Small Is Versatile

Nanomaterials herald a society 
where size will not matter, says Biplab Das 

Recall the scene from the movie Back to the Future, where manic scientist Doc Brown's hover car was energised by the "cosmic power" of the sun in a device no bigger than a tea kettle. This raised the question: how small could machines be? 

That sort of Hollywood creation does not seem outlandish if nanotechnology's promises are to be believed. Nanomaterials are the backbone of nanotechnology. This fascinating subject was recently described by Dr. Dipankar Chakraborty, Mahendralal Sarkar Professor of Physics at the Indian Association for the Cultivation of Science (IACS). 

Speaking on 'The Wonderful World of Nanomaterials' at the 11th annual general meeting of the West Bengal Academy of Science held at the Indian Institute of Chemical Biology, Prof. Chakraborty said, "Crystalline nanomaterials have occupied the centrestage of materials research for the last decade or so." A nano-metre is a billionth of a metre, about the size of two large atoms, and a hundred of them add up to about the size of a virus. 

Nanomaterials aren't a new phenomenon. "Long before the present spurt of research in nanoparticles, Michael Faraday conceptualised that solid materials might be ground to yield minute grains," said Prof. Chakraborty. 

But the ongoing focus on nanoparticles has its roots in a landmark lecture by legendary physicist Richard Feynman at the American Physical Society in 1959. "At that meeting Feynman speculated on the effects of manipulating miniscule bits of condensed matter," said Prof. Chakraborty. 

This was followed by a seminal paper by him in Engineering and Science in 1960. In that paper, wrote Feynman, "There is plenty of room at the bottom. The principles of physics, as far as I can see, do not speak against the possibility of manoeuvring things atom by atom. The problems of chemistry and biology can be greatly helped if our ability to see what we are doing and to do things on an atomic level, is ultimately developed, which I think cannot be avoided." 

Theoretical support came immediately for Feynman's view. "The same year, Japanese physicist R. Kubo propounded a model that depicted quantum mechanical behaviour of tiny clusters of atoms in confined volumes," Prof. Chakraborty said. "But research into nanomaterials really took off only in 1981 when German physicist H. Gilter synthesised nanomaterials in a specially built inert gas chamber." 

Among the nanoparticles synthesised so far is titanium dioxide (TiO₂). Nanoparticles of TiO₂ might be used in the paint industry to manipulate the contrast of colours, said Prof. Chakraborty. They also have tremendous potential in ceramics. 

The fun starts for nano-physicists only below 50 nanometre (nm). Worse, nanomaterials with a diametre of one to 20 nm have a tendency to catch fire. "To avoid danger, their surface has to be carefully monitored," said Prof. Chakraborty, "But it is fascinating too." 

Semiconductors can be greatly improved by nanomaterials. "The presence of nanomaterials increases the number of free electrons available in the conduction zone of a conductor, thereby enhancing its conductivity," Prof. Chakraborty pointed out. 

According to Prof. Chakraborty, another key aspect of nanotechnology is an exotic molecule called carbon nanotube. This structure, discovered by a group of Japanese scientists, is a close chemical cousin of the buckyball. But, while buckyball is a football-shaped molecule of 60 carbon atoms, nanotubes are long pipes of a rolled up sheet of graphite. "Nanotubes are good conductors of electricity, which may give them enormous scope for applications in computers," said Prof. Chakraborty. 

In telecommunications, speech is converted into electrical signals and then electrical signals into optical signals, which are again modulated into electrical signals and then into perceptible speech. But with nanomaterials, the field of photonics can be revolutionised. "By randomly dispersing nonoparticles in a glass medium, the quality of optical fibre can be enhanced so much so that it would write off the role of electrical signals in telecommunication," Prof. Chakraborty observed. 

In the IACS lab, a research team led by Prof. Chakraborty discovered the gas sensing property of nanomaterials. "Having a large surface area, nanomaterials are highly sensitive to humidity changes and the presence of harmful gases like carbon monoxide and nitrogen oxides," Prof. Chakraborty said. This property of nanomaterials could be exploited in devices that monitor the weather or the level of pollution in the atmosphere. 

Solar cells are used to harness energy from solar radiation. "After incorporating nanomaterials, solar cells can tap a wide range of solar radiations, even ultraviolet radiation," Prof. Chakraborty announced. 

A couple of years ago, a paper published in Nature showed that material physicists produced silver nanowire using DNA as a template. Nanowires on this scale will be of great use in micro-electronic devices. Tiny submarines are already being used to cruise through the body's circulatory system, and a research team is preparing to deliver a gene via one such device. 

Though nanotechnology is still in embryonic stage, it provides hope of a society where size will not matter.