Hybrid Graphene and Carbon Nanotube Thin Films: There’s Node Way Out

John Sandford O’NeillMSci Presentation

17/03/2015

ITO and Transparent Electrodes

• Transparent electrodes are a key part of display devices and touchscreens

• Dominant material is Indium Tin Oxide (ITO)– High conductivity (20 Ω/sq

sheet resistance)– High transparency (~90%)– Price fluctuations due to indium

scarcity– Brittle and easily cracked

Image: Planet AnalogGraph: US Geological Survey

Carbon Nanomaterials• Allotropes of carbon

with extraordinary properties– High electron mobility– Mechanical Strength– Optical Transparency

• Potential applications– (Flexible) display devices– Capacitors– Composite materials– Microprocessor

architectures• Liquid-phase processing

→ Industrially scalable

Images: Bae, Sukang, et al. Nature nano, 5.8, 574-578.

Synthesis of Single-Walled Carbon Nanotubes (SWNTs)

Intercalation of bundled carbon nanotubes with sodium metal ammonia

solution

Image credit: The Linde Group

Dissolution of nanotubide salt in DMF organic polar solvent

Synthesis of Single-Walled Carbon Nanotubes (SWNTs)

Intercalation of bundled carbon nanotubes with sodium metal ammonia solution

Dissolution of nanotubide salt in DMF organic polar solvent

Synthesis of Graphene

Graphite intercalated with potassium-ammonia solution to yield KC24(NH3)4

graphite intercalation compound (GIC)

GIC dissolved in THF solvent

Solvated graphene sheet (graphenide)

Thin Film Fabrication

• Deposition methods: drop coating, spin coating

• Inert atmosphere• Solvent evaporates

leaving immobilised nanocarbons on substrate

• Multi-layered films made by allowing each layer to dry before deposition of next layer

SubstrateDeposition Layer 1Deposition Layer 2

Carbon Nanotube Thin Films

MicaCNT0.1 mg/ml SWNTs in DMF drop coated

onto mica substrate

Cross-section indicates a mixture of individualised SWNT and small tube bundles

Carbon Nanotube Thin Films

MicaCNT0.01 mg/ml SWNTs in DMF drop coated

onto mica substrate

Cross-section indicates a mixture of individualised SWNT and small tube bundles

Graphene Thin Films

MicaGIC0.1 mg/ml GIC in THF drop coated onto

mica substrate

Cross-section shows graphene platelets ~1 nm in height and ~300nm diameter (same as starting graphite material)

Hybrid Thin FilmsMicaGICCNT

0.1 mg/ml GIC in THF followed by 0.1 mg/ml SWNT in DMF drop coated onto mica substrate

Experimented with concentration and order of graphene/SWNT layers

ConductivitySheet resistance of thin films measured with 4-point probe

Probes

Thin Film Sample

Thin Film Sample Sheet Resistance

ITO sample 20.4 Ω/sqGraphene ∞

Carbon Nanotubes 51.64 kΩ/sq

1st layer: Graphene 2nd layer: Carbon Nanotubes

15.76 kΩ/sq

1st layer: Carbon Nanotubes 2nd layer: Graphene

80.63 kΩ/sq Hybrid films

Depositing graphene below the CNTs resulted in lower resistances than graphene above the CNTs, or films consisting only of CNTs

Carbon Nanotube Network ‘Nodes’

Carbon Nanotube Film51.64 kΩ/sq

Hybrid Film15.76 kΩ/sq

MicaCNT

MicaGICCNT

Optimisation of Graphene Concentration

0 0.2 0.4 0.6 0.8 1 1.2300

350

400

450

500

550

600

650

700

Varying graphene concentration of hybrid films

Graphene layer concentration / (mg/ml)

Figu

re o

f Mer

it

MicaGICCNT

• Thin films had 1st layer of graphene of varying concentration then 0.1 mg/ml CNT in DMF

• Superior FOM for all hybrid films• Best performance around 0.05 mg/ml

graphene concentration0 0.2 0.4 0.6 0.8 1 1.2

0.75

0.80

0.85

0.90

0.95

Transmission of hybrid films

Graphene layer concentration / (mg/ml)

Tran

smis

sion

Conclusions• The metal-ammonia intercalation method was

successfully used to exfoliate carbon nanomaterials

• Graphene and single-walled carbon nanotubes were individualised in solution

• Hybrid thin films were shown to have superior electrical and optical properties to single-component films

Future Work• Post-deposition treatments: washing,

annealing• Optimisation of CNT concentration• Characterisation with Raman

Spectroscopy• Detailed analysis of deposition techniques• Different substrates – glass• Different solvents – NMP, DMSO

Acknowledgements

• Neal Skipper• Chris Howard• Paddy Cullen• Dave Buckley

• Luca Santarelli• Kashim Bin Subhan• Kathy Cox• Richard Thorogate

Any Questions?

john.o’neill.11@ucl.ac.uk

Characterisation of KC24(NH3)4 GIC: Powder X-Ray Diffraction

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Q/Å-1

Inte

nsity

/arb

. uni

ts

(001) GIC2

(001) GIC3

(001) GIC1

Stage 1 Stage 2 Stage 3

3.35Å

6.37Å

6.50Å6.61Å

Mainly stage 2 and stage 3 GIC → graphene bilayers and trilayers

Characterisation of KC24(NH3)4 GIC: UV-Vis Spectroscopy

• 270nm absorption peak corresponding to interband transitions of graphene in solution 200 300 400 500 600 700 800 900 1000 1100 1200

0

0.2

0.4

0.6

0.8

1

1.2

1.45mg/ml GIC in THF

Wavelength/nm

Abso

rptio

n

Characterisation of SWNT Solution: UV-Vis Spectroscopy

• 270nm absorption peak corresponding to π – plasmon resonance

200 400 600 800 1000 12000

0.2

0.4

0.6

0.8

1

1.2

0.01mg/ml CNT in DMF

Wavelength/nmAb

sorptio

n

Post-Deposition Thin Film Treatment

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.00

2,000.00

4,000.00

6,000.00

8,000.00

10,000.00

12,000.00

No treatmentLogarithmic (No treat-ment)Logarithmic (No treat-ment)

Graphene Concentration / (mg/ml)

Resis

tanc

e/ Ω