Quantum Dots - An Introduction to New World

      Could you think that you can control the atoms by your own by controlling their motions, vibrations, shutting them on or off and assigning them different colours? Now, the answer will be YES. This can be made possible by QUANTUM DOTS. These are just artificial atoms. Quantum dots (QDs) are man-made nanoscale semiconductor crystal and are zero dimensional, that can transport electrons and has a ability to convert a spectrum of light into different colours. Each dot emits a different colour depending upon its size.

      Just like atoms, QDs also have quantized energy levels. So, as in atoms when electrons gets excited to higher level, they returned back by emitting light of same energy as they absorbed. In this way, they emit colours also. QDs will give out different colours of light depending upon how big they are. The bigger quantum dots produce longest wavelengths (minimum energies) and smaller quantum dots produce shortest wavelengths (maximum energies). That’s why bigger dot is red in colour and smaller is blue and intermediate sized dot is green in colour. This is because bigger QDs have more closely band gap so will require minimum energy to excite electrons and smaller QDs have bigger energy gap so require more energy to excite electrons.

QDs have wide ranging applications covering various areas of catalysis, electronics, imaging, sensors and photonics.

Applications in field of optics

• QDs have interesting optical properties. A thin filter made of QDs can be fitted on LEDs and convert its light into different shades. QDs can be used instead of dyes and pigments. They produce different colours that are brighter and more controllable than dyes.
• QDs have brought revolution in the field of solar cells. QDs produce more electrons (or holes) for each photon that strikes them, potentially boosting efficiency upto 10 percent over conventional semiconductors.
• QDs can also be used in TV screens and computer display. QDs produce light themselves and do not need any backlight, so are energy efficient. They produce high resolution images. QDs LEDs are more brighter than OLEDs.

Quantum computing

Optical computers could use quantum dots in the same way as modern computers use transistors. In quantum computers, bits are stored in atoms, ions and photons all are linked together and are called qubits. These can store multiple values simultaneously and work on different problems together.

Medicine

QDs can be used effectively in cancer treatment. They can easily target one single organ of body liver, kidney, stomach etc. dots are designed such they accumulate in particular part of body and eject anti cancer drug associated to them.

Applications of neutrinos- ghost like particles

      An invisible and almost massless particle could be the building block for some incredible new technology. It’s called the neutrino. Neutrinos have a potential to do amazing things like speed up global communication, detect the presence of nuclear weapons and confirm the presence of dark matter. To know more about neutrinos, you can check out this post too https://imbibephysics5794.blogspot.com/2020/03/what-is-mystery-of-ghost-like-particles.html

1. A way to monitor nuclear proliferation

Neutrinos are produced from radiation, so it might be possible for the International Atomic Energy Agency to use neutrino detectors to monitor which countries are following the treaty on the Non-Proliferation of nuclear weapons. In most nuclear reactors, uranium decays into plutonium. But to male a nuclear weapon, the reactor has to be shut down, the plutonium removed, and replaced with fresh uranium. Nuclear reactors and nuclear bombs release staggering numbers of neutrinos, so international monitors could rely on neutrinos for surveillance and help prevent proliferation.

2. A way to ‘x ray’ the earth to find cavities of mineral and oil deposits

Some scientists have proposed that intense beams of neutrinos could be used to probe the earth’s crust for mineral or oil deposits.

3.  Faster global communication

These particles can pass through pretty much anything & it would be faster to send the message through it across the earth. It would be easy to communicate in submarines. Scientists had encode a message in neutrinos using binary code.

4. A way to detect dark matter

The presence of dark matter has still not been directly observed by scientists. But neutrinos can help in this matter. The Icelab has built a neutrino detector in Antarctica that has detected extremely high energy neutrinos. The scientists built the detector by actually boring holes into the ice. Scientists observed that some neutrinos come from space and are produced from things like supermassive black holes and violent star deaths. These neutrinos might also come from decaying dark matter in nearby galaxies.

5. Communication with extra terrestrial life

Since, it is possible to encode messages in neutrinos, those encoded neutrinos could be beamed into space. They would act as terrific messengers between advanced civilizations across the galaxy.

6. Finding exploding stars

It has been over four centuries since astronomers have seen a supernova in the Milky way. If a star explodes in the far side of the galaxy, neutrinos would come from it unhindered which can be detected by our detectors.

7. Figure out what keeps the earth’s interior warm

Part of our planet’s heat comes from the decay of radioactive elements -but we don’t know exactly what fraction. Since radioactivity also releases neutrinos, measuring them, we can find how much uranium and thorium are there in earth’s curst and mantle.

Day and night duration- due to refraction or scattering?

Many students have this doubt and they questioned their teachers whether the duration of day and night is due to refraction or scattering of light? And also, there is a big debate among the physics teachers, some of them supported refraction of light and some supported scattering of light. In this post, let’s clarify this question.

        If we look into in this matter, the day and night duration is neither due to refraction nor due to scattering of light. This phenomenon is purely geographical. The duration depends upon rotation of earth about its axis, revolution around sun, inclination of its axis with the plane of the motion of earth and our location on the earth.

Greenland, Norway, Alaska, finland are some countries where nights and days do happen in very long duration. Earth’s rotation causes the period of day and night. The part facing the sun is in daylight and other facing away is in darkness. Earth rotates about its axis (imaginary line). Earth’s axis is not perpendicular. There is an axial tilt of 23.5°. Due to this tilt, the sun shines at different angles on different latitudes. That’s why areas coming under arctic circle experiences 6 month day in northern hemisphere and 6 month night in southern hemisphere. The axial tilt of earth decides the duration of day and night at different locations on earth.

Some people also comments that the refraction and scattering does increases duration of day as compared to night time. But still both these phenomena do not play much role.

Before sun rises, we still see the light of sun, this is due to refraction of sunlight with the atmosphere of earth. When light touches the atmosphere, its bends due to refraction and we able to see the light before the sun rises. Same with the scattering also, particles present in the atmosphere scatters light and we experience light before the sun rises. Both these phenomena add 3 to 4 min in duration of day but doesn’t mean elongation of day than night. This thing explains by geographical concepts.