Powers point presentation on Properties of nano materials mainly electrical , magnetic and thermal properties

1. Properties of Nano-materials
by:
Mohd Bilal
Aligarh Muslim University,India
04-04-2018 1

2. CONTENTS:
• Introduction
• Properties of nano materials
Electrical Properties
Electric dispersion reaction
Magnetic Properties
Thermal Properties
• References
04-04-2018 2

3. What are nanomaterials?
• Nanomaterials are materials which are characterised by an ultra fine grain
size (< 50 nm) or by a dimensionality limited to 50 nm.
• Nanomaterials can be created with various modulation dimensionalities as
defined by Richard W. Siegel:
 zero (atomic clusters, filaments and cluster assemblies),
 one (multilayers),
 two (ultrafine-grained overlayers or buried layers) and
 three (nanophase materials consisting of equiaxed nanometer sized grains)
04-04-2018 3

4. Influence on properties by "nano-structure
induced effects"
• Due to the small sizes any surface coating of the nano-particles strongly
influences the properties of the particles as a whole.
Roughly two kinds of "nano-structure induced effects" can be
distinguished:
• First the size effect, in particular the quantum size effects where the normal
bulk electronic structure is replaced by a series of discrete electronic levels.
• Second the surface or interface induced effect, which is important because
of the enormously increased specific surface in particle systems.
04-04-2018 4

5. Properties of nano materials:
• Electrical Properties
• Magnetic Properties
• Thermal Properties
• Optical Properties
• Electronic Properties
• Piezoelectric Properties
• Mechanical Properties
04-04-2018 5

6. Electrical properties:
• Electronic band structure changes into discrete energy levels, Ohm’s
law is no longer valid.
• If one electron is transferred to a small particle, the Coulomb energy
of the latter increases by
EC = e2/2 C
where C is the capacitance of the particle.
• If the temperature is low such that
kT < e2/2 C
single electron tunneling processes are observed.
04-04-2018 6

7. • Thermal motion of the atoms in the particle can initiate a change in the
charge and the Coulomb energy so that further electrons may tunnel
uncontrolled Hence, the I-V characteristic of a quantum dot is not linear,
but staircase-like.
• No current flows up to VC = ± e/2 C. If this value is reached, an electron
can be transferred. Following this, an electron tunnelling process occurs if
the Coulomb energy of the particle is compensated by an external voltage
of V = ±ne/2 C. This behaviour is called Coulomb blockade.
• The charging energy increases with decreasing the size of the quantum
dot.
04-04-2018 7

8. Figure I-U characteristic of ideal single electron transport, where Coulomb
blockade is shown as the step function
04-04-2018 8

9. Experimental approaches to measure the
Coulomb blockade.
• Two metallic leads with spacing of a few nm are fabricated. An organic
monolayer is then used to bind nanocrystals to the leads. When a nanocrystal
bridges the gap between the leads, it can be electrically investigated
Figure . (a) Field emission scanning electron micrograph of a lead structure before the nanocrystals are
introduced. The light gray region is formed by the angle evaporation and is 10 nm thick. The darker region is
from a normal angle evaporation and is 70 nm thick. (b) Schematic cross section of nanocrystals bound via a
bifunctional linker molecule to the leads. Transport between the leads occurs through the mottled nanocrystal
bridging the gap
04-04-2018 9

10. Fig. 1.7. (a) I–V characteristic of an isolated 3.3 nm Pd nanocrystal (dotted line)
and the theoretical fit (solid line) obtained at 300 K using a semiclassical model. (b)
The size dependence of the charging energy.
a b
04-04-2018 10

11. Electric dispersion reaction
• Electric dispersion reaction is a precipitation reaction that is carried
out in the presence of a pulsed electric field to synthesize ultra fine
precursor powders of advanced ceramic materials.
• The technique involves subjecting the reactor liquid (metal-alkoxide
solution) to a dc electric field (3 to 10 kV/cm at pulsing frequencies in
the range 1 to 3 kHz).
• Under the applied electric field, the sol is shattered to micron-sized
droplets, termed as microreactors, which contain hydrous precursor
precipitate.
• The formed precursor powders can be thermally processed to obtain
oxide nanoparticles
04-04-2018 11

12. The magnetic properties :
• Magnetic properties Magnetic materials exhibit size-dependent magnetic
properties that range from ferromagnetic to paramagnetic to super paramagnetic
with decreasing size.
• The magnetic properties of nanoparticles differ from those of bulk mainly in two
points.
• The large surface-to-volume ratio results in a different local environment for the
surface atoms in their magnetic coupling/interaction with the neighbouring
atoms, leading to the mixed volume and surface magnetic characteristics .
• Unlike bulk ferromagnetic materials, which usually form multiple magnetic
domains, several ferromagnetic particles could consist of only a single magnetic
domain.
04-04-2018 12

13. • In the case of a single particle being a single domain, the
superparamagnetism occurs, in which the magnetization of the particles
are randomly distributed and they are aligned only under an applied
magnetic field and the alignment disappears once the external field is
withdrawn.
• In ultra-compact information storage the size of the domain determines
the limit of storage density.
• The giant magneto resistance (GMR) and colossal magneto resistance
(CMR) materials offer exciting possibilities for magnetic sensors,
magneto resistive read heads and magnetoresistive random access
memory.
04-04-2018 13

14. Thermal Properties
• The thermal conductivity by mobile carriers, whether waves or
particles, can be expressed in general in the form
K=(1/3)CVl
where C is their specific heat per unit volume, v their speed and l their
mean free path.
• If the carriers are waves (lattice waves or electromagnetic waves)
ranging over a spectrum of frequencies f, this must be generalized to
04-04-2018 14

15. • fm denotes an effective upper limit to the spectrum because either v
or l become very small for f fm
• The energy content of waves consist of quanta, phonons or photons
respectively, and these quanta can also be considered as particles
which carry heat.
• The present treatment emphasizes the wave nature of the carriers of
heat.
04-04-2018 15

16. Refrences:
• A.S. Edelstein (ed), Nanomaterials: Synthesis, Properties and Applications, IOP
publishing, Bristol, (1999)
• R.W. Siegel, Nanomaterials: Synthesis, Properties and Applications, A.S. Edelstein,
R.C. Cammarata (eds), IOP publishing, Philadelphia, (1998)
• Physical properties of nanomaterials by Juh Tzeng Lue, Department of Physics,
National Tsing Hua University, Hsin Chu, Taiwan
• S. Wang and J. Zhao, Ferroelectrics 154, 289 (1994). S. Y. Chen, L. W. Chang, C. W.
Peng, H. Y. Miao, and J. T. Lue, J. Nanosci. Nanotechnol. 5, 1987 (2005); L. W.
Chang and J. T. Lue, ibid 5, 1672 (2005).
• P.G. Klemens, M. Gell, Thermal conductivity of thermal barrier coatings,
Materials Science and Engineering A245 (1998), p.p. 143-149
• L. Braginsky, V. Shklover, H. Hofmann, P. Bowen, High-temperature thermal
conductivity of porous Al2O3 nanostructures, Physical review B 70, 134201 (2004)
04-04-2018 16

17. Thank you
04-04-2018 17