Lecture 2 (Mar. 7th, 2013)
MEE6513: Introduction to
Nanoscience and Nanoengineering
Department of Mechanical Engineering
Sogang University
Jungchul Lee, PhD
Course Objectives
To teach how to synthesize or process
nanomaterials and nanostructures
£ To facilitate understanding of the physical
properties related to the nanometer scale
£ To teach how to design and fabricate nanodevices or devices with nanomaterials as
building blocks
£ To introduce novel tools to characterize
nanostructures and nanomaterials
£
Size and Scale
meter
m
= 1m
millimeter
mm
= 10-3 m
micrometer
mm
= 10-6 m
nanometer
nm
= 10-9 m
angstrom
Å
= 10-10 m
picometer
pm
= 10-12 m
How small is “nano”?
l
Nanotechnology deals with small structures or
small-sized materials with dimensions from
subnanometer to several hundred nanometers
1 nm = 10-9 m or 1 nm = a billionth of a meter
1 nm = 10-3 um= 10 Å
1 m = 103 cm = 106 mm = 109 nm = 1010 Å
1 nm is equivalent to 10 hydrogen atoms or 5 silicon
atoms aligned in a line
Ethane (C2H6) – 0.1535 nm
Fullerene (C60H60) – 1 nm
How small is “nano”?
Examples of nano-/microstructures or materials
with their typical ranges of dimension
Example 1 (Nanometer Games)
l
How many carbon nanotubes 1 nm in diameter can
be tightly packed into a cylinder defined by a
human hair 100 um in diameter? Assume packing is
done parallel to the long axis and that packing
efficiency is not a concern.
Hint)
SWCNT
d~1 nm
Human
hair
100 um
Example 2 (Nanometer Games)
l
Assume that a cubic-shaped transistor in a
computer chip has volume of 10 nm3. How many
would fit into a 5-mL drop of water? If currently
one billion transistors are fabricated every second,
how much time in years is required to manufacture
this number of transistors?
Hint)
Water drop : 5 mL = 5 cm3=5(10-2m)3
Transistor : 10 nm3=10(10-9m)3
Nano and Life Science
Atom 0.1 nm, DNA (width) 2 nm, Protein 5 – 50 nm
Virus 75 – 100 nm, Materials internalized by cells < 100 nm
Bacteria 1,000 – 10,000 nm, White Blood Cell 10,000 nm
Nano and Life Science Applications
Biopharmaceutics
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Drug Delivery
Drug Encapsulation
Functional Drug Carriers
Implantable Materials
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Tissue Repair and Replacement
Implant Coatings
Tissue Regeneration Scaffolds
Structural Implant Materials
Bone Repair
Bioresorbable Materials
Smart Materials
Sensory Aids
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Surgical Aids
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Assessment and Treatment Devices
Implantable Sensors
Implantable Medical Devices
Operating Tools
Smart Instruments
Surgical Robots
Diagnostic Tools
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Implantable Devices
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Retina Implants
Cochlear Implants
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Genetic Testing
Ultra-sensitive Labeling and
Detection Technologies
High Throughput Arrays and
Multiple Analyses
Imaging
Nanoparticle Labels
Size-dependent Properties
£
Nanotechnology is not only a simple continuation of
miniaturization from micron meter scale down to
nanometer scale.
• While materials in the micrometer scale mostly exhibit
physical properties the same as that of bulk, materials in the
nanometer scale may exhibit physical properties distinctively
different from that of bulk.
• Materials in this size range exhibit some remarkable specific
properties; a transition from atoms or molecules to bulk form
takes place in this size range.
£
Significant surface area, departure from continuum,
unusual mechanical/physical properties
Size-dependent Properties (Examples)
£
£
£
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Crystals in the nm scale have a low melting point (the
difference can be as large as 1000 deg. C) and reduced lattice
constants, since the number of surface atoms or ions becomes
a significant fraction of the total number of atoms or ions and
the surface energy plays a key role in the thermal stability.
Crystal structures stable at elevated temperatures are stable
at much lower temperatures in nanometer sizes, so
ferroelectrics and ferromagnetics may lose their
ferroelectricity or ferromagnetism when the materials are
shrunk to the nanometer scale.
Bulk semiconductors become insulators when the characteristic
dimension is sufficiently small (in a couple of nanometers).
Au nanocrystal demonstrates to be an excellent low
temperature catalyst though bulk gold does not exhibit
catalytic properties.
Why is the nanoscale important?
New phenomena not possible at the macroscale
New specific material properties at the nanoscale
• Nanomaterials may have a significantly lower melting
point or phase transition temperature and appreciably
reduced lattice constants, due to a huge fraction of
surface atoms in the total amount of atoms
• Mechanical properties of nanomaterials may reach the
theoretical strength, which are one or two orders of
magnitude higher than that of single crystals in the
bulk form. The enhancement in mechanical strength
is due to the reduced probability of defects.
Why is the nanoscale important?
• Optical properties of nanomaterials 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. The 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 be also enhanced appreciably, due to the
better ordering in microstructure, e.g. polymeric fibrils.
• Magnetic properties of nanostructured materials 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.
Why is the nanoscale important?
• Self-purification is an intrinsic thermodynamic property of
nanostructures and nanomaterials. Any heat treatment increases
the diffusion of impurities, intrinsic structural defects and
dislocations, and one can easily push them to the nearby surface.
Increased perfection would have appreciable impact on the
chemical and physical properties. For example, chemical
stability would be enhanced.
• Example
ü Bulk gold is a shiny yellow metal
ü Nanoscopic gold, i.e. clusters of gold atoms measuring 1 nm across,
appears red
ü Bulk gold does not exhibit catalytic properties
ü Au nanocrystal is an excellent low temperature catalyst.
Properties of nanostructured materials are size-dependent.
Therefore, if we can control the processes that make a nanoscopic
material, then we can control the material’s properties.
Nanotechnology
l
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A technology of design, fabrication and
applications of nanostructures and
nanomaterials
Is concerned with materials and systems
whose structures and components exhibit
novel and significantly improved physical,
chemical and biological properties,
phenomena and processes due to their
nanoscale size
Is a multidisciplinary field: chemists,
physicists, material scientists, engineers,
molecular biologists, pharmacologists, etc.
Nanotechnology classification
Many technologies have been explored to fabricate
nanostructures and nanomaterials. These technical
approaches can be grouped in several ways. One way is to
group them according to Fabrication and processing of
nanomaterials.
l Vapor phase growth (including laser reaction pyrolysis for nanoparticle
synthesis and atomic layer deposition (ALD) for thin film deposition
l Liquid phase growth (including colloidal processing for the formation
of nanoparticles and self assembly monolayers)
l Solid phase growth (including phase segregation to make metallic
particles in glass matrix and two-photon induced polymerization for
the fabrication of three-dimensional photonic crystals
l Hybrid growth (including vapor-liquid-solid (VLS) growth of nanowires)
Nanotechnology classification
Many technologies have been explored to fabricate
nanostructures and nanomaterials. These technical
approaches can be grouped in several ways. Another way is
to group them according to Form of the products.
l Nanoparticles (by colloidal processing, flame combustion, phase
segregation)
l Nanorods or nanowires (by temperature-based electroplating, solidliquid-solid (SLS), spontaneous anisotropic growth)
l Thin films (by molecular beam epitaxy (MBE), atomic layer deposition
(ALD))
l Nanostructured bulk materials for example photonic crystals (by selfassembly of nanosized particles)
Nanotechnology classification
Molecular beam epitaxy (MBE) is one of several
methods of depositing single crystals. Molecular
beam epitaxy takes place in high vacuum or
ultra high vacuum (10−8 Pa). The most important
aspect of MBE is the slow deposition rate
(typically less than 3,000 nm per hour), which
allows the films to grow epitaxially.
Atomic layer deposition (ALD) is a thin film
deposition technique that is based on the
sequential use of a gas phase chemical process.
The majority of ALD reactions use two chemicals,
typically called precursors. These precursors
react with a surface one-at-a-time in a
sequential manner. By exposing the precursors
to the growth surface repeatedly, a thin film is
deposited.
MBE – single crystal
ALD – gas deposition
Emergence of nanotechnology
Nanotechnology is new, but research on nanometer scale is
not new at all.
• The Chinese are known to use Au nanoparticles as an inorganic dye
to introduce red color into their ceramic porcelains.
• The continued decrease in semiconductor device dimensions has
driven the current fever of nanotechnology.
• Moore’s Law
ü # of transistors per unit area doubles every two years.
ü The transistor size has decreased by a factor of 2 every 18
months.
Emergence of nanotechnology
(Invention of the point contact transistor)
1947 : Invention of the Point contact Transistor
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A transistor uses electrical current or a small
amount of voltage to control a larger change in
current or voltage.
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Transistor are the building blocks of computers,
cellular phones, and all other modern
electronics.
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In 1947, William Shockley, John Bardeen, and
Walter Brattain of Bell Laboratories built the
first point-contact transistor.
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The first transistor used germanium, a
semiconductive chemical.
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It demonstrated the capability of building
transistors with semiconductive materials.
First Point Contact
Transistor and
Testing Apparatus
(1947)
[Photo Courtesy of
The Porticus Centre]
There are two approaches to making
structures on the nanoscale
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The bottom-up approach : whereby
structures are made atom-by-atom a
nd molecule-by-molecule, harnessing
covalent, ionic, metallic or non-coval
ent bonds. This approach represents
how nature self-assembles functionin
g nanostructures, such as enzymes an
d viruses, (crystal growth, polymer s
ynthesis, self-assembly)
The top-down approach : whereby st
ructures are etched into bulk materi
als such as silicon. This approach re
presents how silicon chips are fabric
ated, (most lithography techniques),
There are two approaches to making
structures at the nanoscale
Top-down approach
The biggest problem with top-down approach : The imperfection
of the surface structure.
Crystallographic damage to the processed patterns
Defects on the surface during the etching steps
The surface over volume ratio in nanostructures is very large
Significant impact on physical properties and surface chemistry of
nanostructures
Bottom-up approach
For a nanometer scale, all the tools are too big to deal with such tiny subjects à
very little choice for a top-down approach
Bottom-up approach refers to the build-up of a material from the bottom :
atom-by-atom, molecular-by-molecular, or cluster-by-cluster
The advantage of bottom-up approach :
less defects, more homogeneous chemical composition,
and better short and long range ordering
Driven mainly by the reduction of Gibbs free energy
Nanostructures produced by bottom-up process are in a
state closer to a thermodynamic equilibrium state