Nanotechnology (Dr. S. T. Mhaske)-1
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Transcript of Nanotechnology (Dr. S. T. Mhaske)-1
Presented By, Dr. S. T. Mhaske
Is Nanotechnology really new?
During the middle ages, the
Muslims who fought crusaders
with swords of Damascus steel
had a high-tech edge - carbon
nanotubes and nanowires in
their sabres. Damascus sabres
were forged from Indian steel
called wootz. It is likely that the
sophisticated process of
forging and annealing the steel
formed the nanotubes and the
nanowires, and could explain
the amazing mechanical
properties of the swords TEM image of
cementite nanowires
Is Nanotechnology really new?
Lycurgus cup,4th century AD (now at the
British Museum,London).The colors originates
from metal nanoparticles embedded in the glass.
At places, where light is transmitted through the
glass it appears red, at places where light is
scattered near the surface, the scattered light
appears greenish.
Suspensions of spherical gold
particles with various
diameters (150, 100, 80, 60,
40, 20 nm from left to right)
in water. The difference in
colors is due to different
scattering and absorption
behaviour of small and large
gold particles.
Nanotechnology
Derives from nanometer, which is one-thousandth
of a micrometer (micron), or 10–9 of a meter
The study, manipulation and manufacture of ultra-
small structures and machines made of as few as
one molecule
100-500nm: Typical polymer latex particle size
250nm: Hiding grade TiO2 particle size.
Nature is Beautiful
Nanostructure diffracts the light, interference eliminate all the colors except orange/black.
Nanomaterials
Nanomaterials
Nanowires
Fullerenes
Nanofibers Nanotubes
Nanoparticles
Carbon nanotubes,
quantum dots, and other
advanced nanomaterials
Proteins, Biological
motors, and other
nanobiological systems
Real and imagined
human-made
nanomachines
Nanostructure Material
Metals
Ceramics
Polymers
Biomolecular materials
Nanoparticles Nanostructured Surfaces
Nanostructured Materials
e.g. UV absorber
in sun screens
e.g. mortars and
concrete e.g. lotus leaf
Nano-Particles
Fundamental building blocks of nano-
technology
Starting point for “bottom-up” approaches for
preparing nano-structured materials & devices
Their synthesis is an important research
component
Building Complex Structures with Small Objects
Top-down
(i.e. Lithography)
Bottom-up
(i.e. Self-assembly)
Mixing large objects with small
ones
(i.e. nanocomposites) Carbon matrix
Nanotube bundles
Composite
fabrication
This slide is adapted from the presentation on “An Introduction to Nanotechnology,”
by Terry Bigioni, posted at
http://www.homepages.utoledo.edu/tbigion/BigioniGroup/Outreach_Home.html
Top-Down Fabrication
Start with a large piece of material
Remove sections of material to “carve” a
specific pattern or shape
Has been used for centuries to manufacture
artwork, tools and devices
Bottom-Up Fabrication
Start with catalyst particles and/or a substrate
Expose to a gas or liquid
Reaction leads to the growth of a solid
nanostructure or nanoscale self-assembled
layer
Properties such as temperature, pressure,
surface quality, composition, catalyst size, etc.
influence growth characteristics
Nano-Materials Synthesis Methods
Colloidal processes
Liquid-phase synthesis
Gas-phase synthesis
Vapor-phase synthesis
Precipitation
Sonication
Nano-Engineered Products
Semiconductor nano-crystallites for use in microelectronics
Ceramics for use in demanding environments
Polymers with enhanced functional properties
Transparent coatings with UV/ IR absorption properties, abrasion
resistance
Static dissipative/ conductive films
Enhanced heat-transfer fluids
Catalysis
Topical personal care (e.g., sunscreen) & pharmaceutical
applications
Ultrafine polishing of e.g., rigid mememory disks, optical lenses, etc.
Functional Polymer Fillers
To improve visco-plastic properties
By addition of inorganic fillers
Glass fiber, talcum, kaolin
20-60% dosage
Disadvantage: increased density of the composite
materials
Late ’80s: Toyota developed nano-clays (“bentonite”)
for automotive applications
Functional polymers are very versatile, even tiny
amounts can have dramatic impact
Colloidal Process
Nanoparticles produced directly to required
specifications, assembled to perform a specific task
Involves use of surface-active agents
e.g., CdS 50 nm particles by mixing two solutions
containing inverted micelles of sodium bis(2-ethyl
hexyl) sulfosuccinate in heptane
e.g., antiferromagnetic nanoparticles of Fe2O3 by
decomposition of Fe(CO)5 in a mixture of decaline
and oleyl sarcosine
Coordinating ligands used to produce nanoclusters
Surfactants play a major role
Physical Vapor Deposition (PVD)
A schematics illustrating the general steps and physical mechanism for a
PVD process.
Liquid-Phase Synthesis
Used widely for preparation of “quantum
dots” (semiconductor nanoparticles)
“Sol-Gel” method used to synthesize
glass, ceramic, and glasss-ceramic
nanoparticles
Dispersion can be stabilized indefinitely
by capping particles with appropriate
ligands
Sol-Gel Method Aqueous or alcohol-based
Involves use of molecular precursors, mainly alkoxides Alternatively, metal formates
Mixture stirred until gel forms
Gel is dried @ 100 C for 24 hours over a water bath, then ground to a powder
Powder heated gradually (5 C/min), calcined in air @ 500 – 1200 C for 2 hours
Allows mixing of precursors at molecular level better control
High purity
Low sintering temperature
High degree of homogeneity
Particularly suited to production of nano-sized multi-component ceramic powders
Gas-Phase Synthesis
Reactant gases
Precursors/carrier gas
A schematic of a conventional CVD reactor.
Laser beam or plasma can be introduced to enhanced the reaction
Can fabricate: carbon nanotubes, inorganic oxide nanorods, nanowire etc.
Chemical Vapor Synthesis Vapor phase precursors brought into a hot-wall reactor under nucleating
condition Vapor phase nucleation of particles favored over film deposition on surfaces
CVC reactor (Chemical Vapor Condensation) versus CVD
Very flexible, can produce wide range of materials
Can take advantage of huge database of precursor chemistries developed for CVD processes
Precursors can be S, L or G under ambient conditions but delivered to reactor as vapor (using bubbler, sublimator, etc)
Examples: Oxide-coated Si nanoparticles for high-density nonvolatile memory devices
W nanoparticles by decomposition of tungsten hexacarbonyl
Cu and CuxOy nanoparticles from copper lacetonate
Allows formation of doped or multi-component nanoparticles by use of multiple precursors nanocrystalline europium doped yttria from organometallic yttrium & europium
precursors
erbium in Si nanoparticles
zirconia doped with alumina
one material encapsulated within another (e.g., metal in metal halide) ○ Can prevent agglomeration
Flame Synthesis Particle synthesis within a flame
Heat produced in-situ by combustion reactions
Most commercially successful approach
Millions of metric tons per year of carbon black and metal oxides produced
Complex process, difficult to control
Primarily useful for making oxides
Recent advances: g-Fe2O3 nanoparticles
Titania, silica sintered agglomerates
Application of DC electric field to flame can influence particle size
Low-Temperature Reactive Synthesis
React vapor phase precursors directly w/o external addition of heat and w/o significant production of heat
e.g.: ZnSe nanoparticles from dimethylzinc-trimethylamine and hydrogen selenide
by mixing in a counter-flow jet reactor at RT
heat of reaction sufficient to allow particle crystallization
Sonochemical Nano-Synthesis
Sonochemistry: molecules undergo a chemical reaction due to application of powerful ultrasound (20 kHz – 10 MHz) Acoustic cavitation can break chemical bonds
“Hot Spot” theory: As bubble implodes, very high temperatures ( 5,000 – 25,000 K) are realized for a few nanoseconds; this is followed by very rapid cooling (1011 K/s)
High cooling rate hinders product crystallization, hence amorphous nanoparticles are formed
Superior process for: Preparation of amorphous products (“cold quenching”)
Insertion of nano-materials into mesoporous materials
○ By “acoustic streaming”
Deposition of nanoparticles on ceramic and polymeric surfaces
Formation of proteinacious micro- and nano-spheres
○ Sonochemical spherization
Very small particles
Sono- Fragmentation (Size Reduction)
Particles
Bubble Bubble Collapse
due to Implosion
Particle Fragments
due to
a) Violent Bubble
collapse
b) Inter-particle
attrition
Fragmented Particle
Template-based Methods
Nanofibers: What are they? Why are they important?
What is a Nanofiber?
A nanofiber is a continuous fiber which has a diameter in the range of nano-meter.
The smallest nanofibers made today are between 1.5 and 1.75 nanometers.
At the right a human hair (80,000 nanometers) is place on a mat of nanofibers
Nanofibers range in diameter of 2-600
nanometers and are very difficult to see with
the naked eye so they are studied using
magnification…
Spider dragline 3,000 nanometers Electron micrograph of nanofibers used for tissue scaffolds
Making Nanofibers
“Melt” Fibers: some nanofibers can be made by
melting polymers and spinning or shooting
them through very small holes. As the fiber
spins out it stretches smaller and smaller...
Cotton candy is made by heating syrup to a high temperature and then the liquid is spun out through tiny holes. As the fiber spins it is pulled thinner and thinner. It cools, hardens and, presto! Cotton Candy!!
Electrospinning to Make Nanofibers
An electric field pulls on a
droplet of polymer
solution at the tip of the
syringe and pulls out a
small liquid fiber. It is
pulled thinner and thinner
as it approaches the
collection plate.
Electrospinning Apparatus
Uses of Nanofibers…
High surface area: Filtration, Protective clothing.
Filter applications: Oil droplet coalescing on nanofibers increase
the capture rate of the oil fog.
Nano-Tex fabrics with water, cranberry juice, vegetable oil, and mustard after 30 minutes (left) and wiped off with
wet paper towel (right)
• Light Weight: Produce Solar sails in space, Aircraft wings, Bullet-proof vests.
– New breathable bullet-proof vest: Nomex Nanofibers
Image courtesy of Reneker Group – The University of Akron, College of Polymer Science
Nanotechnology is ubiquitous and pervasive. It is an emerging field in all
areas of science, engineering and technology.
Welcome to
NanoWorld!