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