M' Meyyappan

1
Introduction to Nanotechnology
M. Meyyappan Center for Nanotechnology NASA Ames
Research Center Moffett Field, CA 94035 email
mmeyyappan_at_mail.arc.nasa.gov
2
Outline
Definition National Nanotechnology
Initiative Impact on various economic
sectors - Electronics and computing - Health
and medicine - Energy - Transportation - -
- Commercial outlook
3
Nanotechnology is the creation of
USEFUL/FUNCTIONAL materials, devices and systems
(of any useful size) through control/manipulation
of matter on the nanometer length scale and
exploitation of novel phenomena and properties
which arise because of the nanometer length scale
Physical Chemical Electrical Mechanical
Optical Magnetic
Nanometer One billionth (10-9) of a
meter Hydrogen atom 0.04 nm Proteins 1-20
nm Feature size of computer chips 90 nm (in
2005) Diameter of human hair 10 µm
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What Is Nanotechnology?
(Definition from the NNI)

• Research and technology development aimed to
  understand and control matter at dimensions of
  approximately 1 - 100 nanometer the nanoscale
• Ability to understand, create, and use
  structures, devices and systems that have
  fundamentally new properties and functions
  because of their nanoscale structure
• Ability to image, measure, model, and manipulate
  matter on the nanoscale to exploit those
  properties and functions
• Ability to integrate those properties and
  functions into systems spanning from nano- to
  macro-scopic scales

Nanoarea Electron Diffraction of DW Carbon
Nanotube Zuo, et.al
Corral of Fe Atoms D. Eigler
Source Clayton Teague, NNI
5
Examples - Carbon Nanotubes - Proteins,
DNA - Single electron transistors Not just
size reduction but phenomena intrinsic to
nanoscale - Size confinement - Dominance of
interfacial phenomena - Quantum mechanics New
behavior at nanoscale is not necessarily
predictable from what we know at macroscales.
AFM Image of DNA
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Unique Properties of Nanoscale Materials

• Quantum size effects result in unique mechanical,
  electronic, photonic, and magnetic properties of
  nanoscale materials
• Chemical reactivity of nanoscale materials
  greatly different from more macroscopic form,
  e.g., gold
• Vastly increased surface area per unit mass,
  e.g., upwards of 1000 m2 per gram
• New chemical forms of common chemical elements,
  e.g., fullerenes, nanotubes of carbon, titanium
  oxide, zinc oxide, other layered compounds

Source Clayton Teague, NNI
7
What is Special about Nanoscale?
Atoms and molecules are generally less than a
nm and we study them in chemistry. Condensed
matter physics deals with solids with infinite
array of bound atoms. Nanoscience deals with
the in-between meso-world Quantum chemistry
does not apply (although fundamental laws hold)
and the systems are not large enough for
classical laws of physics Size-dependent
properties Surface to volume ratio - A 3 nm
iron particle has 50 atoms on the surface - A
10 nm particle 20 on the
surface - A 30 nm particle only 5
on the surface
MORE IN SECTION II
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What is new about Nanoscience?
Many existing technologies already depend on
nanoscale materials and processes - photography
, catalysts are old examples - developed
empirically decades ago In existing
technologies using nanomaterials/processes, role
of nanoscale phenomena not understood until
recently serendipitous discoveries - with
understanding comes opportunities for
improvement Ability to design more complex
systems in the future is ahead - designer
material that is hard and strong but low
weight - self-healing materials
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1959 Feynman Lecture There is Plenty of Room
at the Bottom provided the vision of exciting
new discoveries if one could fabricate
materials/devices at the atomic/molecular
scale. Emergence of instruments in the 1980s
STM, AFM providing the eyes, fingers for
nanoscale manipulation, measurement
Recently, there has been an explosion of
research on the nanoscale behavior - Nanostructu
res through sub-micron self assembly creating
entities from bottom-up instead of
top-down - Characterization and
applications - Highly sophisticated computer
simulations to enhance understanding as well as
create designer materials
STM
Image of Highly Oriented Pyrolitic Graphite
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For information, www.nano.gov Multiagency
Initiative in nanotechnology starting in FY01
National Nanotechnology Initiative (NNI)
Leading to the Next Industrial Revolution FY05
Nano budget is 1.0 Billion Biggest portion
of the funding goes to NSF - Followed by DoD,
DOE, NIH, NASA - All these agencies spend most
of their nano funding on university
programs Very strong activities in Japan,
Europe, China, Singapore, fueled by Government
Initiatives Nano activities in U.S. companies
IBM, Motorola, HP, Lucent, Hitachi USA, Corning,
DOW, 3M - In-house R D - Funding of new
ventures Nano Centers have been established at
Universities all across the world Emerging
small companies - VC funding on the increase
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NNI Program Component Areas (PCAs)

• Fundamental Nanoscale Phenomena and Processes
• Nanomaterials
• Nanoscale Devices and Systems
• Instrumentation Research, Metrology, and
  Standards for Nanotechnology
• Nanomanufacturing
• Major Research Facilities and
  Instrumentation Acquisition
• Societal Dimensions

Source Clayton Teague, NNI
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The U.S. does not dominate nanotechnology
research. Nearly twice as much ongoing research
overseas as in the U.S. Many foreign
leaders, companies, scientists believe that
nanotechnology will be the leading technology of
the 21st century. The fact that there is still
a chance to get on the ground floor explains
pervasive R D worldwide. Strong nanotechnology
programs in European Union countries, Japan,
Korea, Switzerland, Singapore, Australia,
Taiwan, China and Russia.
Leadership Position
Source WTEC Report
13
Academia will play key role in development of
nanoscience and technology - Promote
interdisciplinary work involving multiple
departments - Develop new educational
programs - Technology transfer to
industry Government Labs will conduct mission
oriented nanotechnology research - Provide large
scale facilities and infrastructure for
nanotechnology research - Technology transfer
to industry Government Funding Agencies will
provide research funding to academia, small
business, and industry through the NNI and other
programs (SBIR, STIR, ATP) Industry will
invest only when products are within 3-5
years - Maintain in-house research, sponsor
precompetitive research - Sponsor technology
start-ups and spin-offs Venture Capital
Community will identify ideas with market
potential and help to launch start-ups Professi
onal societies should establish interdisciplinary
forum for exchange of information reach out to
international community offer continuing
education courses
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Nanotechnology R D
and Related
Nanomaterials
Applications
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Various Nanomaterials and Nanotechnologies
Nanocrystalline materials Nanoparticles Nano
capsules Nanoporous materials Nanofibers Nan
owires Fullerenes Nanotubes Nanosprings Na
nobelts Dendrimers
Molecular electronics Quantum dots NEMS,
Nanofluidics Nanophotonics, Nano-optics Nanoma
gnetics Nanofabrication Nanolithography Nano
manufacturing Nanomedicine Nano-bio
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Extraordinary Space of Nanomaterials

• Atom clusters
• Nanotubes, rods, spheres, belts carbon and
  other materials
• Dendrimers
• Macro-molecular structures
• Biomolecular structures

SiC Flowers
C SWNT
ZnO Belt
ZnO Tube
GaN Rods
TiO2 Spheres
Spherical
Tubular
Rotaxane
Catenane
STM Image of DNA Segment
STM Image and Model of Porphyrin
Source Clayton Teague, NNI
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As Recommended by the IWGN (Interagency Working
Group on Nanotechnology) Panel Nanostructure
Properties - Biological, chemical, electronic,
magnetic, optical, structural Synthesis and
Processing - Enable atomic and molecular control
of material building blocks - Bioinspired,
multifunctional, adaptive structures - Affordabil
ity at commercial levels Characterization and
manipulation - New experimental tools to
measure, control - New standards of
measurement Modeling and simulation Device
and System Concepts - Stimulate innovative
applications to new technologies Application
Development
See www.nano.gov
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(As raised in the IWGN Report)
1. What novel quantum properties will be enabled
by nanostructures (at room temp.)? 2. How
different from bulk behavior? 3. What are the
surface reconstructions and rearrangements of
atoms in nanocrystals? 4. Can carbon nanotubes
of specified length and helicity be synthesized
as pure species? Heterojunctions in
1-D? 5. What new insights can we gain about
polymer, biologicalsystems from the capability
to examine single-molecule properties? 6. How
can one use parallel self-assembly techniques to
control relative arrangements of nanoscale
components according to predesigned
sequence? 7. Are there processes leading to
economic preparation of nanostructures with
control of size, shape for applications?
This is NOT an exhaustive list
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Impact of Nanotechnology
Information Technology - Computing, Memory
and Data Storage - Communication Materials
and Manufacturing Health and
Medicine Energy Environment Transportatio
n National Security Space exploration
Nanotechnology is an enabling technology
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Ability to synthesize nanoscale building blocks
with control on size, composition etc.
further assembling into larger structures
with designed properties will revolutionize
materials manufacturing - Manufacturing metals,
ceramics, polymers, etc. at exact shapes without
machining - Lighter, stronger and
programmable materials - Lower failure rates and
reduced life-cycle costs - Bio-inspired
materials - Multifunctional, adaptive
materials - Self-healing materials
Challenges ahead - Synthesis, large scale
processing - Making useful, viable
composites - Multiscale models with predictive
capability - Analytical instrumentation
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Carbon Nanotubes Nanostructured
Polymers Optical fiber performs through
sol-gel processing of nanoparticles Nanoparticl
es in imaging systems Nanostructured
coatings Ceramic Nanoparticles for netshapes
Source IWGN Report
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More Examples of Nanotech in Materials and
Manufacturing
Nanostructured metals, ceramics at exact shapes
without machining Improved color printing
through better inks and dyes with
nanoparticles Membranes and
filters Coatings and paints (nanoparticles)
Abrasives (using nanoparticles) Lubricants C
omposites (high strength, light
weight) Catalysts Insulators
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Nanoelectronics and Computing
Past Shared computing thousands of people
sharing a mainframe computer
Present Personal computing
Future Ubiquitous computing
thousands of computers sharing each and everyone
of us computers embedded in walls, chairs,
clothing, light switches, cars. characterized
by the connection of things in the world with
computation.
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There is at least as far to go (on a logarithmic
scale) from the present as we have come from
ENIAC. The end of CMOS scaling represents
both opportunity and danger. -Stan Williams,
HP A few more CMOS generations left but cost
of building fabs going up faster than sales.
Physics has room for 109x current technology
based on 1 Watt dissipation, 1018 ops/sec
no clear ways to do it! - Molecular
nanoelectronics ? - Quantum cellular automata
? - Chemically synthesized circuits ? Self
assembly to reduce manufacturing costs, defect
tolerant architectures may be critical to
future nanoelectronics
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Quantum Computing - Takes advantage of
quantum mechanics instead of being limited by
it - Digital bit stores info. in the form of
0 and 1 qubit may be in a superposition
state of 0 and 1 representing both
values simultaneously until a measurement is
made - A sequence of N digital bits can
represent one number between 0 and 2N-1 N
qubits can represent all 2N numbers
simultaneously
Carbon nanotube transistors by several
groups Molecular electronics Fabrication of
logic gates from molecular switches using
rotaxane molecules Defect tolerant
architecture, TERAMAC computer by HP
architectural solution to the problem of
defects in future molecular electronics
- Stan Williams, HP
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Expected Nanotechnology Benefits in Electronics
and Computing
Processors with declining energy use and cost
per gate, thus increasing efficiency of computer
by 106 Higher transmission frequencies and
more efficient utilization of optical spectrum
to provide at least 10 times the bandwidth
now Small mass storage devices multi-tera bit
levels Integrated nanosensors collecting,
processing and communicating massive amounts
of data with minimal size, weight, and power
consumption Quantum computing Display
technologies
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Expanding ability to characterize genetic
makeup will revolutionize the specificity of
diagnostics and therapeutics - Nanodevices
can make gene sequencing more efficient Effe
ctive and less expensive health care using remote
and in-vivo devices
New formulations and routes for drug
delivery, optimal drug usage More durable,
rejection-resistant artificial tissues and
organs Sensors for early detection and
prevention
Nanotube-based biosensor for cancer diagnostics
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DNA microchip arrays using advances for IC
industry Gene gun that uses nanoparticles
to deliver genetic material to target
cells Semiconductor nanocrystals as
fluorescent biological labels
Source IWGN Report
29
Energy Production and Utilization
Energy Production - Clean, less expensive
sources enabled by novel nanomaterials and
processes - Improved solar cells Energy
Utilization - High efficiency and durable home
and industrial lighting - Solid state
lighting can reduce total electricity
consumption by 10 and cut carbon emission
by the equivalent of 28 million tons/year
(Source Al Romig, Sandia Lab) Materials
of construction sensing changing conditions and
in response, altering their inner structure
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Benefits of Nano in the Environment Sector
Nanomaterials have a large surface area. For
example, single-walled carbon nanotubes show
1600 m2/g. This is equivalent to the size of a
football field for only 4 gms of nanotubes. The
large surface area enables - Large adsorption
rates of various gases/vapors - Separation of
pollutants - Catalyst support for conversion
reactions - Waste remediation Filters
and Membranes - Removal of contaminants
from water - Desalination Reducing auto
emissions, NOx conversion - Rational design of
catalysts
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Benefits of Nanotechnology in Transportation
More efficient catalytic converters Thermal
barrier and wear resistant coatings Battery,
fuel cell technology Improved
displays Wear-resistant tires High
temperature sensors for under the hood novel
sensors for all-electric vehicles High
strength, light weight composites for increasing
fuel efficiency
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Improved collection, transmission, protection
of information Very high sensitivity, low
power sensors for detecting
chem/bio/nuclear threats Light weight
military platforms, without sacrificing
functionality, safety and soldier
security - Reduce fuel needs and
logistical requirements Reduce carry-on weight
of soldier gear - Increased functionality
per unit weight
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Why Nanotechnology at NASA?
Advanced miniaturization, a key thrust area to
enable new science and exploration
missions - Ultrasmall sensors, power sources,
communication, navigation, and propulsion
systems with very low mass, volume and
power consumption are needed Revolutions
in electronics and computing will allow
reconfigurable, autonomous, thinking
spacecraft Nanotechnology presents a whole new
spectrum of opportunities to build device
components and systems for entirely new space
architectures - Networks of ultrasmall
probes on planetary surfaces - Micro-rover
s that drive, hop, fly, and
burrow - Collection of microspacecraft
making a variety of measurements
Europa Submarine
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Assessment of Opportunities
Short term (lt 5 years) - Nanoparticles
Automotive industry (body moldings, timing
belts, engine covers) Packaging
industry Cosmetics Inkjet
technology Sporting goods - Flat
panel displays - Coatings - CNT-based
probes in semiconductor metrology -
Tools - Catalysts (extension of existing
market)
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Assessment of Opportunities (Cont.)
Medium term (5-10 years) - Memory
devices - Fuel cells, batteries - Biosensors
(CNT, molecular, qD based) - Biomedical
devices - Advances in gene sequencing - Advanc
es in lighting Long term (gt 15
years) - Nanoelectronics (CNT) - Molecular
electronics - Routine use of new composites in
Aerospace, automotive (risk-averse
industries) - Many other things we havent even
thought of yet
36
Timeline for Beginning of Industrial Prototyping
and Nanotechnology CommercializationFour
Generations
1st Passive Nanostructures Ex. Coatings,
nanoparticles, nanostructured metals, polymers,
ceramics
2000
2nd Active Nanostructures Ex. 3D
transistors, amplifiers, targeted drugs,
actuators, adaptive structures
2005
3rd Systems of Nanosystems Ex. Guided
assembling 3D networking and new hierarchical
architectures, robotics, evolutionary
2010
4th Molecular Nanosystems Ex. Molecular
devices by design, atomic design, emerging
functional systems
2015-2020
AIChE Journal 2004, 50, MC Roco
Source Clayton Teague, NNI
37
Revolutionary Technology Waves
Red Herring, May 2002
Commonality Railroad, auto, computer,
nanotech all are enabling technologies
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NANOSCALE PROPERTIES
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Outline
Size-dependent properties color, specific
heat, melting point, conductivity.. I-V of a
single nanoparticle Adsorption - principles
- some examples Nanomaterial reinforcement in
composites - multifunctionality - self-heating
40
Some 'Nano' Definitions
Cluster - A collection of units (atoms or
reactive molecules) of up to about 50
units Colloids - A stable liquid phase
containing particles in the 1-1000 nm range.
A colloid particle is one such 1-1000 nm
particle. Nanoparticle - A solid particle in
the 1-100 nm range that could be
noncrystalline, an aggregate of crystallites
or a single crystallite Nanocrystal - A
solid particle that is a single crystal in the
nanometer range
41
Percentage of Surface Atoms
Source Nanoscale Materials in Chemistry, Ed.
K.J. Klabunde, Wiley, 2001
42
Surface to Bulk Atom Ratio
Spherical iron nanocrystals J. Phys. Chem.
1996, Vol. 100, p. 12142
43
Nanoscale High Ratio of Surface Area to Vol.
Repeat 24 times
For example, 5 cubic centimeters about 1.7 cm
per side of material divided 24 times will
produce 1 nanometer cubes and spread in a single
layer could cover a football field
Source Clayton Teague, NNI
44
Quantum Size Effect
quantum size effect regime
Regions indicated for QSE for metals,
semiconductors, and semimetals are very rough
estimates
Value of physical property
Metals
Semiconductors
Semimetals
10-100
108
1 nm
100 nm
Number of atoms in cluster
Source Clayton Teague, NNI
45
Size Dependence of Properties
In materials where strong chemical bonding is
present, delocalization of valence electrons can
be extensive. The extent of delocalization can
vary with the size of the system. Structure
also changes with size. The above two changes
can lead to different physical and
chemical properties, depending on
size - Optical properties - Bandgap - Meltin
g point - Specific heat - Surface
reactivity - - Even when such
nanoparticles are consolidated into macroscale
solids, new properties of bulk materials are
possible. - Example enhanced plasticity
46
Some More Size-Dependent Properties
For semiconductors such as ZnO, CdS, and Si,
the bandgap changes with size - Bandgap is
the energy needed to promote an electron from
the valence band to the conduction band - When
the bandgaps lie in the visible spectrum, a
change in bandgap with size means a change in
color For magnetic materials such as Fe, Co,
Ni, Fe3O4, etc., magnetic properties are size
dependent - The coercive force (or magnetic
memory) needed to reverse an internal
magnetic field within the particle is size
dependent - The strength of a particles
internal magnetic field can be size dependent
47
Color
In a classical sense, color is caused by the
partial absorption of light by electrons in
matter, resulting in the visibility of the
complementary part of the light On most
smooth metal surfaces, light is totally reflected
by the high density of electrons no
color, just a mirror-like appearance. Small
particles absorb, leading to some color. This is
a size dependent property. Example Gold,
which readily forms nanoparticles but not easily
oxidized, exhibits different colors depending on
particle size. - Gold colloids have been used
to color glasses since early days of glass
making. Ruby-glass contains finely dispersed
gold-colloids. - Silver and copper also give
attractive colors
48
Specific Heat
C ?Q/m?T Specific heat is the amount of
heat ?Q required to raise the temperature by ?T
of a sample of mass m Units are J/kg K or
cal/g K 1 calorie is the heat needed to
raise the temperature of 1 g of water by 1
degree.
49
Specific Heat (cont.)
Specific heat of polycrystalline materials is
given by Dulong-Petit law - C of solids at
room temp. (in J/kg k) differs widely from one
to another but the molar values (in J/moles
k) are nearly the same, approaching 26 J/mol
K Cv 3 Rg/M where M is molecular
weight Cv of nanocrystalline materials are
higher than their bulk counterparts.
Example - Pd 48 ? from 25 to 37 J/mol.K at
250 K for 6 nm crystalline - Cu 8.3 ?
from 24 to 26 J/mol.K at 250 K for 8 nm - Ru
22 ? from 23 to 28 J/mol.K at 250 K for 6 nm
50
Melting Point
The melting point of gold particles decreases
dramatically as the particle size gets below 5 nm
Source Nanoscale Materials in Chemistry, Wiley,
2001
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Melting Point Dependence on Particle Size
Analytical Derivation
Start from an energy balance assume the change
in internal energy (?U) and change in entropy
per unit mass during melting are independent of
temperature
?? Deviation of melting point from the bulk
value To Bulk melting point ? Surface
tension coefficient for a liquid-solid
interface ? Particle density r Particle
radius L Latent heat of fusion
52
Melting Point Dependence on Particle Size
Lowering of the melting point is proportional
to 1/r ?? can be as large as couple of hundred
degrees when the particle size gets below 10
nm! Most of the time, ? the surface tension
coefficient is unknown by measuring the melting
point as a function of radius, ? can
be estimated. Note For nanoparticles
embedded in a matrix, melting point may be lower
or higher, depending on the strength of the
interaction between the particle and matrix.
53
Electrical Conductivity
For metals, conductivity is based on their band
structure. If the conduction band is only
partially occupied by electrons, they can move
in all directions without resistance (provided
there is a perfect metallic crystal lattice).
They are not scattered by the regular building
blocks, due to the wave character of the
electrons.
v electron speed ?o dielectric constant in
vacuum
?, mean time between collisions, is ?/v For
Cu, v 1.6 x 106 m/s at room temp. ? 43 nm, ?
2.7 x 10-14s
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Electrical Conductivity (continued)
Scattering mechanisms (1) By lattice defects
(foreign atoms, vacancies, interstitial
positions, grain boundaries, dislocations,
stacking disorders) (2) Scattering at thermal
vibration of the lattice (phonons) Item (1) is
more or less independent of temperature while
item 2 is independent of lattice defects, but
dependent on temperature. Electric current
collective motion of electrons in a bulk
metal, Ohms law V RI Band
structure begins to change when metal particles
become small. Discrete energy levels begin to
dominate, and Ohms law is no longer valid.
55
I-V of a Single Nanoparticle
Source Nanoscale Materials in Chemistry, Wiley,
2001
56
I-V of a Single Nanoparticle
Consider a single nanoparticle between two
electrodes, but cushioned by a capacitance on
each side - If an electron is transferred to
the particle, its coulomb energy
by Ec e2/2c - Thermal motion of the
atoms in the particle can initiate a charge Ec,
leading to further electrons tunneling
uncontrollably - So, kT ltlt e2/2c - Tunneling
current I V/RT - Current begins at coulomb
voltage Vc e/2c which is called coulomb
blockade - Further electron transfer happens
if the coulomb energy of the quantum dot is
compensated by an external voltage Vc ne/2c
where n is an integer - Repeated tunneling
results in a staircase with step height in
current, e/Rc - Possible to charge and discharge
a quantum dot in a quantized manner
principle behind some future computers
57
Source Nanoscale Materials in Chemistry, Wiley,
2001
If a bulk metal is made thinner and thinner,
until the electrons can move only in two
dimensions (instead of 3), then it is 2D quantum
confinement. Next level is quantum
wire Ultimately quantum dot
58
Adsorption
59
Adsorption Some Background
Adsorption is like absorption except the
adsorbed material is held near the surface
rather than inside In bulk solids, all
molecules are surrounded by and bound to
neighboring atoms and the forces are in balance.
Surface atoms are bound only on one side,
leaving unbalanced atomic and molecular forces
on the surface. These forces attract gases and
molecules ? Van der Waals force, ? physical
adsorption or physisorption At high
temperatures, unbalanced surface forces may be
satisfied by electron sharing or valence
bonding with gas atoms ? chemical adsorption or
chemisorption - Basis for heterogeneous
catalysis (key to production of fertilizers,
pharmaceuticals, synthetic fibers, solvents,
surfactants, gasoline, other fuels, automobile
catalytic converters) - High specific surface
area (area per unit mass)
60
Physisorption
Physisorption of gases by solids increases with
decreasing T and with increasing P Weak
interaction forces low heats of adsorption lt
80 KJ/mole physisorption does not affect the
structure or texture of the absorbent Desorpti
on takes place as conditions are
reversed Mostly, testing is done at LN2
temperature (77.5 K at 1 atm.). Plot of gas
adsorbed as volume Va at 0 C and 1 atm (STP)
vs. P/Po (Po is vapor pressure) is called
adsorption isotherm.
61
Basic Forces Between the Adsorbent and Absorbate
Adsorption occurs when the interaction
potential energy ? is equal to the work done to
bring a gas molecule to the adsorbed state.
Assuming that the adsorbed state is at the sat.
vap. pressure Po, Assuming that contribution
from adsorbate-adsorbate interaction to ? is
negligible, ? is essentially due to
adsorbate-adsorbant interaction. Consider
surface atom and adsorbate molecule separated
by r. For physisorption, ? is a sum of -
Dispersion energy ?D -A/r6 - Close range
repulsion ?R B/r12 - Contributions arising
from charges on the solid surface
62
Model Arrays for Adsorption
Adsorption in open cylinders
? ? packing factor 0.415 ?cc ?
Lennard-Jones parameter for carbon-carbon
interaction
63
Chemisorption
Much stronger interaction than
physisorption Heat of adsorption up to 800
KJ/mole Adsorbing gas or vapor molecule splits
into atoms, radicals or ions which form a
chemical bond with the adsorption site. ?
Sharing of electrons between the gas and solid
surface may be regarded as the formation of a
surface compound.
64
Chemisorption
Simple reversal is not possible like in
physisorption - O2 chemisorbed on charcoal ?
application of heat and vacuum will result in
CO desorption instead of O2. Under favorable T
P, physisorption takes place on all surfaces.
But chemisorption is localized and occurs on
only certain surface sites Physisorption ?
with ? in T chemisorption ? with ? in T Same
surface can exhibit physiosorption at low T and
chemisorption at high T. Example N2
chemisorption on Fe at 800 C to form iron
nitride but physisorption at LN2 temperatures.
65
Chemisorption Langmuir Theory
Assumes gases form only one monolayer on a
solid Gas molecule collision with solid ?
inelastic, so the gas molecule stays in contact
with solid, for a time before desorbing Writing
a balance between the rate at which molecules
strike the surface and rate at which they
leave Vm quantity of gas absorbed when
the entire surface is covered with
a monolayer Rearranging,
Plot of vs. P should yield a
straight line if the equation applies ? evaluate
Vm and b Specific surface area
Vm molar volume of the gas (22414 cm3) NA
Avogadro number ? surface area occupied by
single adorbed molecule, 16.2 A2 for
N2 m mass of the adsorbing sample
66
Nanomaterial reinforcement in composites
67
Nano-Reinforced Composites
Processing them into various matrices follow
earlier composite developments such
as - Polymer compounding - Producing filled
polymers - Assembly of laminate
composites - Polymerizing rigid rod
polymers - - Purpose - Replace existing
materials where properties can be
superior - Applications where traditionally
composites were not a candidate
68
Benefits of Nanotechnology in Composite
Development
Nanotechnology provides new opportunities for
radical changes in composite functionality Maj
or benefit is to reach percolation threshold at
low volumes (lt 1) when mixing nanoparticles in
a host matrix Functionalities can be added
when we control the orientation of the
nanoscale reinforcement.
69
Multifunctionality in Materials
This always implies structure since in most
cases the major function of a structure is to
carry load or provide shape. Additional
functions can be Actuation
controlling position, shape or
load Electrical either insulate or
conduct Thermal either insulate or
conduct Health monitor, control Stealth ma
naging electromagnetic or visible
signature Self-healing repair localized
damage Sensing physical, chemical variables
NRC Report, 2003
70
Multifunctional Materials with Sensing Capability
Building in additional functionalities into
load-bearing structures is one key
example - Sensing function Strain
Pressure Temperature Chemical
change Contaminant presence Miniaturized
sensors can be embedded in a distributed fashion
to add smartness or multifunctionality. This
approach is pre-nano era. Nanotechnology,
in contrast, is expected to help in assembling
materials with such functional capabilities
71
Examples of Multifunctional Materials
Possible, in principle, to design any number of
composites with multiple levels of functionality
(3, 4, 5) by using both multifunctional matrices
and multifunctional reinforcement additives
- Add a capsule into the matrix that contains
a nanomaterial sensitive to thermal,
mechanical, electrical stress when this breaks,
would indicate the area of damage - Another
capsule can contain a healant - Microcellular
structural foam in the matrix may be
radar-absorbing, conducting or
light-emitting - Photovoltaic military uniform
also containing Kevlar for protection generate
power during sunlight for charging the batteries
of various devices in the soldier-gear
NRC Report, 2003
72
Candidates for Multifunctional Composites
Carbon nanotubes, nanofibers Polymer clay
nanocomposites Polymer cross-linked
aerogels Biomimetric hybrids Expectations -
Designer properties, programmable materials -
High strength, low weight - Low failure
rates - Reduced life cycle costs
73
Example of Self-Healing Material
Self-healing plastic by Prof. Scott White (U.
of Illinois) Nature (Feb. 15, 2001) Plastic
components break because of mechanical or
thermal fatigue. Small cracks ? large cracks ?
catastrophic failure. Self-healing is a way of
repairing these cracks without human intervention
. Self-healing plastics have small capsules
that release a healing agent when a crack forms.
The agent travels to the crack through
capillaries similar to blood flow to a
wound. Polymerization is initiated when the
agent comes into contact with a catalyst
embedded in the plastic. The chemical
reaction forms a polymer to repair the broken
edges of the plastic. New bond is complete in
an hour at room temperature.
74
Nanomaterials in Catalysis
Surface chemistry is important in catalysis.
Nanostructured materials have some advantages
- Huge surface area, high proportion of atoms on
the surface - Enhanced intrinsic chemical
activity as size gets smaller which is
likely due to changes in crystal shape - Ex
When the shape changes from cubic to
polyhedral, the number of edges and corner
sites goes up significantly - As crystal size
gets smaller, anion/cation vacancies can
increase, thus affecting surface energy also
surface atoms can be distorted in their
bonding patterns - Enhanced solubility,
sintering at lower T, more adsorptive
capacity
75
Nanoporous Materials
Zeolite is an old example which has been around
a long time and used by petroleum industry as
catalysts The surface area of a solid
increases when it becomes nanoporous this
improves catalyst effects, adsorption
properties Recall adsorption is like
absorption except the absorbed material is
held near the surface rather than inside How
to make nanopores? - lithography followed by
etching - ion beam etching/milling - electroch
emical techniques - sol-gel techniques
76
Metal Nanocluster Composite Glasses
Composite materials formed by transition metal
clusters embedded in glass matrices exhibit
interesting optical properties - Candidates for
nonlinear integrated optics, photonics ? using
photons instead of electrons to acquire,
store, process and transmit information - Glass
is cheap, ease of processing, high durability,
high transparency ? promising glass-based
structures Dielectric constant is a key
property. ?, effective dielectric
constant Preparation techniques - ion
implantation - ion exchange in a molten
bath - ion irradiation
m ? metal, h ? host p volume fraction
77
Fine Particle Technology
Frequently encountered powders - Cement,
fertilizer, face powder, table salt, sugar,
detergents, coffee creamer, baking
soda Some products in which powder
incorporation is not obvious - Paint, tooth
paste, lipstick, mascara, chewing gum, magnetic
recording media, slick magazine covers, floor
coverings, automobile tires For most
applications, there is an optimum particle
size - Taste of peanut butter is affected by
particle size - Extremely fine amorphous silica
is added to control the ketchup flow - Medical
tablets dissolve in our system at a rate
controlled by particle size - Pigment size
controls the saturation and brilliance of
paints - Effectiveness of odor removers is
controlled by the surface area of adsorbents.
From Analytical methods in Fine Particle
Technology, Webb and Orr
78
Fine Particle Technology (continued)
Adding certain inorganic clays to rubber
dramatically improves the lifetime and
wear-characteristics of tires. Why ? The
nanoscale clay particles bind to the ends of the
polymer molecules - which you can think of as
molecular strings - and prevent them from
unraveling.
79
Integration of Innovations Into Systems
Price-volume relationship for annual U.S.
consumption of structural materials. Source J.H.
Westbrook, General Electric (retired), private
communications, September 27, 2002, NRC Report
2003.
The relationship between cost and usage in
tonnage is inverse Value of weight saving
should be considered in other aspects as
well. - Reduction in weight of vehicle (auto,
plane) reduced gasoline consumption
- Spacecraft cost of launch