2a Nanomaterials
nanomaterials and nanostructures – overview
carbon – nanotubes, graphene
metal-based nanostructures - nanowires, gold
nanoparticles (nanorods, nanocages, nanoshells)
magnetic nanoparticles
polymer nanostructures (dendrimers)
protein-based nanostructures - nanomotors from
microbes and mammalian cells (myosin).
nanomachines based on nucleic acids
Definition
a nanomaterial is a material made up of nanostructures between
1 and 100 nanometres in size
nanostructures can include nanoparticles, nanotubes or nanocrystals, etc.
properties of nanomaterials are different to those of ordinary materials
because of the small size of the structures that make them up
principal parameters of nanoparticles are
– shape
– size
– morphological sub-structure
of the substance
Overview
nanomaterials are manufactured for a wide variety of applications
a typical example might be carbon nanotube-based nanomaterials,
with applications anticipated in
– nanoelectronics (components)
– medicine (transport of drugs in the body)
– information technology (computer memory) ....
composite nanomaterial (combinations of materials that are
normally immiscible) are also being produced
the idea is to introduce nanostructures - nanoparticles, for instance
into a matrix (metal, organic material, etc.) to obtain specific
properties of hardness, mechanical strength, conductivity or
electrical insulation
Biopharmaceutics
Drug Delivery
Drug Encapsulation
Functional Drug Carriers
Drug Discovery
Implantable Materials
Tissue Repair and Replacement
Implant Coatings
Tissue Regeneration
Scaffolds
Structural Implant Materials
Bone Repair
Bioresorbable Materials
Smart Materials
Implantable Devices
Assessment and Treatment Devices
Implantable Sensors
Implantible Medical Devices
Sensory Aids
Retina Implants
Cochlear Implants
Surgical Aids
Operating Tools
Smart Instruments
Surgical Robots
Diagnostic Tools
Genetic Testing
Ultra-sensitive Labeling
and
Detection
Technologies
High Throughput
Arrays and
Multiple Analyses
Imaging
Nanoparticle Labels
Biomed
Properties vary with size of the material
(bulk) gold is a shiny yellow metal
nanoscopic gold, i.e. clusters of gold atoms
measuring 1 nm across, appears red
bulk gold does not exhibit catalytic properties
Au nanocrystal is an excellent low temperature
catalyst
therefore, if we can control the processes that make a
nanoscopic material, then we can control the
material’s properties
Physical properties of nanomaterials
significantly lower melting point or phase transition temperature
– due to a huge fraction of surface atoms in the total amount of atoms
mechanical properties may reach the theoretical strength
– 1 or 2 orders of magnitude higher than that of single crystals in the bulk form
– enhancement in mechanical strength - reduced probability of defects
optical properties can be significantly different from bulk crystals
– e.g. the optical absorption peak of a semiconductor nanoparticle shifts to short
wavelength, due to an increased band gap
– color of metallic nanoparticles may change with their sizes due to surface
plasmon resonance
electrical conductivity decreases with a reduced dimension
– due to increased surface scattering;
– however, electrical conductivity of nanomaterials could also be enhanced
appreciably due to the better ordering in microstructure, e.g. fibrils
magnetic properties are distinctively different from that of bulk materials
– ferromagnetism of bulk materials disappears and transfers to
superparamagnetism in the nanometer scale due to the huge surface energy
self-purification is an intrinsic thermodynamic property of nanostructures
and nanomaterials
– any heat treatment increases the diffusion of impurities, intrinsic structural
defects and dislocations, pushing them to the nearby surface
– increased perfection would have appreciable impact on the chemical and
physical properties – enhanced chemical stability
Special properties of nanomaterials
high surface / bulk ratio
– catalysis
– nanoparticle reagents
– heat dissipation
– laminar flow
finite size effects
– quantum confinement
– inter-particle tunneling
– proximity effects
– high probability of defectfree
crystals
Nanostructures
aerogels
biomolecules
nanocarbon
composites
dendrimers
glasses / ceramics
hydrogels
metals and alloys
nanomagnets
nanoparticles / catalysts
nanostrings
nanowires
quantum dots
self assembled
monolayers (SAMs)
silicon structures and
MEMS devices
thin films
Aerogels
manufactured material with the lowest bulk density of any
known porous solid
derived from a gel in which the liquid component of the gel has
been replaced with a gas
produced by extracting the liquid component of a gel
through supercritical drying
this allows the liquid to be slowly drawn off without causing the
solid matrix in the gel to collapse from
capillary action, as would happen with
conventional evaporation
Space Shuttle tile - alumina-silicate aerogel
black coating on the tiles is Reaction Cured Glass
(RCG, tetrasilicide and borosilicate)
RCG is applied to all but one side of the tile to
protect the porous silica and to increase the
heat sink properties
to waterproof the tile, dimethylethoxysilane is
injected into the tiles by syringe.
densifying the tile with tetraethyl
orthosilicate (TEOS) also helps to protect the
silica and waterproof
Biomolecular nanotechnology
molecular structures and functional complexes
DNA templating
synthetic biology – synthetic biomacromolecules
liposomes and novel cellular structures
… not exactly our field (bionanotechnology)
Nanocarbon
carbon nanotubes - single (SWNT) and multiwalled (MWNT)
graphene
carbon nanospheres
nanodiamonds
Composite materials
carbon nanofibers (CNFs) - vapor grown carbon
fibers (VGCFs) or nanofibers (VGCNFs) are
cylindrical nanostructures with graphene layers
arranged as stacked cones, cups or plates
nano-onion structure observed in nanospheres, and annealed carbon
black (soot)
it is thought that the extended nanostructure forms by wrapping of
graphene over a fullerene seed-like nanostructure
Dendrimers
repetitively branched molecules
– also known as arborols and cascade molecules
typically symmetric around the core
– often adopts a spherical three-dimensional morphology
Glasses and ceramics
glasses are similar to polymers - long chains and
almost a liquid
ceramics are metal - nonmetal compounds with
typically ionic bonding
– high melting points, can be brittle, and typically are non-conductive
– electroceramics can be conductive
– have high temperature properties
Nanoglass coatings
hydrophobic coatings on
glass help water to bead up increased
visibility, easier
cleaning
added mechanical / abrasion
resistance, by promoting
surfaces that are also scratch
resistant
made from fluoropolymers, or
methylated siloxane
materials, both deposited as
plasma polymerized coatings
Hydrogels
hydrogel (also aquagel) is a network of polymer chains that are
hydrophilic, sometimes found as a colloidal gel in which water is
the dispersion medium
highly absorbent (can contain up to 99.9% water) natural or
synthetic polymers
possess a degree of flexibility very similar to natural tissue, due
to their significant water content
highly cross-linked polymers, water insoluble but soak up water,
can be ‘mechanically
interactive’
novel biomaterial with surprising
antibacterial properties that can
be injected as a low-viscosity gel
into a wound where it rigidifies
nearly on contact
delivering a targeted payload
of cells and antibiotics to repair
the damaged tissue
(Univ. Delaware)
Metals and alloys
grain boundary engineering - high performance alloys
careful control chemistry / processing
increase strength / stiffness, fatigue
grain boundary is the interface between two grains, or crystallites, in a polycrystalline
material; defects in the crystal structure tend to decrease the electrical and thermal
conductivity of the material
high interfacial energy and relatively weak
bonding in most grain boundaries often makes
them preferred sites for the onset of corrosion
and for the precipitation of new phases
important to many of the mechanisms of creep
disrupt the motion of dislocations through
a material, so reducing crystallite size is
a common way to improve strength
Nanomagnetic materials
nanotechnology used to ‘freeze’ the positions of atoms in an
orientation that aligns the weak magnetic polarization
nanomagnetic structures are formed by careful control of material
composition and processing parameters
applications in magnetic / data storage
magnetic force microscopy (MFM)
imaging of novel nanomaterials
magnetic structure of a quantum “corral”, which
consists of magnetic iron atoms deposited on
a copper surface that "corral" copper electrons
Nanoparticles
in nanotech, particle is defined as a small object that behaves as a
whole unit in terms of its transport and properties
particles are further classified according to size
coarse - between 10,000 and 2,500 nm
fine - 2,500 to 100 nm
ultrafine particles, or
nanoparticles 100 to 1 nn
TEM (a, b, c) and SEM (d) images
of mesoporous silica nanoparticles,
mean diameter: (a) 20 nm, (b) 45 nm,
(c) 80 nm.
SEM (d) image corresponding to (b)
Nanoparticles and catalysts
high surface area
tailored surface chemistry
added to bulk / composite materials
metal, ceramic, or polymer
can also be ‘powder-like’
dendron conjugated gold
nanoparticle
Nanowires
nanowire is a nanostructure, with the diameter of the
order of a nanometer
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 - "quantum wires“
image width, 5 um
Quantum dots (QD)
QD is a portion of matter (e.g. semiconductor)
whose excitons are confined in all three spatial dimensions
electronic properties intermediate between bulk semiconductors
and discrete molecules
QD are semiconductors whose electronic properties are closely
related to the size and shape of the individual crystal
the smaller the size of the crystal, the
larger the band gap, the greater the
difference in energy between the
highest valence band and the lowest
conduction band
more energy is needed to excite the
dot, and more energy is released when
the crystal returns to its resting state
Smart approach – self-assembling
Self assembled monolayers (SAMs)
most typical – spontaneous adsorption of thiols
on gold
Self-assembly
making nanostructures by letting the
molecules sort themselves out
molecules will always seek the lowest
energy available to them
molecules will align themselves into
particular positions
use for large nanoscale arrays,
different length scales, low cost,
generality
electronic applications, coatings
molecular model (top) of a self-assembled
"mushroom"
photograph (bottom) shows control of surface
wetting by a layer of these mushrooms
Liposomes
artificial composite structures made of phospholipid bilayer and may
contain small amounts of other molecules
vary in size from low micrometer range to tens of micrometers
unilamellar liposomes (shown) are typically in the lower size range
with various targeting ligands attached to their surface allowing for
their surface-attachment and accumulation in pathological areas for
treatment of disease
can be filled with drugs and used to deliver drugs
disrupting biological membranes
– sonication
from natural phospholipids with
mixed lipid chains (e.g. egg
phosphatidylethanolamine) or
other synthetic surfactants
should not be confused with
micelles and reverse micelles
composed of monolayers
Silicon structures / materials
wafers
MEMS (microelectromechanical systems)
LOC (lab-on-chip)
biomimetic structures - learning from nature
– using shape as well as chemistry
– some similar function (light gathering, sensing / detection
Thin films
physical coatings
layered stacks
deposited films
functionalized (SAMs)
magnetic and optical applications
metallization in silicon semiconductors
Nanofabrication techniques
nanoparticles
colloidal processing
flame combustion
phase segregation
nanorods or nanowires
template-based electroplating
solution-liquid-solid growth (SLS)
thin films
chemical vapour deposition
molecular beam epitaxy
atomic layer deposition
nanostructured bulk material
photonic bandgap crystals by self-assembly of nanosized
particles
grouped according to the form of products
Making of nanostructures
the bottom-up approach: whereby structures are
made atom-by-atom and molecule-by-molecule,
harnessing covalent, ionic, metallic or non-covalent
bonds
– this approach represents how nature self-assembles functioning
nanostructures, such as enzymes and viruses
the top-down approach: whereby structures are
etched into bulk materials such as silicon
– this approach represents how silicon chips are fabricated
thus, nanoscale science is more than creating
structures on the length scale of 1-100 nm; it is about
making nanostructures which also function in some
way
How to make things small?
Nature
µµµµm
nm
Å
Biological
World
Structure
leads to
Function
Lithographic Techniques
Covalent Chemistry – Dendrimers
Supramolecular Chemistry – Aggregates
Nanoparticle Synthesis
Molecular Beam Epitaxy
SPM Probes
Nanotechnology
Down
Top
Physics
Non-Biological
World
Up
Bottom
Chemistry
Carbon-based
nanomaterials
Carbon atoms
sp3 and sp2 hybridization
states
diamond
graphite
hard, transparent, insulator, expensive
soft, opaque, conductor, cheap
Buckminsterfullerene
molecule consisting of 60 C atoms
sp2 hybridized bonds
has 20 hexagons, 12 pentagons
other related structures have
70 or 84 C atoms
Nobel Prize in Chemistry 1996: Robert Curl, Sir Harold Kroto,
Richard Smalley “for their discovery of fullerenes”.
Fullerene
empty and enclosing other atom(s)
RbCs2C60 is the highest temperature carbon based
super conductor yet discovered, Tc = 33 K
subject of intense research, both for their unique
chemistry and for their technological applications,
especially in materials science, electronics, and
nanotechnology
rolled up sheet of
sp2 bonded C atoms
can be formed from
a single sheet of C atoms
or several sheets
SWCNT / MWCNT
properties depend on
how they are rolled up
100 times stronger than steel at 1/6 the weight
electrical conductor
electrical insulator
efficient thermal conductors
Carbon nanotubes
Types of SWNCTs
zig-zag
arm-chair
chiral
SWCNT
n,m numbers
(n,m) nanotube naming scheme can be thought of as a vector Ch
in an infinite graphene sheet that describes how to "roll up" the
graphene sheet to make the nanotube
T denotes the tube axis, a1 and a2 are the unit vectors of
graphene in real space
n x n, n =m SWCNTs
Single- and multi-walled CNTs
SWCNT
MWCNT
interlayers
spaced 0.34 nm
Flexibility of CNTs
twisted and spiral CNTs
Properties of CNTs
strength - strongest and stiffest materials known, in terms of tensile
strength and elastic modulus
– a multi-walled carbon nanotube was tested to have a tensile strength of 63 Gpa (highcarbon
steel 1.2 Gpa)
– very high elastic moduli ~1 Tpa
– CNTs have a low density for a solid of 1.3-1.4 g/cm³, its specific strength of up to 48 462
kN·m/kg is the best (high-carbon steel154 kN·m/kg)
electrical - structure of a nanotube strongly affects its electrical properties
– for a given (n,m) nanotube, if n - m is a multiple of 3, then the nanotube is metallic,
otherwise semiconductor
– thus all armchair (n=m) nanotubes are metallic, and nanotubes (5,0), (6,4), (9,1), etc. are
semiconducting
– metallic CMTs can have an electrical current density more than 1000 times greater than
Cu and Ag
thermal - very good thermal conductors along the tube, exhibiting a
property known as "ballistic conduction,"
– but good insulators laterally to the tube axis
– it is predicted that carbon nanotubes will be able to transmit up to 6 kW per meter per
kelvin at RT (Cu only transmits 385 W/m/K)
Potential applications of CNTs
energy storage
– hydrogen storage, 6.5% by weight is needed
– Li intercalation, electrochemical supercapacitors
field emission devices
transistors
– CNTs are p-type; can be doped with K to make them n-type
AFM tips
nanotweezers
composite materials
nano structures
potential for extremely strong light weight cables / space
elevator ( http://www.youtube.com/watch?v=pnwZmWoymeI )
physical memory
NanoBuds
fullerenes covalently bonded to
outer sidewalls of underlying
nanotube.
exhibit properties of both CNTs
and fullerenes.
mechanical properties and
electrical conductivity are
similar to CNTs
however, because of the higher reactivity of the attached fullerene
molecules, the hybrid can be further functionalized through known
fullerene chemistry
the attached fullerenes can be used as molecular anchors to
prevent slipping of the nanotubes in various composite materials,
thus improving mechanical properties
Carbon nanofibers
consist of the graphite sheet completely arranged in various
orientations
outstanding feature - presence of a plenty of sides which in turn
make sites accessible to chemical or physical adsorption
lenght from 5 to several hundred um, 100 - 300 nm in diameter
graphite platelets "perpendicular" and "parallel" to the fiber axis
CNTs are strong
large length (up to several microns) and small diameter
(a few nanometres) result in a large aspect ratio
mechanical properties can improve by 50% or more by
adding carbon nanotubes
Silica fibres +MWCNT
Damascus sabre steel contains CNTs
MWCNTs found in 17th century sword
formed during the synthesis and may have produced
the very good mechanical properties.
Carbon nanotube mechanical oscillator
Force sensitivity of 1 fN Hz-1/2
Preparation of CNTs
Carbon arc discharge. Hold two carbon (graphite) electrodes at
some potential difference in a Helium atmosphere and bring the
electrodes together. At some separation and arc will be
produced, and carbon nanotubes will grow on the cathode.
These will normally be multiwalled nanotubes, but single walled
nanotubes can be grown by adding Ni, Fe, or Co to the cathode
Laser ablation. Heat up a lump of graphite to ~1200 C in an Ar
atmosphere, and then blast it with a laser. This can make single
walled nanotubes if the graphite has a catalyst like Co or Ni
included.
Catalytic growth. Heat up hydrocarbons (e.g. acetylene) to high
temperatures and then let them settle on a substrate coated with
a catalyst (Fe, Co, Ni). This will form either multiwalled
nanotubes or single walled nanotubes depending on the growth
conditions.
CNT synthesis
a metal particle is acts as a catalyst for carbon
nanotube growth
growth takes place in an inert atmosphere, often He
a source of carbon and energy are needed
Metal
Substrate Substrate
Metal
CH2=CH2
CNTs purification
carbon nanotubes must usually be purified in some
way to remove the catalyst
oxidation
acid treatment
annealing
ultrasound
magnetic purification
micro-filtration
chromatography
Functionalization
CNTs can react chemically with different molecules
they can be made soluble in water
– Aldrich sells CNTs with polyaminobenzene sulfonic acid (PABS) a
water soluble conducting polymer covalently bonded directly to
the nanotube.
lipids can be organized around CNTs
benzene can be attached
to carbon nanotubes
CNTs can be opened, filled
with a metal and closed.
Biocompatible CNTs
collagen – CNTs composite material
collagen – belongs to
matrix proteins
surface more compatible for
attachment of cells
Collagen
CNT
Collagen fibril with
incorporated CNT.
Open problems
to be useful for devices, these carbon nanomaterials
need to be prepared on and/or connected reliably to
electrodes.
since the properties of these nanomaterials depend
strongly on structure (e.g. armchair vs zig-zag
nanotubes), we need to have good control over these
structural details.
many unanswered physics questions remain,
including the magnetism, superconductivity, and
optical properties of these materials.
Manufacturers
home.flash.net/~buckyusa/
carbolex.com/
cnanotech.com/
www.fibrils.com/
www.pa.msu.edu/cmp/csc/nanot
ube.html
www.nano-lab.com/
carbonsolution.com/
www.mercorp.com/mercorp/
www.nanocarblab.com/
www.nanocs.com/
www.nanocyl.com/
www.nanoledge.com/
www.e-nanoscience.com/
www.sesres.com/Nanotubes.asp
www.sunnano.com/
www.rsphysse.anu.edu.au/nanot
ube/
www.thomas-
swan.co.uk/pages/nmframeset.html
www.apexnanomaterials.com/
www.timesnano.com/default.html
www.seocal.com/products_pdflist.html
www.simagis.com/nanotubes.htm
www.xintek.com/products/overview.html
www.helixmaterial.com/
store.nanoscience.com/index.asp?
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