chapter 2 properties on the nanoscale nano 101 introduction to nanotechnology 1

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Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

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Page 1: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Chapter 2Properties on the Nanoscale

NANO 101Introduction to Nanotechnology

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Page 2: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Why Miniaturize?

Properties start to change as size decreases!2

Page 3: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

• Particles are small • High surface-to-volume ratio• React differently• Act differently (new properties)• Interact with light differently• Are on the scale of small biological structures

• Quantum Mechanics meet Classical Mechanics

• Interesting “new” structures

Why “Nano” is Interesting

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Page 4: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

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How Much Surface Area?

• 1,000 1 mm cubes, 2/3 of an index card• 1 x 10^21 1nm cubes, larger than a football field!

http://www.nano.gov/nanotech-101/special

Page 5: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Surface energy increases with surface area

• Large surface energy = instability• Driven to grow to reduce surface energy

Surface Area and Energy

C. Nutzenadel et al., Eur. Phys. J. D. 8, 245 (2000).

5

diameter (nm)

S

urfa

ce a

tom

s (%

)

Page 6: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Physical Structure Physical Property

What are the structural differences on the nanoscale?• High percentage surface atoms

• Large surface energy

• Spatial confinement

• Reduced imperfections

What properties are affected?What properties can we tune?

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Page 7: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Melting Points• Lower melting point for nanostructures <100 nm

• Surface energy increases as size decreases

Ichimose, N. et al. Superfine Particle Technology Springer-Verlag London, 1992. 7

Particle diameter (nm)

M

eltin

g po

int (

K)

Page 8: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Mechanical Properties

Mechanical properties improve as size decreases• High atomic perfection

Mechanical Strength of NaCl whiskers

8

d (µm)

S

tren

gth

(kg/

mm

)

Gyulai, Z. Z. Phys. 138, 317 (1954).

Page 9: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Mechanical Properties

Mechanical properties improve as size decreases• High atomic perfection

Can fail due to high internal stress

9http://hysitron.com/Portals/0/Updated%20Address/PICO02AN%20r1.f.pdf

Page 10: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Electrical Properties

• Electron Scattering– Electrons move through a metal to conduct

electricity– Electrons are scattered to cause resistivity– Decreasing size fewer defects less scattering

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Page 11: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

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Band Structure of Nanostructures

• Electronic states in between bulk solid and molecule

Bahnemann, Kormann, Hoffmann, J Phys. Chem. 91, 3789 (1987)

Page 12: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Electronic Structure

Band gap decreases as particle size increases

E

Metal Insulator Semi-conductor NP Semi-conductor

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Page 13: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Particles & Light

Particles interact differently with light Structures are smaller than wavelength of visible light

13Militaries Study Animals for Cutting-Edge Camouflage. James Owen in England for National Geographic News March 12,

2003, Proc. R. Soc. Lond. B (1999) 266, 1403-1411

220X1X 20,000X5000X

• Photonic Crystals• Surface Plasmon Resonance• Quantum Dot Fluorescence

Page 14: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

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Chameleons

Page 15: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

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Polymers that can act like chameleons

• Polymer spheres self assemble to mimic color change of chameleons

Page 16: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

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Optical Properties• Plasmon Resonance -> Surface Plasmon

Resonance

Page 17: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Optical Properties

Localized Surface Plasmon Resonance– “sea of electrons” excited

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Page 18: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Optical Properties

Localized Surface Plasmon Resonance– “sea of electrons” excited

18https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr200908sf5.html

Page 19: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Optical Properties: Quantum Dots

Band gap decreases as particle size increases

E

Metal Insulator Semiconductor 50 nm QD 10 nm QD

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Page 20: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

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Summary• Properties that change on the nanoscale:

– Melting point– Mechanical properites– Electrical properties– Optical properties

• Why?– Nanostructures are mostly surface– Nanostructres may be smaller than electron

orbitals and light wavelengths

Page 21: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Scaling Laws

Model how properties change as things get miniaturized(minimize theoretical calculations)

How do we measure size?

Characteristic dimension: D

Volume

Surface area 21

Page 22: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Using Scale Laws

An elephant has D ~ 1 m.

What is its S/V ratio?

A flea has D ~ 1 mm.

What is its S/V ratio?

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Page 23: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Deriving Scale Laws

You are told strength is proportional to D2

and that weight is proportional to D3

Write the expression for strength to weight ratio.

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Page 24: Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1

Practice with Scaling Laws

How many times greater is the strength to weight ratio of a nanotube (D = 10 nm) than…

• the leg of a flea (D = 100 µm)? • the leg of an elephant (D = 2 m)?

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