Quantum Dots and its applications

very useful for Nanotechnoloy Students

1. QU ANT UM DO TS Submitted by Sibichakravarthy . S II M.Tech ( Integ ) Nano technology

2. 3-D All carriers act as free carriers in all three directions 2-D or Quantum Wells The carriers act as free carriers in a plane.First observed in semiconductor systems. 1-D or Quantum Wires The carriers are free to move down the direction of the wire 0-D or Quantum Dots Systems in which carriers are confined in all directions (no free carriers) Quantum confinement

3. WHAT IS QUANTUM DOT…??? Quantum dot is a nano sized semi conductor crystal.Which leads to many unique optical and transport properties. A typical QD has a diameter in the range of 2–10 nm Examples: CdSe , PbSe , PbTe , InP

4. Basic Structure of QD’s

5. HOW TO Make Quantum dots Quantum dots can be made by various methods such as : LITHEOGRAPHY COLLIDAL SYNTHESIS EPITAXY

6. Lithography Quantum wells are covered with a polymer mask and exposed to an electron or ion beam . The surface is covered with a thin layer of metal , then cleaned and only the exposed areas keep the metal layer. Pillars are etched into the entire surface. Multiple layers are applied this way to build up the properties and size wanted . Disadvantages: slow, contamination, low density, defect formation.

7. Colloidal Synthesis Immersion of semiconductor microcrystals in glass dielectric matrices. Taking a silicate glass with 1% semiconducting phase ( CdS , CuCl , CdSe , or CuBr ). Heating for several hours at high temperature . Formation of microcrystals of nearly equal size. Typically group II-VI materials (e.g. CdS , CdSe ) Size variations (“size dispersion”). i.e : ( PbS ), ( PbSe ), ( CdSe ), ( CdS ), ( InAs ), ( InP )

8. Epitaxy : Patterned Growth Semiconducting compounds with a smaller bandgap ( GaAs ) are grown on the surface of a compoundwith a larger bandgap ( AlGaAs ). Growth is restricted by coating it with a masking compound (SiO 2 ) and etching that mask with the shape of the required crystal cell wall shape . Disadvantage : density of quantum dots limited by mask pattern.

9. Epitaxy : Self- Organized Growth Uses a large difference in the lattice constants of the substrate and the crystallizing material . When the crystallized layer is thicker than the critical thickness , there is a strong strain on the layers . The breakdown results in randomly distributed islets of regular shape and size. Disadvantages : size and shape fluctuations, ordering

10. Cadmium-free quantum dots In many regions of the world there is now, or soon to be, legislation to restrict and in some cases ban heavy metals in many household appliances such as IT & telecommunication equipment, Lighting equipment , Electrical & electronic tools, Toys, leisure & sports equipment. For QDs to be commercially viable in many applications they MUST NOT CONTAIN cadmium or other restricted elements LIKE mercury, lead, chromium. So research has been able to create non-toxic quantum dots using  silicon .

11. Common QD Materials, their size and emitted wavelengths

12. APPLICATIONS

13. Computing Quantum dot technology is one of the most promising candidates for use in solid-state quantum computation. By applying small voltages to the leads, the flow of electrons through the quantum dot can be controlled and thereby precise measurements of the spin and other properties therein can be made. With several entangled quantum dots, or qubits , plus a way of performing operations, quantum calculations and the computers that would perform them might be possible.

14. 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, including white. Quantum dot LED’s are extremely energy efficient. They use only a few watts, while a regular incandescent lamp uses 30 or more watts for the same amount of light

15. Photovoltaic Devices:- Quantum dots may be able to increase the efficiency and reduce the cost of today's typical silicon photovoltaic cells.Quantum dot photovoltaic would theoretically be cheaper to manufacture, as they can be made "using simple chemical reactions."

16. Solar Cells Photovoltaic effect : p-n Junction. Sunlight excites electrons and creates electron - hole pairs. Electrons concentrate on one side of the cell and holes on the other side . Connecting the 2 sides creates electricity

17. Medical imaging The photo belowshows human red blood cells, in which specific membrane proteins are targeted andlabeled with quantum dots. The number of purple features, which indicate the nuclei of malaria parasites, increases as malaria development progresses.

18. Cell imaging Quantum dots last longer in your system and are brighter than many organic dyes and fluorescent proteins previously used to illuminate the interiors of cells. They also have the advantage of monitoring changes in cellular processes while most high-resolution techniques like only provide images of cellular processes frozen at one moment Quantum dots (red dots above) can be designed to bind to specific cell receptors (green things). In this way researchers can monitor all kinds of processes in living cells

19. LOCATING CANCER CELL This picture shows silicon quantum dots fluorescing inside cancer cells.

20. These quantum dots can be put into single cells, or lots of cells, in the tissue of living organisms. In future, it is planned to attach specific antibodies to the quantum dots – when injected into a body, the quantum dots will find and bind to cancer cells, and illuminate them when they fluoresce. CdSe / ZnS QDs used to image cancer cells in a live mouse. CANCER CELL IMAGING

21. TARGETED DRUG DELIVERY In this we attach  drug  molecules to the quantum dots, which will then be able to deliver the drug just to the cancer cells where it is needed. Current anti-cancer drugs tend to have a range of unpleasant side-effects, because they affect the whole body, not just the cancer.