Introduction: The word ‘nano’ has a Greek origin that means dwarf. Nano refers to the 10 -9 power or “one billionth”. When nano
is used as a prefix with science and technology, it constitutes a new emerging field of Physics. Nanoscience is the study of the basic principles of structures at atomic dimensions ranging from 1nm to 100 nm. At the nanoscale, properties at microscopic level become significant such as – “Quantum mechanical and thermodynamic properties”. Nanoscience is becoming an extensive field of research due to the availability of equipment and instruments that are actually able to see and touch the nanoscale and also the future potential in research.
Fig 1: The various molecular dimensional scale
Nanotechnology is the design, characterization, production and application of structures, devices and systems. The shape and size are controlled at the nanometer scale. The National Nanotechnology Initiative (U.S.A.) defines the nanotechnology to be consisting of the following properties:
- Creating and using structures that have novel properties because of their small size.
- Research and technology development at the nanoscale
- Ability to control or manipulate at the atomic scale.
Significance of the Nanoscale
At the nanoscale, the interactions between the atoms exhibit different properties from the bulk material. For example, composites made from particles of nano-size ceramics or metals smaller than 100 nanometers can suddenly become much stronger than predicted by existing materials-science models. The bulk properties of any material are merely the average of all the quantum forces affecting all the atoms.
2 The properties of materials are different at the nanoscale due to the following two reasons:
i) The nanomaterials have a relatively larger surface area as compared to the same mass of material produced in a larger form. As a particle decreases in size, a greater proportion of atoms are found at the surface compared to those inside. For example, a particle of size 30 nm has 5% of its atoms on its surface, at 10 nm 20% of its atoms, and at 3 nm 50% of its atoms
ii) The quantum effects dominate the behavior of matter at the nanoscale. These affect the various
properties of the materials.
Nanoparticles of semiconductors are called quantum dots. The quantum effects at nanoscale, limit the energies at which the electrons and holes exist in the particles. The optical properties of the particle can be tuned depending on its size. The particles may absorb or emit particular wavelengths of light, merely by controlling their size.
Nanoparticles find applications in displays that are cheaper, larger, brighter and more efficient, in ultrahigh performance solar cells , in antibacterial silver coating on injuries, in antireflection coating and for making light based sensors for cancer diagnosis, in computing, communications and consumer electronics, in high quality paints reflective properties are also being manufactured using nanoscale titanium dioxide particles. and even cosmetics
Nanomaterials are those materials which have structured components with at least one dimension less than 100nm. Materials that have one dimension in the nanoscale (and are extended in the other two dimensions) are layers, such as a thin films or surface coatings. Materials that are nanoscale in two dimensions (and extended in one dimension) include nanowires and nanotubes. Materials that are nanoscale in three dimensions are particles,
for example: precipitates, colloids and quantum dots (tiny particles of semiconductor materials). Nanomaterials are hard, are exceptionally strong, are ductile at high temperatures, are chemically very active, are erosion resistant and wear resistance. A number of tools are used to make nanostructures. “Lithography” is an image that is produced by making a pattern on the stone, inking the stone and then pushing the inked stone onto paper. Lithography are classified as:
i) Nanoscale lithography: This technique does not use visible light since the wavelength is about 400nm. Hence, the structures smaller than that are difficult to make directly. George Whitesides, developed the micro imprint lithography in which a pattern is created on the rubber surface and then coated with molecular ink. Inking can then be done on metal, polymer, oxide or any other surface.
ii) Dip Pen Lithography: A nano pen with an atomic force microscope (AFM) tip is needed to write ink lines. This technique is used to create new and complex structures in small volumes
iii) E-beam lithography: In this technique, electrons are used in place of light and finds applications in microelectronics manufacturing.
Richard Smalley , in 1985 first prepared buckminsterfullerene.These are large, closed cage, carbon clusters. Fullerenes are an interesting class of compounds that will be used in future technologies and applications.
They are a class of allotropes which are grapheme sheets rolled into tubes or spheres. Graphene is a one atom thick layer of graphite. Fullerene or bucky balls are C 60 with a cage like structure as shown in Fig. 2. It is the smallest member of this family. The van der Waals diameter of a C 60 molecule is about 1.1 nm. The buckyballs are extremely stable and can withstand very high temperatures and pressures. On doping a buckyball with the right amount of potassium or caesium, a superconductor is created. Bckyballs are a good storage medium for hydrogen fuel because the C 60 molecule can absorb a hydrogen atom for each carbon atom. The buckyballs can deliver drugs directly to the infected regions of the body.They aslo counteract the free radicals in the human body. They are also used to develop stronger polymers and provide an option for silicon chips in computers.
Richard Smalley in 1990, gave the concept that buckyballs can turn into carbon cylinders if their size becomes bigger. However, they were identified by Sumio Lijima and termed ‘nanotubes’.The diameter of a nanotube is a few nanometers and several millimetre in length. The carbon nanotubes have a nanostructure that can have length to diameter ratio greater than 1,000,000. Nanotubes are members of fullerene structural family.
There are two types of nanotubes:
i) Single walled Nanotubes ( SWNT)
ii) Multiwalled Nanotubes ( MWNT)
A SWNT consists of two separate regions with different physical and chemical properties.C-atoms are placed in hexagons and pentagons. SWNTs are also cylindrical and are formed when a graphene sheet is wrapped into a cylinder.It has been shown in Fig.3.They will be used In miniaturizing electronics beyond the micro electro-mechanical scale.
Ordered nanotubes are prepared by the pulse laser vaporization (PLV) of a carbon target in a furnace at 1200°C. A cobalt-nickel catalyst helps the growth of the nanotubes because the catalyst prevents the ends from being capped during synthesis, and about 70-90% of the carbon target can be converted to single-wall nanotubes. A MWNT consists of multiple concentric nanotube cylinders.Their properties are different from SWNT due to the
difference in their structures.
Properties of Carbon Nanotubes
Electronic, molecular and structural properties of carbon nanotubes are determined by the one dimensional structure of the carbon nanotubes. The carbon nanotube reactivity is directly related to the curvature of the tube. A smaller nanotube diameter produces an increased reactivity. The conducting properties of the carbon nanotubes mainly depend on the band gap in their band structures. The optical activity of the chiral nanotubes disappears if the nanotubes become large. The CNTs have a large Young modulus and the nanotubes are very flexible due to their great length.Hence they are ideal for applications in composite materials that need anisotropic
properties.They have light weight and their thermal conductivity is very high.It is more than 10 times of silver.
Applications of Nanotechnology
1.Nanotechnology is finding application in electronic industry where dimensions of nanometer are of great importance. Single electron transistor (SET), spin values and magnetic tunnel junctions (MTJ) are all based on nanotechnology. Spintronic especially is based on nanoscale.
2. Nanotechnology is active in producing effective fibre optic structures which allow high speed, high reliability passage of enormous densities of signal. A single fibre network can carry tens of thousands of data streams and voice conversations.
3. Nanotechnology is helping in medical diagnostics by providing faster, cheaper and portable diagnostic equipments
4. Nanotechnology will also provide methods to utilize our energy resources and offer new alternative fuels.
5. New efficient water purification techniques would be provided by developing nanotechnology.
6.The computer size and its power would be controlled by nanotechnology
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