Quantum dots are making waves in the world of TVs and displays, but what exactly are they? Is this another misuse of the word “quantum” by marketers, or are these points as amazing as they say?
The artificial atom
Quantum dots are particles of semiconductor material only a few nanometers in size. Also called “artificial atoms” (although they are much larger than an atom), these points act similarly to atoms in their relationship to electrons. They are so small that their electrons are “trapped” and behave in the same way as atoms. When UV light hits a quantum dot, its electrons transition to a higher energy state. When the electrons fall back to their base level, the energy difference between the two states is released as light.
They are called “quantum dots” for two reasons. First, they exhibit quantum properties through the way they confine electrons within them. Quantum effects are those subatomic laws of physics that scientists are still trying to fully understand, but we can already apply them in devices like quantum computers.
They are called points because they are so small that they are practically zero-dimensional. In other words, they are a single point with no width, length, or height. Well, okay, they’re a few dozen atoms in diameter, but they’re so close to being zero-dimensional points that the wacky laws of quantum mechanics kick in.
Why are quantum dots so useful?
Quantum dots behave like atoms that have been excited, but they differ in one fundamental respect. The light you get from an atom or quantum dot is equal to the amount of energy absorbed and released, which determines the wavelength and therefore the color of the light. However, one type of atom (eg iron or sodium) will always emit the same color wavelength.
Quantum dots, on the other hand, can all be made from the same semiconductor material, but produce different wavelengths depending on their size. The bigger the dot, the longer the wavelength, and vice versa. Thus, the large dots tend towards the red end of the spectrum and the small towards the blue end.
This attribute of quantum dots means you can precisely control the emission of colored light to achieve vivid and accurate colors.
Quantum dots have a precise structure because they are crystals. The silicon wafers from which our chips are made are also crystals that organize themselves into atomic patterns. This is why we can fabricate quantum dots with precise structures at the nanoscale. If we were to build them atom by atom, they wouldn’t be very practical!
They can be made by beaming atoms at a substrate to build crystals, by beaming ions (free electrons) at your semiconductor substrate, or by using X-rays. Quantum dots can also be created by using X-rays. Quantum dots can also be created using chemical and even biological processes. However, research on biological manufacturing is still in its infancy.
Where are quantum dots used?
Outside of the QD-OLED and QLED displays that most people are familiar with, there are many applications for these invisible dots in many different technologies.
Solar panels are a major potential application of quantum dots. Current silicon-based solar cells are already quite efficient at capturing energy from light, but because quantum dots can be ‘tuned’ to absorb light from various parts of the electromagnetic spectrum, they could give rise to solar panels. much more efficient. Not only would these panels be more efficient, but they would also be cheaper to produce, since the process of making the necessary quantum dots is relatively simple.
In theory, it is possible to make a solar cell with pure quantum dots, but these can also be used in hybrid solar cells. Increase the efficiency of other solar energy technologies.
Quantum dots can be used in photon detectors, have exciting potential in biomedicine, and could even make it possible to make much cheaper and more efficient light-emitting diodes.
An interesting application of quantum dots is in cancer treatment, where the dots are engineered to accumulate in specifically targeted organs to release anti-cancer drugs as well as advanced imaging. They may even play a role in the early diagnosis of tumours.
Quantum dots could also hold the key to photonic computing, as electrical circuits become so small that quantum effects make it impossible for electrons to pass through. Quantum dots could solve many of the problems still facing photonic computing.
The quantum defies the imagination
Richard Feynman, the famous American physicist, often said something like “If you think you understand quantum mechanics, you don’t understand it”. Albert Einstein is also known for not venturing into it. So we’re pretty comfortable admitting that we don’t really understand quantum dots.
What we do know is that they are very versatile and will enable amazing technological innovations, beyond making better looking computer screens. So the next time you marvel at the vividness of your QLED TV, think for a moment about the incredible subatomic magic that happens so you can get a better picture, and how, one day, quantum dots could perform important functions in your body and in the world.