introduction to nanotechnology,nanoscience

8/12/2019 Introduction to Nanotechnology,Nanoscience

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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/

นสตปรญญาโทสายตรง ลงทะเบยน วชา 202596 Select Topic

(Nanotechnology) Sec 1

นสตปรญญาโทสายออม ลงทะเบยน วชา 202472

Nanomaterial Technology Sec 400

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



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Outline

Definitions of Nanomaterials, Nanoscience, andNanotechnology

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 atleast one dimension 100 nanometres or less.

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

They can exist in single, fused, aggregated or

agglomerated forms with spherical, tubular, and irregularshapes.Common types of nanomaterials includenanotubes, dendrimers, quantum dots and fullerenes.

Nanomaterials

Novel properties of nanomaterials are generally not seen in theirconventional, bulk counterparts.

The two main reasons why materials at the nanoscale can have differentproperties are (i) increased relative surface area and (ii) new quantumeffects.

Nanomaterials have a much greater surface area to volume ratio than theirconventional forms, which can lead to greater chemical reactivity and affecttheir strength.

Also at the nanoscale, quantum effects can become much more importantin determining the materials properties and characteristics, leading to noveloptical, electrical and magnetic behaviours.



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Nanoscience

The definition of Nanoscience is the study ofnanomaterials which have at least 100 nm in onedimension.

Nanoscience refers to the science and manipulation ofchemical and biological structures with dimensions in therange from 1-100 nanometers.

Nanotechnology

Nanotechnology is engineering at the atomic or molecularlevel.

Nanotechnology is the construction and use of functionalstructures designed from atomic or molecular scale with atleast one characteristic dimension measured in nanometers.

It is a group of enabling technologies that involve the

manipulation of matter at the nanoscale (generally accepted as100 nanometres or less) to create new materials, structuresand devices.

At this very small scale, the chemical and physical properties ofmaterials can change, such as colour, magnetism and the abilityto 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 medicaltreatments and tools, more efficient energy production, more effectivepollution reduction, and stronger, lighter materials.

The potential benefits of nanotechnology to industry and the community.

However, there are concerns that some applications and products ofnanotechnology may present health, safety and environmental hazards andrisks.

Nanotechnology can be either a „top-down‟ technique, such as etching andmilling of larger material, or a „bottom-up‟ technique that involvesassembling 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 atlarger scales.

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

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

Quantum confinement of both the electron and hole in all three dimensions leads toan 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-dotcolor 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 decreasedby 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 andoptical properties when the material is of sufficientlysmall size - typically 10 nm or less.

The band gap increases as the size of the nanostructuredecreases. Specifically, the phenomenon results from

electrons and holes being squeezed into a dimension thatapproaches a critical quantum measurement, called theexciton 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 holewhich are attracted to each other by the electrostaticCoulomb force.

An exciton may be formed when a photon enters asemiconductor, exciting an electron from the valence

band into the conduction band, leaving a localized hole ofopposite electric charge behind, to which the electron isattracted 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 bestrong and the excitons tend to be small, of the same order asthe size of unit cell, or, in the case of molecular excitons, evenon the same molecule as in fullerenes, so the electron and holeare located in the same cell.

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

Frenkel excitons are realized in alkalihalide crystals and inorganic 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 Coulombinteraction between electrons and holes.

The result is a Wannier exciton, which has a radius larger than thelattice spacing. As a result, the effect of the lattice potential can beincorporated into the effective masses of the electron and hole, andbecause 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 insemiconductor crystals with small energy gaps and high dielectricconstant, but have also been identified in liquids, such as liquidxenon.

Surface excitons

At surfaces it is possible for so called image states tooccur, where the hole is inside the solid and the electronis in the vacuum. These electron hole pairs can only movealong the surface.



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Alternatively, an exciton may be thought of as an excited stateof an atom, ion, or molecule, the excitation traveling from onecell of the lattice to another.

When a molecule absorbs a quantum of energy thatcorresponds to a transition from one molecular orbital toanother molecular orbital, the resulting electronic excitedstate is also properly described as an exciton.

An electron is said to be found in the lowest unoccupiedorbital and an electron hole in the highest occupied molecularorbital, and since they are found within the same molecularorbital manifold, the electron-hole state is said to be bound.


Molecular excitons typically have characteristic lifetimes on theorder of nanoseconds, after which the ground electronic stateis restored and the molecule undergoes fluorescence.

Molecular excitons have several interesting properties, one ofwhich is energy transfer whereby if a molecular exciton hasproper energetic matching to a second molecule's spectralabsorbance, then an exciton may transfer (hop) from onemolecule to another.

The process is strongly dependent on intermolecular distancebetween the species in solution, and so the process has foundapplication in sensing and molecular rulers.



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Years Nanotechnology

Milestone

Explanation

1857 Michael Faradaydiscovers colloid gold

Michael Faraday introduced „colloidal gold‟ samplesto the Royal Society. This suspension of goldnanoparticles in solution was totally transparent insome lighting, but in other lighting conditionscould produce differently coloured solutions of„ruby, green, violet or blue‟.

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

1905 Albert Einstein explainsthe existence of colloids

Albert Einstein provided a thoroughly quantitativetheory for the state of a colloid dispersion. He

considered colloids to behave as „big atoms‟ andexplained their movement in terms of Brownianmotion.This theory was confirmed by the experiments of

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


Years NanotechnologyMilestone

Explanation

1932 Langmuir discoverslayers of atoms onemolecule thick

Langmuir established the existence of monolayers(layers of atoms or molecules one atom thick).These monolayers have peculiar two-dimensionalqualities, and led to the development of a totallytransparent glass produced by forming a thin filmof fluorine compound on the surface.

He was awarded the Nobel prize in 1932 for thiswork on thin films.

1985 Feynman suggests thatthere is „plenty of room‟

to work at thenanoscale

Richard P. Feynman gave a ground-breaking speech„There‟s plenty of room at the bottom‟ where he

discussed the possibility of controlling materials atthe level of atoms and molecules – this was thefirst vision of the possibilities of science andtechnology at the nanoscale.

He became a Nobel laureate in 1965.



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Milestone

Explanation

1974 The word„nanotechnology‟ first

used

The term „nanotechnology‟ was called in 1974 byNorio Taniguchi of the University of Tokyo. Heused the word to refer to „production technology

to get the extra high accuracy and ultra finedimensions, i.e. the preciseness and fineness onthe order of 1 nm (nanometre)‟

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

Proceedings of the International Conference ofProduction Engineering , 1974)

1981 IBM invent a machinewhich can move single

atoms around

„‟STM‟‟

Gerd Binning and Heinrich Rohrer invented theScanning Tunneling Microscope (STM) at IBM. This

microscope allows atomic-scale three-dimensionalprofiles of surfaces to be obtained.

They were awarded the Nobel prize in 1986 forthis work.



Explanation

1985 A new form of carbonis discovered: C60 orbuckminsterfullerene orbuckyball

Richard Smalley, Robert Curl and Harold Krotodiscovered C60 while investigating the outeratmosphere of stars, for which they were awardedthe Nobel Prize in 1996.

the 60 carbon atoms are arranged into a spheremade of 12 pentagons and 20 hexagons (exactly

like a football).

1990 IBM demonstrate abilityto control the positionof atoms

IBM research scientist Don Eigler showed that theposition of atoms could be controlled precisely.Using the STM he manoeuvred 35 xenon atomson a nickel surface so that they spelled out „IBM‟.

This was achieved at high vacuum and in thesupercooled temperature of liquid helium.



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Milestone

Explanation

1991 Carbon nanotubesdiscovered

Sumino Iijima discovered a process to make„graphitic carbon needles ranging from 4nm to30nm in diameter and 1 micron in length‟ (Nature

354, 1991, 56). The needle-like tubes he describedconsisted of multiple sheets of graphite rolled intohollow tubes, which have now become known ascarbon nanotubes. In 1993 the first single-wallednanotubes (SWNT) were produced.

1993 First high-qualityquantum dots prepared

Murray, Norris and Bawendi synthesise the firsthigh quality quantum dots of nearly monodisperse

CdS CdSe and CdTe ( JACS1993, 115).Quantum dots are very small particles withinteresting optical properties: they absorb normalwhite light and, depending on their size, emit arange of bright colours. This property arisesdirectly from the very small size of the particle.



Explanation

1997 Nanotransistor built Lucent Technologies fabricated the „nanotransistor‟ – a complete metal oxide semiconductortransistor. It was only 60nm wide, consisted ofsources, drain, gate and gate oxide and improvedthe key measures of performance. The keyadvance was being able to fabricate a1.2nm thickgate oxide layer. Other companies have since built

smaller nanotransistors.

2000 DNA motor made The first DNA motor was created by LucentTechnologies with Oxford University. Thesedevices are similar to motorised tweezers andhave the potential to make computers 1,000 morepowerful than today‟s machines.

The hope is that DNA motors can be attached toelectrically conducting molecules to assemblerudimentary circuits by acting as switches(Nature 406 (6796), 2000, 605-608).



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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 crystallographyfirst.



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Crystal Structures

If we consider an atom or a group of atoms as a pointmathematically, all crystalline materials can then beconsidered as a repeating pattern of points in the spacecalled a lattice.

Groups of lattices can be classified into seven crystal systemsand 14 Bravais lattices.

The properties of bulk materials are primarily determinedby 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 = 9 o

g = 120o

11

10



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Monoclinic

a = b = c

a= g = 9 o

b = 120o

End – centered

Monoclinic

12 13

Triclinic

a = b = c

a = g = b = 90o

14

Number of Atoms in a Unit Cell: SCC

1/8

1/8

1/8 1/8

1/8

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


46

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

1/2

1/2

Number of Atoms in a Unit Cell: fCC

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



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Calculation of the density of CrystallineNanomaterials 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/ N A

(N A

= 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= r

a = 2r

V = a3

= 8r3



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Face-centered cubic

Pythagorean theorem

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

a2 = 8r 2

a = 81/2r

a

af = 4r

f 2 = a2 + a2

Determination of Volume in a unit cell: fcc

Face-centered cubic

Radius of each atom = ra = 81/2 . rV = 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 N m M d

a r N r

fcc has 4 atoms/ unit cell

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

N A 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 34 x 63.55 g mol 8.90 g cm

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

1/ 2 3

4

8 A

M d

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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Point defect

Vacancy of atoms

Self interstitial defect

Substitutional impurity

Interstitial impurity

vacancy

interstitial

impurity

substitutionalimpurity

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 surfaceatoms are situated in a different environment compared with theirbulk counterparts.

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

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

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

This extra energy is the origin of the surface energy.



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3

Surface Energy

E = ø*S,

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

Exercise: Surface Energy

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

If we have two types of particles with different sizes, 1 µmand 1 nm, which one should consider the surface energy

more significantly?



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3

Applications of Nanomaterials (Homework!)

Students have to do a 2-page report and give 5-min talk in theclass. You can choose one of nanomaterials below for yourreport.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 dots10. Others

The format of the 2-page report!

Material: ?

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

Current Applications of that material

References



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3

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, CRCPress (2007) Chapter 1

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

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

introduction to nanotechnology,nanoscience

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