QUANTUM DOTS

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TARAN PREET SINGH (MS12044)•

What Really Quantum Dots Are??

QUANTUM DOTS (QDs) are nanometer-scale semiconductor crystals composed of groups II–VI e.g.( CdS, CdSe ) or III–V elements, and are defined as particles with physical dimensions smaller than the exciton Bohr radius, whose excitons are confined in all three dimensions of space.

The term “quantum dot” was coined by Mark Reed in 1988; however, they were first discovered in a glass matrix by Alexey Ekimov in 1981 and in colloidal solutions by Louis E. Brus in 1985.

ENERGIES IN SEMICONDUCTOR

Electrons and holes are confined in all three dimensions of space by a surrounding material with a larger bandgap.Discrete energy levels (artificial atom).A quantum dot has a larger bandgap.Like bulk semiconductor, electrons tend to make transitions near the edges of the bandgap in quantum dots.

The confinement of the electrons results in the appearance of the energy states

shown in the figure(right)

The energy of the lowest state is given by:

The energy of the other states is

E1 = h2 8mL2

En = n2h2 = E1 n2

8mL2

Where Energy of the quantum dot is dependent on Size of the quantum dot due to QUANTUM CONFINEMENT EFFECT.

Controlling the size of nanocrystal, quantum dots can be tuned to emit any color of light.

HOW TO MAKE QUANTUM DOTS

Quantum dots can be made by various methods such as :

LITHEOGRAPHY

COLLIDAL SYNTHESIS

EPITAXY•

COLLOIDAL SYNTHESIS

Colloidal semiconductor Nano crystals are synthesized from precursor compounds dissolved in solutions, much like traditional chemical processes.

i.e: lead sulfide(PbS), lead selenide(PbSe), cadmium selenide(CdSe), cadmium sulfide(CdS), indium arsenide(InAs), and indium phosphide(InP)

FABRICATION

CMOS technology can be employed to fabricate silicon quantum dots. Ultra small (L=20 nm, W=20 nm) CMOS transistors behave as single electron quantum dots when operated at cryogenic temperature.

ELECTROCHEMICAL ASSEMBLY

Highly ordered arrays of quantum dots may also be self-assembled by electrochemical techniques. A template is created by causing an ionic reaction at an electrolyte-metal interface which results in the spontaneous assembly of nanostructures.

OPTICAL PROPERTIES OF QUANTUM DOTS

a - EXCITION b - EMISSION

Quantum confinement effects give rise to unique optical and electronic properties in QDs, giving them numerous advantages over current fluorophores, such as organic dyes, fluorescent proteins and lanthanide chelates.

The narrow emission and broad absorption spectra of QDs makes them well suited to multiplexed imaging, in which multiple colours and intensities are combined to encode genes, proteins .

PHOTOSTABILITY

Photostability is yet another factor in most fluoroscence application, where the quantum dot is having the advantage, unlike organic dyes(fluorophores) which BLEACH after only few minutes after exposure of light, QD are photostable can go multiple cycle of excitation and emission for hours with high level of brightness and photobleaching threshold.

QD is shown more photostable than organic dyes Dihydrolipoic acid (DHLA)-capped cadmiumselenide-zinc sulfide (CdSe-ZnS) QDs showed no loss in intensity after 14 h, and were nearly 100 times as stable as, and also 20 times as bright as, rhodamine 6 G.

APPLICATIONS

Q-LED Quantum dots may some day light your homes, offices, streets,and entire cities.Quantum dot LED’s can now produce any color of light, includingwhite.Quantum dot LED’s are extremely energy efficient. They use onlya few watts, while a regular incandescent lamp uses 30 or morewatts for the same amount of light

QUANTUM COMPUTING

A linear array of quantum dots that can be defined by metal electrodes on silicon with voltage applied so that single electron is trapped at each quantum dot at low temperature . Place in a external magnetic field, the Zeeman spin states of these electrons constitute cubits of the QUANTUM COMPUER

MEDICAL IMAGING

Quantum dots may one day save your life. Medical imaging has begun to use colloidal

(in liquid solution) quantum dots much like the ones you’ll look at today. The photo below

shows human red blood cells, in which specific membrane proteins are targeted and

labeled with quantum dots. The number of purple features, which indicate the nuclei of

malaria parasites, increases as malaria development progresses.

Quantum dots last longer in your systemand are brighter than many organic dyesand fluorescent proteins previously usedto illuminate the interiors of cells. Theyalso have the advantage of monitoringchanges in cellular processes (they last along time) while most high-resolutiontechniques like only provide images ofcellular processes frozen at one momentQuantum dots (red dots above) can be designed to bind to specificcell receptors (green things). In this way researchers can monitor allkinds of processes in living cells

QUANTUM DOTS IN HD TV

REFERENCES

T. Jamieson et al. / Biomaterials 28 (2007) 4717–4732

www.researchgate.net/post/What_is_Quantum_confinement_effect

www.wikipedia.com/quantumdot

cs.lbl.gov/news-media/news/2015/what-theblank-makes-quantum-dots-blink