slideshare 1-Nanophysics-quantumwells,wires and dots

M.R.Gurulakshmi

1. E.M.G . YADAVA WOMEN’S COLLEGE, MADURAI – 625 014. (An Autonomous Institution – Affiliated to Madurai Kamaraj University) Re-accredited (3 rd Cycle) with Grade A + and CGPA 3.51 by NAAC NANO PHYSICS TOPIC: Quantum Wells, Wires and Dots By Mrs. M.R. Gurulakshmi , Department of physics,

2. Nano particles The size or dimension of a material is continuously reduced from a large or macroscopic size, such as a meter or a centimetres, to a very small size, the properties remain the same at first then small changes in properties can occur.

3. Quantum wells If one dimension is reduced to the nano range while the other two dimensions remain large, then we obtain a structure known as a quantum well.

4. Quantum wire If two dimensions are so reduced and one remains large, the resulting structure is referred to as a quantum wire. Quantum dots The extreme case of this process of size reduction in which all three dimensions reach the low nanometer range is called a quantum dot.

5. Nano structures

6. The word quantum is associated with these three types of nanostructures because the changes in properties arise from the quantum mechanical nature o physics in the domain of the ultrasmall .

7. Preparation of quantum nanostructures One approach, is called bottom-up approach. to collect consolidate and fashion individual atoms and molecules into the structure. this is carried out by a sequence of chemical reactions controlled by catalysts. it is process that is widespread in biology where, for example, catalysts called enzymes assemble amino to construct living tissue that forms and supports the organs of the body.

8. Quantum Nano Structures

9. Size effects Many properties of solids depend on the size range over which they are measured. A crystal structure is formed by associating with lattice a regular arrangement of atoms or molecules.

10. There are three Bravais lattices in the cubic system, namely, a primitive or simple cubic (SC) lattice in which the atoms occupy the eight apics of the cubic unit cell, as shown in fig. A body- centered cubic (BCC) lattice with lattice points occupied at the apices and in the center of the unit cell as indicated as shown in figure. A face- centered cubic (FCC) Bravais lattice with atoms at the apices and in the centers of the faces, as shown in figure.

11. Unit Cells of the three Bravais Lattices

12. It is appropriate to say something about their sizes relative to various parameters of the systems. If we select the type III-V semiconductor GaAs as typical material, the lattice constant from table.

13. The size or dimension d of the cube are given by, N S =12n 2 N T =8n 3 +6n 2 +3n d= na =0.565n The charge carrier in a conductor or semiconductor has its forward motion in an applied electric field periodically interrupted by scattering off phonons and defects.

14. An electron or hole moving with a drift velocity v will, on the average, experience a scattering event τ seconds, and travel a distance l called the mean free path between collisions, where l=v τ This is called intraband scattering because the charge carrier remains in the same band after scattering, such as the valance band in the case of holes.

15. References Charles P.Poole , Jr.Fank , J.Owens Introduction to Nanotechnology, Wiley students edition, New Delhi,2011. Buzea , C.; Pacheco, I. I.; Robbie, K. (2007). " Nanomaterials and nanoparticles : Sources and toxicity".  Biointerphases .  2  (4): MR17–MR71.  arXiv : 0801.3280 . Kubik T, Bogunia-Kubik K, Sugisaka M (2005). "Nanotechnology on duty in medical applications".  Curr Pharm Biotechnol .  6  (1): 17–33.  doi : 10.2174/1389201053167248 .  PMID   15727553 . National Nanotechnology Initiative  www.nano.gov   . Royal Academy of Engineering and Royal Society 2004  Nanoscience and Nanotechnologies: Opportunities and Uncertainties  http://www.nanotec.org.uk/finalReport.htm   .  

16. Thank you