2. Jens Martensson
INTRODUCTION TO
NANOSCIENCE
• Nanoscience is a pretty new, it was discovered
nearly 4 decades ago, in those years scientists
discovered many things about nanoscience yet
they still have limited knowledge on it and have
not yet uncovered its full potential.
• Nanoparticles are an important scientific
breakthrough that has been and is being explored
in various biotechnological, pharmacological and
technological uses.
• After an experimental invention of a microscope
that could be used to see at atomic levels met the
newly discovered fullerene, nanotechnology was
born in the 1980s.
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HOW SMALL IS A NANOMETER
?
• The size of a nanometre is hard to
comprehend.
• A nanometre, 1 nm, is one billionth
of a metre (or a millionth of a
millimetre). This can also be
written as 10⁻⁹m.
• For a particle to be categorised as a
nanoparticle it has to range from
1nm-100nm
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4. Jens Martensson
NANOTECHNOLOGY
• A NANOMETER is a unit of length in the metric
system, equal to one billionth of a meter (10^- 9).
• Technology is the making, usage and knowledge
of tools, machines and techniques, in order to
solve a problem or perform a specific function.
• The study of controlling or manipulating of
matter on an atomic and molecular scale.
Generally nanotechnology deals with
structures sized between 1-100 nanometer in
at least one dimension, and involves
developing or modifying materials or devices
within that size.
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6. Jens Martensson
CARBON NANO TUBE
• Carbon nanotubes (CNTs) are an allotrope of carbon.
• Allotrope: each of two or more different physical forms in
which an element can exist.
• CNTs are long, thin cylinders of carbon.
• They can be thought of as a sheet of graphite (a hexagonal
lattice of carbon) rolled into a cylinder.
• Nanotubes have been constructed with length-to-diameter
ratio of up to 132,000,000:1.
• The structure of a carbon nanotube is formed by a layer of
carbon atoms that are bonded together in a hexagonal
(honeycomb) mesh. This one-atom thick layer of carbon is
called graphene, and it is wrapped in the shape of a
cylinder and bonded together to form a carbon nanotube.
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STRUCTURE
• Nanotubes can have a single outer
wall of carbon, or they can be made
of multiple walls (cylinders inside
other cylinders of carbon).
Accordingly they are called:
• – Single-walled carbon nanotube
• -Multi-walled carbon nanotube
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CHARACTERISTICS
• Single-walled carbon nanotube structure
• Single-walled carbon nanotubes can be formed in three
different designs: Armchair, Chiral, and Zigzag.
• The design depends on the way the graphene is wrapped
into a cylinder.
• Multi-walled carbon nanotube structure
• There are two structural models of multi-walled
nanotubes:
• – Russian Doll model
• – Parchment model
• In the Russian Doll model, a carbon nanotube contains
another nanotube inside it (the inner nanotube has a
smaller diameter than the outer nanotube).
• In the Parchment model, a single graphene sheet is rolled
around itself multiple times, resembling a rolled up scroll
of paper.ABIN ABRAHAM
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SIMILARITIES
• MWCNTs have similar properties
to SWCNTs.
• The outer walls on MWCNTs can
protect the inner carbon
nanotubes from chemical
interactions with outside
materials.
• MWCNTs also have a higher
tensile strength than SCNTs.
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11. Jens Martensson
LASER ABLATION
METHOD• First developed in 1995.
• Carbon is evaporated at high temperatures from a graphite
target using a powerful and focused laser beam.
• A 1.25-cm diameter graphite target is placed in a 2.5-cm
diameter, 50-cm long quartz tube in a furnace controlled at
1200°C and filled with 99.99% pure argon to a pressure of
500 Torr.
• A pulsed Nd:Yag laser beam at 250mJ (10 Hz) is focused
using a circular lens and the beam is swept uniformly
across the graphite target surface.
• The nanotubes, mixed with undesired amorphous carbon,
are collected on a cooled substrate at the end of the
chamber.
• have limited potential for scale-up. Solid graphite must
be evaporated at >3000°C to source the carbon needed,
the nanotubes produced are in an entangled form, and
extensive purification is required to remove the
amorphous carbon and fullerenes that are naturally
produced in the process.
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12. Jens Martensson
ARC DISCHARGE
METHOD• First method successfully used to synthesize
CNTs in small quantities .
• Opposing anode and cathode terminals made of
6-mm and 9- mm graphite rods respectively are
placed in an inert environment (He or Ar at ~500
Torr).
• A strong current, typically around 100 A (DC or
AC), is passed between the terminals generating
arc-induced plasma that evaporates the carbon
atoms in the graphite. The nanotubes grow from
the surface of these terminals.
• A catalyst can be introduced into the graphite
terminal.
• Although MWNTs can be formed without a
catalyst, it has been found that SWNTs can only
be formed with the use of a metal catalyst suchABIN ABRAHAM
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CHEMICAL VAPOUR
DEPOSITION• CVD has the highest potential for mass production of carbon
nanotubes.
• It can produce bulk amounts of defect-free CNTs at relatively low
temperatures.
• A substrate material (e.g. alumina, quartz), is cleaned in preparation
for the catalyst deposition.
• electrochemical etching with a hydrofluoric acid/methanol solution
may be performed. Nanotubes can grow at a higher rate on a porous
substrate, suggesting that carbon can diffuse through the porous
substrate layer and feed growing nanotubes.
• A catalyst (e.g. iron, nickel) is deposited onto the substrate by thermal
evaporation.
• The furnace is raised to a temperature between 500- 1200°C and a
hydrocarbon gas such as acetylene, ethylene, or carbon monoxide is
slowly pumped into the reactor.
• The atoms arrange themselves into a sheet of nanotubes on the
substrate, combined with impurities such as amorphous carbon,
fullerenes, as well as the catalyst material.
• In most cases these impurities must be removed using a purification
step. An acid treatment followed by sonification is popular.
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PROPERTIES OF CNT
• Carbon nanotubes have a higher tensile strength than steel and Kevlar.
• A nanotube's elasticity does have a limit, and under very strong forces, it is
possible to permanently deform to shape of a nanotube.
• Standard single-walled carbon nanotubes can withstand a pressure up to 25
GPa without [plastic/permanent] deformation. They then undergo a transformation
to superhard phase nanotubes.
• When the structure of atoms in a carbon nanotube minimizes the collisions
between conduction electrons and atoms, a carbon nanotube is highly
conductive.
• The strength of the atomic bonds in carbon nanotubes allows them to withstand
high temperatures. Because of this, carbon nanotubes have been shown to be
very good thermal conductors.
• Field emission results from the high aspect ratio and small diameter of CNTs.
For MWNTs, the field emission properties occur due to the emission of electrons
and light.ABIN ABRAHAM
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APPLICATIONS OF CNT
• SWNT ropes are the most conductive carbon fibers
known.
• CNTs have a very large surface area (e.g., 500 m2
per gram of nanotube) that gives them a high
capacity to retain pollutants such as water soluble
drugs.
• Due to their strong UV/Vis-NIR absorption
characteristics, SWNTs are a potential candidates
for use in solar panels.
• it is possible to condense gases in high density
inside single-walled nanotubes.
• carbon nanotubes present the opportunity to work
with effective structures that have high drug
loading capacities and good cell penetration
qualities.
• CNTs make excellent optical sensors compared to
these fluorescent probes due to photobleaching-ABIN ABRAHAM
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17. Jens Martensson
ELECTRON
MICROSCOPY• An electron microscope is a microscope that uses a
beam of accelerated electrons as a source of
illumination.
• The wavelength of an electron can be up to 100,000
times shorter than that of visible light photons.
• Electron microscopes have a higher resolving power
than light microscopes and can reveal the structure of
smaller objects.
ADVANTAGES OF ELECTRON MICROSCOPY :
• To study objects of >0.2 micrometer.
• For analysis of subcellular structure.
• For study of intracellular pathogens & viruses.
• For cell metabolism.
• For study of minute structure in nature.ABIN ABRAHAM
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19. Jens Martensson
INTRODUCTION
• A scanning electron microscope (SEM) is a type of electron
microscope that produces images of a sample by scanning it with
a focused beam of electrons.
• The electrons interact with atoms in the sample, producing various
signals that contain information about the sample's surface
topography and composition.
IMPORTANT TERMS :
• TOPOGRAPHY : The topography of a surface is known to
substantially affect the bulk properties of a material. Many times
there is nanoscale morphology in surface anomalies and a desired
interest in their resultant influence.
• MORPHOLOGY : morphology is essential in identifying the
shape, structure, form, and size of cells. In bacteriology, for
instance, cell morphology pertains to the shape of bacteria if
cocci, bacilli, spiral, etc. and the size of bacteria.
• Electrons interact with atoms -- produces various signals that
contain information about the sample's surface topography and
composition.
• Produces images of a sample by scanning it with a focused beam
of electrons in a raster scan patternABIN ABRAHAM
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COSTRUCTION AND
WORKING• CONSTRUCTION :
• Electron gun consisting of cathode and
anode.
• The condenser lens controls the amount
of electrons travelling down the column
• The objective lens focuses the beam
into a spot on the sample.
• Deflection coil helps to deflect the
electron beam.
• SED attracts the secondary electrons.
• Additional sensors detect backscattered
electrons and X-rays
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• WORKING :
• A scanning electron microscope scans a beam of
electrons over a specimen to produce a magnified image of an
object. That's completely different from a TEM, where the beam of
electrons goes right through the specimen.
I. Electrons are fired into the machine.
II. The main part of the machine (where the object is scanned) is
contained within a sealed vacuum chamber because precise
electron beams can't travel effectively through air.
III. A positively charged electrode (anode) attracts the electrons and
accelerates them into an energetic beam.
IV. An electromagnetic coil brings the electron beam to a very
precise focus, much like a lens.
V. Another coil, lower down, steers the electron beam from side to
side.
VI. The beam systematically scans across the object being viewed.
VII. Electrons from the beam hit the surface of the object and bounce
off it.
VIII.A detector registers these scattered electrons and turns them
into a picture.
IX. A hugely magnified image of the object is displayed on a TV
screen.
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CONSTRUCTION
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It consists of an electron gun to produce electrons. Magnetic
condensing lens is used to condense the electrons and is also used to
adjust the size of the electron that falls on to the specimen. The
specimen is placed in between the condensing lens and the
objective lens as shown.
The magnetic objective lens is used to block the high angle
diffracted beam and the aperture is sued to eliminate the diffracted
beam (if any) and in turn increases the contrast of the image.
The magnetic projector lens is placed above the fluorescent screen
in order to achieve higher magnification,. The image can be recorded
by using a fluorescent (Phosphor) screen or (CCD – Charged
Coupled device) also.
24. Jens Martensson
WORKING
• Stream of electrons are produced by the electron gun and is
made to fall over the specimen using the magnetic condensing
lens.
• Based on the angle of incidence the beam is partially
transmitted and partially diffracted. Both these beams are
recombined at the E-wald sphere to form the image. The
combined image is called the phase contrast image.
• In order to increase the intensity and the contrast of the image,
an amplitude contrast has to be obtained. This can be
achieved only by using the transmitting beam and thus the
diffracted beam can be eliminated.
• Now in order to eliminate the diffracted beam, the resultant
beam is passed through the magnetic objective lens and the
aperture. The aperture is adjusted in such a way that the
diffracted image is eliminated. Thus, the final image obtained
due to transmitted beam alone is passed through the projector
lens for further magnification.
• The magnified image is recorded in fluorescent screen or
CCD. This high contrast image is called Bright Field Image.
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27. Jens Martensson
CONSTRUCTION AND
WORKING• AFM consists of microscope cantilever with a sharp tip (probe) at
its end used to scan the specimen surface.
• The cantilever is typically silicon or silicon nitride with the tip
radius of curvature of the orders of nm. Basically, AFM is modified
TEM in which limitations of TEM is overcomed. When the tip is
bought close to the sample, force between the tip and sample
leads to the deflection of the cantilever according to the Hook`s
law. Instead of using an electrical signal, the AFM relies on forces
between the atom on the tip and in the sample.
• The force present in the tip is kept constant and the scanning is
done. As the scanning continues, the tip will have vertical
movements depending upon the topography of the sample. The
force present in the tip is kept constant and the scanning is done.
As the scanning continue the tip will have vertical movement
depending upon the topography o the sample.
• A LASER beam is used to have a record of vertical movement of
the needle. This information is later converted into visible from
using photo diode. Depending upon the situation, AFM measures
different types of forces like a Vander Waal’s forces, capillary
force, mechanical contact force etc.
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SCANNING NEAR FIELD
OPTICAL MICROSCOPE
• Near-field scanning optical microscopy (NSOM) or
scanning near-field optical microscopy (SNOM) is
a microscopy technique for nanostructure investigation that
breaks the far field resolution limit by exploiting the
properties of evanescent waves. In SNOM,
the excitation laser light is focused through an aperture with
a diameter smaller than the excitation wavelength, resulting
in an evanescent field (or near-field) on the far side of the
aperture. When the sample is scanned at a small distance
below the aperture, the optical resolution of transmitted or
reflected light is limited only by the diameter of the aperture.
In particular, lateral resolution of 20 nm and vertical
resolution of 2–5 nm have been demonstrated.
• As in optical microscopy, the contrast mechanism can be
easily adapted to study different properties, such
as refractive index, chemical structure and local stress.
Dynamic properties can also be studied at a sub-
wavelength scale using this technique.
• NSOM/SNOM is a form of scanning probe microscopy.
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