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PH8201 Notes r2017 notes

NanoTechnology And Nanomaterials

NanoTechnology And Nanomaterials

NanoTechnology is deeply explained in this page with Nanomaterials and their properties uses and application.

NANOMATERIALS in Nanotechnology

 Nanoparticles are the particles that have three dimensional nanoscale, the particle is between 1 and 100 nm in each spatial dimension.

A nano meter is a unit of measure equal to one-billionth of a meter, or three to five atoms across.

Nanotechnology is the design, fabrication and use of nanostructured systems, and the growing, assembling of such systems either mechanically, chemically or biologically to form nanoscale architectures, systems and devices.

COMPARISON OF DIFFERENT OBJECTS

  1. Diameter of sun    –        1,393,000 km
  2. Diameter of earth –        1,28,000km
  3. Height of Himalaya mountain –        8,848km
  4. Height of man      –        1.65km
  5. Virus –        20-250nm
  6. Cadmium Sulphide nanoparticle       –        1-10 nm

CLASSIFICATION OF NANOMATERIALS in Nanotechnology

Clusters

A collection of atoms or reactive molecules up to about 50 units.

Colloid

A stable liquid phase containing particles in 1 to 1000 nm range.  A colloidal particle is one such 1 to

1000 nm sized particle.

Nanoparticle

A solid particle in the 1 to 100 nm range that could be non-crystalline, an aggregate of Crystalites, or a single Crystalite.

Nanocrystal

A solid particle that is a single crystal in the nanometer size.

Nanostructured or Nanoscale Material

Any solid materials has a nanometer dimension.

Three dimensions  — >   Particles

Two dimensions  — >   Thin films

One dimension  — >   Thin wire

Quantum Dots

A particle that exhibits a size quantization effect in at least one dimension.

TOP-DOWN AND BOTTOM-UP PROCESS

Top-down Process

In this processes, bulk materials are broken into nano sized particles as shown in

In to-down processes, the building of nanostructures starting with small components like atoms and molecules that are removed from a bulk material so as to obtain desired microstructure.

Bottom-up Processes

In this processes, nano phase materials are produced by building of atom by atom as shown in.

This processes building larger objects from smaller buildings blocks. Nanotechnology seeks to use atoms and molecules as those building blocks. This is the opposite of the top-down approach. Instead of taking material away to make structures, the bottom-up approach selectively adds atoms to create structures.

SYNTHESIS TECHNIQUES in Nanotechnology

Nanomaterials are newly developed materials with grain size at the nanometre range (10-9m)

i.e., in the order of 1 –100 nm. The particle size in a nanomaterial is in the order of nm.

PULSED LASER DEPOSITION

Priniciple

The laser pulse of high intensity and energy is used to evaporate carbon from graphite.

These evaporated carbon atoms are condensed to from nano tubes.

Description

The experimental arrangement of pulsed laser4 deposition is shown in fig.

A quartz tube which contains a graphite target is kept inside a high temperature muffle furnace.

Fig. Pulsed Laser Deposition CNT

This quartz tube is filled with argon gas and it is heated to 1473 K.

A water cooled copper collector is fitted at the other end of the tube.

The target material graphite contains small amount of nickel and cobalt as a catalyst to nucleate the formation of nanotubes.

Working

When an intense pulse of laser beam is incident on the target, it evaporates the carbon from the graphite. The evaporated carbon atoms are swept from the higher temperature argon gas to the colder copper collector.

When the carbon atoms reach the colder copper collector, they condense into nanotubes.

CHEMICAL VAPOUR DEPOSITION

The deposition of nano films from gaseous phase by chemical reaction on high temperature is  known as chemical vapour deposition.

This method is used to prepare nano-powder.

Principle

In this technique, initially the material is heated to gaseous state and then it is deposited on a solid surface under vacuum condition to form nano powder by chemical reaction with the substrate.

Description and Working

The CVD reactor built to perform CVD processes is shown in fig.

Chemical vapour deposition (CVD) involves the flow of a gas with diffused reactants (substances to be deposited in the vapour) over a hot substrate surface.

The gas that carries the reactants is called the carrier gas.

While the gas flows over the hot solid surface, the heat energy increases chemical reactions of the reactants that form film during and after the reactions.

The byproduct of the chemical reactions are then removed.

The thin film of desired composition can thus be formed over the surface of the substrate.

PROPERTIES OF NANOPHASE MATERIALS.

Properties of Nanophase Particles

The mechanical, electrical, chemical, magnetic and structural properties of nanophase materials change with the reduction in the particle size of the material.

PHYSICAL PROPERTIES

Variation of physical properties with geometry

Starting from the bulk, the first effect of reducing the particle size is to create more surface sites. This in turn changes surface pressure and interparticle spacing.

(i) Inter particle spacing decreases with decrease in grain size for metal clusters.

For example in copper, it decrease from 2.52 (cluster size –50A) to 2.23A (Cu dimer) fig.

The change in inter particle spacing and large surface to the volume ratio in particles have a combined effect on material properties.

Therefore, the nanophase materials have very high strength and super hardness.

Because of the cluster of grains, the nanophase materials are mostly free from dislocations and stronger than conventional metals.

Fig. Inter atomic distance in Cun as a function of grain size.

(ii)             Melting point reduces with decrease in cluster size.

The melting point of gold in nanophase (Aun) varies as a function of particle size (fig.)

Fig. Melting point of small Aun particles as a function of size

The melting point decreases from 1200 K to 800 K when the particle size decreases from 300 A to 20 A.

(iii) Ionization potential changes with cluster size of the nanograins.

The electronic bands in metals become narrower when the size is reduced from bulk which changes the value of ionization potential.

Fig. shows the ionization potential and reactivity of Fen clusters as a function of size. Ionisation potentials are higher at small sizes than that for the bulk and show marked fluctuations as a function of size.

Fig. Ionisation potential and reactivity of Fen clusters as a function of size (iv) The large surface to volume ratio, the variations in geometry and the electronic structure have a strong effect on catalytic properties.

As an example, the reactivity of small clusters is found to vary by higher orders of magnitude when the cluster size is changed by only a few atoms.

MAGNETIC PROPERTIES

Nanoparticles of non-magnetic solids also exhibit totally new type of magnetic properties.

(i)                Bulk magnetic moment increases with decrease in co-ordination number

The change in magnetic moment on the nearest coordination number is shown in fig.-0

Fig. Change in magnetic moment on the nearest coordination number

As the coordination number decreases, the magnetic moment increases with the atomic value which means that small particles are more magnetic than the bulk material.

The magnetic moment of iron (Fe) of nanoparticles is 30% more than that of bulk.

At smaller sizes, the clusters become spontaneously magnetic.

(ii) The nano-materials shows variation in their magnetic property when they change from bulk state to cluster (nano-particle) state.

(iii) Non-magnetic materials become magnetic when the cluster size reduces to 80 atoms.

MECHANICAL PROPERTIES

 (i)    In nanophase materials, the elastic strength is low however, its plastic behavior is high.

 (ii) In some nanophase materials, it is noted that there is decrease in hardness when the grain size is less than 10 nm.

However for many nanocrystalline, pure metals (10 nm), the hardness is about 2 to 7 times greater than that of large-grained (>1 μ m) metals.

(iii)Higher hardness and mechanical strength (2-7 times) when grain size reduces from 1 μ m to 10 nm.

(iv)It has very high ductility and superplastic behavior at low temperatures.

APPLICATIONS OF NANOPHASE MATERIALS

Materials Technology

We can synthesis harder metals having hardness 5 times higher than normal metals using nanoparticles.

Stronger, lighter, wear resistant, tougher and flame retardant polymers are synthesized with nanoparticles as fillers.

They are used in replacement of body parts and metals (bio-materials).

We can produce unusual colour paints using nanoparticles since nanoparticles exhibit entirely different optical properties.

Nanophase materials are used in nanoelectronic devices such as nanotransistore, ceramic capacitors for energy storage, noise filters and stabilizers.

The special features of these devices include smaller sizes and reduced power losses.

ZnO thermistors are used in thermal –protection and current-controlling devices.

Information Technology

Nanoparticles are used for data storage.

Quantum electronic devices have started replacing bulk conventional devices.

Nanomaterials are used to produce very tiny permanent magnets of high energy products.

Hence, they are used in high-density magnetic recording.

Magnetic devices made of Cu-Fe alloy are used in RAM, READ / WRITE heads and sensors.

Quantum dots, quantum wells and quantum wires are mainly produced from semiconductor nanomaterials.

Hence, they are used in computer storage (memory) devices.

Biomedicals

Biosensitive nanoparticles are used for tagging of DNA and DNA chips.

Controlled drug delivery is possible using nanotechnology.

Diffusion of medicine through nanoporous polymer reservoir as per the requirement is very useful in controlling the disease.

Nanostructured ceramics readily interact with bone cells and bence finds applications as an implant material.

Energy storage

Since the hydrogen absorbing capability increases with decrese of size of nanoparticles, nanoparticles of Ni, Pd and Pt are useful in hydrogen storage devices.

Metal nanoparticles are very useful in fabrication of ionic batteries.

Optical devices

Nanoparticulate zinc oxide is used to manufacture effective Sunscreens.

Nanoparticles are used in the coatings for eye glasses to protect from scratch or breakage.

Transmission lines

 Nanophase materials are used in the fabrication of signal processing elements such as filters,  delay lines, switches etc.

Nanomicro – Electro Mechanical Systems (Nano MEMS) have direct implications on integrated circuits, optical switches, pressure sensors and mass sensors.

Molecular Nano

Technology (MNT) is aimed to develop robotic machines, called assembler son a molecular scale, molecular-size power sources and batteries.

Underwater nanosensor networks are used to detect the movement of ships in an efficient manner with faster response. They can also detect chemical, biological or radio logical materials in cargo containers.

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