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Electrochromic Nanocrystal Quantum Dots

Electrochromic Nanocrystal Quantum Dots. Prof. Philippe Guyot-Sionnest’s group (Univ. of Chigaco) : 1. Electrochromic Nanocrystal Quantum Dots, Science 2001 2. Electrochromic semiconductor nanocrystal films, APL 2002. Yingqi Jiang.

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Electrochromic Nanocrystal Quantum Dots

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  1. Electrochromic NanocrystalQuantum Dots Prof. Philippe Guyot-Sionnest’s group (Univ. of Chigaco) : 1. Electrochromic Nanocrystal Quantum Dots, Science 2001 2. Electrochromic semiconductor nanocrystal films, APL 2002 Yingqi Jiang

  2. Video from Discovery Channel! —Fabrication of QD with Colloidal chemistry method!

  3. Quantum dots (QDs) definition • Quantum dots are nanometre-scale semiconductor crystals. • Nanometer scale: each dimension<100nm • Exactly to say, <one electron Fermi wavelength • Semiconductor crystal: potential excellent optical and electronic properties • Quisi-0 dimension: quantum confinement, discrete energy levels——“artificial atoms”

  4. Structure vs. Energy Bulk Quantum Well 1 Quantum Wire Quantum Dot • Density of states (DoS) δ(E) Brad Gussin, John Romankiewicz

  5. Fabrication Methods • 3 primary methods (to form 3-D confinements) • Colloidal chemistry • Precipitate QDs from solutions • Size variations by reaction dynamics • Epitaxy • Stranski-Krastanov growth (MBE, MOCVD) • Size and shape fluctuations, ordering • Lithography • Etch (EBL) pillars in heterostructures • Slow, contamination, low density, defect formation Victor I. Klimov, Los Alamos Science, 2003 T. Fukui et al. Appl. Phys. Lett. May, 1991 Colloidal chemistry method is cheapest and fastest! A. Scherer and H.G. Craighead. Appl. Phys. Lett., 1986.

  6. QD applications • Fluorescent biological markers • Photovoltaic materials (solar cells) • Lasers of very precise, chosen wavelengths • More efficient, higher material gain, lower threshold • Less thermal dependence, spectral broadening • Quantum computing • Represent binary information by charge configuration • Potentially more! “smart bombs”,…

  7. The optical properties change in response to application of an electric current. Fabrication of electrochromic QDs • CdSe nanocrystals capped with trioctylphosphine oxide • CdSe nanocrystals are cleaned and dried under vacuum, and then dissolved in 9:1 (V/V) hexane:octane mixture. • A drop of the CdSe nanocrystal solution is placed on the surface of the working electrode and allowed to dry slowly to form an optically clear film • Test in a spectroelectrochemical cell

  8. Basic observation • Size tunable absorption (smaller larger distance of discrete energies) • Electrochromic tunable absorption 5.4nm 7.0nm

  9. Detailed electrochromic effects Infra-red Visible • Strong infrared (IR) intraband absorption • Complete bleach of the visible interband transition • Two electrons are injected into 1Se orbital of every nanocrystal

  10. Charging and discharging of the nanocrystal films occur at about the same fast rate • Detailed investigations of the factors that influence the electron injection and ejection processes. Reversibility • Efficient and reversible electron injection simply by adjusting the applied potential. • Changes in the visible and IR follow each other very closely, indicating that they are the results of the same electron injection and ejection process.

  11. Summary • Essential reviews of QDs • Definition: nanoscale semiconductor crystal • Mechanism: 0-D structure • Fabrications: Colloidal chemistry is cheapest and fastest • Applications: promising optical and electrical applications • Electrochromic properties of colloidal nanocrystals • Charge tunable by electron injection • Strong IR absorption: 1Se1Pe • Complete bleach of visible interband transition: two electons injection • Reversibility: potentially to help understand the process

  12. Thank you for your attention!

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