This document discusses carbon nanotube synthesis using chemical vapor deposition (CVD) methods. It describes thermal CVD and laser-assisted thermal CVD processes. For thermal CVD, a hydrocarbon gas is decomposed over a transition metal catalyst at temperatures of 450-1050°C to grow multi-walled nanotubes with diameters from 10-240nm or single-walled nanotubes with diameters from 0.6-4nm. For laser-assisted CVD, a CO2 laser pyrolyzes iron pentacarbonyl and ethylene or acetylene vapors to produce single-walled nanotubes with diameters from 0.7-2.5nm and multi-walled nanotubes with

1. Class: Material Science Engineering
Student : Hoang Van Tien
Hanoi -2012

2. Nanomaterials
 Top -down approaches
 Bottom-up approaches
 Functional approaches
 Biomimetic approaches
 Speculative

3. Bottom up synthesis
 Solgel synthesis
 Precipitation
 Physical vapor synthesis
 Chemical vapor condensation
 Spray conversion processing

4. Chemical vapor condensation
 Chemical vapor deposition (CVD) synthesis is
achieved by putting a carbon source in the gas
phase and using an energy source, such as a
plasma or a resistively heated coil, to transfer
energy to a gaseous carbon molecule.
 Types :plasma enhanced CVD, thermal
chemical CVD, alcohol catalytic CVD, vapour
phase growth, aero gel-supported CVD and
laser-assisted CVD.
-Gaseous carbon sources : methane, carbon
monoxide and acetylene…

5.  Case study: preparation of carbon nano
tube by chemical vapor condensation
method.
-plasma enhanced CVD,
-thermal chemical CVD,
-alcohol catalytic CVD,
-vapour phase growth,
-aero gel-supported CVD
-laser-assisted CVD.

6. the growth mechanism

7. process
 The energy source is used to "crack" the
molecule into reactive atomic carbon.
 The carbon diffuses towards the substrate,
which is heated and coated with a catalyst
where it will bind.
 Carbon nanotubes will be formed if the
proper parameters are maintained.

8. positional control on
nanometre scale
 CVD carbon nanotube synthesis is essentially
a two-step process :
-catalyst preparation
-actual synthesis of the nanotube.
 The catalyst is generally prepared by sputtering a
transition metal onto a substrate and then using either
chemical etching or thermal annealing to induce catalyst
particle nucleation.
 Thermal annealing results in cluster formation on the
substrate, from which the nanotubes will grow.

9. Thermal chemical vapor deposition
a schematic diagram of thermal CVD apparatus in the synthesis of carbon nanotubes.

10. Catalytic growth
Schematics of a CVD deposition oven
This method is based on the decomposition of a hydrocarbon gas over a
transition metal to grow nanotubes in a chemical vapor deposition (CVD)
reactor

11. Thermal chemical vapor deposition
 Catalysts : Fe , Ni, Co …
 Substrate : Si,SiO2,glass…
 Gas flow : 40ml/min
 t = 450-1050 oC
 The diameter range of the carbon nanotubes
depends on the thickness of the catalytic film
example :
- By using a thickness of 13 nm, the diameter distribution
lies between 30 and 40 nm.
- By using a thickness of 27 nm is used, the diameter
range is between 100 and 200 nm.

12. product
 Advantages:
-Typical yield: 20-100%
- Long tubes with diameter ranging from 10-240 nm for
MWNT (multi walled nanotubes) and 0.6-4 nm for
SWNT( single walled nanotubes).
- Easiest to scale up to industrial production; long length,
simple process, SWNT diameter controllable, quite pure
 Disadvantages:
- large diameter range =>>>poorly controlled.
-often riddled with defects

13. Laser-assisted thermal
chemical vapour deposition

14.  Sources of laser:a medium power, continuous
wave CO 2 laser,perpendicularonto a
substrate,
 pyrolyses sensitised mixtures of Fe(CO) 5
vapour and acetylene in a flow reactor.
 Catalyst: Fe (very small iron particles)
 Substrate: sillica.
iron pentacarbonyl
vapour,
single- and multi-
+ethylene walled carbon
+acetylene
nanotubes

16. product
 The diameters of the SWNTs range from 0.7
to 2.5 nm.
 The diameter range of the MWNTs is 30 to 80
nm 43
 prefer grow single rather than multi-walled
nanotubes .
 Hight purity
 High power requirement

17. Purification
 The main impurities :graphite (wrapped up) sheets,
amorphous carbon, metal catalyst and the smaller
fullerenes…
 Rules :
-separate the SWNTs from the impurities
- give a more homogeneous diameter or size distribution.
 The techniques that will be discussed are oxidation, acid
treatment, annealing, ultrasonication, micro filtration,
ferromagnetic separation, cutting, functionalisation and
chromatography techniques.

19. applications
Nanotubes are rolled-up graphene sheets, and graphene is
one of the stiffest materials when subjected to deformations
parallel to the sheet.
⇒nanotubes show exceptional mechanical properties,
especially a high strength-to-weight ratio.
Applications:
 Field emission
 Field emission
 Nanotube sensors
 Nanotube transistors
 Nanotubes as SPM tips….

20. Schematics of a nanotube transistor, with some measurements.

21. Use of a MWNT as AFM tip. VGCF stands for Vapour Grown Carbon Fibre.
At the centre of this fibre the MWNT forms the tip

22. sources
1. D.A.Bochvar and E.G.Gal'pern,
Dokl.Akad.Nauk.USSR, 209, (610, 1973 )
2.http://www.ou.edu/engineering/nanotube, 2003
3. http://nanotube.msu.edu/
4.http://www.pa.msu.edu/cmp/csc/nanotube.htm5
5.http://en.wikipedia.org/wiki/Carbon_nanotube
6.
http://students.chem.tue.nl/carbonnanotubes/applica