Quantum Dots_MEEE_AIUB

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Nanotechnology in Semiconductor Nanostructure.

Presentation on "Quantum Dot", was performed under the Subject "QUANTUM PHENOMENA IN NANOSTRUCTURES" at AIUB. The simulation is done from a website nanoHUB which stands for online simulation for nanotechnology- https://nanohub.org/

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Quantum Dots_MEEE_AIUB

  1. 1. American International University- Bangladesh (AIUB) (School of Engineering) Presenter Nusrat Irin Chowdhury Mary QUANTUM DOT
  2. 2. Quantum  Quantum is the Latin word for amount, meaning the smallest possible discrete unit of any physical property, such as energy or matter.  Max Planck used it in a presentation to the German Physical Society. Planck wrote a mathematical equation involving a figure to represent individual units of energy. He called the units as quanta .  Quantum is sometimes used loosely, in an adjectival form, to mean on such an infinitesimal level as to be infinite, as, for example, you might say "Waiting for pages to load is quantumly boring."
  3. 3. What are Quantum Dots?  Quantum dots are semi- conductors that are on the nanometer scale.  Obey quantum mechanical principle of quantum confinement.  Exhibit energy band gap that determines required wavelength of radiation absorption and emission spectra.  Requisite absorption and resultant emission wavelengths dependent on dot size. Figure: Schematic plot of the single particle energy band gap. The upper parabolic band is the conduction band, the lower the valence.
  4. 4. Quantum Dots Description The name “dot” suggests an extremely small region of space. The number of free electrons in the dot can be very small. The deBroglie wavelength of these electrons is comparable to the size of the dot, and the electrons occupy discrete quantum levels and have a discrete excitation spectrum. Figure: Band gap energy of quantum dots vary with its size.
  5. 5. Quantum Dots Description contd. Cadmium Mercury Telluride (CdHgTe), Cadmium Selenide (CdSe), Cadmium Selenide/Zinc Sulfide (CdSe/ZnS), Cadmium Sulfide (CdS), Cadmium Telluride (CdTe), Cadmium Telluride/Cadmium Sulfide (CdTe/CdS), Lead Selenide (PbSe), Lead Sulfide (PbS)
  6. 6. Figure: The energy band gap associated with semi-conducting materials. In order to produce electric current electrons must exist in the conduction band. Energy Bands in Quantum Dots
  7. 7. Confinement - Infinite Square Well Potential Figure: Quantized energy levels of a particle in a box.
  8. 8. Figure: Solutions of quantum dots of varying size. The variation in color of each solution illustrating the particle size dependence of the optical absorption for each sample. The smaller particles are in the blue solution (absorbs blue), and that the larger ones are in the red (absorbs red). Solutions of Quantum Dots
  9. 9. Characteristics of Quantum Dot  An electron in a quantum dot will act more like an electron in a molecule than an electron in a bulk solid, and for this reason, quantum dots are sometimes called artificial molecules.  The charging energy of QD is analogous to the ionization energy of an atom. This is the energy required to add or remove a single electron from the dot. Measuring their transport properties, i.e., by their ability to carry an electric current, quantum dots are artificial atoms with the intriguing possibility of attaching current and voltage leads to probe their atomic states.
  10. 10. Application of Quantum Dot  Special Quantum Dots could Improve Transparent Solar Cells  Shiny quantum dots brighten future of solar cells  Quantum dot TVs to be launched by mid-2014  Quantum Materials Now Shipping Size-Optimized Metallic Oxide  Quantum dots can charge your Smartphone in 30 seconds
  11. 11. Solar Cells and Photovoltaic  Traditional solar cells are made of semi-conductors and expensive to produce. Theoretical upper limit is 33% efficiency for conversion of sunlight to electricity for these cells.  Utilizing quantum dots allows realization of third- generation solar cells at ~60% efficiency in electricity production while being low cost per square meter of paneling necessary.  Effective due to quantum dots’ ability to preferentially absorb and emit radiation that results in optimal generation of electric current and voltage.
  12. 12. Medical Imaging and Disease Detection  Can be set to any arbitrary emission spectra to allow labeling and observation of detailed biological processes.  Useful tool for monitoring cancerous cells and providing a means to better understand its evolution.  In future, could also be armed with tumor-fighting toxic therapies to provide the diagnosis and treatment of cancer.  Resistant to degradation than other optical imaging probes such as organic dyes, allowing them to track cell processes for longer periods of time.  Offer a wide broadband absorption spectrum while maintaining a distinct, static emission wavelength.
  13. 13. Other Future Quantum Dot Applications  Anti-counterfeiting capabilities: inject dots into liquid mixtures, fabrics, polymer matrices, etc. Ability to specifically control absorption and emission spectra to produce unique validation signatures. Almost impossible to mimic with traditional semi-conductors.  Counter-espionage / Defense applications: Integrate quantum dots into dust that tracks enemies. Protection against friendly-fire events.  Research continues. The possibilities seem endless…
  14. 14. Quantum Dot in nanoHUB  There are two input methods: 1. Device Structure 2. Light Source The Figure shows the view of the tool In simulation part the used tool is “Quantum Dot Lab” under “artificial atom” tag.
  15. 15. Quantum Dot Lab in nanoHUB contd. Device Structure quantify the physical structure of the QD. It consist of the following parameters: a. Number of states it will be having (with corresponding valid numbers with unit of nm) b. Surface Passivation c. physical size (cuboid, cylinder, dime, pyramid, spheroid) d. dimensions (in x-, y-, z- directions with maximum values of 20nm the unit of nm) e. effective mass (as an ex two values are given, the possible values are 0.005 to 3.0) f. discretization (with the unit of nm) g. energy gap (between 0eV to 20eV with the unit of J or eV) The Light Source signify if any light source is fall on to the Quantum Dots. This input is also having some parameters like device structure has
  16. 16. Quantum Dot Lab in nanoHUB contd. Parameter- a Number of states the simulation will be having, which follow some values from 1 to 150.
  17. 17. Quantum Dot Lab in nanoHUB contd. Parameter- b Surface Passivation- Which deals with wave function. It can be turn on/off. If unchecked means wavefunction ‘0’ outside
  18. 18. Quantum Dot Lab in nanoHUB contd. Parameter- c Geometry, which means for physical size, whether its cubic or cylinder, dime, pyramid or spheroid.
  19. 19. Quantum Dot Lab in nanoHUB contd. Parameter- d dimensions (in x-, y-, z- directions with maximum value ranges with the unit of nm). The other parameter’s values were set according to them.
  20. 20. Quantum Dot Lab in nanoHUB contd. Under the “Light Source” tab some parameter is there. Which will also having some respective angle and values and was set according to them.
  21. 21. Quantum Dot Lab in nanoHUB contd. After given with the appropriate inputs, the simulation is done. It will give graphical representations with the “Result” window presenting outputs.
  22. 22. Quantum Dot Lab in nanoHUB contd.  The first result is the “3D Wavefunction”
  23. 23. Quantum Dot Lab in nanoHUB contd.  The second result is the “Energy states”
  24. 24. Quantum Dot Lab in nanoHUB contd.  The third result is “Light and dark transition (X- polarized)”
  25. 25. Quantum Dot Lab in nanoHUB contd.  The third result is “Light and dark transition (Y-polarized)”
  26. 26. Quantum Dot Lab in nanoHUB contd.  The third result is “Light and dark transition (Z-polarized)”
  27. 27. Quantum Dot Lab in nanoHUB contd.  The next is “Light and dark transition (phi= 0, theta= 45)” which is in a spherical coordinate system.
  28. 28. Quantum Dot Lab in nanoHUB contd.  The “Absorption (phi= 0, theta= 45)”
  29. 29. Quantum Dot Lab in nanoHUB contd.  The “Absorption sweep of angle theta”
  30. 30. Quantum Dot Lab in nanoHUB contd. The last two results are “Input deck” & “Output log” which are representing inputs to the simulation and database information corresponding the inputs given to the running tool.

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