CNNanoPhotonics CenterCN

NanoPhotonics Center

Alejandro GalvanMentors: Prof. Roger Dorsinville

Alberto Tonizzo IUSL High School Summer Program

Summer 2006

A Quantum Dot (semiconductor nanocrystal) contains discrete energy, much like an Atom. They are sometimes called “artificial atoms.”

A quantum dot’s energy levels can be controlled by changing their size and shape and the depth of their potential. There are anywhere from 100 to 1,000 electrons in a quantum dot and their size ranges from 2 to 10 nanometers, or 10 to 50 atoms, in

diameter.

AtomQuantum Dot

http://oemagazine.com/fromTheMagazine/oct02/images/quantumdotsill.jpg

http://home.arcor.de/cybertaro/kosmologie/atom.jpg

Quantum Dot Contd.

http://www.nanotech-now.com/images/QDot-nanocrystal-size.jpg

•An Atom ranges from0.1 to 0.5 nanometers (1 × 10-10 m to 5 × 10-10 m).•A quantum dot ranges from 2 to 10 nanometers.

The larger the quantum dot, the redder the fluorescence, and the lower the energy of the emitted light. The smaller the dot, the bluer the fluorescence, and the higher the energy.

Quantum dots have found their way into our homes. For example, the new Play Station 3 and HD DVD players both use a blue laser for data reading.

http://en.wikipedia.org/wiki/Quantum_dot

http://www.evidenttech.com/qdot-definition/images/08-tun.jpg

Reverse Micelle Normal Micelle

H2O

Head:

Hydrophilic Oil

Oil

Tail:

Hydrophobic

H2O

(Water)

We are using QDs (quantum dots) to find a new material that can absorb strong laser light frequency (optical limiting) making the light of the laser weak. This material can protect human eyes, devices etc. It is intensity dependent (i.e., the stronger the laser light the more the material absorbs).

New Material (Filter)

High Intensity Laser Light

Low intensity Light (not harmful)

1.In order to make this new material we are using a toluene dispersion of reverse micelles containing CdSe (Cadmium Selenide) quantum dots.

• Solvent: Toluene• H3C

(Molecular Formula: C10H23N)

2.This solution was put in a polystyrene matrix and also in a PMMA (polymethyl methacrylate) matrix to make a transparent film.

3.We are trying to fabricate (through the spin coating technique) thin films consisting of this mixture. In fact solution are not sufficient for device applications.

NH2

Solution of reverse Micelles and Toluene

Quartz used to make the thin-film

*1 drop/min.

http://www.eng.uc.edu/~dshi/biomat404/lab_tour/Spin.jpg

Our Quantum Dot:

Cluster or Quantum Dot

NH2

Micelles: are organic substances used to stabilize the

Quantum Dot.

http://www.gmi-inc.com/Categories/cary5000.htm

http://lma.in2p3.fr/Images/perkin2.jpg

Thin film of micelle-capped CdSe QDs (in Polystyrene matrix)

0

0.2

0.4

0.6

0.8

1

1.2

300 320 340 360 380 400 420 440 460 480 500

Wavelength (nm)

Ab

sorb

ance

(ar

b. u

nit

s)

Main absorption frequency

* From the peak frequency you can calculate the size of the Quantum Dot

1.Scattering of Light

2.Low absorption Intensity

* From the peak frequency you can calculate the size of the Quantum Dot

Thin Film of Micelle-capped CdSe QDs(in PMMA matrix 20 drops per min)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

300 320 340 360 380 400 420 440 460 480 500

Wavelength (nm)

Ab

sorb

ance

(ar

b.

un

its)

2.Stil some scattering of Light

Main absorption frequency

1.Very low absorption Intensity

Results:

We did see some absorption at 415 nm which indicated the presence of a stable Cadmium Selenide quantum dot. However the preparation methods used (Polystyrene [50mg/ml], PMMA (polymethyl methacrylate [50mg/ml]) did not result in a transparent film due to scattering of light. Ideally we would like a transparent film so that our quantum dot can be more frequency specific in terms of being used as a filter.

Further Work:

Preparation of CdSe QDs capped in micelles made of different alkyl amines (i.e., octadecylamine instead of decylamine).Fabrication of thin films out of this dispersion are anticipated to be more transparent and present a long range order (hexagonal lattice).

Mentors:

Prof. Roger Dorsinville

Alberto TonizzoIUSL High School Summer Program

N.A.S.A./C.O.S.I.The Harlem Children Society