Topics in NanoBT Lecture 17 2006 2007

8/8/2019 Topics in NanoBT Lecture 17 2006 2007

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TOPICS IN (NANO)

BIOTECHNOLOGY

Carbon nanotubes

19th January, 2007


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Carbon nanotubes


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Overview

Introduction

Synthesis & Purification

Overview of applications

Single nanotube measurements

Energy storage

Molecular electronics

Conclusion and future outlook


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Introduction: common facts

Discovered in 1991 by Iijima Unique material properties

Nearly one-dimensional structures

Single- and multi-walled


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Single-wall carbon nanotubes are a new form of carbonmade by rolling up a single graphite sheet to a narrowbut long tube closed at both sides by fullerene-like endcaps..

However, their attraction lies not only in the beauty of theirmolecular structures: through intentional alteration oftheir physical and chemical properties fullerenes exhibitan extremely wide range of interesting and potentiallyuseful properties.

Definition


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1991 Discovery of multi-wall carbon nanotubes

1992 Conductivity of carbon nanotubes

1993 Structural rigidity of carbon nanotubes

1993 Synthesis of single-wall nanotubes 1995 Nanotubes as field emitters

1997 Hydrogen storage in nanotubes

1998 Synthesis of nanotube peapods

2000 Thermal conductivity of nanotubes 2001 Integration of carbon nanotubes for logic

circuits

2001 Intrinsic superconductivity of carbon nanotubes

History


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Nanotube structure

Roll a graphene sheet in a certain directio Armchair structure

Zigzag structure

Chiral structure

Defects result in bends and transitions


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Special properties

Difference in chemical reactivity forend caps and side wall

High mechanical strength

Special electrical properties: Metallic

Semi conducting


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Metallic conductivity (e.g. the salts A3C60(A=alkali metals))

Superconductivity with Tc's of up to 33K (e.g.

the salts A3C60 (A=alkali metals))

Ferromagnetism (in (TDAE)C60 - without thepresence of d-electrons)

Non-linear optical activity

Polymerization to form a variety of 1-, 2-, and3D polymer structures

Special properties


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Nanotubes can be either electrically conductive orsemiconductive, depending on their helicity.

These one-dimensional fibers exhibit electricalconductivity as high as copper, thermalconductivity as high as diamond,

Strength 100 times greater than steel at one sixththe weight, and high strain to failure.

Special properties


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Current Applications

Carbon Nano-tubesare extending the

ability to fabricate

devices such as:

Molecular probes Pipes

Wires

Bearings Springs

Gears

Pumps


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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


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Synthesis: growth mechanism

Metal catalyst Tip growth / extrusion growth


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Mechanisms of Carbon Nano tube

Root Growth Mechanism:

Transition metal as catalyst

Hydrocarbon dissociate atmetal surface into H and C.

Once surface saturated with

C, it starts to form as graphite

sheet with fullerene cap

More C atoms can beinserted into Metal-C bond so

the tube get growing longer.


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Synthesis Methods for CNT

1. Electric Arc Discharge: similar tomethod used for Bucky Ball

2. Laser Vaporization: Graphite

target with Co, Ni powders

sitting in 1200C furnace and hit

by laser pulse. CNT collecteddownstream at cold finger.

3. CVD: pre-patterned structure

with Fe, Mo nano particles in a

tube furnace at 1000C and

methane as precursor of carbon

4. Fullerene recrystallization:

depositing Ni and C60 multi-

layers and recrystallize at 900C


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Synthesis: CVD

Gas phase deposition

Large scale possible

Relatively cheap

SWNTs / MWNTs

Aligned nanotubes

Patterned substrates


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It was first made popular by Ebbessen andAjayan in 1992

It is still considered as one of the best

methods for producing carbon nanotubesother than CVD

In order to produce a good yield of highquality nanotubes, the pressure,

consistent current, and efficient cooling of

the electrodes are very important

operating parameters

Synthesis: Arc Discharge


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Synthesis: Arc Discharge


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Synthesis: arc discharge

MWNTs and SWNTs Batch process

Relatively cheap

Many side-products


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Synthesis: arc discharge

Arc discharge = The electric arc that is a particular discharge between two electrodes in a

gas or vapor which is characterized by high cathode densities and a low voltage drop.


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Synthesis: laser ablation

Catalyst / no catalyst MWNTs / SWNTs

Yield


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Self Assembly of Carbon Nano Tube as

interconnect (Metal)


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Metho

dArc discharge method

Chemical

vapour depositionLaser ablation (vaporization)

WhoEbbesen and Ajayan, NEC, Japan 1992 15 Endo, Shinshu University, Nagano, Japan

53

Smalley, Rice, 199514

How

Connect two graphite rods to a power

supply, place them a few millimetres apart,

and throw the switch. At 100 amps, carbon

vaporises and forms a hot plasma.

Place substrate in oven, heat to 600 oC, and

slowly add a carbon-bearing gas such as

methane. As gas decomposes it frees up

carbon atoms, which recombine in the form

of NTs

Blast graphite with intense laser pulses; use

the laser pulses rather than electricity to

generate carbon gas from which the NTs

form; try various conditions until hit on

one that produces prodigious amounts of

SWNTsTypic

al

yield

30 to 90% 20 to 100 % Up to 70%

SWN

T

Short tubes with diameters of 0.6 - 1.4 nm Long tubes with diameters ranging from

0.6-4 nm

Long bundles of tubes (5-20 microns), with

individual diameter from 1-2 nm.

M-

WNT

Short tubes with inner diameter of 1-3 nm

and outer diameter of approximately 10 nm

Long tubes with diameter ranging from 10-

240 nm

Not very much interest in this technique, as

it is too expensive, but MWNT synthesis is

possible.

Pro

Can easily produce SWNT, MWNTs.

SWNTs have few structural defects;

MWNTs without catalyst, not too

expensive, open air synthesis possible

Easiest to scale up to industrial production;

long length, simple process, SWNT

diameter controllable, quite pure

Primarily SWNTs, with good diameter

control and few defects. The reaction

product is quite pure.

Con

Tubes tend to be short with random sizes

and directions; often needs a lot of

purification

NTs are usually MWNTs and often riddled

with defects

Costly technique, because it requires

expensive lasers and high power

requirement, but is improving


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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


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Purification

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


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Potential applications

< Energy storage:

Li-intercalation

Hydrogen storage

Supercaps

> FED devices:

Displays

< AFM Tip

> Molecular electronics

Transistor

< Others

Composites

Biomedical

Catalyst support

Conductive materials

???


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Conclusions

Mass production is nowadays tooexpensive

Many different techniques can beapplied for investigation

Large scale purification is possible

FEDs and CNTFETs have proven towork and are understood

Positioning of molecular electronics isdifficult

Energy storage is still doubtful,fundamental investigations are needed

Topics in NanoBT Lecture 17 2006 2007

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