Superconductors

An element, inter-metallic alloy, or compound that will conduct electricity without resistance below a
certain temperature, magnetic field, and applied current.

Materials that conduct electricity with no resistance are called superconductors

• Metals and alloys are good conductor of electricity but they offer some resistance to the flow
of electron. The resistivity increases with increase in temperature and vice-versa.

• There are some metals and chemical compounds whose resistivity becomes zero when their
temperature is brought near 0° Kelvin (-273°C). At this stage such metals or compounds are
said to have attained superconductivity.

• Superconductivity was discovered by Heike Kamerlingh Onnes at the University of Leiden in

the Netherlands in 1911.

• A superconductor is a material that can conduct electricity with zero resistance. This means
when the conductors become superconductors below the critical temperature there will not
be any loss of energy due to heat, sound, etc.

• Most of the materials should be in extremely low temperatures in order to become

superconductors.

• Superconductors have two outstanding features:

• Zero electrical resistivity: This means that an electrical current in a superconducting ring
continues indefinitely until a force is applied to oppose the current.

• The magnetic field inside a bulk sample is zero (the Meissner effect): When a magnetic field
is applied current flows in the outer skin of the material leading to an induced magnetic field
that exactly opposes the applied field. The material is strongly diamagnetic as a result. In this
experiment, a magnet floats above the surface of the superconductor.

Types of superconducters

• There are two types of superconductors commonly known as (a) Type I and, (b) Type II
superconductors.

• Type I superconductors are soft superconductors. They are usually pure specimens of some
elements i.e. metals and metalloids. They exhibit complete Meissner effect, they are
completely diamagnetic in applied field. They require the coldest temperature to become
superconductive. They have very little use in technical applications.

• Type II superconductors are hard superconductors. Except for the elements Vanadium,
technetium and niobium, type II comprises of metallic compounds and alloys. They usually
have high value of resistivity in normal state, their transition from a normal to a
superconducting state is gradual across a region of “mixed state” behavior. These are very
useful as compared to Type I materials.
Properties

• Properties of Superconductors

• 1: Critical temperature/Transition temperature

The temperature below which the material changes from conductors to superconductors is called
critical temperature or transition temperature. The transition from conductors to superconductors is
sudden and complete.

• 2: Zero Electric Resistance/Infinite Conductivity

In the superconducting state, the material has zero resistance. When the temperature of the material
is reduced below the critical temperature, its resistance suddenly reduces to zero. Mercury is an
example of a superconductor that shows zero resistance below 4 kelvin.

• 3: Expulsion of Magnetic Field

Below the critical temperature, superconductors do not allow the magnetic field to penetrate inside
it. This phenomenon is called Meisser Effect.

• 4: Critical Magnetic Field

The certain value of the magnetic field beyond which the superconductors return to conducting state
is called the critical magnetic field. The value of the critical magnetic field is inversely proportional to
the temperature. As the temperature increases, the value of the critical magnetic field decreases.

• 5: Josephson Current

If two superconductors are separated by a thin film of insulating material, which forms a low
resistance junction, it is found that the cooper pairs (formed by phonon interaction) of electrons, can
tunnel from one side of junction to the other side. The current, due to flow of such cooper pairs, is
called Josephson Current.

• 6: Critical Current

When a current is passed through a conductor under superconducting state, a magnetic field is
developed. If the current increase beyond certain value the magnetic field increased up to critical
value at which conductor returns to its normal state. This value of current is called critical current.

Application

• In Military Operation- SQUIDs (superconducting quantum interference devices) are being

used in the production of highly sensitive magnetometers. They are generally used for the
detection of land mines and submarines.

• In the field of Medicine- Superconducting magnets are also used in Magnetic Resonance
Imaging (MRI) machines.

• In Electrical field- As we know due to the electrical resistance, there is a power loss while
power transmission. So nowadays, superconducting cables are used in place of ordinary
cable lines to avoid power loss.
 • In the field of Electronics- In miniaturization and increasing the speed of computer chips. In
Electric generator for more efficiency.

• Superconductors are also being used for the development of high-intensity Electro Magnetic
Impulse (EMP). They are used to disable all the electronic equipment within the range.

• In Transportation field- Maglev trains work on the superconducting magnetic levitation

phenomenon. Japanese Maglev train is a real-life example of magnetic levitation.

• Superconducting magnets are used for accelerating the particles in the Large Hadron Collider

Optical Fibres

Introduction

• An optical fiber is a flexible, transparent fiber made by drawing glass (silica) or plastic to a
diameter slightly thicker than that of a human hair.

• Optical fibers are the light guides, they act as a carrier of light signals and electromagnetic
energy at optical length.

• Fiber optic is the technique of transmitting light through long, thin, flexible fibers of glass,
plastics or other transparent materials, bundles of parallel fibers can be used to transmit
complete images.

• The optical fiber can be used as a medium for telecommunication and networking because it
is flexible and can be bundled as cables.

• The light transmitted through the fiber is confined due to total internal reflection within the
material.

• A fiber optic cable can contain a varying number of these glass fibers -- from a few up to a
couple hundred. Surrounding the glass fiber core is another glass layer called cladding. A
layer known as a buffer tube protects the cladding, and a jacket layer acts as the final
protective layer for the individual strand

• In telecommunication applications, the light used is typically infra-red light, at wavelengths

near to the minimum absorption wavelength of the fiber in use.
Types

• The types of optical fibers depend on the refractive index, materials used, and mode of
propagation of light.

The classification based on the refractive index is as follows:

• Step Index Fibers: It consists of a core surrounded by the cladding, which has a single
uniform index of refraction.

• Graded Index Fibers: The refractive index of the optical fiber decreases as the radial distance
from the fiber axis increases.

The classification based on the materials used is as follows:

• Plastic Optical Fibers: The polymethyl methacrylate is used as a core material for the
transmission of the light.

• Glass Fibers: It consists of extremely fine glass fibers.

The classification based on the mode of propagation of light is as follows:

• Single-Mode Fibers: These fibers are used for long-distance (80–140km) transmission of
signals. The transmission cores of single-mode fibers have a diameter of 9 µm. Data rate 40
gigabite/sec.

• Multimode Fibers: These fibers are used for short-distance (300-500 meters) transmission of
signals. The multi-mode cores are available with 50 µm or 62.5 µm. Fibers used in
telecommunications have a diameter of 125 µm. Bandwidth in terabits/sec.

Properties

Following are the benefits of optical fiber cable:

• Extremely high throughput, large data-carrying capacity.

• Very high resistance to noise, high electrical resistance.

• Excellent security, light weight.

• Ability to carry signals for much longer distances before requiring repeaters than copper
cable

• Industry standard for high-speed networking, signals contain very little power.

Fiber’s characteristics are summarized in the following list:

1. Throughput – Fiber is reliable in transmitting data at rates that can reach 100 gigabits(or
100,000 megabits) per second per channel.

2. Cost – Fiber optic cable is the most expensive transmission medium. As technologies
improved, fiber optic cables are cheaper and cheaper.

3. Connectors –With fiber cabling, you can use any of 10 different types of connectors.
 4. Noise immunity – Because fiber does not conduct electrical current to transmit signals, it is
unaffected by EMI.

5. Size and scalability – Depending on the type of fiber optic cable used, segment lengths vary
from 150 to 40,000 meters.

Merits

• Support of higher bandwidth capacities.

• Light can travel further without needing as much of a signal boost.

• They are less susceptible to interference, such as electromagnetic interference.

• They can be submerged in water -- fiber optics are used in more at-risk environments like
undersea cables.

• Fiber optic cables are stronger, thinner and lighter than copper wire cables.

• They do not need to be maintained or replaced as frequently.

• Low loss, so repeater-less transmission over long distances is possible.

• Large data-carrying capacity (thousands of times greater).

• Immunity to electromagnetic interference, including nuclear electromagnetic pulses (but can

be damaged by alpha and beta radiation).

• No electromagnetic radiation, difficult to eavesdrop.

• High electrical resistance, so safe to use near high-voltage equipment or between areas with
different earth potentials.

Demerits

It is important to note that fiber optics do have disadvantages users should know about. These
disadvantages include:

• Copper wire is often cheaper than fiber optics.

• Glass fiber requires more protection within an outer cable than copper.

• Installing new cabling is labor-intensive.

• Fiber optic cables are often more fragile. For example, the fibers can be broken or a signal
can be lost if the cable is bent or curved around a radius of a few centimeters.

• Cannot carry electrical power to operate terminal devices.

• At higher optical powers, is susceptible to “fiber fuse” wherein a bit too much light meeting
with an imperfection can destroy several meters per second.

Applications
• In Medical industry- Because of the extremely thin and flexible nature, it used in various
instruments to view internal body parts by inserting into hollow spaces in the body. It is used
as lasers during surgeries, endoscopy, microscopy and biomedical research.

• In Defense Purpose- Fibre optics are used for data transmission in high-level data security
fields of military and aerospace applications. These are used in wirings in aircraft,
hydrophones for SONARs and Seismics applications.

• In Communication- In telecommunication has major uses of optical fibre cables for

transmitting and receiving purposes. It is used in various networking fields and even
increases the speed and accuracy of the transmission data.

• For Broadcasting- These cables are used to transmit high definition television signals which
have greater bandwidth and speed. Broadcasting companies use optical fibres for wiring
HDTV, CATV, video-on-demand and many applications.

• In Industries- These fibres are used for imaging in hard to reach places such as they are
used for safety measures and lighting purposes in automobiles both in the interior and
exterior. They transmit information in lightning speed and are used in airbags and traction
control.

• For Lightening and Decorations- It is widely used in decorations and Christmas trees.

• In Mechanical Inspections- On-site inspection engineers use optical fibres to detect

damages and faults which are at hard to reach places. Even plumbers use optical fibres for
inspection of pipes.

Nano Materials

Introduction

• Nanomaterials (nanocrystalline materials) are materials possessing grain sizes of the order of
a billionth of a meter. They manifest extremely fascinating and useful properties, which can
be exploited for a variety of structural and non structural applications.

• All materials are composed of grains, which in turn comprise many atoms. These grains are
usually invisible to the naked eye, depending on their size. Conventional materials have
grains varying in size anywhere from 100’s of microns ( m ) to millimeters (mm). A micron ( m
) is a micrometer or a millionth (10–6) of a meter.

• An average human hair is about 100 μm in diameter. A nanometer (nm) is even smaller a
dimension than a μm and is a billionth (10–9) of a meter.
• A nanocrystalline material has grains on the order of 1-100 nm. (The average size of an atom
is on the order of 1 to angstroms ( Å ) in radius.)

• Nanocrystalline materials are exceptionally strong, hard, and ductile at high temperatures,
wear-resistant, corrosion-resistant, and chemically very active. Nanocrystalline materials, or
Nanomaterials, are also much more formable than their conventional, commercially
available counterparts.

• Definitions- Nanotechnology

• Nanotechnology is a field of applied science and technology which deals with the matter on
the atomic and molecular scale, normally 1 to 100 nanometers, and the fabrication of
devices with critical dimensions that lie within that size range.

• Nanomaterials - Nano materials are the materials with grain sizes of the order of nano meter
(10-9 m) i.e., (1-100 nm). It may be a metal, alloy, inter metallic (or) ceramic.

• Nanomaterials are the materials with atoms arranged in nano sized clusters which become
the building block of the material.

• “Any Material with a size between 1 nm and 100 nm [ 10 -9 m to 10 -7 m] is also called

Nanomaterials”

• Synthesis of Nanomaterials: The Nano mateirals can be synthesized by two processes,

they are

• Top – down approach

• Bottom – up approach

• 1. Top – down approach

• The removal or division of bulk material or the miniaturization of bulk fabrication processes
to produce the desired nanostructure is known as top-down approach. It is the process of
breaking down bulk material to Nano size.

• Fig. Synthesis of Nanomaterials for Top – down approach

• Types of Top – down Methods

• 1. Milling 2. Lithographic 3. Machining

Bottom – up approach

Molecules and even nano particles can be used as the building block for producing complex
nanostructures. This is known as Bottom – up approach. The Nano particles are made by building
atom by atom.
 FIG. Synthesis of Nanomaterials for Bottom – up approach

Types of Bottom up Methods

Vapour phase deposition Method

Molecular beam epitaxy Method

Plasma assisted deposition Method

Metal Organic Vapour Phase Epitaxy [MOVPE]

Liquid phase process [Colloidal method and Sol – Gel method]

Fullerene

Introduction

• Fullerene was discovered by Prof. Sir Harry Kroto, Dr. Richard E. Smalley

and Dr. Robert F. Curl Jr. in 1985.

• It was named after American architect R. Buckminister Fuller.

• Fullerene is the third major form of pure carbon; next two are graphite and diamond.

• Fullerene is a large molecule composed of carbon entirely. The general formula is Cn, where n
is even number from 32.

• Their shapes are roughly spherical similar to graphite with a surface net of carbon atoms
connected in hexagonal and pentagonal rings. Most common is C60 known as “buckyball”.

• Manufacturing- It is made by passing a large electric current b/w two graphite electrodes in
an inert atmosphere, resulting in a carbon plasma arc which cooled into soot, in which the
fullerenes could be isolated. Fullerene is formed when vaporized and condensed carbons are
combined in an inert gas.

Properties

• The molecule is three-dimensional and spherical and its properties can be described as
follows:
 • It was proved that the molecule can act as a semiconductor, conductor and under specific
conditions as superconductor.

• They have very high thermal and oxidative stability.

• They can display the photochromic effect.

• They are fairly insoluble in many solvents. On sublimation it forms translucent magneta face
centered cubic crystal.

Applications

• The potential application includes catalysts, drug delivery system, optical devices, chemical
sensors and chemical separation devices.

• Used in medical purpose in antibiotics and cancer cell study.

• To replace steel in bridges

• .

• In Diamond mimics, cosmetics, superconductors, abrasive agent for cutting and grinding
application, Dyes and pigments,

• In Electrodes, Lubricant additive, Antioxidant for medicinal uses, photoactive polymer.

• To produce nanowires of gold and zinc oxide.

• For economical electric motor brushes.

• As artificial muscles to increase strength and halt crack propagation of concrete.

Graphene

Introduction

• Graphene is an allotrope of carbon consisting of a single layer of atoms arranged in a two-

dimensional, honeycomb lattice, nanostructure.[

• The name is derived from "graphite" and the suffix -ene, reflecting the fact that
the graphite allotrope of carbon contains numerous double bonds.

• Graphene is a single layer of graphite. The strong covalent bonds between the carbon atoms
mean that Graphene: has a very high melting point, is very strong.

• Like graphite, Graphene conducts electricity well because it has delocalized electrons that
are free to move across its surface.

• These properties make Graphene useful in electronics and for making composites.
Properties

The most outstanding properties of Graphene are:

• High thermal conductivity, High electrical conductivity.

• High elasticity and flexibility, Transparent material

• High hardness, stronger than steel.

• High resistance. Graphene is approximately 200 times stronger than steel, similar to diamond
resistance, but much lighter.

• Ionizing radiation is not affected

• Able to generate electricity by exposure to sunlight

• Antibacterial effect. Bacteria are not able to grow in it.

• Low electricity consumption compared to other compounds.

• It is the world's first 2D material and is one million times thinner than the diameter of a
single human hair.

Applications

• Graphene’s Applications in Energy Industry- In Solar Cells, Graphene Batteries, in Nuclear

Power Plants, Thermoelectric, Alcohol Distillation, Fuel Cells etc.

• Graphene’s Applications in Medicine- in Drug Delivery, Cancer Treatment, Gene Delivery,

Photo-thermal Therapy, Diabetes Monitoring, Dialysis, Bone and Teeth Implantation, Tissue
Engineering and Cell Therapy, Graphene UV Sensors, Graphene Biosensors, Birth Control,
Deaf-Mute Communication, body scan, etc.

• Graphene's Applications in Electronics- In Generating Light, Graphene Transistors, waterproof

electronics, Wearable Electronics, touchscreen, Flexible Screens, Hard Drives and Memories,
superconductors, Elastic Robots, Optical Sensors, etc.

• Graphene’s Applications in Food Industry- In Food Packaging, Water purification,

Desalination, Food protection, food security.

• Graphene's Applications in Sports- In shoes, helmet, tires, clothes, rackets, Electronic Tattoos
and Fitness Tracking,

• Other Applications of Graphene- Graphene and Silk, in cement, Speakers and Headphones,
insulation, photography, automotive, airplanes, Graphene Paints, in Military Protective
Equipment, Thermal and Infrared Vision, Machinery Lubricants, Corrosion Protection for
Glass, Radiation Shielding etc.
Carbon Nanotubes

Introduction

• This fullerene type was discovered by Japanese scientist Iijima Sumio of NEC Corporation's
Fundamental Research Laboratory, Tsukuba Science City in Japan. In 1991 he investigated
material that was extracted from solids.

• discharged under C60 formation conditions.

• Nanotubes can be described as cylindrical fullerenes. They are not very wide, usually just a
few nanometers,

• This unique structure is the secret of their extraordinary macroscopic properties, such as
high tensile strength, high electrical conductivity, high ductility, relative chemical inactivity
and high resistance to heat.

• Nanotubes are characterized as single-walled nanotubes and multi-walled nanotubes.

• A carbon nanotube is a tube-shaped material, made of carbon, having a diameter measuring

on the nanometer scale.

• A nanometer is one-billionth of a meter, or about 10,000 times smaller than a human hair.

• CNT is unique because the bonding between the atoms is very strong and the tubes can
have extreme aspect ratios.

• CNT is a tubular form of carbon and is configurationally equivalent to a two dimensional

graphene sheet rolled into a tube.

• The characteristics of nanotubes can be different depending on how the graphene sheet has
rolled up to form the tube, causing it to act either metallic or as a semiconductor.
 • The graphite layer that makes up the nanotube looks like rolled-up chicken wire with a
continuous, unbroken hexagonal mesh and carbon molecules at the apexes of the hexagons.

Types

• There are many different types of carbon nanotubes, but they are normally categorized as
either single-walled (SWNT) or multi-walled nanotubes (MWNT).

• A single-walled carbon nanotube is just like a regular straw. It has only one layer, or wall.

• Multi-walled carbon nanotubes are a collection of nested tubes of continuously increasing

diameters. They can range from one outer and one inner tube (a double-walled nanotube) to
as many as 100 tubes (walls) or more. Each tube is held at a certain distance from either of
its neighboring tubes by inter-atomic forces.

Applications

• Carbon nanotubes can be used in these application areas:

• Composite material modification / master batches

• Components for electronics

• Chemical industry

• Oil-refining industry

• Building industry

• Coatings – they are versatile coating materials.

• Lacquer and paints

• Ceramics

• Concrete

• Energy – super capacitors as they are not only great conductors, but also have very big
surface area. Also solar cells, fuel cells, Li-ion batteries (for notebooks and mobile phones)
and hydrogen storage.

• Polymer materials – thermoplastic and thermosetting plastic

• Ecology – Photovoltaic technologies, multiuse absorbents, multiuse filters (water

purification)

• Bioengineering – Very exciting and hopeful is the cancer research, drug and gene delivery,
cell tracking and labelling, biosensors ( they could be used for example in medicine, food
technology or military), synthetic implants, receptors in viv

• Their strength and flexibility can be used in controlling other nano-scale structures securing
their important role in the nanotechnology engineering.
 • Hollow and layered structures of CNT provide for large specific surface areas to be used as an
ideal adsorption material for use in air, gas, and water filtration. A lot of research is being
done in replacing activated charcoal with CNT in certain ultra high purity applications.

• Another important use of CNT’s is in structural reinforcement. It can be added to other

materials like rebar in concrete because of its high strength, low weight and flexibility.

• Electrical Conductivity: CNT’s can act as either metallic or semi conducting in their electrical
behavior. The observed conducting behavior of CNT’s is a function of the chirality, degree of
twist and diameter. Because of the conducting nature CNT can be used as transistors,
rectifying diode, interconnects on semi conducting devices.

• The carbon atoms of a single (graphene) sheet of graphite form a planar honeycomb lattice,
in which each atom is connected via a strong chemical bond to three neighboring atoms.
Because of these strong bonds, the basal-plane elastic modulus of graphite is one of the
largest of any known material. For this reason, CNTs are expected to be the ultimate high-
strength fibers.

• SWNTs are stiffer than steel, and are very resistant to damage from physical forces. Pressing
on the tip of a nanotube will cause it to bend, but without damage to the tip. When the
force is removed, the tip returns to its original state. This property makes CNTs very useful as
probe tips for very high-resolution scanning probe microscopy.

Nanowires

Introductions

• A nanowire is a nanostructure, with the diameter of the order of a nanometre (10−9 metres).

• It can also be defined as the ratio of the length to width being greater than 1000.

• Since the early 2000s, nanowires of various inorganic materials have been synthesized and
characterized. The nanowires can be (a)organic, (b) metallic or inorganic (oxides or non-
oxides), (c) mono or polycrystalline.

• Thus, nanowires of single elements (Si, Ge, SiGe, Si / SiGe), oxides (TiO2), nitrides (BN),
carbides (SiC) and chalcogenides 2 (CdSe) have been produced.

• Alternatively, nanowires can be defined as structures that have a thickness or diameter

constrained to tens of nanometers or less and an unconstrained length.

• Method of Synthesis:

• Mainly by top-down or bottom-up approaches. In laboratories most commonly used

techniques are: Suspension, Electrochemical Deposition, vapour deposition, VLS (vapour-
liquid-solid) growth method.
Types

• Many different types of nanowires exist, including

• (1) Superconducting (e.g. Yttrium barium copper oxide- YBCO),

• (2) Metallic (e.g. Ni, Pt, Au, Ag),

• (3) Semiconducting (e.g. silicon nanowires (SiNWs), InP, GaN) and

• (4) Insulating (e.g. SiO2, TiO2).

• (5) Molecular nanowires are composed of repeating molecular units either organic
(e.g. DNA) or inorganic (e.g. Mo6S9−xIx).

• One of the crucial factors in the growth of nanowires is the control of composition, geometry
and crystallinity.

Advantages

• Phonon scattering - Phonon scattering from free surfaces and grain boundaries decreases the
lattice contribution to the thermal conductivity, thereby increasing.

• Lateral elastic relaxation - Lateral elastic relaxation of strain in nanowires enables coherent
interfaces in large lattice misfit heterostructures.

• Elastic compliance - Improved elastic compliance resulting from free surfaces and/or
interfaces with compliant matrix materials.

• Chemical modification of free surfaces - Access to free surfaces permits chemical

modification that may enhance charge mobility while suppressing phonon transport; short
diffusion lengths less grain growth.

• Crystallographic texture control – interface energy driven.

• Quantum confinement – Potential for power factor enhancement, but only for nanowires
with diameters < 5 nm (for Bi2Te3)

Applications

• Electronic devices- Nanowires can be used for MOSFETs (metal–oxide–semiconductor field-

effect transistor). MOS transistors are used widely as fundamental building elements in
today's electronic circuits. Nanowires are promising materials for development of
Microprocessors, prototype sensors and nanobots.

• In Environment: Silver Chloride nanowire can be used as a photocatalyst to decompose

organic waste in polluted water, silver nanowires to kill bacteria in water, nanowire mats to
absorb oil spills.
• Due to the unique one-dimensional structure with remarkable optical properties, the
nanowire also opens new opportunities for realizing high efficiency photovoltaic devices.

• Conducting nanowires offer the possibility of connecting molecular-scale entities in a

molecular computer.

• Single nanowire devices for gas and chemical sensing- Recent developments in the
nanowire synthesis methods now allow for parallel production of single nanowire devices
with useful applications in electrochemistry, photonics, and gas- and bio-sensing.

• Nanowire lasers- They are nano-scaled lasers with potential as optical interconnects and
optical data communication on chip. Nanowire lasers are built from III–V semiconductor
heterostructures, the high refractive index allows for low optical loss in the nanowire core.

• Sensing of proteins and chemicals using semiconductor nanowires- Several examples of the
use of silicon nanowire(SiNW) sensing devices include the ultra sensitive, real-time sensing
of biomarker proteins for cancer, detection of single virus particles, and the detection of
nitro-aromatic explosive materials such as 2,4,6 Tri-nitro-toluene (TNT) in sensitive superior
to these of canines.

• Limitations of sensing with silicon nanowire FET devices- Useful for dramatically enhancing
the sensitivity of cardiac biomarkers (e.g. Troponin) detection directly from serum for the
diagnosis of acute myocardial infarction.

• Nanowire assisted transfer of sensitive TEM samples- For a minimal introduction of stress
and bending to transmission electron microscopy (TEM) samples, when transferring inside
a focused ion beam (FIB), flexible metallic nanowires can be attached to a typically
rigid micromanipulator. This technique is particularly suitable for in situ electron
microscopy sample preparation.