Chapters 5-8 Presentation Slides for Science at the Nanoscale: An Introductory Textbook by Chin Wee Shong, Sow Chorng Haur & Andrew T. S. Wee National University of Singapore ISBN: Hardcover August pages More information at

Chapter 5

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 cm 3 gold cube 1 cm Total number of atoms ~ 5.9  Number of surface atoms ~ 1.2  % of surface atoms to total atoms ~ 2  nm 3 gold cube Unit cell length of gold ~ 0.4 nm Approximately 2.5 fcc units Total number of atoms ~ 108 Number of surface atoms ~ 84 % of surface atoms to total atoms ~ 78 Percentage of Surface Atoms

Surface Relaxation and Restructuring In surface relaxation, atoms in the surface layer may shift inwardly or laterally (c) (a) d 12 = d bulk d bulk (b) d 12 < d bulk d bulk dangling bonds Dangling bonds may combine to form strained bonds between themselves, the surface layer is restructured with different bond lengths and/or angles. 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 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. 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 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 DLVO Potential

Surfactants Surfactants

AOT-water-isooctane system AOT-water-isooctane system

Chapter 6

Schematic of the energy bands

Energy distribution functions

Band structure of a semiconductor at different temperatures Band structure of a semiconductor at different temperatures

Spherical volume of radius R encompassing a number of possible states

The functions f(E) and g c (E) The functions of f(E) and g c (E)

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

One-dimensional density of states

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

Ballistic conductance

Electronic properties of a quantum dot

Energy level diagram Energy level diagram of the single electron transistor

Chapter 7

Variation of Gibbs energy during the nucleation process

The nucleation and growth processes

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

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 C 60 onto the 6T bilayer patterns

Self-assembled monolayers (SAMs)

Close-packed Assembly SEM images showing close-packed assembly of micron-sized nanoparticles

Capillary actions between particles

Chapter 8

Optical microscope

The Rayleigh criterion

Scanning Electron Microscope

Light beam profile vs electron beam profile

Main components of a SEM

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

Electron trajectory Spiral trajectory of an electron passing through the electromagnetic lens 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

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

Transmission Electron Microscope (TEM)

Detectable signals generated when an energetic electron beam is incident on a thin sample

Scanning Tunneling Microscope

A UHV STM System Close-up of STM sample stage and tip

STM image of Si(111)-(7 × 7)

STM operation (b) Constant current (a) Constant-height

Energy band diagrams of the STM tip (a) (a) without any voltage bias

Energy band diagrams of the STM tip (b) (b) when the tip is negatively biased with respect to the sample

Energy band diagrams of the STM tip (c) (c) when the tip is positively biased with respect to the sample

Atomic Force Microscope Image of the cantilever and probe tip

Various detection modes of AFM

Optical Tweezer

Laser beam profile passing through the microsphere

Optical trapping of an array of microspheres