Chapters 5 -8 Presentation Slides for Science at

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: 9789814241038 Hardcover August 2009 228 pages More information at www. panstanford. com/nanotextbook www. panstanford. com

Chapter 5 www. panstanford. com

Just how small is nano? Name Abbrev. size scale Sci. Unit Representative objects with this 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 C 60 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. www. panstanford. com

Percentage of Surface Atoms Percentage of surface atoms 1 nm 3 gold cube 1 cm 3 gold cube Unit cell length of gold ~ 0. 4 nm Approximately 2. 5 fcc units 1 cm Total number of atoms ~ 5. 9 1022 Number of surface atoms ~ 1. 2 1015 Total number of atoms ~ 108 Number of surface atoms ~ 84 % of surface atoms to total atoms ~ 2 10 -6 % of surface atoms to total atoms ~ 78 www. panstanford. com

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

Sintering and Oswald ripening 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 www. panstanford. com

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. www. panstanford. com

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 www. panstanford. com

DLVO potential DLVO Potential The theory is developed by B. Derjaguin and L. Landau, and independently E. Verwey and J. T. G. Overbeek. www. panstanford. com

Surfactants www. panstanford. com Surfactants

AOT-water-isooctane system www. panstanford. com

Chapter 6 www. panstanford. com

Schematic of the energy bands www. panstanford. com

Energy distribution functions www. panstanford. com

Band structure of a semiconductor at different temperatures www. panstanford. com

Spherical volume of radius R encompassing a number of possible states www. panstanford. com

The functions of f(E) and gc(E) functions f(E) and gc(E) www. panstanford. com

Density of States Density of states for 3 D, 2 D, 1 D, and 0 D structures www. panstanford. com

One-dimensional density of states www. panstanford. com

Ga. As/Al. Ga. As/Ga. As 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 www. panstanford. com

Ballistic conductance www. panstanford. com

Electronic properties of a quantum dot www. panstanford. com

Energy level diagram of the single electron transistor www. panstanford. com

Chapter 7 www. panstanford. com

Variation of Gibbs energy during the nucleation process www. panstanford. com

The nucleation and growth processes www. panstanford. com

Effect of capping molecule Cd. S nanocrystals produced with (a) higher and (b) lower amounts of the capping molecule hexadecylamine www. panstanford. com

STM images of α-sexithiophene (6 T) molecules adsorb on Ag(111) surface Self-assembly of mono- and bi-layer of 6 T to form nanostripes Self-assembly of C 60 onto the 6 T bilayer patterns www. panstanford. com

Self-assembled monolayers (SAMs) www. panstanford. com

Close-packed Assembly SEM images showing close-packed assembly of micron-sized nanoparticles www. panstanford. com

Capillary actions between particles www. panstanford. com

Chapter 8 www. panstanford. com

Optical microscope www. panstanford. com

The Rayleigh criterion www. panstanford. com

Scanning Electron Microscope www. panstanford. com

Light beam profile vs electron beam profile www. panstanford. com

Main components of a SEM www. panstanford. com

Electron gun (a) a thermionic electron gun (b) a field emission electron gun www. panstanford. com

Electron trajectory Magnetic field profile generated by a typical electromagnet used in SEM and the focusing effect of the magnetic field on the electron beam Spiral trajectory of an electron passing through the electromagnetic lens in a SEM www. panstanford. com

Detectable signals generated when an energetic electron beam is incident on a thick sample www. panstanford. com

Transmission Electron Microscope (TEM) www. panstanford. com

Detectable signals generated when an energetic electron beam is incident on a thin sample www. panstanford. com

Scanning Tunneling Microscope www. panstanford. com

A UHV STM System Close-up of STM sample stage and tip www. panstanford. com

STM image of Si(111)-(7 × 7) www. panstanford. com

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STM operation (a) Constant-height (b) Constant current www. panstanford. com

Energy band diagrams of the STM tip (a) without any voltage bias www. panstanford. com

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

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

Atomic Force Microscope Image of the cantilever and probe tip www. panstanford. com

Various detection modes of AFM www. panstanford. com

Optical Tweezer www. panstanford. com

Laser beam profile passing through the microsphere www. panstanford. com

Optical trapping of an array of microspheres www. panstanford. com

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