

Substrates cleanliness• Crucial step for successful deposition

Deposition optimization• Tape selection• Exfoliation method

- Optimal = small crumbs

• Deposition method- Pressing/rubbing/etching

- Optimal = rubbing

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Conclusion

Step 1: COMPLETE• Fast deposition cycle (10-20 samples a day)• Reproducible results

• To be optimized ?- Increased average flakes’ size might be possible




Optical Observation

Spectral Confirmation

Transfer

Route 2

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Optical observation

Finding the flake(s)

Identification (contrast)• SLG• DLG• FLG• MLG• Graphite

Substrate mapping

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Optical observation

GraphiteGlue

DLG ?

FLG

MLGSLG ?




Optical Observation

Spectral Confirmation (reference spectra)

Transfer

Route 2

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Reference spectra

Manchester’s graphene on SiO2

• SLG• DLG• FLG

• Comparison to Graphite reference (NG)

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Reference spectra

1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 35000

100

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1400

SLG DLG FLG

ManchesterGraphene_1,96eV_referenceComparision SLG DLG FLG

Inte

nsi

ty (

a.u

.)

Raman shift (cm-1)

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Reference spectra

2500 2525 2550 2575 2600 2625 2650 2675 2700 2725 2750 2775 2800

0

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1400 GprimeSLG GprimeBLG GprimeFLG

ManchesterGraphene_1,96eV_referenceComparision SLG BLG on flake 1

Inte

nsi

ty (

a.u

.)

Raman shift (cm-1)

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Reference spectra

2500 2550 2600 2650 2700 2750 2800

0

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2000 GprimeSLG GprimeBLG GprimeFLG NaturalGraphite

ManchesterGraphene_1,96eV_referenceComparision flakes SLG DLG FLG with NG

Inte

nsi

ty (

a.u

.)

Raman shift (cm-1)

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Conclusion

Reference samples characterization• Clear identification of the main 3 target samples is possible

- SLG

- DLG

- FLG

- Gprime is a fingerprint (shape and peak-fitting)

- G’/G ratio is also used

• Transpose to our graphene samples




Optical Observation

Spectral Confirmation (deposited samples)

Transfer

Route 2

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Spectral confirmation

Raman spectrum• Red laser

- SLG

2500 2550 2600 2650 2700 2750 2800

0

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500

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1000

1250

1500

1750

Inte

nsi

ty (

a.u

.)

Raman shift (cm-1)

M1flake2 TM1flake6

NGdepositions_1,96eVcomparison SLG flake to Manchester reference

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- DLG

2400 2450 2500 2550 2600 2650 2700 2750 2800

0

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NGdepDLGred ManchesterDLG

DLG deposited from NGRed laser 1,96eVcomparison with reference sample

Inte

nsi

ty (

a.u

.)

Raman shift (cm-1)

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- 3LG

2500 2550 2600 2650 2700 2750 2800

-200

0

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2400 M1BLG TM1flake4

NGdepositions_1,96eVcomparison 3LG flake to Manchester reference

Inte

nsi

ty (

a.u

.)

Raman shift (cm-1)

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Raman spectrum• Green laser

- SLG

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Raman spectrum• Green laser

- DLG

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1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500

0

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3000 NGdepSLGred NGdepSLGgreen

SLG deposited from NGGreen Laser 2,33eV Red laser 1,96eV

Inte

nsi

ty (

a.u

.)

Raman shift (cm-1)

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SLG samples• Red laser

- single peak G’ = 2630 cm-1

- FWHM = 24 cm-1

- G’/G ratio >> 1

• Green laser- Single peak G’ = 2670 cm-1

- FWHM = 26 cm-1

- G’/G ratio >> 1

• SLG identification complete and identical to literature reviews

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1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500

0

500

1000

1500

2000 NGdepDLGred NGdepDLGgreen

DLG deposited from NGGreen Laser 2,33eV Red laser 1,96eV

Raman shift (cm-1)

Inte

nsi

ty (

a.u

.)

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DLG samples• Red laser

- G’ peak = 4peaks

- FWHM ≈ 24 cm-1

- G’/G ratio ≈ 1

• Green laser- G’ peak = 4peaks

- FWHM ≈ 24 cm-1

- G’/G ratio ≈ 1

• DLG identification complete and identical to literature reviews

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Conclusion

Step 2: COMPLETE • Characterization of produced samples

- Non-destructive

- Fast spectra

- Peak-fitting software = reliable results

- SLG / DLG / FLG




Optical Observation

Spectral Confirmation (deposited samples)

Transfer

Route 2

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Transfer

Method 1: IPA• Lifting the “grid/film & flake” off the substrate with IPA• Unsuccessful so far:

- Grids’ stiffness

Method 2: KOH• Etching the SiO2 layer off

• Unsuccessful so far:- Flakes swim away

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Conclusion


• Step 1: DEPOSITION COMPLETE

• Step 2: CHARACTERIZATION COMPLETE

• Step 3: Transfer incomplete



Route 1

Route 2: Free-Standing GrapheneCharacterization

Transfer

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Free-Standing Graphene

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FSGgreen100X FSGgreen20X

Free-Standing GrapheneGreen laser 2,33 eV

Inte

nsi

ty (

a.u

.)

Raman shift (cm-1)

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1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500

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FSGred100X FSGred20X

Free-Standing GrapheneRed laser 1,96 eV

Inte

nsi

ty (

a.u

.)

Raman shift (cm-1)

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1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500

0

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FSGred100X FSGgreen100X

Free-Standing GrapheneRed laser 1,96 eVGreen laser 2,33 eV

Inte

nsity

(a.

u.)

Raman shift (cm-1)

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Conclusion

FSG characterization COMPLETE• With both lasers• Similar results to supported graphene

- Dirtier (Dband, lots of graphitic dirt)

• With 20X objective = ready-to-load at High Pressure



Route 1

Route 2: Free-Standing GrapheneCharacterization

Transfer

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Transfer

Samples size reduction: IN PROGRESS• First cuts successful, without damage/alteration

• Down to 100 µm so far

• FS SLG damaged

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Transfer

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Conclusion


• Step 1: CHARACTERIZATION COMPLETE- SLG available for transfer

- DLG is missing as a free-standing sample

• Step 2: Transfer incomplete


Summary of Conclusions



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Summary of Conclusions

Synthesis of target samples COMPLETE• Supported SLG / DLG

- “tape” method

- Fast, reproducible, reliable

• Free-Standing SLG available

Characterization of available samplesCOMPLETE• Supported SLD / DLG / 3LG• Free-Standing SLG

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Future Work

Synthesis• Get Free-Standing DLG• Optimizing the deposition cycle

Characterization• Correlate spectra with AFM measurements

Transfer• Complete loading for both routes

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Gband 1580cm-1

(intensity a.u.)

G’band 2670cm-1

(intensity a.u.)

Future Work

Gband

G’band

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Acknowledgements

Pr Alexander SOLDATOV• Supervisor, LTU

Dr Kostya NOVOSELOV• University of Manchester (UK)

My saviors• Zoubir Ayadi, EEIGM (France)

• Lennart Wallström, LTU

My colleagues• Dr Shujie You

• Illya Dobryden, PhD

• Murat Özturk, project student

• Johnny Grahn, Johanne MouzonNils Almqvist

• David Olevik & Mattias Mases


Thank you for your attention

Please address your questions NOW !

MORAL Nicolas
