Properties of

A Report on

CONTENTS

TOPIC PAGE NO.

INTRODUCTION 1-2

MECHANICAL PROPERTIES 3-7

MAGNETIC PROPERTIES 8-14

OPTICAL PROPERTIES 15-18

ELECTRICAL PROPERTIES 19-25

INTRODUCTION

• Nanotechnology is the collaboration of the physics ,chemistry,biology,computerand 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.

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•

• 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 nanostructuredmaterials 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;Nanocapsules;Nanorings;Fullerenes;collidal particles;activatedcarbon; nanoporous silicon;quasicrystals.

• b)systems confined in 2 dimensions[One dimension structures]Examples:Nanorods;Nanofilaments;Nanotubes;quantum wires;nano wires.

• c)systems confined in 1 dimension.[two dimension structures]Examples:discs;platelets;ultrathin films;superlattices;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

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MECHANICAL PROPERTIES

• 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

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Modulus = slope

Strain

Stre

ss, 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

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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

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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 nanostructuredmaterial increases with decreasing size

Grain boundaries deformation

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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

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MAGNETIC PROPERTIES

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 microscopyIs it nano?Well, overall size is ~1mm, but the bit has smaller details.Clearly, nano characterization methods are being used to see this.

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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 (SibelTurksen Thesis)

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M

-M

Magnetization

Magnetizationin 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.

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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.

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Superparamagnetic nanoparticles

Stabilizationa) 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.

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MRI imaging

T1 spin-lattice relaxation

T2 spin-spin relaxation

a) SPIO affects T2b) Gd3+ affects T1

c) Core-shell nanoparticleenable both imaging modes.

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• 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

Optical properties

• 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

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• 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.

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• 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

• 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 Drudemetal and insulator in a magnetic field (Xia, Hui, Stroud, J. Appl. Phys. 67, 2736 (1990)

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Quantum confinementIn small nanocrystals, the electronic energy levels are not continuous asin 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 opticalproperties with reduced size will be observed when the energy spacingbetween the electronic levels exceeds the thermal energy (kT).Moreover, nanocrystals possess a high surface are and a large fractionof the atoms in a nanocrystal are on its surface. Since this fractiondepends 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

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Metal (conductor) Insulator Semiconductor

Conductionband

(empty)

Valenceband(full)

band gap band gap

Electronic band theory

Density of states in metal (A) and semiconductor (B) nanocrystals. In each case, the density ofstates is discrete at the band edges. The Fermi level is in the center of a band in a metal, and so kTwill exceed the level spacing even at low temperatures and small sizes. Nevertheless, metalnanoparticles of very small size can exhibit

insulating properties.

Energy levels in metallic and semiconductor nanoparticles

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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

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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.

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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.

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Experimental approaches to measure the Coulomb blockade.Two metallic leads with spacing of a few nm are fabricated. An organicmonolayer is then used to bind nanocrystals to the leads. When a

nanocrystalbridges the gap between the leads, it can be electrically investigated.

(a) Field emission scanning electron micrograph of a leadstructure before the nanocrystals are introduced. The light gray region isformed by the angle evaporation and is 10 nm thick. The darker region isfrom a normal angle evaporation and is 70 nm thick. (b) Schematic crosssection of nanocrystals bound via a bifunctional linker molecule to theleads. Transport between the leads occurs through the mottled nanocrystalbridging the gap.

Schematic illustrationof a single-electron tunnel

junction formed by ananocrystal held between

the STM tip and thesubstrate.

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• (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 nanoparticlesbehave as redox active molecules,showing redox cascades that are well known in inorganic and organometallic electrochemistry

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