Properties of Nano-materials. Mainly focusing on mechanical, magnetic, optical and electrical properties.

1. Properties of
A Report on

2. CONTENTS
TOPIC PAGE NO.
INTRODUCTION 1-2
MECHANICALPROPERTIES 3-7
MAGNETICPROPERTIES 8-14
OPTICAL PROPERTIES 15-18
ELECTRICALPROPERTIES 19-25

3. INTRODUCTION
• Nanotechnology is the
collaboration of the physics
,chemistry,biology,computer
and material sciences integrated
with engineering entering the
nanoscale.This means science and
engineering focused on making
the particles,things and devices at
the atomic and molecular scale.
Definition of Nano Particles:
Nanomaterials or the Nanoparticles are the set of particles or the
substances where atlas one dimension is less than approximately 100nm.
or it can be also classically illustrated as the follows:
Nanomaterial is an object that has atleast one dimension in the
nanometer scale approximately 1-100nm.
1

4. •
• Due to the reduction in the spatial dimension , or
confinement of particles or quasi particles in a
particular crystallographic direction within a
structure generally leads to changes in physical
properties of the system in that direction.
• Hence classification of the nanostructured
materials and systems essentially depends on the
number of dimensions which lie within the
nanometer range.
• a)systems confined in 3 dimensions[Zero
dimension structures]
Examples:Nanoparticles;Nanograins;Nanoshells;Na
nocapsules;Nanorings;Fullerenes;collidal
particles;activatedcarbon; nanoporous silicon;quasi
crystals.
• b)systems confined in 2 dimensions[One
dimension structures]
Examples:Nanorods;Nanofilaments;Nanotubes;qua
ntum wires;nano wires.
• c)systems confined in 1 dimension.[two dimension
structures]
Examples:discs;platelets;ultrathin films;super
lattices;quantum wells.
• In this report we have discussed mainly on on the following properties of
Nanomaterials:
• Mechanical Properties
• Magnetic Properties
• Optical Properties
• Electrical Properties
Classification of Nanomaterials
2

5. MECHANICALPROPERTIES
• Tensile test
Classic Mechanical Properties
Determination of mechanical
properties
Stress: σ = F/S
Strain: ε = Δl / l0
Max
stress :
tensile
strength
Max
elasticity:
Yield
strength
Stress, σ
(Mpa)
Necking
Strain, ε
(%)Elastic
deformation
Plastic
deformation
Fract
ure
Tensile Test curve
3

6. Modulus = slope
Strain
Stress,σ
• Hooke’s law: σ = E ε
• E = Young modulus (Pa)
• Stiffness of material
• Non linear models exist
(visco-elastic behaviour)
Elastic Deformation
Mechanical properties
Yield strength: maximum stress before permanent strain
Tensile strength: maximum stress
Ductility: measure of deformation (Lf – Lo)/ Lo
Toughness: ability to absorbe energy: area under curve
Hardness
Resistance to plastic deformation
Measure of depth or size of indentation
4

7. Nanoparticles
• Conventional materials: Grain size micron to mm
• Nanoparticles increase grain boundaries
• Influence on mechanical properties: Increased hardness, yield
strength, elastic modulus, toughness
Nanostructured materials
Comparison:
Al Mg cryomilled (20
nm)
Al Mg ultra fine grain
(80 nm)
Al Mg coarse (2 mm)
Cryomilling: Milling in
liquid N2
Ultrafine grain:
electrodeposition
Comparison tensile curves
5

8. Mechanical properties of nanomaterials compared
to coarse grain materials
• Higher Young modulus and tensile strength (to 4 times
higher)
• Lower plastic deformation
• More brittle
Strength and Hardness with grain size
Strength and
Hardness of
nanostructured
material increases
with decreasing size
Grain boundaries
deformation
6

9. Elongation nanostructured materials
• Elongation decreased
• Lower density of mobile
dislocations
• Short distance of dislocation
movement
Material Young modulus (GPa)
Rubber 0.1
Al 70
Fe 200
SiC 440
Fe nanoparticles (100 nm) 800
C nanotubes 1000
Diamond 1200
Comparison of Young modulus
7

10. MAGNETICPROPERTIES
Magnetic properties of nanoparticles
• Each spin is a small magnet
• Interaction between neighboring spins is dominated by the spin
exchange interaction.
• In most materials J < 0 and the material is non-magnetic
(paramagnetic or diamagnetic)
Most people relate magnetics to storage
One bit viewed by magnetic force microscopy
Is it nano?
Well, overall size is ~1mm, but the bit has
smaller details.
Clearly, nano characterization methods are
being used to see this.
8

11. Apoferritin, your
body’s iron storage
protein and
precision magnetic
system.
Quaternary structure of the protein. The
pieces make an open cavity that can store
thousands of Fe atoms
Types of Magnetism (Sibel
Turksen Thesis)
9

12. M
-M
Magnetization
Magnetization
in opposite direction
General Hysteresis Plot
Paramagnet, Ferromagnet &
Superparamagnet
I think of the superparamagnet as
a small ferromagnet. Because of
its small size, the magnetic
moment wanders. When given
an order to align (when a
magnetic field is imposed) it
aligns with the same enthusiasm
that a ferromagnet has, which
exceeds that of the paramagnet.
10

13. Paramagnet
Zero field
Applied field
FerromagnetSuperparamagnet
Like the paramagnet, the superparamagnet returns to zero
magnetization when the field is removed. It does so for a
different reason: small size, not intrinsically weak
exchange between the individual moments.
The bottom line is:
Nano scale has a big impact on the
magnetic properties!
In a normally ferromagnetic material,
nano scale reduces the moment, but it can
be restored by applying a magnetic field.
The good news: switchable interactions!
The bad news: There would seem to be a
lower limit to the size of a magnetic
particle that can hold an alignment for
data storage.
11

14. Superparamagnetic nanoparticles
Stabilization
a) By surface coating using appropriate polymeric
stabilizers/surfactants (carboxylates, phospates, cathecols)
b) By deposition of a layer of inorganic metals (e.g., gold),
nonmetals (e.g., graphite), or oxides (e.g. SiO2)
c) By generating polymeric shells that avoid cluster growth
after nucleation (composite particles, nanocapsule).
d) By the formation of lipid-like coatings (e.g., liposomes/
lipid NPs) around the magnetic core.
12

15. MRI imaging
T1 spin-lattice relaxation
T2 spin-spin relaxation
a) SPIO affects T2
b) Gd3+ affects T1
c) Core-shell nanoparticle
enable both imaging modes.
13

16. • They will chain together!
• The chain causes high viscosity.
•  Magnetorheological effect.
Suppose some particles do have magnetic moments.
N S N S N S N S
A magnetic fluid.
Magnetorheological Effect
Fluid becomes solid—and
reverses! 14

17. Opticalproperties
• So lets start with Optical properties. But first, let me ask you a question.
What is the origin of colour? Well its because of SURFACE PLASMONS.
• An SP is a natural oscillation of the electron gas inside a gold nanosphere.
• If the sphere is small compared to a wavelength of light, and the light has a
frequency close to that of the SP, then the SP will absorb energy.
• The frequency of the SP depends on the dielectric function of the gold, and
the shape of the nanoparticle. For a spherical particle, the frequency is
about 0.58 of the bulk plasma frequency. Thus, although the bulk plasma
frequency is in the UV, the SP frequency is in the visible (in fact, close to
520 nm)
Metallic sphere
EM wave
Incident electric field is =E o exp(-i w t)
Surface plasmon is excited when a long-wavelength
electromagnetic wave is incident on a metallic sphere
15

18. • Calculation of SP Frequency
Effective conductivity of a random metal-insulator composite
in the effective-medium approximation
Effective conductivity of a
composite of Drude metal
and insulator: dots,
numerical; full curves,
effective-medium
approximation.
16

19. • Nonlinear optical properties of nanomaterials
Suppose we have a suspension of nanoparticles in a host (or some other
composite which is structured on the nanoscale).
If an EM wave is applied, the local electric field may be hugely enhanced near
an SP resonance.
Ifso,one expects various nonlinear susceptibilities, which depend on higher
powers of the electric field, to be enhanced even more.
The Kerr Susceptibility is defined by
where D is the electric displacement, E is the electric field, and epsilon and chi
are the linear and nonlinear electric susceptibilities.
If the electric field is locally large, as near an SP resonance, then its cube is
correspondingly larger. Thus, near an SP resonance, one expects a huge
enhancement of the cubic nonlinear (Kerr) susceptibility
Kerr susceptibility for a dilute suspension of coated
spheres
Cubic nonlinear (Kerr) susceptibility for a
dilute suspension of coated metal particles
in a glass host, calculated in Maxwell-
Garnett approximation 17

20. • Kerr enhancement factor for a random metal-insulator composite,
assuming (left) metal and (right) insulator is nonlinear. Calculation is
carried out numerically, at the metal-insulator percolation threshold.
Kerr enhancement factor for metal-insulator composite
Faraday Rotation in Composites:
enhanced near SP resonance
Real and imaginary parts of the Faraday
rotation angle in a composite of Drude
metal and insulator in a magnetic field
(Xia, Hui, Stroud, J. Appl. Phys. 67, 2736
(1990)
18

21. Quantum confinement
In small nanocrystals, the electronic energy levels are not continuous as
in the bulk but are discrete (finite density of states), because of the
confinement of the electronic wavefunction to the physical dimensions of
the particles. This phenomenon is called quantum confinement and
therefore nanocrystals are also referred to as quantum dots (QDs).
In any material, substantial variation of fundamental electrical and optical
properties with reduced size will be observed when the energy spacing
between the electronic levels exceeds the thermal energy (kT).
Moreover, nanocrystals possess a high surface are and a large fraction
of the atoms in a nanocrystal are on its surface. Since this fraction
depends largely on the size of the particle (30% for a 1-nm crystal, 15%
for a 10-nm crystal), it can give rise to size effects in chemical and
physical properties of the nanocrystal.
ELECTRICAL PROPERTIES
19

22. Metal (conductor) Insulator
Semiconductor
Conduction
band
(empty)
Valence
band
(full)
band gap band gap
Electronic band theory
Density of states in metal (A) and
semiconductor (B) nanocrystals. In each
case, the density of
states is discrete at the band edges. The
Fermi level is in the center of a band in a
metal, and so kT
will exceed the level spacing even at low
temperatures and small sizes. Nevertheless,
metal
nanoparticles of very small size can exhibit
insulating properties.
Energy levels in metallic and semiconductor
nanoparticles
20

23. The properties like conductivity or resistivity are come under category
of electrical properties. These properties are observed to change at
nanoscale level like optical properties. The change in electrical
properties in nanomaterials are:
1. Conductivity of a bulk or large material does not depend upon
dimensions like diameter or area of cross section and twist in the
conducting wire etc. However it is found that in case of carbon
nanotubes conductivity changes with change in area of cross
section.
2.) It is also observed that conductivity also changes when some shear
force (in simple terms twist) is given to nanotube.
3.) Conductivity of a multiwalled carbon nanotube is different than
that of single nanotube of same dimensions.
4.) The carbon nanotubes can act as conductor or semiconductor in
behaviour but we all know that large carbon (graphite) is good
conductor of electricity.
These are the important electrical properties of nanomaterials.
The electrical properties of the
nanomaterial triggered a response
in the mesenchymal (adult) stem
cells, which we sourced from
human bone marrow. In effect,
they became electrified, which
made them morph into more
cardiac-like cells
21

24. Here we are to discuss about fundamentals of electrical conductivity
in nanotubes and nanorods, carbon nanotubes,
photoconductivity of nanorods, electrical conductivity of
nanocomposites. One interesting method which can be used to
demonstrate the steps in conductance is the mechanical thinning
of a nanowire and measurement of the electrical current at a
constant applied voltage. The important point here is that, with
decreasing diameter of the wire, the number of electron wave
modes contributing to the electrical conductivity is becoming
increasingly smaller by well-defined quantized steps. In electrically
conducting carbon nanotubes, only one electron wave mode is
observed which transport the electrical current. As the lengths and
orientations of the carbon nanotubes are different, they touch the
surface of the mercury at different times, which provides two sets
of information: (i) the influence of carbon nanotube length on
the resistance; and (ii) the resistances of the different nanotubes.
As the nanotubes have different lengths, then with increasing
protrusion of the
fiber bundle an increasing number of carbon nanotubes will touch the
surface of the mercury droplet and contribute to the electrical
current transport.
22

25. Electrical conductivity of bulk metals is based on their electronic band
structures, and the mobility of electrons is related to their mean
free path between two collisions with the lattice. The collective
motion of electrons in a bulk metal obeys Ohm’s law, V = RI, where V
is the applied voltage, R is the resistance of the material and I is
the current. As the 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 E C = e^2 /2C, where C is the capacitance of the
particle. If the temperature is low such that kT < e 2 /2C, single
electron tunneling processes are observed.*
* 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 V C = ±e/2C. 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/2C.
This behaviour is called Coulomb blockade. The
charging energy increases with decreasing the size of the quantum
dot.
I-U characteristic of ideal single
electron transport,
where Coulomb blockade is shown
as the step function.
23

26. 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.
(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.
Schematic illustration
of a single-electron tunnel
junction formed by a
nanocrystal held between
the STM tip and the
substrate.
24

27. • (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.
In voltammetric experiments in solution, metal nanoparticles
behave as redox active molecules,
showing redox cascades that are well known in inorganic and
organometallic electrochemistry
25