Kvanteø

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Quantum Dots with emission maxima in a 10-nm step are being produced in a kg scale at PlasmaChem GmbH

En kvanteø, kvanteprik, nanokrystal eller et kvantepunkt (eng. quantum dot, QD) er et halvlederkrystal indeholdt i en diameter på nogle få nanometer, som pga. sin lille størrelse opfører sig som en potentialbrønd, der fastholder elektroner i 3 dimensioner til et område i en størrelsesorden på elektronens de Broglie bølgelængde, nogle få nanometer i en halvleder. Sammenlign det med kvanteledninger (fastholder i 2D) og kvantebrønde (kvanteslugt?) (fastholder i 1D).

Pga. fastholdelsen er elektronens energiniveauer kvantiserede, ligesom i et atom. Det er grunden til at kvanteøer kaldes "kunstige atomer". Energiniveauerne kan styres ved at størrelsen og formen på kvanteøen ændres.

Anvendelser[redigér | redigér wikikode]

Pga. kvanteøers halv-nul dimensionelle udstrækning har de et skarpere density of states end højere-dimensionelle strukturer. Resultatet er at de har uovertrufne transport- og optiske egenskaber og der bliver forsket i at deres anvendelse i f.eks. højeffektive lysdioder, højeffektiv UVA til hvidt lys fluorescens, fiberoptisk lysregenerering, diodelaserere og detektorer. [1] [2] [3] [4] [5] [6] [7]

En kvanteø er den aktive komponent i en enkelt elektron transistor.

Kvantemekanisk sammenfiltring af flere kvanteøer (i rollen som qubits) er en af de mest håbefulde kandidater til faststof kvantecomputere.

Kvanteøer kan sandsynligvis anvendes til fremstilling af solceller med en virkningsgrad på 65% ifølge (May 2005, American Chemical Society's Nano Letters Journal), hvilket er mere end dobbelt så meget som dagens bedste masseproducerede solceller. [8]

Fabrikation og størrelse[redigér | redigér wikikode]

I halvledere er kvanteøer små områder af et materiale "begravet" i et andet materiale med et større båndgab.

Kvanteøen er i en størrelsesorden på elektronens de Broglie bølgelængde og den er ved stuetemperatur:

\frac{h}{\sqrt{2 m_e E}}

Her gælder der:

E = k_b \cdot T = 1,38 10^{-23} \frac{J}{K}  \cdot 300K

Det giver så:

\frac{6,626 10^{-34} Js}{\sqrt{2\cdot 9,109 10^{-31} kg\cdot 1,38 10^{-23} \frac{J}{K}  \cdot 300K}} \approx 7,6 nm

Kilder[redigér | redigér wikikode]

  1. Fujitsu (September 10, 2004). Fujitsu, University of Tokyo Develop World's First 10Gbit/s Quantum Dot Laser Featuring Breakthrough Temperature-Independent Output. Press Release.
  2. Webarchivebackup: evidenttech.com: Quantum Dots and Non-Linear Optical Capabilities: Quantum Dots and Photonics to Improve Information Technology
  3. Fujitsu Develops World's First Semiconductor Optical Amplifier with Signal Waveform Re-shaping Function at 40Gbps. Uses quantum dots to eliminate waveform degradation and significantly reduce noise
  4. Mighty Small Dots Citat: "..."For years," says Lee, "scientists have been trying to make silicon emit light efficiently and in the visible range. This has been one of the holy grails of science."...What makes our dots unique is that their luminescence can be tuned to any wavelength over a broad spectral range and be stable under ambient conditions. No one else has done this. We also believe we understand the underlying physics..."
  5. 2004-06-23, Sciencedaily: Wireless Nanocrystals Efficiently Radiate Visible Light Citat: "...The efficiency of the energy transfer from the quantum well to the nanocrystals was approximately 55 percent – although in theory nearly 100 percent transfer of the energy is possible and might be achieved with further tweaking...The work is another step in creating more efficient white-light-emitting diodes..."
  6. 2005-10-21, sciencedaily: Quantum Dots That Produce White Light Could Be The Light Bulb's Successor Citat: "...The report of their discovery, which happened by accident, appears in the communication “White-light Emission from Magic-Sized Cadmium Selenide Nanocrystals”...As a result, the light produced by the quantum dots looks more nearly like the “full spectrum”...either 33 or 34 pairs of atoms, which happens to be a “magic size”...The quantum dots were supposed to emit blue light, but instead they were giving off a beautiful white glow..."
  7. Sept. 25, Science Daily: Quantum dots are made brighter Citat: "...While the researchers report an enhancement of fluorescence intensity by a factor of up to 108 compared with quantum dots on an unpatterned surface, Cunningham said more recent, but unpublished, work has exceeded a factor of 550..."
  8. May 23, 2005, physorg: Quantum Dot Materials Can Reduce Heat, Boost Electrical Output Citat: "..."We have shown that solar cells based on quantum dots theoretically could convert more than 65 percent of the sun's energy into electricity, approximately doubling the efficiency of solar cells," Nozik said..."

Se også[redigér | redigér wikikode]

Eksterne henvisninger[redigér | redigér wikikode]