Moungi Bawendi at the Massachusetts Institute of Technology in Cambridge, Louis Brus at Columbia University in New York City and Alexei Ekimov at New York City-based company Nanocrystals Technology will each receive one-third of the 11-million-Swedish-krona (US$1-million) prize.
“It’s an amazing result for the quantum-dot community,” says Mark Green, a physicist at King’s College London. “The theoretical frameworks provided by Brus and Ekimov were made into a reality with Bawendi’s seminal paper in 1993, from which this now-mature science sprung Quantum dots are semiconductor crystals consisting of just a few thousand atoms, which have some properties of single atoms. This allows them to be tuned so they can emit specific wavelengths of light. Very small quantum dots of cadmium selenide, for example, can emit blue light, but bigger crystals of the same compound emit red light. Quantum dots are used in applications that need specific wavelengths of light, from bright television displays to biological imaging.
The names of the winners were leaked a few hours before the official announcement, when a press release was accidentally emailed to Swedish media. At a press conference after the announcement, Bawendi said that he had been “sound asleep”, and therefore unaware of the leak. He was woken by a call from the Nobel committee, and felt “very surprised, sleepy, shocked” and “very honoured” to learn that he had won the prize. “I didn’t think it would be me that would get this prize, because we’re all working together on this,” he said. “There’s still a lot of exciting work to be done in this field.”
Joining the dots
Ekimov was first to report observing size-dependent light effects, in coloured glass doped with copper chloride particles, in 19811. Two years later, Brus described making quantum dots in a solution, while looking at semiconducting particles for solar-energy applications2. “It was Brus who made the link between semiconductors and particle size,” says Green. But “it would have remained a relatively inaccessible and poorly developed materials system until Bawendi developed the chemistry”.
Bawendi discovered a way to make quantum dots in specific sizes, combining inorganic and organometallic techniques for precise control3. The method involved injecting the chemical ingredients into a hot solvent until it became saturated, causing crystals to form suddenly. When the mixture was removed from the heat, the growth of the crystals slowed down. The resulting dots were all of the same size and quality.If you want every atom to count and to be able to do it in a scalable manner, then a chemist’s approach is a very valuable one,” says Christopher Murray, a chemist at University of Pennsylvania in Philadelphia who was a PhD student working with Bawendi at the time and co-author of the 1993 paper. He says he was really happy to hear the news, having woken up oblivious to the controversy over the leak.
He explains that the quantum effects that give the particles their name come from how electrons and their quantum energy levels change when particles get smaller and smaller. As quantum dots reach the nanoscale, the electrons start to be confined by the size of their surroundings. Once that size becomes smaller than the natural volume that an electron can move around in, the electrons respond by changing their energy levels. This in turn changes how those systems interact with light.
Nanotech milestone
For a long time, nobody thought you could ever actually make such small particles. But this year’s laureates succeeded,said Johan Åqvist, chair of the Nobel committee for chemistry at the Royal Swedish Academy of Sciences in Stockholm, during the announcement. This achievement represents an important milestone in nanotechnology.
Quantum dots have now made it into the mainstream, and are used in television displays in a multimillion-dollar industry. When he and Bawendi started their work, Murray says, there was scepticism around whether it was worth funding efforts to control materials on such a small level using chemistry. “It’s nice to see a significant return on that investment, he says.
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