Transcript - M E S KVM College Valanchery.

Nano means ‘dwarf ‘in Greek
Nano = 1 billionth
1nm = 10-9m
smallest thing visible to human eye; 10,000nm diameter
Nano world – world of atoms and molecules
How big is that?
• Nanotechnology is the manipulation of matter on an atomic and molecular
scale
• Materials, devices, and other structures with at least one dimension sized
from 1 to 100 nanometres
• Nanoparticles: one of the dimensions is less than 100nm
• Eg: DNA (2.5nm), Hb (6.5nm), viruses (10-100nm)
• Nanostructures: at least one dimension roughly between 1nm and 100nm
• Exhibit novel physical, chemical and biological properties
• Nanotechnology: fabrication of nanostructures
• Create new materials, machines, and devices to change the mode of our
living and work
• Deliberate design, construction, characterization and utilization of
functional structures , devices and systems through the control of matter at
nanometre dimensions.
• Design, assemble and build well defined intricate structures by putting
atoms or molecules at predesigned position using direct mechanical control
& extended to even macroscopic scales
• Aim: to learn to exploit the exceptional properties of nanostructures
Professor Geoffrey Ozin (University of
Toronto).
The Lycurgus Cup is a 4th-century Roman glass
cage cup made of a dichroic glass
red when lit from behind and green when lit
from in front
The dichroic effect is achieved by making the
glass with tiny proportions of nanoparticles of
gold and silver "dispersed" (the technical term
in chemistry) in colloidal form throughout the
glass material
The particles are only about 70 nanometers
across
Dichroic glass: glass containing multiple micro-layers
of metals or oxides which give the glass dichroic
optical properties.
It has a particular transmitted color and a completely
different reflected color
Nanofabrication: preparation of nanomaterials
Top-down method
 Offers reliability of the
product
 Involve high energy
usage
Bottom-up method
1. Positional assembly
 Move atom one by one into required specific
arrangement using nanoprobe of an AFM
 Allows control over individual atom during
construction
 Laborious, time cosuming, get few grams of
matreial
 Not used to create complex nanostructures
Bottom-up method
2. Self-assembly
 Atoms and molecules spontaneously arrange
themselves into final product
 Preferred method for making large
nanostructure arrays like computer memories
 Advantage: Assemble large structures
•
•
Eg:- Crystal growth carried out for
semiconductor industry
chemical synthesis of nanomatrerials
AFM
Quantum size effect
• As the system size approaches quantum mechanical
length (nano), there is a modification of the
properties of the system
• ie: the properties of nanostructured materials are
different from that of corresponding bulk materials
• A metal with bulk properties is reduced to a nanostructure
• size of the metallic particle < de Broglie wavelength of
electrons
• Boundaries of the particle confine the electrons into a localized
state: Particle in 1D box – Quantum confinement
• Material does not exhibit bulk metallic behaviour: most of the
electrons are tightly bounded or localized –quantum size effect
• Electronic and optical properties are tunable via particle size
Classification of inorganic nanomaterials
A) Commercial classification
1. Carbon based
2. Metal based
3. Dendrimers
4. Nanocomposites
B) Based on nanoscale dimensionality
 Carbon based nanomaterials
• Composed of carbon
• Hollow spheres, ellipsoid – fullerenes
• Tubes – carbon nanotubes
 Metal based nanomaterials
• Metals in nano scale range (nanoAu, nanoAg, …),
• Metal oxide nanopowders (SiO2, TiO2, Al2O3, Fe3O4, Fe2O3)
• Semiconductor nanocrystals or quantum dots (CdTe, GaAs,
etc)
 Dendrimers
• Nanosize polymers built from branched units
• Tree-like structure
• Interior: cavities and surface: numerous
chain ends
• Tailored for a specific chemical function
• Applications: Drug delivery, Gene Delivery,
Sensors, Blood substitution, nanoparticles
• eg:-Poly(propylene imine)
 Nanocomposites
• Composites: materials made from two or more constituent
materials with significantly different physical or chemical
properties
• produce a material with characteristics different from the
individual components
• Two components: Matrix & Reinforcing filler
• Matrix: polymers ,metals and ceramics, cement
• Filler: Fiber, metals, polymers
asphalt concrete
bitumen
 Nanocomposites
• At least one of the components in nanoscale range
• exhibit overall best properties of each component
• Reinforcing phase has exceptionally high surface to volume
ratio and/or its exceptionally high aspect ratio
• aspect ratio: ratio of the width of a shape to its height
 Nanocomposites
• Behavior dependent on:
– properties of components
– Interaction between them
– Distribution of filler on matrix
• Nanofillers: nanosized clays, carbon fibers, CNT, fullerenes,
metalsetc.
• Applications: nonlinear optics, batteries, sensors, catalysis
Fullerenes
• Molecule composed entirely of pure carbon in the form of a hollow
sphere, ellipsoid,
• Spherical fullerenes are also called buckyballs
• Discovered (1985) by Richard Smalley, Robert Curl, and Harold
Kroto ( 1996 chemistry Nobel Prize)
• Carbon-60 (C60) : Buckminster fullerene
• Diameter: 1nm
• 20 hexagons & 12 pentagons
• C70, C76, C80, etc - fullerenes
• Applications: Ball bearings, drug delivery vehicles, in electronic
circuits
.
Richard Buckminster Fuller
B) Based on nanoscale dimensionality
• Based on the number of dimensions which lie within the
nanoscale
1. Nanosystems confined in one dimension
–
–
–
–
Materials with 1 dimension within the nanoscale range (thickness)
Extended in other two dimensions
nanolayers
Thin films, surface coatings
2. Nanosystems confined in two dimensions
– 2 dimensions are in the nano scale range - Width & thickness
– Nanowires & nanotubes
– Nano wires: ultra fine wires or linear array of dots
– Depending upon the starting materials- different optical,
electronic and mechanical properties
– Applications: electronics, sensors, optical components &
displays, polymer composites.
– Eg: semiconductor wires fromsilicon, gallium notride,
indium phosphide, ….
• Nanotubes
– Tubular carbon nano structures (diameter is in nanoscale)
– Eg: Carbon nanotubes
• Carbon nanotubes
 discovered by Sumio Iijima (1991) with the help of an electron
microscope
 Just like rolled graphene sheets
 C- sp2 hybridisation
 some are closed at one or both the ends and some are open
 Closed tubes: caps are pentagon lattices

 Each C-atom bonded to other three – hexagonal lattice
 Two types: single walled & Multi walled
 Armchair
 Chiral
 Zig zag
Synthesis of CNTs
Arch discharge methode
– 1st successful method for small scale production
– graphote anode (6mm) & cathode(9mm) placed in an inert
environment (He/ Ar at 500mm Hg)
– Strong current (~100A) passed between anode & cathode
– Produce an electric arc that evaporates the C-atoms of
graphite
– The C-atoms condense on the surface of the electrodes and
results in NTs
– Fe or Co catalyst – SWNT
– No catalyst -- MWNT
 Laser Ablation method (1995)
 carbon is evaporated at high temp. from graphite target
using powerful & focused laser beam
Nts are collected on a cooled substrate at the end of the
chamber
2.5cm
50 cm
Furnace temp—1200oC
laser frequency- 10Hz
1.25cm
 Chemical vapour deposition (CVD)
 catalyst such as Ni or Fe is deposited onto substrate
(porous alumina or quartz)surface by thermal evaporation
Hydrocarbons (ethylene, acetylene) or CO is pumped
slowly into the reactor at furnace temp of 500 – 1200 oC
 Carbon dissociate from the feedstock & diffuses onto the
catalyst
Atoms arrange themselves into nanotubes on the substrate
• Nanosystems confined in three dimensions
o All the three dimensions in nanoscale range
o Metal & metal oxide nano particles, quantum dots, fullerenes,
dendrimers
• Quantum dot : nanocrystals of semiconductor materials
• Small enough to display quantum mechanical properties in
electronic & optical processes
• Quantum confined in 3 diensions
• Applications: in transistors, solar cells, LED, and diode lasers.
• due to their excellent fluorescent properties used as
fluorescent probe in biomolecular & cellular imaging
Properties of CNTs
 Mechanical properties
• Very high mechanical strength & tough
• Flexible & elastic
• Light weight (density 1/4th of steel)
• Tensile Strength >100 times that of steel
• Young’s modulus > 5 times that of steel
 Conductivity
• Thermal & electrical conductors (thermal conductivity >10
times that of Ag)
• Conductivity varies with diameter & helicity of the tube
lattice
• Slight change in these parameters can cause a shift from
metallic to semiconducting state
Applications of CNTs
• Reinforced fillers in nanocomposites, sensors, nanoelectronics &
high resolution display devices
• Quantum wires from CNTs carrying electricity 1000s of miles at
faster rate and more economically
• Negligible energy loss: Superior heat conductance & nanoscale
properties
• Replace Si (semiconducting channel) in Field Effect Transistors :
CNT- FET
• High current carrying capacity & structural & thermal stability:
Used as interconnect in IC in place of Cu
Nano fibers
Oxide nanoparticles
• Preparation
Spray drying
Precipitation
Sol-gel process
Q
• A nanowire is a nanostructure, with the diameter of the
order of a nanometer (10−9 meters). It can also be defined
as the ratio of the length to width being greater than 20.
Alternatively, nanowires can be defined as structures that
have a thickness or diameter constrained to tens of
nanometers or less and an unconstrained length. At these
scales, quantum mechanical effects are important — which
coined the term "quantum wires". Many different types of
nanowires exist, including metallic (e.g., Ni, Pt, Au),
semiconducting (e.g., Si, InP, GaN, etc.), and insulating (e.g.,
SiO2, TiO2). Molecular nanowires are composed of
repeating molecular units either organic (e.g. DNA) or
inorganic (e.g. Mo6S9-xIx).