Introduction to Nanotechnology

IUPAC Definition: a nanoparticle is a particle of any shape with dimensions in the range of
10−9 to 10−7 m (1-100 nm).

Nanotechnology: A more generalized description of nanotechnology was subsequently

established by the National Nanotechnology Initiative, which defines nanotechnology as the
manipulation of matter with at least one dimension sized from 1 to 100 nanometers.

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 Brief History
Dr. Richard P. Feynman
• “Why cannot we write the entire 24
volumes of the Encyclopedia Britannica on
the head of a pin?”

"There's Plenty of Room at the Bottom: An

Invitation to Enter a New Field of Physics"
was a lecture given by physicist Richard
Feynman at the annual American Physical
Society meeting at Caltech on December 29,
Stained glass windows.
1959.

Birth of Nanotechnology
In1974, Professor Taniguchi of Tokyo Science University used the word
“nanotechnology” to describe the science and technology of processing or building parts
with nanometric tolerances.
To date, nanotechnology has become an interdisciplinary bridge due to unique properties
of nanomaterials, widely applied to pharmacy, therapeutics, electromagnetics and
catalysis.
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 Long back ago
As far back as the fourth century, nanoparticles were used by artisans for generating
a glittering effect on the surface of pots. One the left is a famous artefact called the
Lycurgus Cup resides in the British Museum in London. What makes this cup unique is
that its color changes from green (when illuminated from the outside) to red (when
illuminated from within) due to nanoparticles of gold and silver in the glass.

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 How small is “nano”?

On this scale, interatomic (coulombic) forces become large, and must be

considered when undertaking studies to characterize, experiment, and model
the behaviors of nanomaterials

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 An Interdisciplinary Endeavor

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 Three (of several) Senses of Small
What do we mean by small particle and why does their chemistry change?

Size and surface area effects

1 nm –100 nm Fundamental materials properties remain the same but size, shape and
surface area alter some behaviors work function, solubility, chemical potential, contaminate
sorption.

Critical Size and Characteristic Length Scale

Interesting or unusual properties because the size of the system approaches some critical
length (includes quantum effects). Many characteristics of material may have normal or
nearly normal behaviour

New (Non-extensive) Properties

Systems not large enough to have extensive properties. Particles become effectively
polymorphs of “bulk” materials and statistical homogeneity may not be valid.

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 Some examples
Size decreases ---- Surface energy increases ---- Thus Melting point decreases.
Eg.: 3 nm CdSe nanocrystal melts at 700K compared to bulk CdSe at 1678 K.

Reactivity
Melting point
Strength
Conductivity
Color

Suspensions of gold nanoparticles of various

sizes. The size difference causes the difference
in colors.

Size and Shape Matter

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 Where does the inspiration comes from ?
and the answer is nature……………….. Lotus-Inspired Nanotechnology Applications

1. The Lotus effect

http://iopscience.iop.org/0957-4484/17/5/032

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 Where does the inspiration comes from ?
2. Gecko adhesion: If geckos had not evolved, it is possible that humans would never have
invented adhesive nanostructures.

Applications for gecko-inspired adhesive

nanostructures
• dry self-cleaning adhesive
• Biomedical applications such as
endoscopy and tissue adhesives
• MEMS switching
• wafer alignment
• micromanipulation
• robotics

https://doi.org/10.1098/rsta.20
07.2173

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 Difference between bulk and nanomaterials

BULK carbon as graphite Nano carbon as graphene

Two principal factors cause the properties of nanomaterials to differ significantly from bulk
materials:
• Increased relative surface area
• quantum effects

These factors can change or enhance properties such as reactivity, strength and electrical
characteristics.
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 Confinement in nanomaterials
If two dimensions are so reduced and one remains large, the resulting structure is referred
to as quantum wire. Quantum wires, which are confined in two dimensions, can be
thought of as nanometer-sized cylinders that can measure several microns in length.

Finally, the quantum dot is a zero-dimensional nanometre-sized sphere, confined in all

three dimensions.

Thin films Nanorods Nanoparticles

Quantum wells Nanowires Quantum dots
nanotubes
https://royalsocietypublishing.org/doi/10.1098/rsos.180387
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 What is the Big Deal About Nanoscience

The drastic increased ratio of surface area to

volume makes interactions between the
surfaces of particles very important. If
something has more surface area, there are
more places for other chemicals to bind or react
with it. For example, fine powders offer greater
reaction speed because of the increased surface
area. Think about how much faster you can
cool a glass of water if you put crushed ice in it
rather than ice cubes.
Nanoscale particles maximize surface area, and therefore maximize possible reactivity.

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 Surface area to volume ratio
Macro-scale
A typical material possesses:
~ 1023 atoms/cm3 (volume density); ~ 1015 atoms/cm2 (surface density)
Assume that, we’ve a cube of unit length
Total number of atoms ~ 1023 atoms/cm3 x (1 cm)3 ~ 1023
Total number of surface atoms ~ 1015 atoms/cm2 x 6 x (1 cm)2 ~ 6 x 1015
So, the ratio of surface to total atoms will be ~ 6 x 10-8.
Nano-scale
A typical material possesses:
~ 1023 atoms/cm3 (volume density); ~ 1015 atoms/cm2 (surface density)
Assume that, we’ve a cube of length = 10 nm = 10-7 cm
Total number of atoms ~ 1023 atoms/cm3 x (10-7 cm)3 ~ 100
Total number of surface atoms ~ 1015 atoms/cm2 x 6 x (10-7 cm)2 ~ 60
So, the ratio of surface to total atoms will be ~ 0.6.

Nanoscale objects have a greater surface area than volume.

Very important property

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 Nanoparticles: their properties
HOW and WHY do these large numbers of surface atoms compared to interior atoms
make nanoparticles so different?

Interior Atoms Surface Atoms

Attracted to lots of nearest neighbors Attracted to few nearest neighbors

High Coordination Numbers Low Coordination Numbers
Surface atoms have Higher energy!

Esurface atoms – Einterior atoms = Esurface (Surface Energy)

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 Effect on the rate of chemical reactions

 Size of the particles taking part in a reaction and surface area

 Concentrations of reactants
 Temperature
 Presence of a catalyst

As the size of nanoscale particles decreases, the surface area to volume ratio
increases. Therefore, the surface energy increases!
Increases the rate of some chemical reactions.

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 Effect on the melting point
Assume the change in internal energy (∆U) and change in entropy per unit mass during
melting are independent of temperature.
𝛥𝜃 = deviation of melting point from the bulk value
2𝑇0 𝜎 𝑇0 = bulk melting point
𝛥𝜃 = 𝜎 = surface tension coefficient for a liquid-solid interface
𝜌𝐿𝑟
𝜌 = particle density
𝐿 = Latent heat of fusion
𝑟 = particle radius
 Lowering of the melting point is proportional to 1/𝑟.
 𝛥𝜃 can be as large as couple of hundred degrees when
the particle size gets below 10 nm!!
 Most of the time, 𝜎 the surface tension coefficient is
unknown; by measuring the melting point as a function
of radius, 𝜎 can be estimated.
 For nanoparticles embedded in a matrix, melting point
may be lower or higher, depending on the strength of
the interaction between the particles and matrix.
Melting point of gold nanoparticles
 Nanoparticles have a lower melting point than their as a function of size. Phys. Rev. A 13,
bulk counterparts. 2287–2298 (1976).
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 Effect on mechanical properties
 The mechanical properties of nanomaterials increase with decrease in size, because
smaller the size, lesser is the probability of finding imperfections such as dislocations,
vacancies, grain boundaries.
 Strength of material improves significantly as the particle size decrease due to perfect
defect free surface.
 Hardness and yield strength of material also increases as particle size decreased.
 Elastic modulus and toughness of material also increases as the particle size decreased.
Lower number of defects
Fewer surface defects

Effect on the Electronic Properties

Size plays an important role in electrical properties and is based on mainly following
mechanisms:
• Surface scattering
• Change of electronic structure
• Quantum Transport
• Change of microstructure
• Discrete Charging

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 Synthesis of Nanoparticles

Uses macorscopic structures, which Build up of a material atom by atom,

can be externally-controlled in the molecule by molecule. Physical forces
processing of nanostructures. Slicing operating at nanoscale are used to
or successive cutting of a bulk combine basic units into larger stable
material to get nano-sized particle. structures.
Typical examples are etching through Typical examples are quantum dot
the mask, ball milling. formation during epitaxial growth and
formation of nanoparticles from
colloidal dispersion.

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 Top-Down approach Bottom-up approach
All the Bottom-up techniques, the starting
In Top-down techniques, the
material is either gaseous state or liquid
starting material is solid state
state of matter

Physical processing methods Physical and chemical processing methods

Mechanical methods: Physical Vapor Deposition (PVD):

cutting, etching, grinding, ball milling • Involves condensation of vapor phase species
• Evaporation (Thermal, e-beam) sputtering
• Plasma Arcing
Lithographic techniques: • Laser ablation
Photo Lithography
CVD: Deposition of vapor phase of reaction
Electron Beam Lithography
species
Self-assembled Monolayer
Electrolytic deposition
Sol-gel method

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 Ball Milling
Simplest method of making nanoparticle in powder form Begin with bulk materials (top)
that are subsequently reduced to nano-size (down) by the way of physical, chemical and
mechanical processes.
e.g. Mechanical-ball milling, grinding etc.

• Macro or micro scale particles are ground in a ball mill, a planetary ball mill, or other
size reducing mechanism.
• 2:1 mass ratio of balls to materials
• Material is forced to the walls and pressed against the walls.
• The resulting particles are separated by filters and recovered.
• Broad size distribution and varied particle geometry
• May contain defects and impurities from the milling process.
• Metallic and ceramic nanomaterials are produced, generally.

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 Ball Milling
 A hollow steel cylinder containing tungsten balls
rotates about its central axis (partially filled with
the material to be grounded plus the grinding
medium).
 Particle size is reduced by brittle fracturing
resulting from ball-ball and ball-wall collisions.
 Milling takes place in an inert gas atmosphere to
reduce contamination.
 Control the speed of rotation and duration of
milling-grind material to fine powder( few nm to
few tens of nm).

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 Chemical Vapour Deposition
Reactant gases introduced in the
chamber, chemical reactions occur on
wafer surface leading to the deposition
of a solid film.
e.g. APCVD, LPCVD, PECVD, MOCVD
most commonly used for dielectrics and
Si.

CVD major steps:

• Introduce reactive gases to the chamber. One or more than one gas may be used plus
carrier gases (nonreactive gases)
• Activate gases (decomposition) by heat or plasma.
Deposition of film through chemical
• Gas absorption by substrate surface .
reaction and surface absorption.
• Transport of volatile byproducts away form substrate.
• Exhaust waste.

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 Chemical Vapour Deposition
Advantages
 High coating hardness • Gaseous compounds react to form a
 Good adhesion (if the coating is not dense layer on a heated substrate.
too thick) • The most widely deposited wear
 Good uniformity of coating resistant coatings are TiC, TiN,
Disadvantages chromium carbide and alumina.
 High temperature process • Deposition temperatures are generally
(distortion) in the range 800-1000°C which
 Sharp edge coating is difficult restricts the range of materials that can
(thermal expansion mismatch be coated and can also lead to
stresses) component distortion.
 Limited range of materials can be
coated
 Environmental concerns about
process gases

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 CVD Benefits
• Can be applied to a wide variety of base materials including ceramics, glass, metals
and metal alloys.
• Can coat precision surfaces and intricate surfaces including seal areas and internal
surfaces.
• Can withstand exposure to low and high temperature and extreme temperature
variation.
• A durable coating to substrate bond means the coating remains bonded in high stress
environments, even when the substrate surface flexes or bends.
• Precursor gas can be optimized for chemical inertness, high lubricity, corrosion
resistance, fouling resistance, high purity, or wear resistance.

Coating Drawbacks
•Typically applied at higher temperatures (depending on the precursor).
•Difficult to mask surface. Usually an all or nothing coating.
•Size limited to reaction chamber capacity.
•Parts must be broken down into individual components
•Not an "on site" process, parts must be shipped to a coating center.

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 Types of CVD reactions
• Thermal decomposition
AB(g) ---> A(s) + B(g)
Si deposition from Silane at 650oC: SiH4(g) → Si(s) + 2H2(g)
Ni(CO)4(g)  Ni(s) + 4CO(g) (180oC)
• Reduction (using H2)
AX(g) + H2(g)  A(s) + HX(g)
W deposition at 300oC: WF6(g) + 3H2(g)  W(s) + 6HF(g)
SiCl4(g) + 2H2(g)  Si(s) + 4HCl (1200oC)
• Oxidation (using O2)
AX(g) + O2(g)  AO(s) + [O]X(g)
SiO2 deposition from silane and oxygen at 450oC (lower temp than thermal
oxidation): SiH4(g) + O2(g) ---> SiO2(s) + 2H2(g)
2AlCl3(g) + 3H2(g) + 3CO2(g)  Al2O3 + 3CO + 6HCl (1000oC)
(O is more electronegative than Cl)
• Compound formation (using NH3 or H2O)
AX(g) +NH3(g)  AN(s) + HX(g) or AX(g) + H2O(g )  AO(s) + HX(g)
Deposit wear resistant film (BN) at 1100oC: BF3(g) + NH3(g)  BN(s) + 3HF(g)
(CH3)3Ga(g) + AsH3(g)  GaAs(s) + 3CH4 (650 – 750oC)

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 Typical example: CVD
The simplest CVD process involves the pyrolytic decomposition of a gaseous
compound on the substrate to provide a coating of a solid reaction product. For
example, the following reactions are used to produce solid coatings of tungsten
metal (W), titanium carbide (TiC) and titanium nitride (TiN) respectively:

WF6 + 3H2 = W (solid) + 6HF (gas)

TiCl4 + CH4 = TiC (solid) + 4HCl (gas)
TiCl4 + ½ N2 + 2H2 = TiN (solid) + 4HCl (gas)

Alumina may be deposited by the reaction:

Al2Cl6 + 3CO2+ 3H2 = Al2O3 (solid) + 3CO (gas) + 6HCl (gas)

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 Application of CVD technique
CVD has applications across a wide range of industries such as:

Coatings – Coatings for a variety of applications such as wear resistance, corrosion resistance,
high temperature protection, erosion protection and combinations thereof.

Semiconductors and related devices – Integrated circuits, sensors and optoelectronic devices.

Optical Fibres – For telecommunications.

Composites – Preforms can be infiltrated using CVD techniques to produce ceramic matrix
composites such as carbon-carbon, carbon-silicon carbide and silicon carbide-silicon carbide
composites.

Powder production – Production of novel powders and fibres

Catalysts

Nanomachines, Nanomedecine, Nanofiber, etc.

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 Carbon based materials
Carbon is a unique material, and can be a good metallic conductor in the form of graphite, a
wide band gap semiconductor in the form of diamond, or a polymer when reacted with
hydrogen.

Carbon atom Aromatic ring Graphene sheet

Graphite (Ambient conditions) sp2 hybridization: planar

Carbon Diamond (High temperature and pressure) sp3 hybridization: cubic
Nanotube/Fullerene (certain growth conditions) sp2 + sp3 character:
cylindrical

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 Carbon nanotube (CNT)

Buckytube C1,000,000

CNT

Finite size of graphene layer has dangling bonds. These dangling bonds correspond to high
energy states.
Eliminates dangling bonds
Nanotube formation + Decrease in total energy

Increases Strain Energy

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 Carbon nanotube
 Carbon nanotubes are tubular forms of
carbon that can be envisaged as graphene
sheets rolled into cylindrical form.
 These nanotubes have diameters of few
nanometers and their lengths are up to
several micrometers.
 Each nanotube is made up of a hexagonal
network of covalently bonded carbon
atoms. CNT is configurationally equivalent
to a two dimensional graphene sheet
rolled into a tube.
 A single-walled carbon nanotube (SWNT)
consists of a single graphene cylinder
whereas a multi-walled carbon nanotube
(MWNT) comprises of several concentric
graphene cylinders.
 A CNT is characterized by its chiral Vector:
C = nâ1 + mâ2; and  is the chiral angle
with respect to the zigzag axis.

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 Carbon nanotube
 Depending on the way of rolling of
graphene sheets, SWNT of different
types, viz. armchair, zig-zag and chiral
could be produced.
 They can be represented using the
method given by Hamada.
 For example, to realize an (n, m)
nanotube, one has to move n times a1
from the selected origin and then m
times a2.
 On rolling the graphite sheet about
bravis vectors, these points coincide to
form the (n, m) nanotube.
 Thus armchair, zig-zag and chiral
nanotubes can be represented as (n, n),
Rolling of a graphene layer to form single-walled carbon
(n, 0) and (n, m), respectively.
nanotubes of (a) armchair, (b) zig-zag and (c) chiral type.

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 Carbon nanotube

Armchair Zig Zag Chiral

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 Diameter of Carbon nanotube
𝑎𝑐𝑐
CNT diameter 𝑑= 3 𝑚2 + 𝑚𝑛 + 𝑛2 𝑎𝑐𝑐 =0.142 nm C-C bond length
𝜋
= 0.0783 𝑚2 + 𝑚𝑛 + 𝑛2 nm

Chiral angle 3𝑚
𝜃= tan−1
2𝑛 + 𝑚

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 Properties of CNT
• remarkable electrical conductivity
• exceptional tensile strength,
 Strong Like Steel
 Light Like Aluminum
 Elastic Like Plastic
• thermal conductivity

These properties are expected to be valuable in many areas of technology, such as

electronics, optics, composite materials (replacing or complementing carbon fibers),
nanotechnology, and other applications of materials science.

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 Electrical properties of CNT
 Electrical conductivity six orders of magnitude higher
than Cu.
 Can be metallic or semiconducting depending on
chirality.
 Tuneable band gap
 Electronic properties can be tailored through
application of external magnetic field, mechanical
deformation etc.
 Very high current carrying capacity
 Can be functionalized

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 Synthesis of CNTs
To produce nanotubes in sizable quantities, following techniques have been used:
1. Arc discharge
2. laser ablation
3. chemical vapor deposition
Mostly, these processes take place in a vacuum or with process gases.

The CVD growth method is popular, as it yields high quantity and has a degree of control
over diameter, length and morphology. Using particulate catalysts, large quantities of
nanotubes can be synthesized by these methods, but achieving the repeatability becomes a
major problem with CVD growth.

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 CNT Application
 CNT technology in a number of their bicycle components – including flat and riser
handlebars, cranks, forks, seatposts, stems and aero bars.
 carbon nanoepoxy resin: wind turbines, marine paints and a variety of sports gear such as
skis, ice hockey sticks, baseball bats, hunting arrows, and surfboards.
 “Gecko tape" (also called "nano tape“ , double-sided adhesive tape): It can be used to
hang lightweight items such as pictures and decorative items on smooth walls without
punching holes in the wall. No residue after removal and can stay sticky in extreme
temperatures.
Under development
 Using carbon nanotubes for environmental monitoring due to their active surface area and
their ability to absorb gases.
 The Boeing Company has patented the use of carbon nanotubes for structural health
monitoring of composites used in aircraft structures. This technology will greatly reduce
the risk of an in-flight failure caused by structural degradation of aircraft.
 IBM expected carbon nanotube transistors to be used on Integrated Circuits.
 Many more..

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 Nanotubes Growth Methods: Arc Discharge
The arc discharge technique generally involves
the use of two high-purity graphite electrodes as
the anode and the cathode.

The electrodes were vaporized by the passage of

a DC current (~100 A) through the two high-purity
graphite separated (~ 1–2 mm) in 400 mbar of
Helium atmosphere.

After arc discharging for a period of time, a

carbon rod is built up at the cathode. This method
can mostly produce MWNTs but can also
produce SWNT with the addition of metal catalyst
such as Fe, Co, Ni, Y or Mo, on either the anode
or the cathode.

The quantity and quality such as lengths, diameters, purity and etc. of the nanotubes obtained
depend on various parameters such as the metal concentration, inert gas pressure, type of gas,
plasma arc, temperature, the current and system geometry.

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Nanotubes Growth Methods:Pulsed Laser Deposition
Advantages
• Flexible, easy to implement
• Growth in any environment
• Exact transfer of complicated materials
(YBa2Cu3O7)
• Variable growth rate
• Epitaxy at low temperature
• Atoms arrive in bunches, allowing for much
more controlled deposition
• Greater control of growth (e.g., by varying laser
parameters)
Disadvantages
• Particulates
• Loss of volatile elements
• Small area deposition, Uneven coverage
• High defect or particulate concentration
• Mechanisms and dependence on parameters
not well understood

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 Nanotubes Growth Methods: CVD
Hydrocarbon + Fe/Co/Ni catalyst 550-750°C CNT

Steps:
• Dissociation of hydrocarbon.
• Dissolution and saturation
of C atoms in metal nanoparticle.
• Precipitation of Carbon.

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 CNT Application
 CNT technology in a number of their bicycle components – including flat and riser
handlebars, cranks, forks, seatposts, stems and aero bars.
 carbon nanoepoxy resin: wind turbines, marine paints and a variety of sports gear such as
skis, ice hockey sticks, baseball bats, hunting arrows, and surfboards.
 “Gecko tape" (also called "nano tape“ , double-sided adhesive tape): It can be used to
hang lightweight items such as pictures and decorative items on smooth walls without
punching holes in the wall. No residue after removal and can stay sticky in extreme
temperatures.

 Using carbon nanotubes for environmental monitoring due to their active surface area and
their ability to absorb gases.
 The Boeing Company has patented the use of carbon nanotubes for structural health
monitoring of composites used in aircraft structures. This technology will greatly reduce
the risk of an in-flight failure caused by structural degradation of aircraft.
 IBM expected carbon nanotube transistors to be used on Integrated Circuits.
 Many more..

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