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Quantum Dots
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  1. Quantum Dots KE – 31.5530 Nanopartikkelit 4.5.2011 Lauri Lehtola

  2. Outline • Quantum dots • structure • Preparation methods • Applications • Excisting and visionary http://www.lbl.gov/Science-Articles/Archive/Quantum-Dot-Electronics.html

  3. Quantum dots • Nanocystals • Both atom and bulk-like properties • Commonly made from semiconductor materials or heavy metals • Research began in 1980s • Smaller semiconductor devices • Quantum wells (2D), quantum wires (1D) DNA 1/2

  4. Quantum Dots • Current carriers are confined in all three dimensions • Dimension size ~ electron wave length • Quantum mechanical particle in a box –situation • Solution: • Discrete energy levels

  5. Quantum Dots • Discrete energy levels • Fluorescence • Controlling of energy gaps • Small size  high gap  high energy • Different wavelengths • Tunable or ”man-made” atoms http://www.rsc.org/Publishing/ChemTech

  6. Quantum Dots • Easily in situ –alterable • Energy level structure • Modified with voltage • Magnetic phases • Controlled with external magnetic fields • Electrical, catalyst properties… • Onion-like architecture, etc. http://www.enc.edu/~john.u.free/

  7. Preparation • Chemical synthesis from colloids • Precursor, surfactant, solvent • Typical precursors: CdSe, CdS, InAs • Correct temperature and precursor concentration • Highly monodisperse particles • Commercially used method http://www.nanocotechnologies.com/

  8. Preparation • Self-assembling during molecular beam epitaxy • Quantum dots on a surface • Stranski-Krastanov growth • Certain layer thickness islands nucleate http://www-thz.physics.ox.ac.uk/publications.html

  9. Preparation • New cheaper and faster methods • Restrictions of using heavy metals • Room temperature preparation • Sonochemical Synthesis http://pubs.acs.org/doi/full/10.1021/cm0505547

  10. Applications • Solar cells • Traditional cells: excess kinetic energy • This energy is lost soon • Quantum dot coating • Multiple excitons from a single photon • MEG (Multiple Exciton Generation) http://www.nanoprinttech.com/quantum_dot.html

  11. Applications • Biological tracking • Tag molecules with quantum dots • Only particlular molecules • Processes inside living cells • Clusters of quantum dots • No blinking http://www.ieeeghn.org/wiki/index.php/Quantum_Dots

  12. Applications • QLEDs and QLED displays • Direct utilization of electroluminescence • Electrons to photons • Easy patterning • Inkjet printing • Pure colors • No color masks  smaller energy consumption • Short lifetime (10 000 h) http://www.physorg.com/news/2011-02-fabricate-large-area-full-color-quantum-dot.html

  13. Applications • Other possibilities: Quantum computer • Quantum dots as ”qubits” • ”Application”: scientific tool • Theoretical information of few-body effects in finite and reduced dimensions • Already now new phenomena • New phases, magnetic ground states • More to come

  14. Conclusion • Structure • Confined electrons and holes • Preparation • Chemical, MBE • Applications • Variety of ways to utilize