Quantum DotsKE 31.5530 Nanopartikkelit4.5.2011Lauri Lehtola

OutlineQuantum dotsstructure

Preparation methods

ApplicationsExcisting and visionaryhttp://www.lbl.gov/Science-Articles/Archive/Quantum-Dot-Electronics.html

Quantum dotsNanocystalsBoth atom and bulk-like propertiesCommonly made from semiconductor materials or heavy metals

Research began in 1980sSmaller semiconductor devicesQuantum wells (2D), quantum wires (1D)DNA 1/2

Quantum DotsCurrent carriers are confined in all three dimensionsDimension size ~ electron wave lengthQuantum mechanical particle in a box situationSolution:

Discrete energy levels

Quantum DotsDiscrete energy levelsFluorescence

Controlling of energy gapsSmall size high gap high energyDifferent wavelengths

Tunable or man-made atomshttp://www.rsc.org/Publishing/ChemTech

Quantum DotsEasily in situ alterableEnergy level structureModified with voltage

Magnetic phasesControlled with external magnetic fields

Electrical, catalyst propertiesOnion-like architecture, etc.

http://www.enc.edu/~john.u.free/

PreparationChemical synthesis from colloidsPrecursor, surfactant, solventTypical precursors: CdSe, CdS, InAs

Correct temperature and precursor concentrationHighly monodisperse particles

Commercially used methodhttp://www.nanocotechnologies.com/

PreparationSelf-assembling during molecular beam epitaxyQuantum dots on a surface

Stranski-Krastanov growthCertain layer thickness islands nucleatehttp://www-thz.physics.ox.ac.uk/publications.html

PreparationNew cheaper and faster methods

Restrictions of using heavy metals

Room temperature preparationSonochemical Synthesis http://pubs.acs.org/doi/full/10.1021/cm0505547

ApplicationsSolar cellsTraditional cells: excess kinetic energyThis energy is lost soon

Quantum dot coating

Multiple excitons from a single photon

MEG (Multiple Exciton Generation)http://www.nanoprinttech.com/quantum_dot.html

ApplicationsBiological trackingTag molecules with quantum dotsOnly particlular molecules

Processes inside living cells

Clusters of quantum dotsNo blinkinghttp://www.ieeeghn.org/wiki/index.php/Quantum_Dots

ApplicationsQLEDs and QLED displaysDirect utilization of electroluminescenceElectrons to photons

Easy patterningInkjet printingPure colorsNo color masks smaller energy consumptionShort lifetime (10 000 h)

http://www.physorg.com/news/2011-02-fabricate-large-area-full-color-quantum-dot.html

ApplicationsOther possibilities: Quantum computerQuantum dots as qubits

Application: scientific toolTheoretical information of few-body effects in finite and reduced dimensionsAlready now new phenomenaNew phases, magnetic ground statesMore to come

ConclusionStructureConfined electrons and holes

PreparationChemical, MBE

ApplicationsVariety of ways to utilize