Date Content Lecturer

08.04.13

Size matters – An Introduction Mühl

15.04.13 Nanoscaled materials / Nanotechnology Mühl

22.04.13 Scanning Probe Methods Mühl

29.04.13 TEM Lecture Mühl

06.05.13 Nanoscaled Probes Mühl

13.05.13 Carbon / Bonds Hampel

27.05.13 Synthesis of CNT/Fullerenes/Nanoparticles Hampel

03.06.13 Functionalisation and Biomedical/Industrial

Applications of CNT Hampel

10.06.13 Physical properties of CNT Büchner

17.06.13 Graphene – an introduction Büchner

24.06.13 Graphene – electronic structure Büchner

01.07.13 Lab Tour Hampel

08.07.13 Molecular Magnets Büchner

15.07.13 Transport through molecules Dufouleur

Molecular nanostructures

Synthesis of Carbon Nanotubes

and fullerenes

Molecular nanostructures

Diamond

Fullerenes

Nanotubes

Graphite

Allotropes of Carbon:

3D

2D

1D

0D

Increasing particle size

Increasing number of walls

SWCNT DWCNT TWCNT

Substrate

(oxide)

Catalyst particle: Fe, Co, Ni

How do nanotubes grow?

catalyst particles: 1 nm - 50 nm

catalyst: must form carbides (metastable)

catalyst: transition metal

Catalytic process: we need a catalyst particle and a carbon source.

Gas: N2, Ar, H2

How do nanotubes grow?

carbon

The metal particles on the surface are exposed to gaseous hydrocarbons, which

decompose catalytically on the surface of the catalyst particle. An exothermic

decomposition is assumed and a carbon concentration as well as a temperature gradient

form. After its decomposition the carbon diffuses from the hot area with a higher

concentration to the colder region of the particle and precipitates to form the graphitic

structure of the CNT wall. The particle remains attached to the substrate.

Base growth mode:

Gas: N2, Ar, H2

How do nanotubes grow?

carbon

Tip growth mode:

The metal particle is only weakly bound to the substrate surface. The decomposition of

the hydrocarbons takes place at the upper side of the particle. Again an exothermic

decomposition is assumed and the temperature and carbon concentration increases at the

top of the particle which gets deformed during this process and detaches from the

substrate. The carbon now diffuses to the colder side of the particle and precipitates to

form the CNT shells.

Schematics of the three established CNT production techniques.

Synthesis of CNT

Arc Discharge

Chemical Vapour Deposition

Laser-Ablation

Synthesis of SWCNT

SWCNT yield and diameter distribution

vs. T, p, laser pulse, gas, catalyst, …

Optimised: 70 wt% SWCNT, d=1.2 nm Needs purification!!!

Laser Ablation

TEM of SWCNT:

dmean=1.4 nm, 5-20 nm bundles

Length of CNT: sub-µm to cm

Images of SWCNT

Fixed bed method: 1. synthesis of the catalyst

550°C, air, 10‘

+ citric acid + dest. H2O

Fe-, Co-, Mg- Nitrate

+ (NH4)6Mo7O24 4 H2O

Reagents Cat.-Ø:

~1 nm SW

1-4 nm DW

>4 nm MW MgO + catalyst partikel well separated

Fixed bed method: 2. CNT Synthesis

Reduction: in hydrogen 30 min at 650°C: Reduction of the iron and cobalt oxidesto the metals, MgO is the support

Pyrolysis: Gas mixture CH4/H2 (Ar) at temperatures between 900 and 1000°C Different ratios of MgO/Fe/Co

Synthesis of MWCNT and SWCNT

Chemical Vapour Deposition

> 15 at%Fe MWCNT

Ø 10- 50nm

1 at% Fe DW/SWCNT:

Ø 1- 4nm

5 at% Fe

Mix von DW/MWCNT

< 0.8 at% Fe

SWCNT Ø < 1,4nm

Images of MWCNT

Synthesis of MWCNT and SWCNT

Chemical Vapour Deposition

CxHy

H2, Ar

Substrate with Fe-particles

TEM of MWCNT:

dmean=8-10 nm, 2-20 walls

l = 2 mm l = 1 mm Streichholzkopf

very long, well aligned MWCNT

Images of MWCNT

Synthesis of in situ filled MWCNT (Fe, Co, Ni)

280 nm

40 nm Fe filled MWCNT

(C5H5)2Fe Fe + 10 C + 5 H2 T > 750 °C

(C5H5)2Fe Fe + 2(C5H5) T > 450 °C

Chemical Vapour Deposition

additional metal source

metal organic compound

Ferrocene

Nickelocene

Cobaltocene

How do nanotubes grow?

In step C the deposition of iron particles at the growing site takes place continuously.

Thereby the growth mode changes from base to tip growth mode (step C+D). When further

material deposits from the gas phase the growth continues (step E) until a stable cap is

formed. If the cap is closed the growth for this CNT is stopped, but the so called secondary

growth might occur (an additional CNT starts to grow). This is often tip growth since the

wettability of the metal catalyst is low and the particles easily detach (step F and G).

in situ filled CNT with a combination of tip and base growth:

Aerosol

Ferrocene/ Acetonitril

Solvent and C-Precursor: Acetonitril (CH3CN) Cyclohexan (C6H12)

20-30 mg Ferrocene pro ml solvent

Catalyst-Precursor: Ferrocene [(C5H5)2Fe]

Aerosol Assisted CVD

Advantage:

No cleaning with acids

Nitrogen doping is possible

Synthesis of N-doped MWCNT

Chemical Vapour Deposition

500 nm

Fe- catalysts, base growth

bamboolike

Advantage:

• very long, well aligned CNT

• high yield production

• constant diameter, small distribution

Synthesis of MWCNT

0 5 10 15 200

5

10

15

20

25

30

35

40

45

l / µ

m

c / mg*min1

The length of the CNTs

will be controlled by the

precursor concentration.

precursor concentration

700 800 9000

20

40

60

80

100

ms p

er

are

a /

µe

mu

mm

2

T / °C

Optimum at ~ 800°C

X-ray: T ↓ ferromagnetic a-Fe

T ↑ g-Fe

process temperature

Influence of the

Synthesis Parameter

IFW Research devices

3g per day

HiPco Factory

Carbon Nanotechnologies inc.

Houston

Germany:

Bayer AG 200 tons per year

Mass production/Up scaling

1985 H.W. Kroto, R. Curl, R.E. Smalley

Cluster during

Laser ablation

Nobelprize chemistry 1996

Discovery of C60

Krätschmer Huffman 1990

Graphite plates/electrodes

were evaporated with arc

discharge in He atmosphere

Fullerens, soot

Synthesis of Fullerenes

T = 2600 – 3000 K

inert atmosphere

Synthesis of Fullerenes

Mass spectra of a fullerene extracts

mixture of different fullerene types

C60 C70

High performance liquid chromatography (HPLC)

C60 C70 C84 C86

Separation of Fullerenes

Fullerenes are soluble in different solvents

Example: Sc3N@C78

Retentionszeit [min]

Absorp

tion/

320 n

m [

a.u

.]

Retentionszeit [min]

Absorp

tion/

320 n

m [

a.u

.]

Retentionszeit [min]

Absorp

tion/

320 n

m [

a.u

.]

Several steps with different solvents

different columns

different columns fill material

Separation of Fullerenes

High performance liquid chromatography (HPLC)

Example: C76

Separation of Fullerenes

High performance

liquid chromatography

(HPLC)

Several steps with

different solvents

different columns

different columns fill material

Structures of clusters obtained with various temperature control Tc

MOLECULAR SIMULATIONS OF THE

FORMATION PROCESS OF FULLERENE

Yasutaka YAMAGUCHI and Shigeo MARUYAMA

Calculations of the formation of Fullerenes

Fig. 8. Fullerene formation model.

Computer simulation of formation of carbon fullerenes

Alexander I. Melker, Sergei N. Romanov, and Dimitri A. Kornilov

Snapshots of clustering process at Tc = 3000K

MOLECULAR

SIMULATIONS OF THE

FORMATION PROCESS

OF FULLERENE

Yasutaka YAMAGUCHI

and Shigeo MARUYAMA

Migration of pentagons observed

for Tc = 2600 K

Calculations of the formation of Fullerenes