SIGNIFICANCE OF QUANTUM DOTS IN NANOTECHNOLOGY
Alexei I. Ekimov, Louis E. Brus, and Moungi G. Bawendi have been awarded the 2023 Nobel Prize for chemistry “for the discovery and synthesis of quantum dots”.
What is a quantum dot?
- A quantum dot is a really small assembly of atoms (just a few thousand) around a few nanometres wide.
- The ‘quantum’ in its name comes from the fact that the electrons in these atoms have very little space to move around.
- Quantum dots have also been called ‘artificial atoms’ because the dot as a whole behaves like an atom in some circumstances.
Why are they of interest?
- There are two broad types of materials: atomic and bulk.
- Atomic refers to individual atoms and their specific properties.
- Bulk refers to large assemblies of atoms and molecules.
- Quantum dots lie somewhere in between and behave in ways that neither atoms nor bulk materials do.
- The properties of a quantum dot change based on how big it is.
- Just by tweaking its size, scientists can change their melting point or how readily it participates in a chemical reaction.
- When light is shined on a quantum dot, it absorbs and then re-emits it at a different frequency.
- Smaller dots emit bluer light and larger dots, redder light.
- This happens because light shone on the dot energises some electrons to jump from one energy level to a higher one.
- So, quantum dots can be easily adapted for a variety of applications including surgical oncology, advanced electronics, and quantum computing.
What did the Nobel laureates do?
- Alexei Ekimov added different amounts of copper chloride to a glass before heating it to different temperatures for different durations.
- They found that the glass’s colour changed depending on the size of the copper chloride nanocrystals.
- In 1983, a group led by Louis Brus in the U.S. succeeded in making quantum dots in a liquid.
- Moungi Bawendi at the Massachusetts Institute of Technology achieved this with the hot-injection method.
- A reagent is injected into a carefully chosen solvent (with a high boiling point) until it is saturated.
- It is heated until the growth temperature, that is, when the reagent’s atoms clump together to form nanocrystals in the solution.
What are quantum dots’ applications?
- An array of quantum dots can be a TV screen by receiving electric signals and emitting light of different colours.
- Scientists can control the path of a chemical reaction by placing some quantum dots in the mix and making them release electrons by shining light on them.
- The dot can operate like a semiconductor.
- Solar cells made with quantum dots are expected to have a thermodynamic efficiency as high as 66%.
- A quantum dot can also highlight a tumour that a surgeon needs to remove.
- It can hasten chemical reactions that extract hydrogen from water.
- It can act as a multiplexer in telecommunications.
NEW TOOLS TO FATHOM THE WORLD OF ELECTRONS
The 2023 Nobel Prize for physics was awarded to Anne L’Huillier, Pierre Agostini, and Ferenc Krausz “for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter”.
What is an attosecond?
- An attosecond is one quintillionth of a second, or 10^-18 seconds.
- This is the timescale at which the properties of an electron change.
What is attosecond science?
- Attosecond science deals with the production of extremely short light pulses and using them to study superfast processes.
What is the physics of producing an attosecond pulse?
- Anne L’Huillier and her colleagues in Paris passed a beam of infrared light through a noble gas.
- They found that the gas emitted light whose frequency was a high multiple of the beam’s frequency.
- This phenomenon is called high-harmonic generation, and the emitted waves are said to be overtones of the original.
- By increasing the frequency of the original beam, the intensity of the emitted light dropped sharply, then stayed constant for a range, and then dropped again.
- A beam of light consists of oscillating electric and magnetic fields.
- ‘Oscillating’ means that at a given point, the field’s strength alternately increases and decreases.
- So an electron at this point would be imparted some energy and then have it taken away.
- when energy is imparted, the electron would come loose from an atom, and when it is taken away, the electron and the atom would recombine, releasing some excess energy.
- This energy is the light re-emitted by the gas.
How is an attosecond pulse produced?
- When the infrared beam strikes the noble gas atoms, it produces multiple overtones.
- If the peak of one overtone merges with the peak of another, they undergo constructive interference and produce a larger peak.
- When the peak of one overtone merges with the trough of another, however, they undergo destructive interference, ‘cancelling’ themselves out.
- By combining a large number of overtones in this way, physicists could fine-tune a setup to produce light pulses for a few hundred attoseconds.
What are the applications of attophysics?
- Pocket-sized gizmos to study electrons.
- Femtochemistry allow us to finely manipulate chemical reactions.
- To understand mechanisms governed by electrons, attosecond physics is necessary
HOW WAS mRNA RESEARCH USED TO FIGHT COVID?
- On October 2, Nobel Prize in Physiology or Medicine was awarded to Katalin Karikó and Drew Weissman.
- They were awarded the prize for their “discoveries concerning nucleoside base modifications that enabled the development of effective mRNA vaccines against COVID-19”.
What are mRNA vaccines?
- mRNA, which stands for messenger RNA, is a form of nucleic acid which carries genetic information.
- Like other vaccines, the mRNA vaccine also attempts to activate the immune system to produce antibodies that help counter an infection from a live virus.
- However, while most vaccines use weakened or dead bacteria or viruses to evoke a response from the immune system, mRNA vaccines only introduce a piece of the genetic material that corresponds to a viral protein.
- This is usually a protein found on the membrane of the virus called spike protein.
- Therefore, the mRNA vaccine does not expose individuals to the virus itself.
How are these vaccines different?
- A piece of DNA must be converted into RNA for a cell to be able to manufacture the spike protein.
- To preserve its integrity, the mRNA needs to be wrapped in a layer of oily lipids, or fat cells.
- A challenge with mRNA vaccines is that they need to be frozen from -90 degree Celsius to -50 degree Celsius.
- They can be stored for up to two weeks in commercial freezers and need to be thawed at 2 degrees Celsius to 8 degrees Celsius at which they can remain for a month.
- But a major advantage of mRNA and DNA vaccines is that because they only need the genetic code, it is possible to update vaccines to emerging variants and use them for a variety of diseases.
- Viral vector vaccines, like Covishield, carry DNA wrapped in another virus, but mRNA are only a sheet of instructions to make spike proteins wrapped in a lipid (or a fat molecule) to keep it stable.
- A major advantage of mRNA vaccines is that because they only need the genetic code, it is possible to quickly update vaccines to emerging variants