1. Nanotechnology Lecture 3 Carbon Nanotubes

2. Carbon nanotubes Introduction of Carbon Nanotubes History and Impacts
Structure of Carbon Nanotubes (SWNT MWNT)
Properties of Carbon Nanotubes
Synthesis of Carbon Nanotubes (fabrication)
Potential and current Applications

3. What is Carbon Nanotube?

4. Introduction of Carbon Nanotube
Allotropes of carbon (graphite ，diamond， Amorphous carbon and Fullerene ) (cylindrical members of the fullerene structural family)
with a nanostructure. length-to-diameter ratio of up to 132,000,000:1,which is significantly larger than any other material.
extraordinary strength and unique electrical properties, efficient thermal conductors. (limited by their potential toxicity)
amazing objects? creates by accident, without meaning to, but that will likely revolutionize the technological landscape of the century ahead.
Our society stands to be significantly influenced by carbon nanotubes, shaped by nanotube applications in every aspect, just as silicon-based technology still shapes society today.
Indeed, should pristine nanotubes reach any limitation in some area, their ready and close association to foreign atoms, molecules, and compounds offers the prospect of an even magnified set of properties. Finally, we will describe carbon nanotube applications supporting the idea that the future for the science and technology of carbon nanotubes looks very promising.

5. History and Impacts
Carbon nanotubes have been synthesized for a long time as products from the action of a catalyst over the gaseous species originating from the thermal decomposition of Hydrocarbons.
The worldwide enthusiasm came unexpectedly in 1991, after the catalyst-free formation of nearly perfect concentric multiwall carbon nanotubes (c-MWNTs） was reported as by-products of the formation of fullerenes by the electric-arc technique.
Consequently, about five papers a day with carbon nanotubes as the main topic are currently published by research teams from around the world, an illustration of how extraordinarily active – and highly competitive – is this field of research.
Economical aspects are leading the game to a greater and greater extent. According to experts, the world market is predicted to be more than 430M$ in 2004 and estimated to grow to several b $ before 2009.

6. Structure of Carbon Nanotubes
Carbon nanotubes are fullerene-related structures which consist of graphene cylinders closed at either end with caps containing pentagonal rings(五角环).
Nanotubes could be produced in bulk quantities by varying the arc-evaporation conditions. This paved the way to an explosion of research into the physical and chemical properties of carbon nanotubes in laboratories all over the world.
Discovered in 1991 by the Japanese electron microscopist Sumio Iijima.
Nanotubes could be produced in bulk quantities by varying the arc-evaporation conditions.

7. Tetrahedral Junction of four Nanotubes
Nanotube w/ hemispheric

8. Structure of Carbon Nanotubes Single-Wall Nanotubes SWNTs
The (n,m) nanotube naming scheme can be thought of as a vector (Ch) in an infinite graphene sheet that describes how to "roll up" the graphene sheet to make the nanotube. T denotes the tube axis, and a1 and a2 are the unit vectors of graphene in real space.
Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer, with a tube length that can be many millions of times longer. The structure of a SWNT can be conceptualized by wrapping a one-atom-thick layer of graphite called graphene into a seamless cylinder. The way the graphene sheet is wrapped is represented by a pair of indices (n,m) called the chiral vector. The integers n and m denote the number of unit vectors along two directions in the honeycomb crystal lattice of graphene. If m = 0, the nanotubes are called "zigzag". If n = m, the nanotubes are called "armchair". Otherwise, they are called "chiral".

9. Single-Wall Nanotubes SWNTs
The chiral vector is bent, while the translation vector stays straight
The chiral vector is bent, while the translation vector stays straight
Armchair (n,n)
Graphene nanoribbon
n and m can be counted at the end of the tube
Zigzag (n,0)
Chiral (n,m)
Graphene nanoribbon

10. Single-Wall Nanotubes SWNTs
zigzag nanotube (9, 0)
(n,n)
armchair nanotube (5, 5)
(n,m)
helical (chiral) nanotube (10,5)
纳米碳管中的碳原子以sp2杂化，但是由于存在一定曲率所以其中也有一小部分碳属sp3杂化。在不考虑手性的情况下，SWNT可以由两个参量完全确定（直径和螺旋角或两个表示石墨烯的指数（n,m）或者螺旋向量Cn和垂直向量T〕，MWNT则需要三个以上的参数表示。
- hexagonal rings,
pentagonal rings at each tips;
- C=C bond and C≡C bond,
inducing a unique versatile
electronic behavior.
( n and m are the integers of the vector OA considering the unit vectors a1 and a2. )

11. Single-Wall Nanotubes SWNTs
Fig. 3.3 Image of two neighboring chiral SWNTs within a SWNT bundle as seen by high resolution scanning tunneling microscopy (by courtesy of Prof. Yazdani, University of Illinois at Urbana, USA)

12. SWNT Rope

13. Multiwall Nanotubes MWNT
Multi-walled nanotubes (MWNT) consist of multiple rolled layers (concentric tubes) of graphite;
In the Russian Doll , sheets of graphite are arranged in concentric cylinders;
In the Parchment model, a single sheet of graphite is rolled in around itself, resembling a scroll of parchment or a rolled newspaper. (3.3 Å);
Fig. 3.5 (longitudinal view) of a concentric multiwall carbon nanotube (c-MWNT) prepared by electric arc. In insert, sketch of the Russian-doll-like display of graphenes

14. Multiwall Nanotubes MWNT
(a) as-grown. The nanotube surface
is made of free graphene edges.
(b) after 2,900 ◦C heat-treatment. Both the herringbone and the bamboo textures have become obvious.
Fig. 3.6a,b A herringbone(箭尾型） (and bamboo) multi-wall nanotube (bh-MWNT, longitudinal view) prepared by CO disproportionation on Fe-Co catalyst.

15. Fig. 3.7 (a) A bamboo-herringbone multi-wall nanotube (bh-MWNT) showing the nearly periodic feature of the texture,which is very frequent; (b) high resolution image of a bamboo-concentric multi-wall nanotube (bc-MWNT) .
They are sometimes referred as “nanofibers”.

16. Nanobud carbon nanotubes + fullerenes.
useful properties of both fullerenes and carbon nanotubes.
In particular, they have been found to be exceptionally good field emitters.
In composite materials, the attached fullerene molecules may function as molecular anchors preventing slipping of the nanotubes, thus improving the composite’s mechanical properties

17. Extreme carbon nanotubes
The longest carbon nanotubes (18.5 cm long) was reported in These nanotubes were grown on Si substrates using an improved chemical vapor deposition (CVD) method and represent electrically uniform arrays of single-walled carbon nanotubes
The thinnest carbon nanotube is armchair (2,2) CNT with a diameter of 3 Å
The thinnest free standing single-walled carbon nanotube is about 4.3 Å in diameter. Researchers suggested that it can be either (5,1) or (4,2) SWCNT, but exact type of carbon nanotube remains questionable.

18. Properties of Carbon Nanotube
Strength
the strongest and stiffest materials .
In 2000, a MWCN was tested to have a tensile strength of 63 gigapascals (the ability to endure tension of 6300 kg on a cable with cross-section of 1 mm2.)
low density for a solid of 1.3 to 1.4 g·cm−3
Standard single walled carbon nanotubes can withstand a pressure up to 24GPa without deformation (hardness)
Kinetic
Multi-walled nanotubes, multiple concentric nanotubes precisely nested within one another, exhibit a striking telescoping property whereby an inner nanotube core may slide, almost without friction, within its outer nanotube shell thus creating an atomically perfect linear or rotational bearing.
Electrical
moderate semiconductor.

19. Synthesis of Carbon Nanotube 1 Laser Ablation – Experimental Devices
- graphite pellet containing the catalyst put in an inert gas filled quartz tube;
oven maintained at a temperature of 1,200 ◦C;
energy of the laser beam focused on the pellet;
vaporize and sublime the graphite
Sketch of an early laser vaporization apparatus
A graphite pellet containing the catalyst is put in the middle of an inert gas-filled quartz tube placed in an oven maintained at a temperature of 1,200 ◦C. The energy of the laser beam focused on the pellet permits it to vaporize and sublime the graphite by uniformly bombarding its surface. The carbon species swept by a flowof neutral gas are thereafter deposited as soot in different regions: on the conical water-cooled copper collector, on the quartz tube walls, and on the backside of the pellet.
The carbon species are there after deposited as soot in different regions: water-cooled copper collector, quartz tube walls.

20. 2 Synthesis with CO2 laser
Vaporization of a target at a fixed temperature by a continuous CO2 laser beam (λ = 10.6μm). The power can be varied from 100Wto 1,600 W.
The synthesis yield is controlled by three parameters: the cooling rate of the medium where the active, secondary catalyst particles are formed, the residence time, and the temperature (in the 1,000–2,100K range) at which SWNTs nucleate and grow.
The power can be varied from 100Wto 1,600 W. The temperature of the target is measured with an optical pyrometer, and these measurements are used to regulate the laser power to maintain a constant vaporization temperature. The gas, heated by the contact with the target, acts as a local furnace and creates an extended hot zone, making an external furnace unnecessary. The gas is extracted through a silica pipe, and the solid products formed are carried away by the gas flow through the pipe and then collected on a filter.
Fig Sketch of a synthesis reactor with a continuous CO2 laser device

21. 3 Electric-Arc Method – Experimental Devices
After the triggering of the arc between two electrodes, a plasma is formed consisting of the mixture of carbon vapor, the rare inert gas (helium or argon), and the vapors of catalysts.
The vaporization is the consequence of the energy transfer from the arc to the anode made of graphite doped with catalysts.
The principle of this technique is to vaporize carbon in the presence of catalysts (iron, nickel, cobalt, yttrium, boron, gadolinium, and so forth) under reduced atmosphere of inert gas (argon or helium). After the triggering of the arc between two electrodes, a plasma is formed consisting of the mixture of carbon vapor, the rare gas (helium or argon), and the vapors of catalysts. The vaporization is the consequence of the energy transfer from the arc to the anode made of graphite doped with catalysts. The anode erosion rate is more or less important depending on the power of the arc and also on the other
experimental conditions. It is noteworthy that a high anode erosion does not necessarily lead to a high carbon nanotube production.
SWNTs are deposited (provided appropriate catalysts are used) in different regions of the reactor:
(1) the collaret, which forms around the cathode;
(2) the web-like deposits found above the cathode;
(3) the soot deposited all around the reactor walls and bottom.
Sketch of an electric arc reactor. It consists of a cylinder of about 30 cm in diameter and about 1m in height.

22. Electric-Arc Method – Experimental Devices
In view of the numerous results obtained with this electric-arc technique, it appears clearly that both the nanotube morphology and the nanotube production efficiency strongly depend on
the experimental conditions and, in particular,
on the nature of the catalysts.

23. 4 Solar energy reactor
Sketch of a solar energy reactor in use in Odeilho (France).
Gathering of sun rays, focused in F;
(b) Example of Pyrex® chamber placed in (a) so that the graphite crucible is at the point F.
3.14. The solar rays are collected by a plain mirror and reflected toward a parabolic mirror that focuses them directly onto a graphite pellet under controlled atmosphere. The high temperature of about 4,000K permits both the carbon and the catalysts to vaporize. The vapors are then dragged by the neutral gas and condense onto the cold walls of the thermal screen. The reactor consists of a brass support cooled by water circulation, on which Pyrex® chambers with various shapes can be fixed
(Fig. 3.14b). This support contains a watertight passage permitting the introduction of the neutral gas and a copper rod on which the target is mounted. The target is surrounded by a graphite tube that plays both the role of a thermal screen to reduce radiation losses (very important in the case of graphite) and the role of a duct to lead carbon vapors to a filter in order to avoid soot deposits on the Pyrex® chamber wall.
The high temperature of about 4,000K permits both the carbon and the catalysts to vaporize. The vapors are then dragged by the neutral gas and condense onto the cold walls of the thermal screen.

24. Application: Nanotube-based SPM (scanning probe microscopy) tips
Fig Scanning electron microscopy image of a carbon nanotube (MWNT) mounted onto a regular ceramic tip as a probe for atomic force microscopy.
Small diameters of SWNTs were supposed to bring higher resolution
than MWNTs due to the extremely short radius of curvature of the tube end. But commercial nanotubebased tips use MWNTs for processing convenience.

25. Application: Efficient Field Emitters
The electrons are taking out from the tips and sent onto an electron sensitive screen layer.
Replacing the glass support and protection of the screen by some polymer-based material will even allow the develop of flexible screens.
As opposed to regular (metallic) electron emitting tips, the structural perfection of carbon nanotubes allows higher electron emission stability, higher mechanical resistance, and longer life time. First of all, it allows energy savings since it needs lower (or no) heating temperature of the tips and requires much lower threshold voltage. As an illustration for the latter, producing a current density of 1mA/cm2 is possible for a threshold voltage of 3V/µm with nanotubes, while it requires 20V/µm for graphite powder and 100V/µm for regular Mo or Si tips. The subsequent reductions in cost and energy consumption are estimated at 1/3 and 1/10 respectively. Generally speaking, the maximum current density obtainable ranges between 106 A/cm2 and 108 A/cm2 depending on the nanotubes involved (e.g., SWNT or MWNT, opened or capped, aligned or not) [3.219–221]. lthough nanotube side-walls seem to emit as well as nanotube tips, many works have dealt (and are still dealing) with growing nanotubes perpendicular to the substrate surface as regular arrays (Fig. 3.28b). Besides, using SWNTs instead of MWNTs
Fig (a) Principle of a field-emitter-based screen. (b) SEM image of a nanotube-based emitter system (top view). Round dots are MWNT tips seen through the holes corresponding to the extraction grid.
The first commercial
flat TV sets and computers using nanotube-based screens are about to be seen in stores. (Motorola, NEC, NKK, Samsung, Thales, Toshiba, etc.)

26. Application: Chemical Sensors
(a) Increase in a single
SWNT conductance when 20 ppm of NO2 are added to an
argon gas flow.
(b) Same with 1% NH3 added to the argon
gas flow
Fig. 3.29a,b Demonstration of the ability of SWNTs in detecting molecule traces in inert gases.

27. rhodium铑 nanoparticles supported on MWNT surface
Fig Transmission electron microscopy image showing
rhodium铑 nanoparticles supported on MWNT surface