Significance of quantum dots in nanotechnology

Why in the News?

The Nobel Prize for chemistry 2023 was awarded to Alexei I. Ekimov, Louis E. Brus, and Moungi G. Bawendi “for the discovery and synthesis of quantum dots”.

What is a quantum dot?

1. It is a small assembly of atoms around a few nanometres wide.
2. The small assembly of atoms gives very little space to the electrons in these atoms to move around, which leads it to displays the effects of quantum mechanics.
3. Quantum dots are also called ‘artificial atoms’ as the dot as a whole behaves like an atom in some circumstances.

Why are they of interest?

1. There are two broad types of materials:
   1. Atomic- it refers to individual atoms and their specific properties.
   2. Bulk- it refers to large assemblies of atoms and molecules.
2. Quantum dots behave in ways that neither atoms nor bulk materials do.
3. A distinguishable behaviour of quantum dots is that the properties of a quantum dot change based on its size.
4. Also, when light is shined on a quantum dot, it absorbs and then re-emits it at a different frequency.
   1. Smaller dots emit bluer light
   2. Larger dots, redder light.

Work of the Awardees:

1. In 1980s, Louis Brus and Alexei Ekimov succeeded independently creating quantum dots, which are nanoparticles so tiny that quantum effects determine their characteristics.
2. In 1993, laureate Moungi Bawendi revolutionised the methods for manufacturing quantum dots, making their quality extremely high – a vital prerequisite for their use in today’s nanotechnology.
3. Usually, every element exhibits specific properties which will be same regardless of its size. This form one of the fundamental facts of chemistry.

• For instance, a piece of pure gold, whether it is a large 100-gram piece or a small 10 milligram one, has exactly the same properties.

4. However, very small particles, in the nanoscale range (1 to 100 billionth of a metre) behave slightly differently from larger particles of the same element. 
5. Alexei Ekimov was the first to notice this deviant behaviour in Copper Chloride nanoparticles around 1980, and manufacture these nanoparticles to show this change in behaviour.
6. Louis Brus, an American scientist working independently, discovered similar behaviour in Cadmium Sulphide nanoparticles.
7. The deviant behaviour of small nanoparticles arises because of the emergence of quantum effects.
8. The quantum theory explains that, usually, electrons move around in a large empty space, relatively, outside the nucleus of the atom but when the size of the particles is reduced drastically, electrons in the atoms find themselves increasingly squeezed giving rise to the strange quantum effects.
9. Such strange effects and special properties were found in nanoparticles and hence were called quantum dots.

What are quantum dots’ applications?

1. Surgical oncology
2. Advanced electronics including semiconductors.
3. Quantum computing.
4. Solar cells can be made as quantum dots as they have a thermodynamic efficiency as high as 66%.
5. Multiplexer in telecommunications.
6. Hasten chemical reactions that extract hydrogen from water