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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’[email protected]
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