Presentation for my masters project on the synthesis and characterisation of hybrid graphene and carbon nanotube thin films.

1. Hybrid Graphene and Carbon Nanotube Thin
Films: There’s Node Way Out
John Sandford O’Neill
MSci Presentation
17/03/2015

2. 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 Analog
Graph: US Geological Survey

3. 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.

4. 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

5. 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

6. 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)

7. 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
Substrate
Deposition Layer 1
Deposition Layer 2

8. Carbon Nanotube Thin Films
Mica
CNT0.1 mg/ml SWNTs in DMF drop coated
onto mica substrate
Cross-section indicates a
mixture of individualised
SWNT and small tube
bundles

9. Carbon Nanotube Thin Films
Mica
CNT0.01 mg/ml SWNTs in DMF drop coated
onto mica substrate
Cross-section indicates a
mixture of individualised
SWNT and small tube
bundles

10. Graphene Thin Films
Mica
GIC0.1 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)

11. Hybrid Thin Films
Mica
GIC
CNT
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

12. Conductivity
Sheet resistance of thin films
measured with 4-point probe
Probes
Thin Film
Sample
Thin Film Sample Sheet
Resistance
ITO sample 20.4 Ω/sq
Graphene ∞
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

13. Carbon Nanotube Network ‘Nodes’
Carbon Nanotube Film
51.64 kΩ/sq
Hybrid Film
15.76 kΩ/sq
Mica
CNT
Mica
GIC
CNT

14. Optimisation of Graphene Concentration
300
350
400
450
500
550
600
650
700
0 0.2 0.4 0.6 0.8 1 1.2
FigureofMerit
Graphene layer concentration / (mg/ml)
Varying graphene concentration of hybrid films
Mica
GIC
CNT
• 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 concentration
𝐹𝑖𝑔𝑢𝑟𝑒 𝑜𝑓 𝑀𝑒𝑟𝑖𝑡:
𝐹𝑂𝑀 = 𝑅 ln(
1
𝑇
)
0.82
0.84
0.86
0.88
0.90
0.92
0.94
0 0.2 0.4 0.6 0.8 1 1.2
Transmission
Graphene layer concentration / (mg/ml)
Transmission of hybrid films

15. 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

16. 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

17. Acknowledgements
• Neal Skipper
• Chris Howard
• Paddy Cullen
• Dave Buckley
• Luca Santarelli
• Kashim Bin Subhan
• Kathy Cox
• Richard Thorogate

18. Any Questions?
john.o’neill.11@ucl.ac.uk

20. Characterisation of KC24(NH3)4 GIC: Powder
X-Ray Diffraction
0 1 2 3 4 5
Intensity/arb.units
Q/Å-1
(001)
GIC2
(001) GIC3
(001)
GIC1
Stage 1 Stage 2 Stage 3
3.35Å
6.37Å
6.50Å
6.61Å
Mainly stage 2 and stage 3
GIC → graphene bilayers
and trilayers

21. Characterisation of KC24(NH3)4 GIC: UV-Vis
Spectroscopy
• 270nm absorption
peak corresponding
to interband
transitions of
graphene in solution 0
0.2
0.4
0.6
0.8
1
1.2
1.4
200 400 600 800 1000 1200
Absorption
Wavelength/nm
5mg/ml GIC in THF

22. Characterisation of SWNT Solution: UV-Vis
Spectroscopy
• 270nm absorption
peak
corresponding to
π – plasmon
resonance
0
0.2
0.4
0.6
0.8
1
1.2
200 400 600 800 1000 1200Absorption
Wavelength/nm
0.01mg/ml CNT in DMF

23. Post-Deposition Thin Film Treatment
0.00
2,000.00
4,000.00
6,000.00
8,000.00
10,000.00
12,000.00
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Resistance/Ω
Graphene Concentration / (mg/ml)
No treatment
Annealing
Washing