Big Little Matter

Imagine your house equipped with a smart window — one that will allow only light and not heat to enter in the blazing summer months.

Written by L RAMAKRISHNAN | New Delhi | Published: October 7, 2012 9:36 pm

Imagine your house equipped with a smart window — one that will allow only light and not heat to enter in the blazing summer months.

Imagine your house equipped with a smart window — one that will allow only light and not heat to enter in the blazing summer months. Or the ability to “tune” quantum dots,which might just change the core of computing in the future. Two Indian scientists are working in these exciting fields and have been recognised (September/October,2012) in their annual “35 Innovators Under 35” honour roll. The innovators,four in all from Inby Massachusetts Institute of Technology (MIT)’s Technology Review dia,work in various field,but have one thing in common,say the editors of the magazine,“their work is likely to be influential for a very long time.”

Sarbajit Banerjee,33

When water boils into steam or freezes into ice,it undergoes a phase transition,meaning the change of a substance from one phase to another. Food scientists,for example,are using the mechanism of phase transitions to study the nature of ice formation,and the behaviour of milk fat at low temperatures to improve the making of ice cream. Substances can show altered physical properties at different temperatures,such as a variation in structure while interacting with external agents such as light or electricity.

Sarbajit Banerjee,an associate professor of chemistry at the University at Buffalo,US,while researching phase transitions hit upon a novel innovation,which has potential applications in making smart windows — one that can be tuned to “switch off” the sun’s heat in summer and “switch it on” in winter by the flick of a button.

Banerjee,who hails from Kolkata,and studied chemistry at St Stephen’s College,Delhi,earned his doctorate at the State University of New York at Stony Brook researching materials chemistry and nanoscience,later shifting focus to solid-state chemistry and the science of thin films.

His material of choice was vanadium oxide that exhibits an interesting property. At 67 degrees celsius,its structure changes and it no longer reflects infrared light,but allows only visible light to pass through. Blocking infrared light essentially means blocking heat,and allowing only sunlight to enter. Banerjee then altered the very structure of the material at the microscopic level. He fabricated the material as long thin nanowires — no easy task,it took him five years — and found that the phenomenon occurs at room temperature.

This temperature falls further if tungsten (the material in light bulbs) is artificially added. Banerjee also discovered that vanadium oxide blocks out heat at a range of temperatures if an electric current is sent through it — the basis of the switching effect. “Practical utilisation of these materials will significantly decrease air-conditioning costs while also allowing buildings to benefit from natural lighting,” says Banerjee.

His USP is mastering the technique of fabricating a coating that does not degrade. “Our major breakthrough was to fabricate materials that can withstand this cycle (blocking and unblocking) thousands of times without degradation and that allows precise control over switching temperatures since the windows you’ll need in Delhi will be quite different from those in Srinagar,” says Banerjee.

He is already working with manufacturers to commercialise the technology. He says,“We expect the first commercial products to be available within two-three years.” The possibilities for Banerjee and his “novel compounds” are endless. He confesses that an invisibility cloak working on the same principle might not be too distant a reality. Harry Potter fans are you listening?

Such hi-tech work leaves him with no time for other pursuits. “Science is a jealous mistress. I do not get much time outside the lab,” says the scientist.

Prashant Jain,30

Tiny particles that have diameters ranging from two to 10 nanometres (one nanometre is a millionth of a millimetre) of a semiconductor material are called quantum dots. These nanoparticles,owing to their size,display properties that are different from the bulk material.

The study of these properties,electrical and optical,is an exciting field in physics that has engaged scientists worldwide. Since the behaviour of quantum dots is governed by the size,meaning diameter,of the particle,the interaction with radiation results in the emission of photons (light particles) of different energies,  that is perceived by the human eye as light of a particular colour.

On an industrial scale,the particle size can be customised to make it emit a particular colour of light in the visible spectrum when exposed to ultraviolet radiation (see photo) that we can see,or into the ultraviolet and infra-red regions,which we cannot see.

This ability to “tune” a quantum dot has potentially many applications from making better displays (for TVs,computers),or as drug tracers in medical diagnostics that could replace radioactive tracers. Tuning coupled with a radical new innovation could result in these dots forming the core component of future computing devices.

The innovator is Prashant Jain,assistant professor of chemistry at the University of Illinois-Urbana Champaign (UIUC). For the Mumbai-born Jain,it is another triumph in a promising scientific career. He trained at the University Institute of Chemical Technology (UICT),Mumbai,to be a chemical engineer,only to realise that his real interest was in atomic and molecular phenomena. “I found engineering a bit unsatisfying. My passion had always been to look at the world at the molecular and atomic levels. I always wanted to understand something that no one had understood before. Or to make something work that no one before me had,” says Jain.

Jain went on to Georgia Institute of Technology for his doctorate in chemical physics where he examined optical properties of ultra-small particles of gold and silver. This was followed by stints at Harvard University and University of California Berkeley,which laid the foundation for the latest accomplishment. He then dropped anchor at UIUC,the hub of material science with a roster of 20 Nobel laureates.

Taking off from tuning a nanoparticle,Jain and his team found that by artificially adding electrons to that quantum dot,it could interact strongly with light. The nature of the interaction with light is determined by the number of “charges” (each electron carries a charge) and not just the size. So,by adding or removing charges on a quantum dot of a certain size,it can be made to “switch on” its capacity to absorb light,or it can be “switched off”. “We had turned the quantum dot into the smallest possible optical switch,a switch that can be controlled by voltage or electrical signals,” says Jain.

Which means,these quantum dots can act as “switches” for light transport,forming the basis of photonics,an emerging field in physics,where circuits and computers would function by transporting light or an “optical current”. Currently they need wires or pathways on printed circuit boards that transport electrons (electrical current),which travels much slower than light and generates a lot of heat. This paradigm shift was met with resistance initially and it took several experiments to convince the naysayers. Jain’s next move is to develop an optical transistor,before thinking of commercial possibilities.

Jain collaborates with many scientists from home. “I do not think science needs to be constrained or defined by national boundaries. The problems science can solve are global in nature,” he says. One such problem is clean energy. He is working at improving an artificial system that mimics photosynthesis,which could generate hydrogen to power our future.

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