Applications of Quantum Dots

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Applications of Quantum Dots

• Chris Young
• OSU ECEN 5060 Nanotechnology Dec 12, 2006

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Applications of Quantum Dots

• Abstract
• This OSU ECEN 5060 research paper describes
  theory and uses of the semiconducting particle
  called the quantum dot. The theory behind the dot
  is shown to have come from the semi conducting
  structure called the quantum well. Quantum dots
  have additional properties as zero dimensional
  structures over the quantum well. They are able
  to completely contain electrons because they are
  on the order of the De Broglie electron
  wavelength. This lets them act as tailored
  artificial atoms when emitting photons and are
  used for studying quantum phenomena. The leading
  current commercial use is for biological tags for
  fluorescence spectroscopy. Future uses of quantum
  dots include quantum dot LED white lights,
  commercial and military identity inks, quantum
  dot solar cells and in quantum computers. All
  these applications use the unique properties of
  the quantum dot.

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What is a Quantum Dot?

• Introduction/Background
• The quantum dot is a unique semiconducting
  nanostructure. The photon absorbing and emitting
  properties of a quantum dot are only a function
  of the size of the dot.
• The size of a Quantum dot can be hand tailored by
  engineers. This gives huge flexibility in which
  photons can be emitted or absorbed in any given
  application.
• Many new and exciting applications are being
  researched. Quantum dots will soon be part of our
  lives and careers!

Figure 1 Computer model of a Cadmium Sellenuim
Quantum Dot(7)
Figure 2 Different sized Quantum Dots emitting
different wavelength of photons according to
size. Largest to smallest (7)
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Quantum Dot History/ Literature cited

• The theory behind Quantum dots started in the
  field of photonics with the creation of Quantum
  wells. Other fields, namely inorganic chemistry,
  have contributed since then. Quantum dot creation
  is enabled through a top down process using the
  science of lithography, or made in a bottom up
  process using the science of colloidal self
  assembly.
• History
• Unique quantum effects were first observed in
  thin film Quantum wells(9)
• (early 1980s) A. I. Ekimov and his colleagues at
  the IoÝe Physical-Technical Institute in St.
  Petersburg (10) noticed unusual optical effects
  in semiconductor glass.
• Bell Labs created a colloidal suspension of
  semiconductor crystals (10)
• (mid 1980) The first quantum dots were made with
  lithographic techniques at Texas Instrument. (9)
• Literature
• Work is cited from various fields.
• See references at end of presentation

Figure 3 Quantum Dots created with lithography at
Texas Instrument(9)
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Theory Quantum Dots, Wires, and Wells
All Quantum structure has at least one dimension
less than the De Brolie wavelength for an
electron. This is typically on the order of 100 Å
(10) to confine electrons. Quantum Wells
confine electrons in one dimension. Quantum Wires
confine them in two dimensions. Quantum Dots
confine them in three dimensions making them
zero dimensional structures
Figure 4 De Brolie equation. This can calc.
wavelength of electrons(18)

• Figure 5
• Quantum Well
• Quantum Wire (20)

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Theory Quantum Dot energy levels

• The physics of trapped electrons in a Quantum Dot
  operate under their wave nature as explained in
  quantum mechanics.
• As these dots gain or lose energy the electron
  wave, see Figure 6, changes harmonics. This lets
  Quantum dots emit photons like a single atom does
  when electrons change energy states (10).
• Tailoring a Quantum Dots size gives it unique
  emission and absorption properties, see Figure 7.

Figure 6 How one electron wave can make different
energy states (10)
Figure 7 How size changes the shape and spectrum
of Q Dots(17)
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Current Use Fluorescence spectroscopy

• The main commercial use for Quantum Dots is
  biological imaging with fluorescence
  spectroscopy.
• A need exists for researches to identify many
  specific parts of biological structure.
  Traditionally they used fluorescent dyes.
• Quantum Dots
• Dyes are not limited to a specific molecule,
  researches can use any color.
• All use the same excitation source, eliminating
  the complexity of using multiple dyes
• Are much brighter and last longer than
  traditional dyes
• Can be tailored to bind to specific structures.

Figure 8 Quantum Dot with additional layers to
make it water soluble and able to bind biological
structure (7)
Figure 9 Quantum Dots binding to mouse cancer
cells(8)
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Future Use Identification Inks

• The bright frequency emission of quantum dots
  give it two novel uses for identification.
• Security Inks A need exists for better
  anti-counterfeiting codes to identify items.
• Quantum Dots
• Give unique frequency lines created by mixing
  different sized Quantum dots together.
• Being a new technology this would be hard to
  reverse engineer(7).
• Military Identification A need exists for the
  military to identify friendly targets in
  daylight.
• Quantum Dots
• Give sharp enough frequency lines they can fit
  sunlights fraunhofer lines, letting it be used
  in daylight.
• This identification would be invisible until
  scanned with a simple UV (4).

Figure 11 How scanning for military Quantum Dot
identification could work (4)
Figure 10 Q Dots security inks (7)
Figure 12 Fraunhofer Lines (21)
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Future Use White Light

• Quantum dots can be used to create a rich white
  light, like the light that comes out of a light
  bulb.
• A need exists to create a light that is as
  durable and energy efficient as an LED, but with
  the light quality of a light bulb. The spectrum
  of different light sources can be seen in Figure
  14. White LEDS are created by combining blue LEDS
  and phosphors, but this light is still not light
  bulb quality(14).
• Quantum Dots
• If a Quantum Dot becomes small enough it emits
  rich white light.
• Quantum Dots can cover a blue or UV LED to create
  this light as shown in Figure 14(2).

Figure 15 UV LED covered by Quantum Dots(2)
Figure 14 The light spectra of various light
sources. Q Dot LED, Phosphor LED, Fluorescent
light, Light bulb, Sunlight(14)
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Future Use Solar Cells

• Quantum Dots unique absorption characteristics
  let it boost traditional solar cell output.
• A need exists for solar cells to be more
  efficient if they will ever become a commercially
  viable source of clean free energy. Traditional
  solar cells have a theoretical limit of 33
  efficiency (7) with cells on the market getting
  around 12 efficiency (15).
• Quantum Dots
• Have a unique absorption property called impact
  ionization that lets them release up 3 electrons
  per photon.
• This raises the efficiency of Quantum Dot solar
  cells to 66 (12). Enough to make them cost
  effective.

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Future Use Quantum Computers and Studying
Quantum effects

• The Quantum nature of electrons in a Quantum Dot
  make them perfect for studying quantum effects
  and as possible building blocks of a Quantum
  Computer.
• A need exists to study Quantum Phenomena if
  electronics start getting down to the atomic
  level.
• Quantum Dots
• Provide ways to study single electrons.
• Enable ways to study effects like spins state,
  tunneling, standing waves, and entanglement (3).
• Can hold a single electron for Quantum
  computations.

Figure 16 Device made at Duke University to study
two coupled Q Dots. (Numerals used in the
original schematic) (3)
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Future of Quantum Dots

• Quantum Dots have an exciting future. They have
  numerous exciting uses that just need time to
  become commercially viable. Any many more uses
  that have not been mentioned in this
  presentation.
• Quantum Dots are with out a doubt an amazing new
  tool in the hands of scientists. If things go as
  researchers plan Quantum Dots will change our
  life style in the near future.

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References
1 "Ultimate Alchemy", Wired Magazine 9.10, October, 2001lthttp//www.wired.com/wired/archive/9.10/atoms.htmlgt
2 Bowers II, Michael J., Mcride, James R., and Rosenthal, Sandra J., White-Light Emission from Magic-Sized Cadmium Selenide Nanocrystals, J. AM. CHEM. SOC. Vol 127, No. 44, 2005
3 Chang, Albert M., The Kondo Effect and Controlled Spin Entanglemnt in Coupled Double-Quantum-Dots, CP, Nuclei and Mesoscopic Physics WNMP 2004
4 Chang, Shoude, Zhou, Ming, and Grover, Chander P. Passive Illumination infor retrieval used for status identification, Sensors, and Command, Control, Communications, and intelligence (C31) Technologies for Homeland Security and Homeland Defense iii, E. M. Carapezza, ed., Proc. of SPIE Vol. 5403
5 Chen, Hsueh, Hsu, Cheng-Kuo, and Hong, Hsin-Yen, InGaN-CdSe-ZnSe Quantum Dots White LEDS, IEEE Photonics Technology Letters, Vol. 18, No. 1, January 1, 2006
6 Chou, Stephen Y., Krauss, Peter R., and Renstrom, Preston J., Nanoimprint Lithography, J. Vac.Sci, Technol. B, Vol. 14, No. 6, Nov/Dec 1996
7 Evident Technologies, Quantum Dot Products - Evident Technologies lthttp//www.evidenttech.com/gtAll citations come from within their website. And all images from this site are used with permission
8 Gao, X., and Emory, S. Nie, Bioimaging A slide show, Science lthttp//www.sciencemag.org/feature/data/bioimaging/qd.htmlgt
9 M. A. Reed, J. N. Randall, R. J. Aggarwal, R. J. Matyi, T. M. Moore, and A. E. Wetsel, Observation of discrete electronic states in a zero-dimensional semiconductor nanostructure, Phys. Rev. Lett. 60, 535 (1988)
10 M. A. Reed, Quantum Dots, Scientific American 268, Number 1, 118, 1993 lthttp//www.eng.yale.edu/reedlab/publications/5820QDotsSciAm1993.pdfgt
11 Nadler-Olenick, Rae, Engineers harness quantum dots for neurological research, On Campus, university of texas austin publication, Nov 28, 2001, Vol. 28, No. 13 lthttp//www.utexas.edu/opa/pubs/oncampus/01oc_issues/oc011128/oc_quantum.htmlgt
12 Nozik, A. J., Quantum dot solar cells, Physica, E 14, 2002, p.115-120
13 Ozin, Geffrey A., and Arsenault, Andre C., NanoChemistry, RSC Publishing 2005
14 Quantum dots that produce white light could be the light bulb's successor, Physorg.com, lthttp//www.physorg.com/pdf7421.pdfgt image. provided by Bowers II, Michael J
15 Queisser, Hans J., Photovoltaic conversoin at reduced dimensions, Physica E 14, 2002, p1-10
16 Segelken, Roger, 3-D imaging inside living organism, using quantum dots coursing through mouse's body, reported by Cornell researchers, Cornell News May 29, 2003 lthttp//www.news.cornell.edu/releases/May03/quantum_dots.hrs.htmlgt
17 Wang, Jun, Synthesis, Functionalzation, and Biological Tagging Applications of II-VI Semiconductor Nanocrystals, PhD dissertation University of New York at Buffalo 2006
18 Wikipeida the free encyclopedia, De Broglie hypothesis, Last modified 21 Nov 2006, lthttp//en.wikipedia.org/wiki/De_Broglie_wavelength_note-0gt
19 Yih-Yin-Lin, PhD disertation Low Dimensional Systems for Electronic and Optoelectronics Devices, University of Michigan, 2005, pg. 5
20 Žukauskas, A, and Gavryushin, V, Quantum Structures, 2002 lthgtttp//www.mtmi.vu.lt/pfk/funkc_dariniai/nanostructures/quant_structures.htm
21 Wikipeida the free encyclopedia, Fraunhofer lines, Last modified 04 Dec 2006, lthttp//en.wikipedia.org/wiki/Fraunhofer_linesgt