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Chapters 5-8 Presentation Slides forScience at the Nanoscale: An Introductory Textbookby Chin Wee Shong, Sow Chorng Haur & Andrew T. S. WeeNational University of Singapore

ISBN: 9789814241038HardcoverAugust 2009228 pages

More information at www.panstanford.com/nanotextbook

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Chapter 5

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Name Abbrev. Sci. Unit Representative objects with this size scale

metre m 100 Height of a 7-year-old child.

deci- dm 10−1 Size of our palm.

centi- cm 10−2 Length of a bee.

milli- mm 10−3 Thickness of ordinary paperclip.

micro- μm 10−6 Size of typical dust particles.

nano- nm 10−9 The diametre of a C60 molecule is about 1 nm.

pico- pm 10−12 Radius of a Hydrogen Atom is about 23 pm.

femto- fm 10−15 Size of a typical nucleus of an atom is 10 fm.

atto- am 10−18 Estimated size of an electron.

Just how small is nano?

Percentage of surface atoms

1 cm3 gold cube

1 cm

1 cm

1 cm

Total number of atoms ~ 5.91022

Number of surface atoms ~ 1.21015

% of surface atoms to total atoms ~ 210-6

1 nm3 gold cube

Unit cell length of gold ~ 0.4 nmApproximately 2.5 fcc units

Total number of atoms ~ 108Number of surface atoms ~ 84

% of surface atoms to total atoms ~ 78

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Percentage of Surface Atoms

Surface Relaxation and Restructuring

In surface relaxation, atoms in the surface layer may shift inwardly or laterally

(c)(a)

d12 = dbulk

dbulk

(b)

d12 < dbulk

dbulk

dangling bonds

Dangling bonds may combine to form strained bonds between themselves, the surface layer is restructured with different bond lengths and/or angles.

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Surface Relaxation and Restructuring

Sintering and Ostwald ripening

Sintering : the individual nanostructures change their shapes when they combine with each other, and this often results in a

polycrystalline material

Ostwald ripening produces a single uniform structure with the larger nanostructures growing at the expense of

the smaller ones

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Sintering and Oswald ripening

Catalysis at the Nanoscale

With kind permission from Springer Science Business Media: J.Phys. D, Atomic Resolution electron microscopy of small metal clustes, 19, 293 (1991), J.-O. Boyin and J.-O. Malm. Copyright © 1991, Springer Berlin/Heldelberg.

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Catalysis at the Nanoscale

The electrical double layer

Stern layer : the fairly immobile layer of ions that adhere strongly to

the particle surface

Guoy layer : a diffuse layer of oppositely charged mobile

ions that are attracted to the first layer

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The electrical double layer

The theory is developed by B. Derjaguin and L. Landau, and independently E. Verwey and J.T.G. Overbeek.

DLVO potential

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DLVO Potential

Surfactants

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Surfactants

AOT-water-isooctane system

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AOT-water-isooctane system

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Chapter 6

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Schematic of the energy bands

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Energy distribution functions

Band structure of a semiconductor at different temperatures

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Band structure of a semiconductor at different temperatures

Spherical volume of radius R encompassing a number of possible states

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The functions f(E) and gc(E)

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The functions of f(E) and gc(E)

Density of states for 3D, 2D, 1D, and 0D structures

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Density of States

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One-dimensional density of states

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GaAs/AlGaAs/GaAs heterostructure

Band diagram, i.e. the energy of the conduction band. The

dashed line is the Fermi energy

Cross-section through the heterostructure grown by MBE with nearly atomically sharp interfaces

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Ballistic conductance

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Electronic properties of a quantum dot

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Energy level diagram

Energy level diagram of the single electron

transistor

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Chapter 7

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Variation of Gibbs energy during the nucleation process

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The nucleation and growth processes

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Effect of capping molecule

CdS nanocrystals produced with (a) higher and (b) lower amounts of the capping molecule

hexadecylamine

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STM images of α-sexithiophene (6T) molecules adsorb on Ag(111) surface

Self-assembly of mono- and bi-layer of 6T to form nanostripes

Self-assembly of C60 onto the 6T bilayer patterns

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Self-assembled monolayers (SAMs)

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Close-packed Assembly

SEM images showingclose-packed assembly of micron-sized nanoparticles

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Capillary actions between particles

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Chapter 8

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Optical microscope

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The Rayleigh criterion

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Scanning Electron Microscope

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Light beam profile vs electron beam profile

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Main components of a SEM

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Electron gun

(a) a thermionic electron gun (b) a field emission electron gun

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Electron trajectory

Spiral trajectory of an electron passing through

the electromagneticlens in a SEM

Magnetic field profile generated by a typical electromagnet used in SEM and the focusing effect

of the magnetic field on the electron beam

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Detectable signals generated when an energetic electronbeam is incident on a thick sample

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Transmission Electron Microscope (TEM)

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Detectable signals generated when an energetic electron

beam is incident on a thin sample

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Scanning Tunneling Microscope

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A UHV STM System

Close-up of STM sample stage and tip

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STM image of Si(111)-(7 × 7)

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STM operation

(b) Constant current

(a) Constant-height

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Energy band diagrams of the STM tip (a)

(a) without any voltage bias

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Energy band diagrams of the STM tip (b)

(b) when the tip is negatively biased with respect to the sample

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Energy band diagrams of the STM tip (c)

(c) when the tip is positively biased with respect to the sample

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Atomic Force Microscope

Image of the cantileverand probe tip

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Various detection modes of AFM

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Optical Tweezer

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Laser beam profile passing through the microsphere

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Optical trappingof an array of microspheres

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