Lecture 3 Nanotech

8/10/2019 Lecture 3 Nanotech

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NANOTECHNOLOGY

(SCT3022)

Topic 2:The Fundamental Science Behind

Nanotechnology


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What will you learn from

this chapter

Various types of nanostructures.

Energy bands formed from a solid.


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Structure:Size dependence of properties

Many properties of solids depend on their size range.

Microscopic details become averaged when

investigating bulk materials. Macro- or large- scale range: size (mm to km)

mechanics, electricity and magenetism & optics

averaged properties .

Nanometer range: properties of material change e.g.

mechanical, ferroelectric & ferromagnetic properties.


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Structure:crystal structures

Most solids are crystalline

Atoms arranged in regular manner

Regularity extended long range order

Amorphous materials

E.g. glass and wax

Non regular arrangement - Short range order

What would the find out about the

following:

Amorphous

Atomic orders in liquid and gases

Crystalline structure

Amorphous structure


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Can be presented using Bravais lattices i.e. a

fundamental concept in the description of crystalline

solids.

There are only 5 Bravais lattices in 2D

Structure:crystal structures


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Structure:5 Bravais lattices in 2D

Square

Primitive

rectangular

Centeredrectangular

Hexagonal

Oblique


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Structure:Unit cell

It is very cumbersome to draw entire lattices in 3D so

some small portion of the lattice, having full symmetry

of the lattice, is usually drawn. This small portion when

repeated can generate the whole lattice and is calledthe unit cell.


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Unit cell for each bravais

lattice


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Structure:14 bravais lattices in 3d

There are 14 different Bravais lattices in 3D that are

classified into 7 different crystal systems (only the unit

cells are shown below)

Lowest symmetrya b c,

Triclinic type

Highest symmetry

a = b = c, = == 90oCubic


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Structure:14 bravais lattices in 3d

end-

centered

(FCC)(BCC)(SC)


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Building fcc lattice

First hexagonal close-packed

structure generated

Second face-centred cubic lattice

results (when viewed at different

angle)


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Spaces between atoms

in a lattice

Octahedral arrangement

Tetrahedral

arrangement

Spaces left for smaller

atoms to reside

Number of octahedral

site = number ofspheres

Number of tetrahedral

site = 2 x number of

spheres

Examples : MgO, MgS,

MnO, MnS


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Structures of some

nanoparticles

Source:http://boomeria.org/chemtext


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video for further understanding

http://www.youtube.com/watch?v=QIj0t8MNKls

http://www.youtube.com/watch?v=CsnNbuqxGTk

http://www.youtube.com/watch?v=NYVSI83KiKU

http://www.youtube.com/watch?v=Mm-jqk1TeRY

http://www.youtube.com/watch?v=TIXWnr3sdY4
http://www.youtube.com/watch?v=CsnNbuqxGTkhttp://www.youtube.com/watch?v=CsnNbuqxGTkhttp://www.youtube.com/watch?v=NYVSI83KiKUhttp://www.youtube.com/watch?v=Mm-jqk1TeRYhttp://www.youtube.com/watch?v=TIXWnr3sdY4http://www.youtube.com/watch?v=TIXWnr3sdY4http://www.youtube.com/watch?v=TIXWnr3sdY4http://www.youtube.com/watch?v=Mm-jqk1TeRYhttp://www.youtube.com/watch?v=Mm-jqk1TeRYhttp://www.youtube.com/watch?v=Mm-jqk1TeRYhttp://www.youtube.com/watch?v=NYVSI83KiKUhttp://www.youtube.com/watch?v=NYVSI83KiKUhttp://www.youtube.com/watch?v=CsnNbuqxGTkhttp://www.youtube.com/watch?v=CsnNbuqxGTkhttp://www.youtube.com/watch?v=CsnNbuqxGTkhttp://www.youtube.com/watch?v=CsnNbuqxGTkhttp://www.youtube.com/watch?v=CsnNbuqxGTk


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Atom stabilization

Au55

Purely metallic FCC nanoparticles.

very reactive, short lifetimes.

Need to be stabilized by adding atomic groups

between atoms and on surfaces.

Au55(PPh3)12Cl6 diameter of 1.4 nm


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Energy bands

When solid is formed, the energy level of the atoms

broaden and form bands with forbidden gaps between

them.

Energy values of electrons exist within one of the bands.

Lower energy bands: narrower & full of electronsdo

not contribute to the electronic properties of a material.

Outer energy bands (valance bands): electron that bond

the crystal together


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Insulators

Contain fixed electrons (localized)

No moving electrons to carry current

Conduction band is far above the valance band (notthermally accessible)

Heat content of insulating material is not sufficient to

raise electrons from VB to CB.

Energy bands:Insulators, semiconductors & Conductors

CB

VB


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Semiconductors

Less gap between CB and VB

Heat content of the material can thermally excite

electrons and produce current

Small electrical current produced

Can be doped with electron donating /accepting

atoms


CB

VB


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Conductors

Full with delocalized conduction electrons

Efficient in carrying electric current flow


CB

VB


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http://www.youtube.com/watch?v=um-YimkrWMM

http://www.youtube.com/watch?v=y_GZn4o8gaE

video for further understanding
http://www.youtube.com/watch?v=um-YimkrWMMhttp://www.youtube.com/watch?v=y_GZn4o8gaEhttp://www.youtube.com/watch?v=y_GZn4o8gaEhttp://www.youtube.com/watch?v=y_GZn4o8gaEhttp://www.youtube.com/watch?v=um-YimkrWMMhttp://www.youtube.com/watch?v=um-YimkrWMMhttp://www.youtube.com/watch?v=um-YimkrWMM

Lecture 3 Nanotech

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