Unit 4

Question 1

nano

Answer 1

Greek = dwarf
approx 10 H or 5 Si
atoms aligned in a line

btw bulk
material and atoms/molecules

quantum effects are seen as the dimensions
are closer to atoms or molecules

Materials with at least one external dimension btw 1 and 100 nm

Question 2

Properties of nanomaterials are different from bulk
materials

Answer 2

Au-bulk is yellowish

Au- nanoparticles
red in colour

• Al stable becomes combustible in the
  nanoparticle = solid fuel in rocket propulsion
• Melting point of materials is lower in nano-range

Question 3

Classification of Nanomaterials

Answer 3

(0D) => no dimension is allowed to be outside of nanorange.

Like quantum dots ,
nanoclustures eg. fullerene.

(1D):
one of their dimensions out nanotubes , nanowires

(2D) :
2 of their dimensions out
eg. Nanofilms, nanocoatings

(3D):
all the 3 dimensions out
eg. Dispersions of
nanoparticles, bundles of nanowires

Question 4

Spatial confinement- (quantum confinement)

Answer 4

3D-free carriers in 3 directions

2D-free carriers in 2 directions (quantum well), observed in semiconductor system

1D- quantum wires
free to move in the direction of the wire

0-D- dots
confined in all directions (no free carriers)

Question 5

Properties of Nanomaterials

Answer 5

*Properties of any bulk material are independent of its size

nanomaterials change with size

material can be altered only by structure and composition

Question 6

Surface Area dependant properties

Answer 6

Many physical and chemical properties =depend on
surface properties

• Surface area high -> nano
  scale.
• Properties like catalytic activity, gas adsorption depend on surface area

e.g. Bulk gold is catalytically inactive but gold nanoparticles are
catalytically active

• Surface energy is also high so chemical reactivity is high
  e.g. Al is combustible

Question 7

Electrical Properties
spatial confinement:

Answer 7

Electrical conductivity decreases = nanoparticles

spatial confinement:

• The electronic bands in bulk = continuous
• nano = discrete
  and band gap increases

Question 8

Electrical Properties
surface scattering:

Answer 8

• e- have mean free path
• If dimensions of the nanomaterial < mean free
  path

elastic or inelastic surface scattering can happen

• Elastic scattering will not affect conductivity

inelastic scattering e- loses its velocity and
electrical conductivity decreases

Question 9

Increase in Energy gap

Answer 9

• Increases in energy gap btw the valence band and conduction band
• As size of nanoparticles decreases the energy gap increases and the
  wavelength of light absorbed moves towards smaller values .

=> ‘blue shift’

Question 10

Mechanical properties

Answer 10

Strength of nanomaterials >bulk material

e.g bending of bulk Cu happens

Cu particles < 50 nm are
hard materials show same malleability and ductility as bulk Cu.

Large lattices in bulk materials have imperfections like dislocations, kinks
and vacancies

lattice with smaller cross-section, less probability of finding imperfections.

Question 11

Thermal properties in nano

Answer 11

lot of surface atoms

Atoms on the surface bound by lesser number of bonds

*number of bonds need to be broken per atom

• Size of the particles is smaller than path length of phonons arising
  due to lattice vibrations .
• Phonon scattering = decrease in thermal conductivity

Question 12

Magnetic Properties

Answer 12

ferromagnetic materials like Fe,Co,Ni =>
superparamagnetism in the nanometer due to the high surface
energy.

domains can flip directions with magnetic field ,

get magnetised with high susceptibilities.

• Bulk gold and platinum are non-magnetic but at the nano-size they act
  as magnetic particles