The wondrous world

of carbon nanotubes

Final Presentation IFP 2

February 26, 2003

Group members:

Client:• Prof. P.H.L. Notten (Philips / TU/e)• ir. R.A.H. Niessen (Philips)

Tutor:• X.E.E. Reynhout

IFP group 2

• M.Daenen (N) • P.G.A.Janssen (ST)

• R. de Fouw (ST) • K. Schouteden (N)

• B. Hamers (ST) • M.A.J. Veld (ST)

Overview

• Introduction

• Synthesis & Purification

• Overview of applications

• Single nanotube measurements

• Energy storage

• Molecular electronics

• Conclusion and future outlook

Introduction: common facts

• Discovered in 1991 by Iijima

• Unique material properties

• Nearly one-dimensional structures

• Single- and multi-walled

Introduction: nanotube structure• Roll a graphene sheet in a certain direction:

• Armchair structure

• Zigzag structure

• Chiral structure

• Defects result in bends and transitions

Introduction: special properties• Difference in chemical reactivity for

end caps and side wall

• High axial mechanical strength

• Special electrical properties:– Metallic– Semi conducting

Synthesis: growth mechanism• Metal catalyst

• Tip growth / extrusion growth

Synthesis: overview• Commonly applied techniques:

– Chemical Vapor Deposition (CVD)– Arc-Discharge– Laser ablation

• Techniques differ in:– Type of nanotubes (SWNT / MWNT / Aligned)– Catalyst used– Yield– Purity

Synthesis: CVD

•Gas phase deposition

•Large scale possible

•Relatively cheap

•SWNTs / MWNTs

•Aligned nanotubes

•Patterned substrates

Synthesis: arc discharge

• MWNTs and SWNTs• Batch process

• Relatively cheap

• Many side-products

Synthesis: laser ablation• Catalyst / no catalyst

• MWNTs / SWNTs

• Yield <70%

• Use of very strong laser

• Expensive (energy costs)

• Commonly applied

Purification• Contaminants:

– Catalyst particles– Carbon clusters

– Smaller fullerenes: C60 / C70

• Impossibilities:– Completely retain nanotube structure– Single-step purification

• Only possible on very small scale:– Isolation of either semi-conducting SWNTs

Purification: techniques• Removal of catalyst:

– Acidic treatment (+ sonication)– Thermal oxidation– Magnetic separation (Fe)

• Removal of small fullerenes– Micro filtration– Extraction with CS2

• Removal of other carbonaceous impurities– Thermal oxidation– Selective functionalisation of nanotubes– Annealing

Overview of potential applications

< Energy storage:

•Li-intercalation

•Hydrogen storage

•Supercaps

> FED devices:

•Displays

< AFM Tip

> Molecular electronics

•Transistor

< Others

• Composites

• Biomedical

• Catalyst support

• Conductive materials

• ???

Overview of potential applications

< Energy storage:

•Li-intercalation

•Hydrogen storage

•Supercaps

> FED devices:

•Displays

< AFM Tip

> Molecular electronics

•Transistor

< Others

• Composites

• Biomedical

• Catalyst support

• Conductive materials

• ???

Overview of potential applications

< Energy storage:

•Li-intercalation

•Hydrogen storage

•Supercaps

> FED devices:

•Displays

< AFM Tip

> Molecular electronics

•Transistor

< Others

• Composites

• Biomedical

• Catalyst support

• Conductive materials

• ???

Energy Storage

Experiments & Modelling

• Electrochemical Storage of Lithium

• Electrochemical Storage of Hydrogen

• Gas Phase Intercalation of Hydrogen

• Supercapacitors

Energy Storage3-electrode cell

- + -2

reduction

oxidationCNT H O e CNT H OHx x x x

+ -

2

reduction

oxidationNi OH NiOOH H e

Work Electrode

Counter Electrode

Lithium Electrochemical Model

•Equilibrium saturation composition for graphite: LiC6

•Purified SWNT bundles: Li1.7C6

•Ball-milled SWNTs: Li2.7C6

20 min

10 min

0 min

Lithium Electro Chemical

Lithium Electro Chemical

Etching•Two types: lengths of 4 and 0.5 μm•Good Crev (Li2.1C6)•Smaller hysteresis

Cut SWNTs have better properties concerning Li intercalation

Vol

tage

[V

]

Hydrogen ElectrochemicalLennard Jones Potential

12 6

H-H H-HLJ H-H4U r

r r

Hydrogen Electrochemicalstorage model

Model of Hydrogen Storage at room temperature for different diameters of SWNTs

Hydrogen Electrochemical Charging & Discharging

Charge Discharge Cycle

Hydrogen Electrochemical

• Many contrasting conclusions:– Positive Ranging from: 0.4 – 2.3 wt% H– Negative: No systematic relationship

between purity and storage storage not due to SWNTs

• More investigations on the mechanism of storage are needed in order to explain this wide range of results

Gas Phase Intercalation of Hydrogen model

Gas Phase Intercalation of Hydrogen

• Contrast in results is very high: range from 0-67 wt%

• Reasonable range: 2-10 wt%

• More modelling needed

• To compare models they have to use the same parameters

Super Capacitor

Electrochemical double layer

Electrode (+) E lectrode (-)

Separator

Molecular electronics

• FEDs

•CNTFETs

•SETs

Field Emitting Devices

Single Emitter

Film Emitter

Field Emitting Devices

Single Emitter

Film Emitter

Field Emitting Devices

Single Emitter

Film Emitter

Patterned Film Field Emitters

•Etching and lithography•Conventional CVD•Soft lithography

Transistor Principle in CNTFETs

Transistor

CNTFET

Doping of CNTs

Single Electron transistor

Conclusions

• Mass production is nowadays too expensive• Many different techniques can be applied for

investigation• Large scale purification is possible• FEDs and CNTFETs have proven to work

and are understood• Positioning of molecular electronics is difficult• Energy storage is still doubtful, fundamental

investigations are needed