nano materials nano engineering

1. Lectures in Nanoscience & Technology
1. Nanomaterials & Structures
K. Sakkaravarthi
Department of Physics
National Institute of Technology
Tiruchirappalli – 620 015
Tamil Nadu
India
sakkaravarthi@nitt.edu
ksakkaravarthi.weebly.com

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Objectives
Education and Research for a better scientific
understanding on the Preparation & Characterization
of Materials in Nanoscales towards enhanced Utilization
& Applications.
Normal/Bulk materials Nanomaterials
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My sincere acknowledgments to
Introduction to Nanoscience and Nanotechnology,
Chris Binns, Wiley Publications, New Jersey (2009).
Nanotechnology: Basic Sciences and Energy
Technologies, M. Wilson, K. Kannangara, G. Smith, M.
Simmons and B. Raguse, CRC Press, New York (2005).
Introduction to Nanotechnology,
C.P. Poole and F.J. Ownes, Wiley India, New Delhi (2007).
Introduction to Nanomaterials and Nanotechnology
(Lecture Notes: University of Tartu), Vladimir Pokropivny,
Rynno Lohmus, Irina Hussainova, Alex Pokropivny, Sergey
Vlassov (2007).
Many other free & copyright internet resources.
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Nanoscience & Technology
Discussion?
NANO: Definition for nano?
Nanoscience
Technology in Nanoscience
Need for NANO
Utilize the possibility to vary fundamental properties of
materials without changing their chemical compositions.
The size can change the behavior of the material!
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Nanomaterials
Peculiar Reasons?
Nanomaterials have a relatively larger surface area
compared to the same mass of material produced in a
larger/bulk form.
This makes materials more chemically reactive
(sometimes inert materials in larger bulk form can become
reactive when produced in their tiny nanoscale), and affect
their (mechanical/electrical/optical/magnetic) properties.
Quantum effects begin to dominate the behavior.
The mechanical, thermal, optical, electrical and magnetic
behaviour of materials exhibit huge difference in the
nanoscale size.
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Nanomaterials: Properties
Mechanical properties: Surface to volume ratio increases
with decreasing size. Grain size, Cavities, dislocation,
Strength of materials...
Thermal properties: Surface atoms are less constrained
than interior atoms and thus can vibrate more freely about
their equilibrium.
Better specific heat and thermal conductivity in
nanomaterials. Also, have lower melting temperature/point.
Electrical conductivity: Free electrons yield an energy
continuum with no forbidden energy levels. The energy
levels become discrete/quantized and then form bands with
forbidden zones when move from bulk to nano scale. Hence,
bulk metals are good electrical conductors.
In the reverse, in nanoscale materials the energy levels will
have more forbidden zones & reduces the electrical
conductivity of nanomaterials.
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Nanomaterials: Properties...
Electrical conductivity: If size decreases bandgap increases!
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Types of Nanomaterials
Classification Based on Confined dimensions?
1D nanomaterial: One-dimension in nanoscale range &
two other dimensions free (any scale).
Ex.: Surface coatings and thin films.
2D nanomaterial: Any two dimensions in nanoscale range
& one dimension free.
Ex.: Biopolymers, nanotubes, and nanowires.
3D nanomaterial: All three dimensions in nanoscale.
Ex. Nanoparticles, Colloids, Quantum dots, fullerenes, etc.
0D nanomaterial: Zero dimensions in nanoscale :-(
i.e. Bulk materials in macroscale ) NOT NANO.
Violates basic definition ) NOT acceptable
But, actual/acceptable classification??
Should be based on the
“Number of Free Dimensions!"
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Types of Nanomaterials
Classification: Based on the Number of free dimensions!
0D nanomaterial: None can be outside nanoscale.
All the three dimensions are in nanoscale range.
Ex. Nanoparticles, Colloids, Quantum dots, fullerenes, etc.
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Types of Nanomaterials...
Classification: Based on the Number of free dimensions!
1D nanomaterial: One dimension outside the nanoscale
& two other dimensions in the nanoscale range.
Ex.: Nanowires, Nanorods, Nanotubes & Biopolymers.
2D nanomaterial: Any two dimensions can be outside the
nanoscale & one dimension in nanoscale range.
Exhibit plate-like shapes!
Ex.: Nanolayers, Surface coatings and thin films.
3D nanomaterial: Bulk nanomaterials & all three
dimensions can be outside nanoscale. But, made up of a
collection of nano-particles/materials.
Ex.: Dispersions of nanoparticles, bundles of nanowires/
nanotubes & multiple nanolayers.
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Types of Nanomaterials...
Classification: Based on the Number of free dimensions!
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0D: Nanoparticles (single/composite/coated)
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1D: Nanowires/Nanorods/Nanotubes
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All-in-One Example
Carbon: Basic element of life & its special ability to bond with
many elements in different ways.
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Allotropes of carbon: 0D to 3D
Eight allotropes of carbon:
a) diamond, b) graphite, c) lonsdaleite,
d) C60 buckminster fullerene, e) C540, Fullerite
f) C70, g) amorphous carbon, and h) single-walled carbon
nanotube.
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1. Nanowires
One to few-tens of nanometer (109 m).
The ratio of the length-to-width greater than 1000
(aspect ratio: Length
Thickness ' 1000).
Structures with a thickness/diameter constrained to tens of
nanometers or less and an unconstrained length.
At these scales, quantum mechanical effects are important
) “quantum wires".
Many different types of nanowires exist.
Superconducting, metallic, Semiconducting, & insulating.
Ex. Semiconducting nanowires: Silicon, Gallium Nitride
and Indium Phosphide.
Remarkable optical, electronic and magnetic characteristics!
(Silica nanowires can bend light around very tight corners).
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1. Nanowires: Applications
High-density data storage, either as magnetic read heads or
as patterned storage media.
Electronic and opto-electronic nanodevices.
Metallic interconnects of quantum devices and nanodevices.
1. Nanowires: Synthesis
Self-assembly processes, where atoms arrange themselves
naturally on stepped surfaces.
Chemical vapor deposition (CVD) onto patterned
substrates
Electroplating or molecular beam epitaxy (MBE)
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2. Nanorods
A solid wire-like structure in nanometer-scale.
Diameter: One to 100 nanometer (1 100 nm).
The ratio of the length-to-width is very small.
(aspect ratio: Length
Thickness ' 2 20).
Structures with a thickness/diameter constrained to tens of
nanometers or less and an unconstrained length.
2D view 3D view
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3. Nanotubes
A tube-like (hollow) structure in nanometer-scale.
Diameter in the order of nanometer (109 m).
The ratio of the length-to-width huge.
Aspect ratio: Length
Thickness up to 132,000,000
(significantly larger than for any other material).
Exceptional strength and stiffness.
Nanotubes maybe single-walled or multi-walled! Mainly
made of carbon!!
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Synthesis Approaches
1 Top-down:
* Breaking down bulk matter into basic building blocks.
* Slicing or successive-cutting (crushing, milling or
grinding) of a bulk material to get nano sized particles.
* Not suitable for preparing uniformly shaped materials.
Mainly, chemical or thermal or mechanical methods.
1. Ball milling 2. Plasma arching
3. Laser sputtering 4. Vapour deposition
2 Bottoms-up:
* Building complex systems by combining simple
atomic-level components.
* Devices ‘create themselves’ by self-assembly.
* Much cheaper than top-down methods.
* Able to generate a uniform size, shape and distribution.
* Normally made by chemical synthesis.
1. Sol-gel 2. Colloidal
3. Electrodeposition 4. Solution phase reductions
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Synthesis Approaches...
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Synthesis Approaches...
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Synthesis Approaches...
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0D Nanoparticles: Ball Milling
1 Grinder used to grind & blend materials.
2 Principle of impact and attrition: Size reduction by impact
(balls drop from near the top of the shell).
3 A hollow cylindrical shell rotating about its axis.
It is partially filled with balls (made of steel, stainless steel,
ceramic, or rubber).
4 The length of the cylindrical mill ⇡ its diameter.
5 Grinding can be carried out either wet or dry (speed).
6 Effective for production of amorphous materials.
7 Properties of balls: size, density, hardness, & composition.
8 Advantages: Cost effective; Suitable for both open &
closed grinding and batch & continuous operation;
Materials of all degrees of hardness
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0D Nanoparticles: Ball Milling - Schematic
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0D Nanoparticles: Ball Milling - Factors to consider
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0D Nanoparticles: Gas Condensation
Inert Gas evaporation-Condensation (IGC) technique:
Formation of nano-powders/particles on a metallic source/
substrate without chemical reactivity (inert gas environment).
1 Evaporating a metallic source using resistive heating
(radio frequency heating or electron gun or laser beam)
inside an evacuated chamber (to about 10 7 torr) filled
with inert gas at a low pressure.
2 The metal vapour migrates from the hot source into the
cooler inert gas by a combination of convective flow and
diffusion. Here the evaporated atoms collide with the gas
atoms within the chamber, thus losing kinetic energy.
3 The particles are collected usually by deposition on a
cold surface (cooling the substrate with liquid nitrogen to
enhance the deposition efficiency).
4 Highly concentrated deposition on the substrate.
Have complex aggregate morphology: need to be classified
based on the size (smaller or larger structures).
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0D Nanoparticles: Gas Condensation
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Gas Condensation: 1. Thermal evaporation
Most popular technique: easy handling & good yield.
Suitable to synthesis several pure nanocrystalline metals
(Cu, Au, Pd, Ni, Fe,) with a narrow particle size 5-20 nm.
Able to change particle size by varying gas pressure & temp.
Cons.: Alloys with different vapor pressures of constituent
elements are difficult to make :-(
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Gas Condensation: 2. Magnetron-sputtering
Suitable for elements with different vapour pressures.
Good for metals with very high melting point (Mo and
oxides like ZrO2) - very difficult in thermal evaporation.
For thin films: at very low pressures (around 10 3 mbar).
For powders/particles: Pressure around 10 1 mbar in IGC.
Cannot change the particle size by changing gas pressure :-(
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Gas Condensation: 3. Pulsed-laser-ablation
High power laser pulses to melt, evaporate and ionize
material from the surface of a target.
Pico-second pulsed laser irradiation in a vacuum chamber
(base pressure 10 7 mbar) with helium or argon.
Ablated atoms condense into clusters/nanoparticles &
collected on a liquid nitrogen cooled collection device.
Production of superconducting & insulating circuit
components to improved wear and biocompatibility.
Wider range of nanopowders of metals, metallic alloys,
semiconductors, and metal oxides can be synthesized :-)
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Gas Condensation: 3. Pulsed-laser-ablation
Laser parameters: Laser energy/fluence [Joule/cm2] and
ionization degree.
Surface temperature: Has a large effect on the nucleation
density. Nucleation density decreases as the temperature is
increased. Heating of the surface can involve a heating
plate or the use of a CO2 laser.
Substrate surface: Surface preparation, the miscut of the
substrate, and roughness of the substrate.
Background pressure: Common in oxide deposition, an
oxygen background is needed to ensure stoichiometric
transfer from the target to the film. This will affect the
nucleation density and film quality.
Three growth modes are possible:
1. Step-flow growth 2. Layer-by-layer growth, 3. 3D growth.
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Electron beam (physical vapor) deposition
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Synthesis: 2D films/layers
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Synthesis: Sol-Gel
Wet-chemical process: Formation of an inorganic colloidal
suspension (sol) and gelation of the sol in a continuous liquid
phase (gel)!
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Synthesis: Sol-Gel
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Synthesis: Sol-Gel
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Spray Pyrolysis
Vertical spray set-up
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Spray Pyrolysis
45o spray set-up
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Dip Coating
1 Coating process to manufacture bulk products.
2 Thin-film coatings: Single layer or Multilayer.
3 Suitable for
4 Mainly involves five stages:
1. Immersion: The substrate is immersed in the solution at
a constant speed.
2. Start-up: Pulled up back (constant speed) after a while.
The speed determines the thickness of the coating.
(faster withdrawal gives thicker coating material)
3. Deposition: Thin layer deposits on the substrate.
4. Drainage: Excess liquid is drained from the surface.
5. Evaporation: The solvent evaporates from the liquid.
For volatile solvents, such as alcohols, evaporation starts
already during the deposition and drainage steps.
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Dip Coating: Schematic 1
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Dip Coating: Schematic 2
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Dip Coating: Factors to consider
The dip coating technique can give uniform, high quality films
even on bulky, complex shapes.
1 Initial substrate surface
2 Submersion time
3 Withdrawal speed
4 Number of dipping cycles
5 Solution composition
6 Concentration and temperature
7 Environmental factors
Dip Coating: Few Advantages
Single/Multilayer coatings for sensor applications
Hydrogels/ Sol-Gel nanoparticle coatings
Layer-by-layer nanoparticle assemblies
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Multilayer Materials
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Multilayer Coating: Semiconductor Applications
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Molecular-beam epitaxy
Thin-film deposition of single crystals!
1 Epitaxy: Method of depositing a mono crystalline film or
deposition and growth of mono crystalline layers.
2 Growing crystalline layers on a crystalline substrate.
Similar to Ink-Jet-Color printing!!
3 Widely used in the manufacture of semiconductor devices.
4 1. Homoepitaxy: Same type substrate & material (Si-Si).
2. Heteroepitaxy: Different substrate & material (Ga-As).
3. Pseudo-homoepitaxy: Same material with a doping layer.
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Molecular-beam epitaxy...
1 MBE is an ultra high vacuum (UHV) based based
production of high quality epitaxial structures with mono
layer (ML) control.
2 “Beam” molecules do not collide to either walls of the
vacuum chamber (pressure: 10-11 Torr) or existing gas
atoms.
3 Very slow process: Growth rate: 1 m/hr.
4 To produce layers of metals, insulators & superconductors.
5 1. Ultra pure elements are heated in separate quai-effusion
cells until they begin to sublimate slowly.
6 2. Epitaxial growth takes place due to the interaction of
molecular or atomic beams on the surface of heated
crystalline substrate.
7 3. Atoms on a clean surface are free to move until finding
correct position in the crystal lattice to bond.
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Molecular-beam epitaxy...
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Molecular-beam epitaxy...
1 Basic elements of MBE system:
* Heated substrate. * Effusion cells and shutter.
* Reflection High Energy Electron Diffraction (RHEED)
system: RHEED gun & screen.
* Ultra High Vacuum * Liquid Nitrogen cryopanelling.
2 MBE Working Conditions:
* Mean free path of the particles > size of the chamber.
* Ultra-high vacuum (UHV= 10-11 Torr) for clear epilayer.
* Chemically stable as crucibles even at high temperature.
* Molybdenum and tantalum are widely used for shutters.
* Ultrapure materials are used as source.
3 Pros: Clean surfaces & free from oxide layer. Good control
of layer thickness & composition. Low growth rate
(1µm/h) gives high purity. Precisely controllable thermal
evaporation of each component.
4 Cons: Expensive (106 $ per MBE chamber).
Very complex system. Ultra-high vacuum conditions.
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Molecular-beam epitaxy...
Molecular-beam epitaxy: Applications
* Heterojunction bipolar transistors (HBT’s) used in satellite
communications.
* Electronic and optoelectronic devices (LED’s for laser
printers, CD/DVD players).
* Construction of quantum wells, dots and wires.
* To build a thin film of a photo voltaic solar cells.
* Low temperature Superconductor.
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