Quantum Dots
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Quantum Dots
KE – 31.5530 Nanopartikkelit4.5.2011Lauri Lehtola
Outline
• Quantum dots– structure
• Preparation methods
• Applications– Excisting and visionary
http://www.lbl.gov/Science-Articles/Archive/Quantum-Dot-Electronics.html
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
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
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
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/
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/
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
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
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
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
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
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
Conclusion
• Structure– Confined electrons and holes
• Preparation– Chemical, MBE
• Applications– Variety of ways to utilize