Nano technology is a diverse form of science that incorporates the study and development of structures which are at the atomic and molecular level. The potential of Nano Technology has opened up a world of possibilities in every field. This article gives an insight on the detailed description of what is Nano Technology, Nano elements in the nature, types of synthesis of Nano materials, applications, advantages and disadvantages.
What is Nano Technology
Nano Technology was invented by Richard Feynman who discovered the idea of building things at an atomic and molecular level. “Nano” is evolved from the Greek word meaning “dwarf”. Nano is used as the prefix for units of 10-9.
Nano Technology is the controlled study of matter which is manipulated and created at atomic and molecular scale. They are technically produced structures that evolve from processes that exhibit the control of the physical and chemical attributes of atoms and molecules.
Fig. 1 – Introduction to Nano Technology
They are used in wide range of applications such as medicine, electronics and energy production. Nano technology has revolutionized our ability to see the minute structures which are as small as one-billionth of a meter.
With the advancement of Nano Technology, toxicity and environmental impact on global economy becomes the biggest concern and perhaps the major challenge that lies ahead.
Nano Elements in the Nature
In the history of human evolution, Nano technology has transformed every aspect of our lives. Nano particles which are the building blocks of Nano technology are present everywhere. Nano particles are of two types:
- Naturally Occurring Nano Particles
- Synthetic (Manmade) Nano Particles
Naturally occurring Nano Particles
They are found in fine sand, dust, volcanic ash and viruses.
Synthetic (Man-made) Nano Particles
They are found in cosmetics, sports items, plastics, gold and silver particles, textiles etc.
Man-made Nano particles are further divided into two categories:
- Incidental Nano Particles
- Engineered Nano Particles
Incidental Nano Particles
Incidental Nano Particles emerge from diesel engines, smoke and fire.
The size and shape of these Nano particles cannot be controlled and hence it is less advantageous.
Engineered Nano Particles
Engineered Nano particles include Nano tubes, Nano wires, quantum dots, etc.
The size and shape of these Nano particles can be controlled and it’s more advantageous.
Fig. 2 – Natural and Man-made Nano Particles
Types of Nano Fabrication
The main aim of Nano fabrication is to synthesize ultra-fine and Nano sized materials which is an important aspect in the development of innovative products. The techniques used to fabricate Nano sized structures are classified as:
- Top Down Approach
- Bottom Up Approach
Top Down Approach of Fabrication in Nano Technology
This is perceived as an approach where the building blocks are removed from the substrate to form Nano structures. The Nano structures are synthesized by etching out the substrate thus miniaturizing the existing technologies.
This method is best suited for producing structures at the scale of micrometer. Top down approach is used in the fabrication of integrated circuits and severe plastic deformation.
The advantage of this approach is the ability to include the required entity or a feature in an exact location as the process is externally controlled.
Bottom Up Approach of Fabrication in Nano Technology
This is perceived as an approach where building blocks are added onto the substrates to form Nano structures. In this process the Nano structures are synthesized onto the substrate by assembling atoms together which forms new substrates. They further stack on each other resulting in the production of Nano structures.
Bottom-up approach is used in the formation of quantum dots where the Nano particles are formed from colloidal dispersion. This method is widely used in chemical synthesis. It involves building more complex molecular devices atom by atom.
They are best suited for assembling and establishing structures which are of short range order at the scale of Nano Meter (nm). Fabrication in Bottom Up approach is less expensive as compared to Top Down approach.
Fig. 3 – Top Down and Bottom Up Approach in Nano Synthesis
Methods of Nano Synthesis Using Top Down Approach
Different methods use Top Down approach for Nano synthesis and fabrication. The methods include:
- High Energy Ball Milling
- Photo Lithography
- Gas Condensation
High Energy Ball Milling
A ball mill comprises of a hollow cylindrical enclosure rotating on its axis. It is filled partially with balls which are made of steel, ceramic or rubber. As the shell rotates the balls rise up and drop down on the metal precursor so that the particles are ground.
The ball milling process is similar to grinding machine where in a powder mixture is exposed to high energy collision from the balls which produces finer oxide particles and this method is widely used in mechanical alloying. The exposed powder particles are flattened and is followed by fracturing and cold welding procedure where the particle size is reduced to micrometer range.
In the final stage of mechanical alloying the particles are more refined, homogenous and the size is considerably reduced and an alloy is formed.
Fig. 4 – High Energy Ball Milling Process
The word “Lithography” is derived from a Greek word where “Lithos” means stone and “graphy” means to write. In ancient times paper was pressed against stone to transfer the pattern.
A pattern was drawn on the stone and colored using printing ink. When this patterned stone was pressed against the paper the design was successfully transferred. Several lithography techniques were explored using these fundamentals.
Hence, Lithography can be defined as the patterning of a required design on the substrate using different medium (UV light, X-ray, and e-beam) is known as lithography.
Fig. 5 – Process of Photo Lithography
In this method, positive photo resists is exposed to UV light which changes the chemical structure of the resist. The exposed area is dissolved in a developer solution. Negative resists behave in an exactly opposite manner.
The areas that are exposed to UV light does not get dissolved but gets polymerized. In the subsequent stage of synthesis, mask alignment and etching are done using chemicals like acids.
Once this is completed, the resists are further subjected to stripping leaving behind the desired pattern. This technique is applied in designing integrated circuits. Other types of Lithography includes Electron beam (e-beam) Lithography and X-ray Lithography.
Gas condensation uses a vacuum chamber that consists of a heating element, the feed (metal that is to be reduced), deposit chamber and vacuum hardware. Inert gas (He, Xe, Ar) at high pressure is used in this process to initiate particle formation.
Initial stage of the process includes melting of the feed (metal) which is imported onto the heating element. The temperature rises which is slightly below the boiling point so that sufficient vapor pressure is achieved.
Fig. 6 – Gas Condensation
The evaporated metal moves away from the heated element by the gas flowing through the chamber. The gas cools down the metal vapor and the Nano particles are formed.
These particles are still in liquid state and further collision takes place when it is subjected to controlled environment so that the particles formed have specific shape and texture.
They are further cooled down to attain a solid state. The process completes with a coating of a material on to the particles which prevents interaction with other Nano particles as they are very reactive.
Methods of Nano Synthesis Using Bottom Up Approach
Different methods use Bottom-up approach for Nano synthesis and fabrication. The methods include:
- Sol Gel Process
- Chemical Vapor Deposition (CVD)
Sol Gel Process
This is a method used for the production of solid materials from small molecules. The ‘Sol’ is a liquid suspension of solid particles whose size ranges from 1nm to 1 micron. A di-phase material in which the solids encapsulate the solvent is called ‘gel’.
In this process, a stable colloidal solution called sol is formed which is the result of rapid hydrolysis of the metal precursor. This is followed by condensation process which results in the formation of three dimensional gels.
Fig. 7 – Sol Gel Process
Produced gels are subjected to further drying or evaporation and the product is converted to xerogel or aerogel based on the mode of evaporation used.
This is one of the well-established approach used in the synthesis of metal oxide or mixed oxide composites.
Chemical Vapor Deposition (CVD)
CVD process is typically carried out under vacuum to produce high quality, high performance solid materials. The substrate is exposed to one or more volatile precursors which reacts or/and decompose to produce thin film on the substrate, producing volatile byproducts.
Fig. 8 – CVD Process
These unwanted deposits on the substrates are removed by gas flow through the gas chamber. CVD deposits are mainly used in micro fabrication.
Applications of Nano Technology
Nano technology has considerably revolutionized each and every industry. It is rapidly growing and finds its applications in diverse fields. Some of the applications of Nano Technology are listed below:
- Medicine – Nano particles are engineered to treat the target cells. They are also used to deliver drugs, heat and light to specific cells, mainly cancer and tumor cells.
- Electronics– Nano technology has reduced the size of transistors used in Integrated circuits. They are also used in increasing the density of memory chips, improving display screens on electronic devices.
- Environment– Nano technology has helped us in cleaning the existing pollution. Recent research has shown that iron Nano particles effectively clean up the organic solvents that are polluting the water.
- Energy– Nano technology is used in increasing the electricity generated by windmills, used in the production of solar cells and paper batteries which are cost effective.
- Consumer products– From clothing to skin lotions, Nano technology has found its way into textile and cosmetics industries. Nano particles are used in various skin care products and fabrics.
- Sports equipment’s– Nano technology is used in the manufacturing of sports equipment’s like tennis/ badminton rackets and bicycles as it reduces the weight substantially and efficiency is increased.
Fig. 9 – Applications of Nano Technology
Advantages of Nano Technology
The advantages of Nano technology are as follows:
- Nano computers are faster and million times smaller.
- Regulates existing pollution.
- Production of solar cells and paper batteries.
- It is a boon to medical field in treating diseases like cancer.
- Manufacturing of sports equipment’s.
- Electronics industry is benefited by Nano technology in creating devices which are smaller in size.
- In agriculture, Nano technology will minimize the usage of chemical fertilizers.
Disadvantages of Nano Technology
The disadvantages of Nano technology are as follows:
- Initial investment cost is high.
- It is impossible to revert any damage done at the molecular level.
- Toxic materials are released in the atmosphere which causes serious health hazards.
- Loss of jobs in every sector.
- Misuse of technology by terrorists, irresponsible users may lead to more security issues.
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