introduction to nanomaterials, nanoscience, and...

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Introduction to Nanomaterials, Nanoscience, and Nanotechnology

Dr Montree Sawangphruk (DPhil)

Chemical Engineering, Kasetsart University, Room #1209-5, email:[email protected]

http://pirun.ku.ac.th/~fengmrs/ https://course.ku.ac.th/

http://pirun.ku.ac.th/~fengmrs/

นิสติปรญิญาโทสายตรง ลงทะเบยีน วชิา 202596 Select Topic

(Nanotechnology) Sec 1

นิสติปรญิญาโทสายออ้ม ลงทะเบยีน วชิา 202472

Nanomaterial Technology Sec 400

http://pirun.ku.ac.th/~fengmrs/

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Outline

Definitions of Nanomaterials, Nanoscience, and Nanotechnology

Surface area-to-volume Ratio and Quantum Confinement

History of Nanotechnology

Surface Science of Nanomaterials Crystal Structures

Surface Energy

etc

Applications of Nanomaterials (Homework!)

Pre-Exercises

1. What is Nano?

2. What is Nanotechnology?

3. What is Nanomaterial?

4. What is Nanoscience?

5. What are the applications of nanomaterials?

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Nanomaterials

The definition of nanomaterials is a material having at least one dimension 100 nanometres or less.

Nanomaterials can be nanoscale in zero dimension (e.g. fullerence), one dimension (e.g. nanowires), two dimensions (e.g. fibres, nanotubes), or three dimensions (e.g. particles).

They can exist in single, fused, aggregated or agglomerated forms with spherical, tubular, and irregular shapes. Common types of nanomaterials include nanotubes, dendrimers, quantum dots and fullerenes.

Nanomaterials

Novel properties of nanomaterials are generally not seen in their

conventional, bulk counterparts.

The two main reasons why materials at the nanoscale can have different

properties are (i) increased relative surface area and (ii) new quantum

effects.

Nanomaterials have a much greater surface area to volume ratio than their

conventional forms, which can lead to greater chemical reactivity and affect

their strength.

Also at the nanoscale, quantum effects can become much more important

in determining the materials properties and characteristics, leading to novel optical, electrical and magnetic behaviours.

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Nanoscience

The definition of Nanoscience is the study of

nanomaterials which have at least 100 nm in one

dimension.

Nanoscience refers to the science and manipulation of

chemical and biological structures with dimensions in the

range from 1-100 nanometers.

Nanotechnology

Nanotechnology is engineering at the atomic or molecular level.

Nanotechnology is the construction and use of functional structures designed from atomic or molecular scale with at least one characteristic dimension measured in nanometers.

It is a group of enabling technologies that involve the manipulation of matter at the nanoscale (generally accepted as 100 nanometres or less) to create new materials, structures and devices.

At this very small scale, the chemical and physical properties of materials can change, such as colour, magnetism and the ability to conduct electricity.

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Nanotechnology

Nanotechnology, its products and applications have the potential to offer significant social and environmental benefits.

For example, it is anticipated that nanotechnology will lead to new medical treatments and tools, more efficient energy production, more effective pollution reduction, and stronger, lighter materials.

The potential benefits of nanotechnology to industry and the community.

However, there are concerns that some applications and products of nanotechnology may present health, safety and environmental hazards and risks.

Nanotechnology can be either a „top-down‟ technique, such as etching and milling of larger material, or a „bottom-up‟ technique that involves assembling smaller subunits to produce the nanoscale product.

IBM Nanotechnology

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Nanotechnology

Somorjai, G. A., et al Topics in Catalysis 2008, 47, 1572.

Why is Nanotechnology so popular?

Properties of matter at nanoscale may not be as predictable as those observed at larger scales.

Important changes in behavior are caused not only by continuous modification of characteristics with diminishing size, but also by the emergence of totally new phenomena such as quantum confinement, a typical example of which is that the color of light emitting from semiconductor nanoparticles depends on their sizes.

Quantum confinement is the physics that governs the motion and interaction of electrons in atoms.

Quantum confinement of both the electron and hole in all three dimensions leads to an increase in the effective band gap of the material with decreasing crystallite size.

Colloidal CdSe quantum dots dispersed in hexane.

Quantum confinement effects allow quantum-dot color to be tuned with particle size.

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Example: CdS Nanocrystals vs Bulk CdS

Size dependence of the melting temperature of CdS nanocrystals (Reproduced fromAlivisatos, A.P., J. Phys. Chem., 100, 13226, 1996.)

Moor’s Law

Moore‟s Law” plot of transistor size versus year. The trend

line illustrates the fact that the transistor size has decreased by a factor of 2 every 18 months since 1950.

Smaller means Faster!

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Moor’s Law

Surface area to volume ratio

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Geometry Formula Summary

Quantum confinement

Quantum confinement is the change of electronic and

optical properties when the material is of sufficiently

small size - typically 10 nm or less.

The band gap increases as the size of the nanostructure

decreases. Specifically, the phenomenon results from

electrons and holes being squeezed into a dimension that

approaches a critical quantum measurement, called the exciton Bohr radius.

http://en.wikipedia.org/wiki/File:Bohr-atom-PAR.svg

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Quantum Size Effect

What is Exciton?

An exciton is a bound state of an electron and hole

which are attracted to each other by the electrostatic

Coulomb force.

An exciton may be formed when a photon enters a

semiconductor, exciting an electron from the valence

band into the conduction band, leaving a localized hole of

opposite electric charge behind, to which the electron is attracted by the Coulomb force.

Ref: A. I. Ekimov, A. A. Onushchenko, Sov. Phys. Semicond. 16, 775 (1982)

http://en.wikipedia.org/wiki/File:Bohr-atom-PAR.svg

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Classification of Excitons

Frenkel excitons

Wannier excitons

Surface excitons

Atomic and molecular excitons

Frenkel excitons

For nanomaterials with small dielectric constant.

Coulomb interaction between electron and hole may be strong and the excitons tend to be small, of the same order as the size of unit cell, or, in the case of molecular excitons, even on the same molecule as in fullerenes, so the electron and hole are located in the same cell.

This Frenkel exciton, named after Yakov Frenkel, has typical binding energy on the order of 0.1 to 1 eV.

Frenkel excitons are realized in alkalihalide crystals and in organic molecular crystals composed of aromatic molecules.

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Wannier excitons

In semiconductors, the dielectric constant is generally large, and as a result, electric field screening tends to reduce the Coulomb interaction between electrons and holes.

The result is a Wannier exciton, which has a radius larger than the lattice spacing. As a result, the effect of the lattice potential can be incorporated into the effective masses of the electron and hole, and because of the lower masses and the screened Coulomb interaction, the binding energy is usually much less than a hydrogen atom, typically on the order of 0.01eV.

This type of exciton was named for Gregory Wannier and NevillFrancis Mott. Wannier-Mott excitons are typically found in semiconductor crystals with small energy gaps and high dielectric constant, but have also been identified in liquids, such as liquid xenon.

Surface excitons

At surfaces it is possible for so called image states to

occur, where the hole is inside the solid and the electron

is in the vacuum. These electron hole pairs can only move along the surface.

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Alternatively, an exciton may be thought of as an excited state

of an atom, ion, or molecule, the excitation traveling from one

cell of the lattice to another.

When a molecule absorbs a quantum of energy that

corresponds to a transition from one molecular orbital to

another molecular orbital, the resulting electronic excited

state is also properly described as an exciton.

An electron is said to be found in the lowest unoccupied

orbital and an electron hole in the highest occupied molecular

orbital, and since they are found within the same molecular orbital manifold, the electron-hole state is said to be bound.


Molecular excitons typically have characteristic lifetimes on the

order of nanoseconds, after which the ground electronic state

is restored and the molecule undergoes fluorescence.

Molecular excitons have several interesting properties, one of

which is energy transfer whereby if a molecular exciton has

proper energetic matching to a second molecule's spectral

absorbance, then an exciton may transfer (hop) from one

molecule to another.

The process is strongly dependent on intermolecular distance

between the species in solution, and so the process has found

application in sensing and molecular rulers.

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Years Nanotechnology Milestone

Explanation

1857 Michael Faraday

discovers colloid gold

Michael Faraday introduced „colloidal gold‟ samples

to the Royal Society. This suspension of gold

nanoparticles in solution was totally transparent in

some lighting, but in other lighting conditions

could produce differently coloured solutions of

„ruby, green, violet or blue‟.

(Philosophical transactions of the Royal Society, 1857, 147, 145)

1905 Albert Einstein explains

the existence of colloids

Albert Einstein provided a thoroughly quantitative

theory for the state of a colloid dispersion. He

considered colloids to behave as „big atoms‟ and

explained their movement in terms of Brownian

motion.

This theory was confirmed by the experiments of

Jean-Baptiste Perrin, which contributed toward Perrin‟s 1926 Nobel prize.



Explanation

1932 Langmuir discovers

layers of atoms one

molecule thick

Langmuir established the existence of monolayers

(layers of atoms or molecules one atom thick).

These monolayers have peculiar two-dimensional

qualities, and led to the development of a totally

transparent glass produced by forming a thin film

of fluorine compound on the surface.

He was awarded the Nobel prize in 1932 for this

work on thin films.

1985 Feynman suggests that

there is „plenty of room‟

to work at the

nanoscale

Richard P. Feynman gave a ground-breaking speech

„There‟s plenty of room at the bottom‟ where he

discussed the possibility of controlling materials at

the level of atoms and molecules – this was the

first vision of the possibilities of science and

technology at the nanoscale.

He became a Nobel laureate in 1965.

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Explanation

1974 The word

„nanotechnology‟ first

used

The term „nanotechnology‟ was called in 1974 by

Norio Taniguchi of the University of Tokyo. He

used the word to refer to „production technology

to get the extra high accuracy and ultra fine

dimensions, i.e. the preciseness and fineness on

the order of 1 nm (nanometre)‟

(„On the Basic Concept of “NanoTechnology”‟,

Proceedings of the International Conference of Production Engineering, 1974)

1981 IBM invent a machine

which can move single

atoms around

„‟STM‟‟

Gerd Binning and Heinrich Rohrer invented the

Scanning Tunneling Microscope (STM) at IBM. This

microscope allows atomic-scale three-dimensional

profiles of surfaces to be obtained.

They were awarded the Nobel prize in 1986 for this work.



Explanation

1985 A new form of carbon

is discovered: C60 or

buckminsterfullerene or

buckyball

Richard Smalley, Robert Curl and Harold Kroto

discovered C60 while investigating the outer

atmosphere of stars, for which they were awarded

the Nobel Prize in 1996.

the 60 carbon atoms are arranged into a sphere

made of 12 pentagons and 20 hexagons (exactly like a football).

1990 IBM demonstrate ability

to control the position

of atoms

IBM research scientist Don Eigler showed that the

position of atoms could be controlled precisely.

Using the STM he manoeuvred 35 xenon atoms

on a nickel surface so that they spelled out „IBM‟.

This was achieved at high vacuum and in the

supercooled temperature of liquid helium.

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Explanation

1991 Carbon nanotubes

discovered

Sumino Iijima discovered a process to make

„graphitic carbon needles ranging from 4nm to

30nm in diameter and 1 micron in length‟ (Nature

354, 1991, 56). The needle-like tubes he described

consisted of multiple sheets of graphite rolled into

hollow tubes, which have now become known as

carbon nanotubes. In 1993 the first single-walled nanotubes (SWNT) were produced.

1993 First high-quality

quantum dots prepared

Murray, Norris and Bawendi synthesise the first

high quality quantum dots of nearly monodisperse

CdS CdSe and CdTe (JACS1993, 115).

Quantum dots are very small particles with

interesting optical properties: they absorb normal

white light and, depending on their size, emit a

range of bright colours. This property arises directly from the very small size of the particle.



Explanation

1997 Nanotransistor built Lucent Technologies fabricated the „nanotransistor‟

– a complete metal oxide semiconductor

transistor. It was only 60nm wide, consisted of

sources, drain, gate and gate oxide and improved

the key measures of performance. The key

advance was being able to fabricate a1.2nm thick

gate oxide layer. Other companies have since built smaller nanotransistors.

2000 DNA motor made The first DNA motor was created by Lucent

Technologies with Oxford University. These

devices are similar to motorised tweezers and

have the potential to make computers 1,000 more

powerful than today‟s machines.

The hope is that DNA motors can be attached to

electrically conducting molecules to assemble

rudimentary circuits by acting as switches

(Nature 406 (6796), 2000, 605-608).

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Explanation

2001 Prototype fuel cell

made using nanotubes

Nanohorns, irregularly shaped nanotubes, were

developed as fuel cell for hydrogen-based fuel such

as methanol. They group together creating a high

surface area ideal for catalysts. NEC corporation

announced that the latest generation weigh under

2 pounds, when fully fuelled, and power a laptop for 5 hours before needing refuelling.

2002 NanotextilesStain-

repellent trousers reach

the high street

Clothing embedded with nanoparticles that

produce a stain-repellent coating has been

developed. Nano-care™khakis have the fabric fibres

coated with nanowhiskers 10–100nm in length.

This new stain-repellent fabric is available from a

number of high street retailers and is available in trousers, shirts and ties.



Explanation

2003 Prototype nano-solar

cells produced

Prototype solar cells have been made by

Nanosolar Inc. in California. They use conducting

polymers and nano-based particles. This

technology has great advantages, compared to that

for traditional silicon-based solar cells, including

making the products much cheaper and easier to

make. These cells are also produced in flexible

sheets, making them suitable for many applications.

2004-2010

Research and

development continues

to advance

‘Graphene won the

2010 Nobel Prize’

Research and development in many

nanotechnology fields continues apace; some

recent developments include the following:

Nanospectra Bioscience has used gold-coated

nanoshells to destroy cancer tumours in mice

(Cancer Letters, 209, 171).

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Surface Science of Nanomaterials

Crystal Structure and Crystallography

Surface Crystallography

Surface Energy

Surface Reconfigurations

Surface Area and Surface Thermodynamics

Crystal Structure and Crystallography

To understand the difference between bulk and surface,

we need to discuss crystal structure and crystallography first.

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Crystal Structures

If we consider an atom or a group of atoms as a point

mathematically, all crystalline materials can then be

considered as a repeating pattern of points in the space

called a lattice.

Groups of lattices can be classified into seven crystal systems

and 14 Bravais lattices.

The properties of bulk materials are primarily determined by their crystal structures.

Bravais Lattices

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a = b = c

a = b = g = 90o

Simple cubic Body cubic Face centered cubic

1 2 3

X

YZ

a

cb

g

X

YZ

a

X

YZ

b

Tetragonal Body-centered Tetragonal

a = b = c

a = b = g = 90o

4 5

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Body-centeredOrthorhombic

OrthorhombicEnd-centeredOrthorhombic

Face-centeredOrthorhombic

a = b = c

a = b = g = 90o

6 7 8 9

a = b = c

a = b = g = 90o

RhombohedralHexagonal

a = b = c

a= b = 90o

g = 120o

1110

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Monoclinic

a = b = c

a= g = 90o

b = 120o

End –centered

Monoclinic

12 13

Triclinic

a = b = c

a = g = b = 90o

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Number of Atoms in a Unit Cell: SCC

1/8

1/8

1/8 1/81/8

1/81/8

1/8

Simple cubic

(scc)

# Atoms at the corners = 8 Atoms

# Atoms in a Unit cell =

8 x 1/8 = 1 Atom

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Body-centered cubic(bcc)

(8 x 1/8)+ 1 = 2 Atoms

Number of Atoms in a Unit Cell: bcc

# Atoms at the corners = 8 Atoms# Atom inside the cubic = 1 Atom


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Face-centered cubic (fcc)

or Cubic closed-packed (ccp)


(8 x 1/8)+(6 x 1/2) = 4Atoms

1/2

1/2

1/2

1/2

1/21/2

Number of Atoms in a Unit Cell: fCC

# Atoms at the corners = 8 Atoms# Atoms on the faces = 6 Atoms

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Calculation of the density of Crystalline Nanomaterials from their structures

Density (d) =mass (g)/volume (cm3) Mass of crystalline nanomaterials in a unit cell = mass of all

atoms in a unit cell Mass of each atom in a unit cell = molecular mass/ NA

(NA = 6.02 x 1023) Volume can be calculated from a unit cell

Determination of Volume in a unit cell:SCC

Simple cubic

Radius of each atom= ra = 2rV = a3 = 8r3

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Face-centered cubic

Pythagorean theorem

a2 + a2 = (4r)2 = 16r2

a2 = 8r2

a = 81/2r

a

af = 4r

f2 = a2 + a2

Determination of Volume in a unit cell: fcc

Face-centered cubic

Radius of each atom = ra = 81/2 . r

V = a3 = 83/2 . r3

Determination of Volume in a unit cell: fcc

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Exercise 1. Calculate the density of copper

(Cu) with the crystalline structure of fcc

3 1/ 2 3 1/ 2 3

4 / 4

(8 ) 8

A

A

M Nm Md

a r N r

fcc has 4 atoms/ unit cell

M (molar weight) of Cu = 63.55 g mol-1

NA is Avogadro's number = 6.02 x 1023 atoms mol-1

R is radius of Cu atom= 128 pm = 1.28 x 10-8 cm

-13

1/ 2 23 -1 -8 3 3

4 x 63.55 g mol8.90 g cm

8 (6.02 x 10 mol ) (1.28 x 10 cm )d

1/ 2 3

4

8 A

Md

N r

From

Answer the density of copper = 8.90 g cm-3

Note that the density of Cu reported = 8.93 g cm-3

Why is it different?

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Hexagonal close packed

Face -centered cubic Other structures

Body-centered cubic

Li

NaK

RbCs

Be

MgCa

SrBa

Sc

YLa Hf Ta

NbZr

Ti V Cr Mn Fe Co Ni Cu Zn Ga

InTl Pb

Al

CdHg

AgAu

SnMo Tc Ru Rh PdW Re Os Ir Pt

Hexagonal close packed: Be, Mg, Sc, Y, La, Ti, Zr, Hf, Tc, Re, Ru, Os, Co, Zn, Cd, Tl Face -centered cubic: Ca, Sr, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Al, Pb Body-centered cubic: Li, Na, K, Rb, Cs, Ba, V, Nb, Ta, Cr, Mo, W, Fe,

Other structures: Mn, Hg, Ga, In, Sn

Crystal Structure of Metals

Defect of crystal

Disorder packing-point defect-line defect

Defect is the origin of difference between the calculated Value (i.e. density) and the experimental value

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Point defect

Vacancy of atoms

Self interstitial defect

Substitutional impurity

Interstitial impurity

vacancy

interstitial

impurity

substitutional impurity

self interstitial

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Line defect

Edge dislocation Screw dislocation

Surface Energy

The origin of the surface energy arises from the fact that surface atoms are situated in a different environment compared with their bulk counterparts.

For example, any atom in bulk materials with fcc or hcp structure will have 12 nearest neighbors and, thus, 12 interatomic bonding.

However, for the atoms on the surface, as discussed previously, they will have fewer neighbors due to their unique terminating locations.

As a result, those atoms will have some unsaturated or dangling bonds, which, in turn, will add some extra energy to the surface atoms compared with those in the bulk materials.

This extra energy is the origin of the surface energy.

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Surface Energy

E = ø*S,

where E is the total energy, S is the surface area, and ø is the surface energy.

Exercise: Surface Energy

Assume we have made some perfect spherical particles with a uniform radius R. So each individual particle has a volume of 4/3 πR3 and surface area of 4πR2.

If we have two types of particles with different sizes, 1 µm and 1 nm, which one should consider the surface energy more significantly?

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Applications of Nanomaterials (Homework!)

Students have to do a 2-page report and give 5-min talk in the class. You can choose one of nanomaterials below for your report.

1. Zinc Oxide (ZnO)

2. Titanium dioxide or titania (TiO2)

3. Silver (Ag)

4. Gold (Au)

5. Silicon (Si)

6. Carbon nanotubes (CNTs)

7. Graphene (2010 Nobel Prize)

8. Platinum (Pt)

9. Quantum dots

10. Others

The format of the 2-page report!

Material: ?

Introduction: What is it?, How to make it? and Why is it so interested?

Current Applications of that material

References

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IBM Reveals 5 Innovations That Will

Change Lives in the Next Five Years

Nokia-Cambridge Nanoscience Centre

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References Nanomaterials and Nanochemistry by C. Brechignac, P. Houdy, and M.

Lahmani, Springer (2006)

Nanoscale Devices by G.F. Cerofolini, Springer (2009) Chapters 1-3 and 9-12

Nanocomposite Science and Technology by P.M. Ajayan, L.S. Schadler, and P.V. Braun (2003) Chapters 1-3

Handbook of Nanoscience, Engneering, and Technology (second edition)by W. A. Goddard III, D. W. Brenner, S. E. Lyshevski, and G.J. Iafrate, CRC Press (2007) Chapter 1

Carbon Nanotubes Properties and Applications by M. J. O’Connell, CRC Press (2006) Chapters1, 4, 7, and 9

Nanotechnology: An Introduction to Nanostructuring Techniques by M. Kohler and W Fritzsche, WILEY-VCH (2004) Chapter 1

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