On Wednesday, October 4, the Nobel Committee confirmed that it had awarded the Nobel Prize in Chemistry to Moungi Bawendi (Massachusetts Institute of Technology), Louis Brus (Columbia University) and Alexei Ekimov (Nanocrystals Technology Inc.) for the development of quantum dots. The names of the winners were leaked to the Swedish press following a "blunder" on the part of the committee, which had mistakenly sent a press release to certain Swedish media outlets earlier that morning.
Discovered in the early 1980s, quantum dots have since been used in many industrial sectors. On television screens, they facilitate the full range adjustment of diode blue light, typically enhancing color richness. They are also used in optoelectronics (thermal cameras) as infrared light detectors in particular, at a lower cost than microelectronics techniques. In biology, they can be attached to proteins or markers, aiding in pinpointing their presence in small, highly specific quantities. Some people also dream of using quantum dots as future processors for quantum computers. "We've been waiting a long time for this award. It highlights the founders of a field that is still very active," noted Thomas Pons, an Inserm physicist at ESPCI-Paris-PSL, who studies neuronal activity using these nanocrystals.
Following this year's Nobel Prize in Physics, the chemistry prize also acknowledges the significance of electrons. This time, the laureates haven't tried to capture their lightning-fast movement around nuclei with attosecond precision. Instead, they've managed to harness and confine electrons within materials, enabling them to generate various colors on demand.
What they have in common is the development of a very small component, just a few nanometers in size, or one billionth of a meter. It is 10,000 times smaller than the diameter of a human hair...
This component, originally made of cadmium sulfate or selenide, but which can also contain gallium, indium, phosphorus or arsenic, is like a mini-crystal in which electrons are trapped. This confinement gives them their quantum character. While within the same massive material, they could move freely with any energy, within this context, their energy is "quantized". It cannot take on any value. It's like pushing a boulder up a slope: you can't just push it, you have to push it up a series of steps. Electrons are no longer free but can jump from one level of a ladder to another.
The tighter the confinement, i.e., the smaller the crystal, the further apart the levels of the ladder become and the more violet the light emitted will be after a laser has exited the box. Varying the dimensions therefore changes the colors emitted. It's exactly as if the electrons were enclosed in an artificial atom, even though the object itself is made up of several hundred atoms.
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