الشريحة 1

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Transcript الشريحة 1

Nanotechnology
Prof. Dr. S. Taha •
Physics department •
Vice Dean for Postgraduate •
Studies and Research Affairs •
Faculty of Science •
Fayoum university •
Egypt •
1- definition of nano Particles .
•
A nano cluster is a tiny chunk of the bulk measuring a •
few nanometers with a Finite number of atoms in
it.
2- Physical Properties of Nanocrystals .
•
a- The electronic Structure of a nano crystal Critically •
depends on its Size .
The electronic level are not Continuous as in bulk •
materials , but discrete , due to the confinement of the
electron wave - function because of the Physical
dimensions of the Particles . This Phenomenon is
Called quantum confinement, therefore , nanocrystals
are also Known as quantum
dots.
b- The average electronic energy level Spacing of •
Successive quantum levels , Known as the so-Called
Kubo gap , is given
by
δ = 4 EF /3n •
c- The resultant discreteness of energy levels . ( the •
nano crystals Can be discretely charged with
electrons ) . ( i . e ) nano crystal Carrying an extra
electrons can exhibit Properties different from those
of a neutral species also brings about fundamental
changes in the characteristic Spectral features of the
nano particles , especially those related to the valence
band .
•
3- The nano Sized clusters display a remarkable •
endency to remain Single – Crystalline and hence are
also called nano crystals . In addition , nano crystals
Possess a high surface area : A great fraction of
atoms in nanocrystal is on its surface
.
The nano crystals is their Size – dependent Properties •
( i . e ) the electronic , magnetic , and optical
Properties of a nano crystal depend on its size
( quantum size effects )
.
4- a - The nano crystals akin to covalent systems Self- •
assemble into ordered arrays in one , two and three
dimensions under the right conditions .
b- Lattices of nano crystals consist of interacting •
nano crystals and may exhibit novel Properties arising
out of such interaction .
c- Thus , the ability to engineer such assemblies •
extends the reach of current lattices of nano crystals
and holds promise for a new generation of electronics
of the nanoworld .
5- size control •
6- Shape control . •
7- Example CNT . •